Rotary expansible chamber devices – With wear surface treatment or integrally plated wear layer
Reexamination Certificate
1998-10-15
2001-03-27
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
With wear surface treatment or integrally plated wear layer
C418S179000, C418S206900, C417S218000, C073S204270
Reexamination Certificate
active
06206667
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to pumps and, more specifically, to gear pumps designed to meter epoxy resins.
BACKGROUND OF THE INVENTION
Metering gear pumps operate by squeezing out accurate volumes of liquid between meshing gears. Typically, the gears are mounted within stacked plates that are appropriately ported to receive liquid between the gears and discharge the liquid in one or more streams.
In highly accurate gear pumps useful for metering resins, for example, tolerances are critically maintained between pump bearings and shafts as well as between support plates (often referred to as “kidney plates”) and gears. Theoretically, these part relationships maintain so-called “zero clearance.” Due to the close tolerances maintained on the various internal components of the gear pump, frictional heat build-up can become a significant problem. At times, this can cause relatively moving parts to adhere to one another when dispensing materials such as certain epoxy resins. This problem is believed to be most prevalent in areas of the pump where there is little or no clearance between relatively moving parts and little or no flow of liquid, such as resin, to act as a lubricant or coolant. In this latter regard, undesirable temperature increases between the gears and the support plates can be prevented by resin flowing through such areas to essentially act as a lubricant or coolant. However, frictional temperature increases between a bearing surface and associated shaft, for example, may be much higher due to the combination of close dimensional tolerances and a low flow or amount of resin between these components. Particularly when both the bearing and associated shaft are formed of metal, this heat build-up can cause the associated bearings and shafts to adhere to one another and decrease pump performance. The resulting pump downtime and maintenance or replacement of the pump considerably increases costs to the user.
In one type of metering gear pump, the above-mentioned problem has been experienced between an idler gear and its associated shaft when these components move relative to each other, and also between the various shafts and their associated bearings or bushings, which also move relative to each other. While non-metallic parts, such as ceramic bushings, have been used to reduce the problem, the use of such parts throughout the pump may not be practical. This experience prompted the need to evaluate the effect of resins on the internal moving parts of a pump and, specifically, evaluate situations in which the internal parts move relative to each other with very close tolerances. Solving the problems related to heat build-up and particularly part adherence in such pumps will result in pumps requiring lower maintenance and having longer useful lives.
SUMMARY OF THE INVENTION
The present invention provides a gear pump for dispensing resin wherein the pump includes internal metal parts with a coating of a nitride, carbide or oxide of a metal. Generally, the coating is applied to at least one surface of an internal metal part that interacts with another metallic or non-metallic part in a relatively moving fashion. In other words, at least one part is moving against or in very close relation to the other to create undesirable frictional heat. The coating has been found to prevent adherence of the parts to one another as a result of resin curing between the parts. The internal coated parts are preferably made from such metals as stainless steel or other metals that are heat treatable to a Rockwell C hardness of about 56 or higher and generally of high strength and wear resistance. The preferred coating also has a Rockwell C hardness of at least about 56. Other non-coated parts may be made from various ceramic, polymeric or metallic materials.
The coating material of this invention is most preferably a metal-based material such as nitride, carbide or oxide of a metal such as tungsten, titanium, aluminum or chromium. The coating is most preferably applied in at least one layer to the interacting, relatively moving internal metal surfaces of a pump. The coating thickness has been advantageously applied in a range of about 2 to 5 microns. The coated surfaces may be associated with shafts or bushings, but any desired internal parts may be coated in accordance with the invention to help prevent the consequences of frictional heat build-up especially when dispensing resins employing a flame retardant additive. The coatings of the present invention improve gear pumps for metering resins in several ways. These pumps will have high wear resistance, longer useful lives and less maintenance when, for example, pumping various epoxy resins such as those employing a flame retardant additive.
These and other objects and advantages of the present invention shall become more apparent from the accompanying drawing and the following detailed description.
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Romanin Mario
Turner, Jr. Herman E.
Denion Thomas
Nordson Corporation
Trieu Thai-Ba
Wood Herron & Evans L.L.P.
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