Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Ptfe
Reexamination Certificate
1998-12-31
2001-04-03
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Ptfe
C508S182000, C508S183000
Reexamination Certificate
active
06211121
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a fire-resistant lubricant designed for use within high temperature environments such as die casting machines.
BACKGROUND OF THE INVENTION
In many industrial forming processes, such as the molding, die casting, drawing, and forging of various metals or other similar materials, it is necessary to apply a lubricant to the working surfaces of such dies or other forming apparatus between machine-cycle operations. Further, the application of air and lubricants to the working surfaces tends to cool the dies between operational cycles thereby prolonging the life of the dies.
Industrial processes such as die casting often subject hydraulic systems to extremely high temperatures. In the past, many die casting operations used well-known hydraulic fluids as lubricants, despite their flammability. Given the safety considerations, conventional hydraulic fluids within high temperature hydraulic applications were replaced with nonflammable water/diethylene glycol or water/ethylene glycol mixtures. Although nonflammable, water glycol mixtures exhibit poor lubricity properties thereby resulting in equipment failure and escalating maintenance costs due to friction wear.
Conventional fixed and movable die casting molds are substantially formed from heat resistant metal. In a typical die casting process, a piston slidably moves within an injection sleeve causing molten metal contained therein to be injected and filled into a mold assembly. Over time, the hydraulic equipment and molds sustain repeated thermal shocks caused by heat transfer from the hot molten metal often ranging from about 600 to 1650 degrees Celsius. In the absence of an effective lubricant, the molds rapidly erode and fracture resulting in a complete crack or breakage. The hydraulic equipment is subject to the same stresses and will certainly require frequent maintenance in the absence of an effective lubricant. Properties such as the tensile strength and fatigue-resistance are detrimentally affected thereby reducing the life of the equipment.
The surfaces of the die cast molds typically require maintenance after several cycles since the surfaces gradually wear out through constant use. When maintenance is required, the entire die cast frame must be disassembled to facilitate removal of the molds. This is typically a very time-consuming operation resulting in an idle production line. The time spent to maintain the die therefore reduces the production time.
It would therefore be an improvement to provide a fire-resistant fluid having enhanced lubricating and cooling properties.
SUMMARY OF THE INVENTION
The present invention solves the aforesaid problems by forming an industrial fluid useful as a hydraulic and/or lubricating fluid, wherein the industrial fluid contains a lubricating additive combined with nonflammable water/glycol mixtures. The lubricating additive includes water/glycol fluids blended with an aqueous solution of polytetrafluoroethylene (hereinafter PTFE). PTFE is generally provided as either a granular, micropowder, or aqueous substance. Applicant has further discovered that due to its higher density, the PTFE aqueous solution when compared to granular or powdered PTFE, forms a denser and more effective lubricant between opposing interfaces.
In accordance with the present invention, a preferred embodiment comprises aqueous PTFE containing about 50-60% PTFE and about 33-50% water, wherein the aqueous PTFE constitutes about 0.2 to 5% by weight of the total lubricant. The preferred lubricating additive further contains, in weight percentages, a glycol-based fire-resistant fluid at about 75-95%, a dispersant at about 2-10%, a first surfactant at about 2-12%, a second surfactant having nonionic character at about 0.25-6%, and a defoaming agent at about 0.1-4%.
REFERENCES:
patent: 58-037094 (1983-03-01), None
patent: 08060175 (1996-03-01), None
Lyon P.C.
Medley Margaret
Toomer Cephia D.
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