US2027787A - Wire drawing die - Google Patents

Description

Jan. 14, 1936. R. R. RIDGWAY E1- AL N WIRE DRAWING DIE Filed Nov. 13, 1933 I2 '15 IO Ema/WW4 WITNESSES RAYMQND R.F?/DGWAY BRUCE Z..BA/1.EY

" feet of the diamond is related to the fact that 4 it is a product of nature which varies widely in its physical and chemical composition giving widescan 1.... 14, 1936 UNITED STATES 2.92am WIRE DRAWING DIE laymondllllidgwsy'andlrneelcnailenmsgaravlalls, N. Y.-, assignors to hlicrtonrcomm 00m 011 0 l H I m Application November 13, 19:3, sci-m No. 897,744

This invention relates to dies, and morepartlcularly to metal shaping dies and to a method of making the same.

The value of a wire drawing die is largely dependent on the length of wire which can be drawn to size through a given die after its open-- ing has been carefully shaped to produce a given wire size. The limits and variations permitted in drawn wires varies over a large range. In some cases wire must be held to very close limits in the drawing. .A satisfactory die, therefore, must be made of a hard materialwhich will resist the abrading action resulting from the travel. of

hundreds of thousands of feet of wire through the-die opening. 7 Wire varies greatly in the nature of its abrading action on the die and in the mechanical forces imposed by the reduction proces as the wire is drawn through the die opening. In the present state of the art there are four materials generally used for wire drawing dies. 'l'hese are crystalline diamonds, cemerited tungsten carbides,sapphires, and chilled Theme of diamonds for wire drawingis distinctly limited by the fact that this material is expenslveasarawmaterialandcanbehadonly iii-relatively small nibsiaes. Another de- 7 variations in its resistance tothe strains involved and in its wearing qualities. The same general defects occur in the case of sapphires.

The chilled iron alloys which have formerly been used in large quantities for the drawing of vari-' ous types of wire are relatively inexpensive to manufacture but they are so easily wornbythe wire drawing operation thatonly -a relatively sbortlengthofwlrecanbe'drawn before a new dlemust be provided.

The cemented carbide alloysaresubstitutedin many operations for the chilled iron alloys be-.

cause theirlife is somueh greater-due to their =increased wear-'resistance-that it is economical tend to split the die. In practice cemented car;-

'. aremuch more expensive than the dies formerly usedforthepurposeandwhiletheyhaveagreaterc wearresistance thantheichilled iron alloys, they are madeof materials in two definite of hardness so that they cannot be finished to to use the more expensive cemented carbide ma- The cemented carbide alloys have a wear resistance greater than the chilled iron alloys coupled with" a certainldesree of strength to producedin drawing which bide alloys have certain definite defects. 'lhey a high polish and, therefore'the reduction area and bearing surfaces oil'er friction to the drawing .of wire and placela certain amount of scratches on-the drawn product The not equal to that of thediamond and, therefore,

the wear resistance of the finished die is not the equivalent of a diamond die.

It is the primary object of this invention to produce a die which will be free-from the unfavorable characteristics of the diamond and yet 10 will have some of its desirable properties, namely itscrystalline nature and its high degree of wear resistance. Further objects will be apparent from the followingdescription.;

In accordance with this invention we propose to make suchdies of boron carbide and thus to overcome various problems heretofore met in, the industry. The boron carbide of commerce has heretofore consisted of-a black powder of variable and uncertain composition. It has been contaminated with a high degree of free graphite and other metallic impurities such as boron, iron, Y aluminum silicon, and the like. Such a material is-of no use for the manufacture of wire drawing dies and cannot be manufactured into suitable for a wire drawing nib.

