Electric heating – Metal heating – By arc
Reexamination Certificate
2001-09-04
2003-07-01
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S074000, C219S075000
Reexamination Certificate
active
06586708
ABSTRACT:
BACKGROUND OF THE INVENTION
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 “MIG” 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 “Water cooled semi-automatic welding gun”. 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 “Water cooled gas metal arc welding gun”, 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 “Welding member and welding method” 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 “Melding gun” (corrected title is “Welding gun”) 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 “Pressurized air cooled tungsten inert gas welding apparatus”. 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 “Method for dissipating heat”. 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.
SUMMARY OF THE INVENTION
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 “specific heat”, 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 “latent heat”. 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 wa
Shaw Clifford C.
Sylvester Bradley P.
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