US2342772A - Stripping apparatus - Google Patents

Description

Feb. 29, 1944. s. K. WELLMAN STRIPPING APPARATUS Original Filed Jan. 9, 1939 3 Sheets-Sheet 1 A v m H 8% D2 w 5 4 M m 2 m. B z w w 3 6 m n v 6 B 3 Fig-1 Feb. 29, 1944. ELLMAN 2,342,772

STRIPPING APPARATUS Original Filed Jan. 9, 1939 3 Sheets-Sheet 3 A Tree/vs).

Patented Feb. 29,1944

STRIPPING APPARATUS Samuel K. Wellman, Cleveland Heights, Ohio, as- V signor to The S. K. Wellman Company, Cleve land, Ohio, a corporation of Ohio Original application January 9, 1939, Serial No.

249,899. Divided and this application Septemoassr. In Great Britain her 4, 1941, Serial No.

January 9, 1940 4 Claims.

This invention relates to apparatus for making bodies of compacted powdered .material or of mixtures of such materials and is especially ap plicable to the production from metal powders, or mixtures of powdered metal and other powdered materials, of such articles as antifriction bearing members and friction brake and clutch linings or facings.

This application is a division of application Serial No. 249,899, filed January 9,- 1939 (Patent No. 2,259,094). a

In the production of such bodies of compacted powdered material and especially .of materials including metals, the body, after being formed,

is subjected to a heat treatment to effect sintering for the purpose of securing increased strength and other desirable properties. Prior tosuch sintering, the bodies of compacted material, while a strong enough to permit ordinary handling, are relatively weak and frangible as compared with the sintered product.

In the usual manufacturing practice, the body is formed by compressing the constituent powdered materials in the cavity of a suitable die structure and then removing from the die the article thus formed. The compressed body is sufficiently weak and friable to be easily brokenor abraded while it is being forced from the cavity of the die. The breakage of such bodies at this stage of manufacture has constituted a very serious difllculty and-the primary object of the present invention is to provide a method by which bodies may be formed of compressed pow dered materials and withdrawn from the mold or die without .the customary breakage which has usually accompanied such removal.

which lie between the confined peripheries. This distortion, in the case of disk shaped bodies having their peripheries confined, has been observed to take the form of bulges, wrinkles, cracks, etc., while in a few instances where the stresses were more uniformly distributed through the material,

,the body has been observed to dish outwardly, the

center portion moving out of the plane of the edges to form a shallow cone.

Under some conditions, however, the internal stresses set up by this expansion tendency may not be relieved by distortion, due usually to the application of external forces which oppose and prevent the distortion. However, when these opposing forc'es are eventually removed, the, ex-

pansion occurs with the consequent formation of the above mentioned defects. For example, when A further object of my invention is to provide V apparatuswh'ich, is especially suitable for carrying out the above method.

My invention has grown out of the discovery that the ,objectionable breakageabove referred to is due in large measure tothe tendency of the Q bodies of compacted powdered material to expand in size following the removal of the compacting pressure- The amount of such expansion on each dimension is approximately proportional to the magnitude of the dimension. While such expansion is relatively slight andof little significance in the case of small dimensions, when dimensions of greater magnitude are involved, the

expansion is proportionately greater and may be very considerable. For example, in the case of a facing or a clutch'plate or ring compacted in a 12" diameter' die, an expansion of nearly on the diameter has been observed.

I have found that if the expansion of such bodies is permitted to occur while the body is yet partially confined by the walls of the die, internal stresses are created which tend to produce distortion of those portions of the body a plurality of stacked disc-shaped compressed bodies are removed from the compression die by pushing them out-of one end. of the die, the axial pressure needed to so push them out may be sufiicient to prevent any dishing, warpin or bulging of the bodies while they are still within the die, but when a disk has been pushed to the open end so that a portion of it extends beyond the die, that portion which is no longer confined by the walls of the die will tend to expand, while the balance of the disk is still prevented by the diefrom such expansion. The result is that the edges of the dlskcrack, 'spall, or crumble. This has been the customary defect observed in a large proportion of the compressed bodies which have been removed from the compression die in this manner.- Furthermore it is a defect which has seriously hindered commercial-operations, since breaking or chipping ofthe edge' ordinaribr prevents further use of the article, especially where the die cavity has been designed to produce a body which is very close to the size of the element desired in the finished product;

For this reason, the defect has caused-much waste of time, labor, and material, and 'conse-' quently has created a serious problem which heretofore has not been solved.

