WO1997034089A1

WO1997034089A1 - Elastomeric spring

Info

Publication number: WO1997034089A1
Application number: PCT/US1996/002258
Authority: WO
Inventors: Erich D. Fidziukiewicz
Original assignee: Lamina, Inc.
Priority date: 1996-03-13
Filing date: 1996-03-13
Publication date: 1997-09-18
Also published as: AU5296696A

Abstract

An elastomeric die spring (12) has a fibre reinforced elastomeric cylindrical block (14) enclosed within a Neoprene sheath (16) with heat conductive retainers (24) and (26) overlying opposite ends of the block to act as heat sinks. Each retainer has a tubular portion (44, 46) pressfitted within a bore (18) of the block with a precompression member (74) extending between the retainers and holding them against the ends of the block (14) to precompress it between 7 % and 12 % of its free length. The construction permits compression of the block up to 40 % of its free length. The retainers serve as heat sinks for heat developed within the block during repetitive compressions and expansions in the operation of the stamping press in which the spring is used.

Description

ELASTOMERIC SPRING

Technical Field

This invention relates to elastomeric springs, and particularly to an elastomeric die spring.

Background ofthe Invention

Because of the repetitive action of a stamping press, and the tendency of elastomeric springs to break down under repetitive cycling, elastomeric springs have not been successfully used as die springs, except under essentially static loading such as storage springs placed between the press platens to hold them apart. However, elastomeric springs have advantages over steel springs which would make them desirable for use in stamping presses if their life expectancy could be improved. For example, they will maintain the same force after a prolonged period of stress, while a steel spring will fade. The force of an elastomeric spring for its size is greater than that of a steel spring. Nitrogen springs are now commonly used in presses. Such springs are relatively expensive. If an elastomeric spring with an equivalent life and a lower cost could be developed, it should displace many if not most of the nitrogen die spring applications.

However, there are several problems with elastomeric springs which have made them unsuitable for the sever service of die springs. When they are compressed, they bulge, and therefor the cavity in which they are received may not allow for this and inhibit proper operation of the spring. If the proportion of the length of the spring to its diameter is too great, a "banana" effect occurs, ie. the spring will go out of column. In addition, the rubber will take a "set" in which the free length will be reduced up to 8%-10%, depending upon its diameter, over the life of the spring. As a result, a member to be moved by the spring may not be returned to the proper point and cause a malfunction of the press. An elastomeric spring generates heat during use which causes the rubber to continue to cure which changes its characteristics. Heat is the biggest problem in using e. asto eric springs as die springs. Also, when rubber is exposed to oil it is quickly destroyed, and oil is used in presses and comes into contact with all parts of the press.

A search of the prior patent art uncovered the following U.S. Patents: 1,689,883; 3,120,382; 3,263,985; 3,342,506; 3,434,708; 3,677,535; 3,892,398; 4,133,392; 4,573,842; 4,623,162; 4,688,777; 5,240,269.

None of these patents addresses the problems of utilizing elastomeric springs as die springs subjected to sustained and repetitive pounding during press operation. For example, none are described as useful as die springs. Rather, they are for the most part, concerned with vehicle suspension systems, where the loading is much lighter and the spring is not for long periods repetitively compressed to the maximum where heat generation becomes a problem. Typically of the patents, 5,240,269 is described in the context of a bicycle spring and 3,434,708 is a vehicle spring for accommodating variable loads. Summary of the Invention

The elastomeric spring disclosed herein overcomes the above disadvantages and enables the use of elastomeric springs as die springs in presses. The springs are much less costly than nitrogen springs, will not take a set, and will maintain the same force over their lifetimes.

The design of the spring is such that the compression is limited to not more than about 40% of the free length of the elastomer and as a result the working of the spring is controlled. This will reduce the heat generated in the spring. If too much compression is asked of the spring the structure will bottom out preventing over stressing.

The elastomeric block is a fibre belted spring of the type disclosed in U.S. Patent 3,982,398 and sold by Firestone Tire and Rubber Company as a "Marshmallow" spring. It is mounted between retainers which are so designed and arranged that heat generated by working of the spring is conducted away by the heat sink action of the retainers, and the retainers themselves are designed to conduct heat to the press in which the die springs are used. By eliminating the build-up of heat in the springs their life expectancy is greatly increased and their performance in reliable.

