US1869959A - Method and apparatus for rolling disks - Google Patents

Description

A g- 1932- c. L. EKSERGIAN ET AL 3 3 Filed Dec. 51. 1929 Sheets-Sheet 2 i FISH l N VIS .X' 'I'Oh 5, EDWAQD GBUDD. m' CAROLUS LEKSERGIAN W .'u'my l JFE?:

xx A A wz a 5 a mw s atented Aug. 2, 1932 NITED STATES PATENT OFFICE CAROLUS LEVON EKSERGIAN,

'WEEEL COMIPANY, OF

PHILADELPHIA, PENNSYLVANIA, A. CORPOBATION OF PENNSYLVANIA BIETHOD .AND APPARATUS FOB ROLLDQ 'G DISKS Application filed December 31, 1929. seral No. 417,613.

The outstanding object of our invention is to achieve an improvement in the rolling of relatively thin tapered disks of the nature of automobile disks, particularly an improvement in the forming of such disks by obtuse anglo dies from billets of substantially cylindrical form such as can be most cheaply supplied from hot bar stock. Dsks of this order are of such thinness that their cross-section has a thickness but a fraction of the crosssection of relatively heavy disks such as used in car wheels. These relatively thin disks possess a lightness and an adaptation to forming by die stamping, and ultimate resiliency and resistancetodistortion in marked contrast to the heavy massive disk-like bodies of car Wheels. Such disks have today a trenendous market not only as automobile wheel disks per se, but also as brake drum disks, brake drum covers, ete. Our invention partakes jointly of the nature' of a method and apparatus From one point of view, an outgrowth of the one appears bound up in the other. Together they not' only result in an improved disk over former methods and apparatuses, but valso in a greatly enlarged range of adaptation of the obtuse angle process of rolling such disks.

It has been found that when the obtuse anglo process is used to produce relatively thin disks of the natue of automobile disks, if the reduction is extreme`anel the more especially where the disk is a tapered disk, rather than one'of uniform section as in the case of disks for brake drum formation, the more especially also Where it has been sought to reduce a disk with a relatively thin center or with no center at all, a disk independent of hub structure rather than a disk integral with such structure there results inordinate reduction 'of section of the inner marginal zone of the disk, and sometimes actual rup-- ture of the metal. This occurrence has heretofore prevented the general application of the process to all forms of relatively .thin disks of the nature of automobile disks. The range of the process as practiced has therefore been limited. Our invention removes, these limitations. p r

It has also been found that with certain forms of obtuse angle dies there results an irregularity or sometimes a broken or sharply deflected or a distorted or twisted, flow of metal; and that while the rolled section itself is perfect, the directionof such flow is contrary or at an anglo to that direction which it should follow to attain maximum strength and best drawing qualities in the resulting product. Our invention tremendously improves the general direction of flow irrespective of the particular form of the dies being used.

The cause of these difliculties which our invention has overcome we do not clearly understand. Different angular velocities of complemental portions of dies, misalignments, temperature difi'erentials between inner .and outer zones (the outer and more expansive cool more rapidly than the inner zone, especially in contact with the cooler outer portions of the dies and-therefore have greater strength), and the angular direction of the rolling enlarging the circumference at a greater rate than radial flow can efiectually follow, are amon the causes. Sometimes one alone may be e ective, at other times several or all of them may be effective, in conjunction with or without others. But whatever the causes are, the efl'ects are found to be removed by our method and apparatus.

According to our method, while the blank is being rolled in the obtuse angle dies, we maintain a central cross-section' of metal in- OF DETBOIT, MICHIGAN, .AND EDWARD G. BUDD,` OF PHILADELPHIA, PENNSYLVANIA, ASSIGNORS TO BUDD dependently of the main body of the disk, and

of a thickness considerably greater than the .thickness of the main body, and'simultaneously express metal from the center ofthe blank outwardly by way of this increased cross-section, and along lines which are graduall and smoothly converged into the metal of t e main body of the disk. Obtuse angled rolling, as well known,- is by simultaneous' axial compression and circumferential rolling on a line extending radially outwardly vfrom the center or inner periphery to the outer periphery of the blank. The thickened cross-section of metal which we maintain in wardly of 'the'inner eriphery or main body of the disk is preferably of a structural form unrelated 'to tle main body; of the disk,

one-half.

though it may be so related if desired. It is thereafter reduced to related form, or carrying the reduction to the extreme, is removed altogether from the main body.

T e apparatus is simple. It consists of an obtuse angle die having a central boss, an adjoining depression, and an outwardly disposed main body, which latter is complemental to the face form of the resulting product desired, and which central boss and adjoining depression are sinuous in form with the walls of the depression merged smoothly and unbrokenly along converging lines into the walls of the main body of the die. Preferably each of a pair of obtuse angle dies is Similarly formed, but this is not necessarily so, and there are a wide range of variations between the embodiment of one or all of these features on the one die with none of them on the other and the distribution of these features between the faces of a pair of obtuse angle dies.

The drawings illustrate both the apparatus and the method.

Fig. 1 is a transverse cross-section of a pair of dies embodying our invention in each of which its features are constructed, and a fresh blank just inserted.

Fig. 2 is a similar cross-section showing a fresh blank in position to be operated upon, and the operation just started.

Fig. 3 shows the operation when the axial length of the blank has been reduced about Fig. 4 is a simlar cross-section showing i the operation almost completed.

Fig. 5 shows the operation completed.

Figs. 6 and 7 are axial cross section of a re-press used in forming of the blank for the rolling Operations and of the blank formed by it.

Fig. 8 is a great enlargement of the central portion of Fig. 1.

spectively. Wit

dlg. 9 shows a finally completed hubless Figs. 10 and 11 are the opposed dies. The zone 12 constitutes the main body of the die in each case. Its face is complemental to the face of the finished product. Within the zones 12 and immediately adjoining them are zones 13 constituted b depressions 14 and 14 rein the 'zone 13 are zones 15 and 15' constituted by bosses 16 and 16' respectively. The walls of the' bosses 16 and 16' and the adjoining depress'ions 14 and 14' are P of approximately sinuous form merging smoothly one into the other, and the walls of depressions 14 and 14' are in turn merged smoothly and unbrokenly, still in sinuous form into the main body of the dies in zones 12. A As shown, each die is so formed and as above stated, each or all of these features may be embodied in either die or various combinations of the same.

The blank 17 to be rolled is formed from a cylindrical billet 18 cut from hot bar stock by means of the re-press mechanism shown in Figs. 6 and 7. The auxiliary reciprocable dies 19 and 20 of this pre-press apparatus when they close in on each other along the axial line 21 as shown in Fig. 6 and finally approach each other to the extent shown in Fig. 7 impart to the billet 18 the substan: tial ball shaped form of the blank 17, and on the axis 21 provide opposed spherical cavities 22. The method and apparatus for re-pressing the billets 18 into the form of Blank 17 is described fully in the co-pending application SerialNo. 403,402 filed October 30, 1929. Sulfice it to say here that the spherical centering cavities 22 formed by dies 20 constitute preliminary centering formations for the obtuse angle rolling formations while the general convex ends 23 of the blank constitute final centering formations for the rolling operation.

- The ball shaped blank 17 so formed is end tered into the obtuse angled dies of Fig. 1 by placing the axis 21 of the blank in approximate coincidcnce With the axis 24 of the relatively fixed obtuse angled die 10 and approaching the ward the die 10 until the blank 17 is engaged in its spherical preliminary centers 22 by the bosses 16 and 16' associated with the respective dies 10 and 11. The advantage of the spherical shape is that there is accurate fitdie 11 along its axis 25 toa ting of the complementally shaped spherical the center areas of its ends are of convex surface contour approximating so nearly as general conditions will permit a ball shape. Such shape precludes the formation of folds in the surface of the disk during rolling. The corners 27 of the pre-pressed billet through which the convex sides 28 are merged into the centering and Sections 22 are very steep. This has a two fold advantage; first in securing the very strongest centering comonent of forces as the dies approach each other, the major portion of the axial pressure. being thereby translated into a centering force. and secondly, in providing the most easy flow of the metal under this strong force and the still strenger rolling force to the more perfectly fill the cavities 14 of the centering zone 13 of the dies. Conplemental relative shaping of the centering zone 13 of the dies is at a slightly greater acute angle between the tangents 30 to the exterior corners 31 of the centering zone andthe axis 21. Relatively locating the corners 27 of the centering zone of the billet with respect to the outer corners 31 of the centering zone ofthe dies is substantially interiorly thereof whereby strong initial centering grip is assured. This is more than merely making the centering end of the blank similar in form at the outer corners 27' and inwardly of the centering zone 13 of the die in that it involves a radial distance 32 to the corner 27 of the prepressed billet less than the radial distance 33 from the axis 2 1 of the fixed die to the corner 31 of the centering zone 13 of the angularly disposed adj'ustable axis die.

