US3455132A - Exothermic extrusion lubricants - Google Patents

Description

limited States Patent O 3,455,132 EXOTHERMIC EXTRUSION LUBRICANTS Courtland M. Henderson, Xenia, Ohio, assignor to Monsanto Research Corporation, St. Louis, Mo., a corporation of Delaware No Drawing. Filed May 31, 1967, Ser. No. 642,338 Int. Cl. B21c 29/04, 23/32; C10m 7/02 U.S. CI. 72-42 9 Claims ABSTRACT OF THE DISCLOSURE An improvement in the process of metal extrusion in which an exothermic composition including a calclum silicide and an oxidizing agent is used as a lubricant.

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 older methods of metalworking including casting, 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 is subjected 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 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 US. 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, 1956 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 sufliciently 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. Cooling, at the interface between the die and the piece being extruded, can result when phase changes (e.g., melting, vaporization) occur. Such cooling can cause loss of sensible heat from the ingot and a stiffening of the metal at the die restriction. This can contribute to a high initial extrusion pressure. Cooling can cause agglomerates and occlusions of hard materials in the area of the neck of the die and damage to the surface of both the die and the material being extruded.

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My present invention overcomes these and other problems.

SUMMARY This invention relates to an improvement in the method of extruding a metal workpiece, through a die at above 800 F., wherein the improvement comprises applying to the surface of the workpiece an exothermic composition including a reducing agent selected from the group consisting of calcium silicides and calcium-silicon mixtures in which from 20% to by weight of said silicides or mixtures is calcium, and an oxidizing agent selected from the group consisting of iron oxides, titanium dioxide, sodium nitrate, the fusion product of sodium carbonate and iron oxide, and the fusion product of sodium carbonate and ilmenite, said oxidizing agent being present in the range of 0.5 to 10 times the weight of the reducing agent.

The invention further provides the limitation wherein the exothermic composition contains, in addition to the reducing and oxidizing agents, at least one boron compound selected from the group consisting of boron oxide, boric acid, sodium borates, and potassium borates, the said boron compounds being present as equivalent B 0 in the range of from 2% to 45% by Weight of the entire exothermic composition.

The improvement of the present invention over the older methods of metal extrusion lies in the use of certain exothermic compositions as extrusion lubricants. Some of these compositions have been used as explosive primers; for instance, mixtures of sodium nitrate and calcium silicide disclosed by Berger in Comptes rendus 170, 1492-4 (1920), Chem. Abst. 14, 2765. Others have been used as exothermic metallurgical compositions; for intance, mixtures of calcium silicide with a boron compound and the fusion product of sodium carbonate and iron oxide, disclosed in US. Patent 3,153,605 issued Oct. 20, 1964 to C. M. Henderon et al.

These compositions characteristically are ignitable, whereupon they release heat by an exothermic reaction and produce a fluid or partially fluid slag or flux. Such a slag or flux is formed at the site at which it is most useful as a lubricant, i.e., in contact with the hot surface of the billet, so that it is immediately available to act as a lubricant. The combined effect of releasing heat and forming a fluid product offers an advantage over older lubricants which must first be melted by absorbing sensible heat from the billet. Even when the contact time of the lubricant with the billet is so short that older glass-based lubricants would be incompletely softened or melted, the present materials are quickly ignited and converted to a useful fluid or pasty state which is particularly desirable in a lubricant.

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 wherein exothermic combinations are used as lubricants.

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 13, 211 (1961). The die may yield simple or complex shapes, e.g., rods, channels, etc., or may, in

'1 a 4- conjunction with a mandrel, yield tubing. The die may be and ordinarily these are present to the extent of less than made of a hardened tool steel, and may be coated, e.g., 40% by weight of the total composition. Typical formuwith A1 or ZrO lations containing graphite are shown in Table II.

In operation, the billet of metal to be extruded is heated to the extruding temperature, which varies with TABLE IL-TYPICAL FORMULATIONS CONTAINING T i L Y the metal but may be in the range of 2100-2500 F. The 5 GRAPHI USEFU AS EATRUSIOBT LUBiRwANTS die is generally preheated to 800l000 F. to prevent (3mposltwniweght Percent OllTlLllZliZlOl'lS, chilling the workpiece. The die lubricant is inserted and components B C I) E J K 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.

Composition from table I: B

EXAMPLE 1 The compositions used in the present invention are pre- Typical formulations which I have found eful as pared by first comminuting or crushing the individual extrusion lubricants are shown in Table 1. components to a finely divided state, e.g., passing a TABLE I.-TYPICAL FORMULATIONS USEFUL AS EXTRUSION LUBRICANTS Composition, weight percent Formulations, components A B C D E F G H I J K Calcium and silicon (0g. Cassia) 50 37. 5 37. 5 14. 7 20 20 20 19. 4 11.9 Sodium nitrate- 5 o. 10 Iriiu oxide, F62 16. 9 Ilmonitc 404 8 Fosion pi'odueti in 57 parts by weight N oo; and 43 parts F8203 50 50 0 30 30 40 74. 9 Fusion product from 43 parts by weight NmCOi and 57 parts ilmenite 50 Sodium carbonate, anhy Boric acid Sodium totraborate, anhy. 5. 7 6. 0 Coetlicient of friction 0. 05 0. 05 0- 07 0- 04 0- 04 0. 03 0. 04 0. 04 0. 03 0. 04