The "banana" effect is eliminated by designing the springs such that the length to diameter is kept below a critical ratio which has been discovered to be on the order of 2.5 (or less) to 1. The springs are designed as units and will be offered as such to press manufacturers and users. They may be stacked to increase their travel and yet prevent the "banana" effect.

To prevent the elastomer from taking a set, it is preloaded on the order of from 7%-10%, with the preferred preloading being 10%, ie. the fibre belted block is pre-compressed 10% of its free length. This then leaves 30% for working travel or compression of the spring.

To prevent attack of the spring by oil, the retainers at opposite ends of the elastomeric block fit tightly against the ends of the block and in a modification of the invention 0-rings may be provided to seal against the entry of oil between the retainers and the block. A neoprene wrapping encircles the block to keep oil away from the block between the retainers.

Other advantages and details of construction will be found in the following description and the drawings.

Brief Description Of The Drawings

Fig. 1 is a perspective view of an elastomeric spring embodying the invention and suitable for use as a die spring;

Fig.2 is a top end view of the structure of

Fig. 1;

Fig. 3 is a cross-sectional view taken on the line 3-3 of Fig. 2;

Fig. 4 shows the spring nearly fully compressed;

Fig. 5 is an outside side elevation of the elastomeric spring of this invention showing an O-ring for sealing against entry of oil between the retainers and the elastomeric block;

Fig. 6 is a detail view taken of the area designated in circle 6 of Fig. 5;

Fig.7 shows two of the spring units stacked together;

Fig. 8 shows two spring units in a stack of three or more units stacked together where the retainer flanges are welded together; and

Fig. 9 is a cross-sectional view taken on the line 9-9 of Fig. 7. - 6 -

Brief Description of Preferred Embodiment

The elastomeric springs of this invention are intended to be provided as modular units so that height, amount of compression and spring rate can be varied by selecting the desired unit and by stacking units on end.

A typical unit embodying the invention is shown in Fig.

1 at 12. It comprises a cylindrical fibre reinforced elastomeric block 14 of a construction typically shown in U.S. Patent 3,892,398, which is incorporated herein by reference. The exterior of the block is covered by a Neoprene rubber sheath 16 (see Fig. 3) to prevent contamination of the cylindrical surface of the elastomeric block by oil. The block has a coaxial bore 18 with flat and smooth opposite ends 20 and 22 disposed perpendicular to the bore 18. Overlying opposite ends of the block 14 are a pair of retainers 24 and 26 of good heat conductive material. Retainer 24 has a circular flange 28 while retainer 26 has a flange 30. The flanges are of equal diameters and have parallel opposite faces, 32 and 34 for retainer 24, and 36 and 38 for retainer 26. These faces may extend all the way to the circumferential edges 40 and 42 except for small bevels to eliminate sharp edges.

The diameter of the faces 20 and 22 is equal to the diameter of the block throughout its length when in an uncompressed condition. The diameter D-l of each flange (see Fig. 2) is at least equal to the diameter D-

2 of the block when the same is under its maximum compression as shown in Fig. 4, and of course greater than the diameter D-3 when the block is preloaded as shown in Fig. 3. This will insure that the spring will not be placed in a cylindrical opening in the body or a part of a stamping press which is diametrically too small and thereby insures that the spring will not be inadvertently confined upon compression, changing its spring rate or otherwise affecting its operation.