In thecourse of our experimentation, we have discovered that the unusual propertiesof boron carbideof the formula Bic, or as made in accordance with the method described in the patent to Ridgway No. 1,897,21Lof February 14, 1938, make this material particularly well adapted for use as a metal shaping or drawing die, such as dies for drawing wire, tubes, etc., or for extrusion operations and other purposes. This boroncarbideischaracterizedby ahardnessap- .proaching'that of the diamond. It is wear-resistant or durable and is particularly suited for use under the action of abrasion during a drawing operation. It is only slightly below the dia- 4 mondin the scale of hardness, besides being appreciably harderthan the standard abrasive materlals, as tungsten carbide. crystalline ammina and con carbide. The boron bide. as described, further characterized by ving a I terised by its being devoid of parting planes of 5 .graphite and uncombined carbon.- and it is undiluted by any foreign and'undeiired impurities, :such as borides and carbides ofiron, aluminum, siliconand other metals. It has a very high melting point of about 2300" or 100 C. and 7 probably meltsat about 225 0., as measured by opticalmeth'ods. The boron carbide isvery stable and is not decomposedby the furnace heat, and in particular it does not vaporize in the abody manner in which boron metal does, but it melts q to a liquid phase and crystallizes therei'rom so that it is capable of being formed into a molded shape. Hence, it is, therefore, particularly desirable for use as a material for a wire drawing die, due to its superior abrasion resistance, and when suitably mounted and supported it is strong enough to withstand thelargestresses which tend to split the die in use.

In accordance with our invention, we so make the die nib or body that its eilective portion comprises boron carbide, as above described, and is soconstitutedas tobeadapted forametalshaping operation. We propose to shape the boron carbide, as made in accordance with the Ridgway patent, by a suitableprocedure, in accordance with which the eflective surface of the die is so made as to mntain this extremely hard material in suificient proportion to satisfy the desired ends. It is necessarythat cementing matrices or impurities be present only in relatively small amounts. We prefer to make the die in accordance with the disclosurein our copending application Serial No. 694,502 filed October 20, 1933, whereby we mold the 34C material into a unitary body havingv a substantially continuous one-phase crystalline structure. The material may be molded into a desired shape for use as a die, either with or without the die opening under high temperature furnacing conditions which cause the. boron carbide to be melted or softened and shaped by a mold and then crystallized into a one-phase crystalline body of high density, and preferably of from 2.3 to 2.55. The process is preferably so carried on that the body is not contaminated in particular with substantial amounts of dissolved graphite and does not contain parting planes of graphite within its mass and which, therefore, has great strength. density and rigidity as well as hardness.

This method is preferably accomplished by heating boron carbide powder of a required de; gree of purity and grain size to a temperature at which it will melt or soften and be capable of being molded, after which the material may be shaped under pressure in a mold of suitable refractory material, while conditions are maintained which prevent the 34C material from reacting chemically with or physically dissolving foreign substances capable of detrimentally affectingithe properties of the die. Since boron carbide dissolves carbon readily, the manufacture of the die is arranged so that the material is heated to a softened condition and caused to be shaped while it, istoo viscous, or insufficiently heated, to dissolve or react with the graphite mold parts to any detrimental extent. If the material is fully melted so as to become completely fluid, it is desirable then that it be rapidly cooled, after it has assumed its final shape, to a temperature at which it is'stable. In this way, the material is not permitted to remain in contact with graphite while in the molten state,

' or only for the minimum of time required for it to become shaped by the mold under the conditions of the molding or casting operation.

In the forming operation, it is desirable that the process be carried on in the presence of an inert atmosphere or in the absence of oxygen or other substances which cause oxidation or decomposition of the boron carbide. It is also essential that the material be prevented from absorbing more carbon than is necessary to satisfy the ratio of 34C. Our experiments have also indicated that liquefaction or softening of the boron carbide powder may be brought about at a temperature appreciably below its melting point when it is subjected to a high pressure. Under such conditions of temperature and pressure, liquefaction of the compound may be without the solution of additional carbon over whatisnecessarytoproducetheformofboron carbide as set forth in the Rid way mtent. It has also been-found, by experimental tests. that thematerialcrystallines againwhenthepressin'e is released, even though the temperature is held constant. The following examples from test records show a comparison between typical analyses of the composition of the boron carbide powder before molding into the form of a metal drawing die and the composition ofthe formed pieces resulting from the high temperature molding process.

