CLIAMS:We Claim:
1. An elastomer cushion, in plurality on axially stacking up, forming a compression spring, comprising:
an elastomer cushion made of preformed polyurethane elastomer material shaped through the process of die casting or molding having stress free contours of the cushion providing long cyclic elongation usage and long fatigue life of the said cushions.
2. The elastomer spring cushion as claimed in the claim 1, wherein said spring cushion size and shape predefined.
3. The elastomer spring cushion as claimed in the claim 1, wherein said spring cushion may have a cavity at the center.
4. The elastomer spring cushion as claimed in the claim 1, wherein said cushion in plurality on axially stacking over one another may be interspaced with non-deformable metal plates.
5. The elastomer spring cushion as claimed in the claim 1, wherein said cushions on axially stacking one to twelve times over one another, interspaced with non-deformable plates, forms spring having energy storing capacity between 10 Kilo Joule (kJ) and 100 kJ.
6. The said cushions on axially stacking one to twelve times over one another as claimed in the claim 5, wherein initial perforce between 10KN and 50 KN and end load between 200 and 1500 KN provides stroke length of 105 ± 5 millimeter (mm) or as required by the specific application and over forty percent damping forming installation height between 75 to 700 mm.
7. The elastomer spring cushion as claimed in the claim 1, wherein said polyurethane material has a hardness value between 40 and 78 on Shore D scale.
8. The elastomer spring cushion as claimed in the claim 1, wherein said stress free contours of the elastomer cushion provides a high fatigue life of the cushion with a Bulging Factor between 0.5 to 1.0 for springs with energy absorption between 10 KJ to 100 KJ formed by 1 to 12 said elastomer cushions.
9. The elastomer spring cushion as claimed in the claim 1, wherein said higher damping means 40 percent or more absorption of the stored energy for springs with static energy storage capacity between 10 KJ to 100 KJ formed by 1 to 12 said elastomer cushions.
10. The elastomer spring cushion as claimed in the claim 1, wherein said cushion may be of elliptic or disk or ring or any other shape.
11. The elastomer spring cushion as claimed in the claim 1, wherein said preformed polyurethane elastomer material may not be a preformed material.
,TagSPECI:BACKGROUND
Technical Field
The embodiments herein generally relate to an elastomer cushion in plurality, which on axially stacking up interspaced by non-deformable discs forms a compression spring, used as an energy absorption device with elastomer cushions stacked axially one over the other to impart spring like properties, and, more particularly, to utilize the robust physical properties of the elastomer spring cushions.
Description of the Related Art
The US patents 3,814,412, 4,198,037 and 4,566,678 introduced springs, made up of co-polyester polymer cushions, absorbing energy upon application of pressure and releasing the same upon release of the pressure. The polymer cushions upon stacking up axially one over the other formed higher pressure absorbing longer lasting springs.
The US patent 4,198,037 discloses branded polymer HYTREL to be used as elastomer polymer material for making polymer cushions used in the spring assembly. HYTREL contains dimethyl terephthalate, poly glycols such as poly-tetra-methylene ether glycol, and diols like butanediol and ethylene glycol. The patent discloses the art of forming a bond between the polymer cushions and the multi-aperture plates. Further it teaches about roughening of the faces of the plates bearing against the cushions by sandblasting for achieving higher force capacity. The objective of the disclosure was to provide a method whereby copolyester polymer elastomers may be processed to produce a product, which will serve as a compression spring in applications wherein the force applied to the spring is such as to compress the spring significantly over ten percent. Further the patent disclosed a copolyester polymer elastomer spring that will not take permanent set when operating under conditions such that the spring is compressed significantly over ten percent. The disclosure was the copolymer elastomer block that could return to the original position even after sustaining the pressure that compresses the block over thirty percent of its original dimension.
The US patent 4,566,678 discloses about the functional characteristics of a hollow elastomer body formed by compressing a solid block of elastomer material with a selected axial core opening extending at least partially there through. When the body is utilized as a compression spring, the spring characteristics of the hollow body have been changed, compared to a solid body of the same material. The spring rate is changed, and the amount of dynamic and static energy that can be absorbed by the spring has been varied. The functional characteristics of the hollow elastomer bodies produced pursuant to this invention thus expands the flexibility of design and the scope of application for spring units utilizing copolyester polymer elastomer materials. Moreover, the operating characteristics of the hollow elastomer body produced by this invention can be varied in a simple manner by changing the shape and size of the core opening provided in the body before compression. The provision of a core opening extending at least partially through the elastomer body before the application of the compression force has been found not to cause the side-walls of the body to collapse, as may be expected.
The improvements in the copolyester polymer elastomer spring were introduced through several patents. The US patent 5,868,384 presents the copolyester polymer elastomer spring wherein the outer layer of the elastomeric material having different durometer hardness than the interior block provides increased energy absorption while resisting excessive rebound.
The US patent 8,038,134 describes a compression spring that is formed by a stack of annular flanges made of thermoplastic elastomer whose manufacturing is easier and less onerous than that of the known springs. The patent addressed the problem of deformation by compression exceeding the elastic limit of the thermoplastic elastomer, wherein the initial compression is followed by the reduction of the pressure in the block (decompression). After the decompression, the thermoplastic elastomer block preserves a residual deformation, which depends on the amount of the compressive effort and on the selected thermoplastic elastomer. The patent discloses formation of the spring by a stack of annular flanges made of thermoplastic elastomer wherein the two flanges are separated by a non-deformable collar encompassing the central bore.
The US patent 8,196,912 addresses the problem faced in the elastomer having a Durometer hardness ranging between 40 and 45 on the Shore D hardness scale: the thermoplastic elastomer of those springs tends to radially expand towards an inner surface of the housing upon axial compression of the spring pack. When the elastomer of the spring rubs or otherwise engages within the inner surface of the railcar housing, performance of the elastomeric spring is adversely affected. In extreme conditions and largely due to continued rubbing of the outer surface of the elastomer against the inner surface of the housing, one or more of the elastomeric springs can fail resulting in poor performance. The patent discloses a railcar elastomer spring having a hardness ranging between 40 and about 45 on the Shore D scale that is securely fastened to a pair of metal plates and is preferably configured to resist radial expansion beyond predetermined limits in response to axial compression of the spring.
Modern elastomer spring assembly includes impact-absorbing cushions made of elastomeric polymers. The elastomeric polymer cushions are stacked axially one over the other interspaced by non-deformable plates, to form a spring assembly that is fitted into a housing. The non-deformable plates typically include a surface incongruity, which is intended to capture a portion of the elastomer cushion that is forced into the incongruity during a cold forming process.
The polymer elastomer cushions are manufactured using a cold-forming process, where a compressive axial force is applied to a cylindrical polymeric element to cause a permanent bulge and render the shape of a spring element to the cylindrical polymeric element. This transformation also renders spring-like properties to the erstwhile cylindrical element that is typically made up of a copolyester elastomer, which before compression did not have spring properties required for forming an energy absorbing spring. Further, the elastomeric cushions, when stacked up to form a spring include non-deformable plates sandwiched between each two consecutive elastomeric cushions. In order to tightly attach the elastomeric cushions to the plates, the plates are provided with surface incongruities in which the elastomeric material must flow during the cold forming process in order to lock the elastomeric cushions to the plates. In order to ensure uniform load distribution and optimum performance of the spring, it is essential during this process that the elastomeric cushions are centered or arranged concentrically relative to the plates during the cold forming process. Ensuring proper and accurate centering of the plates with respect to the elastomeric cushions during the cold forming process is a complex procedure and requires highly skilled operators or very accurate and sophisticate equipment.
The patent documents such that US 4,566,678 and US 4,198,037 have also disclosed that copolyester polymer elastomer material has inherent physical properties that makes it unsuitable for use as a compression spring; the material is treated for rendering the material usable as a compression spring.
Therefore, there is need for a material that does not need to be subjected to cold forming in order to develop spring-like properties thereby leading to an easier manufacturing process that does not require any cold forming operations on cylindrical spring elements for producing elastomeric cushions.
BRIEF SUMMARY OF THE INVENTION
An elastomer cushion, in plurality on axially stacking up, interspaced with non-deformable plates forming a compression spring, comprising an elastomer cushion made of preformed polyurethane elastomer material shaped through the process of die casting or molding having stress free contours of the cushion having a high stroke length and damping, and providing long service life.
In view of the foregoing, an embodiment herein provides the elastomer elliptic, disk or ring shaped cushion made of preformed polyurethane elastomer material. The disclosure relates to the polyurethane material having hardness between 40 and 78 on Shore D scale. The molding process of the preformed polyurethane elastomer material makes the elastomer cushions stress free at ends. Further, for a specific embodiment of elastomer cushions spring having static capacity to store between 10 Kilo Joule (KJ) and 100 Kilo Joule (KJ) energy consisting of a number of cushions between 1 to 12, falling under the category of International Union for Railways’ UIC-526 or UIC 528 or AAR or DIN EN or other relevant standards, providing over 40% damping and a Shape or Bulge Factor between 0.5 to 1.0 with an end load between 200 to 1500 Kilo Newton (KN). The parameters vary with the static capacity of energy absorption of elastomer spring formed by stacking up the elastomer cushions, interspaced by non-deformable plates.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 provides a photograph of a preferred embodiment of the polymer spring assembly.
Figure 2 depicts semantic diagram of the axial cross-section of the polymer spring assembly.
Figure 3 depicts semantic diagram of the polyurethane elastomer in the shape of a ring or donut having a convex surface along the outer circumference and a concave surface along the inner circumference.
Figure 4 depicts an elastomer spring in the shape of a ring or donut with a convex surface along the outer circumference and a concave surface along the inner circumference having protrusions on the top and bottom surfaces that would fit into corresponding holes or cavities in the non-deformable spacer plates.
Figure 5 depicts semantic diagram of a graph drawn between the parameters of force and compression wherein compression is on X-axis and force is on Y-axis.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The embodiments herein provide an elastomer cushion that in plurality on axially stacking up forms a compression spring. The elastomer cushion made of preformed polyurethane elastomer material that is shaped through the process of die casting or molding. The properties of polyurethane elastomer and the die casting method to give the elastomer the shape of the cushion makes the cushion stress free contours. The stress free contours provide to the said cushions long cyclic elongation usage and long fatigue life.
Elastomers are made up of long chains of carbon, hydrogen and oxygen atoms, which have a degree of cross-linking with their neighboring chains. The cross-linking bonds pull back the elastomer into shape when the deforming force is removed. The chains of the atoms consist of three lakh or more monomer units. The chains could be composed of repeated units of the same monomer or made up of two or more different monomers. The cross linking among the chains ensures that the elastomer returns to its original configuration on removal of the stress under which it went through deformation.
The embodiments herein provide an elastomer cushion that is made of preformed polyurethane elastomer material. The cushions are formed using die casting or molding technique applied on the disclosed polyurethane elastomer material. The following are the properties of the disclosed polyurethane elastomer material:
Polyurethane Elastomer Properties
Property Value Value Unit Standard
Stress at 50% Strain > 4 MPa ISO 527 -1/-2
Stress at 100% Elongation > 6 MPa ISO 527 -1/-2
Stress at Break TPE > 40 MPa ISO 527 -1/-2
Strain at Break > 300 % ISO 527 -1/-2
Stress at Break TPE > 200 MPa ISO 527 -1/-2
Compression Set under Constant Strain, 23 °C < 50% % ISO 815
Shore A Hardness, 3s > 90 - ISO 868
Shore D Hardness, 15s > 40 - ISO 868

The spring pads are manufactured from polyurethane elastomer material having high elasticity and good abrasion resistance.
The polyurethane elastomer material of suitable hardness from the range of 40 Shore-D to 78 Shore-D is selected depending on the requirements of spring pack height, end load, hysteresis load, stroke length, and energy storage capacity. The elastomer material is fed directly into a horizontal/vertical urethane casting or molding machine. The pads are horizontal/vertical cast from the polyurethane elastomer material of suitable hardness and then trimmed / finished and machined to give the required shape and size. After machining, the cushions are kept at 100-110 °C for 2 to 3 hours in air circulating oven or dehumidifier air dryer. Before left for drying, for bringing to a desired consistency, texture, or hardness by a process of gradually heating and cooling, the cushions are post-cured at 100 °C for 20 hours. Further, the cushions are subject to maturing at room temperature for a period of 30 days to give them a stable shape and spring-like properties.
While the present disclosure of the invention has disclosed embodiments in several different forms, a particular embodiment is described further in the following paragraphs as the preferred embodiment.
The Figure 1 depicts the preferred embodiment of the spring assembly and a drawing of the axial cross-section of the device is provided in Figure 2. In Figure 2 at the base of the device is a non-deformable base plate (1) on which a non-deformable central cylindrical rod or spindle (4) is mounted. The spring elements that include elastomer rings (2) and non-deformable round plates or spacer plates (3) having a central bore radially surround the central spindle (4) and are axially interspaced such that each spacer plate (3) is sandwiched between two consecutive elastomer rings (2). Another non-deformable base plate along with a suitable fixture (5) is provided at the other end of the elastomer spring assembly. A locking device is used to hold the spindle (4) and each of the spring elements in place. The locking device presented in the preferred embodiment of the device shown in the Figure 2 is a lock nut (6) made of a non-deformable material, preferably steel.
According to the disclosed embodiments, the process for manufacture of the elastomeric rings (2) contained in the said elastomer spring assembly involves die casting or molding of the base polyurethane elastomer in the shape of a ring or donut having a convex surface along the outer circumference and a concave surface along the inner circumference, as depicted in Figure 3. In order to achieve a concave surface along the inner circumference of the ring during casting, it is important to use a collapsible core that can be extracted through the central bore of the cast elastomeric ring upon completion of the casting operation, by collapsing into smaller axially removable pieces.
The aforementioned disclosed casting operation does not impose the application of any extrusion operation on the polyurethane elastomer. It further eliminates the need for cold forming or compression of a preformed elastomeric cylinder. This process is especially advantageous as it eliminates the problem of stress development along the periphery of the elastomer rings, which is inherent in the process of cold forming of preformed elastomeric elements. This process is substantially simpler to cold forming of preformed elastomeric elements. This process does not involve forcing the elastomeric spring members into their final position by application of axial force. The aforementioned disclosed process further eliminates the difficulties associated with holding the elastomeric preform in place during compression and with ensuring the centering and alignment of the spring elements during compression.
In a modified embodiment of the elastomeric spring assembly produced according to the invention, the elastomer rings can be molded such that the inner surface around the central bore is flat and without any groove along the inner periphery. In the disclosed embodiment, a groove along the inner periphery may be introduced by machining along the inner surface of the elastomeric ring after the completion of casting and post-curing processes.
In the disclosed embodiments, post casting or molding, the elastomeric rings are post-cured for a specific time-period at a specific temperature, and thereafter matured for a specific time-period at room temperature. The time-periods and temperatures required for post-curing and maturing are dependent upon the properties of the specific grade of base elastomer used to produce the elastomeric rings. Once matured, the elastomeric elements can easily be assembled to form an elastomeric spring as shown in Figure 2 by stacking the elastomeric rings (2) around the non-deformable spindle (4) interspaced by non-deformable round plates (3). Elastomeric springs of several different heights, each comprising of a different number of spring elements, can be assembled using the aforementioned manufacturing and assembly process. Once built, the assembly is held in place using a locking device, such as a metallic lock nut (6) used in the preferred embodiment of the device shown in Figure 2.
