The present invention relates generally to shapemeters that measure the flatness of metal strip under tension as the strip passes over a shapemeter roll.
It is well known in the art that the best and perhaps the only practical way of measuring flatness of strip as it is being rolled by a strip rolling mill, with tension applied to incoming and outgoing strip, is to measure the tension distribution across the width of the strip, as it leaves the rolling mill and travels to a coiler or take-up reel, or some other downstream process.
In general, a strip which has uniform tension distribution would lie flat on a horizontal table if it was subsequently unwound from the coiler and set down with the tension removed. Strip having non-uniform tension distribution would, in general, not lie flat, but would be seen to have wavy or buckled portions, corresponding to the zones of the strip which had been rolled with the lowest tension.
An early shape or flatness measuring device is disclosed in Pearson, U.K. 1,160,112 and corresponding U.S. Pat. No. 3,499,306. The Pearson device of FIG. 1 of ""112 was not a commercial success, but the Pearson device shown in FIG. 7 of ""112 or the Pearson ""306 patent was. This device and the one shown on FIG. 3 of Pearson ""306 operated by sensing the tension distribution in the material, by passing it over a measuring roller.
The measuring roller of Pearson ""306 consists of a central stationary (xe2x80x9cdeadxe2x80x9d) shaft, and a series of bearings mounted concentrically on the shaft. These bearings are placed side by side across the full width of the strip material. Transducers are provided at each bearing location to measure the radial force on the bearing, this being a measure of the tension in that portion of the material passing over that bearing. The Pearson device in FIG. 7 of ""306 utilized fluid film bearings, and pressure transducers were used to measure fluid pressure, which is a measure of radial force. The device in FIG. 3 of ""306 utilized roller bearings, with a flexible portion on each bearing inner race within the load zone of the bearing. A displacement transducer was used to measure the deflection of this flexible portion, this deflection being a measure of radial force.
Another stationary shaft shapemeter is disclosed in Muhlberg (U.S. Pat. No. 3,557,614), which is similar in concept to the FIG. 3 embodiment of Pearson ""306 (but with additional features). The essential features in Muhlberg are a series of bearings mounted upon a common shaft, with suitable covering for the bearings and with a force sensing transducer mounted underneath some or all of these bearings, to measure the radial force developed on these bearings as a result of the strip wrapping around the roll under tension.
Yet another stationary shaft shapemeter is disclosed in Flinth (U.S. Pat. No. 3,413,846). Flinth used a shapemeter roll as a billy roll (which is normally understood in the art to be a roll located between a mill and a coiler, and is used to maintain a constant pass line level through the mill, while the coil diameter is building up (coiling), or reducing (uncoiling). The billy roll consisted of a central, stationary shaft, an outer casing rotatably mounted on the shaft, and a number of pressure sensing means arranged to be influenced by the pressure between the outer casing and the shaft.
The way in which all commercially available shapemeters work is by providing a roll around which the strip passes on its way from the rolling mill to the subsequent process. The strip wraps around the roll usually by an angle in the range 5xc2x0 to 90xc2x0. In some applications this angle can be fixed. In others, for example when the roll is used as the only deflector roll (sometimes called a billy roll) between a rolling mill and a coiler, the wrap angle varies as the coil builds up in diameter as rolling progresses and more strip is added to the coil. However, in all cases a radial force develops on the roll as a result of the strip under tension wrapping around it, and shapemeters work by measuring the distribution of this force across the face of the roll, this being a measure of the distribution of tension across the width of the strip.
In these conventional shapemeters, the distribution of force is measured by a row of transducers mounted within this roll, usually spaced at fixed intervals in the range 20-60 mm across the face of the roll. Because the tension at the strip edges is very criticalxe2x80x94since excessive tension at the edges can lead to strip breakage, particularly if the strip edges are cracked or otherwise defectivexe2x80x94some shapemeters use smaller intervals or pitches in areas of the roll closer to the strip edges than in areas close to the middle of the strip. The portion of the roll corresponding to an individual transducer is known as a measuring zone, and each transducer measures the radial force produced by the portion of strip passing around the corresponding zone of the roll.
