Modern Steel Products (2014) - Overview of Tandem Mill Designs (Cold- Strip Mill): lecture 13
CC Attribution 3.0 Unported:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor.
Cooman, Bruno C. de
Professor de Cooman talks about the cold rolling of steels to achieve the right thickness, shape profile and surface condition, after which the strip may be coated. This is a part of a course of lectures given at the Graduate Institute of Ferrous Technology, POSTECH, Republic of Korea.
 So today we will be discussing topics related to the cold rolling mill. This, the cold mill usually also involves the, in terms of the production, it's also associated with the annealing. And as we concentrate on strip for the technology, the description in this course will be talking about batch annealing and continuous annealing. And there is also a temper rolling involved. The, for coded products, the root is slightly different. And we'll discuss that in a separate lecture. Okay, so let's get started here. So what do we get out of, or produce in a cold strip mill? We obtain a strip that has the right exit thickness and the right shape, flatness and profile. And it must be defect free. And after the cold strip mill, the coils, as I said, will be annealed, batch annealed or continuous annealed, or they can go to a separate coating line, which is usually separate entity to be electro-galvanized, hot-dip galvanized, etc. The material, the way it's put on the market, will be temper rolled. Yes, it means it's given a final cold rolling step after the coating or after the annealing to achieve a number of strip characteristics, in particular, a particular roughness on the, applies a particular roughness on the surface of the strip. And the, as I said, in addition to being electro-galvanized or galvanized, the strip can, in addition, then go through an additional coating process, whereby a paint layer is applied. And this may involve actually two paint layers, a primer and a top coat. Again, these are usually separate production plants. Okay, so we'll be talking about the different technologies and designs for these, the cold strip mills. And we'll also talk a little bit more detail about lubrication in the cold strip mill, because that's really very important. Okay. Good. So, basically, in the cold rolling, we get the strip with the right exit thickness. Yes, the material is heavily cold deformed, so it cannot be used in practice, so you need to anneal it in a continuous annealing line or a batch annealing line. After that, after this annealing, the material can be electro-galvanized. Or you can do both the annealing and the galvanizing in a hot dip galvanizing line. So these lines, the HDG lines, you actually make, you recrystallize the steel and you galvanize the steel. And eventually you get a cold rolled galvanized or not galvanized coil. Okay, so the cold strip mill traditionally will consist of a decoyler, a number of stands, and a coiler unit. Nowadays, as if you remember from the discussion, the presentation on the pickling lines, nowadays, there is a, the units are usually built in a way that you have continuous operation which involves the pickling line and the cold rolling. So the exit of the pickling line goes straight into the cold rolling. So usually modern cold strip mills are very highly automated and there's really not much to see in the exterior of this, of the line. It's usually the mill stands are not visible and what you see here are the work rolls that are ready for, to replace the worn out work rolls. Okay, so this is an example here. Nowadays, you get lots of six high stands, yes, to get perfect strip control, strip profile control. So a few words about this and we'll have a separate lecture on it also. So these are these stands and then we usually have two coilers, yes, and these are what we call exit tension reels or exit tension coilers. So that means you can apply attention on the out exit strip and you remember why we do this because it has a big impact on the friction peak in rolling. Okay. Right, so these coilers, why do we have two coilers? That's because you can, while you are coiling one, using one of the coilers to coil, you have the other coil is being unloaded, yes. And you, there may also be a shear to cut the strip to the right length. These coilers, as they are presented here, have separate units. You also have coilers where you have a drum, a big drum, with two mandrels, yes, and you have one mandrel is in a position for coiling and the other mandrel is in a position for unloading. There are different ways in which this can be done. Now, you don't always have tandem coil rolling. You can have single stand coil rolling units. In particular, if you visit stainless steel mills, very often they will have single stand reversing mills for the coil rolling. This is an example here of a six high gold mill, a single stand, with an exit tension reel, so you can apply tension on the exit, but it's only got a payoff reel. It's just a, you unwrap the strip here and there's no tension. This unit cannot apply any tension. So, in this particular case, this type of setup is for situations where the coils are loaded, they're rolled once, coiled on the other side, and then removed. This is a non-reversing situation. So, that's when you only do one pass. What you don't see this more often, what you often see are single stand coil rolling mills where you have a reversing mill. So, the strip passes through the same mill back and forth a few times, as many times as you need to achieve a final thickness. And it does this, yes, in the following years, so you have a payoff reel that allows you to load the strip into the mill, yes, and then once you have put the strip on one of the tension reels, then you pass it through and you attach it to an entry tension reel also. So, the strip passes through the mill with forward and backward tension, yes. So, how does this work? So, you start here on the right hand side, yes. So, you arrive with the hot rolled coils, yes, and you have two coilers here. The first coiler is a payoff reel. So, here you just unwrap the hot rolled pickled coil and then you pass it through the mill and then you pick it up here, yes, on this tension reel, all right. Now, the strip here will eventually come off, come off the mandrel, right, and you don't want it to flap around and you want it to, there should be some tension on the strip. So, you have a strip press, yes, that will keep, give you some tension by friction, yes, and also prevents the strip from moving around, yes, okay, okay. All right, so then most of this strip is now here, yes, and this end part here is now put on the tension reel here, yes, so it puts here and you start rolling, yes. So, this is the first pass, this is the second pass, yes, okay. So, you can do even number passes or uneven number of passes, okay. So, if you do an even number of passes, one, two, the coil ends up here, you have to unload it from here, or if you do an uneven odd number of passes, the coil will be here, yes, okay. Now, remember that when you go back and forth, yes, you always keep the end parts, the end parts here of the strip on the mandrel, so they never get rolled, okay. So, if they don't get rolled, they remain thick, yes, so you have to get rid of these ends, yes, that didn't get rolled, yes. So, what you do here is you cut it, for instance, in this case, you can see here you will take out this coil, so you come here, yes, you cut the end and then you go back and you roll up what's left, yes. So, here you get a small piece of coil, yes, small piece of coil that is, has the, that's off thickness, yes, and you call this a pup coil, yes. And on this side, of course, the central part of the coil will be off-gauge, will not have the right thickness, okay. So, this odd number of passes is what you see is most common, you get off-gauge sections remain inside and the outside off-gauge section makes a pup coil, yes. These are, these are pup coils, these are the small coils that are off-gauge and this is a puppy, it's the same pup, okay. So, that means it's because there's the pup coils, you call them pup coils because they're small and cute, like this dog, okay. Okay, so, and that's very common, these reversing mills, yes, and you produce pup coils and then you sell the pup coils also to smaller companies that can do something with them. What you also have are mill stands where you don't have one stand but you have two stands, yes. And so, for instance, here you have a situation where you have four high stands, you have two of them, yes, and you have two tension reels. So, that means you can do twice the number of reductions per pass, yes. So, it has a higher productivity, but it's basically a reversing mill also, you can just do more, you can produce faster. And of course, because you have two stands, it's going to be a more expensive mill. There are also double-cold rolling mills, like they, but that are different, yes, and they're not reversing mills and they're used to make tin plate. And tin plate is a product with which you make, it's packaging steel, yes. And these, they're non-reversing, so you only go, you pass once through this mill, so you only need a payoff reel, no tension, yes. And a tension reel where you wrap up the strip after the rolling. And so, usually you have two stands, you have a reduction stand, and then a surface conditioning stand that basically gives the right surface roughness to the strip. Okay, and this is the same situation here, you have a reduction stand and a surface treatment stand in succession here. And it's for, as I said, tin plate production. We said a few things about gauge control in when we discussed the hot strip mill, yes. I just want to say a few things at this point, at this juncture about the tandem mill. So in a tandem mill, you have the strip goes from one stand into the other stand, yes. And the, what you have to do in order to have stable rolling, you have to have a constant mass flow through the mill. That means, what does that mean? It means that the, whatever, the mass that comes in has to go out, yes, exactly the same value. Otherwise, if the value that comes out is higher than what comes in, there will be a rupture. Or if the value that comes out is lower than what you put in, you will have a cobble, yes. So what does that mean, this constant mass flow? It means that the product of the velocity of the strip out times the thickness of the strip should be equal to the velocity in and the thickness in of the next, of the next stand. So the speed exit, the exit speed after the first mill, first stand, excuse me, is V1 and thickness H1. Then the mass flow out of V1, out of the first stand is V1 H1, V2 H2 after the second one, etc. V5 H5. So the constant mass flow requirements means that V1 H1 should be equal to V5 H5. And of course, H1 is the entry thickness and H5 is the required exit thickness. The thickness might be the actual gauge that's needed. So the mass flow or the volume flow out of each stand is the product of the gauge, yes, times the strip out of each stand. So if there is an error, yes, of gauge here, yes, it will always propagate through the mill, yes, through the mill. Say if we have a constant mass flow out of V1, out of one, stand one, and say we have an exit gauge error, we can exit here, right, we can correct it by changing the