Now I have discovered, however, .that the exthat it exerts a component which is perpendicu 1 lar to the direction in which the major expansion of the compressed body tends to occur.

My improved method of manufacture is based upon the discovery last referred to and I have devised apparatus especiallx. adapted for manufeature by the improved method. Several forms of this apparatus are shown in the accompanying drawings and reference is now made to them since explanation of the apparatus at this point gill aid in the further explanation of the inven- In the drawings, Fig. l is a vertical section taken through a hydraulic press, and showing a compression die mounted in operative position thereon and holding a charge of .the powdered material to be compressed.

Fig. 2 is a similar cross-section showing the side walls of the die stripped from around the compressed articles.

Fig. 3 is a fragmentary vertical section showing a stripping device in which rubber'padsare compressed against the charge during the stripping operation.

Figs. 4 and 5 are plan and elevation, respectively, of a type multipart die from which compressed articles may be removed in accord ance with the invention disclosed herein, while 6 is an elevation of one of the halves of the mo d.

Fig. 7 is a perspective view of a clamp suitable for-use with the die of Figs. 4, and 6.

Fig-8 is an expanded isometric view of a modiflcation or the mold shown in Figs. 4-6, in which the base or the mold is made integral with one of the side wall sections.

Since a variety of shapes may be formed with the apparatus shown inthe drawings, by providing an appropriately shaped die, it will be understood thatthe specific dies shown in the drawings are used. merely for purposes of illustration.

In the figures, in which like parts bear like numerals. l is the. press main-frame joining the stationary press head 2 with base 3. Base 3 supports stationary piston 4 on which is guided main hydraulic cylinder 5. 0n the surface of cylinder 5 rests stripping head designated'generally by the numeral 6 which is suitably centered thereon, and secured by appropriate means those skilled in the art. Positioned within the stripping head 6 are a plurality ,of pistons l and 8, 8 capable of being raised by hydraulic pressure, or otherwise, in the corresponding cylinders '9 and III, III, respectively, each being surrounded :by a compression spring 32.

A forming die composed of outer ring H and core member I 3 spaced from each other by a botwell known to tom compression ring l6 to form an annular die chamber I2, is so positioned on the surface of l stripping head 3 that the outermost pistons 8, 3'

may, when raised, contact the outer die ring I! without entering die chamber l2; and so-that central piston 1 may, when raised, contact core member l3. A stationary compression ram I1 is rigidly secured to press head 2, as through bar 30, screws 3| and 32, and is so shaped as to enter the die cavity II when main cylinder 5 is raised toward press head 2.

. Chamber I2 is partially filled with powdered metal mixture ll distributed alternately between spacer rings IS, the whole pile being closed top and bottom with the heavy compression rings l8 and I6. It will be obvious, of course, that a plurality of such layers otpowder may be included. or a single layer alone. The number which may be so formed depends on the travel of the press,

the thickness or the individual layers making up thepile, the compressibility of the powder, the length of the die, and the frictional characteristics of the powder against the die walls.

Hydraulic fluid under pressure is admitted from any suitable pump or pressure reservoir through conduit A to main valve B and then through conduit l8 into chamber I 9 which is formed between piston 4' and cyinder 5. An opening 20 in cylinder 5 permits hydraulic fluid to flow from chamber I9 through conduit 2| as far as valve 22 when the latter is closed. When it is opened the fluid may then pass through conduit 23 into chambers 24 beneath pistons 1 and 8, 8,-where it may act thereon to force each of them upwardly toward press head 2.

