In the art of arc welding, particularly in the area using inert gas as a shield, (commonly known in the art as metal inert gas or xe2x80x9cMIGxe2x80x9d systems), generated heat is extensive, being in excess of 10,000 to 12,000 degrees Fahrenheit, at the arc point. It is not uncommon for heat to be transferred to metal parts of the welding apparatus in excess of 1,000 degrees Fahrenheit. There have been multiple ongoing efforts to remove generated heat from these type of welding units and similar units. Excessive heat makes workers uncomfortable, but it also degrades the working apparatus much more quickly during high temperature heat exposure. Replacement of the arc welding apparatus parts that degrade is an expensive and time-consuming process.
When robotic welding units are used, the loss of time required for maintenance becomes significant. For this reason and others, efforts to remove the built-up heat generated during the welding process has been ongoing, but thus far no system has realized a truly efficient process.
Some of the earlier attempts at cooling the welding apparatus is exemplified in U.S. Pat. No. 4,864,099 (Cusick), entitled xe2x80x9cWater cooled semi-automatic welding gunxe2x80x9d. This invention utilized a liquid cooled welding gun assembly. Power, gas and cooling liquid hoses were contained within the cable assembly and intercommunicated the connector block of the welding gun assembly with the rear connector block. This welding gun assembly included a liquid cooled nozzle assembly, with internal cooling passages. Although liquids showed a great propensity for cooling, the amount of water to be used in removing the heat because burdensome, and further improvements were needed.
Referring now also to U.S. Pat. No. 5,670,073 (Kiilunen), entitled xe2x80x9cWater cooled gas metal arc welding gunxe2x80x9d, a water cooled gas metal arc welding (MIG) gun was disclosed in which a water cooling system for the gun barrel introduced coolant water at the bottom of the barrel to create a coolant water flow through the gun. One of the goals and benefits of this invention was that it did not allow the coolant water to stagnate and heat up. Again, the amount of water and burden of maintenance made this particular welding apparatus problematic for heavy use. Another dangerous use of water in the TIG and MIG welding systems was the significant levels of electricity used in the welding process, which made a water leak extremely hazardous, due to electrical shock.
Water generally presents other problems to the welding processes, beyond increasing the danger of electrical shock. Water intrusion into the welding process often degrades the welding quality of the finished product. There have been numerous patents directed to avoiding the use of water exposure to the welding process. For example, in U.S. Pat. No. 6,153,847 (Nakatani et al.), entitled xe2x80x9cWelding member and welding methodxe2x80x9d a water-repellent film was applied directly onto the surface of a welding member between two mating welding bevels, a welding bevel of a base member to be welded, and a coated welding rod formed by coating a metallic core wire with a flux. The water-repellent film was formed of a hydrophobic material having a contact angle of 90.degree. or above and providing minute concavities and convexities. Thus, in a highly humid environment, during rainfall or even in water, welding could be effected without weld defects such as blow holes, cracks and the like.
In a effort to avoid the problems associated with water cooled systems, further improvements were made. Referring now to U.S. Pat. No. 5,248,868 (Cusick), entitled xe2x80x9cMelding gunxe2x80x9d (corrected title is xe2x80x9cWelding gunxe2x80x9d) Cooling in this instance was accomplished through a plurality of open recesses or channels whereby pressurized air was conveyed. This welding gun assembly also included a pressurized air cooled nozzle assembly. In this invention, pressurized and refrigerated air cooled non-insulated conductor wires along with cooling a rear connector assembly, a cable assembly, a front connector assembly or handle assembly, a conductor tube assembly, and a nozzle assembly.
Further improvements were made in which air was used as a heat exchanger. Referring now to U.S. Pat. No. 6,005,221 (Cusick), entitled xe2x80x9cPressurized air cooled tungsten inert gas welding apparatusxe2x80x9d. This invention was directed toward an improved tungsten insert gas (TIG) arc welding process, having a means to remove heat energy using pressurized air, and a method for removing the heat away from the torch head area. A source of pressurized air was delivered though a hose to the torch head, and directed through heat conductive air tube coils within the torch head. As the air moved through the coils, it acquired some of the heat energy within the welding head. The heated air was then vented into an outer jacket, which contains the electrically conductive cables, and an airspace surrounding the cables. As the heated air moved toward a rear connector block, it contacted the length of the cables, and was further able to transfer some of the heat to the cables. This allowed some of the heat energy contained within the pressurized air to be transferred through physical contact to the metal cable, so that as the air moved farther along the length of the metal cable, it transferred more of its heat energy.
Use of heat exchanging/removal substances directly on surfaces being welded was shown in U.S. Pat. No. 6,168,843 (Hallo), entitled xe2x80x9cMethod for dissipating heatxe2x80x9d. In this invention, a method was shown for increasing the dissipation of heat from one portion of a surface when heat was applied to another portion of the same surface. A composition of a gel or paste with high water content and a thickener of a mineral clay in a colloidal suspension was used. This system had problems associated with the need to make all of the various applications of the gel or paste, and due to the time constraint requirements, was virtually unworkable in a robotic setting.
