Gas spring

Abstract

A gas spring (1) comprising: an outer casing (2) internally provided with a closed cavity (3); a piston-rod (4) which is fitted in the outer casing (2) in axially slidable manner and is structured so as to form / delimit, inside said closed cavity (3), a variable- volume closed chamber adapted to contain a pressurized gas; and one or more annular gaskets (7, 10, 11) that are interposed between the piston-rod (4) and the outer casing (2) and / or between separate pieces (5, 6) of the outer casing (2) and at least one of which is made of a graphite-filled and / or carbon fibre-filled polymeric material.

Description

[0001] GAS SPRING

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This Patent Application claims priority from Italian Patent Application No . 102023000013392 filed on June 28 , 2023 , the entire disclosure of which is incorporated herein by reference .

[0004] TECHNICAL FIELD

[0005] The present invention relates to a gas spring .

[0006] More in detail , the present invention relates to a gas spring adapted to be used in the field of sheet metal forming . Use to which the following disclosure will make explicit reference without thereby losing generality .

[0007] BACKGROUND OF THE INVENTION

[0008] As is known, the gas springs that are used in the dies for sheet metal forming general ly comprise : a cup-shaped body substantially cylindrical in shape ; a guide bushing, separate and distinct from the cup-shaped body, which fluid- tightly closes the mouth of the cup-shaped body via the interposition of a series of annular sealing gaskets ; and a substantially cylindrical-shaped, piston-rod which is fitted in pass-through and axially slidable manner in the hole at centre of the guide bushing, so as to be able to move axially with respect to the cup-shaped body between a retracted position and an extracted or extended position . The piston- rod is moreover fitted f luid-tightly into the guide bushing, so as to form / delimit , together with the cup-shaped body and the guide bushing, a variable-volume closed chamber that is filled up with a high-pressure gas .

[0009] Clearly, a series of annular sealing gaskets , usually made of polymeric material , are moreover interposed between the cup-shaped body and the guide bushing and / or between the guide bushing and the piston-rod .

[0010] The high-pressure gas keeps the piston-rod in the completely extended or extracted position, i . e . with the inner end of the piston-rod in abutment on the guide bushing, until the piston-rod undergoes an axial force capable of overcoming the thrust of the gas .

[0011] In the gas springs most widespread on the market , the nominal gas pressure inside the variable-volume closed chamber ( i . e . the gas pressure with the piston-rod in the completely extended or extracted position) usually ranges between 20 and 200 bar .

[0012] As a result , during normal operation of the gas spring the gas pressure inside the variable-volume closed chamber can rise up to easily reach values above 500- 600 bar, with sealing problems that this entails .

[0013] Having to prevent the leakage of pressuri zed gas with such high pressure di fferences , in fact , the annular sealing gaskets are the components of the gas spring that are mostly stressed and subj ect to breakage , and therefore they condition the average li fe of the component .

[0014] SUMMARY OF THE INVENTION

[0015] Aim of the present invention is to reali ze annular sealing gaskets that can extend the average li fe of the gas springs , without excessively increasing the production costs thereof .

[0016] In accordance with these aims , according to the present invention there i s provided a gas spring as defined in Claim 1 and preferably, though not neces sarily, in any one of the claims depending on it . BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will now be described with reference to the attached drawings , which show a non-limiting embodiment thereof , wherein :

[0018] - Figure 1 is a perspective view o f a gas spring reali zed according to the teachings of the present invention, with parts removed for clarity ' s sake ;

[0019] - Figure 2 is a side view of the gas spring shown in Figure 1 , sectioned along the midplane and with parts removed for clarity ' s sake ; whereas

[0020] - Figure 3 is a side view of a second embodiment of the gas spring shown in Figure 1 , sectioned along the midplane and with parts removed for clarity ' s sake .

[0021] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] With reference to Figures 1 and 2 , number 1 denotes as a whole a gas spring that can be advantageously used in the presses or dies for the cold forming of metal sheets and the like .

[0023] The gas spring 1 comprises : an outer casing 2 with a rigid and sel f-supporting structure , which is internally provided with a large closed cavity 3 advantageously complementary in shape , which is insulated from the outside ; and an oblong-shaped piston-rod 4 , which is fitted in the outer casing 2 in axially slidable and fluid-tight manner, so as to protrude cantilevered outside of the casing 2 , and is shaped / structured so as to form / delimit , inside and together with the inner cavity 3 of casing 2 , a variablevolume closed chamber that contains / is adapted to contain nitrogen or other pressuri zed gas .