speed, yes, because if this difference is between, sorry, if you have to correct for H, yes, you can do this by changing the velocities, yes, yes. And so this brings in a new concept of gauge control in the cold strip mill, and that is gauge control with via speed, yes, and it's based on basically this here. So the way to control the thickness is with speed, right. So again here just as in the case of the hot strip mill, yes, the gauge control, yes, is achieved by actuators, and we have mechanical screw down actuators and hydraulic capsules, yes, and we know, we already discussed this, mechanical screw downs have a slow response and the hydraulics are fast responders, yes, okay. So how does it work? You remember that hydraulic gap control is done by controlling the pressure in the hydraulic capsules, yes, right, and you put the pressure on the backup roll chock, yes, all right, or it can be electromechanical screw down, and that means that you have a motor, yes, and then via a gear box and screw and nut geometry you can apply pressure, yes, and increase or decrease the gap by applying pressure on the backup roll chock, yes. In most, as I had said, in most of the modern mills, yes, we will also have the possibility to improve the strip profile, that's the cross-sectional, remember that's the cross-sectional shape of the strip, and that is done, for instance, in this case, by bending, by roll bending capsules, yes, and here for instance you have, that means that you have little hydraulic capsules here that can bend the roll, so you achieve the right roll profile, okay. In addition to this, you can also have lateral roll shifting, yes, and you see the rolls here are asymmetric, yes, and it allows you to do some additional types of bending, which we'll discuss in more detail, yes, or later on, to achieve the right strip profile, so that's the cross-sectional shape of the strip, and you can have lateral roll shifting, or you can even have cross-bare rolls, yes, okay. All these things are very common in modern cold rolling mills. In addition, because we're working at low temperature, we can do a lot more in-line measurements on the strip, so standard cold rolling mills will have thickness gauges, which can be x-ray gauges, or isotope gauges, or even contact gauges, although contact gauges are only suitable when you have low strip speeds. You have tension control, it's also available, and of course you measure the force with load cells, and you also have strip velocity measurements, yes, okay. Again, we'll talk about this in more detail later on when we talk about strip profile. Let's go back to some data about the cold rolling mill, how, what are typical cold rolling mill parameters. Well, if you look in terms of the reduction, yes, the cold strip mill will typically produce material that's less than 2 millimeters thick, and so you can see here if the strip is about 0.8 millimeters, yes, depending on the type of steel you're processing, DDQ meaning deep drawing quality, deep drawing quality that will be batch annealed, it will be continuous annealed, the carbon manganese structural steel, or niobium HSLA steel, the reductions are typically of the order of 75 percent, okay, for a width here of 1250. The number of mill stands is 4 to 5, nowadays it can be different, it can be more like 5 or 6 perhaps. The thickness that a cold rolling mill can take in is typically maximum, as a maximum around 5 to 6 millimeters, yes, and the thickness out, you can see here about 0.2 millimeters, yes, minimum. So the maximum reductions that we can give are 80 percent, 90 percent, yes, these are very high reductions, usually a cold strip mill will operate at 70, 75 percent, yes. The very high reductions are given to strip where we want to achieve texture control, very strong texture control. And there's also usually a strip tension, yes. So remember that when we did discuss the rolling fundamentals, we saw that what is very important in rolling is friction. And we also described the fact that in the roll gap, yes, there was a considerable flattening of the roll, yes. So you have a elastic deformation of the roll surface and it's flattened, it's strongly flattened. And again there is forward slip, yes, and you have a shearing of the surface in the roll gap. And remember this plot here shows that if we decrease the friction, we can decrease the rolling load, yes. Now in the hot strip mill that was difficult to achieve, this reduction of friction through lubrication. But you can achieve it very easily in the cold strip mill, yes. And so we're going to take some time to discuss lubrication in the cold strip mill. What are the functions of the lubrications? Well, number one, of course, most important is reduction of friction. Because then you have a direct economic advantage and technical advantage is you reduce, you have considerable reduction of rolling forces, yes. And because of that you also have a higher quality strip surface, yes, better control of the strip profile and a reduced work roll wear. So very important, yes, to have lubricants whenever you can. The additional benefit of the lubrication is cooling, yes. Because you use less forces, less load, you will have less heating also. You will have less heating of the roll because there's less friction, yes. And the heating is caused by friction and by deformation, we know. Now, one of the things we could be using is water, yes, because water is a very good coolant, yes. So we could use water. But water is a very poor lubricant, yes, it's very poor lubricant. And so we will not be using water or not only water in the lubricants for the cold strip mill. We use emulsions, dispersions or stabilized dispersions. Emulsion is a product that typically contains a few percent of surfactant. We'll see what it is in a moment, which limits the breaking up of the oil particles into a separate layer, yes. And so it means we don't need to agitate, mix the emulsion, the water-oil mixture, continuously to achieve, to make our lubricant. A dispersion, here we have added surfactants, yes, which forms a protective colloidal layer on surface of oil particles, yes. Again, the reason why we do this is to eliminate coalescence of the oil film. In dispersions, what's the big difference between dispersion and emulsion, because it's rather similar, is the fact that the distribution of particles, the control of the particle, oil particle size, is much narrower than in the case of an emulsion, yes. And in a dispersion, the oil layer will tend to split off, yes. And so you need to keep a dispersion well dispersed, yes, by agitating it, by mixing it, basically. And then you have stabilized dispersions, which are newer systems, with something between emulsions and dispersion, but they don't need agitation. Now, the fact that you reduce friction and you reduce, and the lubricants also work as coolants, is positive. There is a negative about lubricants. Lubricants are basically organic products, and they will, because of the very high pressures in the roll gap, they are sensitive to breakdown. And so lubrication will cause carbon deposits, yes, which you will need to remove, yes. And of course, you will also need to remove residues of lubricants on your strip, okay. So let's have a look at the basics, some basics of the oil, water, mixtures that we call emulsions, yes. So we add oil, yes, and emulsifiers. And emulsifier is basically a molecule which has a hydrophilic end and a lipophilic end. So the lipophilic end is oil soluble, and the water soluble, or hydrophilic end is water soluble. And so these molecules will orient themselves this way, yes, and this will stabilize our emulsion, okay. Now, if you ever work later in a hot strip mail, the providers of lubricants are very specialized companies. Usually they tend to be, it's a side product of petrochemical industry. So for instance, Texaco, Shell, and others are big suppliers of lubricants, yes. Because it's a side product of the petroleum industry. These are very complex chemistries, yes. So don't try to, by all by yourself, try to improve the chemistry or whatever, right. It's pretty complex. There are many chemicals going into, and what I'm going to tell you here is just the tip of the iceberg. But typically, these lubricants can easily contain, you know, 15 chemicals in their compositions, yeah. The major constituents are mineral oils, which we call mineral oils, esters or mineral oils. They're major constituents, yes. And so there's the base lubricants, and they are important in what we call elasto-hydrodynamic lubrication. So EHD is, and I am sorry, I didn't, it's not included here, but EHD stands for elasto-hydrodynamic lubrication. Or hydro-hydrodynamic lubrication. Or hydro, these stands for hydrodynamic. And then you have additional important compounds. You have fatty acids, yes. They are important in boundary lubrication. Boundary lubrication is when the two surfaces, the strip surface and the roll surface, for instance, are in physical contact, in strong physical contact, yeah. And we also have antioxidants that will protect the lubricant from oxidation, polymerization, in other words, degradation over time. We have emulsifiers, of course, that we add so we can mix the oil and water mixtures. Then we also have phosphorus and sulfur-containing additives, and those are not organic molecules. They tend to, they're added to form very strong films, yes, at the surface, yes. The phosphorus-containing additives for films that can easily, very thin films that can easily be sheared, yes. And the sulfur-containing additives are very resistant to high pressures, yes, and they prevent welding, yes. Cold welding, I mean with this, we'll see where the cold welding occurs. So let's have a look at two surfaces, two technical surfaces. So technical surfaces of all kinds are never atomically smooth, yes. They have a certain roughness and waviness at the surface. So let's have a look now at metal-to-metal contact. They say there's no oil, right? So we call this dry lubrication. There's no lubricant, it's just dry. And so this kind of lubrication is also called boundary lubrication when there is little or no lubricant. So what happens if I bring these two surfaces together? Well, the hails, the tops of the surface profiles will make contact, yes. And if I press them together, yes, these tops here, these asperities will be squeezed, yes. And if I squeeze hard enough, I may even cold weld them to each other, yes. And in the case I have a little bit of lubricant, yes, there will be pockets of lubricants, yes. Pockets of lubricant. So in what we call boundary lubrication, yes, I have tiny pockets of lubricants, and I have asperities that are flattened and there may be cold welding on these surfaces. So what kind of situations do we have now? If the two surfaces move relative to each other, yes. If we have, say, hard asperity, hard top, or we have a hard surface, like a roll surface, it's hard, and we have a soft strip surface, yes, we can get scratching, pulling of the soft surface by a hard asperity, yes. Or we can have bonding, they can, they can cold weld, and then when the surfaces move away from each other, you can have breakage of that bond, yes. And that process, these two first processes give rise to what we call iron finds. Iron finds are typically found on cold deformed products, and they're very fine iron