In practice, it has been found advantageous to maintain in the boron carbide powder a-small amount of free uncombined boron in excess over that required to make the carbide set forth in the aforementioned Ridgway patent. It may be assumed that this excess of uncombined boron metal will act to neutralize or react with the carbon vapors resulting from the carbon mold and the related parts.

In the examples above noted, it will be seen that the high temperature molding operation used in making the molded article results in the composition taking up additional carbon, with the consequent decrease of the free boron content, as compared to the ideal composition desired, and the further reduction of the small amounts of impurities, by volatilization, to insignificant quantities. 7 observed that the analysis of Sample No. 3 approach closely to the ideal composition.

In forming a die in accordance with this inven-' tion, the boron carbide in a finely divided condition or powdered form is subjected to pressure while it is heated to a point at which it becomes molten or sufllciently soft to be molded, the pressure being sufllciently high to consolidate the par- In the above table, it will also be ticles into a structure of the required density and employed, the apparent density may be raised to a value substantially equal to or within 2% of the real density of boron carbide, which is about 2.52. Also, if necessary, the carbide grains may be subjected to suitable chemical treatment to remove any chemically reactive constituents from the finely divided powder in order that a substantially chemically pure boron carbide may be obtained. p v A non-reactive refractory material should be utilized for the mold or container for the molten carbide, and wefind that ordinary commercial graphite having a strong non-porous form and which has been processed to give a maximum density, such as is used as an electric furnace electrode, can be used as a practical material for the mold. This graphite is well known in the electrometallurgical art and consists essentially of pure .carbon with only negligible amounts of ash constituents. Owing to the availability and cheapness of graphite, we prefer .to use a graphite of l the purest and highest quality for this mold.

' "carbide grains to the molten phase as the ma-.

The molding apparatus is preferably equipped with a movable graphite plunger fitted into themold so that by applying pressure to the plunger. it is possible to follow the conversion of the solid 40 this way, the' molten material is permitted to remain in contact with the graphite only for the minimum of time required for the molding opera- 1 tion.

In the manufacture ofa niolded boron carbide die. the exact conditions will be deter-' mined by the nature of the material used and the size and density of the finished product. In the manufacture ofa wire drawing die which is of comparatively small dimensions but is required to beof the maximum obtainable density a and to be accurately dimensioned, it is prefer-H degree ofpurity and of the required comable tow-make the article. in accordance with the following-procedure. Boron carbide of a position of boron and carbon. preferably that type of material which is obtained in accordance with the process set forth in the Ridgway Patent No. 1,897,214 and treated with acid as above described, is crushed to a suitable size, and preferabiy one which'is finer than will be retained by a screen of 200meshes to the linear inch.

'Ihe powdered materialwill have a real density er movements. Adefinite 'weighed amount of of approximately 2.52, and the size of the particles will be so selected and distributed'as to-give the' maximum apparent'density to avoid large plungthis carefully selected material, as predetermined by suitable calculations. is placed lathe-graphite mold and heated rapidly under pressure until coalescence takes place. The material may be preliminarilypressed to shapeiin the mold 'or priortoitsbeingplacedinthemoldsothat itwill have an apparent density of about 2.0, thuslessening the pllmger movement during the pressure casting operation.

It has not definitely been proved, not a may be conveniently assumed that the pressure appliedto the plunger may also serve to lower the fusion point of the boron carbide grains to a point where the rate of solution of carbon from the containing walls is greatly reduced, thereby making possible the production of the fused article without the inclusion of excess graphite. The

temperature range within which the product has I been found to have useful properties has been from 2000 C. up to 2500" C. However, by applying suflicient pressure to insure the required density of product, and by carefully limiting the temperature so as to reduce it below the melting point as soon as the material has been sufliciently heated to shape it to the mold,a boron carbide article may be made which has not dissolved materlal amounts of carbon from the graphite mold. If desired, the plunger movement during the casting operation may be so controlled that a definite amount or weight of grains which has been calculated to occupy a desired volume percentage of the final product will be caused to occupy that volume in the shaped body, so that the porosity will likewise constitute a desired volume.