It will, of course, be apparent that instead of supplying hydraulic fluid to valve 22 from cham- 15 her ",it may equally well be supplied directly from main conduit A or from a separate pump or reservoir. vIn either of these constructions, however, flexible high pressure connections must be used in order to accommodate the vertical movement of cylinder 5 with its attached stripping head 6. The arrangement shown in Figs. 1 and 2 therefore has the advantage that such connections are avoided.

Pistons I, l and 8, 8 are each provided with the usual gaskets 25 and 25a, respectively, which seal the piston and cylinder assemblies against leakage of the hydraulic fluid. The gaskets are suitably reinforced by retainer plates 26 and 26a which are in turn secured to the pistons.

Die members H and I3 and ram ll are pro- Havingnow described one form of apparatus which may be used, its operation will be explained in terms of a specific application. The method of operation and the apparatus are applicable to a wide variety of shapes and compositions, but the production of friction clutch rings will serve to illustrate the operations involved.

' In preparing the press for operation, an appropriate stripping head is mounted on the main cylinder, the stripping head being chosen so that its pistons l and 8, 3 are properly spaced to fit the die members II and 13 which are to be used. A proper stationary ram I1 is fltted to the press head. Cylinder 5 and pistons I and 8, 8 are then lowered by opening valves B and 22, respectively, and when the latter pistons are in their lowermost positions, valve 22 is closed.

The press is then ready for use.

posed. for example, of the following ingredienmz Percent cu 70.9 Pb 10.9 Sn 6.3 Graphite 7.4 Air-blown silica 4.5

The charge is poured into chamber l2 and there thoroughly distributed upon the surface of ring it so as to form a .thin layer of uniform thickness. A spacer ring li, conforming precisely to the shape and dimensions of cavity l2, and having been ground so as to have plane parallel surfaces and uniform thickness throughout, is then admitted into chamber t2 and gently eased into position ontop of the powder I peated.

layer. A second weighed charge is then added, and distributed, and the above procedure re- After a suitable number of charges have been added, the top compression ring I6 is inserted on top of the last powder layer. The charges are then ready to be compacted inthe press.

The charged die'assembly is now transported to the press and is positioned on the surface of stripping head 6, its position thereon being adjusted so that cavity I2 is in alignment'with ram 11, and so that holes 21, 28 and 23 are in alignment in the same vertical plane. Valve B is opened slightly to admit hydraulic fluid into chamber ill under main cylinder 5 whereupon the die assembly is forced upwardly until ram l'l enters the compression cavity and contacts upper compression ring it. The movement is' made slow so that air in the cavity and in the charge may be permitted toescape without disturbing the layers of powder. Main valve B is then opened wide to subject the charge to full' compression pressure. For the above composition, suitable full pressure has been found to be about 22,000 pounds per square inch It will be appreciated, of course, that this value is merely illustrative, since with any given composition, the pressure may be varied widely depending on the properties which are desired in the sintered article. After this predetermined pressure has been attained, and the layers of powder have been compacted the desired amount, valve 22 is cracked to allow hydraulic fluid to escape into cylinders 9 and l0, Ill. The valve is manipulated in such manner that the pressure exerted on the charge by the main cylinder is maintained not much'below the desired compression pressure, i. e., 22,000 pounds per square inch. The fluid permitted to escape from chamber l3 through valve 22 gradually accumulates in cylinders 9 and I0 and forces pistons I and 8, 3 upwardly against the bases of die members II and I3, respectively. As the pressure under these cylinders gradually increases, die members II and i3 are forced upwardly and away from the charge l4, l4 until the full charge is exposed to view. It should be particularly noted at this point that with proper manipulation of valves B and 22 the charge will have been. held under. full compression pressure even though ,fluid has been withdrawn from beneath the main cylinder and passed into the stripping head. When the die members ll and-i3 have reached such a height above the charge that holes 21, 28 and 29 are in axial alignment, a pin 34 is inserted through them. -This condition is shown in Fig. 2. The main hydraulic pump isnow stopped and .with valve' B open, the fluid in chambers l9 and 24 is permitted to be forced out by the springs 33 surrounding pistons I and 8, 8 and by the weight carried by cylinder 5, until these parts are again in their normal positions. Die members H and i3 remain suspended around ram I! from pin 34, while the charge in cavity l3 remains on the surface of stripping head i and is lowered away from ram l1.