[0024] Clearly, the pressuri zed gas present inside the closed cavity 3 , or rather inside the variable-volume closed chamber, has a pressure higher than the external one so as to maximi ze the volume of the closed chamber .

[0025] More in detail , the piston-rod 4 is fitted in axially slidable manner in a substantially complementary-shaped straight hole , which is made in the outer casing 2 so as to connect the cavity 3 directly with the outside .

[0026] In addition, the piston-rod 4 is f luid-tightly coupled to the outer casing 2 via the interposition of at least one annular sealing gasket , which is structured so as to prevent the leakage / passage of pressuri zed gas in the interstitial space between the piston-rod 4 and the outer cas ing 2 , and optionally also with the interposition of at least one protective annular gasket , which is structured so as to prevent oils , powders and / or other solid or liquid contaminates from reaching the inner cavity 3 of casing 2 .

[0027] Preferably, the gas spring additionally includes one or more guide and / or centring rings , which are placed inside the straight hole of the outer casing 2 and are adapted to be engaged in axially slidable manner by the piston-rod 4 .

[0028] Preferably the piston-rod 4 is moreover structured / shaped so as to protrude cantilevered also inside the closed cavity 3 . In addition, the part of piston-rod 4 that remains stably inside the casing 2 , or rather protrudes cantilevered inside the closed cavity 3 , preferably has an anti-extraction structure that is adapted to prevent the complete coming out of the piston-rod 4 from the casing 2 due to the thrust exerted by the pressuri zed gas .

[0029] The pressuri zed gas present inside the closed cavity 3 , or rather inside the variable-volume closed chamber, is therefore adapted to bring and keep the piston-rod 4 in a completely extended or extracted position ( see Figures 1 and 2 ) , wherein the anti-extraction structure of the piston-rod 4 abuts on the inner surface of the cavity 3 .

[0030] In the example shown, in particular, the nominal pressure ( i . e . the pressure of the gas with the piston-rod 4 in the extracted or extended position) of the gas contained in the cavity 3 , or rather in the variable-volume closed chamber, preferably ranges between 20 and 200 bar .

[0031] Preferably, the outer casing 2 is furthermore subdivided into at least two complementary-shaped pieces , which are f luid-tightly coupled to each other via the interposition of one or more annular sealing gaskets , which is / are structured so as to prevent the leakage / passage of the pressuri zed gas in the interstitial space between the same pieces of the outer casing 2 .

[0032] In addition, at least one among the annular gasket or gaskets that are interposed between the piston-rod 4 and the outer casing 2 , and / or at least one of the annular gasket or gaskets that are interposed between the various pieces of the outer casing 2 , is / are made of a graphite- filled and / or carbon fibre- filled polymeric material .

[0033] More in detail , said polymeric material is preferably an elastomeric polymer advantageously of thermoplastic type and / or has a surface hardness ( ISO 868 or DIN 53505 ) preferably higher than or equal to 90 ShoreA.

[0034] Even more speci fically, said polymeric material is preferably polyurethane ( PU) .

[0035] In other words , at least one among the annular sealing gasket ( s ) and / or protective gasket ( s ) that are interposed between the piston-rod 4 and the outer casing 2 , and the annular sealing gasket or gaskets that are interposed between the pieces of outer casing 2 , is preferably made of graphite- filled and / or carbon fibre- filled polyurethane .

[0036] Alternatively, said polymeric material may also be a nitrile rubber (NBR) or a fluorinated elastomer ( FKM or FFKM) , traditionally called Viton .

[0037] Furthermore , the amount of graphite and / or carbon fibre is preferably lower than 20% by weight of the polymeric material , and more conveniently lower than 10% by weight of the polymeric material . Preferably, the amount of graphite and / or carbon fibre is furthermore higher than 0 , 05% by weight of the polymeric material .

[0038] More in detail , the amount of graphite and / or carbon fibre is preferably higher than 0 , 5% by weight of the polymeric material and more advantageously even higher than 1 % by weight of the polymeric material .

[0039] With reference to Figures 1 and 2 , in particular, the outer casing 2 is preferably substantially cylindrical in shape , and its inner cavity 3 is preferably substantially cylindrical in shape and preferably extends inside the casing 2 substantially coaxial to the longitudinal / central axis A of the same casing 2 .

[0040] The piston-rod 4 , in turn, is preferably substantially cylindrical in shape and preferably extends substantially coaxial to the longitudinal / central axis A of casing 2 .

[0041] In addition, the outer casing 2 is preferably divided into a plurality of substantially complementary-shaped pieces , advantageously made of metallic material . The piston-rod 4 , on the other hand, preferably has a monolithic structure and is advantageously made of metallic material .