particles. They come from these processes, yes. If we have, yes, an oil film in between, these processes can be avoided, yes, because now the deformation is what we call viscous drag, yes, and this is basically when the two surfaces move with respect to each other, we are not making bonding, we're not plowing the surfaces, but we're just shearing, shearing this lubricant film, okay. So let's have a look at this shearing process, yes, the shearing process, okay. The shearing process of an, of oil is determined by its viscosity, and the viscosity is equal to the shear stress divided by the shear rate, yes. Okay, so if I have a high viscosity material, high viscosity oil, I will need a high, high shear stress to achieve the same shear rate, yes, okay. Now, so viscosity is an important parameter, it's the main parameter of the lubricant, and from a mechanical point of view, yes, and it's very much pressure and temperature dependence. Well, we're all familiar with the temperature dependence, we know that if you have an oil, yes, and you warm it up, it will become thinner, it will lose its viscosity. So the viscosity decreases with increasing temperature. What we usually do not know from experience is the fact that with pressure, the viscosity increases, yeah. And of course, why is this so important? It's so important because in rolling, we have very high pressures, yes. Okay, now let's have a look at the pressure influence, the influence of pressure on viscosity. So let's look at water first, and we increase the pressure, say here from 0.1 megapascal to 1 gigapascal. You see that water, the viscosity doesn't change very much, yes, it goes from 1 to a little bit less than 2, yes. By the way, the viscosity is in centipoise, so it's Pascal's times seconds, yes. And with mineral oils, yes, of course we start with a lubricant that's a lot more viscous than water, but as you increase, you get a dramatic, huge increase in the viscosity, not just a little bit, not just doubling, but a very, very large increase in the viscosity, yes. Okay, so in a mill, the viscosity is much, much higher than the one you feel with your fingers, okay, because of these very high pressures. Alright, now with lubrication, there are many parameters, yes. Let's just look at the process of rolling, yes. We know that locally there will be a pressure, yes. We also know that there will be a relative velocity, yes. The strip will, is never at the same velocity, yes, as the roll surface, yes, so there is a relative velocity. And then the lubricant has a certain viscosity, yes. So how is it possible to talk in a simple manner about lubrication, taking into account all these parameters, yes. Well, yes, it just turns out that you can plot a master curve for a lubricant, yes, where you get, so on the y-axis, you get the coefficient of friction, mu, which is the shear stress divided by pressure. So you know what friction is, if you have two surfaces, yes, and they're under pressure, right. The friction coefficient is the ratio of the shear stress to the applied pressure, yes. And you want, so when a lubricant works well, yes, the friction coefficient will be low, because the shear stress to get the thing moving will be lower, okay. So, well, so in the y-axis, you do speed time viscosity divided by the pressure. And this is, this parameter, yes, allows you to draw a single curve for the friction coefficient, and it looks like this. This is what it looks like. So, when this parameter has a low value, I have high friction, yes. When this parameter has a high value, I have low friction. So, let's first look at pressure, yes. If I have a high pressure, yes, the velocity and the lubricant viscosity being the same, yes. An increase in P means that I'm on this side. So when P increases, I'm on the, yes, I mean, so I have high friction conditions, yeah. So if I have a high velocity, yes, then I'm going this way, yes. I will get the reduction in friction, all other things being the same. The viscosity of my lubricant and the pressure being the same. Why is it that this happens? Well, the reason is very simple. It's because something happens to the lubricant film thickness. The lubricant film thickness goes like this. So, and what happens, well, it's shown here, yes. When this parameter here, yes, by the way, this curve is called the street back curve, yes. So when this parameter is small, you have metal to metal contacts and you have dry lubrication conditions, so high friction conditions, yes. And typically the friction coefficient is then between 0.1 to 1, yes. As this parameter increases, because you've increased the viscosity or you've increasing the speed or you're decreasing the pressure, yeah, you have, you're creating lubricant pockets, lubricant pockets. You can see the thickness of the film increases, yes. And you get a situation that's called mixed lubrication, yes. The minimum is reached when we have so-called elasto-hydrodynamic lubrications, where you have a large number of lubricant pockets. And the hydrodynamic lubrication is the case here, when you, thickness of the film is such that the two surfaces are separated, yes. And the friction is then a function of the properties of the lubricant only, okay. Right, so when are we in the right working conditions? So we know we'd like to avoid boundary type lubrication and we'd like to have elasto-hydrodynamic lubrication with low friction. So what, the situation will depend on the roughness of the, the combined roughnesses of your surfaces, which in the case of rolling is the roll surface and the strip surface, and the lubricant film thickness. So when we have a rolling situation, we have a work roll roughness and a strip roughness, yes. And the combined roughness is taken as the square root of the roughness of the work roll square times the strip roughness square. The lubricant film thickness, we call H. So when H is about the same as this sigma, we have boundary lubrication. If the film thickness is one to three times the combined roughness, then we are in mixed condition and we have the right elasto-hydrodynamic, this is a typo here, EHD, elasto-hydrodynamic lubrication, if the thickness is about three times the combined roughness, okay. This is kind of a picture here, so you have an idea of what happens. So at the inlet here, yes, we have the, the oil is entrapped, yes, between the work roll and the strip, yes. So in this contact area, we have lubricant pockets and we may have places where the surface is in contact, yes. Where they're touched, touching. So in the case of boundary lubrication, I have very small, these pockets are very small, yes. In the case of the elasto-hydrodynamic lubrication, I have a lot more lubricant between the two surfaces. You get in areas, in many areas, you get total separation of the surfaces. Now, having said this, it's also important to realize that at the surface here, yes, because there is a relative movement between the surfaces, these contact places don't remain like this, yes. In particular, these lubricant pockets will become undeeper and they will flatten out, yes. And also the surface will be stretched like this, okay. So the shape doesn't stay like this, no. So we get asperities that are crushed and there is plastic shear deformation at the surface. And the process here of these asperities being deformed, yes, being sheared off, leads to carbon fines and also these extreme mechanical conditions here also lead to decomposition of these mineral oils and you'll form carbon residues, yes. Which, again, both of these things need to be reduced. In the roll gap itself, the film thickness is pretty flat, because the roll gap is actually very flat, because the roll flattening is very flat, yes. At the beginning, of course, we get the start at the entry, you have the oil is taken into the roll gap, and at the exit, you get an interesting phenomenon, is that the thickness of the oil is decreasing and we get a pressure peak, which is called Petrusevich pressure peak. And the reason why we have this precious peak is because when the strip leaves the roll gap, there is an elastic, the roll surface is now free, yes, it's free. And so it will elastically bounce back, yes. It's been flattened very much, it's going to bounce back, yes. And so it will actually squeeze the oil film a little bit, and that gives us this pressure peak, all right. So very important, this E-E-H-D elasto-hydrodynamic lubrication, and it's lubrication by a lubricant film, full lubricant film, in condition of elastic contact and high pressure. So this high pressure results in a very flat contact area, and because of these high pressures, your oil is very, very viscous, yes. And there where you have no contact between the two, you have what we call glide-like conditions, yes. You basically shear the oil film, okay. Let's have a look now at velocity, the impact of the velocity. What happens with the velocity? So you can already see here, yes, that when I keep the viscosity of the oil the same, I keep the pressure the same, I just increase the velocity, that means my oil film will increase in thickness, okay. And you can measure this. It's a rather complicated way, tests to do this, but it's possible to measure the film, the oil film thickness as a function of the velocity. And you can do this for neat oils, or you can do this for emulsions. When you talk about neat oils, that means you're not mixing it with water. You just use the pure oil as such, yes. So you can use neat oil or water plus oil emulsions. And so you see that as you increase the velocity, you get the thickness of the film increases. And you can see here what type of thicknesses we're talking about, 10 nanometers, 100 nanometers, very thin films, yes. And you also see the effect of the temperature. So the temperature increases, that means the lubrication, the, your, viscosity decreases. And so there is a shift of this line to the right. And basically you basically get a decrease in film thickness. Okay? Right, so quite a complex thing happens when you entrap the lubricant film in the roll gap. So, so in the roll gap, the oil, or the lubricant, is sucked into the roll gap, yes. And you get a, what's called a phase inversion of the oil-water emulsion, yes. And what actually happens is this oil-water emulsion turns into a water-oil emulsion. Yes, you get the inversion of this thing here. The other thing that happens, yes, is that if we increase the speed too much, yes, there will not be enough, you need to, so the oil goes through the roll gap, right. So you will, you need to suck in the lubricant at the entry. So if you roll too fast, you turn too fast, there's not going to be enough oil supplied at the entry, yes. And you can get what's called oil starvation, yes, where there's not enough oil being supplied at the entry, yes, and you get a collapse of the oil film, yes. Okay, and so H decreases suddenly, yes, and when H decreases, of course, we're going into boundary lubrication situation, yes. Now, these things can happen, yes, and then suddenly you find yourself with very little lubricant, yes, and you start making contacts between the two metal surfaces, very high pressure contacts, and there's going to be shear forces, shear, yes. So that's why we add these sulfur and phosphorus compounds, yes, to prevent welding, yes, at the surface. When we have, when you happen to have boundary