US2894625A - Extrusion die assembly with flow-correcting baffle plate - Google Patents

Description

July 14, 1959 c. s. HARRIS ET AL 2,894,625

I EXTRUSION DIE ASSEMBLY WITH FLOW-CORRECTING BAFFLE PLATE Filed Dec. 18, 1955 I 2 Sheets-Sheet 1 C/are 6. Harris- C/ifian J. Huffman ATTORNEYS.

July 14, 1959 c. s. HARRIS ET AL 2,894,625

I EXTRUSION DIE ASSEMBLY WITH FLOW-CORRECTING BAFFLE PLATE Filed Dec. 18. 1953 v 2 Sheets-Sheet 2 IN VENTORS Clare .5. Harm's C/i/Yon J Huffman Maw-4 ATTORNEYS.

United States Patent EXTRUSION DIE ASSEMBLY WITH FLOW- CORRECTING RAFFLE PLATE Clare S. Harris, Midland, Mich.,.and Clifton J. Hufiman,

Ferguson, -M0., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware .Application December; 18, 1953,*=SerialNo. 398,972

1 Claim. (Cl. 207-17) This invention relates to the extrusion of metals. It pa.rticularly. concerns. a dieassembly including a baflie plate-tor controlling: the flow of metal through a die of non-uniform. flow; characteristics.

In: the, pressure extrusion of metals, the size .and shape of. the dienorifice influence greatly theresistance tor-the flow. of .theametal through the die. With many dies, the .rateofifiow through one section of .the orifice may ma- .terially exceed that. throughanother section. As a re- ..sult, the extruded product may be curved as it issues from the die,--or may :exhibit surface imperfections, suchras scufiing. This-tendency is most pronounced withdies for making extruded products haying thin-walled sections in- ,tegral with metal of greater thickness.

,Die designers, aware of this problem, usually try. to 1 build into each die structural features intended to equalize .theurateofflow at all. cross-sections. of the die orifice. Several. types of. equalization have been used. In one, the lengthof the land or beating of the die is increased at regions tendingto rapid flow in order to provideadded :frictionalresistance atthese regions. In another, the ,entrance to: the die. orifice, rather than. being straight, is made tapered or choked. Thedegree. of taper. is varied 1 to provide greater or lesser resistance-to. flowv at' various ;sections.'of the orifice as'required. Asimilar result-is 1 obtained byvarying the radius of the curved surface over -.,whi chthe metal flows. into the. orifice.

,These measures, while effective, so complicate the construction of the extrusion die as .to necessitate much precision. machine work inmaking it. Likewise, when such adie needs repair, or requires modification in some minor respect, only experienced. toolmakers. of the highest skill .canbe trusted with the Work. Forthis reason, the established methods of providing extrusion dies With .equalized flow characteristics have all proved extremely expensive.

It is accordingly the principal object of the invention .to provide an extrusion die assembly. in .Which equalizationof metal flow at all sections is achieved at far less expense than heretofore. Another object is to provide .-a die assembly of such simplified construction that it .may the-easily made, and'whennecessary repaired, by regular machinists. A further object is to provide an assemblyin which the adjustments necessary for equalizing .flow are carried out simply andtefifectively on auxiliary bafilemeans and without having to alter the extrusion dieitself. An additional object is to provide a die as- -sembly employing simpler dies and requiring alesser quantity of expensive tool. steel than has been customary ,heretofore.

The. invention is applicable to correct the flow through any extrusion ,die having .at leastone metalfshaping .orifice and being of such design that the rate of metal Xjflowlduring extrusion tends to. bev less rapid at one-sec- .tionof the. die than at some other section. Briefly, the ,invention comprises, in combination with such a ,die, a bafii'le mounted .ahead of the inner face, of the die and having an opening in line with and larger than that of each die orifice. The openingin the baffle is made of such size and shape that the flow of-metal to the least rapid section. of the die opening is unimpeded while the flowtojthe more rapid sections of the dieis restricted-Ito a degree such as to equalize flow through allsections of the die. To this, end, the size andshape of tthebaffie opening are made such that the ratio .of the width ofthe bafile opening at any section .to ,the width. of the .die orifice at the corresponding, section is. greater at..the,sections tending to less rapid flow- .than at the sections, tending to more rapid flow.