Each retainer includes a tubular portion of good heat conductive material which is connected in heat conductive relation to the flange. Retainer 24 has a tubular portion 44 and retainer 46 a tubular portion 46. While these tubular portions may be formed of the same material as the flanges 24 and 26, they may formed of a different material and the flanges and tubular portions rigidly connected in any suitable fashion. In the drawings the flanges and tubular portions are shown as being integrally formed, and are preferably made by investment casting. The retainers are preferably formed of a material such as S-7 or 1117 steel. This will provide the requisite hardness, strength and heat conductivity. If desired the flanges 24 and 26 may be formed of S-7 steel and the tubular portions of 1117 steel. In either event the material must provide good heat conductivity and be capable of withstanding the pounding of the repetitive action of a stamping press. In some instances the flanges must bridge across grooves or slots in an abutting surface of the press, and therefor shear strength becomes important. The surfaces 32 and 38 are smooth and flat to abut closely against a mating surface of an adapter plate or a portion of the stamping press so that good heat transfer from the retainers to the press is accomplished. The retainer themselves comprise heat sinks for drawing heat generated in the block therefrom, and the flat and smooth faces 32 and 38 allow this heat to be bled off into the greater mass of the press. The tubular portion 44 of retainer 24 is longer than portion 46 of the opposite retainer and is provided with a counterbore 48 terminating at a shoulder 50 at the lower or inner end, and opening outwardly through the flange 28 at the upper end. At the inner end the counter bore opens into a reduced diameter bore 50 which extends through the inner end face 52 of the retainer. Adjacent the inner end of the retainer the tubular portion is chamfered as at 54 to facilitate press fitting of the tubular portion of the retainer into the block. As shown in Fig. 3, the retainer 24 has its tubular portion 44 pressed into the block 14 deforming outwardly the bore 18 adjacent the tubular portion to improve the heat transfer between the block and the retainer. This in-pressing of the retainer is continued until the face 34 of the flange 28 is in flush abutment with the end face 20 of the block and this also improves the heat transfer between the block and the retainer flange 28.

The other retainer 26 which overlies the opposite end of block 14 has a threaded counterbore 56 with a shoulder 58 at its inner end opening into a smaller threaded bore 60 which opens through an inner end face 62. A threaded spud 64 may be threaded into bore 56 and in turn into a threaded hole 66 in an adapter plate 68 for attaching the spring to a surface 70 of a press. The adapter plate 68 may be designed for retrofitting a press by substituting this elastomeric spring for a previously installed nitrogen spring. The adapter plate may be secured to the press by bolts 72. The adapter plate 68 and the press to which it is attached serve as a large heat sink for heat generated in the block 14 during compression. The inner end of retainer 26 is chamfered at 72 to facilitate press fitting the tubular portion 46 into the bore 18 of the block 14 for the reasons described for retainer 24.

A precompression member 74 in the form of a bolt having a head 76 at one end of a shank 77 and a reduced diameter threaded portion 78 at the opposite end, is received down through the counterbore 48 of the retainer 24 and threaded into the retainer 26. A shoulder 80 on the bolt surrounding the reduced diameter threaded end 78 limits the distance the bolt may be threaded into the retainer 26. The head 76 of the bolt may be provided with a tool receiving socket 79 for torquing the bolt into the retainer 26, the tool (not shown) being extended down though the counterbore 48 through the flange 28. The distance D-4 between the underside of the head 76 and the shoulder 80 determines the amount of precompression imposed on the elastomer block.

Desirably this precompression should be from 7%-l2% of the free length of the block, and preferably 10% of the free length. As the maximum compression which should be allowed on the block is 40%, the precompression of 10% will leave 30% for a working distance. In Fig. 4 there is shown a compression of the block 14 of 40% of the free length of the block. The maximum compression of the block is determined or limited by the abutment of the opposed end faces 52 and 62 at the inner ends of the tubular portions of retainers 24 and 26. In Fig.4 such end faces are shown closely approaching each other but still slightly spaced apart.

Because the ends of the block 14 are pressed tightly against the retainers 24 and 26, and the ends of the block are perpendicular to the bore and the cylindrical shape of the block, and are smooth, oil from the press should not normally be able to work its way into the interface therebetween. However, to increase the sealing action between the flanges of the retainers and the block, the modification shown in Figs. 5 and 6 may be employed. The flanges 280 and 300, which correspond for the most part to flanges 28 and 30, are provided with encircling lips 302 and 304, and O-rings 306 and 308 are disposed between the lips and the Neoprene sheath 16 on the block under a slight compression as a result of the precompression, and such O-rings prevent the entry of oil between the outer surface of the Neoprene surrounding the block and the lip on the flange.

In Figs. 7, 8 and 9 the springs are shown stacked. In Fig. 7 two of the spring units 120 and 122 which are of identical construction to that shown in Figs. 1-4, are placed end to end with the flanges 26 placed in abutment and with a spud 64 threaded thereinto as best shown in Fig. 9. Wrench engaging slots 82 may be provided in the edges of the flanges to facilitate tightening the spud. Where the spring units are to be stacked more than two high, the flanges of adjacent units may be welded together as at 84.