lubrication problems, yes, and you will have those, for instance, when for some reason or another you have to go and work into low speed conditions or higher temperatures for some reason or high roughness, yes, the surface happens to be high roughness, yes. Then we luckily have, in the compounds of the lubricant formulation, you have boundary films, phosphates and sulfides, oxides and sulfides, at the surface. So your boundary film, very close to the steel surface, is inorganic, yes, and the oil is on top of that. That's how you, a good picture here. So when the oil film collapses, these two inorganic compounds will play a role, because they adhere to the steel surface, so they can easily shear, yes, and they have very high resistance against being squeezed out, yes, and they're very pressure resistant, and they, because they're there, they also make it difficult for the two surfaces to cold weld to each other. So that's why we have phosphates and sulfides. So, you know, the situation where the conditions become bad during rolling happens, for instance, when you have to reduce the velocity, yes, for instance, you're rolling and then you have to stop rolling because you finished the strip, the strip comes out of the mill, so you have to reduce the velocity, right, so, or when you're starting to roll, yes, you're not suddenly at very high rolling speeds, you build up, right, so you start at low velocities, yes, and in these cases, you can be in high friction conditions, okay, and this is one of the reasons why working continuously is so important, so if you're asking yourself, why do we have a, why do we put our pickling line, yes, and put it right into the cold mill, that's because the cold mill then can work all the time, yes, you can just attach the coils after the other and the cold mill never stops, so you never have these big speed variations, yes, so it makes economic sense because you put things together and some equipment disappears, but it also makes a sense from a product point of view to work in constant and continuous conditions, okay, so let's get back to our cold mill here, so when we start, we have, if it's a carbon steel, we have our grains here, yes, you pass through the cold rolling mill, so you basically have a plane strain deformation which leads to a pronounced preferred orientations of all these grains, so you get these grains are now pancake, yes, highly deformed, deformations can be, as I said, 75%, 80%, so a lot more, a lot larger than the deformation you give, for instance, in a tensile test, yes, and as a consequence, the orientation, crystallographic orientation distribution changes, yes, and in the case of carbon steels, yes, what we want to have in our product is what's called a very strong gamma fiber, we want to have all these little crystals, we want them to have the 1, 1, 1, 1 orientation parallel to the 1, 1, 1 direction, parallel to the normal direction of the sheet, yes, okay, and this is achieved by a combination of high levels of deformation and recrystallization and annealing, yes, so the cold rolled material is a very high level of crystallographic preferred orientation, but you cannot do anything with it because it's deformed, heavily deformed, it has no residual plasticity, so you need to do, to anneal this, yes, and during the annealing process you recreate low defect density grains, yes, and a highly textured microstructure with 1, 1, 1 parallel to normal direction being the preferred orientation for the grains, yes, and this situation gives you a high r value, so high plasticity and a very low planar anisotropy, so the r value doesn't change much as a function of direction in which it's tested, okay, now the process of going from this to this, yes, is a kinetics process, it depends on time, it depends on temperature, it also depends on the amount of deformation you've given, yes, so typically if you, if your deformation, the amount of deformation is less than 50%, it's going to take a long time to recrystallize, yes, and that's why in cold rolling, in cold deformation we like to give large amounts of deformations because that will speed up the recrystallization, why is that? Well, because the dislocation density here is the driving force for the recrystallization, the more I have deformed the material, the higher the driving force, the faster it will recrystallize, okay, so there are two ways to recrystallize the steel product, you can do it by batch annealing, yes, you basically take your coil of cold rolled material, you put it in a furnace for a long time, yes, and you let it recrystallize, this is one of these furnaces that's being opened, you can't see the coils, the coils are inside this tube here, that's what the furnace is, and this here is a continuous annealing furnace, there you, instead of annealing the coil, you anneal the strip, yes, so you uncoil the strip and you pass the strip through a furnace, yes, so you see here the strip, I guess, coming out of, or going into the furnace, I can't tell the furnaces here, and this is an accumulator where you store some few hundreds of meters of uncoiled strip, so let's start with the batch annealing furnace, so in this furnace let's have a look at, okay, so this is what they look like, in the interior we stack the coils, yes, and we let gas flow through this, the furnace, okay, and it's protective gas, it's hydrogen-nitrogen mixture, and it's a protective atmosphere, so where do you do the heating, you do the heating on the outside of this furnace, so there is this here, that's where you have burners, yes, and so that will heat up the interior wall of this furnace and this radiation heat will then heat up your coils, let's see here, okay, and this is what you see here, the coils are inside this furnace, and this is a cover, yes, the cover which contains the burners, okay, so you can have this, the amount of weight that you can anneal here is for instance of the order of 115, so that means there's quite a few coils can go, be put in there on top of each other, height, 5 meters, annealing capacity, 2.7 tons per hour, that's not very high, so because the process is very slow, you need many of these furnaces in parallel, so if you visit a batch annealing section of a cold rolling mill, you will not see one furnace, you'll see many furnaces, for instance 47 furnaces, and there may be more bases, yes, bases are these places on which you can put a furnace, yes, why are there much more bases than you have annealing hoods, because you have to heat, you only need the hoods, yes, when you heat up, yes, when you cool down, you just don't need this cover here, so capacity 80,000 tons per year, surface cleanliness, that's the carbon residue that I talked about, and the gas in for this particular picture here was hydrogen, but in general it's hydrogen plus nitrogen, and I will say something about the use of hydrogen, and the heating itself is done by LPG or by electricity, I'm seeing I'm over time here, so I will stop at this point, and we'll continue, I guess we'll continue next week, because Thursday is first of May, yes, and I think we don't have class, right, on first of May, I guess I will reconvene a week from now. Next Tuesday also, is next Tuesday a holiday? I don't know, is that number, is it an official post-ec day? I haven't heard about that, is it official post-ec day? Okay, oh it's not official post-ec day, then I'm not going to say anything about this. Right, so we will need to perhaps have a make-up class or something, okay, but so, well then we will meet next week on Thursday, okay, don't forget that there will be a regular quiz. Thank you. Thank you.
 So today we will be discussing topics related to the cold rolling mill.  This, the cold mill usually also involves the, in terms of the production, it's also associated with the annealing.  And as we concentrate on strip for the technology, the description in this course will be talking about batch annealing and continuous annealing.  And there is also a temper rolling involved.  The, for coded products, the root is slightly different.  And we'll discuss that in a separate lecture.  Okay, so let's get started here.  So what do we get out of, or produce in a cold strip mill?  We obtain a strip that has the right exit thickness and the right shape, flatness and profile.  And it must be defect free. And after the cold strip mill, the coils, as I said, will be annealed, batch annealed or continuous annealed,  or they can go to a separate coating line, which is usually separate entity to be electro-galvanized, hot-dip galvanized, etc.  The material, the way it's put on the market, will be temper rolled.  Yes, it means it's given a final cold rolling step after the coating or after the annealing to achieve a number of strip characteristics,  in particular, a particular roughness on the, applies a particular roughness on the surface of the strip.  And the, as I said, in addition to being electro-galvanized or galvanized, the strip can, in addition, then go through an additional coating process,  whereby a paint layer is applied.  And this may involve actually two paint layers, a primer and a top coat.  Again, these are usually separate production plants.  Okay, so we'll be talking about the different technologies and designs for these, the cold strip mills.  And we'll also talk a little bit more detail about lubrication in the cold strip mill, because that's really very important.  Okay.  Good.  So, basically, in the cold rolling, we get the strip with the right exit thickness.  Yes, the material is heavily cold deformed, so it cannot be used in practice, so you need to anneal it in a continuous annealing line or a batch annealing line.  After that, after this annealing, the material can be electro-galvanized.  Or you can do both the annealing and the galvanizing in a hot dip galvanizing line.  So these lines, the HDG lines, you actually make, you recrystallize the steel and you galvanize the steel.  And eventually you get a cold rolled galvanized or not galvanized coil.  Okay, so the cold strip mill traditionally will consist of a decoyler, a number of stands, and a coiler unit.  Nowadays, as if you remember from the discussion, the presentation on the pickling lines, nowadays, there is a, the units are usually built  in a way that you have continuous operation which involves the pickling line and the cold rolling.  So the exit of the pickling line goes straight into the cold rolling.  So usually modern cold strip mills are very highly automated and there's really not much to see in the exterior of this, of the line.  It's usually the mill stands are not visible and what you see here are the work rolls that are ready for, to replace the worn out work rolls.  Okay, so this is an example here.  Nowadays, you get lots of six high stands, yes, to get perfect strip control, strip profile control.  So a few words about this and we'll have a separate lecture on it also.  So these are these stands and then we usually have two coilers, yes, and these are what we call exit tension reels or exit tension coilers.  So that means you can apply attention on the out exit strip and you remember why we do this because it has a big impact on the friction peak in rolling.  Okay.  Right, so these coilers, why do we have two coilers?  That's because you can, while you are coiling one, using one of the coilers to coil, you have the other coil is being unloaded, yes.  