US2946369A - Method of bending sintered material - Google Patents

Description

M 26, 1960 R. w. BIGGS ,94 9

METHOD OF SENDING SINTERED MATERIAL Filed June 18, 1957 2 ShQetSP-Sheet 1 VW mm mm, :1. 3 I. a l lllMunr NX m Om m INVENTOR. v ROBERT W 81665 fibc/md WmQUZhE/n ATTORNEY July 2%, 1%0 R. w. BIGGS 2,946,369

METHOD OF SENDING SINTEREID MATERIAL Filed June 18, 1957 2 Sheets-Sheet 2 INVENTOR.

ROBERT W B/GGS y m1 m1 5% midi-8mm ATTORNEY METHOD OF BENDING snvrnnnn MATERIAL Robert W. Biggs, Shaker Heights, Ohio, assignor to The S. K. Wellman Company, Bedford, Ohio, an Ohio corporation Filed June 18, 1957, Ser. No. 666,319 1 Claim. (Cl. 153-48) This invention relates to a method of imparting a curved shape to an article.

Articles of the type referred to are produced by pressing or briquetting metal powders with minor amounts of powders of one or more non-metallic ingredients, such as graphite, and then heating the briquette to a sintering temperature. In the past it was usually felt that such a sintered briquette always had to be rather porous and of low tensile strength, and that consequently it was necessary to provide a reinforcing backing of a stronger metal, and this was acco'mplisheed by conducting the sintering step with the briquette held by pressure against a clean and properly prepared surface of a backing member as of steel. In the past, the necessity of pressing the powder to form the briquette, and of bonding the briquette during or after sintering by the application of pressure, tended to limit the processes as a practical matter to the production of articles of flat configuration. For one thing, it is difficult to briquette the powder to a curved shape and avoid uneven pressure and density, and subsequent cracking. On the other hand, it is not diflicult to press in the flat. Bonding is also simple when the members are flat. Since it is frequently desirable to produce long, i.e. 13 long, contrasted with or A" thick, sintered metallic containing material articles of curved form, for example so they can be used for brake shoes adapted to engage a cylindrical or conical surface, it has been known to use a bending press and suitable dies. It has also been known, as fully described and claimed in Tower and Lowey Patent 2,446,891, issued August 10, 1948, to utilize a method of bending to a predetermined curvature by what might be termed roll-bending, comprising the steps of applying pressure to laterally extending areas of a bi-metallic article successively and progressively along the length of the article, and controlling the amount of pressure (radial pressure then being contemplated) so as to elongate more plastic facing to a sufficiently greater extent than a less plastic backing member to bend the article to the predetermined curvature and produce a curved article having an outer more plastic face substantially free from cracks. In the case of thick truck brake blocks of too large dimensions and/or too great a curvature to press directly, and too thick to roll bend, it has also been known, as disclosed and claimed in copending application Serial No. 390,178, now Patent No. 2,873,517, to make up an article by first flat compacting, and then cutting arcuate curves from the flat compact, and then assembling the arcuate curves in flat side by flat side relation and then pressing in the direction of the curvature to bind them to each other and against a backing.

None of these prior art practices have been satisfactory for all applications. Unbacked material can not be formed by any of the prior methods, for example -roll bending of a uni-metallic compact of pressed powders without backing will lead to failure .to bend at all and with :the roll bending techniques applied to bi-metallic .articles one roll sometimes indents into the sintered or atent Q F 2,946,369 1 Patented July 2 60 friction material to cause localized stretching through oblique shear planes and subsequent cracking. And even if the materials are not too thick to press to a curved shape, it is often too expensive to provide the dies to do so. Making up -a flat compact first, and then cutting it into arcuate segments later assembled into side by side relation is often found uneconomical, particularly in view of the present invention.

It is therefore an object of the present invention to provide an improved method by which sintered facing material articles, with or without a backing material, may be readily and rapidly bent, curved, or otherwise formed to desired curvature without injuring or cracking the facing.

Other objects and advantages will become apparent and the invention may be better understood from consideration of the following description taken in connection with the accompanying drawing, in which, by way of example:

Fig. 1 is a plan view of a flat bi-metallic blank to be bent to curved shape;

Fig. 2 is a side elevation of the blank of Fig. 1;

Fig. 3 is a vertical section on line 3-3 of Fig. 2;

Fig. 4 is a diagrammatic plan view of a machine useful for forming the blank of Figs. 1-3;

Fig. 5 is a perspective view of a push bender useful for bending sintered predominately metallic articles according to the invention.