This invention and method process combines the benefits of heat extraction, using not only water, but also with the use of air supplying a volume area usable as a means to transport water that has undergone conversion to steam away from the welding head. This invention avoids problems of the risk of electrical shock, while still using water, or any liquid capable of undergoing a phase change from liquid to gas when absorbing a significant amount of heat energy per unit of liquid during the phase change, as compared to heat absorption per unit without any phase change, to absorb vast quantities of heat.
Water is a cheap and readily available heat transfer means, which is undoubtedly why it was originally used in the inventions cited above. The problems with water usage, however, drove the inventive ideas of people using these products to turn to air as a means to remove heat. It is clear that a greater quantity of air is required to achieve the same heat removal properties that a much smaller quantity of water is capable of doing, and thus volumes of air needed to be pumped through the system. While remaining a better alternative than liquid water, it still could only provide reasonable cooling.
What was not considered in any of the above inventions, was the incredible heat absorption capacity of water during an evaporation process. The absorption of heat by a substance always produces some change. In addition to thermal expansion, its temperature may rise or it may undergo a phase change in which its physical characteristics are altered without a change in temperature. This is the difference between xe2x80x9cspecific heatxe2x80x9d, which considers the number of calories or heat energy units required to raise the temperature of one gram of a substance one degree Celsius. The amount of heat transferred during changes of phase is called xe2x80x9clatent heatxe2x80x9d. The heat of vaporization for water is extremely large because of the strong attraction between water molecules and the consequently large amounts of energy that must be expended to separate then into the vapor state. For water, the latent heat of vaporization to convert water to steam, where both remain at 100 degrees Celsius is 540 cal/g.
Steam, by its very nature of being in an excited state, requires a great deal more volume then it""s a previous liquid state. None of the above inventions provide for the transfer of latent heat energy, and are thus restricted to much lower levels of heat energy transfer, since they must rely solely on xe2x80x9cspecific heatxe2x80x9d transfers.
This invention takes advantage of the xe2x80x9clatent heatxe2x80x9d transfer, by providing a small quantity of water which is directed through a common atomizer, and then directed into the welding head unit so it can contact those parts of a welding head that absorb great quantities of heat. The atomized water, being presented in a mist form, is able to fill the airspace provided, contact a heated nozzle, and quickly convert into steam which is then able to be injected directly out of the rear of the arc welding nozzle, away from the user. The amount of water used, and thus the amount of steam generated, is extremely small, especially when used in conjunction with other cooling methods. Typically, the user will not even see any appreciable amount of steam exiting the apparatus.
Using only liquid water in the prior art forms shown above, are vastly inefficient as compared with the present invention. For example, a cubic centimeter of water, introduced to absorb heat, where the water is 25 degrees Celsius, is only able to absorb 75 calories of heat, before being expelled for cooling. Then, there is the problem of cooling the water, if it is going to be recycled through the system. Contrast the same cubic centimeter of water with the atomizer steam process, and the ability to absorb heat, has the same cubic centimeter of water absorbing the 75 calories, plus an additional 540 calories that is required to convert the water to steam, for a total of 615 calories. This is over eight times as efficient as the liquid water transfer. The efficiency is further enhanced, since the atomized water, having such a small diameter size, is able to undergo the steam conversion virtually immediately when contacting an extremely hot welding head. This makes quicker use of the latent energy transfer, since only small amounts of atomized water are contacting the hot surfaces at any given time, so that they are raised to 100 degrees Celsius almost immediately, and then undergo the acquisition of latent heat, which is the actual efficient energy transfer. By using an atomizer, the efficiency of the system is virtually always using latent heat exchange.
Using atomized water allows a mist to be introduced to the heated portions of the welding apparatus. This does not cause temperature gradient stress on the parts of the apparatus, that would otherwise occur if a quantity of liquid were simply splashed onto the part. The instantaneous boiling would produce a problem with the rapid expansion of steam, as well as cause the parts themselves to be subject to cracking and other degradations.
The advantages of this innovative system, being able to rely on latent heat transfer is quickly realized when the welding itself is ceased, and the welding apparatus is able to be touched with unprotected human hands within seconds of the termination of the welding. Interchanging parts is able to be done immediately, with the chief benefit, however, being that the parts do not absorb significant amounts heat that causes them to degrade. Therefore, repairs to a welding apparatus are minimized. This system does not produce vast quantities of steam that put other workers at risk, or introduce undesirable amounts of water vapor against other objects.
It is therefore the object of this invention to provide an improved welding apparatus that is able to remove undesired quantities of heat energy from a welding apparatus, with the heat transfer being done virtually immediately through use of latent energy transfer.
It is also a further object of this invention to provide an improved method of removing undesired quantities of heat energy from a welding apparatus, with the heat transfer being done virtually immediately through use of latent energy transfer with atomizer water vapor converted to steam.
It is also a further object of this invention to provide an apparatus and method suitable for robotic, semi-automatic and automatic welding apparatus, that allows continuous use of a welding apparatus with only minimal repairs necessary to the welding apparatus due to heat degradation.