US2469473A - Method of lubricating metal surfaces during cold working - Google Patents

Description

Patented May 10, 1949 METHOD'OF LUBRICATING METAL SUB- FACES DURING COLD WORKING Gilbert 11. Orozco, Euclid, and John A. Henricks,

Cleveland, Ohio, assignors to Gilron Products Company, Cleveland, Ohio, a partnership composed of Gilbert H. Orozco and Roland Whitbeck N Drawing. Application August 2, 1943,

Serial No. 497,117

4 Claims. Cl. 205-21) This invention relates to the lubrication of worked metallic surfaces in the processing of metals in contradistinction to that encountered in a fixed machine or engine. The difference does not lie in the nature of the friction encountered but in the dimensional variations which exist in the case of worked metals but which do not exist in machine. Any machine or engine is designed and built to perform its function with a definite and as nearly as possible constant clearance between the moving surfaces and thus only encounters a uniform sliding friction. On the other hand, in metal processing such as machining, drawing, and forming of metals the only fixed dimensions are those of the cutting tool or the forming dies that are set up for the specific operation. Thus the clearance between the tools and the metal being processed are a resultant between the pressure and force applied to the work and the counter and resisting forces offered .by the work. Thus the high points between the tool and the work are subjected to a tremendous thrusting friction which will cause actual metal to metal contact and with it a welding and scor ing of the surfaces.

An object of the invention is to control by a novel means of lubrication the dimensional variation which is a necessary incident to metal working but partically does not exist in functional machinery.

In the present process we utilize a planned succession of endothermic reactions initiated by the frictional heat or mechanical equivalent thereof (e. g. pressure) that not only cool the frictional surfaces by absorbing heat but which produce nascent fluid lubricants at points of extreme heat and pressure. The preferred procedure uses both fusible organic and fusible inorganic materials to produce such succession of reactions.

Bowden and Ridler (Proceedings Royal Society 1936, Series A No. 883, page 154) made a classical and incontrovertible study of the sliding friction of metals in which the contacting metals were a part of an accurate thermocouple. It was con- 2 vincingly demonstrated in this study that in dry sliding friction, the junction point between the two metals reaches ahd maintains the melting point of the lower melting metal. This fact is as startling as the recent proof by the application of the electron microscopewhich showed that the amorphous Beilby layer actually existed on polished metals, which meant that it was possible to cause a metal to melt and flow by bufling it with a cloth buffing wheel on a polishing lathe.

When iron is alloyed with other elements specific to the purpose, the hardness is thereby increased, but the melting point of the alloy is usually lowered. Thus when a steel is alloyed for hardening and .used as a tool in metal processing, high melting point has been sacrificed for the hardness attained. Therefore. when some failure in lubricationallows a sliding frictional contact between the hardened tool and the processed metal, the tool rather than the work will usually be softened and scored or otherwise damaged. The efi'ectiveness of chromium plated or tungsten carbide tools and dies is due not only to their inherent hardness, but to their high melting point, well above that of a steel being processed.

When a steel cup, for example, is pickled to remove the annealing scale, the surface is etched and dully crystalline. When this rough surfaced cup is drawn in a press to a 25 to 40% elongation, the rough surface is flowed to a highly reflective surface which, at points of maximum contact and pressure. could be described as mirror-like. Likewise, when the mill scale is removed from rod by acid, the surface is dull and etched. When etched quarter inch rod, however, is drawn to 0.0095 in twenty successive drafts the surface of the fine wire has a brightness of highly buffed amorphous metal.

These mirror-like drawn surfaces give a different electron diffraction pattern than the oriented etched surface, indicating amorphous metal. Thus in drawing metal'we form, as we do in bufling, a Bielby layer at points of extreme pressure and friction. This, as pointed out above,

means that the metal has melted and flowed at these mirror-like contact area.