And you, there may also be a shear to cut the strip to the right length.  These coilers, as they are presented here, have separate units.  You also have coilers where you have a drum, a big drum, with two mandrels, yes, and you have one mandrel is in a position for coiling and the other mandrel is in a position for unloading.  There are different ways in which this can be done.  Now, you don't always have tandem coil rolling.  You can have single stand coil rolling units.  In particular, if you visit stainless steel mills, very often they will have single stand reversing mills for the coil rolling.  This is an example here of a six high gold mill, a single stand, with an exit tension reel, so you can apply tension on the exit, but it's only got a payoff reel.  It's just a, you unwrap the strip here and there's no tension.  This unit cannot apply any tension.  So, in this particular case, this type of setup is for situations where the coils are loaded, they're rolled once, coiled on the other side, and then removed.  This is a non-reversing situation.  So, that's when you only do one pass.  What you don't see this more often, what you often see are single stand coil rolling mills where you have a reversing mill.  So, the strip passes through the same mill back and forth a few times, as many times as you need to achieve a final thickness.  And it does this, yes, in the following years, so you have a payoff reel that allows you to load the strip into the mill, yes, and then once you have put the strip on one of the tension reels, then you pass it through and you attach it to an entry tension reel also.  So, the strip passes through the mill with forward and backward tension, yes.  So, how does this work? So, you start here on the right hand side, yes.  So, you arrive with the hot rolled coils, yes, and you have two coilers here.  The first coiler is a payoff reel. So, here you just unwrap the hot rolled pickled coil and then you pass it through the mill and then you pick it up here, yes, on this tension reel, all right.  Now, the strip here will eventually come off, come off the mandrel, right, and you don't want it to flap around and you want it to, there should be some tension on the strip.  So, you have a strip press, yes, that will keep, give you some tension by friction, yes, and also prevents the strip from moving around, yes, okay, okay.  All right, so then most of this strip is now here, yes, and this end part here is now put on the tension reel here, yes, so it puts here and you start rolling, yes.  So, this is the first pass, this is the second pass, yes, okay.  So, you can do even number passes or uneven number of passes, okay.  So, if you do an even number of passes, one, two, the coil ends up here, you have to unload it from here, or if you do an uneven odd number of passes, the coil will be here, yes, okay.  Now, remember that when you go back and forth, yes, you always keep the end parts, the end parts here of the strip on the mandrel, so they never get rolled, okay.  So, if they don't get rolled, they remain thick, yes, so you have to get rid of these ends, yes, that didn't get rolled, yes.  So, what you do here is you cut it, for instance, in this case, you can see here you will take out this coil, so you come here, yes, you cut the end and then you go back and you roll up what's left, yes.  So, here you get a small piece of coil, yes, small piece of coil that is, has the, that's off thickness, yes, and you call this a pup coil, yes.  And on this side, of course, the central part of the coil will be off-gauge, will not have the right thickness, okay.  So, this odd number of passes is what you see is most common, you get off-gauge sections remain inside and the outside off-gauge section makes a pup coil, yes.  These are, these are pup coils, these are the small coils that are off-gauge and this is a puppy, it's the same pup, okay.  So, that means it's because there's the pup coils, you call them pup coils because they're small and cute, like this dog, okay.  Okay, so, and that's very common, these reversing mills, yes, and you produce pup coils and then you sell the pup coils also to smaller companies that can do something with them.  What you also have are mill stands where you don't have one stand but you have two stands, yes.  And so, for instance, here you have a situation where you have four high stands, you have two of them, yes, and you have two tension reels.  So, that means you can do twice the number of reductions per pass, yes.  So, it has a higher productivity, but it's basically a reversing mill also, you can just do more, you can produce faster.  And of course, because you have two stands, it's going to be a more expensive mill.  There are also double-cold rolling mills, like they, but that are different, yes, and they're not reversing mills and they're used to make tin plate.  And tin plate is a product with which you make, it's packaging steel, yes.  And these, they're non-reversing, so you only go, you pass once through this mill, so you only need a payoff reel, no tension, yes.  And a tension reel where you wrap up the strip after the rolling.  And so, usually you have two stands, you have a reduction stand, and then a surface conditioning stand that basically gives the right surface roughness to the strip.  Okay, and this is the same situation here, you have a reduction stand and a surface treatment stand in succession here.  And it's for, as I said, tin plate production.  We said a few things about gauge control in when we discussed the hot strip mill, yes.  I just want to say a few things at this point, at this juncture about the tandem mill.  So in a tandem mill, you have the strip goes from one stand into the other stand, yes.  And the, what you have to do in order to have stable rolling, you have to have a constant mass flow through the mill.  That means, what does that mean?  It means that the, whatever, the mass that comes in has to go out, yes, exactly the same value.  Otherwise, if the value that comes out is higher than what comes in, there will be a rupture.  Or if the value that comes out is lower than what you put in, you will have a cobble, yes.  So what does that mean, this constant mass flow?  It means that the product of the velocity of the strip out times the thickness of the strip should be equal to the velocity in and the thickness in of the next, of the next stand.  So the speed exit, the exit speed after the first mill, first stand, excuse me, is V1 and thickness H1.  Then the mass flow out of V1, out of the first stand is V1 H1, V2 H2 after the second one, etc. V5 H5.  So the constant mass flow requirements means that V1 H1 should be equal to V5 H5.  And of course, H1 is the entry thickness and H5 is the required exit thickness.  The thickness might be the actual gauge that's needed.  So the mass flow or the volume flow out of each stand is the product of the gauge, yes, times the strip out of each stand.  So if there is an error, yes, of gauge here, yes, it will always propagate through the mill, yes, through the mill.  Say if we have a constant mass flow out of V1, out of one, stand one, and say we have an exit gauge error,  we can exit here, right, we can correct it by changing the speed, yes, because if this difference is between,  sorry, if you have to correct for H, yes, you can do this by changing the velocities, yes, yes.  And so this brings in a new concept of gauge control in the cold strip mill, and that is gauge control with via speed, yes,  and it's based on basically this here.  So the way to control the thickness is with speed, right.  So again here just as in the case of the hot strip mill, yes, the gauge control, yes, is achieved by actuators,  and we have mechanical screw down actuators and hydraulic capsules, yes, and we know, we already discussed this,  mechanical screw downs have a slow response and the hydraulics are fast responders, yes, okay.  So how does it work?  You remember that hydraulic gap control is done by controlling the pressure in the hydraulic capsules, yes, right,  and you put the pressure on the backup roll chock, yes, all right,  or it can be electromechanical screw down, and that means that you have a motor, yes, and then via a gear box  and screw and nut geometry you can apply pressure, yes, and increase or decrease the gap by applying pressure on the backup roll chock, yes.  In most, as I had said, in most of the modern mills, yes, we will also have the possibility to improve the strip profile,  that's the cross-sectional, remember that's the cross-sectional shape of the strip, and that is done, for instance, in this case,  by bending, by roll bending capsules, yes, and here for instance you have, that means that you have little hydraulic capsules here  that can bend the roll, so you achieve the right roll profile, okay.  In addition to this, you can also have lateral roll shifting, yes, and you see the rolls here are asymmetric, yes,  and it allows you to do some additional types of bending, which we'll discuss in more detail, yes, or later on,  to achieve the right strip profile, so that's the cross-sectional shape of the strip,  and you can have lateral roll shifting, or you can even have cross-bare rolls, yes, okay.  All these things are very common in modern cold rolling mills.  In addition, because we're working at low temperature, we can do a lot more in-line measurements on the strip,  so standard cold rolling mills will have thickness gauges, which can be x-ray gauges, or isotope gauges, or even contact gauges,  although contact gauges are only suitable when you have low strip speeds.  You have tension control, it's also available, and of course you measure the force with load cells,  and you also have strip velocity measurements, yes, okay.  Again, we'll talk about this in more detail later on when we talk about strip profile.  Let's go back to some data about the cold rolling mill, how, what are typical cold rolling mill parameters.  Well, if you look in terms of the reduction, yes, the cold strip mill will typically produce material that's less than 2 millimeters thick,  and so you can see here if the strip is about 0.8 millimeters, yes, depending on the type of steel you're processing,  DDQ meaning deep drawing quality, deep drawing quality that will be batch annealed, it will be continuous annealed,  the carbon manganese structural steel, or niobium HSLA steel, the reductions are typically of the order of 75 percent, okay,  for a width here of 1250.  The number of mill stands is 4 to 5, nowadays it can be different,  it can be more like 5 or 6 perhaps.  The thickness that a cold rolling mill can take in is typically maximum,  as a maximum around 5 to 6 millimeters, yes, and the thickness out, you can see here about 0.2 millimeters, yes, minimum.  So the maximum reductions that we can give are 80 percent, 90 percent, yes, these are very high reductions,  usually a cold strip mill will operate at 70, 75 percent, yes.  The very high reductions are given to strip where we want to achieve texture control, very strong texture control.  And there's also usually a strip tension, yes.  So remember that when we did discuss the rolling fundamentals,  we saw that what is very important in rolling is friction.  And we also described the fact that in the roll gap, yes,  there was a considerable flattening of the roll, yes.  