The invention may be understood more. clearlyby reference to the accompanying drawings, in which Fig. 1 is a vertical partialsectionrshowing a. .direct metal extrusionpress (indicatedschematically) .with,.a bafile plate according to the invention, extrusion ,die, and backer plate all in place, the section .being taken along the line.1-1Iin Fig. 5;

Fig. 2 is an elevation, ofuthe baffle plate. of.Fig.,l, viewed from the inlet side; I

Fig. 3 is a similar elevation of the die, plate ofrFig. 1; P Fig 4 is a similar elevation of the backerplateof .Fig. 5 is another elevation viewed from the. inlettside, showing the bafile plate,- die plate, and. backer .plate assembled together;

Fig. 6 is a section through'the die assembly, taken along the line-66 of Fig. 5;

Fig. '7 is another section through the die .assembly, along the line 77 of Fig. 5;

Fig. 8 is a fragmentary perspective view of, anextr-uded angle beam made with the die assembly of Figs.. 1.1017;

Fig. 9 is an enlarged fragmentary section .of one typical baffie plate anddie plate according .to theinvention, dimensioned for explainingina general. way the-interrelation of the sizes of the baflleand ,dieopenings;

Fig. 10 is, an elevation from the inlet side. of another type of baffle plate according. to. the. invention,. for use with a.single rectangulardie orifice; I

Fig. 11 isa similar elevation ,of still anotherlbafiie plate and die assemblyaccording to ,the inventiomtor makinga finned tubular extrusion; and

Fig. 12 is an elevation from, the inlet side of abafile plate in placebefore, aHmultiple-opening die.

The die assembly of Figs. 1 to 7 is designed for making an extruded opensection, in this instance the angle beam 11 shown in Fig. 8. This. beam has two relatively. thinwalled flanges 12 and 1-3 which join at. a. thicker vertex When an attempt isv made to, produce sucha beam by extruding metal through. a die 15 havingan inner or entrance face. 30 containing an appropriately shaped die orfice 16 (Fig. 3), they rate of metal flow tends'tobe non-uniform. The metal forming thevertex 14Epas5es through the widest section of the die orifice, and, because of the relatively low'resistanceto flow there, .tends to issue at acomparatively rapid rate. Onthe otherhand, the metalforrning the flanges 12 and'13, particularly that near the outside edges, moves through the most,restricted sections ofthe die orifice, which offer higher flow resistance, and hence tends to extrude. at .a.slower rate. This difference in flow tendency between the parts -of the extruding beam subjects the metal to stresses which,. if extreme, .cause serious imperfections in the product.v .The baflle plate. 17 shown provides a simple means of equalizing flow at all points of the die orifice 16.

Because, in theinvention the means for equalizing the metal flow rateare not included inthe extrusiondie itself, the ,die maybe of greatly simplified. construction. As shown, the die 15 is merelya disk or plateofatool steel with plane parallel faces. ,It may be,.made.,quite thin, with athickness usually, less.than a twentieth ..its diameter; e.g. it need be no more than one-eighth to onefourth of an inch thick. Cut through the die plate is the die orifice 16 corresponding in every detail to the cross-sectional shape of the product to be extruded. This orifice is quite satisfactorily made with sharp (90) edges at the inlet and outlet (Fig. 9), although it may have a slight entering radius, or slight relief at the outlet end, as desired. The orifice 16 is also most conveniently formed With parallel walls, as shown, although a taper or choke is permissible.

As will be seen in Fig. l, the plate-like die 15, together with the bafile plate 17 and a supporting pia like backer 18, fit snugly into a supporting die ring 19. The latter is held seated against the outlet end of the cylinder 20 of a conventional direct extrusion press also provided with a plunger 21 and dummy block 22. A billet of magnesium-base alloy or other metal to be extruded (not shown) is placed in the space 23 between the block 22 and the die assembly. The thrust of the billet on the die assembly is resisted by a bolster 24 or other conventional die holding means.

The baffle plate 17 is also a steel disk, of the same size as the die plate 15, and is usually, though not always necessarily, considerably thicker than the latter. For sturdiness, a thickness of at least three-eighths inch is preferred. The bafile 17 also has plane parallel faces, and is mounted ahead of the inner face of the die plate 15, being seated against the latter. Cut through the baffle plate is the baffle opening 25, the shape of which is an essential feature of the invention, and will be described in detail later. As is especially clear from Fig. 5, this opening 25 is in line with the die orifice 16, and is larger than the latter, so that the baffie does not mask the orifice. Each cross-sectional dimension of the opening 25 is larger than the corresponding dimension of the die orifice 16, making the latter the ultimate constriction which imparts the finished shape to the metal being extruded. The baffle opening is preferably made straight through, i.e. with parallel walls normal to each face of the plate as shown, through some degree of taper, either forward or reverse, is permissible.

The backer plate 18 is also a steel disk of the same diameter as the die plate 15, and with plane parallel faces, and rests against the exit face of the die plate. It is provided with an opening 26 in line with and larger than that of the die orifice to allow free passage of the extruded product. The backer plate is made thick enough to rest against the bolster 24 and thus to support the die plate 15 Without significant deformation under the heavy pressure of extrusion.

To prevent rotation of the baffle plate 17, die plate 15, and backer 18 relative to one another, registering holes 27, 27a, and 2712, are drilled in each. in the assembled die structure (Fig. 1), locking pins 28 inserted in the registering holes insure alignment of the die elements during extrusion. The bafile plate, die plate, and locking pins are all made of the tool steel commonly used for extrusion dies, and are heat-treated in the usual way before installation.

In making extruded product with the press and die assembly as in Figs. 1 to 7, a preheated billet is inserted in the space 23 and the plunger 21 is actuated to force the billet against the die assembly. The plastic metal of the billet flows through the opening 25 in the baffie plate, thence through the die orifice 16 where it is finally shaped, and finally out of the rear of the die as finished product. Aside from the presence of the baffle plate, and the thinness of the die plate, the entire assembly, and the extrusion process, are in accordance with standard practice.

As has been mentioned, the cross-sectional shape of the opening in the baffle plate 17 is a major feature of the invention. The outline of the baffle opening never fully parallels that of the die opening. Rather, the shape is such that the ratio of the width of the baffle opening to the corresponding width of the die orifice varies from point to point along the periphery of the orifice. The ratio of these widths is made greater at points of high resistance to flow of metal through the die orifice than at points of lower resistance. For the die of Fig. 3, the maximum resistance to flow through the orifice 16 is at the outside ends of the orifice, while minimum resistance is at the vertex. Accordingly, the baffle opening 25 is made widest relative to the die opening at its outside ends and narrowest near the vertex, producing the shape illustrated in Fig. 2. (The interrelation of the bafile opening and die opening is shown best in Fig. 5.) The precise shape of the opening 25 is that required to equalize the rate of metal flow through all points of the die orifice 16. Under this circumstance, the arithmetic difference between each cross-sectional dimension of tile batlie opening and the corresponding dimension of the die orifice varies throughout the cross-sections of the orifice substantially directly as the resistance to metal flow of the sections.

These dimensional considerations may be further explained with reference to Fig. 9, which is a fragmentary generalized section through a baffie plate and die plate according to the invention. There, the die plate 15, of thickness t, defines the die opening 116, which, at any particular crosssection, has a width w. At the same section the baffle plate 17, of thickness t, defines the baffle opening 25, of width w. The distance between the edge or wall of baffle opening 25 and the edge or wall of the die opening 116 may be termed the offset 0. Preferably this offset is the same on both sides of the die opening, in which case 0= /2 (w'w).

In the invention, the ratio w/w varies from point to point along the periphery of the die opening, the degree of variance being just that required to equalize flow rates of the extruding metal through the various points of the orifice. Stating the same thing another way, the offset 0 varies from crosssection to cross-section along the orifice to equalize flows. (The cross-sections are taken normal to the centerline or centerlines of the orifice.) Each of these related quantities, viz. w/w and 0, is greater at regions of the die orifice where the resistance to flow of metal is higher than Where it is lower. In general, at those sections of the die orifice where the resistance to flow is the greatest, the offset 0 should be at least equal to the baffle thickness t. (For instance, the offset 0 should be /2-inch or more when the baffle plate is /2-inch thick.) Under this condition, the baffie edge is remote enough from the orifice to add little if any resistance to the flowing metal. The metal enters the die orifice almost unimpeded. On the other hand, at those sections of the die orifice where the resistance to flow is the least, the baffle offset 0 is advantageously made less than half the thickness of the bafile plate, and may, in case of extreme flow differentials in a die, be as little as a third to a fourth the bafile thickness. With this small degree of offset, the bafile edge is so close to the orifice as to impart considerable resistance to the flowing metal, i.e. to choke it, and thus to slow it down materially.

