US3380278A - Method and apparatus for drawing solid wire stock - Google Patents

Description

April 30', 1968 3,380,278

METHOD AND APPARATUS FOR DRAWING SOLID WIRE STOCK Filed Oct. 21. 1965 e. b. DILLING 5 Sheets-Shet 1 April 30, 1968 E. D. DILLING 3,380,278

METHOD AND APPARATUS FOR DRAWING SOLID WIRE STOCK Filed Oct. 21, 1965 5 Sheets-Sheet 2 INVENTOR.

[0169 0. .D/LL/NG BY HTTOQ YEYS E- D. DILLING April 30, 1968 6 Sheets-Sheet 3 Filed Oct. 21, 1965 INVENTOR. fave D. DIAL/NG- United States Patent 3,380,278 METHOD AND APPARATUS FOR DRAWING SOLID WIRE STOCK Elmer D. Dilling, Las Vegas, Nev., assignor to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware Continuation-impart of application Ser. No. 257,607, Feb. 11, 1963. This application Oct. 21, 1965, Ser. No. 499,186

12 Claims. (Cl. 72224) ABSTRACT OF THE DISCLGSURE A wire forming tool made up of sets of rolls with grooved peripheries which combine to define rolling apertures of selected configuration and size for reducing the diameter of metal wire pulled therethrough.

This is a continuation-in-part of a copending application, Ser. No. 257,607, filed Feb. 11, 1963, now abandoned.

This invention relates to metal forming and more particularly it concerns a novel method and apparatus for cold drawing wires from bar stock.

In the past, wire drawing operations involved the use of a fixed die consisting essentially of an apertured plate of hardened metal. The entrance end of the aperture was rounded to provide a gradual transition for the stock from a larger input diameter to a smaller output diameter as it passed through the plate.

Great difiiculties have been experienced with the fixed die method of wire drawing especially where titanium and titanium base alloys were used in the wire. For example, with such wire, the maximum permissible reduction obtainable in any given pass through a fixed die was about lll3%. Also, the wire stock had to be annealed between frequent passes. A further difiiculty associated with the conventional fixed die technique was that it required large amounts of power to pull a wire through the reducing aperture. This, of course, resulted in excessive tension on the wire stock, and the resulting stresses often produced fracture or surface imperfections.

In the past, various proposals have been advanced concerning the possibility of applying rolling techniques to wire stock. These rolling techniques, which involved the passage of stock through a circular aperture defined by the peripheries of several adjacent rolls, had been used successfully in connection with the reduction of tubes and pipes. However, it had not been possible to obtain satisfactory reduction of solid stock such as wire in this particular manner. In the case of tubular stock, the displacement of material was readily absorbed within the tube or pipe itself. In the case of solid stock however, there was nowhere for the displaced material to go except to be forced up in between the adjacent rolls. This resulted in the development of flash or fins about the wire which could not be removed except by very expensive and complex finishing operations. This flashing problem was especially prominent in cold working operations for there the material is less ductile in regions even slightly displaced from the point of actual working and therefore there is a greater resistance to metal fiow back away from the aperture through which the wire passes.

The present invention makes it possible to produce cold drawn wire having excellent surface quality, good roundness, and essentially complete freedom from center porosity; such cold drawing further being accomplished with a minimum of power. Moreover, even using titanium wire, reductions of 32-45% per pass are attainable with the 3,38%,278 Patented Apr. 30, 1968 present invention; and reductions of up to 93% in seven passes have been achieved without annealing.

The present invention provides additional advantages in that it makes it possible to orient the crystalline structure of the material being drawn in a particular manner such that maximum tensile strength is achieved. Also, during drawing it is not necessary to coat the wire as is required in conventional fixed aperture dies, only a soluble oil coolant being required to keep the temperature at a reasonable level.

According to the present invention, solid round wire stock is cold drawn to a smaller diameter by pulling the wire through two closely spaced apertures, each of which is defined by the adjacent peripheral surfaces of a number of die rolls. The axes of the die rolls defining each aperture are in a common plane which also includes the aperture.

The peripheral surfaces of the rolls defining the first aperture are curved in a concave manner, but their centers of curvature are beyond the axis or center of the aperture. The effect of this is to provide a certain amount of reduction in the wire drawn through the aperture; and at the same time, to change the cross sectional configuration of the wire to an out of round or lobal shape.

