US3553995A

US3553995A - Extrusion process

Info

Publication number: US3553995A
Application number: US705880*A
Authority: US
Inventors: Robert J Fiorentino; John M Cigan; Alvin M Sabroff; Richard L Jentgen
Original assignee: St Joseph Lead Co
Current assignee: New Jersey Zinc Co
Priority date: 1968-01-30
Filing date: 1968-01-30
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12
Also published as: BE727679A; DE1903231A1; FR2000989A1; GB1254641A

Abstract

A WORKPIECE IS FORCED THROUGH A DIE THAT IS FORMED WITH A FLAT FACE AND AN ORIFICE OF LESSER DIMENSIONS THAN THE WORKPIECE WHILE OUTWARD LATERAL MOVEMENT IS RESTRAINED, THE SURFACE OF THE WORKPIECE IS PROVIDED WITH A "THICK FILM" LUBRICANT COATING THAT CONSISTS OF AN ORGANIC MATERIAL AND A GRANULAR MATERIAL, AND THE OUTERMOST POR-

TION OF THE WORKPIECE IS ANGULARLY DIRECTED INWARDLY TO FLOW LATERALLY ALONG THE FLAT FACE OF THE DIE TO AND THROUGH THE DIE ORIFICE.

Description

Jan. v12j;` 1971 R. .LFIQRENTINO ET AL EX'IRUSION PROCESS Filed Jan, so,- 196e 2 Sheets-Sheet I Fig. 2

United States Patent O1 hee 3,553,995 EXTRUSION PROCESS Robert J. Fiorentino, Worthington, Ohio, John M. Cigan, Leetsdale, Pa., and Alvin M. Sabrolf and Richard L. Jentgen, Columbus, Ohio, assignors 'to St. Joseph Lead Sompany, New York, N.Y., a corporation of New ork Filed Jan. 30, 1968, Ser. No. 705,880 Int. Cl. B21c 23/32 U.S. Cl. 72--42 11 Claims ABSTRACT OF THE DISCLOSURE A workpiece is forced through a die that is formed with a flat face and an orifice of lesser dimensions than the workpiece while outward lateral movement is restrained, the surface of the workpiece is provided with a thick lm lubricant coating that consists of an organic material and a granular material, and the outermost portion of the workpiece is angularly directed inwardly to flow laterally along the llat face of the die to and through the die orifice.

BACKGROUND This invention relates to improvements in the extrusion of shapesand relates in particular to the use of a die formed with a at face for the streamline flow extrusion of complex shapes.

In the extrusion process a solid or hollow block of material, normally cylindrical in shape, is formed into a desired shape of uniform cross-section by forcing it to flow through a die orifice under the action of an externally applied force. The externally applied force is commonly applied by means of an extrusion ram located at the opposite end of the block of material (or workpiece) from the die face; however, such force may be applied by other means such as hydrostatic uid pressure.V Such externally applied force urges the workpiece toward the die face and, restrained from lateral movement by a strong-walled container, it is forced through the die orifice or opening.

As the material is forced through the container and die orice, it flows somewhat in the manner of a highly viscous liquid, such flow being generally parallel to the axis of the die. However, at the throat of the die, material remote from the axis of the die, must ilow inwardly to pass through the die orifice.

In conventional extrusion practices the die may be shaped to symmetrically taper from the outer periphery of the container to the die orice so as to guide the owing metal inwardly through the die orifice. In many instances, however, such a die conguration or taper is not possible so that the outer periphery of the workpiece that is not aligned with orifice of the die contacts a llat die surface and must change 90 in direction of o'w to reach the die orifice. Such a flow pattern within the extrusion billet when utilizing dies with at working faces is such that internal shearing of the billet material occurs. When the extrusion process is initiated, a zone of slower moving or stagnant billet material accumulates in the corner formed by the container liner and the working face of the die. This relatively inert region is commonly 4referred to as a dead metal zone.

When extrusion lubricants are employed to reduce the frictional forces between the workpiece surface and the container and die surfaces (normally for the purposes of lowering the applied pressures required for extrusion and/or reducing the wear on tooling surfaces) the extent of the dead metal zone may be reduced considerably. However, when employing flat-faced dies, the inert (or dead metal) zone cannot be entirely eliminated. In

the course of the extrusion of a lubricated billet, conventional lubricants are forced into the inert zone in its ow pattern from the billet surface to the die orifice. The lubricant is then trapped between billet material layers and results in improper welding, causing defects at or near the surface of the extruded section. These may take the form of blisters, folds, laps, or laminations on the extruded section surface.