The reducing agent employed in the present invention mesh sieve, then thoroughly mixing the components in may be a calcium silicide or a mixture of calcium silicides the desired proportions. The compositions may be used Or a mixture of calcium and silicon. It is essential that in a powdered form, e.g., by scooping into a mold having the calcium content in the calcium-silicon combination a die located at one end, thereafter ramming the heated be in the range of from 20% to 80% by weight of said billet in contact with the powder and thence through the silicides or mixtures. Such combinations may be Supplied die; or may be used more efficiently by molding the comas a starting material consisting of mechanical mixtures p ition first in a pellet or disc shape which is then posiof elemental calcium and silicon as well as alloys and tioned across the die opening so that the billet is rammed h i l compounds h as C Si Th l ium d/or directly against it and thence through the die. Other methsilicon may also be obtained from various sources such ds of applying the exothermic composition to either as ferrosilicon and calcium alloys, although the elemental the die or the workpiece may be employed, with the obf r are f d jective of interposing the composition between the surface The oxidizing agent may be selected from a number 45 0f the die and the workpiece that the Composition of oxygen-containing compounds which react with alserves to lubricate the die while the metal is being excium silicides. As examples of such materials, there may tr d- In the preparation of pellets or shaped forms, be employed iron oxides such as FeO, Fe O Fe O or binders such as sodium silicates, animal or vegetable their mixtures, titanium oxides such as TiO, Ti O 'riO glues, casein resins, p y y chloride, polyurethanes, or their mixtures, ilmenite, alkali metal ferrates such as 50 9 3 Cements, are useful for holldmg the Pressed are contained in the fusion products of alkali metal hy CGmPOSitiOII into a Suitably Strong formsufficient n r droxides or carbonates with iron oxides or ilmenite, nifor this P p usually not 5% y lWight 0f the trates of the alkali or alkaline earth metals including total Q 'hP P may be mixed with the exothermic NaNO KNO Ca(NO etc. An important and criticompos tion WIihPlIt adversely affecting its lubricating cal composition requirement for the exothermic extrusion p hp LIkeWlSe, lhold release g h Such as t am: lubricants of this invention is that the: oxidizing agent 301d y be pr s t In the composition, usually to the be present in the range of 0.5 to 10 times the amount of extent of not Over 5% y Weightthe reducing agent. The exothermic nature of these com- EXAMPLE 2 positions is dependent upon the oxidation of the calcium silicides or calcium-silicon mixtures and it is for this purh h of COIhPOSIUOIIS that ar useful for this inpose that the oxidizing agents are present. ventloh 1S Presented 111 Table III.

Boron compounds have been found to be effective ad- TABLE HIrRANGE OF USEFUL COMPOSITIONS AND ditives in these compositions for the purpose of i RATIOS FO R EXOTHERMIC EXTRUSION LUBRICANTS proved extrusion lubrication, and may be employed in OFTHISIN\ I N amounts up [0 50 parts Of equivalent B203 per 100 parts Rangetoi components, ercen a e b It by weight of total composit on. There may be used, for Components w example, boron oxide, boric acid, sodium borates and Broad Preferred potassium borates. Additives that have been found effec- Types 1H); tive in modifying the melting, wetting, or spreading chargglg fi gggg gq 10-60 20-50 acteristics are sodium carbonate, potassium carbonate, indium nigate g N aNoii) 5-00 10430 usioii pro uct rom 57 parts by weig t sodium sulfate etc. N tooa and 43 parts F0203 10 00 30-50 Other additives that have been effective in modifying fi i g i l Y Weight 10 {L2 11 the lubricating characteristics are graphite, molybdenum pal-ts f izi lgt 2,3 3 by 60 30 50 disulfide, boron nitride and metal-free phthalo yanine, 7 Weightofcalcium and Silicon 0- ,000 501,000

TABLE IIICn tinued Iron oxide (F0203) -25 -20 Ilmenite (essentially Fc0-TiO2) 20-60 20-50 Sodaash (NZIQOOS) 5-35 10-30 Parts of oxidizing agent per 100 parts by weight of calcium and silicon 10-1, 000 50-700 Types F-J:

Calcium-silicon (Ca Si 10-60 -35 Oxidizing agent, e.g.:

Sodium nitrate (NaNO 2-20 5-15 Fusion product from 57 parts by weight NQQCO: and 43 parts F6203 10-90 -80 Boron Compound, e.g.:

Boric acid (H313 O 15-55 20-50 Sodium tetraborate. (Na4B2O1) 2-10 3-8 Parts of oxidizing agent per 100 parts by weight of calcium and silicon 100-800 150-600 Parts of equivalent B20 per 100 parts by weight of total composition 1-50 2-45 Type K:

Calcium-silicon (Ca Si 10-40 10-15 Oxidizing agent, e.g.:

Iron oxide (Feg0 10-68 10-20 llmenite (essentially FeO -T10z) 10-68 10-50 Soda ash (NagCOg) 12-55 20-30 Boron compound, e.g.:

Sodium tetraborate (Na4B2O 2-24 3-10 Parts of oxidizing agent for 100 parts by weight of calcium and silicon 50-1, 000 100-700 Parts of equivalent B203 per 100 parts by Weight of total composition 1:10 1-5 Types A-D include those formulations containing the calcium-silicon reducing agent and one or more oxidizing agents. Type E contains, in addition, sodium carbonate. Types F-I include those formulations containing the calcium-silicon reducing agent, one or more oxidizing agent, and one or more boron compound. Type K contains, in addition, sodium carbonate.

EXAMPLE 3 The coefiicient of friction for these lubricants was determined in a TRW test machine as follows: A rotating member heated to 800 F. and a stationary member heated to 2100 F. were held against each other under about 5000 p.s.i. pressure. The lubricant was applied between these members and the deceleration of the rotating member measured. The rotating member consisted of H-2l tool steel simulating a steel die; the stationary member was molybdenum-0.5% titanium. The preheated steel piece was inserted in a cylindrical cavity in the center of a rotating flywheel; the lubricant was applied; and the preheated stationary member was dropped in on top of the lubricated steel piece. The motor drive was removed from the flywheel and pressure was immediately applied to the exposed end of the stationary member. The angular velocity of the flywheel was recorded until it stopped. A plot of the angular velocity against time gave substantially a straight line whose slope was proportional to the coefficient of friction. The coefiicients of friction obtained for old, established materials were acceptably close to values reported in the published literature.

Data for useful compositions of the present invention are shown in Tables I and II.

EXAMPLE 4 Extrusions were performed on a 700 ton horizontal extrusion press which permitted a pressure loading of up to 184,000 p.s.i. on the billet. Billets were machined to about 3 inches in diameter. Dies were prepared from I-I-21 tool steel and yielded /2 rounds. Entrance to the die had a 120 included angle cone.

Lubricant was introduced into the extrusion chamber as a compressed disc about 3 inches in diameter by /2" thick and pushed against the face of the die.

TABLE IV.EXTRUSION OF 4340 STEEL USING EXOTHERMIO EXTRUSION LUBRICANTS Results Condition of die after extrusion 2 Conditions, ram speed, nL/sec.

Composition from table I Extrusion 1 Judged by surface (smoothness, freedom from scoring, etc.) and minimum dimensional variation.

2 Judged by freedom from erosion, cracking, etc.

It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What I claim is:

1. In a method of extruding a metal workpiece through a die at above 800 F. an improvement which comprises applying to the surface of the die and the workpiece an exothermic composition including a reducing agent selected from the group consisting of calcium silicides and calcium-silicon mixtures in which from 20% to by weight of said silicides or mixtures is calcium, and an oxidizing agent selected from the group consisting of iron oxides, titanium dioxide, ilemenite, sodium nitrate, the fusion product of sodium carbonate and iron oxide, and the fusion product of sodium carbonate and ilmenite, said oxidizing agent being present in the range of 0.5 to 10 times the weight of the reducing agent.

2. The method of claim 1 further limited in that the exothermic composition contains the calcium silicide to the extent of 10-20% by weight, and the oxidizing agent is a mixture of iron (III) oxide, ilmenite, and sodium nitrate, together with sodium carbonate.

3. The method of claim 1 further limited in that a dry film lubricant selected from the class consisting of graphite, molybdenum disulfide, boron nitride, and metal-free phthalocyanine is present to the extent of less than 40% by Weight of the total composition.

4. The method of claim it further limited in that graphite is present to the extent of less than 40% by weight of the total composition.

5. The method of claim 1 further limited in that the exothermic composition contains, in addition to the reducing and oxidizing agents, at least one boron compound selected from the group consisting of boron oxide, boric acid, sodium borates and potassium borates, the said boron compounds being present as equivalent B 0 in the range of from 2% to 45% by weight of the entire exothermic composition.

6. The method of claim 5 further limited in that the exothermic composition contains as the oxidizing agent the fusion product of sodium carbonate and iron (III) oxide and as the boron compound sodium tetraborate.

7. The method of claim 5 further limited in that the oxidizing agent is a mixture of iron (III) oxide and the fusion product of sodium carbonate and iron (III) oxide, and the boron compound is boric acid.

8. The method of claim 5 further limited in that a dry 7 8 film lubricant selected from the class consisting of graph- References Cited ite, molybdenum disulfide, boron nitride, and metal-free UNITED STATES PATENTS phthalocyanine is present to the extent of less than 40% by weight of the total composition.

9. The method of claim 5 further limited in that graphit is present to the extent of less than 40% by Weight 5 CHARLES LANHAM Primary Exammfir of the total composition. E. M. COMBS, Assistant Examiner 3,153,605 10/1964 Henderson et a1 149-40