A small axial load is applied to the final assembled spring assembly to eliminate any residual spaces between the elements of the elastomer spring assembly and to achieve the final assembled height of the spring assembly as per the requirement of the application.
In the preferred embodiment of the elastomeric spring assembly shown in Figure 2, the axial load applied after final assembly is between 2.0 to 5.0 tons. The height of the assembly after the first axial compression is recognized as the final assembled height of the polymeric spring assembly. In principle, this first axial loading can be done at any predetermined load value up to and including the maximum specified axial load of the particular elastomer spring under assembly. Once assembled, the elastomeric spring assembly is free to rotate about its own central axis.
There is no physical or chemical bonding required between the elastomeric rings (2) and the non-deformable spacer plates (3), as shown in the preferred embodiment of the elastomer spring assembly in the Figure 2. However, in certain modified embodiments, the elastomeric rings (2) may be provided with protrusions on the top and bottom surfaces, as shown in Figure 4, and corresponding holes or cavities be provided on the surfaces of the non-deformable spacer plates (3) such that the protrusions on the surface of the elastomer rings (2) fit snugly inside the cavities provided on the surface of the non-deformable spacer plates (3). Such protrusions and cavities would help lock the elastomeric springs (2) relative to the non-deformable spacer plates (3) and prevent the elastomeric rings (2) from rotation with respect to the non-deformable spacer plates (3). Protrusion on the surface of the elastomeric rings, if designed, must be created at the time of casting by incorporating the profiles of such protrusions within the mold cavity.
An elastomeric collar on the non-deformable spacer plates (3) can also be used to for the purpose of achieving a snug fitment between the elastomeric rings (2), the non-deformable spacer plates (3) and the non-deformable central cylindrical rod or spindle (4). Using a combination of protrusions on the elastomeric rings (2), corresponding holes or cavities on the non-deformable spacer plates (3) and the use of an elastomeric collar along the inner periphery of the non-deformable spacer plates (3), a range of alternative embodiments of the elastomeric spring assembly according to the invention can be created.
The embodiments herein provide more specifically for a specific embodiment of elastomer cushions spring consisting of 8 to 9 cushions for static capacity to store 35 Kilogram Joule (KJ) energy falling under the category of International Union for Railways’ UIC-526 specification, provides 67% damping and 0.69 Shape or Bulge Factor with the end load of 735 Kilogram Newton (kN). The parameters vary with the static capacity of energy absorption of elastomer spring formed by stacking up the elastomer cushions.
The static load-deflection graph shown in the Figure 5 consists of three curves of which the first curve, represented by dotted line, pertains to the load deflection characteristics during the first closure. The second curve, just beneath the first (dotted line) curve, pertains to the load deflection characteristics during the third closure. The final curve, the last curve beneath the first (dotted line) curve, pertains to the unloading cycle of the polymer spring.
The area under the second, i.e. the third-closure loading curve, denotes the total stored energy of the polymer spring. The area between the second and the third curve represents the absorbed energy, i.e. the energy absorbed by the polymer spring during the complete loading and unloading cycle.
Static Load vs. Deflection Data for 35 kJ Buffer Spring
Load in Tonnes Load in kN Deflection (mm)
1st Closure 3rd Closure Unloading
0.0 0 0 0 0
3.0 29.4 0 0 46
5.0 49 8 12 58
10.0 98 27 32 70
15.0 147 40 46 79
20.0 196 48 55 87
25.0 245 56 64 92
30.0 294 63 71 96
35.0 343 68 76 98
40.0 392 73 81 99.5
45.0 441 78 85 101
50.0 490 83 89 102
55.0 539 87 92 103
60.0 588 91 95 104
70.0 686 100 102 105
75.0 735 103 105 105
80.0 784 105

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.