The peripheral surfaces of the rolls defining the second aperture are also curved in a concave manner. However, the centers of curvature of these rolls do lie at the center of the aperture defined by them so that the cross sectional configuration of this second aperture is circular. The rolls of the second aperture also are oriented such that each of the lobes formed on the Wire by the first aperture is centered on the peripheral surface of a particular one of these second rolls. The pressure of the second rolls is thus directed so as to produce cross sectional deformation rather than twisting of the wire.

By causing the wire to go through an intermediate lobal configuration as it is being drawn in a two stage rolling operation, it is possible to avoid forcing metal in between adjacent rolls and generating flash on fins thereby.

According to the present invention, the two sets of rolls forming the two apertures are mounted in a common frame in an arrangement such that the rolls of one set are partially interleaved with the rolls of an adjacent set. This partial interleaving permits the use of relatively large diameter rolls, yet it allows the two apertures defined by the rolls to be located very close to each other. This is especially important for it permits the rolls of the second aperture to act upon the lobes of the partially drawn wire before the wire becomes twisted sufficiently to allow the pressure of these second rolls to produce twisting rather than reduction of the wire.

A further feature of the present invention lies in a unique structural arrangement which permits the above described die roll interleaving. According to this further feature, there is provided a common frame member having parallel surfaces on opposite sides thereof. Each surface is formed with grooves or slots which extend radially in equal spaced angular relationship from a common axis passing perpendicularly through the two parallel surfaces. The slots in one surface however are angularly disposed intermediate those in the opposite surface, and the depth of these slots is such that they overlay. However, because the slots in one side are intermediate those in the opposite side, they do not interfere with each other. Mounting blocks are arranged in the various slots and these mounting blocks support die rolls for free rotation with their peripheries adjacent to each other to define first and second apertures as above described.

There has thus been outlined rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course,

additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a representation of a wire drawing set up incorporating the present invention;

FIGS. 2 and 3 are end elevational views, respectively, and partially cut away of a drawing head according to the present invention;

FIG. 4 is a section view taken along line 4-4 of FIG. 2;

FIG. 5 is a partially exploded perspective view of a drawing head according to the present invention;

FIGS. 6 and 7 are enlarged fragmentary views respectively, of the aperture portions of the drawing head as shown in FIGS. 2 and 3;

FIG. 8 is an enlarged view of the wire stock passing through the rolls shown in FIG. 4;

FIG. 9 is a section view taken along line 99 of FIG. 8;

FIG. 10 is a section view taken along line 1010 of FIG. 8; and

FIG. 11 is a section view taken along line 1111 of FIG. 8.

As shown in FIG. 1, wire stock 10, to be reduced is taken from a supply coil 12 and is pulled through a draw head 14. The reduced wire, indicated at 10, is taken out from the draw head 14 and is wound up on a take up coil 16 which is rotated by means of a drive motor 18. Suitable means (not shown) may be provided to restrain the rotation of the supply coil 12 in order that a prescribed degree of draw or back tension may be applied to the wire stock 10 as it enters the draw head 14 so as to facilitate the reducing operation.

The draw head 14 is of special construction and forms a very important part of the present invention. As shown in FIG. 1, the draw head includes a central frame 20 of essentially cylindrical configuration, and a pair of circular cover plates 22 and 24 bolted to opposite sides respectively of the frame 20.

FIGS. 2-7 show various aspects of the internal configuration of the draw head 14. As shown in FIG. 4, the central frame 20 of the draw head is formed from a single piece of solid material and has fiat and mutually parallel surfaces forming input and output sides 26 and 28 to which the cover plates 22 and 24 are bolted. A central opening 30 extends centrally through both cover plates and the central frame in a direction perpendicular to the sides 26 and 28.

The central frame 20 is formed with three radially extending input side slots 32 (FIG. 2), and three radially extending output side slots 34 (FIG. 3). The slots in each side are equiangularly spaced and, as shown in FIGS. 2 and 3, the slots 32 on the input side 26 are arranged angularly intermediate the slots 34 on the output side 28. All of the slots communicate with the central opening 30; and, as shown in FIG. 4, they each extend well over half way into the central frame 26 so that there is an overlapping within the frame. However, because of the relative angular displacement between those slots in the input side 26 and those in the output side 28% they do not interfere with each other.