In the initial approach of the dies 10 and 11 toward each' other, centering pin 16 of movable die 11 is forced back to the position shown in Fig. 2 against yielding pressure and a stop. The blank is preliminarily centered through the axially disposed depressions 22 free of contact with the major centering zone 13 of the angularly adjusted die. This is for the reason that until the final centering surface 23 has been completed by the forging and rolling operation its engagement would preclude or destroy accurate centering by the preliminary centering surfaces 22. It is to this end the centering pin 16 of the adjustable die when the dies are open is yieldingly held forward of its position durng rolling.

In this final centering operation the axially disposed spherical depressions 22 in the billet are sutficient to keep the billet centered accurately against the initial outward forces set up by the acute angled corner formations 29 and 31 in producing the completed final centering surfaoes 34: on the ends of the billet. Modification of final centering surfaces 23 is shown as set in in the approach of Fig. 2. The axial depressions 22 might well be in-- sufiicient, and probably in most cases are insuflicient, to center the billet during the further rolling Operations. In fact, in 'most cases in the last stages of rolling the axial center of the disk is very materially reduced. The product is ctered entirely upon the greater end areas of the zone 13 surrounding its ends. From this standpoint, the method comprehends the formation of minor and preliminary centering surfaces 22 on the axis of the billet, by pre-pressin'g, the initiation of major and final centering surfaces 23 on the billet by pre-pressing, completion of such major and final surfaces to the form 34 by the initial forging and/or rolling operation, together with a-transfer of the centering formation during rolling from the axial reliminary centers 16 substantially or entirely to the final centers of the zone 13 surrounding, a transfer of seating from the axis to the end peripheries of the blank.

Further axial compression being applied to the dies 10 and 11 and rolling being started either simultaneously with the further compression or an appropriate time thereafter, the blank is very quickly reduced to the shape shown in Fig. 3, after which the reduction of the blank toward its final form is accomplished more by rolling and less by compression, though the compression is maintained as an incident to the rolling rather than a principal factor in the formation. Rolling rapidly further reduces the section to the form shown in Fig. 4 where the product assumes a disk-like form, relatively thick and of the order of railway car wheel thickness. From this point the disk is reduced toward and into the degree of thinness commonly found in disks of the nature of automobile wheel disks, relatively very thin, very light, and most times tapered in thickness from center or inner periphery to the outer periphery. The full reduction is shown in Fig. 5.

Throughout this operation through the use of the depressions 14 we have maintained a thickness of cross section at the center of sufficient cross-seetional area so that the resulting stresses will not be suflicient to cause rupture or undue lateral straining of the various portions of the blank and irrespective of other causes tending to reduce the section of or to rupture the blank in the neighborhood of the inner margin of the Zone 12 of the main body. This thickness we adjust by appropriate trial and error, or by calculation as may be most convenient to accomplish our aim. Preferably we maintain a thickness somewhat in excess of that sufficient for the purpose to allow for a margin of safety.

The flow of the metal during the rolling operation takes place through the throat 37 formed by the endmost sinuous sections'of the `dies, where centering zone 13 ends, fed from the mass of metal within the complemental cavities 14 of the centering zone 13. This mass 36 of metal is of such cross sectional thickness as against the cross sectional thickness of the center 35 of the blank that starving exteriorly thereof is precluded and is confined to 'the central area of the blank within the portion 36 of the thickened cross section. The thickened section 36 also retains the heat better than a thinner section and guarantees regular and consistent flow through the throat 37 under the force set up by the increasingly greater enlargement of diameter progressively outward from the center. Still further, the massive centering action of the section 36 as' progressively derived from the massive end portions of the 3 metal and their continued approach toward each other nore closely than the walls of the adjoining depression 14 and 14' causes a flow of the mass of metal at the center of the blank and in the adjoining margins of the mass within the depression 14 and 14', radially outwardly along smoothly converging lines indicated by the arrows 18 into the main body of the disk. Smoothness and regularty of the lines of flow is therefore cnforced under the expressin action and by the appropriate shaping o the walls of the boss 16 and the depresson 18. This enforced and controlled action greatly augments the action of the excess cross-section of the zone 13 in maintaining strength and still further widens the range of adaptation of the obtuse angle rolling mill to fabrication of relatively thin disks and the like.

