US3255621A

US3255621A - Lubrication

Info

Publication number: US3255621A
Application number: US302674A
Authority: US
Inventors: Ernest O Ohsol
Original assignee: Haveg Industries Inc
Current assignee: Champlain Cable Corp
Priority date: 1963-08-16
Filing date: 1963-08-16
Publication date: 1966-06-14
Anticipated expiration: 1983-06-14

Description

United States Patent 3,255,621 LUBRICATION Ernest 0. Ohsol, Wilmington, Del., assignor to Haveg Industries, Inc., a wholly-owned subsidiary of Hercules Powder Company, New Castle, Del., a corporation of Delaware Filed Aug. 16, 1963, Ser. No. 302,674 9 Claims. (Cl. 72-42) This invention relates to fluorocarbon polymers.

In the forming of refractory metals by extrusion through dies at high temperatures lubrication of the die is a very critical problem. The pressures and temperatures encountered, e.g. a temperature of 3500 F. (1927 C.), are extremely high and conventional die lubricants such as molten glass have insuflicient film strength and too low a viscosity to be satisfactory lubricants for formingrefractory metals such as tungsten, columbium, titanium and molybdenum and the like.

Previously employed solid lubricants for refractory materials provide insufficient lubrication at low temperatures, leave abrasive residues after high temperature exposure an-d are physically removed before the lubrication function is complete.

Graphite powder and molybdenum sulfide have been tried in paste form, but are readily displaced. Furthermore, at very high temperatures carbon and graphite lose their adsorbed film and become non-lubricating.

Teflon inserts by themselves are unsatisfactory because they have poor resistance to mechanical displacement. Additionally the Teflon tends to be volatilized away too soon.

Accordingly it is an object of the present invention to prepare a superior type of ablative lubricating die insert.

A further object .is to prepare novel lubricants.

Yet another object is to prepare improved rocket noz zles.

Still further objects and the entire scope and applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

It has now been found that these objects can be attained by preparing perfluorocarbon polymer impregnated silica or glass cloth. The impregnated cloth is then molded into an ablative lubricating die insert or a rocket nozzle.

The invention will be best understood in connection with the drawings wherein:

FIGURE 1 is a view of an apparatus for'extrusion of a refractory metal; and

FIGURE 2 is a sectional view of a polytetrafluoroethylene impregnated glass cloth.

The polytetrafluoroethylene impregnated glass or silica cloth is old per se and can be prepared by any convenient prior art process such as that shown in Sanders Patent 2,539,329 or Fay Patent 2,843,502.

T 0 give improved results it is frequently desirable to incorporate 4 to 8% of molybdenum disulfide based on the total weight of the Teflon, cloth and molybdenum disulfide. The molybdenum disulfide is readily incorporated by including it in powder form in the Teflon dispersion applied to the cloth, e.g. there can be employed a dispersion of 40 parts Teflon (polytetrafluoroethylene) and parts of molybdenum disulfide in 55 parts of water containing 3.6 parts of Triton X-100 (octyl phenyl polyglycol ether) to impregnate glass cloth to obtain a product containing 40% Teflon, 5% molybdenum disulfide and 55% glass cloth by weight.

ice

preferably dried at relatively high temperatures, e.g.. 300 C., which are within 50 C. of the fusion temperature of Teflon. Drying can even be done at the sintering temperature or above, eLg. 330 C.

T 0 form the die insert a well bonded dense laminate of the Teflon impregnated glass cloth (or silica cloth) with or without the molybdenum disulfide is prepared. This can be accomplished by stacking or wrapping the Teflon impregnated cloth around a mandrel and then sintering the product at a high pressure, e.g. 300 to 2,000 psi. at a temperature above the sintering temperature (327 C.) for Teflon. Thus the Teflon-60% carbon cloth wrapped around a mandrel to form several thicknesses of cloth can be heated to 350 C. at a pressure of 1000 psi. and then cooled to room temperature under pressure.

Instead of wrapping the Teflon impregnated cloth around the mandrel a plurality of layers can be laminated together to form the die insert by compressing them lightly, e.g., 100 psi. then sintering the product, e.g., at

340 C. with no applied pressure and then finally pressing at :high pressure, e.g., 500 psi. and then machined to dimensions.

The products of the present invention are characterized by absence of void spaces, high strength and dimensional stability.

The glass or silica cloth inserts of the present invention can contain 25 to 75% Teflon (preferaby 30 to 65%), and 75 to 25% glass or silica cloth (preferably '70 to 35%). If molybdenum disulfide is employed it is present in minor amount, e.g. 4 to 8%. p

The glass or silica phase provides the high temperature lubrication, eg at temperatures of 900 to 2000 C. to

' an excellent degree, having previously been kept cool by the vaporizing polytetrafluoroethylene. Essentially a solid-liquid lubrication system is employed.

Typical examples of refractory metals which can be formed with the aid of the ablative lubricating die insert or plug of the present invention are tungsten, columbium, tantalum, titanium, molybdenum, uranium, thorium and zirconium and alloys such as certain stainless steels.

In place of employing the preferred material, polytetrafluoroethylene, other fluorocarbon polymers can be used such as polyhexafluoropropylene and copolymers of tetrafluoroethylene with hexafluoropropylene having weight ratios of :25 or 30:70 or 34:66 or 19:90 or 1:2 or 4:3 or 23.8:30 or :15.