The use of glass pads or refractory discs as extrusion lubricants in the manner taught by U.S. Pats. 3,063,560, Edgecombe, and 2,907,454, Sejournet, are often not suitable for extruding at extrusion temperatures below about l000 F. as are necessary for metals such as lead, zinc, aluminum and magnesium. Such materials generally are too viscous within this temperature range to provide a desired result. The use of conventional lubricants such as greases containing graphite or molybdenum disulfide for extruding such metals through flat-faced dies results in surface defects in the manner described above.

As stated above the problem is largely eliminated by the use of conical entry extrusion dies to streamline material ow into or towards the die orifice. However, in many instances it is not possible to achieve such streamline flow by using conventional extruding techniques. For example, streamline flow is not possible where it is desired to extrude a workpiece into a complex structural configuration as may be desirable in the airframe industry by utilizing conventional extrusion practices. In these instances, the configuration of the die opening prohibits symmetrical entry die design. Streamline flow is also not possible where multiple die openings are utilized. We have now found that where it is not possible to attain symmetry between the die orifice and container wall in the utilization of at-faced dies, defects may be avoided and streamlined metal flow may be achieved during extrusion by providing a partial conical entry zone to the die orice and by providing organic lubricants that contain solid Igranular materials.

iIt is, therefore, the object of the present invention to provide a means whereby materials may be extruded through a flat-faced die while avoiding surface and internal defects.

It is also the object of the present invention to provide an improved means for extruding materials into complex shapes, using a flat-faced die.

Other objects and advantageous features of the present invention will be Obvious from the following description and the drawings.

DETAILED DESCRIPTION FIG. 1 is a cross sectional side view of a tooling arrangement for the extrusion of metal shapes.

FIG. 2 is a cross sectional view of a die designed for use with the tooling arrangement of FIG. l and embodying features of the present invention.

FIG. 3 is a plan view of the die of FIG. 2.

IFIG. 4 is a cross sectional view of a die that also embodies features of the present invention.

In the tooling arrangement shown by FIG. 1 a billet or workpiece 10 is shown in the act of being extruded through a die 112'. The apparatus is relatively basic consisting of a container 14 constructed to accommodate die 12 at its lower opening (as shown), a die holder 15 and backing block 16 disposed to seat on a hydraulic press platen 18. Die holder 15, backing block 16, and platen 18 are all formed with mating openings 20; 22, and 24 positioned to permit the extruded portion 21 of billet 10 to flow from the apparatus. A dummy block 2,6 is positioned between the stem Z8 of the hydraulic press (not shown) and the workpiece 10l to protect the stem. Thus, pressure on billet 10 effected by the press through stem 28 causes the material of billet 10 to tiow through the orifice of die 1|2`.

The die is formed with a fiat face 30 surrounding the die orifice 11. Such a flat face is necessary since the shape of the orifice is complex (see orifices 42 and 44 of FlG. 3) and it is accordingly impractical to taper the container or the die at the juncture 32 where the die meets the container to provide streamline metal flow. Juncture 32, however', constitutes the dead metal zone which adversely affects the surface condition of the extruded part.

In lubricated extrusion we have found that when the dead metal zone is eliminated, materials (such as metals) readily flow laterally along the die face to and through the complex die opening. This is surprising and unexpected to those skilled in the art since it has been previously thought that streamline flow could not be achieved and that surface blistering and internal defects could not be eliminated without eliminating lateral flow along the flat die surface.

A particularly advantageous die to use in conjunction with the method of the present invention is illustrated by FIGS. 2 and 3. As may be seen, this die 40 is formed with two orifices 42 and 44, both of L-shaped configuration, so that a symmetrical taper (taper in direction of the die opening evenly from all points) between the die orices and container is not possible. The die face, however, is recessed so that a taper 46 symmetrical to the container but not to the complex orifices is provided. Shoulder 48 abutts the shoulder 17 (FIG. 1) of container 14 in the manner of shoulder 19 of die 12 (FIG. 1) so that a workpiece expressed through the die orifices 42 and 44 will first contact taper 446 and effect streamline fiow towards orifices 42 and 44 eliminating the adverse effects of a dead space, such as dead metal zone 32. However, such streamline metal flow must be accompanied by the unique lubrication of the present invention to obtain the desired defect-free extrusion.

The die of FIG. 4 is identical to die 12 except an adapter ring 50 has been seated on the shoulder 19 to provide taper 56 and shoulder 58. Such a modified die structure will obviously perform the function of die 40.

Tapers 46 and 56 of the present apparatus may vary from about 75 to 15 from the chamber wall or the fiat surface of the die and may vary in length from afbout D-tl 2 of the total die face diameter D, where d is the diameter of a circle circumscribing the die orifice or orifices (see FIG. 3). However, it is preferable that such taper be uniform and within the range of 30 to 60 to the container wall and/ or fiat-face die.