The action described above can be more readily understood by converting the foot pounds utilized in the drawing operation into the mechanical equivalent of heat. For example, in drawing a .75 millimeter steel shell casing in an 180 ton press with travels eight inches in the draw, the mechanical heat equivalent is equal to over 38,000 calories which, if there were no heat radiation, would be sufficient to melt over a pound and a half of steel.

From literature on the subject of metal working and experience in that field it appears that two fundamental requirement factors operate or would operate coniointly to effect ideal or perfect lubrication when a metal is formed or drawn. One of these factors is adequate cooling, and the other is the prevention of actual direct physical contact between the metal and the tool or die at any point. Contact as used herein indicates the apparent but not actual relationship between the metal and working element in a successful method of lubrication. By preventing actual contact between the tool or die and the work we prevent the dry sliding friction that would cause the lower melting metal to melt and flow in the manner revealed by Bowden and Ridler.

Since the melting point of high carbon steel is below that of the lower carbon steels it processes, it is important to protect it from harm. It is therefore readily understood how it becomes necessary to remove frictional heat and to prevent. any metal to metal contact which would cause scoring of the tool or welding of the processed metal thereto. Similarly when chromium plated or tungsten carbide tools are used, the lower melting steel must be protected.

It is a further purpose of this invention, in the case of alloy steel processing tools, to protect the tool against such a temperature rise as would approach the softening or welding point of the relatively lower melting tool steel, or in the case of chromium plated or tungsten carbide steel, the melting of the lower melting steel being processed. Inasmuch as such a temperature is far above the carbonization point of normally fluid lubricating materials commonly spoken of as oil, we utilize inorganic compounds to achieve the essential cooling and lubrication of the sliding surfaces at the elevated temperatures existing when combustible organic lubricants are ordinarily no longer capable of functioning; but, in addition, we utilize properties of the inorganic materials to increase the thermal stability of the preferred organic lubricants used.

A specific object of the invention is to provide an improved method of treating metals preparatory to the cold drawing or forming thereof in order to insure both stepwise cooling and stepwise lubrication of the metal. That object is accomplished, for example, by coating the surface of the metal to be worked with a composition, the ingredients of which will act progressively and successively both as coolants and as lubricants when the coating is subjected to the extreme' pressures incident to drawing or forming operations and temperatures approaching the melting point of the worked metal or, in the case of a non-metallic tool or die, the point at which such working element might be damaged by working that particular metal,

A correlative object is to prepare the stock so that it may be drawn or formed more efllciently and with increased tool or die life.

A specific object, in connection with wet drawing or wet metal processing, is to afford stepwise lubrication at high temperature contact points, where the aqueous solvent is evaporated and ineffective to prevent seizure. so that a mixture of fusible organic and inorganic lubricants that are identical in lubricating action to a predeposited will come into action.

In one modification of the present method we achieve cooling and lubrication by coating the surface to be drawn or formed not only with a low melting point fusible, polar, organic lubricant but with certain inorganic glass forming materials, such as hydrated alkali metal salts which will melt stepwise under frictional heat, and will then boil in their water of crystallization or hydration and thereby act successively or progressively as coolants after which, when the water of crystallization or hydration has been removed the residue, upon suflicient rise in temperature, becomes a fluid glass and a hydraulic lubricant. Characteristic hydrated alkali metal salts, along with their primary melting points and their boiling points are as follows: (centigrade scale) The large and valuable heat absorbing capacity of the hydrated alkali metal salts listed above can best be understood by comparison of their latent heats with those of other common substances used for cooling or lubricating metal surfaces. .The latent heat of a body represents the quantity of heat necessary to change one gram of the body from a solid to a liquid or from a liquid to a vapor.

The heat of fusion expressed in gram calories per gram of the common bearing metals is about 6 for lead, about 14 for tin, while disodium phosphate (NazHPO4-12Hz0) has a latent heat of fusion of about 67 gram calories per gram or ten times that of lead. Added to this is the unexcelled latent heat of vaporization of water which is about 500 gram calories per gram and which is present as water of crystallization in our preferred glass forming hydrated alkali metal salts. As a comparison the ethylene glycol used in liquid cooled engines has a latent heat of vaporization of about 190 gram calories per gram, and lubricating oils about gram/calories per gram.

