US3641795A

US3641795A - Method and apparatus for wire drawing with pressure dies

Info

Publication number: US3641795A
Application number: US887843A
Authority: US
Inventors: Raymond H Lester; James N Snyder
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1969-12-24
Filing date: 1969-12-24
Publication date: 1972-02-15
Anticipated expiration: 1989-02-15

Abstract

Improved surfaces on drawn wires and especially on wires drawn while precoated with a metallic coating are obtained by drawing the wires in a pressure-type die which has been initially prepacked with lubricant under a high pressure.

Description

O Umted States Patent [151 3,641,795

Lester et al. 1 Feb. 15, 1972 [54] METHOD AND APPARATUS FOR WIRE 3,080,962 3/1963 Fleischman et ..72l42 DRAWING WITH PRESSURE DIES 3,413,832 12/1968 Lang et a] ..72/42 3,526,115 9/1970 Armstrong et .....72/45 1 Inventors: Raymond Lester; James Snyder, 3,344,636 10/1967 Pugh ..72/60 both of Bethlehem, 3,328,998 7/1967 Sabrofi' et al. ..72/362 [731 Sigma FOREIGN PATENTS OR APPLICATIONS [221 Filed: 1969 1,107,872 3/1968 Great Britain ..72/253 [21] Appl. No.: 887,843

Primary ExaminerCharles W. Lanham Assistant Examiner-E. M. Combs U-S- "72/42, Attorney-Joseph J OKeefe [51] lnLCl. ..B2lc l/00,B21c 3/l4,B2lc9/00 [58] Field otSearch ..72/4l,42,43,44,45,286, [57] ABSTRACT Improved surfaces on drawn w1res and especially on w1res drawn while recoated with a metallic coatin are obtained b [56] References Cited p g y drawing the wires in a pressure-type die which has been ini- UNITED STATES PATENTS tially prepacked with lubricant under a high pressure.

Elfstrom ..72/43 14 Claims, 5 Drawing Figures PATENTEBFEB 15 m2 3.641.795

F/a. y

INVENTORS y nd/9. Leszer am as M Sn d METHOD AND APPARATUS FOR WIRE DRAWING WITH PRESSURE DIES BACKGROUND OF THE INVENTION This invention relates to the drawing of wire and particularly hot metal coated or other clad wire in pressure dies.

Great difficulty has heretofore been experienced in the drawing of a wire which has previously been coated with another metal, and particularly with wire having a fairly heavy coating of a soft metal such as aluminum applied in a hot metal bath. It has been found in such cases that defects in the surface coating of the wire are liable to result from various causes mostly related to improper lubrication of the wire as it passes through the die. So-called pressure dies designed so that lubricant is continuously drawn into the die with the wire where it backs up within a restricted chamber anterior to the drawing orifice have been used to provide better lubrication. Since the wire continuously draws lubricant into the die faster than it can normally leave the die, a considerable pressure builds up in the lubricant within the die until the pressure is high enough to expel a substantial layer of lubricant through the reducing die orifice with the wire. When sufficient pressure is built up a balance is attained between the lubricant entering the die with the wire and the lubricant passing through the reducing orifice with the wire. Even the customary pressure dies have proved inadequate for the lubrication of wires coated with heavy deposits of soft metals, however.

Normally in a pressure die sufficient pressure is built up in the lubricant to approach the normal yield value of the metal being drawn. This pressure may be of the order of about 80 tons per square inch for a steel cored wire. Thus as the metal passes through the die it is squeezed by the lubricant and does not normally contact the reducing surface of the die at all. This effect reduces the drawing force necessary to draw the wire through the die because the metal is in effect squeezed from the side causing a natural elongation of the wire without excessive forward pull along the wire.

This squeezing effect is most important in the reduction of a wire or the like which has been coated with a soft metal since it allows both the coating and the underlying base metal to be reduced transversely from the side, as it were, without any tendency for the die to strip the overlying soft coating from the base wire surface as it passes through a restricted die orifice. In order that the stripping tendency may be reduced to a minimum it is important that this fluid-dynamic squeezing effect begin as far in front of the actual reducing orifice as possible so that the angle of reduction approaching the die orifice is as shallow as possible. The only effective way in which the angle of incidence of the reducing action can be reduced is to increase the pressure within the die chambers and to some extent also the length of the chambers so that adequate pressure in the die is reached farther away from the actual die orifice.

