US3061093A - Method of scalping billet during extrusion - Google Patents

Description

Oct. 30, 1962 D. A. EDGECOMBE ETAL 3,061,093

METHOD OF SCALPING BILLET DURING EXTRUSION Filed April 21, 1959 2 Sheets-Sheet 1 ZEN wa V. B

Oct. 30, 1962 D. A. EDGECOMBE EIAL 3,061,093

METHOD OF SCALPING BILLET DURING EXTRUSION Filed April 21, 1959 2 Sheets-Sheet z V/D 14.50 OM86 ATTORNEY 3,061,093 METHOD F SCALPING BILLET DG EXTRUSEGN David A. Edgecombe, Beaver Falls, William R. Walker, New Brighton, and Clark P. Church, Beaver Falls, Pa, assignors to The Babcoclr & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Apr. 21, 1959, Ser. No. 807,783 1 Claim. (Cl. 207) This invention relates to the extrusion of metals having relatively high melting temperatures, such as carbon and alloy steels, titanium and titanium alloys and the like, wherein a relatively refractory material, such as glass, is interposed between the metal and the press parts to act either as a separating or parting material, or as a lubricant. More particularly, the invention relates to an improved method of scalping the extrusion billets to avoid inclusion of peripheral surface metal of the billets in the extrusions, and using a refractory lubricant placed against the upstream face of the die.

In the extrusion of such metals, the billets are heated to a temperature of the order of the extrusion temperature in a heating furnace or in a heating bath, such as a molten salt bath, prior to being charged into the extrusion press. After removal from the heating means for transfer to the extrusion press, the billets may have at least their external circumferential surface coated with a layer of refractory material having the property of becoming and remaining viscous at the extrusion temperature. in the case of tubular or axially pierced or drilled billets used for tubular extrusions, the surface of the billet passage may be similarly coated before the billet is charged into the billet receiving passage of the extrusion press container. Before the billets are thus charged into the press, a plate, disk, plug or block of such refractory material is placed against the upstream face of a die at the exit end of the container to provide lubricant for the die surfaces during extrusion.

While efforts are made to protect the heated billet from oxidation, including the protection afforded by heating in an inert atmosphere or in a molten salt bath, neither of these expedients nor the coating with such refractory material completely prevent surface oxidation or scaling of the billet. Such surface oxidation results in undesirable scale inclusions in the extrusions. Also, it is known that billets may contain surface defects, as well as defects immediately subjacent the surface, other than oxidation or scale.

Various expedients have been tried in an effort to prevent these surface defects being included in the extrusions, such as by breaking the scale from the billet before charging the billet into the press, for example. This expedient can be used only where the billet circumferential surface is not coated with lubricant. If, after the scale breaking, it is desired to apply such coating to the billet, the time interval between the scale breaking and the coating operation is sufilcient for further oxidation and scaling to take place on the surface of the heated billet.

In extruding some metals and alloys, particularly those of the non-ferrous type such as copper and aluminum and their alloys, it has been possible to prevent inclusion of such billet surface defects in the extrusions by scalping the billet during the extrusion. This is effected by making the usual dummy block, interposed between the end of the ram and the billet, of a diameter slightly less than that of the billet receiving passage of the container. Thus, as the billet is extruded, a thin shell of billet surface metal is left in and along such passage.

The prior art has taught that scalping of relatively high temperature metals, such as titanium and its alloys, for example, cannot be effected using a lubricant at the up- Patented Oct. 30, 1962 stream face of the die, and particularly a lubricant of the relatively refractory type, such as glass. In a report to the Air Materiel Command, Wright-Patterson Air Force Base, entitled, Extrusion of New Titanium Alloys, dated November of 1957, an aluminum manufacturer (Harvey Aluminum Company) having considerable experience with titanium and its alloys states that, in extruding titanium, the lubricant on the die face must withstand the abrasion and erosions only until a shear zone is established in the extrusion billet between metal flowing to the die opening and dead metal hung up" at the corner between the die and the container. It is further stated that lubricant on the die face, remote from the die opening, does not enter into the lubricating action and its only function is to effect easy separation between the die face and the extrusion butt or discard. The report then states that the principal lubricant to the die cavity after establishing the shear zone is carried on the billet skin from the container wall.

With respect to scalping an extrusion billet of titanium alloy, the aforementioned report states that this is possible using an undersize dummy or pressing disk behind the billet but, in this case, the lubricant from the container wall is not carried through the shear zone and clean metal is presented to the die cavity. According to the report, this resulted in welding and scoring of the dies in which the tests were made.