So you have a elastic deformation of the roll surface and it's flattened, it's strongly flattened.  And again there is forward slip, yes, and you have a shearing of the surface in the roll gap.  And remember this plot here shows that if we decrease the friction, we can decrease the rolling load, yes.  Now in the hot strip mill that was difficult to achieve, this reduction of friction through lubrication.  But you can achieve it very easily in the cold strip mill, yes.  And so we're going to take some time to discuss lubrication in the cold strip mill.  What are the functions of the lubrications?  Well, number one, of course, most important is reduction of friction.  Because then you have a direct economic advantage and technical advantage is you reduce,  you have considerable reduction of rolling forces, yes.  And because of that you also have a higher quality strip surface, yes,  better control of the strip profile and a reduced work roll wear.  So very important, yes, to have lubricants whenever you can.  The additional benefit of the lubrication is cooling, yes.  Because you use less forces, less load, you will have less heating also.  You will have less heating of the roll because there's less friction, yes.  And the heating is caused by friction and by deformation, we know.  Now, one of the things we could be using is water, yes, because water is a very good coolant, yes.  So we could use water.  But water is a very poor lubricant, yes, it's very poor lubricant.  And so we will not be using water or not only water in the lubricants for the cold strip mill.  We use emulsions, dispersions or stabilized dispersions.  Emulsion is a product that typically contains a few percent of surfactant.  We'll see what it is in a moment, which limits the breaking up of the oil particles into a separate layer, yes.  And so it means we don't need to agitate, mix the emulsion, the water-oil mixture, continuously to achieve, to make our lubricant.  A dispersion, here we have added surfactants, yes, which forms a protective colloidal layer on surface of oil particles, yes.  Again, the reason why we do this is to eliminate coalescence of the oil film.  In dispersions, what's the big difference between dispersion and emulsion, because it's rather similar,  is the fact that the distribution of particles, the control of the particle, oil particle size, is much narrower than in the case of an emulsion, yes.  And in a dispersion, the oil layer will tend to split off, yes.  And so you need to keep a dispersion well dispersed, yes, by agitating it, by mixing it, basically.  And then you have stabilized dispersions, which are newer systems, with something between emulsions and dispersion, but they don't need agitation.  Now, the fact that you reduce friction and you reduce, and the lubricants also work as coolants, is positive.  There is a negative about lubricants. Lubricants are basically organic products, and they will, because of the very high pressures in the roll gap,  they are sensitive to breakdown. And so lubrication will cause carbon deposits, yes, which you will need to remove, yes.  And of course, you will also need to remove residues of lubricants on your strip, okay.  So let's have a look at the basics, some basics of the oil, water, mixtures that we call emulsions, yes.  So we add oil, yes, and emulsifiers.  And emulsifier is basically a molecule which has a hydrophilic end and a lipophilic end.  So the lipophilic end is oil soluble, and the water soluble, or hydrophilic end is water soluble.  And so these molecules will orient themselves this way, yes, and this will stabilize our emulsion, okay.  Now, if you ever work later in a hot strip mail, the providers of lubricants are very specialized companies.  Usually they tend to be, it's a side product of petrochemical industry. So for instance, Texaco, Shell, and others are big suppliers of lubricants, yes.  Because it's a side product of the petroleum industry.  These are very complex chemistries, yes. So don't try to, by all by yourself, try to improve the chemistry or whatever, right.  It's pretty complex. There are many chemicals going into, and what I'm going to tell you here is just the tip of the iceberg.  But typically, these lubricants can easily contain, you know, 15 chemicals in their compositions, yeah.  The major constituents are mineral oils, which we call mineral oils, esters or mineral oils. They're major constituents, yes.  And so there's the base lubricants, and they are important in what we call elasto-hydrodynamic lubrication.  So EHD is, and I am sorry, I didn't, it's not included here, but EHD stands for elasto-hydrodynamic lubrication.  Or hydro-hydrodynamic lubrication.  Or hydro, these stands for hydrodynamic.  And then you have additional important compounds. You have fatty acids, yes.  They are important in boundary lubrication.  Boundary lubrication is when the two surfaces, the strip surface and the roll surface, for instance, are in physical contact, in strong physical contact, yeah.  And we also have antioxidants that will protect the lubricant from oxidation, polymerization, in other words, degradation over time.  We have emulsifiers, of course, that we add so we can mix the oil and water mixtures.  Then we also have phosphorus and sulfur-containing additives, and those are not organic molecules.  They tend to, they're added to form very strong films, yes, at the surface, yes.  The phosphorus-containing additives for films that can easily, very thin films that can easily be sheared, yes.  And the sulfur-containing additives are very resistant to high pressures, yes, and they prevent welding, yes.  Cold welding, I mean with this, we'll see where the cold welding occurs.  So let's have a look at two surfaces, two technical surfaces.  So technical surfaces of all kinds are never atomically smooth, yes.  They have a certain roughness and waviness at the surface.  So let's have a look now at metal-to-metal contact.  They say there's no oil, right?  So we call this dry lubrication. There's no lubricant, it's just dry.  And so this kind of lubrication is also called boundary lubrication when there is little or no lubricant.  So what happens if I bring these two surfaces together?  Well, the hails, the tops of the surface profiles will make contact, yes.  And if I press them together, yes, these tops here, these asperities will be squeezed, yes.  And if I squeeze hard enough, I may even cold weld them to each other, yes.  And in the case I have a little bit of lubricant, yes, there will be pockets of lubricants, yes.  Pockets of lubricant.  So in what we call boundary lubrication, yes, I have tiny pockets of lubricants,  and I have asperities that are flattened and there may be cold welding on these surfaces.  So what kind of situations do we have now?  If the two surfaces move relative to each other, yes.  If we have, say, hard asperity, hard top, or we have a hard surface, like a roll surface, it's hard,  and we have a soft strip surface, yes, we can get scratching,  pulling of the soft surface by a hard asperity, yes.  Or we can have bonding, they can, they can cold weld,  and then when the surfaces move away from each other, you can have breakage of that bond, yes.  And that process, these two first processes give rise to what we call iron finds.  Iron finds are typically found on cold deformed products, and they're very fine iron particles.  They come from these processes, yes.  If we have, yes, an oil film in between, these processes can be avoided, yes,  because now the deformation is what we call viscous drag, yes,  and this is basically when the two surfaces move with respect to each other,  we are not making bonding, we're not plowing the surfaces,  but we're just shearing, shearing this lubricant film, okay.  So let's have a look at this shearing process, yes, the shearing process, okay.  The shearing process of an, of oil is determined by its viscosity,  and the viscosity is equal to the shear stress divided by the shear rate, yes.  Okay, so if I have a high viscosity material, high viscosity oil,  I will need a high, high shear stress to achieve the same shear rate, yes, okay.  Now, so viscosity is an important parameter, it's the main parameter of the lubricant,  and from a mechanical point of view, yes, and it's very much pressure and temperature dependence.  Well, we're all familiar with the temperature dependence, we know that if you have an oil, yes,  and you warm it up, it will become thinner, it will lose its viscosity.  So the viscosity decreases with increasing temperature.  What we usually do not know from experience is the fact that with pressure, the viscosity increases, yeah.  And of course, why is this so important? It's so important because in rolling, we have very high pressures, yes.  Okay, now let's have a look at the pressure influence, the influence of pressure on viscosity.  So let's look at water first, and we increase the pressure, say here from 0.1 megapascal to 1 gigapascal.  You see that water, the viscosity doesn't change very much, yes, it goes from 1 to a little bit less than 2, yes.  By the way, the viscosity is in centipoise, so it's Pascal's times seconds, yes.  And with mineral oils, yes, of course we start with a lubricant that's a lot more viscous than water,  but as you increase, you get a dramatic, huge increase in the viscosity, not just a little bit, not just doubling,  but a very, very large increase in the viscosity, yes.  Okay, so in a mill, the viscosity is much, much higher than the one you feel with your fingers, okay, because of these very high pressures.  Alright, now with lubrication, there are many parameters, yes.  Let's just look at the process of rolling, yes.  We know that locally there will be a pressure, yes.  We also know that there will be a relative velocity, yes.  The strip will, is never at the same velocity, yes, as the roll surface, yes, so there is a relative velocity.  And then the lubricant has a certain viscosity, yes.  So how is it possible to talk in a simple manner about lubrication, taking into account all these parameters, yes.  Well, yes, it just turns out that you can plot a master curve for a lubricant, yes, where you get, so on the y-axis,  you get the coefficient of friction, mu, which is the shear stress divided by pressure.  So you know what friction is, if you have two surfaces, yes, and they're under pressure, right.  The friction coefficient is the ratio of the shear stress to the applied pressure, yes.  And you want, so when a lubricant works well, yes, the friction coefficient will be low,  because the shear stress to get the thing moving will be lower, okay.  So, well, so in the y-axis, you do speed time viscosity divided by the pressure.  And this is, this parameter, yes, allows you to draw a single curve for the friction coefficient, and it looks like this.  This is what it looks like.  So, when this parameter has a low value, I have high friction, yes.  When this parameter has a high value, I have low friction.  So, let's first look at pressure, yes.  If I have a high pressure, yes, the velocity and the lubricant viscosity being the same, yes.  An increase in P means that I'm on this side.  So when P increases, I'm on the, yes, I mean, so I have high friction conditions, yeah.  So if I have a high velocity, yes, then I'm going this way, yes.  I will get the reduction in friction, all other things being the same.  