A bifurcated or U-shaped yoke 36 is located in each of the slots 32 and 34. These yokes are dimensioned to fit closely within their respective slots and to be guided by these slots for radial movement toward and away from the central opening 30. The yokes 36 have legs 38 which extend toward the central opening 30, and these legs are formed with holes 40 near their ends for accommodating axles 42 about which input and output die rolls 44 and 46 can turn. The legs 38 of the yokes 36 are split as at 48 beyond the holes 49 and bolts 50 are provided to span the splits 48 and tighten the holes 40 for securing the axles 42 in place.

The die rolls 44 and 46 are provided with internal hearings (not shown) which permit them to turn freely about their respective axles 42. The hub regions of the die rolls are wide enough to extend nearly fully across the space between the yoke legs 38 so as to provide maximum hearing surface and minimum stress. There is however a small clearance 52 between the rolls and the yoke legs for allowing lateral adjustment of the rolls as will be described more fully hereinafter.

The die rolls 44 and 46 have tapered sides 54 and beveled edge surfaces 56 near their peripheries on each side thereof. The peripheries themselves are formed with grooves 58 and 66 of arcuate cross section.

As shown in FIGS. 6 and 7, when the yokes 36 are adjusted to bring the peripheries of each group of die rolls toward each other, their mutually adjacent beveled edge surfaces 56 are brought to within approximately 0.004" of each other so that there is formed substantially closed input aperture 62 between the arcuate grooves 58 of the input rolls 44 (FIG. 6), and a substantially closed output aperture 64 between the arcuate grooves 66 of the output rolls 46 (FIG. 7).

It will be noted in FIG. 6, that the radius of curvature of the three arcuately cross sectioned grooves 58 defining the input aperture 62 extends, in each case, beyond the center of the aperture itself. Accordingly, the shape of the input aperture 62 is essentially triangular with bowed out sides.

As shown in FIG. 7, the radius of curvature of the three arcuately cross sectioned grooves 60 defining the output aperture 64, extends, in each case, precisely to the center of the aperture, so that the shape of the output aperture 64 is essentially circular.

It will be appreciated that the configuration and alignment of the input and output apertures 62 and 64 is very dependent upon the positioning of the die rolls 44 and 46. Various means are provided in order to effect positive and accurate control of the positioning of these rolls. As shown in FIG. 3, there is provided a radial tension screw 66 for each yoke 36. This tension screw enters through the cylindrical surface of the central frame 20 and threadedly engages the base of the yoke 36. A pair of radial compression screws 68 are threaded into the frame 20 on each side of each tension screw 66 and abut against the back of the yoke 36. These compression screws 68 push radially inward on the yoke while the tension screw 66 pulls radially outward on it so that the yoke becomes securely locked in a given radial position. This, of course, establishes the radial position of the beveled contact surfaces 56 and the peripheral grooves 53 or 60 of the associated die roll 44 or 46.

As mentioned previously, the die rolls 44 and 46 are capable of a certain degree of lateral adjustment within the clearance spaces 52 between their hub regions and the associated yoke legs 38. This lateral adjustment is achieved by means of elongated push rods 7!! which enter through the cylindrical surface of the frame 20 on each side of each yoke 36 and abut against opposite ends respectively, of the associated die roll axle 42. The push rods 70 have adjustment screws 71 pivotally connected to their outer ends. There adjustment screws are threaded to the frame 20; and by adjusting them their respective push rods will cause the axle 42 to be moved from side to side within the clearance 52. Of course, during such adjustment, the bolts 50 would be loosened so that the axle 42 can move freely within the holes 40 in the yoke 38. Once the desired adjustment is made, the bolts 50 are then tightened to lock the axle in place. The relative posi tion of the tension and compression screws 56 and 63, and of the push rods 70 for adjusting a given die roll are shown in FIG. 5.