The charge is now free of pressure and may be removed from the press. The compressed bodies are separated from separator rings l and after being brushed free from any adhering loose powder, are ready to-be sintered or othere I wise treated. I

Returning again to the press, cylinder 5 is now raised until stripping head 3 again contacts die members H and i3 and supports them. The

pin 34 which was passed through holes 21, 28

and 29 is now withdrawn and cylinder 3 lowered, whereupon die members H and I3 ,become separated from ram I1 and are again ready for assembly in preparation for another charge.

In the above described procedure, while the die side walls H and ii are being stripped from the charge the compressed bodies l4 are maintained under sufliciently high pressure at right angles to their faces and preferably out to theirouter peripheries, to insure that the internal expansive stresses in the compressed bodies are counteracted sufllciently by the frictional forces thus established to prevent expansion of said bodies when they are moved out of engagement with the restraining die walls. In otherwords, no expansion of the compressed bodies is permitted until they have been entirely removed from contact with the restraining side walls of the die and, consequently, when the pressure upon the faces of the compressed bodies is later removed and radial expansion of said bodies is permitted, there is nothing to restrain such expansion in any part of the compressed body so that there is no tendency to fracture the edge parts thereof in the manner which has characterized the prior methods of manufacture. The intensity of themessure needed to secure this result in any particular case will depend upon the various factors indicated in the foregoing description. The remarkable restraining effect of the pressure to which the faces of the disk-shaped bodies are subjected is visually demonstrated in a striking manner in the procedure which has been described, for as the said pressure is released the I compressed disks may be seen to expand radially beyond rings l5 and i6. Furthermore, by the simple expedient of holding the compressed bodies under pressure after the side walls of the die have been stripped from them, the expansion of the compressed bodies can be delayed or prevented for anydesired length of time.

It will be understood that the stripping head may take a variety of forms since its pistons must necessarily be placed in conformity with the dies which are to be used on it. Furthermore, it is not necessary that hydraulic pressure be used to strip the dies. For example, one form ofstripping head which may be used is shown in Fig. 3,

in which the pressure applied on the compressed bodies is obtained by compressing the rubber pad 35, while the die members are pushed upwardly by fingers 38. The operation of this device is obvious. After the charge 31 has been compressed, but before main cylinder 5 has been lowered, books 38 are/attached to the die assembly and screws 39 inserted into ring Iia from die member 40. The main cylinder is then lowered. and the stripping head 45 placed thereon. The cylinder is now again raised, and enough rubber pads inserted under the charge that appreciable "compression of them will occurbei'o're fingers 36 contact die member 40. The cylinder is now raised until fingers 36 touch and support die 40.

Screws 33 are removed, and hooks 38 loosened. Now on raising the cylinder further, die 40 is forced upward and stripped from around the charge, while rubber pads 35 compress more and more against the charge. To'complete the operation, die 40 is now hooked in its uppermost position. the cylinder lowered to relieve the pres sure on the charge, and the charge removed.

While this type of stripping device accomplishes the desired results, its use requires many ress operations which consume much time. The

hydraulic stripper, on the other-hand, is easier to use and is much faster. Because of these advantages the hydraulic device is to be preferred for commercial operations.

In connection with. the use of rubber pads for stripping, it is to be noted that while the compressed charge is hooked up against the ram, and before the stripper has'been raised to exert pressure on the charge, the charge may be under very little pressure. Indeed the only pressure acting on it may be due to the weight of the suspended ram. Even so, however, no damage to the compressed bodies occurs during stripping since pressure is again applied to them before the die is stripped off.

In connection withstripping it is to be pointed out further that the pressure which need be exerted against the charge during stripping is small. Indeed, it need only be the value obtained by dividing the value of internal stress in the compressed body by the coefficient of friction between the body and the material of the separator. Obviously, if a separator'material is used which has a low coefiicient of friction with the body, the pressure needed to prevent expansion may be relatively large, while if the separator material against the compressed body has a large coeflicient of friction, the pressure will be proportionately small. In practice, using high carbon steel separators with the powder composition given above, pressure as low as 1000 pounds per square inch can be used.