The viscosity of my lubricant and the pressure being the same.  Why is it that this happens?  Well, the reason is very simple.  It's because something happens to the lubricant film thickness.  The lubricant film thickness goes like this.  So, and what happens, well, it's shown here, yes.  When this parameter here, yes, by the way, this curve is called the street back curve, yes.  So when this parameter is small, you have metal to metal contacts  and you have dry lubrication conditions, so high friction conditions, yes.  And typically the friction coefficient is then between 0.1 to 1, yes.  As this parameter increases, because you've increased the viscosity  or you've increasing the speed or you're decreasing the pressure, yeah,  you have, you're creating lubricant pockets, lubricant pockets.  You can see the thickness of the film increases, yes.  And you get a situation that's called mixed lubrication, yes.  The minimum is reached when we have so-called elasto-hydrodynamic lubrications,  where you have a large number of lubricant pockets.  And the hydrodynamic lubrication is the case here,  when you, thickness of the film is such that the two surfaces are separated, yes.  And the friction is then a function of the properties of the lubricant only, okay.  Right, so when are we in the right working conditions?  So we know we'd like to avoid boundary type lubrication  and we'd like to have elasto-hydrodynamic lubrication with low friction.  So what, the situation will depend on the roughness of the,  the combined roughnesses of your surfaces, which in the case of rolling is the roll surface  and the strip surface, and the lubricant film thickness.  So when we have a rolling situation, we have a work roll roughness and a strip roughness, yes.  And the combined roughness is taken as the square root of the roughness of the work roll  square times the strip roughness square.  The lubricant film thickness, we call H.  So when H is about the same as this sigma, we have boundary lubrication.  If the film thickness is one to three times the combined roughness,  then we are in mixed condition and we have the right elasto-hydrodynamic,  this is a typo here, EHD, elasto-hydrodynamic lubrication,  if the thickness is about three times the combined roughness, okay.  This is kind of a picture here, so you have an idea of what happens.  So at the inlet here, yes, we have the, the oil is entrapped, yes,  between the work roll and the strip, yes.  So in this contact area, we have lubricant pockets  and we may have places where the surface is in contact, yes.  Where they're touched, touching.  So in the case of boundary lubrication, I have very small, these pockets are very small, yes.  In the case of the elasto-hydrodynamic lubrication,  I have a lot more lubricant between the two surfaces.  You get in areas, in many areas, you get total separation of the surfaces.  Now, having said this, it's also important to realize that at the surface here, yes,  because there is a relative movement between the surfaces,  these contact places don't remain like this, yes.  In particular, these lubricant pockets will become undeeper and they will flatten out, yes.  And also the surface will be stretched like this, okay.  So the shape doesn't stay like this, no.  So we get asperities that are crushed and there is plastic shear deformation at the surface.  And the process here of these asperities being deformed, yes, being sheared off,  leads to carbon fines and also these extreme mechanical conditions here  also lead to decomposition of these mineral oils and you'll form carbon residues, yes.  Which, again, both of these things need to be reduced.  In the roll gap itself, the film thickness is pretty flat,  because the roll gap is actually very flat, because the roll flattening is very flat, yes.  At the beginning, of course, we get the start at the entry,  you have the oil is taken into the roll gap,  and at the exit, you get an interesting phenomenon,  is that the thickness of the oil is decreasing and we get a pressure peak,  which is called Petrusevich pressure peak.  And the reason why we have this precious peak is because when the strip leaves the roll gap,  there is an elastic, the roll surface is now free, yes, it's free.  And so it will elastically bounce back, yes.  It's been flattened very much, it's going to bounce back, yes.  And so it will actually squeeze the oil film a little bit,  and that gives us this pressure peak, all right.  So very important, this E-E-H-D elasto-hydrodynamic lubrication,  and it's lubrication by a lubricant film, full lubricant film,  in condition of elastic contact and high pressure.  So this high pressure results in a very flat contact area,  and because of these high pressures, your oil is very, very viscous, yes.  And there where you have no contact between the two,  you have what we call glide-like conditions, yes.  You basically shear the oil film, okay.  Let's have a look now at velocity, the impact of the velocity.  What happens with the velocity?  So you can already see here, yes,  that when I keep the viscosity of the oil the same,  I keep the pressure the same, I just increase the velocity,  that means my oil film will increase in thickness, okay.  And you can measure this.  It's a rather complicated way, tests to do this,  but it's possible to measure the film, the oil film thickness  as a function of the velocity.  And you can do this for neat oils, or you can do this for emulsions.  When you talk about neat oils, that means you're not mixing it with water.  You just use the pure oil as such, yes.  So you can use neat oil or water plus oil emulsions.  And so you see that as you increase the velocity,  you get the thickness of the film increases.  And you can see here what type of thicknesses we're talking about,  10 nanometers, 100 nanometers, very thin films, yes.  And you also see the effect of the temperature.  So the temperature increases, that means the lubrication,  the, your,  viscosity decreases.  And so there is a shift of this line to the right.  And basically you basically get a decrease in film thickness.  Okay?  Right, so quite a complex thing happens when you  entrap the lubricant film in the roll gap.  So, so in the roll gap, the oil, or the lubricant,  is sucked into the roll gap, yes.  And you get a, what's called a phase inversion of the oil-water emulsion, yes.  And what actually happens is this oil-water emulsion turns into a water-oil emulsion.  Yes, you get the inversion of this thing here.  The other thing that happens, yes, is that if we increase the speed too much, yes,  there will not be enough, you need to, so the oil goes through the roll gap, right.  So you will, you need to suck in the lubricant at the entry.  So if you roll too fast, you turn too fast, there's not going to be enough oil supplied at the entry, yes.  And you can get what's called oil starvation, yes,  where there's not enough oil being supplied at the entry, yes,  and you get a collapse of the oil film, yes.  Okay, and so H decreases suddenly, yes, and when H decreases, of course,  we're going into boundary lubrication situation, yes.  Now, these things can happen, yes,  and then suddenly you find yourself with very little lubricant, yes,  and you start making contacts between the two metal surfaces,  very high pressure contacts, and there's going to be shear forces, shear, yes.  So that's why we add these sulfur and phosphorus compounds, yes,  to prevent welding, yes, at the surface.  When we have, when you happen to have boundary lubrication problems, yes,  and you will have those, for instance, when for some reason or another you have to go  and work into low speed conditions or higher temperatures for some reason  or high roughness, yes, the surface happens to be high roughness, yes.  Then we luckily have, in the compounds of the lubricant formulation,  you have boundary films, phosphates and sulfides,  oxides and sulfides, at the surface.  So your boundary film, very close to the steel surface, is inorganic, yes,  and the oil is on top of that.  That's how you, a good picture here.  So when the oil film collapses, these two inorganic compounds will play a role,  because they adhere to the steel surface, so they can easily shear, yes,  and they have very high resistance against being squeezed out, yes,  and they're very pressure resistant, and they, because they're there,  they also make it difficult for the two surfaces to cold weld to each other.  So that's why we have phosphates and sulfides.  So, you know, the situation where the conditions become bad during rolling  happens, for instance, when you have to reduce the velocity, yes,  for instance, you're rolling and then you have to stop rolling  because you finished the strip, the strip comes out of the mill,  so you have to reduce the velocity, right,  so, or when you're starting to roll, yes, you're not suddenly at very high  rolling speeds, you build up, right, so you start at low velocities, yes,  and in these cases, you can be in high friction conditions, okay,  and this is one of the reasons why working continuously is so important,  so if you're asking yourself, why do we have a, why do we put our pickling line,  yes, and put it right into the cold mill, that's because the cold mill  then can work all the time, yes, you can just attach the coils after the other  and the cold mill never stops, so you never have these big speed variations, yes,  so it makes economic sense because you put things together and some equipment disappears,  but it also makes a sense from a product point of view to work in constant  and continuous conditions, okay, so let's get back to our cold mill here,  so when we start, we have, if it's a carbon steel, we have our grains here, yes,  you pass through the cold rolling mill, so you basically have a plane strain  deformation which leads to a pronounced preferred orientations of all these grains,  so you get these grains are now pancake, yes, highly deformed, deformations can be,  as I said, 75%, 80%, so a lot more, a lot larger than the deformation you give,  for instance, in a tensile test, yes, and as a consequence, the orientation,  crystallographic orientation distribution changes, yes, and in the case of carbon  steels, yes, what we want to have in our product is what's called a very strong gamma  fiber, we want to have all these little crystals, we want them to have the 1, 1,  1, 1 orientation parallel to the 1, 1, 1 direction, parallel to the normal direction  of the sheet, yes, okay, and this is achieved by a combination of high levels of  deformation and recrystallization and annealing, yes, so the cold rolled material  is a very high level of crystallographic preferred orientation, but you cannot do  anything with it because it's deformed, heavily deformed, it has no residual  plasticity, so you need to do, to anneal this, yes, and during the annealing process  you recreate low defect density grains, yes, and a highly textured microstructure  with 1, 1, 1 parallel to normal direction being the preferred orientation for the  grains, yes, and this situation gives you a high r value, so high plasticity and a  very low planar anisotropy, so the r value doesn't change much as a function of  direction in which it's tested, okay, now the process of going from this to this,  yes, is a kinetics process, it depends