FIG. 5 additionally illustrates the nesting effect produced between the input and output die rolls 44 and 46. As can be seen, these die rolls are of considerable diameter, so that a very gradual transition to the drawing aperture can be effected; and yet the distance between the input and output apertures 62 and 64 is far shorter than the diameter of the rolls. This feature, the advantages of which will be explained hereinafter, is accomplished by means of the unique slotted frame arrangement which securely holds the input and output die rolls in proper positional relationship for nesting and for alignment of apertures.

The common frame arrangement moreover is rugged and rigid; and yet it permits of very fine adjustments of the input and output apertures as above described. Furthermore, as illustrated in FIG. 5, any or all of the die rolls 44 or 46 may be removed along with their yokes 36 for repair of replacement simply by removing the cover plates 22 and 24, loosening the various adjustment screws, and removing the yokes 36 from their respective slots 32 and 34.

FIG. 8 shows in enlarged scale the wire stock as it appears in FIG. 4 during drawing through the two apertures 62 and 64. As can be seen in FIG. 8, the wire 10 in passing through each aperture, undergoes a gradual transition along its length, first from an unreduced circular cross section 72 to a trilobal cross section 74, and secondly, from the trilobal cross section 74 to a reduced circular cross section 76.

The purpose for going through an intermediate stage of non-circular cross section can be appreciated from a consideration of the manner in which the input and output apertures 62 and 64 are formed. Reverting to FIGS. 6 and 7, it will be noted that while the apertures 62 and 64 are substantially closed, there remains nevertheless, a finite spacing between the beveled edge surfaces 56 of the die rolls in each group. Accordingly, there is produced a pinching effect between the beveled edge surfaces in the region near each actual aperture. Because of the very great forces involved in deforming solid metal wire, and because of the die roll configuration leading into the forming apertures, there is a tendency for metal to flow up between adjacent rolls and into the spaces between their adjacent beveled edge surfaces 5'6. This displaced metal then becomes pinched between these beveled edge surfaces and forms a flash or longitudinal fin along the wire which cannot be removed by ordinary means.

By forming the input aperture such that the adjacent beveled edge surfaces 56 are displaced radially outward even a slight distance from the displaced metal, the forcing of metal between them is avoided. Further, the lobal arrangement thus produced permits the use of circular aperture forming die roll grooves which can push the wire stock back to circular shape with little or no tendency for metal to be pushed up in between their own adjacent contact surfaces.

As shown in FIG. 6, the trilobally shaped input aperture 62 varies from a minimum radius (R near the center of each grooved periphery, to a maximum radius (R where the peripheries come together. The radius of the unreduced wire stock at 72 is between the minimum and maximum radii R and R of the input aperture. Thus the input die rolls 44 act to squeeze in only on displaced regions about the circumference of the wire while allowing other regions to bulge slightly with a net reduction in overall cross sectional area. The combination of this inward pressing and outward bulging produces a trilobal intermediate cross sectional configuration shown at 74. This intermediate cross section has a minimum radius (r which coincides with the minimum radius (R of the input aperture 62. The intermediate cross section has a maximum radius (1 however, which is less than the maximum radius (R of the input aperture by a slight amount shown at d. This difference in maximum radii (zi=R r serves to prevent the wire stock from being squeezed up between the adjacent beveled edge surfaces 56 of the various input die rolls 44. Thus while the wire stock becomes converted from circu lar to trilobal cross section in the first stage of reduction, no flash or fins are produced by the coming together of the various input die rolls 44.

FIG. 7 shows the relationship of the intermediate section 74 of the wire stock to the output aperture 64. As shown in the drawing, the output aperture 64 is of a fixed radius (R out), which is less than the maximum radius (r of the incoming wire stock but is greater than its minimum radius rmin, Moreover, and very importantly, the various output die rolls 4-6 are arranged such that the centers of their peripheral grooves 6% line up with the points of maximum radius rmax, of the intermediate trilobal cross section 74 while their beveled contact surfaces 56 line up with and are displaced outwardly from the points of minimum radius (r As a result of this, the output die rolls 46 operate to press the wire stock back to a circular configuration with little or no forcing of metal against the adjacent beveled edge surfaces 56, and consequently with no tendency toward pinching of the wire to develop flash or fins.