Various means have been tried to increase the pressure of the lubricant in the die such as roughening the surface of the wire and coating the surface of the wire with a tacky substance to draw additional lubricant into the die, providing additional apparatus to increase the operating pressure in the die and similar expedients. Also with the thought that perhaps the initial pressure in the die was insufficient resulting in insufficient lubrication of the initial portions of the drawn wire, lengths of uncoated or scrap leader wire have been secured to the end of the wire to be drawn and initially passed through the pressure die to build up the pressure in the die prior to the coated wire reaching and passing through the die.

While effective in some cases, none of these previous expedients have proven completely satisfactory. The present invention obviates the necessity of using, and the difficulties associated with, these previous methods and in particular provides superior lubrication without the necessity for increasing the normal supply of lubricant drawn into the pressure die by a bare wire during the drawing operation.

SUMMARY OF THE INVENTION It has been discovered that the lack of initial pressure in pressure dies when drawing coated and the like wire causes insufficient initial lubrication and that by the time sufficient lubrication is established the surfaces of the reducing orifices are already so damaged that the damaged die surface will extensively damage the relatively soft surface of subsequently drawn soft metal coated wire even though adequate lubrication is present during the actual drawing of said subsequently drawn wire. An additional result of the poor initial lubrication due to low initial pressure in the die seems to be that the maximum attainable lubrication pressure never is actually attained even after prolonged periods of operation.

The effects of poor initial lubrication are overcome according to the'present invention by initially prepacking the pressure die with lubricant under a very high pressure so that adequate lubrication is almost instantaneously obtained prior to any damage to the surface of the die orifices by drawing without adequate lubrication. It has been discovered that if the initial lubrication is increased by means of this invention, even after the initial high lubrication pressure is no longer detectable as such, the drawing operation continues with no difficulties due to scoring or scratching of the surface or tendency to strip the surface coating off the wire and without the necessity of supplying any additional lubrication over that available merely by drawing the bare wire through a supply of lubricant. Thus the necessity of roughening the surface of the wire, providing tacky substances, or using other means for providing additional lubrication during operation is obviated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a longitudinal cross section of a pressure die.

FIG. 2 shows the pressure die of FIG. 2 curing initial prepacking.

FIG. 3 shows the pressure die of FIG. 3 during final prepacking in a pressure apparatus.

FIG. 4 shows a longitudinal cross section of a pressure die modified to facilitate prepacking.

FIG. 5 is a diagrammatic plan view of a pressure die according to the present invention being used to draw coated wire.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 is shown a typical pressure die assembly 11 comprising a holder or assembly body 13 with a threaded retainer 15 threaded into one end and bearing against a die orifice section 17 which in turn bears against die orifice sections 19 and 21. Carbide inserts 23 form the reducing orifice faces of each of the orifice sections I7, 19 and 21, the opening through the inserts being progressively smaller from section 17 through 21. Preferably only orifice section 21 actually closely approaches the surface of the wire to determine the final outside diameter of the coated wire. An entrance opening 25 through retainer 15 provides a fairly long prepacking chamber in the pressure die and an entrance for coated wire during drawing,

while an exit orifice 27 provides an exit from the die assembly for the drawn wire. During drawing of wire through die assembly 11 the assembly will be positioned within a die mounting block 28 having cooling chambers 30 located within it.

During prepacking a plug 29 is initially placed in exit opening 27 as shown in FIG. 2 to prevent loss of lubricant through this opening. Powdered lubricant and preferably a soap-type lubricant such as for example a calcium stearate composition containing approximately 8 percent molybdenum disulfide is poured into entrance opening 25 until the die assembly appears to be completely filled with lubricant. A vibrating wire 31 such as is shown in FIG. 2 is then lowered into opening 25 to agitate and pack the lubricant within the die. As the lubricant settles additional lubricant is added. The vibrating wire 31 may be vibrated by any suitable means such as a commercial vibrator or more simply by a rotating portable drill head or the like turning a slightly eccentric or bent wire. It will be understood that the vibrating wire 31 will be moved and positioned at various heights within the die during vibration to facilitate complete packing. Alternatively the entire die may be vibrated by any suitable apparatus to shake down the lubricant. It has been found, however. that a vibrating wire provides superior results because it also exerts a physical packing or patting action upon the lubricant. Both a vibrating wire and external vibration may be on occasion used together with good results. As many cycles of filling and vibrating as may be necessary to completely fill the die assembly 1! will be used.

Preferably after as much lubricant as possible is packed in the die, the plug 29 is removed, entrance opening 25 closed with a plug 33, the die assembly 11 inverted and the vibrating wire 31 inserted into exit opening 27 to break any lubricant bridges or the like at this end of the die. After vibration at this end of the die any resulting openings are filled with additional lubricant and this in turn vibrated. As many cycles of filling from both ends as may be necessary to solidly or completely fill the die assembly 11 with lubricant will be applied.

After as much lubricant has been packed within the die assembly as is possible with the aid of vibration both

plugs

29 and 33 are positioned in

openings

27 and 25 respectively and the entire die assembly 1] is transferred to a hydraulic or other suitable press apparatus 35 as shown in H6. 3.

It is most convenient if hydraulic press apparatus 35 is arranged to exert pressure on the die assembly 11 while it is positioned vertically but a horizontal press apparatus can also be used. Press 35 may comprise an anvii base 52 having an insert orifice 54 into which plug 29 fits and a movable plunger 53 operated by a hydraulic cylinder 55 which exerts a compressive force on plug 33. Hydraulic press 35 places a force of about 2,600 pounds upon each

plug

29 and 33, each of which may be approximately 36 of an inch in diameter, forcing them inwardly as far as they will go and further compressing the lubricant within die assembly II by the plunger action of the plugs. By this externally applied force the lubricant is converted into a substantially solid block 37 of lubricant filling all interstices of the die and often containing a significant degree of prestressing compressive force which tends to expand the block of lubricant. ln general the higher the pressure the better the results.

For a calcium stearate composition with approximately 8 percent included molybdenum disulfide best results require a pressure of at least 15,000 to 20,000 and more preferably 24,000 to 26,000 pounds per square inch. This is sufiicient to compress the soap composition to a condition approaching its final consolidation point or maximum density as a solid at normal surface conditions. There should be no voids within the body of lubricant greater than approximately of the order of half the size of the component lubricating powder grains. The lubricant may in this condition be partially prestressed also so that it has a tendency to expand when released and particularly when heated by the passage of wire through it. llf too high a pressure is applied to the die assembly such as for instance greater than about 35,000 pounds per square inch the assembly may be damaged, particularly with respect to displacement of the carbide inserts 23. The design of the die therefore should be suitably modified and strengthened if higher pressures are to be used.

Since the degree of compaction of many, if not most, lubricants is a function not only of pressure but also temperature and time, it is advisable in many cases, if time permits, to leave the die under pressure in the hydraulic compression means for several minutes or so to obtain superior compaction and consolidation of the lubricant. A somewhat elevated temperature during compaction may also be an aid, particularly if the compaction period is to be fairly short or less than full pressure is to be applied due to some peculiarity of the die construction or the like.

The most suitable exact pressures will differ for different lubricating substances and compositions, of course. However, in each case the condition of the lubricant which must be attained by the application of the pressure is a state approaching or attaining the final consolidation point or maximum density of the particular lubricant. Since a powder or solid will not transmit pressure evenly throughout its volume as will a liquid, the pressure within the packed die may tend to decrease toward the central portions of the die due to partial support of the lubricant by the end walls of the die and friction between the particles during compression. it is desirable therefore for sufficient pressure to be exerted by the press 35 to compact substantially the entire mass of powder to its final consolidation point.

The prepacked die assembly may be used immediately or may be stored until used. In either case when the die assembly is to be used a wire insertion hole appropriate to the size of the last reducing orifice section 21 is drilled, preferably from both ends of the die assembly, into the block of lubricant 37 to allow the wire to be pulled through the die. Preferably the insertion hole is drilled with an ordinary straight wire of appropriate diameter rather than by the use of a twist drill or the like as the rotating straight wire contributes to the prepacking.

The wire to be drawn is preferably tapered by suitable abrasion or cutting means for about 6 inches so that it may be more easily entered into the hole through the lubricant.

The die assembly 11 is next mounted in the drawing apparatus 39 as shown schematically in FIG. 5 and the wire 41 to be drawn is, after insertion through the hole in the lubrication and the die assembly, pulled by means of wire drawing block or capstan 49 from a reel 45 through a wire guide 46 and then through a lubricant reservoir 47 containing aerated powdered lubricant preferably agitated by a vibrator 48 or other suitable means. The strand picks up a surface coating of lubricant which is carried with the wire into the prepacked die assembly 11 where the wire is drawn down due to the immediate lubrication afforded by the prepacked die without damage to either the wire surface or the die. After initially passing around the capstan 49 the drawn wire may be collected on the upper portion of the capstan and coiling posts 50 as is conventional in the art of wire drawing.

FIG. 4 shows a cross section of a pressure die modified by the addition of spacer inserts or rings 51 between the respective orifice sections l7, l9 and 21 to space these orifice sections from each other and provide additional or more capacious chambers between orifice sections. It has been found that this additional capacity between the orifice sections is an aid in establishing a uniform high pressure throughout the body of lubricant and in the attainment of wire compression or reducing pressures at significant distance in front of the reducing orifices in order to provide a shallow angle of incidence in the buildup of wire reducing pressure.

By the use of the prepacked die of the present invention coated wire can be drawn without breakage of the wire, scoring of the coating surface, scratching, or any evident flakes of aluminum, indicating that excellent lubrication is present from the beginning of drawing. Furthermore the present invention allows the wire to be continuously drawn without the provision of any additional pressure inducing expedients once the drawing of the wire is begun.

Modifications of the prepacking procedure can be made so long as packing occurs under a high pressure. For instance, the lubrication might be injected into the die assembly in a liquid state and then be subjected to pressure. Alternatively each orifice section might be prepacked separately prior to assembly into the complete die assembly. It is also possible and advantageous in some instances to initially cast the end of the wire to be drawn integrally into position within the center of the block of prepacked lubricant within the individual orifice sections or the entire prepacked die assembly.

We claim:

1. A method of drawing in a pressure-type die a wire coated with a soft metal to reduce the wire and provide a smooth surface finish on the coating metal layer, comprising:

a. prepacking a normally particulate soap-type wire drawing lubricant in a pressure-type die prior to the beginning of the drawing operation under a predetermined elevated prepacking pressure at least sufficient to consolidate said lubricant within said die to a condition approaching its final consolidation point by the use of external pressure applying means for applying said predetermined elevated pressure to the said soap-type lubricant within said die,

b. relieving the consolidated lubricant within said prepacked die from the predetermined pressure applied by said external pressure applying means,

c. piercing said prepacked soap lubricant contained in said die to form an orifice through the prepacked lubricant not larger than the reducing orifice in the die to provide a path through the die for the wire to be drawn,

d. applying a soap-type lubricant to the surface of said wire,

and

e. drawing said wire through said prepacked die to reduce the diameter of said wire.

2. A method of drawing coated wire according to claim 1 wherein said die is prepacked by inserting powdered soap-type lubricant uniformly in said die and applying said predetermined pressure to said lubricant in said die within independent external pressure applying means and subsequently mounting said prepacked die in separate wire drawing means prior to drawing said wire through said die.

3. A method of drawing coated wire according to claim 2 wherein said predetermined pressure is applied to said lubricant within said die by capping said die within said independent pressure-applying means with a movable plunger means and applying a predetermined pressure to said plunger means to in turn apply a predetermined pressure to said unconsolidated particulate lubricant within said die.

4. A method of drawing coated wire according to claim 1 wherein said predetermined applied pressure is at least 15,000 to 20,000 p.s.i.

5. A method of drawing coated wire according to claim 1 wherein said predetermined applied pressure is at least 24,000 p.s.i.

6. A method of drawing coated wire according to claim 2 wherein said predetermined applied pressure is at least 15,000 to 20.000 p.s.i.

7. A method of drawing coated wire according to claim 3 wherein said predetermined applied pressure is on the order of at least 24,000 p.s.i.

8. A method of drawing coated wire according to claim 3 wherein said unconsolidated soap-type lubricant is initially distributed and lightly packed uniformly within said die before the application of said predetermined pressure within said independent pressure applying means by the action of a vibrating wire agitator inserted into said die.