Referring to Figs. :1-3, which, for clarity, are not to scale, I have illustrated a fiat metallic blank 11 comprising a backing member 12 of solid metal such as steel, to which is integrally bonded a sintered facing 13 of originally powdered materials including at least one metal. The bi-metallic blank 11 may be to A thick by 2 wide by 13" long, thus many times as long as it is thick, and may be formed in any suitable manner, but I prefer to construct it in the manner described in Wellmans US. Patent No. 2,178,527, issued October 31, 1939. Generally speaking, the sintered facing 13 comprises a pressed and sintered mixture of one or more metal powders to which minor amounts of one or more non-metallic substances are added. In connection with the present invention good results have been obtained using a two component mix of (by weight) of iron powder and 15% of graphite, and good results .have also :been obtained using a copper base mix comprising 7 1% copper, 8.5% iron, 5% tin, 1% lead, 5% silica, 4.5% graphite, and 5% molybdenum disulfide. The powdered mixture is pressed under a pressure of about eleven tons per square inch to form a flat briquette, which may then .be clamped against a clean and suitably prepared face of the metal backing member 12 and the whole heated to a temperature of from 1200-1800 F. for a suflicient length of time to sinter the metal powders together and to cause them to integrally bond to the backing member.

Broadly speaking, the present invention relates to methods for rapidly and smoothly bending either the flat blank shown in Figs. 13, or a sintered material article without a backing, so that its facing will not crack whether on the finally outer convex or inner concave surface of the member. The invention has its basis in .my discovery that by forcing lengthwise against a restraint, which places the neutral axis of bending outside the piece and away from the radius of bend and puts all the material in compression, such cracking can be avoided.

As one suitable means .of obtaining this all-over compression, I have discovered that it is .possible to use a free-revolving roller and an opposed .curved die between which the blank is pushed. In Fig. 4 -l have diagrammatically illustrated apparatus of this type comprising a roller 20 and a correspondingly curved pressure block die 21 between the two of which the bimetallic blank is pushed. In this illustration the apparatus is provided with a hydraulic ram cylinder 22 having a piston 23 actuating a piston rod 24, clevis block 25 and an ejector or pusher bar 26 with the latter operating through. a .slot 27 in a main base plate 28 to push thestock (such -as"11 of Fig. 1) between the roller 20, which is free to revolve, and the pressure block 21. By sutably. selecting the diameter of the roller, the width of gap (to provide friction and/ or compression restraint), and the pressure applied by the ejector, it is possible to bend the bi-metallic blank to an accurate predetermined curvature in a very short period of time, and as successive fiat blanks 11. are introduced in the slot, for example by hand one at a time with each retraction of the pusher bar 26, arcuate shaped pieces are made to hop out of the machine as shown at 11, and when the run is finished it is an easy matter to remove the last piece 11 left in the machine by releasing the radial pressure imposed by the die with respect to the roller.

If desired, slot 27 may be made adjustable widthwise to accommodate different thickness of stock 11' as by providing a guide bar 29 made transversely adjustable as it slides along pins 30 as determined by a spring biased bolt 31. The roller 20 and die 21 may also be changed to provide a different size or radii of arcuate gap and some means (not shown) may be also provided for sliding guide bar 29 lengthwise so as to leave a minimum of unsupported space between it and the new roller 20. When different thicknesses of stock are to be run on a single machine, it is desirable to vary the pusher ejector width as by replacing part 26 with another part of different size so that the ejector width will always be about the same size as or slightly smaller than the stock being run.

Other suitable apparatus is shown in more detail in the perspective view of Fig. in which like parts are like numbered as before and there is also shown a handwheel 51 for advancing a screw 52 through a screw block 53 which is fixed with respect to the main base 26. Ad-

Vance or retraction of the screw causes corresponding movement of a main mounting plate 54 slidable with respect to a dovetail block 55 fixed with respect to the base 28 and provided with a dovetail slot mating with a dovetail 56 on the mounting plate 54.