Thus each of the hydrated alkali metal salts identified above has a heat capacity far exceeding that of a bearing metal in heat of fusion as well as the unexcelled latent heat of water in the water of hydration or crystallization. The hydrated alkali metal salts become highly efiicient tool-protective coolants in preventing the occurrence of extreme frictional heat such as would result from actually sliding contact between the metal and tool.

In addition, the polar organic compounds which operate as primary or introductory lubricants, as already mentioned, are preferably hydrated colloids which likewise liberate water in melting.

The steam generated when the glass forming alkali metal salts give up their water of crystallization or hydration and when the hydrated first wet with water so that the glass will be cushioned by steam to prevent it from actually invention to an even greater degree by the application of an aqueous solution of fusible organic and inorganic lubricants selected for stepwise action in the case of wet drawing. grinding or wet machining operations.

While coolin is of great importance in the drawing or forming of metals it is, of course, to be understood that successful cold working of metals can onlybe accomplished by proper lubrication. The function of lubrication is well expressed in the following quotation from an excellent text, by Dr. Jevons, The Metallurgy of Deep Drawing and Pressing," Chapman 8: Hall, 1941:

Since the primary function of a lubricant is to reduce the coefficient of friction between two surfaces, it follows that the quality of slipperiness is equalled in importance only by that of film strength, or ability to maintain this slipperiness under severe conditions of temperature and pressure. slipperiness may be defined as ability to reduce the coefllcient of friction between sliding surfaces after the break down, or in the entire absence of a viscous film. This definition applies also to the filler type of lubricant.

In the rather special lubricants which have been developed specifically for deep drawing operations, some distinction needs to be made between the property of true oiliness and the wider attribute here termed slipperiness. Oiliness is attained by the addition to the lubricant of a suitable oily substance, either free or in a combined state; slipperiness is attained by the addition of solids ranging from graphite, a substance held by some to possess truly oily characteristics, to substances such as chalk, which although not oily in the accepted sense of the word, yet produces a measure of apparent slipperiness in drawing lubricants containing them.

In the prior metal drawing, some of the fillers or so1ids," mentioned in the above quotation, apparently performed their function by absorbin the fluid lubricant used therewith. Other solids, for example, mica and graphite, have a -natural lubricating quality and in some forms may also absorb oil. The various oxides, chalk or clay used in prior practice act, as would a sponge due to well known interfacial phenomena, to absorb the oil. After the absorption of lubricant fluid, those fillers functioned as would, theoretically, a solid drop of oil somehow fastened in place against the contacting" walls. In each case the essential lubrication at extremely high pressures could be considered to be mechanical 'in nature in the prevention of contact between the sliding surfaces since those temperatures would ordinarily be upwardly beyond the'carbonization points of the oils used. In the present invention 1 we utilize with naturally slippery" substances a type of filler which will melt and flow under the frictional heat of the formingoperation. Since commercially practicable organic lubricants are destroyed by heat, we utilize glass forming substances as additional lubricants or previously formed glass particles suitably small.

It is of significance that the commercially used fillers in pigmented drawing compounds such as lime, clay, mica, calcium, or magnesium carbonate and titanium dioxide are infusible. When these materials are used in drawing, minute particles of them canbe found embedded in the drawn work, resultin in an undesirable dull surface that is very diflicult to clean. We provide coolants such as water and low melting inorganic compounds before the organic lubrication is en-i dangered. The inorganic materials act as fillers during the life of the organic lubricant and, a series of mineral fiuid lubricants after the organic lubricant has been burned oil or is otherwise destroyed or rendered ineffective.

As well known in the ceramic arts, glasses consist of certain basic oxides such as K, Na, Pb, Ca etc. combined with acid oxides such as those of silicon, boron, or phosphorous. The compounds are melted down commercially to form a fluid which when solidified we recognize as glass.