on time, it depends on temperature, it also  depends on the amount of deformation you've given, yes, so typically if you, if  your deformation, the amount of deformation is less than 50%, it's going to take a  long time to recrystallize, yes, and that's why in cold rolling, in cold deformation  we like to give large amounts of deformations because that will speed up the  recrystallization, why is that? Well, because the dislocation density here is the  driving force for the recrystallization, the more I have deformed the material, the  higher the driving force, the faster it will recrystallize, okay, so there are two  ways to recrystallize the steel product, you can do it by batch annealing, yes, you  basically take your coil of cold rolled material, you put it in a furnace for a  long time, yes, and you let it recrystallize, this is one of these furnaces that's  being opened, you can't see the coils, the coils are inside this tube here, that's  what the furnace is, and this here is a continuous annealing furnace, there you,  instead of annealing the coil, you anneal the strip, yes, so you uncoil the strip  and you pass the strip through a furnace, yes, so you see here the strip, I guess,  coming out of, or going into the furnace, I can't tell the furnaces here, and this  is an accumulator where you store some few hundreds of meters of uncoiled strip,  so let's start with the batch annealing furnace, so in this furnace let's have a  look at, okay, so this is what they look like, in the interior we stack the coils,  yes, and we let gas flow through this, the furnace, okay, and it's protective gas,  it's hydrogen-nitrogen mixture, and it's a protective atmosphere, so where do you do  the heating, you do the heating on the outside of this furnace, so there is this  here, that's where you have burners, yes, and so that will heat up the interior wall  of this furnace and this radiation heat will then heat up your coils, let's see  here, okay, and this is what you see here, the coils are inside this furnace, and this  is a cover, yes, the cover which contains the burners, okay, so you can have this,  the amount of weight that you can anneal here is for instance of the order of 115,  so that means there's quite a few coils can go, be put in there on top of each other,  height, 5 meters, annealing capacity, 2.7 tons per hour, that's not very high, so  because the process is very slow, you need many of these furnaces in parallel, so if  you visit a batch annealing section of a cold rolling mill, you will not see one  furnace, you'll see many furnaces, for instance 47 furnaces, and there may be more  bases, yes, bases are these places on which you can put a furnace, yes, why are there  much more bases than you have annealing hoods, because you have to heat, you only need  the hoods, yes, when you heat up, yes, when you cool down, you just don't need this  cover here, so capacity 80,000 tons per year, surface cleanliness, that's the carbon  residue that I talked about, and the gas in for this particular picture here was  hydrogen, but in general it's hydrogen plus nitrogen, and I will say something about  the use of hydrogen, and the heating itself is done by LPG or by electricity, I'm  seeing I'm over time here, so I will stop at this point, and we'll continue, I guess  we'll continue next week, because Thursday is first of May, yes, and I think we don't  have class, right, on first of May, I guess I will reconvene a week from now.  Next Tuesday also, is next Tuesday a holiday? I don't know, is that number, is it an official  post-ec day? I haven't heard about that, is it official post-ec day? Okay, oh it's  not official post-ec day, then I'm not going to say anything about this. Right, so we  will need to perhaps have a make-up class or something, okay, but so, well then we  will meet next week on Thursday, okay, don't forget that there will be a regular quiz.  Thank you.  Thank you.
Modern_Steel_Products_-_2014__Cold-strip_mill__13_0_47.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_48_107.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_108_2243.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_2244_6047.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_6048_7403.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_7404_8507.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_8508_8555.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_8556_9299.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_9300_10823.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_10824_11747.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_11748_11795.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_11796_11963.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_11964_12503.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_12504_14795.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_14796_16775.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_16776_22415.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_22416_22871.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_22872_23543.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_23544_24659.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_24660_26303.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_26304_26819.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_26820_33359.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_33360_34163.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_34164_34919.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_34920_36707.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_36708_37703.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_37704_39167.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_39168_42959.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_42960_43331.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_43332_44459.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_44460_45227.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_45228_51359.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_51360_51815.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_51816_52331.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_52332_53495.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_53496_59399.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_59400_62027.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_62028_64787.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_64788_65363.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_65364_65531.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_65532_65951.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_65952_66083.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_66084_66347.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_66348_67667.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_67668_68411.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_68412_70091.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_70092_79259.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_79260_81983.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_81984_85559.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_85560_87707.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_87708_88919.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_88920_88991.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_88992_89063.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_89064_92123.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_92124_96419.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_96420_101951.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_101952_103955.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_103956_105899.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_105900_105947.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_105948_107483.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_107484_107771.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_107772_108443.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_108444_108551.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_108552_108971.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_108972_109031.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_109032_109307.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_109308_109391.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_109392_109619.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_109620_109823.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_109824_111227.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_111228_111299.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_111300_114479.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_114480_114575.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_114576_114623.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_114624_115787.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_115788_115847.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_115848_115895.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_115896_115943.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_115944_115991.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_115992_116039.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116040_116099.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116100_116147.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116148_116195.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116196_116243.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116244_116291.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116292_116363.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116364_116423.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116424_116471.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116472_116519.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116520_116591.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116592_116639.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116640_116687.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116688_116735.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116736_116795.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116796_116879.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116880_116939.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116940_116987.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_116988_117047.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117048_117095.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117096_117263.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117264_117359.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117360_117419.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117420_117491.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117492_117563.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117564_117623.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117624_117695.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117696_117743.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117744_117791.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117792_117839.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_117840_118019.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_118020_118091.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_118092_118139.png Modern_Steel_Products_-_2014__Cold-strip_mill__13_118140_118150.png