The method of this invention may also be practiced without using any sort' of stripping head, as for instance, with multipart or sectional dies such as are represented by the die assembly shown in Figs. 4, ,5, 6 and 8. Figures 5 5 and 6 show a sectional die comprising a plurality of sections 4| and 42 adapted to fit together to form the desired shape of compression cavity. Each section carries a number of lugs 43 so positioned as to cooperate with similar lugs on adjacent sections, whereby a clamp 44 may be tightl fitted therearound to hold the sections together. Such a die assembly may have the bottom separate from the sides as at 46 in Figs. 4 and 5, or integral with one side wall as in the modified construction shown in Fig. 8, where the die comprises sections 10 fixed upper compression member, and a lower shell structure of the mold assembly to-move the compression member movable vertically toward and away from said fixed member, said lower member serving to support the shell structure of said mold assembly while the powdered material is being compressed therein; stripping means carried by said movable compression member for displacing said shell structure parallel to the relative telescoping movement of the plunger and shell structure out of contact with the peripheral Ma and 4211 with clamp lugs 43a and section 42a is formed with a bottom wall section 46a.

When using this type of die shown in Figs. 4 to 8, the ram is forced into the open upper end of the die cavity to compress the charge. After the charge has been compressed, the compression pressure may be held at its maximum value or reduced to that pressure which will just prevent expansion. "I'heclamps 44 may then be knocked oil of the lugs 43 or 43a, and one of the die sections, such as 4| or Ha, removed or stripped away. The pressure may then be fully released and the compressed bodies removed. Obviously, when the die sections are of irregular shape, the portion or portions of the die which must be removed as described will be such as to permit the compressed body to expand freely when the pressure is released.

It will be understood thatthe various modifications described above have been chosen merely to illustrate the invention, and should not be regarded in allmiting sense since other modifications are possible within the bounds oi'the following claims, which indicate the scope of the invention.

' What I claim is:

1. Apparatus for making a coherent body of 7 boundaries of said powdered material after the latter has been compacted and while it is maintained under compression between said plunger and said movable compression member.

2. Apparatus as claimed in claim 1 wherein said shell structure comprises an outer shell and an inner shell cooperating with each other to form an annular compression chamber, and wherein said plunger is annular in shape.

3. Apparatus as claimed in claim 1 wherein said lower compression member comprises one element ofa main hydraulic piston-and-cylinder assembly, and wherein said stripping means comprise an hydraulic piston-and-cylinder assembly which is actuated hydraulically by fiuid admitted thereto from the main piston-and-cylinder assembly. Y

4. Apparatus for making a coherent body of compacted powdered material, said apparatus comprising the combination of: a telescoping mold assembly which includes an annular plunger and a shell structure comprising concentric outer and inner shells cooperating with each other to form an annular compression chamber,

, said plunger and shell structure being adapted to cooperate to form a compression chamber for powdered material; means for forcing said plunger into said compression chamber to compress powdered material confined in said chamber and maintaining it under. compression, said means comprising a fixed upper compression member, and a lower compression member movable vertically toward a'nd away from said fixed member, said lower member serving to support .the shell structure of said mold assembly while the powdered material is being compressed therein; stripping means carried by said movable compression member for dlsplacmg said shell structure parallel to the relative telescopingmovement oi. the plunger and shell structure of the mold assembly to move the shell structure out of contact with the peripheral boundaries of said powdered material alter the latter has been compacted and while it is maintained under compression between said plungeran'd said movable compression memher, said stripping means comprising three piston and cylinder assemblies disposed with their axes in a plane which includes the axis of the said shells, said piston and cylinder assemblies being spaced apart sufilcientlyto elfect the displacement of the inner and outer shells of the mold assembly without penetrating the annular compression chamber thereof.

SAMUELKWE JMN,

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