The amount of pressure to be applied to the mmaterials in the mold will be determined in accordance with the size and desired density of the die to be made. For example, in making dies, the

pressure limits may be maintained within a range 0 lower pressures will not result in the production of a product of sufiiciently high density.

In the case of the manufacture of nibs of very small dimensions such as are ordinarily used for the drawing of small wires, we have found that it is necessary tense the higher range of pressures in order to produce a satisfactory piece. 'Ihis is related to the mold friction which'serves to neutralize the. pressure applied to the plungers. Therefore, in the manufacture-of dies of highest quality, the highest pressure which is consistent with the strength of the, plunger should be applied due to the small total pressure which is called for by a small nib. The ordinary frictional losses are abnormally high ii proportion to the totalapplied force. We have also observed in practice that there is a certain tendency for the pow er in the mold to pack and resist-the pres- ,sur of the plunger due to friction along the side of the mold. In such cases, accuracy cess of the molding operation depends Dim the d sucuse of sufficiently high pressureto overcome this elfect and also requiresa smooth and highly pol- 7 ished mold surface. In practice, we have found that the point of highest density is that part of the finished article which is nearest to the plunger.

Fora die nib of approximately 0.600" outside diameter and api mximately 0.300" thickness with conical depressions, one on each face but, without the molded hole, a pressureof 3300 lbs.

'persq. inch has been found satisfactory and will form a completed article with a density of from 2.4 to 2.55, when the maximum temperature,

reacheddn theformation of this piece was approximately 2250 C. In practice, it may be desirable to have the mold parts constructed so as to-produce a greater density at the bearing length of the .die opening which is advantageous as wear isgreatestatthatend, dueto thepullofthewire through the die.

However, one may so control the length of the heat softening and compacting period as to keep the boron carbide from contacting with the graphite mold any longer than necessary while it is in a molten condition; and, if desired, the pressurecastingoperationmaybestopped atapoint short of that at which the material has become fully molten. The degree of pressure and temperature applied,aswellas thegritsizeusedwlll determine the density of the article. The pressure limits of course, be governed largely by theslrengthoithemoldand the furnace mate- It will be evident to any metallurgist that various methods are available for the refining of the grain in the products produced by the molding operation. Rates of cooling, variations of temperature, pres'ure, length ofheating period, and original grain size of the powder all influence the sh'ucture of the resultant formed article, and thcircontrolareallwithintheskillof one familiar with this art.

The body thus formed has'a purity in excess of 99% of IhQanditisbeiie edtobe made up of a substantially continuous crystalline phase of boroncarbide, which is substantially free from any cementing material of a low degree. of hardhes. Thebodyhasaconchoidalcrystallinefrace ture and freedom from any material amount of graphite and other undesired impurities, and it appear-stobesimilartotheboroncarbidematerial asoriginallymadeinthe electric furnace in accordaneewith the Ridgwaypatent. Zita density of 2.3 or greater hm been attained, the body is of a metal iike appearance capable of takingahighpolishanditsmodulus ofrupture in compression is in excess of 100,000 lbs. per q. in.

Referring to the drawing which illustrates one embodiment of the invention, we have there illustrated in an enlarged sectional view a molded wiredrawingdienibcomposedofboroncarbide of the formula BQC molmted in a metal back-V ing or reinforcing holder for a wire drawing operation. This die construction is shown as comprisingawiredrawingbody ",whichis composed of dense, homogeneous boron carbide made inthemannerabovedescribedmndhavingacen theatandardpracflceofdrlllimdiamonddies toi'ormaholebctweenthedepressions. Inthe preaoureeastingmethodoftorminganopeninga celeofsuitableslaemaybeemployedinthe mold,andincertaincaaesaholeofsmallerdideelredwirediameter. 1

Asaresultoffliebomcarbidediematerial belngacrystalllnematerlalofahlshd reeof hardnmitlssomewhatbrlttleincharacter. ibis acarerulotthenlbs the'meofsoldersweatedina in a suitable hacking or' a protective casing to take up the strains induced in the material by the drawing operation. The conical reduction area of the die acting'on the wire'during the drawing operation results in a component of 5 force which tends to split the die. Therefore, great care must be taken in mounting the boron carbidenibinthecasingtoinsurethatthebrittie die material does not bear all of the force which tends to split the die in the drawing 'operation. It is necessary also that the force exerted on the die nib be equally applied throughout its entire circumference so that no distortion may he produced in the hard brittle material-by the Iorces resulting from wire Itwillbeapparenttothoseskilledintheart of molmting nibs that care must be taken to insure that the backing material is thus equally and smoothly applied to the carbide and that it has such characteristics under heat and pressure that it will continuously act to support the hard wear resisting material in all types of severe operation. To this end it is to provide a backing material of theproper coeflicient of expansion and tensile strength to protect the die against abusive treatment. It is recognized among die manuiacturers that various wire drawing machines andtypes oi wire-drawing require suitable adaptation of reduction area angles, bearing surfaces, and back openings. The adaptation of our material to any commercial operationwiilbeevidenttoone skilledinthe art of die makingif its properties of great hardn& and brittleness are properly known.

Various methods of moimting the die nibs may be employed. For example, the die nib ll may be mountedinacasing' llinsucha mannerthatit will be reinforced against the high disruptive pressure set up when drawing wire of a maximum size for the die dimensions. For this the casing l2 willbe shaped to dimensions slightly lamerthanthoseoftheboroncarbidenihandit will be provided with a central opening it which isdirectlyinlinewithbutlargerthanthedie opening II and towards and thiough whichthe wireisdrawn. 'Ihedienib llmaybebraaedor cemented or otherwise secured therein. Also, since boroncarbideiscapahle ofinkingahigh polishorotbeingmadetoextremelyaccurate dimensionaitmaybe feasibleto embedtheboron carbide directly in a backing which has been accurately shaped to ilt the same. In that case. the beefing or reinforcing casing may be made to correct dimensions and then be heated and shrunkontothenib. Ifdemredonemayalso employ a procedln'e in which the boron carbide diemaybeflrstmadeassmoothaspoesibleasby a suitable operation, and then (electroplated with a suitable metal, suchua' heavy coating liotcoppenaiterwhlchitwillbemountcd inasteelholderinahydrogen atmosphere; The holder will be heated to a suillclently high temperature to expand it for mounting on the die. afterwhichitmaybethencooledandshrunkin place, the copper serving as a jointing material which insures perfect union between-the parts. Othermethodsofmountingtheboroncarbide diearefeaaiblemchasbycopperbrazlng orbyholder of niche] Itwillbeapparentthahinwith thisinvention, wehaveprovidedadieconstructionwhlchhas alonglite due'tothe greathardnees and ty-ot the material. Moreover, the high density and comequent glass-like 1o While this invention is directedto the adaptation of a pure crystalline material boron carbide such as is described in the U. S. Patent 1,897,214, formed in accordance with the copending application serial #694,502, it is within the spirit of this invention that the crystalline material may be altered by slight variations in the boron and carbon content of the product or by the addition of toughening materials in order to resist certain specially abusive conditions. It must be recognized that such small additions do not change the essential nature of the die material but maybe used to alter its crystallinity. This is distinct from processes where large amounts of a relatively soit'cementing metal are incorporated with the hard carbide such as is well known in the cemented carbide art. It is well known to metallurgists that the crystalline properties of metals may be altered with minute additions of various agents to control the crystallinity. In the metallurgy of tungsten, various agents are known which when added in amounts of 1% will modify the crystalline nature of the metal which is formed in a semiplastic condition. It should'be pointed out that the product forming thedie covered by this invention is essentially a single crystalline individual formed in a'semi-plastic or molten condition and self-bonded, but such alterations and additions of. other materials to modify the crystallinity or produce various slightly altered,