The choice of the precice degree of bafile offset 0 to equalize fiow throughout any particular die orifice involves a number of factors. When the die orifice is of nonuniform width, the sections of highest resistance to metal flow are nearly always the sections Where the orifice is the narrowest. Hence, in the invention, the baffle offset 0 is in general made the greatest where the orifice Width w is the smallest, and is made the smallest where the orifice is the widest. However, end effects and other phenomena also affect the resistance to flow through a die orifice, and these also must be taken into account. For instance, in the case of a die orifice of uniform width, e.g. a rectangular opening, the distance of the flowing metal from the container wall, and to a lesser extent end effects, are the main ones operative. In such a case, the offset 0 is made greater near the ends of the die orifice than at the middle. Such an assembly is illustrated in Fig. 10, the die orifice 16a being rectangular, and the baffle opening 25a being bulbous at each end.

For any specific die for making some desired extruded shape, the balancing of these various factors, such as orifice width, wall distance, end efiects, and others may not always be susceptible of easy mathematical analysis, and calls for judgment on the part of the die designer. However, extrusion men are aware of the flow characteristics of various types of die orifices, and will have no difliculty in applying the principles of the present invention to any particular case. For utmost precision, the baflie design may be worked out by machining out a first approximation, testing the bafile in an actual extrusion operation, and, if necessary, removing it from the die assembly and making further minor corrections as required to equate flow at all parts of the die orifice.

While the invention is primarily useful in making open extruded sections having a relatively thicker and a relatively thinner section, it is also applicable in making tubular extruded products of unusual contour. As an example, the die assembly of Fig. 11 is adapted to make a simple tube with two opposite thin-walled fins. In this assembly, the die orifice 16!) consists of a circular portion with two peripheral slots. For forming the tube, a mandrel 29, supported by a conventional spider or bridge mandrel holder, not shown, projects into the orifice 16b. The baflle opening 25b is made with small ofiset from the die orifice in the middle, with larger oifset near the ends.

Another area of usefulness of the bafile principle of the invention is in the case of multiple orifice dies. In such dies, the rate of metal flow is in part aifected by the relative distances of the various orifices from the wall of the press container. When one of a plurality of identical orifices is nearer the wall than another, the rate of metal flow during extrusion tends to be more rapid at the orifice most remote from the Wall. In this case, a baflie plate is mounted ahead of the die having openings each in line with and larger than the corresponding die orifice. The ratio of the width of the bafiie opening to the width of the corresponding die orifice is made greatest at the orifice of least rapid flow. Such an assembly is shown in Fig. 12, in which the die plate is provided with three identically sized orifices 16c, one being centered in the die plate and the other two being eccentric. In this case, the baffle openings 25c corresponding to the eccentric openings are made larger than the opening 25d corresponding to the central orifice.

In comparison to prior practice, die assemblies according to the invention exhibit a number of important advantages. The die plate may be a simple disk, and the orifice can be cut to shape by a milling operation. The same is true of the baflle plate, with the further simplification that the baffle opening, not requiring the precision of the die orifice, may in many cases be roughed out by sawing. Expensive machine work is nearly eliminated. Further, the die plate and bafile plate can be made thin in comparison to the massive dies often used heretofore, realizing a saving in expensive tool steel. Necessary corrections for a final equalization of flow rates on all parts of a die of complex shape are made entirely on the bafiie plate. The die, which is the precision element of the assembly, remains untouched. Moreover, wear and distortion of the die assembly during prolonged extrusion occur mainly on the baffie plate, so that the die orifice maintains exact dimensions for a longer period than heretofore. As a result of these factors, overall extrusion costs are lowered without sacrifice, and indeed, with improvement, of quality.

The claim is:

A composite die assembly for extrusion comprising a die plate of uniform thickness, a die aperture in said plate having parallel walls perpendicular to said plate, said aperture being of differential width, a baffle plate of uniform thickness ahead of said die plate through which the metal is extruded toward said die aperture, an aperture in said bafiie plate having parallel walls perpendicular to said bafiie plate, said baffie plate aperture being of the same general configuration as said die aperture but larger in opening by spacing the walls of said baffie aperture away from the walls of said die aperture, the spacing being greater in the locations where said width of said die aperture is smallest, said die plate being formed of die material and said baffie plate being formed of inexpensive material.

References Cited in the file of this patent UNITED STATES PATENTS 182,611 Stevenson Sept. 26, 1876 1,916,645 Taylor July 4, 1933 2,341,749 Webb Feb. 15, 1944 2,402,281 Green June 18, 1946 2,750,034 Gersman June 12, 1956 2,757,794 Walgren Aug. 7, 1956 FOREIGN PATENTS 7,427 Great Britain Aug. 31, 1837 24,948B Great Britain a

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