In the utilization of the die of the present invention, such as that illustrated by FlGS. 2-4, it is necessary to provide a relatively thick-film lubrication to assure an even or lstreamline flow of metal through the die opening without sticking or galling and to provide a clean relatively blister-free surface. As stated above, the use of glass and similar materials results in a generally poor surface, particularly when used at lower temperatures. Conventional organic lubricants do not provide the necessary thick film lubrication.

We have found that organic lubricants are satisfactory if they are provided with a granular or particulate lubricating solid which remains solid at the extrusion temerature but which is softer than the billet at the temperature of extrusion.

We have found that the organic portion of the lubricant may be any organic substance having a viscosity that is lcss than that of the metal being extruded at the temperature of extrusion but which is characterized by an average molecular weight of at least about 300. Stich materials can be polymers such as the aliphatic or aromatic resins and plastics but include paratlins, naphthenes, and

1/10D to greases that are relatively stable at the extrusion tempercombined with a suitable garnular material) but also does the thermoplastic resins such as the polyolefins and polyacrolates depending on the metal being extruded. We have had particular success utilizing the polyolefins such as liquid polybutene. Polybutene provides particularly desirable lubricating qualities at extrusion temperatures of from about 500 F. to 1500 F. in that this polymer not only provides the desired lubricating qualities (when combined with a suitable granular material) but also does not stain the extrusion surface in the manner of most organic lubricants.

The solid granular fraction of the lubricant utilized in the process of the present invention may `be any inorganic solid such as metal salts, metal oxides, and minerals such as mica, talc, etc. The purpose of these granules is to maintain a barrier between the workpiece and the die or provide what is known as discrete film lubrication as opposed to the ordinary or boundary lubrication provided by conventional lubricating oils. Should these granules be harder than the workpiece or die at the temperature of extrusion they would scratch or scour the workpiece or die surface. Consequently, these granules must be no harder than the workpiece or die at the extrusion temperature, but must remain a solid at such temperatures to provide the required discrete film lubrication.

Although the particle size of the granules is not critical and may vary widely in accordance with the exact parameters of the specific extrusion operation, we have found it to `be desirable to employ granules having an average diameter that is not less than 1 micron. Although ordinarily the average diameter of such granules will not exceed about 7 microns, such average diameter may be much larger (up to 1A inch) in specific instances as where the granules are composed of materials such as flake graphite.

The granules of the present lubricant should be distinguished from the extremely fine particles that are colloidally dispersed in mineral oils to thicken or raise the viscosity of such oils. These particles are far too small to lend continuous film type lubrication to the present extrusion process or to scratch the surface of either the workpiece or the die. Such colloidally suspended particles may consist of either organic or inorganic materials. Such colloidally thickened oils are included as the basic vehicle (organic fraction) of the lubricating oil employed in conjunction with the process of the present invention.

We have found that the granular content of the lubricating oil may vary from 5 percent by weight to 60 percent by weight (of the total lubricant) without destroying its effectiveness; however, a preferred range is from about 10 percent by weight to 20 percent by weight.

To demonstrate the present invention a 700 ton hydraulic press utilizing tooling equipment such as that depicted by FIG. 1 was used to extrude L-shaped metal members from round billets through dies such as those illustrated by FIGS. 2 to 4. The metal billets were zinc alloys of the following analyses:

(2) Zn-0.65 Cu-0.l8 Ti alloy (3) Spectial high-grade zinc (4) Zn0.l Al0.1 Mg alloy EXTRUSION CONDITIONS The extrusion trials were conducted under selected combination of the following conditions:

Billet diameter, inches-33/16 Billet length, inches-8 Container diameter, inches-3.275

Extrusion ratio (Lsection)15 :1 (Z-port) Extrusion length, feet--7.5

Section size, inch- (Ms x 1A) x (1/2 X 1As) Lubricant-20 percent by weight lead oxide in polybutene (Oronite No. 32)

' Results were as set forth in Table I below.

For the purposes of the present application and claims where the term symmetrical is applied to a die structure or method, it shall mean that any point along the die opening is equidistant from the periphery of the die or the die container wall. Thus, if the orifice is round and centrally positioned and the die is provided with a circular periphery (shoulders or container wall), the orifice and die are symmetrical. Also, if the orifice is square, rectangular, hexagonal, etc., and the die and container wall periphery is of similar configuration with the orifice centrally positioned and oriented so that it is equidistant from any position along the edge of the orifice to a corresponding point at the periphery of the die (i.e., the container wall) the arrangement is symmetrical. It will be readily appreciated that in any such symmetrical arrangement the container wall and/or die surface may be made to taper to the die orifice in a uniform equidistant (symmmetrical) manner.