We utilize the frictional heat generated by nearly actual sliding contact between the metal and tool, which actual sliding contact is initially prevented by interposition of an organic lubricant, to form both cooling and lubricating fluids at temperatures beginning approximately at the breakdown temperatures of commonly used organic lubricants.

An important feature of the process is the fact that we combine with the inorganic fluid-glassforming materials, as a binder and vehicle for said materials and also as a primary introductory lubricant, a fusible film-forming organic material which is preferably a polar compound capable of forming an efficient lubricating film at a temperature below the fusion point of the inorganic materials used and which may be below the melting point of said organic material. We are aware that polar compounds are commonly used as lubricantsin the metal working arts.

The polar compounds are so used because due to their surface activity they cannot be as readily displaced from position on the metal to be worked as can non-polar compounds of similar nature sometimes used asllubricants. The polar compounds such as soaps, fatty acids, wetting agents or waxes fall into an'active chemical group that form an absorption complex with the metal and thereby an anchored layer on the surface of the metal. In the ordinary use of such polar compounds the extreme frictlonal heat and pressure converts the organic materials into a black insoluble substance commonly referred to in internal combustion engines as varnish. The preferred glass forming ingredients of the composition by which the present process is carried out protect the hydrated colloids (polar compounds) in a manner to inhibit the deterigration thereof, and avoid the formation of such black insoluble deposits.

We have noted particularly that when boric acid or borax are used in the composition the hydrated colloids remain on the worked metal as an amber colored soluble substance which remains slippery to the touch which has no appearance of having been carbonized or polymerized and is readily removed in H20. A further explanation for the protective action of the glass forming ingredients particularly when these comprise hydrated glass forming salts is that since said inorganic materials melt and then boil in the liberated water, there is sufllcient cooling effect on the organic material so that thelatter does not reach carbonizing or polymerizing temperatures during working of the metal. Probably the reason for the conversion of soaps into the black insoluble varnish-like substance is that the sodium hydroxide formed by hydrolysis'of the soap causes the polymerization of the unsaturates formed by the thermal cracking of the soap. If the composition contains, for example. borax, it is probable that such polymerization is prevented by the presence in the composition of borax in an amount in excess of the chemical equivalent of the. sodium hydroxide which the borax would take up to form sodium metaborate, viz:

2NaOH+ NaaBaOr-"iNaBOz-kHzO Such a mixture of sodium metaborate with excess sodium tetraborate would buffer around Additionally, the preferred organic compound provides a plastic binder and vehicle for the inorganic components which, without such binder, can be scraped oflf as powder. Scraping oif of the present coating as with a knife results in pro ducing pliable ribbons of the coating material.

In addition to plasticizing and binding of the inorganic glass forming materials or glass, the soap or equivalent organic lubricant performs another valuable function. Using for illustration die drawing of wire, metal coated with inorganic glass forming materials containing no soap or equivalent readily fusible organic lubricant is not slippery to the touch, so that when it enters the die and before frictional heat brings into play the cooling and lubricating properties of the inorganic materials, the coating would seize and drag at the die throat and tend to be removed. In the presence of soap, however, the coating is safely lubricated through the die throat.

The importance of using in the process fusible inorganic materials of different melting and flowing points, all above that of the binder or vehicle material but below the melting or welding point of the tool or the seizure point of the metal worked on thereby, is largely that these materials act as coolants when they take up their heat of fusion,

whereas in the case of lnfusible materials such as graphite, chalk, lime, etc. these materials, which are not actually lubricants but mainly act as barriers between the metal and tool, sometimes tend to increase the working temperatures by acting as abrasives, and thus increase die wear. That is never true of hydrated glass forming salts for example which actually decrease temperature, primarily by liberating water and secondarily taking up heat to melt and produce lubrication fluids of unusually high film strength.