This report, which is representative of the teachings of the prior art, further states that experiments with refractory lubricants, such as glass, did not evolve a satisfactory die lubricant, although glass powders or frits of the proper melting range were successfully used as lubricants for application to the billet container. The prior art teaching is thus that extrusion of alloys, such as those of titanium, cannot be effected with a scalping technique when using a lubricant applied to the die face, and that a superior extrusion product could be realized if pressures and materials were such as to permit extrusion without the use of any lubricant.

In accordance with the present invention, and in direct contrast to such teaching of the prior art, it has been found that scalping to a depth sufiicient to remove all surface defects and those subjacent the surface can be effected utilizing, against the upstream face of the die, a plate, disk, plug or block of refractory lubricant material having the property of becoming and remaining viscous at the extrusion temperature, and then extruding the billet utilizing a dummy block or pressing disk whose diameter is smaller than that of the container passage by the amount of the desired thickness of Surface metal to be scalped. This leaves a thin Walled cylinder or can in the container at the end of the extrusion stroke. The refractory lubricant at the die face progressively melts during the extrusion to provide a continuing layer or film of lubricant between the die surfaces and the metal flowing through the die. No lubricating material need be applied to the external surface of the billet as such lubricant would not be of any assistance in providing lubrication at the die face.

However, it is advantageous to coat the external surface of the billet with a uniform viscous layer of such refractory material. Such coating avoids scoring of the container wall during charging of the billet into the container and provides a separating or parting layer facilitating removal of the shell or can from the container after the extrusion stroke. In accordance with the invention, when a coating of such viscous refractory material is applied to the external circumferential surface of the billet, it has a substantially higher range of meltthe lubricant in the plate, disk or block placed at the upstream face of the die. Due to this characteristic, the coating on the external surface of the billet holds the shell or can stationary during the extrusion and, in particular, inhibits any tendency of the billet surface metal to flow toward the die due to the drag of the metal engaged by the undersized dummy block or pressing disk. Such forward movement of the surface metal is further inhibited by utilizing a die whose upstream face is substantially perpendicular to the inner surface of the container, thus providing a sharp corner at which surface metal and metal immediately subjacent the surface of the billet tends to hang up during the extrusion.

For an understanding of the invention principles, reference is made of the following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings:

FIG. 1 is a vertical sectional view of an extrusion press, charged with an externally lubricated billet arranged to be scalped during extrusion, the press parts being shown prior to the extrusion stroke; and

FIG. 2 is a similar view illustrating the extrusion stroke partly completed.

Referring to the drawings, a typical extrusion press which may be utilized in practicing the invention is illustrated, by way of example only, as including a relatively massive cylindrical container having a liner 11 therein in which is telescoped a liner insert 12 whose inner diameter is substantially equal to the overall diameter of the extrusion billet with a coating of viscous refractory material on its circumferential surface. The illustrated press is a horizontal hydraulically operated press, but the invention method is operable equally with other than a horizontal press or with one which is operated other than hydraulically.

The downstream end of liner insert 12 is formed with a frusto-conical seat 13 engaged by a frusto-conical surface 14 on a die holder ring 15 having a frusto-conical inner peripheral surface 16. Ring 15 is secured to a die carrier (not shown) movable toward and away from the downstream or exit end of container 10, by means including a locking ring 17, and is engaged by an annular bolster block 18 locked in the die carrier. The inner peripheral surface 16 serves to seat a two-part die assembly including a die 20 and a backing member or ring 21,. which have frusto-conical outer peripheral surfaces. Die 20 and its backing ring 21 are shown, by way of example only, as multi-port elements for simultaneous extrusion of solid cross-section shapes. However, the invention method is applicable equally to the extrusion of tubes or hollow shapes, or to single port extrusion of solid shapes. It will be noted that the general plane of the inner faces of ring 15 and die 20 are in a diametric plane and at right angles to the inner surface of liner insert 12.

Before each extrusion, a disk, plug, block or plate of refractory lubricant, such as glass, is placed against the upstream face of die 20 to provide the lubrication of the die surfaces during extrusion. The composition, structure, and temperature characteristics of block or plug 30 are described more fully hereinafter, but it should be stated at this point that the refractory lubricant material of the plug or block is one which becomes and remains viscous over a relatively wide range of temperatures below, but approaching, the extrusion temperature.