On the other hand, where the shape of the die, orifice, and/or the container wall (or their equivalents) are such that the distance from points along the orifice edge to corresponding points along the die periphery or container wall varies (as where there are two orifices or the orifice is asymmetrical such as an L, I, T, or U shape while the periphery is circular) the die cannot be made to taper in a symmetrical fashion and the term unsymmetrical shall apply.

said orifice or orifices inwardly towards said orifice or orifices adjacent the face of said die; and

(c) providing the surface of said billet with a lubricant that consists of a mixture of an organic material 0f less viscosity than said billet at the billet extrusion temperature and a granular material of solids that are softer than said billet at said billet extrusion temperature.

2. The method of claim 1 wherein the outermost portions of said billet are directed inwardly symmetrically in respect to the billet and unsymmetrically in respect to said orifice or orifices.

3. The method of claim 1 wherein there is more than one orifice in said flat-faced die.

4. The method of claim 2 wherein the outermost portions of said billet are directed inwardly at an angle of from about 75 to 15 from the axis of said die.

5. The method of claim 2 wherein the outermost portions of said billet are directed inwardly at an angle of from about 60 to 30 from the axis of said die.

6. The method of claim 1 wherein said lubricant consists essentially of a mixture of an organic material having an average molecular weight of at least 300 and said granular material has an average particle size of from 1 to 7 microns.

7. The method of claim 6 wherein said granular material makes up from about 5 to 60 percent, by weight, of the lubricant.

TABLE I.-DATA FROM EXTRUSION INTO L-SECTION [Die Design=TWo Port with M Inch x 45 Taper on Periphery (FIGS. 2 and 3)] Extrusion pressure, 1,000 p s.i. Extruded f- Billet Speed, i.p.m. v surface defects Binet temp., Extrusion Maxi- Mini- Die design Orifice material Lubrication Trial ratio Stem Exlt mum mum Blisters Cracks FF norma" sHGzinc No 211 o 00:1 20 1,200 117 76 d Y 231 350 60:1 20 1, 200 75 61 232 350 60:1 20 1, 200 74 60 337 450 15:1 80 1, 200 125 75 328 450 15:1 80 1, 200 76 64 M dorate.-- Yes. 327 450 15:1 80 1,200 73 60 Slight N0. 341 450 15:1 20 300 161 74 Sli ht N 330 450 15:1 80 1, 200 97 75 331 450 15:1 80 1, 200 89 70 FF-at-face die. b CF-conical-fiat die.

It will be noted from the data of Table I that the use 8. The method of clarrn 7 whereln sald lubricant conof the polybutene-PbO lubricant dramatically reduced the required maximum or breakthrough extrusion pressures. Where the lubricant was used with conVentionalfiat-face dies surface defects occurred. Where both the lubricant and the conical-fiat die of the present invention were employed the breakthrough extrusion pressures were again reduced and there were no significant surface defects.

It will be understood that the fiat-face of a fiat-face die need not be perfectly flat, i.e., form a 90 half-angle with the die axis, but may deviate as much as about 15 to form a 75 half-angle with the die axis. Half-angles smaller than about 75 would not be practical due to the large variations introduced into the bearing length. It is possible that half-angles several degrees greater than 90 could be tolerated, however, greater angles than this would defeat the purpose of the present die design. Consequently, the term flat face as used in the present specification and claims shall be interpreted to include such a variation in half-angle.

We claim:

1. A method for providing streamline plastic flow when extruding a billet of temperatures below about 1000" F. through a fiat-faced die formed with an unsymmetrical orifice or multiple orifices comprising:

(a) urging said billet against the flat-faced surface of said die while restraining outward lateral movement of said billet at a pressure disposed to force said billet to plastically ow through said orifice or orifices;

(b) directing at least a portion of the outermost portions of said billet that are not axially aligned with sists essentially of polybutene and the extrusion temperature is from 500 F. to 1500 F.

9. The method of claim 8 wherein said granular material consists essentially of lead oxide.

10. The method of claim 4 wherein said outermost portions of said billet are directed inwardly at said angle of from about 75 to 15 for a distance of of the total die face diameter D, where d is the diameter of a circle circumscribing the die orifice or orifices.

11. The method of claim 1 wherein said lubricant consists essentially of a polyolefin.

CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner gyg UMTED STATES PATENT OFFICE CERTIFICATE OF CORRECTEON Patent No. 3 553, 995 Dated January l2, 1971 Inventor(s) Robert J. Fiorentino, John M. Cigan, Alvin M. Sabr and Richard L. Jentgen It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 2, "combined with a suitable garnular material) but also does" should read ture. For example, such organic material may be one of Signed land sealed this 30th day of Merch 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents