US3379642A - Extrusion lubricants - Google Patents

Description

United States Patent 3,379,642 EXTRUSION LUBRICANTS Morris L. Nielsen, Dayton, and Roger M. Niemi, Hamilton, Ohio, assignors to Monsanto Research Corporation, St. Louis, Mo., a corporation of Delaware No Drawing. Filed July 7, 1967, Ser. No. 651,686 6 Claims. (Cl. 252-29) ABSTRACT OF THE DISCLOSURE An improvement in the process of metal extrusion in which a composition comprising a reaction product of melamine and a phosphorus (V) acid or anhydride is used as a lubricant. A laminar lubricant such as graphite may also be present.

BACKGROUND OF THE INVENTION This invention relates to the extrusion of metals and alloys having melting points above 1000 C., and particularly to means of lubricating such metals and alloys in conjunction with their passage through extrusion dies. Extrusion of metals such as copper, lead, zinc or aluminum is a well-known commercial operation. Many configurations of shapes and tubing have been made available as this technology has advanced over other methods of metalworking including casting, machining, forging, rolling, etc. Certain other metals or alloys having higher melting points, especially above 1000 C., have been less amenable to extrusion so that for them this method has been slow in developing. Such metals as steel, molybdenum, tantalum, tungsten, and superalloys require very high temperatures and pressures for extrusion and as a consequence the extruding die issubjected to considerable friction. Not only does this friction increase the amount of energy necessary to effect the extrusion, but it shortens the operating life of the die through erosion and wear. Equally important, it often results in a poorly extruded metal piece having a rough surface with scratches, pits, cracks, laps, tears and gouges. Many attempts to solve this problem have been made in the past, principally through extrusion aids or lubricating materials such as glass or graphite. In U.S. Patent 2,538,917 issued Jan. 23, 1951, to I. Sejournet et al. and in US. Patent 3,181,324 issued May 4, 1965, to D. Labino, various forms of glass are disclosed as extrusion lubricants. In US. Patent 2,757,138 issued July 31, 1965, to A. Clatot et al., graphite is shown in combination with a combustible organic substance such as sawdust and a higher metal oxide.

These various methods do not yield entirely satisfactory results. The glass may not be sufiiciently softened in the short contact time that it is exposed to the hot metal, so that there may result occlusions of glass in the metal, or surface defects due to uneven lubrication and excessive wear of the die. When greases are used, the contact of hot metal with organic substances may lead to undesired carbides and surface hardening by carburization.

vWhen graphite is used alone, extrusion is usually unsatisfactory, due to failure of the solid non-fusible graphite toflow and replenish the film of lubricant between the die and workpiece. Graphite alone suffers from the further disadvantage that it has high thermal conductivity which hastens the transfer of heat from the hot billet to the cooler die. This results in two undesirable effects: the workpiece is cooled and the die is heated.

Our present invention overcomes these and other problems.

SUMMARY This invention relates to an improvement in the method of extruding a metal workpiece, wherein the improvement "ice comprises applying to the surface of the workpiece a composition comprising a reaction product of melamine and a phosphorus compound selected from the class consisting of a phosphorus (V) acid and phosphorus pentoxide. The composition may also include a laminar lubricant selected from the class consisting of graphite, molybdenum disulfide, boron nitride and metal-free phthalocyanine.

The melamine phosphates prepared from melamine and various phosphorus acids, e.g. ortho-, pyro-, or metaphosphoric acid are well-known compounds. Thus, there are melamine orthophosphate, C H N -H PO melamine pyrophosphate, (C H N -H P O melamine metaphosphate, C H N -HPO etc., as reported in Chemical Abstracts 42, 7781h.

By heating melamine with phosphorus pentoxide in a ratio of 2 to 4 moles of melamine to one mole of phosphorus pentoxide at 300500 C., there is obtained a product disclosed in US. Patent 2,544,706 issued Mar. 13, 1951, to I. E. Malowan. We have found that these materials soften or melt at high temperature, often with decomposition, and are transformed to a viscous, fluid or partly fluidstate. For example, the melamine-P 0 composition becomes soft and tacky about 900-1000" C.

It is an object of the invention to provide a lubricant for metalworking. It is a further object to provide a lubricant for the extrusion of metals having melting points above 1000 C. It is still a further object to provide an improvement in the process of extruding metals in which a composition comprising a reaction product of melamine and a phosphorus (V) acid or anhydride is used as a lubricant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the extrusion of metals having high melting points, e.g. above 1000 C., it is common practice to employ a 1500 to 2500 ton horizontal extrusion press, see for example, Extrusion of Steel, by D. A. Edgecombe, Journal of Metals, vol. 13, page 211, 1961. The die may yield simple or complex shapes, e.g. rods, channels, etc., or may in conjunction with a mandrel yield tubing. The die maybe made of a hardened tool steel, and may be coated, eg with A1 0 or ZrO In operation, the billet of metal to be extruded is heated to the extruding temperature, which varies with the metal but may be in the range 11-O02000 C. The die is generally preheated to 450550 C., to prevent chilling the workpiece. The die lubricant is inserted and then the hot billet. The ram then moves forward at a speed of 5-6 inches/ sec. and the workpiece assumes a cross-section corresponding to that of the die. In the present invention, the improvement lies in the die lubricant. The following examples illustrate certain specific embodiments of the present invention.