An exemplary composition for use in cold wire drawing but which can be used effectively for other cold forming processes is in accordance with the following table showing the primary and secondary melting points of the ingredients used, so far as said ingredients have two melting points:

Soltens. The particular high titre soap mentioned above ordinarily decomposes at 340 0. and carbonizes at 375 0.

As substitutions for part of the borax we may use up to 10% disodium phosphate which primarily melts at 34.6 C. or sodium metasilicate up to 10%, (primary melting point 47 0.). In the event of using either of such substitute ingredients the borax content of the formula would be reduced proportionately, for example, up to 10%.

The above composition may, for example, be dissolved in water using from four ounces to saturation of the composition in one gallon of water. For wire drawing the wire is dipped in the solution while the latter is heated somewhere near the boiling point or at boiling temperature and the solvent is then suitably evaporated from the wire leaving a deposited coating of the organic and inorganic materials of the composition thereon.

For wet process drawing, grinding or machining and for use primarily as a coolant in such process, we may use from one quarter ounce up to four ounces of composition per gallon of water.

Where the metal working takes place under conditions of high relative humidity less hygroscopic alkali salts are substituted in place of the more hygroscopic salts. While the soap acts as a wetting agent and other suitable wetting agents may be added, excess moisture is a hindrance to the process because it tends to cause premature flow of the coating compositions and failure of the glass forming materials properly to reach the working region. In the case of wire drawing, for

example, the materials must be fairly dry when introduced into the-die aperture for otherwise the coating may be partially sloughed off by the. excess moisture. Water of crystallization or hydration (in case of hydrates) is not liberated until the endothermic reactions thereof earlier described take place and the reactions occur stepwise both in point of time and linear position in the working direction because, as apparent in wire drawing, the frictional heat increases as a particular point on the work progresses through the reducing portions of the die. Under humid weather conditions it is desirable to heat the coated work above the boiling point of waterin an even, a flash baker or by means of infra red light to expell any moisture picked up by the somewhat hygroscopic sodium salts and other hygroscopic materials which may be used. In addition to grading the ingredients according to melting points, hydroscopic action etc. the ingredients are balanced in respect to acidity and alkalinity so that .the aqueous solution thereof, ordinarily used in order to apply the composition to the metal to be worked will be substantially neutral with the object of protecting human skin from deleterious effects of high acidity and alkalinity.

As an instance of the efficiency of the present process, finishing dies for drawing stainless steel Further to explain the operation of the process it will be seen that by the incorporation of sodium tetraborate (borax) with high titre soap'we have a naturally slippery composition, the borax of which melts at 75 (3., gives up its water of crystallization at 200 C. and intumesces at that temperature to form an impalpable powder. The powder so formed after intumescence could be considered analogous to a solid filler in known types of lubricant; but said powder has, in addi-' tion, an important physical property. At 741 C. the intumesced borax becomes fluid and thereby serves to lubricate the metal being worked. Similarly the higher secondary melting point glass forming substances, following dehydration and intumescence, become fluid lubricants at respective increased temperatures and those added ingredients and the proportions thereof are selected so as to fill in any gaps that may occur. that is to bridge over from one temperature range to another.

Thus the invention enables selective use of a large variety of materials not previously believed useful as lubricants in metal forming processes. For example, we can utilize not only the lower melting glass forming alkalis but a frit which will melt at higher temperatures still below the melting point of the forming tool. On carburized tool work steel which in case hardening acquires about a 0.9 or less carbon with a melting point of 1420" C. we may utilize in the composition or possib y all by itself with appropriate introductory lubricant such as .high titre soap, a frit Per cent Per cent K 5.5 A1203 5.5 CaO ..12.'? S102 64.5 F6203 3.6 13203 8.2

For a further example of a working formula the following is given:

Per cent Borax Boric acid 12%, Infusorial earth or clay Litharge 12%.; Soap 10 The formula just given may be used to form a frit by fractional heat in situ of the composition 0.5 PbO, 0.5 NazO- 2.0 SiOz and 1.0 B203 with a melting point of 580-600 C. We may use a concentration of two to four pounds per gallon and a 10 temperature near boiling to form a slurry for coating the work.

