US3488985A - Metal extrusion with solid fabric lubricant - Google Patents

Description

United States Patent 3,488,985 METAL EXTRUSION WITH SOLID FABRIC LUBRICANT Erie V. Peterson, Linthicum Heights, Md., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Aug. 25, 1965, Ser. No. 482,616 Int. Cl. B21b 45/02 US. C]. 72-42 1 Claim ABSTRACT OF THE DISCLOSURE Processes for extruding high melting billets are improved by (1) covering the billet, at least laterally, with a flexible, solid-state carbonaceous fabric and (2) thereafter extruding the billet while so covered. This fabric remains in the solid state at extrusion temperatures and prevents adhesion between the billet and the extrusion equipment.

The problems of lubrication in the extrusion of refractory metals are severe because of the high pressures and high temperatures used. Most liquid lubricants are too volatile to remain in place during the extrusion. In recent years glass has been employed, the glass being so selected that it is a viscous fluid at the extrusion temperature. However, as with all fluids, glass tends to drain downward and give uneven lubrication. Solids like powdered graphite and molybdenum disulfide and even talc have been incorporated into fluids or pastes using various oils and greases. These, too, give non-uniform lubrication. Such nonuniformity is usually a result of the ditficulty in obtaining a continuous coating of the lubricant on the inner surface of the liner in the hot container or on the billet. Due to the thermal decomposition of these compositions the residues, which would otherwise provide lubrication, crack and spall off leaving bare spots. These bare spots permit metal-to-metal contact seizure and galling which in turn give rise to undue tool wear and imperfections in the product. Briefly, it may be said that one of the main difficulties encountered in the high temperature metal extrusion is the lack of a satisfactory method for providing an unbroken lubricating film between the opposing working surfaces and maintaining it throughout the extrusion process.

An object of this invention is to provideiimproved and substantially complete interposition of a durable lubricating or parting film between the workpiece and at least the working surface of the container liner in a metal extrusion process. A further object is to provide a method for interposing a substantially solid lubricant between mating metal surfaces during metal extrusion. Another object is to improve the distribution of lubricant throughout the interface between the tools and workpiece. Still another object is to provide such lubrication at the high temperatures employed in refractory metal extrusion.

These objects and others are attained by this invention which comprises enclosing at least the lateral working surface of a metal extrusion billet with a flexible, solid, carbonaceous fabric during at least the extrusion stages of a metal extrusion operation.

The fabric chosen is solid and remains substantially solid during the operation. This means that it does not melt at the billet temperature and that any binders present are in such small amount that they do not render the fabric soft or tacky, so that adherence to the billet would cause the fabric to tear. The carbonaceous fabric may be graphite cloth, or cellulosic cloth impregnated with carbon, graphite or molybdenum disulfide. Woven or non-woven fabrics are used. Cotton cloth and paper are typical of the ICC cellulosic fabrics used since they do not melt but char to yieldsolid products analogous to the graphite or carbon powders.

The piece of fabric used for a given extrusion operation is of sutficient size to form a sleeve large enough to enclose the billet. The fabric can extend only over that portion of the billet which contacts the liner surface at the start of the upset. In this case other known lubrication is supplied to the die faces. On the other hand the sleeve can be long enough, and bag-like in shape, to enclose the sides and nose of the billet. Since these fabrics are quite fragile a rather loose fit around the billet is preferred.

Preferably the fabric is slipped over the billet just as the latter enters the extrusion container. To facilitate this the appropriate sleeve is fastened at its opening, or rear end, to the periphery of the liner opening so that the billet slides into the sleeve as it advances on the guides. Spring clips or other clamping devices at the rear of the container can be employed to hold the sleeve. It is not necessary that the sleeve in this initial position be positioned or shaped to contact the inner surface of the liner. It can simply be draped inside the liner, held only by its edge at the periphery of the container opening. In this way the billet slips into the fabric in the same way an arm enters a loose coat sleeve. By following this or similar procedure the fabric is subjected to minimum contact with hot metal prior to upset and extrusion of the billet.

Alternatively, an ancillary device or holder, which can be portable or capable or being swung aside to clear the path of the moving press parts, can be used to slip the sleeve over the billet as it approaches the container. It is preferable, however, that the sleeve be located in the container at approximately the position it will occupy as upset takes place.

These solid fabrics can be used also in conjunction with the known fluid lubricants. To obtain full advantage of this combination of materials the fabric is preferably impregnated with the fluid lubricant. Such fluid lubricants include colloidal dispersions of graphite or molybdenum disulfide in oil or water, preparations available commercially such as Fisk #604, BMI #4, and others. Although these preparations become very thin and mobile during heating, they are, however, held in place by the fabric, and their action is thereby improved. Almost any auxiliary lubricant can be used with the fabric except those which, under the conditions present as the billet enters the sleeve, become tacky to the extent that the fabric is torn.

The choice of fabric for a given extrusion will depend on the working temperature employed. Graphite cloth will survive the highest working temperatures but, because of its combustibility, may have to be protected from air by use of an inert gas. Such inert gas atmospheres are often used in this work to protect the metal and, hence, are readily available. In some cases the impregnation of the fabric with the auxiliary lubricant will protect it long enough to accomplish the desired result.

Glass has been recognized as a good lubricant for high temperature extrusion. Its behavior can be markedly improved by the combined use of a solid fabric. For example. a graphite or cotton cloth can be filled or impregnated with glass powder or fine glass fibers. In this case the extrusion temperature should be high enough to soften the glass which in its fluid state is held in place by the still-solid, carbonaceous fabric.

Sufficient clearance between billet and liner must be provided, and this depends on the nature and thickness of the fabric. In practice this clearance has not been found to be much greater than that normally needed to avoid scrapping off the fragile layer of charred lubricants previously used.

One of the advantages of this invention lies in the fact that the solid fabric, being carbonaceous, is in itself a lubricant or at least an effective separating agent for the opposing metal faces. The materials used do not detract from lubrication, nor are they abrasive.

A further advantage is that the solid fabric, acting alone or in conjunction with other fluid lubricants, stays in place even during the high temperature extrusion. In the absence of such fabric the known lubricant preparations which melt tend to run down, thus starving the upper section. When the extrusion is set up horizontally, as is most commonly done, the top side of the billet will not be as well lubricated as the bottom and, and, as a result, the dimensional control of the extrusion is poor. This is particularly evident when using glass alone.

Another advantage relates to the conservation of billet heat during transfer from the furnace to the extrusion chamber. In prior art processes the lubricant is almost invariably applied to the billet during the early stages of this passage, necessarily extending the time of transfer, with the result that a considerable drop in billet temperature occurs. The method of this invention avoids this difficulty by eliminating that part of the transfer time required for applying the lubricant. When the sleeve of fabric is properly placed it immediately surrounds the billet with no extension of transfer time and completely separates the desired working surfaces.

When the solid fabric, especially preformed graphite fabric, is used alone an improved dimensional control is obtained. When used in conjunction with another lubricant normally suited for the particular extrusion, an improvement in both dimensional control and perfection of surface can be expected.

The invention is illustrated by the following example.

EXAMPLE A columbium base alloy containing tungsten, 1% zirconium and about 0.1% carbon was melted, extruded, and machined to a cylindrical billet 7 inches long and 3.4 inches in diameter. A pure columbium nose piece chamferred to 45 was fixed to the front end of the billet by means of a threaded columbium stud. A horizontal hydraulic extrusion press was set up with a heated, lined container and a 43 cone die. The container was heated -to 900 F., flooded with argon from the die end, and a sleeve of graphite cloth 3.5 inches in diameter and about 17 inches long, the liner being several inches longer than the billet, was mounted in a clamping ring set at the mouth of the container. The ring opening was aligned with the container and was large enough toadmit the billet. The loose sleeve was gently pushed into the container where it hung loosely from the clamping ring. The billet was heated in argon to 3800 F. and dropped rapidly into position on the billet guides where the ram imme diately pushed it into the container and extruded it to an H section one inch wide, 1% inches high with the web and flanges .080 inch thick. The resulting extrusion was improved, as compared with the use of glass rolled onto the hot billet with respect tostraightness and uniformity of dimensions. The variation in thickness along the 12 foot length Was not over 5 mils from front to back. Without the graphite cloth but with glass lubrication the variation was 20 to 30 mils, due to longitudinal striations in the surface.

In another similar extrusion in which the graphite cloth was first impregnated with a proprietary lubricant, BMI #4, these improvements and also a smoother surface were obtained.

I claim:

1. An improved method of lubricating the high temperature extrusion of a refractory metal billet from an extrusion chamber which essentially consists of (l) suspending at the entrance of the extrusion chamber a sleeve of flexible, graphite cloth which does not melt at the extrusion temperature, (2) moving the billet forward into said sleeve, (3) thereafter moving said billet enclosed in said sleeve into said chamber, and (4) completing the extrusion.

References Cited UNITED STATES PATENTS 2,757,138 7/1956 Clatot et al 7242 3,021,594 2/1962 Clatot et a1 7242 2,630,220 3/1953 Sejournet 7242 2,706,850 4/1955 Sejournet et a1. 29-423 2,738,062 3/1956 Edgecombe 56 CHARLES W. LANHAM, Primary Examiner CQMBS, Assistant Examiner