Example 1 Typical formulations which we have found useful as extrusion lubricants are shown in Table 1. The melamine reaction products may be used alone or in combination with laminar lubricants such as graphite. The compositions used in the present invention are prepared by first comminutingor crushing the individual components to a finely divided state, e.g. passing a 20 mesh sieve, then thoroughly mixing the components in the desired proportions. The compositions may be used in a powdered form, e.g. by scooping into a mold having a die located at one end, thereafter ramming the heated billet in contact with the powder and thence through the die; or may be used more efliciently by molding the composition first in a pellet or disc shape which is then positioned across the die opening so that the billet is rammed directly against it and thence through the die. Other methods of applying the composition to either the die or the workpiece may be employed, with the objective of interposing the composition between the surface of the die and the workpiece so that the composition serves to lubricate the die while the metal is being extruded. In the preparation of pellets or shaped forms, binders such as sodium silicates, animal TABLE l.TYPIGAL FORMULATIONS USEFUL AS EXTRUSION LUBRICANTS Composition, Weight percent Formulations, Components A B C D E F Melamine orthophosphate (1 :1) 100 67 Melamine-P composition of U.S. Patent 100 67 50 33 2,544,706. Graphite 33 33 50 67 Coefficient; of Friction at l,100 C 0.1 0.02 0.12 0. 02 0. 02

or vegetable glues, casein resins, polyvinyl chloride, polyinch thick and pushed against the face of the die. vinyl acetate, polyurethanes, epoxy cements, etc., are Billets of 4340 steel were heated to about 1150" C., useful for bonding the pressed composition into a suitably in an inert atmosphere induction furnace and were transstrong form. Suflicient binder for this purpose, usually not ferred to the extrusion press. over 5% by weight of the total composition, may be The results of extrusions with two compositions as mixed with the composition without adversely affecting its lubricants are shown in Table 2. lubricating properties. Likewise, mold release agents such TABLE2 EXTRUSION OF 4340 STEEL USING EXTRUSION as stearic acid may be present, usually to the extent of LUBRICANTS not 5% by Weight- Conditions, Results, Not only are the melamine reaction products useful Composit on F o Tablel m Speed Extruded lubricants per se, but by virtue of their softening and (L/Sec) Surface melting characteristics they may be used with and do 0 yh i p p flr p u 5-5 i enhance the usefulness of laminar lubricants. While we gg fi gifffhffffifhhfi g8 53;, do not have a complete understanding of the mechanism by which these desirable results are achieved, we postulate I i to b understood that l h h invention h that the melamine reaction products act as a matrix or b d ib d i h ifi reference to particular h dispersion medium for the laminar lubficahts- We have bodiments thereof, it is not to be so limited since changes found that intim e miXhlreS 0f the melamine-P205 and alterations therein may be made which are within the POsition and graphite become pasty at aboh'E 900-1000 full intended scope of this invention as defined by the C., and we therefore presume that under the extrusion appended i conditions this combination flows and replenishes the What We l i i lubricating film between the metal surfaces. In this way 40 1 In a method f extruding a metal workpiece h h the combination surprisingly produces a superior result a i an improvement which comprises l i to the t0 obtained either component alone. For the urface of the and the workpiece a omposition com P p of this invention the h hlbncaht may h prising a reaction product of melamine and a phosphorus Prbseht t0 the extent of 90% y Welght of the c011113051" compound selected from the class consisting of a phostioh; however, the Preferred pg is p to a maximum of phorus (V) acid formed at about the temperature of 70% y Whight of the position. 0-300 C. and phosphorus pentoxide formed at about Example 2 the temperature of 300 500 C. 2. The method of cla1m 1 111 which the reaction prod The coefficrent of friction for these lubrlcants was deuct is melamine orthophosphate termined in a TRW test machine as follows. A rotating The method of claim 1 in which the reaction prod member heated to about 4500 and a sfahohary uct obtained by heating 2 to 4 moles of melamine with one ber heated to 1100 C., were held against each other mole of phosphorus pentoxide at 300 to 5000 under about 5000 p.s.i. pressure. The lubricant was ap- The method of claim 1 in which the composition P between these members and the lecelemhoh of the includes a laminar lubricant selected from the class conrotating member measured. The rotating member c ni m f graphite, molybdenum disulfide, boron nitride, sisted of H- 21 tool steel simulating a steel die the staand metahhee phthalocyanhm tionary member was molybdenum-0.5% tltamum. Th 5. The method of claim 4 in which the reaction product preheated steel piece was inserted in a cylindrical cavity is melamine orthophosphate and the laminar lubricant is in the center of a rotating flywheel; the lubncant was apa hite, the graphite being present in the ran e of 2 to plied; and the preheated stationary member was dropped 70% by weight of the composition a in on top of the lubricated steel piece. The motor drive The method of claim 4 in which the reaction Prod was removed h the flywheel and Pressure h uct is obtained by heating 2 to 4 moles of melamine with mediately applied to the exposed end of the stationary one le of phosphorus pentoxide at 300 to 500 C., memberh angular ve'loclty of the flywheel was h and the laminar lubricant is graphite, the graphite being corded until it stopped. A plot of the angular velocity present in the range of 2 to by weight of the against time gave substantially a straight line whose slope position was proportional to the coefiicient of friction. The coeffi- References Cited cients of friction obtained for old, established materials were acceptably close to values reported in the published UNITED STATES PATENTS literatur 70 2,544,706 3/1951 Malowan 260249.6 Data for useful compositions of the present invention 3, 13,024 10/1965 Blake et al. 252-25 are shown in Table 1. 3,265,617 8/1966 Allen 252-25 Example 3 DANIEL E. WYMAN, Primary Examiner.

Extrusions were performed on a 700 ton horizontal ex- I. VAUGHN, Assistant Examiner.