characteristics in the die material are well within the scope of this invention, which comprises a 1 crystalline boron carbide grown from the molten as found in the claims is notintended to limit this case to any particular theory of formation of the body, nor as to the physical condition of the product. It is immaterialin so far as this invention is concerned whether the individual grains have melted completely during the pressure molding operation and then have crystallized into a single homogeneous body, or whether the individual grains have not been wholly melted. but havebeen merely softened and molded together'into an integral body, or have recrystallized without melting. The expression is, however, intended to cover a body which is substantially devoid of parting planes of graphite and of any large amount of other impurities which can seriously interfere with the homogeneity and inte'grality of the body, and with its functions for the purposes herein described. The body, as thus formed, is made up substantially wholly of boron carbide, depending upon. the degree of purity of the materials initially employed.

Having thus described thev invention, what we I claim as new and desire to secure by Letters Patent is: v I a 1. A die shaped as a perforated nib of. required dimensions having a wire drawing surface, the

effective portion of which comprises boron carbide I substantially continuous crystalline phase and be- 'ing substantially devoid of graphite and structure weakening impurities. I

3. A die shaped as a perforated nib of required dimensions, the effective portion of which comprises boron carbide grains of high purity molded 5 under heat and pressure into a body having a substantially continuous crystalline phase of boron carbide having a composition conforming substantially to the formula 134C.

4. A die for wire drawing comprising a molded 10 body having a substantially continuous single phase of boron carbide conforming substantially to the formula B which is substantially free from parting planes of graphite and structure weakening impurities.

5. A die for wire drawing comprising a perforated body of required shape and dimensions having a wire engaging surface consisting oi. boron carbide granules of the formula B40 compacted into a dense, coherent mass in which the 20 structure of said body is made up of a single, hard constituent having a substantially continuous crystalline phase which is devoid oi graphite and other impurities and being substantially free from cementing materials of a low degree of hardness.

6. A wire drawing die comprising a perforated body formed of granules of boron carbide of. the formula B40 which individually have a substantially continuous crystalline phase and are devoid of graphite and detrimental impurities and which have been molded under heat and pressure while in a softened condition to form a coherent body presenting a substantially homogeneous wire drawing surface of uniform hardness and having a density above 2.4.

7. A wire drawing die of required shape and dimensions, the effective portion of which. is of a substantially continuous phase of. boron carbide having a composition conforming substantially to the formula B46 which when molded to the required dimensions and shape is substantially free from parting planes of graphite and structure Y weakening impurities, said article having a density between 2.4 and 2.55 and a modulus of rupture in-compression in excess of 100.000 lbs. per sq. in. and being capable of taking a high polish.

8. A die for wire drawing comprising an inner perforated drawing nib of boron carbide of the formula 34C having a substantially continuous crystalline phase which is shaped and adapted for drawing wire and a metal supporting member which makes a rigid contact with the nib and reinforces'it against the pressure of a wire drawmg operation.

9. A molded wire drawing die composed of boron carbide of the formula B40 of a substantially single continuous crystalline phase, said die having an electroplating of-copper upon its outer exposed surface.

11.A wire drawing die' comprising a molded 05 body having. a substantially continuous single phase of boron carbide of the formula 34C and 1 formed with a shaped aperture presenting an extremely smooth, polished, wire drawing surface, a

metal coating on the molded body and a metal 7 supporting holder integrally united thereto.

RAYMOND R. runaway. BRUQE L. BAILEY.

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