In the working of metals illustrated for example by cold drawing of wire or steel shell casings there are a number of variables which affect the present process or perhaps all metal working processes in respectively different ways. The speed at which the wire is drawn regardless of the amount of reduction in the die inherently creates different temperatures at the working region. The amount of reduction and size of the stock create additional variable factors in each of the dies and these variables are multiplied when the drawing speed variable is taken into consideration. It should be mentioned that size of the wire affects the problem of lubrication mainly because in the case of a small wire there is less opportunity for heat dissipation along the wire away from the working surfaces of the die than in the case of large wire.

A further and important variable is introduced by the fact that a smooth die (unscored or not built up by welding of particles of drawn stock) requires much less lubrication than one which is worn or scored or built up. For example, in the case of building up by welded on metal certain portions of the die present separated points of contact with the work which tend to bite through any lubricant film regardless of its strength and in such cases a much greater cooling and lubricating effect is necessary in order to secure proper drawing.

Additional variables result from dies having different throat angles since the more gradual the reduction is, the greater is the opportunity for heat to become dissipated, particularly by the die metal as well as byv the metal being worked. In addition, of course, there are other variables arising from the heat conductivity of different metals to be drawn and the composition of the dies. 1 A diamond die for instance will not conduct heat as rapidly as an alloy steel die. Copper wire will conduct heat away from the working region very rapidly, carbon steel wire less rapidly and stainless steel wire still less rapidly.

Accordingly, it is important, since one sup-' plying a drawing compound for a particular class of work would not ordinarily be apprised of all the variable factors which might apply to make the process as nearly universally applicable as possible at least to certain classes of work. Therefore we provide a sumcient range both of primary and secondary lubricatingly effective points (initial melting and subsequent glass forming points) so that if, for example, drawing or forming speed is actually greater than specified by the customer or user, or the material to be worked on, is different from that for which the user purchased the materials, or some other or unexpected variable is introduced, satisfactory results will nevertheless be obtained.

.Illustrating further by reference to multiple die wire drawing, it will be apparent from the formula heretofore given that the first ingredient (e. g. soap) will necessarily function as 'a lubricant at the first die and in case of high speed or considerable reduction by that die a considerable portion of that ingredient will be removed or chemically changed so that there will be less of that ingredient capable of operation at the second or third die. The soap all by itself is a very good drawing lubricant and none of the other ingredients might be called upon to do any work in the first die, particularly since the speed at which the wire passes through the first die is 11- much slower than in the case of the second die and still slower as compared to the operation of the third die and so on due to the elongation of the wire. The second mentioned material in the in aqueous solution for wet process wire drawing and also deposited as a dry coating on wire prior to drawing-through dies. These have the disadvantage of marked hydroscopicity.

formula which is an inorganic glass forming ma- Furthermore, we are aware of the prior emterial but yielding a relatively low melting point ployment of certain alkaline materials some 01' glass may be called upon to do its principal work which are glass forming materials as peptizers in in the second die where because of the greater connection with aqueous suspensions of water speed, the heat generated by forming pressure insoluble, high melting point, argillaceous mateand fr ct n m y d r a lar e part of the soap rials for operation in cold drawing as barrier partially ineffective upon subjection to the'workmaterials as hereinbefore explained. Such prior ing pressure of that die yet be insufficient to more employment of glass forming materials with barthan cause primary fluidity of the third or fourth rier particles is not operative to supply between ingredient (as by melting thereof and releasing the metal surfaces of the material worked upon some or all of the water of crystallization or hyand the tool fluid glass to prevent metal-to-metal dration). Accordingly, it is necessary in order contact, nor is any stepwise succession of operafully to take advantage of the present process or tions produced thereby. Instead the alkaline mamethod to provide a sufflcient range of lubri-' terials used for peptizing purposes combine accant film forming temperatures so that any intively with the argillaceous particles to form high staneous condition which could normally be eX- melting point ceramic bodies of complex sodium pected will be met. aluminum or sodium magnesium silicate at the The following table illustrates one manner of surface temperatures which occur during cold arranging known glass forming materials for enworking of metal. Glaze films would be formed abling ready selection of a formulae for difleron those ceramic bodies during fluxing at relaent work. Proportions are arrived at in the mantively high temperatures if attained but the argilner already indicated: laceous' materials themselves prevent any and all Prim"? 11,0 lost (or Parts i221? ra ag 5g} fat? point), 0