After plug, disk, plate or block 30 is positioned against die 20, a billet is charged into liner insert 12 and against disk 30. Before charging into the press,

billet 35 preferably has its external circumferential or peripheral surface coated with a layer of refractory material 36 having the property of becoming and remaining viscous over a relatively wide range of temperatures of 4 invention, for reasons stated above and discussed more fully hereinafter.

Coating of the external peripheral surface of the billet, to provide the layer 36, may be effected, for example, by rolling the billet, previously heated to at least the extrusion temperature, over a relatively thick layer A to of the refractory material, such as glass, spread substantially uniformly or combed over an area having a width at least equal to the length of the billet and a length at least equal to the circumference of the billet. The heavy, heated billet, rolling toward the press over the layer of granular or particulate refractory material, picks up the material onto its external surface where the material, due to the temperature of the billet, forms a viscous layer 36 coating such external surface.

Extrusion of billet '35 is effected by a ram 31 operated by hydraulic pressure of a high value (i.e. 2500 tons). Ram 31 is shown as a tubular ram adapted for extruding either solid cross-section shapes or tubular or hollow extrusions. Within the ram, and concentric therewith, is a mandrel holder 32 to which mandrels may be interchangeably connected for projection through a die to form tubular or hollow extrusions. In the arrangement for extruding solid shapes, shown by way of example only, a collared pin 33 is secured in holder 32 and has a projecting end releasably supporting a dummy block or pressure disk 34 held thereon by a snap ring 37.

In accordance with the invention, the diameter of dummy block 34, while greater than the outer diameter of ram 31, is less than the diameter of billet 35 when compressed in the liner insert 12 by the desired thickness of the shell 38 (-FIG. 2) which is to be scalped from billet 35. For example, the diameter of dummy block 34 may be less than that of billet 35 by an amount of the order of 0.100. In a specific example, the thickness of the scalped shell or can 38 may be 0.05", which is suflicient to eliminate all billet surface defects, and billet defects subjacent the surface, from the exrusions. Thus, when ram 31 carrying dummy block 34 is advanced into the container, the dummy block engages only that area of billet 35 which is Within the inner surface of shell 38. Accordingly, this core of billet 35 is extruded through the ports 25 of die 20.

As stated, when this core" of the billet is pushed through the die, the lubricant plug 30 progressively melts to provide a layer or film of lubricant between the die surfaces and the billet metal continuously throughout the entire extrusion. The plug 30 provides the entire quantity of lubricant needed for the extrusion, and the extrusions are characterized by surfaces of good quality and by dimensional stability.

Galling of the container surface is avoided and movement of the billet longitudinally of the container is prevented by the layer 36 of relatively high temperature glass on the billet peripheral surface and engaged or in contact with the inner surface of liner 12. This glass, whose melting temperature range is substantially above that of the glass of block or disk 30, provides a frictional resistance layer between the external surface of the billet and the internal surface of liner insert 12. This frictional resistance is enhanced by the increase in viscosity of the layer 36 due to contact with the relatively cool inner surface of liner insert 12.

Furthermore, the coating layer 36 provides a continuous layer of separating or parting material for easing ejection of the scalp or shell 38 from the liner insert following the extrusion stroke.

Typical low temperature lubricating materials. for the plug or element 30 may comprise glasses having the following percentage compositions:

5 This glass may be used with extrusion temperatures up to the order of 1650 R, such as used for extrusion of titanium and titanium alloys.

Glass 3KB" SiO 48.4 13,0 27.3 A1 0, 3.78 F3203 1 2 CaO 11.83 MgO 0.21 N320 K 0.07 By difference 0.07

This glass may be used with extrusion temperatures of the order of 1700 F. to 2100 R, such as used in extruding titanium and its alloys, as well as the softer stainless steels.

A suitable material for the refractory material layer 36 is an ordinary window glass, such as one having the following approximate percentage composition:

Percent N320 1 9 CaO SiO 73 Such glass is ordinarily used with extrusion temperatures of the order of from 2000 F. to 2350 F.

Another suitable glass for layer 36 is E glass manufactured by Owens-Corning Glass Co. and having the following percentage composition:

S10 53 .0 B 0, 10.4 Al O +Fe O CaO 16.8 Mg() 4.4 Na O 0.3 K 0 0.3

The extrusion use temperature of this glass is approximately 2300 F.

A third glass suitable for layer 36 is known as TV glass and has the following approximate percentage composition:

The extrusion use temperature of this glass is approximately 2300 F.

The high temperature glass for layer 36 is preferably used in the granular or particulate form, as described, but also may be applied as a fiber glass sheet wrapped around the billet. Except in the case of dies having ports of small cross-sectional area, the glass of the element 30 may be in any form, such as, for example, a plate or pane of glass, a formed plug, disk or block of fiber glass, or a disk of agglomerated glass powder preformed by use of a binder or by sintering, as described in David A. Edgecombe, U.S. Patent 2,946,437. However, the agglomerated disk form of element 30 is preferred in all instances, and is necessary where the cross-sectional area of the ports is small, to prevent bridging or blocking of the ports as occurs when using fiber glass, for example.

As set forth in said Edgecomb patent, disk 30 may be formed of powdered glass bonded by a sodium silicate binder, the following proportions being used:

Glass powder pounds 100 Seal brand water glass ounces 45 Water do 15 The glass powder is prepared by ball mill grinding. It

need not be carefully graded with regard to grain size but it has been found to be satisfactory if the powder is of such grain consist that at least passes through a screen having 50 meshes per lineal inch, not over 5% is is retained on a screen having 14 meshes per lineal inch and not over 25% passes through a screen having 100 meshes per lineal inch.

Binders other than water glass (sodium silicate) can be employed in forming the agglomerated glass disks. Where the metal billet to be extruded has a relatively low extrusion temperature and, accordingly, where it is desirable to use an agglomerated disk of glass powder having a relatively low softening point, a suitable binder for the glass powder is phosphoric acid.

Moreover, instead of employing a binder for agglomerating the glass powder into a disk, agglomerated disks may be made by sintering a compacted or uncompacted body of glass powder.

The disk of agglomerated glass powder should have a density of about 30 to and preferably from 45 to 70%, of the density of the glass from which the powder is made. The density of the disk can be readily regulated by the amount of pressure applied during formation of the disk.

The invention is applicable equally to the extrusion of hollow or tubular articles using a mandrel secured to holder 32 and projected through an annular die in advance of the extrusion stroke. In such case, a tubular billet and an annular die are used, and the billet is coated on its inner peripheral surface as Well as on its outer peripheral surface. However, the glass of the inner coating is a low temperature" glass, preferably of the same composition as the glass of the plate or disk placed against the upstream face of the die, while the external surface of the billet may have a layer 36 of high temperature glass thereon as in the illustrated example. The interior surface of the billet may be coated with glass in the manner described in Walker U.S. Patent No. 2,908,385 or Capron et al. U.S. Patent No. 2,980,384.

While specific embodiments of the invention have been shown and/ or described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

The method of scalping a peripheral surface layer from a billet of high melting temperature metal during extrusion of the billet comprising the steps of placing at the upstream face of a die at the discharge end of the billet receiving passage in the container of an extrusion press a layer of refractory lubricant material having the property of becoming and remaining viscous over a relatively wide range of temperatures below but approaching the extrusion temperature; coating the external peripheral surface of the billet with a layer of refractory friction-producing material having the property of becoming and remaining viscous over a relatively wide range of temperatures close to the extrusion temperature and substantially higher than the range of said refractory lubricant material; charging the coated billet into such passage with its inner end against said first mentioned layer of lubricant material;

positioning centrally against the outer end of the billet a dummy block whose outer periphery is spaced from the peripheral surface of the billet by an amount equal to the desiredthickness of the surface layer to be scalped from the billet; and exerting pressure against said dummy block to extrude the core of the billet defined by the periphery of the dummy block through the die leaving a shell of billet metal within the container passage; said first layer of lubricant material facilitating flow of billet metal through the die, by virtue of its viscosity at the extrusion temperature, and being adequate in amount to furnish a continuous layer of lubricant between the billet metal and the die throughout the extrusion, and said second layer of refractory frietion-producing material interposing a frictional resistance to movement of billet metal along the surface of the container passage to inhibit flow of the metal of the shell along the passage, preventing scoring References Cited in the file of this patent UNITED STATES PATENTS 2,3 37,804 Dempsey Dec. 28, 1943 2,538,917 Sejournet et al Jan. 23, 1951 2,773,593 Schmollinger Dec. 11, 1956 2,798,286 Anderson July 9, 1957 2,832,468 Krause Apr. 29, 1958 2,946,437 Edgecombe July 26, 1960 FOREIGN PATENTS 781,737 Great Britain Aug. 21, 1957 1,l48;824 France July 1, 1957

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