Referring to FIGURE 1 of the drawing there is provided a frusto-conical ablative lubrication die insert 2 -made of 40% Teflon-60% glass cloth. The cloth had a thread count per inch of 60 x 47, yarn size 900 /2, ounces per square yard 1.43. The insert had the dimensions shown in FIGURE 1. Thus at its front end or inlet 4 it had a diameter of 3.05 inches and tapered to its rear surface or outlet 6 where it had a diameter of 1.00 inch. The clearance at the inlet was 2.414 inches. The side 8 of the trusto cone made a 30 angle with the vertical axis and the side 10 made a 45 angle with the horizontal axis. Thus the inner and outer sides of the frusto cone embraced an angle of 15. The Teflon-glass cloth composite was preferentially made by arranging the laminates of the glass cloth in acircumferential pattern coaxial with the center line of the insert. Successive layers of the lamination had a slight angle to the inside surface, e.g. 10. It is also possible as previously indicated to make a block of substantially flat laminations of the Teflon and glass cloth and to machine the die insert from such a thick block.

The die insert is fitted into a larger hardened steeldie 12. The die 12 similarly has a conical entrance section tapering from 3.05 inches at the inlet to 1 inch at the outlet. The throat 14 of the die is only a fraction of an inch long and is immediately expanded to an outlet 16 diameter of 1.5 inch over a distance of 1 inch. There is also provided a billet 18 of the refractory metal, e.g. tungsten. The billet has an outside diameter close to the 3 inch entrance diameter of the die and issues with a diameter of about 1 inch. The entering portion 20 of the billet is chamfered, e.g. with a 35 chamfer, to facilitate entrance into the die. There is also provided a plunger 22 to force the billet 18 into the die insert 2 and die 12.

In operation the hot billet, cg. tungsten at 1800 C. is rammed through the die at a pressure of 100,000 p.s.i. In an extrusion of a 10 or 20 foot metal rod by this means, an operation which lasts only a few seconds, the Teflon in the die insert will first act as a lubricant, but will be rapidly vaporized upon contact with the hot metal surface. The film of vaporizing Teflon helps to provide lubrication and keep the surface of the metal clean. It also helps to keep the outer portions of the die insert and the metal die itself cool by virtue of its heat of ablation. At the same time, the layers of glass cloth remaining provide a solid-liquid type of lubrication.

FIGURE 2 shows a laminate of layers of glass cloth 24 impregnated and bonded with Teflon 26 to form a die insert. As indicated, silica cloth, e.g. 9099% silica, can be used in place of glass cloth.

I claim:

1. In a method of extruding a refractory metal workpiece at high temperature from an extrusion chamber having an opening through which the workpiece is extruded the improvement comprising providing an ablative lubricating die insert in said die, said insert comprising a cloth of the group consisting of glass cloth and silica cloth impregnated with a perfluorocarbon polymer, heating the workpiece and introducing it into the extrusion chamber, extruding the workpiece through said die insert at a temperature and pressure suificient to vapor- 4 ize said perfiuorocarbon polymer to provide lubrication and to expose and melt said cloth to provide solid-liquid lubrication of the workpiece.

2. A process according to claim 1 wherein the extrusion is carried out at a temperature of at least 900 C.

3. A process according to claim 2 wherein a minor amount of molybdenum disulfide is incorporated in said polymer.

4. A process according to claim 1 wherein the polymer is selected from the group consisting of polytetrafluoroethylene, polyhexafluoropropylene and copolymers of tetrafluoroethylene and hexafiuoropropylene and the extrusion temperature is at least 900 C.

5. A process according to claim 1 wherein the polymer.

is polytetrafluoroethylene.

6. A process according to claim 5 wherein the extrusion temperature is at least 900 C.

7. A process according to claim 6 wherein there is incorporated with the polytetrafluoroethylene a minor amount of molybdenum disulfide.

8. A process according to claim 1 wherein the polymer is polytetrafluoroethylene, the cloth is glass cloth and the extrusion temperature is at least 900 C.

9. A process according to claim 1 wherein the polymer is polytetrafluoroethylene, the cloth is silica cloth and the extrusion temperature is at least 900 C.

References Cited by the Examiner UNITED STATES PATENTS CHARLES W. LANHAM, Primary Examiner. MICHAEL V. BRINDISI, Examiner.

E. D. OCONNOR, H. D. HOINKES,

Assistant Examiners.

Claims

1. IN A METHOD OF EXTRUDING A REFACTORY METAL WORKPIECE AT HIGH TEMPERATURE FROM AN EXTRUSION CHAMBER HAVING AN OPENING THROUGH WHICH THE WORKPIECE IS EXTRUDED THE IMPROVEMENT COMPRISING PROVIDING AN ABLATIVE LUBRICATING DIE INSERT IN SAID DIE, SAID INSERT COMPRISING A CLOTH OF THE GROUP CONSISTING OF GLASS CLOTH AND SILICA CLOTH IMPREGNATED WITH PERFLUOROCARBON POLYMER, HEATING THE WORKPIECE AND INTRODUCING IT INTO THE EXTRUSION CHAMBER, EXTRUDING THE WORKPIECE THROUGH SAID DIE INSERT AT A TEMPERATURE AND PRESSURE SUFFICIENT TO VAPORIZE SAID PERFLUROROCARBON POLYMER TO PROVIDE LUBRICATION AND TO EXPOSE AND MELT SAID CLOTH TO PROVIDE SOLID-LIQUID LUBRICATION OF THE WORKPIECE.