By proper adjustment of the input rolls 44, the cross sectional area of the wire stock entering the output rolls 46 can be controlled to a degree such that the output rolls will produce true round wire with no flat regions and with no fins. This is because the input rolls control the minor diameter of the intermediate wire cross section so that in the second stage of reduction the minor diameter regions become bulged out to the contour of the desired final diameter without being forced up between the rolls. Moreover, because of the resistance to drawing produced by the input rolls, there is established a back or reverse tension on the wire as it passes through the output rolls. This back tension, has the effect of controlling metal fiow during the second stage of reduction so that the displaced metal, instead of bulging entirely radially outward toward the adjacent edges of the roll peripheries, it is actually caused to flow to a great extent longitudinally along the wire. This, of course, reduces the possibility of flash orfins developing.

FIGS. 9, 10 and 11 show the various cross sectional configurations of the wire stock in relationship to each other as a result of passing through the input and output apertures 62 and 64. As can be seen in FIG. 9, the wire, in passing through the input aperture 62, grows radially in certain directions to form a maximum radius (r which is greater than its original radius; while in other directions, it undergoes a decrease in radius to (r which is less than its original radius. The net change in cross sectional area however is a negative one so that an overall reduction is produced in the input aperture. Similarly, as shown in FIG. 10, the wire in passing through the output aperture 64- also grows radially along its regions of minimum radius (r while decreasing along its regions of maximum radius (r as it feturns to circular configuration. Again, the net change in cross sectional area is negative so that a second overall reduction is produced in the output aperture 64. The difference between the diameters in the input and output cross sections 72 and 76 is illustrated in FIG. 11.

The nested arrangement of input and output die rolls described above makes possible the successful reduction of solid metal wire with smooth surface characteristics and very circular cross sectional configuration. This is so because the nested arrangement, by bringing the input and output apertures very close together, ensures that the trilobal intermediate cross section 74 will enter the output aperture 64 in perfect alignment with the die rolls.

If, for example, the trilobal cross section were to be even slightlytwisted its points of maximum radius (r would not be aligned with the line of action of the output die rolls 44. As a result, the combined force of these rolls would produce a torque on the wire about its longitudinal axis in the direction of the twist. The increased pressure of the rolls would then produce further twisting of the wire so that its regions of maximum radius (r would become trapped between the adjacent beveled contact surfaces 56 and a fin or flash would develop.

The nested arrangement however prevents this for the input and output apertures are extremely close to one another and there is no tendency for the wire to twist significantly in passing from one to the other.

A further advantage of the reverse tension effect produced by the input rolls is that it reduces the amount of pull required to pass the wire through the output rolls. Thus, the total amount of pull required to draw wire through the two sets of reducing rolls is far less than the sum of the pulls that would be required to a pull a wire separately through two individual sets of similar rolls. Because of this, the amount of draw tension is minimized, and a far greater reduction is obtainable than has heretofore been possible.

Having thus described the invention with particular reference to the preferred form thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding the invention, that various changes and modifications may be made therein without departing from the spirit and scope of the invention, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent is:

1. Wire drawing apparatus comprising: two sets each of a plurality of forming rolls and means rotatably mounting the same on a common frame with the roll axes of each set disposed substantially on a common plane, the axes planes of the two roll sets being spaced apart and substantially parallel, the rolls of each set being equiangularly disposed about a common axis perpendicular to said axes planes, said rolls being peripherally grooved and edge-bevelled, means individual to said rolls for adjustably positioning the same with respect to said common axis for causing the bevelled edges of contiguous rolls of each set to come toward one another whereby the grooved portions of said rolls form about said common axis, a Wire drawing aperture substantially surrounded by said grooved portions, said rolls being so mounted on said frame that the rolls of each set are angularly disposed intermediate those of the other set about said common axis and with the peripheral portions of rolls of each set further disposed respectively in the crotches between contiguous rolls of the other set with the roll edges of each set closely adjacent those of the opposite set for minimzing the distance along said common axis between the wire drawing apertures formed by said roll sets respectively, the peripheral grooves of one set of rolls being configured to define a first lobal, aperture having successive regions of mini mum and maximum radius, and the peripheral grooves of the other set of rolls being configured to define a second, circular, aperture having a constant radius which is less than said maximum radius but greater than said minimum radius.

2. Apparatus according to claim 1 wherein said roll sets comprise clusters of three rolls each, and wherein the rolls of one set are grooved to form a substantially triangular wire drawing aperture, and wherein the rolls of the other set are grooved to form a circular wire drawing aperture.