In principle there are two types of shapemeters covered by the above description. The first type utilizes a single roll mounted in bearings. Transducers are mounted within the roll, which is machined to provide cavities in which the transducers can be fitted. Each measuring zone, and hence each transducer, is covered with a thin ring of steel, which itself may be covered in an elastomeric material. The entire roll consists of a body which is sufficiently long to cover the maximum width of strip to be rolled, and an integral neck at each end of the body. Each neck is bearing mounted within fixed housings. The transducers all rotate with the roll, and therefore, they are only subjected to load for a small portion of each revolution of the roll. If the wrap angle of the strip is 30 degrees, for example, the transducers are loaded for only 30 degrees for each revolution, and are unloaded for the remaining 330 degrees.
In order to obtain electrical signals of load from the transducers (which are rotating), it is necessary to provide slip rings or other devices, such as multi-channel inductive or optical pickups or FM radio links, to transfer these signals to a computer or other display device that is positioned at a fixed location. Since there are multiple transducers, their signals are typically sampled and combined into one overall load-relative signal, thereby requiring multiple analog or digital comparators to choose the presently active signal (i.e., the signal of the greatest magnitude).
The second shapemeter type utilizes a stationary (non-rotating) shaft which spans across the width of the strip, and is supported in stationary support blocks. A separate bearing is mounted upon this shaft at each measuring zone, and on the outside of this bearing a plain or elastomer covered steel ring is mounted, covering the full width of the zone. On the inside of each bearing a fixed transducer is mounted within the shaft, this transducer measuring the radial force on the bearing. The output signal from each transducer can be directly wired to a stationary external computer or other display device, usually through an axial hole passing through the shaft, provided for this purpose. The transducers are loaded for the full 360xc2x0 rotation of the roll. The shapemeter of U.S. Pat. No. 5,537,878 for example, as well as those of Pearson ""306 FIG. 7, Muhiberg ""614 and Filinth ""846 are all the stationary shaft type.
Each of the above types of shapemeters has its advantages. The first type (rotating shaft) has the advantage that the shaft diameter is effectively the full diameter of the roll, and therefore this has greater rigidity and lower shaft stress and deflection than the second type. The second type (stationary shaft) has the advantage that no slip rings are required, and that the output signal is steady, and does not need to be sampled. The greater shaft deflection may not be significant when tensions are not too high, wrap angles are not too large, or roll face length is not too long. The deflection can also be reduced by using bearings with a very small section height, such as air film or oil film bearings, or by increasing the roll diameter.
All of the above shapemeter types are very expensive, because they all require a multiplicity of very accurately machined sleeve rings to be mounted on a central shaft, and the diameter of the central shaft must be large, in order to ensure that the effect of the shaft deflection does not render the flatness measurement inaccurate.
In general, the roll diameters of shapemeters available commercially lie in the range 313-406 mm (12.3-16 in.), with a shapemeter having a roll as small as 150 mm (5.9 in.) available only for aluminum strip (where tensions are very low) based on the Pearson device of FIG. 7 of Pearson ""306. This shapemeter is considerably less expensive than the ones having larger rolls, but is still too expensive for many mills.
It is remarkable that, in general, only the largest cold rolling mills are equipped with shapemeters, even though the operators of the smaller mills would like to have them. The problem remains primarily one of cost. For a small mill the cost of some of the above types of shapemeter can approach the cost of the entire electrical drive system, and so is prohibitive.
In order to reduce the cost, the present invention incorporates rollers which are much smaller in diameter than prior art shapemeters. This not only reduces the weight and the cost, but also enables the shapemeter of the present invention to be fitted into spaces enabling it to be installed on a large number of cold rolling mills in which there is insufficient space for prior art shapemeters.
The invention will now be described by way of example.