9. A method of drawing coated wire according to claim 8 wherein said wire is precoated with an unconsolidated particulate soap-type lubricant by passing said wire through a container of powdered lubricant prior to its entrance into said prepacked die.

10. A method of drawing coated wire according to claim 8 wherein the prepacked lubricant is pierced by a rotating wire to form an orifice through the prepacked lubricant not larger than the reducing orifice in the die to provide a path for passage of said coated wire.

11. A method of prepacking a pressure die with soap-type lubricant prior to using said die comprising:

a. capping one end of said die,

b. filling said die with a powdered soap-type lubricant while agitating said lubricant to provide a uniform lightly packed body of lubricant within the orifice in said die, and

c. applying a predetermined pressure to the said body of lubricant within the interior of said die by means of a plunger inserted into the orifice in said die whereby the lubricant within said die is subjected to at least 24,000 p.s.i. pressure.

12. A method of prepacking a pressure die according to claim 11 wherein said lubricant is agitated and lightly packed by means of a vibrating rod.

13. A prepacked drawing die suitable for drawing coated wire without initial damage to the die comprising:

a. a series of consecutively smaller orifices within a die body at least one of which comprises a reducing orifice,

b. elongated entrance and exit chambers extending from said endmost orifices,

c. a densely packed soap-type lubricant prepacked under a temporarily exerted high pressure within said die chambers such that a substantially solid body of lubricant having a density approaching the maximum density physically possible for said lubricant under ambient surface conditions fills said chambers after said temporarily exerted high pressure is relieved and the prepacked die is removed from the influence of the means used to exert said high pressure.

14. A prepacked die according to claim 13 wherein said series of consecutively smaller orifices are defined in movable members and additionally comprising:

d. insertsbetween the said movable members to define substantial chambers substantially longer and wider than the opening between the orifices in said movable members would otherwise be, each chamber being substantially packed solid with said maximum density lubricant.

Claims

1. A method of drawing in a pressure-type die a wire coated with a soft metal to reduce the wire and provide a smooth surface finish on the coating metal layer, comprising: a. prepacking a normally particulate soap-type wire drawing lubricant in a pressure-type die prior to the beginning of the drawing operation under a predetermined elevated prepacking pressure at least sufficient to consolidate said lubricant within said die to a condition approaching its final consolidation point by the use of external pressure applying means for applying said predetermined elevated pressure to the said soap-type lubricant within said die, b. relieving the consolidated lubricant within said prepacked die from the predetermined pressure applied by said external pressure applying means, c. piercing said prepacked soap lubricant contained in said die to form an orifice through the prepacked lubricant not larger than the reducing orifice in the die to provide a path through the die for the wire to be drawn, d. applying a soap-type lubricant to the surface of said wire, and e. drawing said wire through said prepacked die to reduce the diameter of said wire.

6. A method of drawing coated wire according to claim 2 wherein said predetermined applied pressure is at least 15,000 to 20,000 p.s.i.

11. A method of prepacking a pressure die with soap-type lubricant prior to using said die comprising: a. capping one end of said die, b. filling said die with a powdered soap-type lubricant while agitating said lubricant to provide a uniform lightly packed body of lubricant within the orifice in said die, and c. applying a predetermined pressure to the said body of lubricant within the interior of said die by means of a plunger inserted into the orifice in said die whereby the lubricant within said die is subjected to at least 24,000 p.s.i. pressure.

13. A prepacked drawing die suitable for drawing coated wire without initial damage to the die comprising: a. a series of consecutively smaller orifices within a die body at least one of which comprises a reducing orifice, b. elongated entrance and exit chambers extending from said endmost orifices, c. a densely packed soap-type lubricant prepacked under a temporarily exerted high pressure within said die chambers such that a substantially solid body of lubricant having a density approaching the maximum density physically possible for said lubricant under ambient surface conditions fills said chambers after said temporarily exerted high pressure is relieved and the prepacked die is removed from the influence of the means used to exert said high pressure.

14. A prepacked die according to claim 13 wherein said series of consecutively smaller orifices are defined in movable members and additionally comprising: d. inserts between the said movable members to define substantial chambers substantially longer and wider than the opening between the orifices in said movable members would otherwise be, each chamber being substantially packed solid with said maximum density lubricant.