A feature of the method includes starving of the axially disposed 'centers of the disk. This is deliberately brought about by the ini tial provision of the axially disposed spherical centering cavities 22, and their subseuent naintenance by the complenentally isposed spherical centering pins 16 and 16' of the dies, which pins 16 are fixed relative to the dies after complete centering and are approached toward each other at the same rate as the dies. Thereby the center of the billet is axially always the thinnest and radial strength incident to rolling upon the billet least at this point. Starving in all regions radially removed from the center is therefore effectually precluded.

l`he rolling; having been completed to the stage shown in'Fig. 5, the dies are then raised from each other and the product removed from the machine. Thereupon fixed center portion 36 within the zone 13 of the dies is removed by a blanking operation and the hublcss disk of F ig. 9 becomes the inal project.

If desired the removed mass of metal 36 may be subjected to further Operations to form hubs per se or other articles. Indeed, through appropriate modification without departing from the generic spirit of my invention the portion may be given the form of forged ring or hub, or at least, the form which is transmutable into such construction by efii'- cient and economical subsequent Operations.

Summarizing in part, it will be noted that in the carrying' out of the process the bosses or pins 16 projecting: from the faces ofthe dies afford the initial or preliminary centering, and that after the centering is taken over by the walls of the depressions 14 and 14', they no longer have this function except in a subordinate way and for aportion ofthe rollingperiod. In fact, as the final major centering is taken over by the walls of the depressions 14 and 14' the axis 21 of the billet 17 is approached more and more nearly to the axis 24.- of the male die 10. The starving of the center incident to the radial flow of the mass material likewise relieves the bosses 16 and 16' of this centering function. Yet while they are relieved of this centering function, they progressively take on another important function, that of coring out and interiorly rolling the center of the mass prior to and during such starving as may occur dependiig upon the mass condition, this coring out comes about by the rolling action interiorly of the cored part as clearly appears in F igs. 4 and 5, particularly on the part of the boss 16' of the female die.

Relative proportions of the male and female dies should also be especially noted.

'The depressions 14' in the face of the female die are much deeper than the corresponding depressions 14 in the face of the male die. Thereby the radial pushing out of the central mass of metal is aided rather than retarded. On the other hand, the deeper depression in the female die insures sufficient hump at the center section to guarantee ade uate centering in the presence of the angu arity of the female head 11.

The contour of each die and the relative contours of the dies 10 and 11 have a definite relation to the volume of material of the billet 17. If the fiare of the walls of the depressions 14 is not sufiiciently large for a given volume of material, a flash will result between the two dies. This is intimately related with the shape of the billet 17 As previously emphasized, the shape of the billet and the shape of the depressions conjoin to prevent the formation of slivers or cold cracks. Thus, it is seen that the relation between the shape of the dies and the shape of the billet is an intimate one, intinately a part of our general process. The shape of the billet is not only one which can be rolled without the development of adverse factors as outlined in this specification, but also one which can be pre-pressed effectively and efiiciently. It is not only one which can be effectively centered in the rolling dies but also one the centering portions of which can be effectively developed in the pre-press. Still further back, the centering formations on the ends of the billet, both the preliminary and the final, are formations which can be readily effected from a blank having its ends in the convergent planes as shown in Fig. 6. These convergent planes'are in turn formed by the cut-off knives. The cut-off is achieved by the process and apparatus described in the copending application of C. L.- Eksergian and William A.` Weightman, 'filed October 18, 1929, Seri'al No. 400,480.

L. Eksergian and William AWeightman, filed October 30, 1929` Serial No. 403,402.

Especial note should be taken of the functions of the central mass of metal during the rolling operation. As has appeared, it initially serves as a massive centering means Pre-pressing is *achieved by the apparatus and method described in the co-pending 'application of C.

' efiectually flow. The coring econte guaranteeing concentricity of rolling under the extremely heavy radial strains. Such massive centering means are the more effective by reasons of the high temperature and greater plasticity of the central mass as distinguished from the lower temperature and less plasticity of the ever thinning disk portion of the blank. While`the relation between stress and strain is not constant with plastic flow, the radial stresses are very marked and become the more critical as the thinning of the disk proceeds. The metal rolling of the obtuse mill is, of course, an annular rolling in the circumferential direction. The displaced metal results in a greater annular or circuniferential dimension by direct addition to the length of any given circle of rolling. By reason of this, there is progressive perimetral enlargement and by the same token, progressive dimensional enlargement of each Circular element of the entire disk surface. The radial movement of the material being rolled is therefore primarily a. function of the direct cir-' cumferential or tangential travel of the material produced by the rolling action. The central mass of metal provided according to our process by the contouring of the dies described, particularly the depressions 14, establish an equilibrium of radial flow under these conditions with the natural center feeding of the material. In other words, as the inner peri hery of the disk-like body being rolled ten s to enlarge in circumference, material is drawn from the center mass to maintain its dimension and to relieve it of undue stresses incident to the tendency to enlarge under the radial strains. The axial compression of the central mass adds this radial compensating and equilibrium maintaining out action of the pins which roll the inner surface of the cored out hollow of the mass assist this same action. The rolling action of the pins or bosses 16 and 16" is virtually an internal rolling. By

all of these actions the material is expressed radially from the 'central mass. Equilibrium is established between the radial forces set up by axial compression and the coring out action and the pulling radial forces induced by the circumferential rolling. The resultig radial outward flow is stimulated by the a vantageous sinuous sections of the dies which set up good flow lines for the central metal mass. However, the important function of cntering first mentioned, as performed by the central mass of metal in coaction with the complemental die formation, necessitates a compromise between ideal flow lines and ideal centering. The form of dies we have disclosed constitute one of the best such compromises now known to us.

According to our method, we regulate the axial thickness of the central hub or hub-like mass particularly at the throat between the disk-like portion to effect an annual cross sectional area in the throat sufficient to give enough strength to more than compensate for the reduced tensile strength incident to the higher temperature of the. central mass and the thicker portions of the threat. All starving, reductons of section, tearing and other irregularities in this region are thereby efi`ectually prevented.

The scope of our invention is the purview of its generic spirit as determined by the prior art rather than the circumstantial terminology of the foregoing specification and the anneXed claims. This is especially true in view of the fact that it is without doubt susceptible to considerable'modification and to embodiment in other forms than that disclosed herein.

What we claim is v 1. The method of rolling relatively thin disks such as automobile wheel disks which consists in simultaneously axially compressing and radially rolling the blank, the while maintaining an excess of metal of substantial thickness at the center of the blank integral with the body thereof, and continuously feeding metal outwardly from the center 'to prevent reduction of section incident to the radial stresses incident to the relatively extreme thinning. n

2. The method of rolling relatively thin disks of the nature of automobile disks and the thinness of which commences in a zone outwardlyof the center of the disk which consists in simultaneously axially compressing and circumferentially rolling the blanks, the while maintaining at the zone where the thinness commences, a, cross-section of metal integral with the main body of the disk maintaining a substantial depth of metal at the center of the blank and continuously feeding metal outwardly from the center to prevent reduction of section incident to the radial stresses set up by the operation.

3. The method of rolling relatively thin disks of the nature of automobile disks and the thinness' of which commences in a zone outwardly of the center of the disk which consists in simultaneously axially compressing and circumferentially rolling the blanks, the While maintaining at the zone where the thinness commences, a cross-section of metal integral with the main body of the disk and of sufiicient depth to prevent reduction of section incident to the radial stresses set up by the operation, and smoothly flowing the metal from the maintained greater depth of cross-section toward and into the main body of the disk. i

4. The method of rolling relatively thin disks of the order of automobile wheel disks which consists in simultaneously axially compressing and circumferentially rolling on a radius extending from center to periphery of a blank, and the while radially expressing metal at the center considerably in excess o to the main body on lines of flow mergng smoothly into the main body.

5. The method of rolling relatively thin disks of the nature of autonobile wheel disks which consists in simultaneously axially compressing and circumferentially rolling blanks and the while maintaining a cross section o the cross section of the main body of the disk, radially expressing the metal from the center of the blank through said cross-section into the main body of the disk, and flowing said expressed metal on converging lines smoothly into the main body.

6. The method of rolling relatively thin disks ofthe nature of automobile wheel disks which consists in simultaneously axially compressing and circumferentially rolling on a radial line from center to periphery of a blank, the Whilemaintaining cross-section at the center structurally unrelated to the final production and of sufiiciently greater thickness to prevent reduction of cross-section incident to radial strains of the operation, and after the operation is complete, removing the said structurally unrelated central crosssection.

7. A die for rolling relatively thin tapered disks in an obtuse angled rolling mill, which die comprises an outer zone substantially of a face form complemental to the main body of the disk to be rolled, and a recessed inner zone of a depth sufficient to provide a crosssection of metal of an aggregate radial strength in the rolling area sflicient to resist reduction of section under radial strains.

8. A die for rolling relatively thin tapered disks in an obtuse angled rolling mill, which die comprises an outer zone substantially of a face form complemental to the main body of the disk to be rolled, and a recessed inner zone of a depth suflicient to provide a crosssection of metal of an aggregate radial strength in the rolling area suflicient to resist reduction of section under radial strains, and the walls of which recessed inner zone are smoothly and gradually merged into the outer zone. 4

9. A die for rolling relatively thin tapered disks in an obtuse angled rolling mill, which die comprises an outer zone substantially of a face form complemental to the main body of the disk to be rolled, and a recessed inner zone of a depth sufiicient to provide a cross-section of metal of an aggregate radial strength in the rolling area sufficient to resist reduction of section under radial strains, together with an axially arranged coring out boss.

10. An obtuse angled die for rolling relatively thin tapered disks comprising a centrally locatedaxially extending boss, an adjoining depression and a main body outwardly of the depression, the boss and the depresf body of f tal to the main body of the disk to be rolled,

Sion bein of sinuous form and merged unbrokenly into the main body.

11. An obtuse angled die for rolling relatively thin tapered disks embodying an axially located coring out boss of sinuous crosssection.

12. An obtuse angled die for rolling rela tively thin tapered disks comprising a main a face form substantially complemenand a central depression of sinuous form merging unbrokenly into the main body of the die.

13. Die structure for rolling thin disks comprising a die having a main body portion complemental to the shape of one side of the ultimate disk, a depression of substantial radial extent and smooth contour at the center of the die and a coring pin of considerably smaller radial extent than said depression arranged centrally within the depresson.

14. Die structure for rolling thin disks comprising a die having a main body portion complemental to the shape of one side of the ultimate disk, a depression of substantial radial extent and smooth' contour at the center of the die and a coring pin of considerably smaller radial extent than said depression arranged centrally within the depression, said coring pin being reciprocably mounted within said die.

15. A die assembly for rolling thin disks including, a male die, and a female die structure comprising a die having a main body portion complemental to the sha e of one side of the ultimate disk, a. depresson of substantial radial extent and smooth contour at the center of the die and a coring pin of considerably smaller radial extent than said depression arranged centrally within the depression.

16. The method of rolling thin disks which comprises rolling the outer peripheral portions of a blank, expressing metal outwardly from a central portion of the blank during the rolling operation and maintaining a constricted throat of smooth contour between the said central portion and' the outer peripheral portions to restrict the flow' of metal under such expressing action.

17. The method' of formin thin disks which comprises pre-pressing a illet to form concavities in the opposite ends thereof, placing said billet between a air of rolling dies, initially centering said billet between said dies by means of bosses centrally located with respect to said dies, simultaneously coring the central portion of the billet and rolling -the outer peripheral portions thereof and restricting the flow of metal outwardly during the coring and rolling operation.

18. The method of forming thin disks which comprises pre-pressing a billet to form concavities in the opposite ends thereof, placing said billet betwen a pair of rolling dies, initially centering said billet between said dies by means of bosses centrally located with respect to said dies, rolling the outer peripheral portions of the billet to gradually thin the same and restricting the flow of metal outwardly toward the periphery of the disk during the rolling operation by means of a concavity formed in one of said dies.

19. The method of forming thin disk Which comprises pre-pressing a billet to form concavities in the opposite ends thereof, placing said billet between a pair of rolling dies, initially centering said billet between said dies by means of bosses centrally located with respect to said dies, rolling the outer peripheral portions of the billet to graduaL ly thin the same and restricting the flow of metal outwardly toward the periphery of the disk during the rolling operation by means of a concavity formed in one of said dies. said concavity blending smoothly with the conour of the outer peripheral portions of the In testimony whereof they hereunto aflix their Signature.

CAROLUS LEVON EKSERGIAN. EDWARD G. BUDD.

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