Sodium Silicate:

Mata. 47 100 6 1,088 Nam-2810 s14 Sodium Phosphate:

Monobasic, NaH;P0|-2H;O 20001) 4 98s Disod. Phosphate, NmHPOr-HHgO 34. 6 100 12 1, 340 B Tr isod. Phos., NagPOr-12Hg0 1 3.4 100(d) 12 1,340 aid. 'letrabcrate, Na;'B|0r-l0Hg0 75 200 741 Sod. Metaborate, NaB o,-2H,o s7 2 m Boric Acid:

OI'thO HrBOL 185 300 577 Meta HBO- 200 577 Pyro H1340! 57'] Sodium Carbonate, NflgCOz-HgO 100 851 Potassium Carbonate, K O 0 89! Potassium Borate:

Mata M7 K3890! 950 Sodium Aluminate, Nauo, 1,650

l Loses 2H10. 1 Anhydrous.

We recognize that certain partially dehydrated lubricating flow of the glass between the metal alkali metal salts have been used prior hereto surfaces.

as alternatives in the hot drawing of tungsten Our selection of 1000 C. as an upper limit for wire. Said salts were fused on the wire before the melting point of the glass forming materials the wire entered the die, and were then conducted in accordance herewith and in conjunction with to the die aperture by the hot wire. Solid sublower melting lubricantsismadeinorderto sharpstances, or at least finely divided graphite, were ly distinguish them from the prior art abrasive proposed as additives in said process. When used fillers which melt above 1000 C. and in recognias a fused bath such salts as mentioned would tion of the evidence of Bowden and Ridler, cited have lost all of their water of crystallization plus above, that high melting metals in dry sliding part of their chemically combined H2O or hydrafriction do not tend to develop junction temperation and therefore no advantage was taken of the tures higher than 1000 C. probably because of latent heat of fusion and the cooling effect on the radiation and conduction of heat away from the metal and tool surfaces which occurs when the junction point. primary melting point has been reached and the We claim: water of crystallization given up in accordance 1. In the cold working of metals, the improvewith the present process as described above, and ment comprising: stepwise lubrication of the no advantage was taken of the cushioning effect working surface of the tool by simultaneously of entrapped steam. Additionally, relatively insupplying between the work and tool dry organic fusible materials such as graphite or, for further low melting point lubricating-film-forming and examples of known "barrier" materials: lime and water liberating material and a plurality of dry mica, cannot possibly act as a plastic binder and inorganic hydrated glass forming materials havvehicle for the alkali metal salts as will for ex- 10 ing melting points below 1000 C. and selected ample high titre soap as preferably employed in to provide, stepwise, a range of melting water the present process or method of lubricating liberating and glass fusion points all below the metals during cold working thereof. welding point of the metal and tool.

We are also aware that certain alkaline ortho- 2. The process according to claim 1, characterphosphates have been previously proposed for use ized in that said materials are simultaneously supplied by providing them on the stock, preparatory to the forming operation, in the form of a dry self-adherent homogeneous film.

3. The process according to claim 2, characterized in that said film is free from barrier material.

4-. The process according to claim 1, characterlzed in that said organic material is a high titre soap and at least one of the dry inorganic materials 1s borax.

- GILBERT H. OROZCO.

JOHN A. HENRICKS.

REFERENCES CITED The following references are of record in the me of this patent:

Number Number 15 11,439