Claims

What Is Claimed Is:

1. An elastomeric die spring for cyclic use in a stamping press comprising, in combination: a cylindrical fibre reinforced elastomeric block having a co- axially extending hollow bore and flat opposite ends arranged perpendicularly to said bore,- a pair of retainers at opposite ends of the block; each retainer having a flange of heat conductive material having opposite flat parallel faces with one face of each flange abutting an end of said block and having a face width at least equal to the diameter of said block when the same is axially compressed to its maximum limit, and the other face of each flange adapted to abut in heat transfer relation a heat sink portion of a press in which the die spring is to be used; each retainer having a tubular portion of heat conductive material press fitted into said bore,- said tubular portions of the pair of retainers having inner ends disposed in opposed and spaced apart relation in the bore and outer ends connected in heat transfer relation with said flanges to conduct heat build-up in the fibre reinforced elastomeric block to said end flanges,- and an elongated pre-compression member extending axially within the bore through said tubular portions and between the retainers and cooperating therewith to urge the end flanges toward each other pre-compressing the block with the precompression member being axially slidable relative to at least one of the retainers.

2. The invention of claim 1 wherein said block has an uncompressed length not greater than about 2.5 times its diameter.

3. The invention of claim 1 wherein the space between the inner ends of the tubular portions is such that they will abut each other and prevent further compression when the block has been compressed a total of about 40% of its uncompressed length.

4. The invention defined by claim 1 wherein said pre-compression is between 7%-l2% of the uncompressed length of the block.

5. The invention defined by claim 1 wherein the said precompression is 10% of the uncompressed length of the block.

6. The invention defined by claim 1 wherein the flange of each retainer is formed of a harder metal than the tubular portion.

7. The invention defined by claim 1 wherein said block includes an oil resistant seal between the block and the flange of at least one of the retainers for preventing of ingress of oil between the flange and the abutting flat end of the block.

8. The invention defined by claim 7 wherein there is an oil resistant seal between the block and the flange of each retainer for preventing the ingress of oil between the flange and the abutting flat ends of the block.

9. The invention defined by claims 7 or 8 wherein the flange includes a peripheral lip upstanding from the flat face of the flange abutting the end of the block and encircling the block, and an O-ring disposed between the lip and the block to seal against the ingress of oil between the flange and block.

10. The invention defined by claim 1 wherein the flange of at least one retainer of each pair is provided with a coaxial threaded opening for receiving a mounting stud, for securing the flange to a portion of a press or a similar flange of the retainer of another die spring when the springs are stacked end-to-end.

11. The invention of claim 1 wherein each retainer is provided with a coaxial bore extending lengthwise of the tubular portion and opening outwardly through the flange and the inner ends of the tubular members, and said pre-compression member being threadedly connected with the inner end of one of said tubular portions and slidably passing through the bore of the other tubular portion and having a head overlying a shoulder within the bore of said other tubular portion holding the retainers against the block and precompressing the block.

12. The invention defined by claim 11 wherein said head having a tool engaging portion facing the opening in the flange of the associated retainer whereby said precompression member may be threadedly adjusted at the inner end of the opposite tubular member.

13. A stacked elastomeric die spring for cyclic use in a stamping press comprising, in combination: a plurality of cylindrical fibre reinforced elastomeric blocks each having a coaxially extending hollow bore and flat opposite ends arranged perpendicularly to said bore; each block having a diameter to length ratio not exceeding 2.5 to 1,- a pair of heat conductive retainers at opposite ends of each block overlying the flat ends of the block in abutting relation,- each retainer having a heat conductive tubular portion connected in heat conductive relation with the flange and press fitted in the bore of the block, with the tubular portions of opposite retainers being spaced apart in the bore of the block; a pre-compression member extending through the bore of each block and urging the retainers of each pair against the ends of toe block to precompress the block between each pair of retainers,- said blocks with retainers disposed as aforesaid being arranged in a stack with retainers of adjacent blocks in abutting relation,- and the flanges of adjacent retainers in the stack being secured together.

14. The invention of claim 13 wherein said abutting retainers having a threaded part threadedly connected thereto holding them secured together.

15. The invention of claim 13 wherein said abutting retainers are welded together.