Pressure block 21 is secured for back and forth movement with plate 54, as by the tabs 57, providing easy adjustability to provide different pressures and, to some extent, to accommodate different size work. Thus the hand wheel provides vennier adjustability to accommodate whatever thickness of stock might be desired to be run and, more importantly, to adjust the width of the arcuate gap with respect to original thickness of stock in the fiat thereby to regulate the pressure imposed during the bending. To facilitate runs for stock of different size and/or to be curved to different radii the roller 20 is made removable to be interchanged with one of a different size while the pressure block is also arranged to be changeable.

Secured to rotate with screw 52 is a sprocket 58 for driving an endless chain 59. Near the other end of the base 28, chain 59 drives a sprocket 60 secured to rotate a screw 61' to advance or retract it through a screw block 62 and thereby cause corresponding movement of base 54 and supports including a front guide bar support 63 which in turn moves a front ejector support 64. An assembly of jointly movable parts includes plate 54, front and rear ejector supports 64, 7641', ejector 26, clevis 25, rod 24, a cylinder support bracket 65, and cylinder 22, all moving with respect to the main base 28.

Front and rear ejector supports 64, 641' may each be U-shaped to provide a central clearance for passage of the clevis 25 (compare Fig. 4, where ejector and clevis and piston rod are full out, with Fig. 5, where they are retracted) while at top and bottom the ejector supports are spaced apart to provide a clearance gap (preferably adjustable) to accommodate top and bottom portions of the ejector pusher bar 26.

Near the middle of the machine the front guide bar support 63 may be considered bolted to drive a spacer 66 and a front guide bar 67, fiat stock 11 (if any) and rear guide bar 29 adjustably held in this case by being spring biased from a rear guide bar support 69 which is, preferably, adjustably secured with respect to sliding base plate 54.

In operation the operates the ejector responsive to introduction of pressure through one or the other of hydraulic feed and exhaust conduits 7273, and this causes compression and bending of any article in the die and ejection of any article immediately previously therein. The slot clearance at the arc gap, where the piece 11" is shown in Fig. 4, is adjusted slightly smaller than the original thickness of the flat stock, particularly where sintered friction material or ultimate wear face is to be on the outside of the curvature, for otherwise the friction material might be stretched and crack. Machinery and process according to the invention will be operative to produce desirable pieces in a single pass whereas with prior roll bender techniques it took many passes.

I am not too positive as to the actual theory of operation, but it is my opinion that placing the material in initial lengthwise compression, as by forcing lengthwise against restraint on the sides and opposite end, permits, at the start of bending, placing the neutral axis of bending outside the sintered powdered material. and on the side opposite the bending fulcrum so that all the sintered material is in compression and cracking thereof is avoided. Where a solid metal backing is used, it is believed desirable but not necessary to have the steel backing in compression by placing the neutral axis of bending also outside of it and on the side opposite the fulcrum.

Particularly with a high graphite content of friction material it has been found that prior roll bender techniques tended to crack the material and because of shear plane stresses render it useless. Processes according to the present invention prevent such cracking by keeping all. material being processed in compression without any shear planes, and there are further advantages over roll bending in that a product may be made without backing and final product may be formed right up to its end to a true radius all around without leaving a flat on either the leading or trailing end. In the case of bimetallic articles (as already described and with solid metal backing and sintered material facing) shearing at the bond line is not likely to occur using the process of the invention regardless of whether the friction material is to be ultimately on the inside or on the outside. For all the above reasons there is achieved a new design freedom because any friction material mix can be used and in fact, solely friction material without any backing has been successfully processed according to the longitudinal force bending method of the invention which puts the processed piece under compression without tension or stretching and without expensive'tooling.

There is thus provided a method of the type described capable of meeting the object above set forth.

One aspect of the method of the invention is that all easily tearable parts of a piece to be formed are kept in compression. Compression is placed on the piece even prior to the forming process and is kept on critical portions of the piece during the forming. In other known methods, there are some regions not in compression so that shear and tensile forces may bring about fracture.

While I have illustrated and described particular embodiments, various modifications may obviously be made without departing from the true spirit and scope of the invention, which I intend to define in the appended claim. 1

I claim:

The method of bending a sintered compact of powdered materials arranged in a fiat strip, which method References Cited in the file of this patent UNITED STATES PATENTS Lignian June 10, 1941 Scully June 5, 1951 Redmon June 12, 1956 FOREIGN PATENTS Great Britain Nov. 9, 1936 Great Britain Feb. 6, 1952

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