3. Apparatus according to claim 1 wherein the peripheral grooves of the rolls of one said set are of arcuate contour to form an aperture between said rolls of arcuately radial triangular configuration and wherein the peripheral grooves of the rolls of the other said set are such as to form an aperture between said rolls of circular configuration.

4. Apparatus according to claim 1 wherein the rolls of each set are of substantially the same diameter.

5. Apparatus according to claim 1 wherein said frame comprises a solid metal block having oppositely disposed parallel faces and an opening therebetween about an axis perpendicular to said faces, said block being radially slotted about said axis in each said face and wherein the respective rolls of one set are rotatably mounted on hearing yokes disposed in the respective slots in one face of said frame blocks and wherein the respective rolls of the second set are similarly rotatably mounted on hearing yokes disposed in the respective slots in the opposite face of said frame block, and wherein means are provided individual to said bearing yokes for adjustably positioning the same radially along said slots.

6. Apparatus according to claim 5 wherein said metal frame block is of substantially cylindrical contour and wherein said block has secured to its opposite parallel faces, cover plates which are apertured at said common axis, said cover plates acting to cover said bearing yokes to aid in holding said yokes in place.

7. Apparatus according to claim 5 wherein said bearing yokes are of bifurcated and substantially U-shaped configuration and are disposed in said frame slots respectively with the bifurcated portions thereof directed toward said common axis and wherein said bearing yokes are longitudinally adjustable along said slots by means of tension bolts threaded thereto within said slots and which are rotatably supported by said frame block.

8. Apparatus according to claim 7 wherein each of said die rolls are mounted to rotate about an axle which extends through holes near the ends of the legs formed by the bifurcated U-shaped configuration of the yokes.

9. Apparatus according to claim 7 wherein a pair of compression bolts are threaded through said frame block and abut against each bearing yoke on opposite sides of its tension bolt.

16. Apparatus according to claim 8 wherein the die roll axle in each of said bearing yokes is laterally adjustable in its associated yoke by push rods threaded in said frame block on opposite sides respectively of said yoke, said wedge rods abutting against the opposite ends, respectively, of said die roll axle.

11. Apparatus for drawing solid wire to a reduced size, said apparatus comprising a common housing, said housing being shaped with a central opening extending therethrough, first and second groups of die rolls with grooved peripheries, means within said housing supporting the rolls of each of said groups for free rotation with their axes in a common plane perpendicular to the axis of said central opening so that their peripheries come toward each other to define an aperture aligned with the axis of said central opening, said means within said housing being arranged to support the die rolls in one group in a manner such that they are disposed intermediate to and are nested among the die rolls in the other group so that the distance between the apertures in each group is substantially less than the diameter of said die rolls to permit continuous drawing of wire through said two apertures in succession without appreciable twisting of such wire between said apertures, the peripheral grooves of one set of rolls being configured to define a first, lobal, aperture having successive regions of minimum and maximum radius, and the peripheral grooves of the other set of rolls being configured to define a second, circular, aperture having a constant radius which is less than said maximum radius but greater than said minimum radius.

12. A method for drawing solid wire of circular cross section to a reduced diameter, said method comprising the steps of first passing said wire through a lobally shaped aperture having maximum radii greater than the cross sectional radius of said wire to shape said wire to a lobal cross sectional configuration while effecting a first cross sectional area reduction in the wire, and thereafter passing the wire through a second circularly shaped aperture having a radius between the maximum and minimum radii 3,129,618 4/ 1964 Hergeth 72224 of the lobally configured wire to reshape the wire to a cir- 2,710,433 6/ 1955 Properzi 72224 cular cross sectional configuration while effecting a further 175,522 3/ 1878 Tasker 72224 cross sectional area reduction in the wire. 1,930,698 10/ 1933 Stiefel 72-224 5 562,825 6/1896 Hill 72224 References clted 324,867 8/1885 Meatyard 72224 UNITED STATES PATENTS 10,569 2/1854 Jackson 72 224 CHARLES W. LANHAM, Primary Examiner.

14,551 4/1856 Brooks 72224 H. D. HCINKES, Assistant Examiner.

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