[0042] More in detail , the outer casing 2 preferably comprises : a cup-shaped body 5 advantageously substantially cylindrical in shape , which preferably has a monolithic structure and is preferably also made of metallic material ; and a plug body 6 , separate and distinct from the cup-shaped body 5 , which has a shape substantially complementary to that of the mouth of the cup-shaped body 5 , and i s at least partially fitted into the mouth of cup-shaped body 5 so as to form / delimit , inside the cup-shaped body 5 , the closed cavity 3 . Furthermore , similarly to the cup-shaped body 5 , the plug body 6 preferably also has a monolithic structure and is preferably made of metallic material .

[0043] In addition, the plug body 6 is f luid-tightly coupled to the cup-shaped body 5 via the interposition of at least one annular sealing gasket 7 , which is adapted to prevent the leakage of pressuri zed gas in the interstitial space between the cup-shaped body 5 and the plug body 6 and is preferably made of graphite- filled and / or carbon fibre- filled polyurethane .

[0044] More in detail , the amount of graphite and / or carbon fibre present in the annular sealing gasket 7 is preferably ranging from 1 % to 5% by weight of the polymeric material .

[0045] Preferably, the annular sealing gasket 7 moreover has a surface hardness ( ISO 868 or DIN 53505 ) ranging between 90 and 95 ShoreA.

[0046] In a di f ferent embodiment , however, the annular sealing gasket 7 may be made of a di f ferent graphite- filled and / or carbon fibre- filled thermoplastic elastomer .

[0047] Preferably, the outer casing 2 is furthermore provided with a locking member 8 , which is placed at the mouth of the cup-shaped body 5 and is adapted to lock / retain the plug body 6 stably in place inside the cup-shaped body 5 .

[0048] With reference to Figures 1 and 2 , in addition, the piston-rod 4 is preferably fitted in pass-through and axially slidable manner in the plug body 6 .

[0049] In other words , the plug body 6 is preferably provided with an advantageously circular-shaped, straight through hole that preferably has a section substantially complementary to that of the piston-rod 4 , and is engaged in pass-through and axially slidable manner by the piston-rod 4 .

[0050] Preferably, the piston-rod 4 is thus f luid-t ightly coupled to the plug body 6 via the interposition of at least one annular sealing gasket 10 , which is placed in the through hole of plug body 6 , is structured so as to prevent the leakage / passage of the pressuri zed gas in the interstitial space between the piston-rod 4 and the plug body 6 , and is preferably made of a graphite- filled and / or carbon fibre- filled polyurethane .

[0051] More in detail , the amount of graphite and / or carbon fibre present in the annular sealing gasket 10 preferably ranges between 3% and 9% by weight of the polymeric material .

[0052] Preferably, the annular sealing gasket 10 moreover has a surface hardness ( ISO 868 or DIN 53505 ) higher than or equal to 94 ShoreA.

[0053] In a di f ferent embodiment , however, the annular sealing gasket 10 may be made of a di f ferent graphite- filled and / or carbon fibre- filled thermoplastic elastomer .

[0054] Preferably, the gas spring 1 additionally comprises a protective annular gasket 11 , which is placed at the outer mouth of the straight through hole of plug body 6 , and is structured so as to prevent oils , powders and / or other solid or liquid contaminates from penetrating inside the plug body 6 .

[0055] Furthermore , similarly to the annular sealing gasket 10 , the protective annular gasket 11 is also preferably made of graphite-filled and / or carbon fibre-filled polyurethane.

[0056] More in detail, the amount of graphite and / or carbon fibre in the protective annular gasket 11 preferably ranges between 3% and 9% by weight of the polymeric material.

[0057] Preferably, the protective annular gasket 11 moreover has a surface hardness (ISO 868 or DIN 53505) higher than or equal to 92 ShoreA.

[0058] In a different embodiment, however, the protective annular gasket 11 may be made of a different graphite-filled and / or carbon fibre-filled thermoplastic elastomer.

[0059] Preferably, at least one guide and / or centring ring 12 advantageously made of a hard polymeric material, i.e. with surface hardness (ISO 868 or DIN 53505) higher than or equal to 98 ShoreA, is also placed inside the straight through hole of plug body 6.

[0060] Optionally also the polymeric material forming the guide and / or centring ring(s) 12 may eventually be graphite-filled and / or carbon fibre-filled.

[0061] More in detail, the gas spring 1 is preferably provided with two guide and / or centring rings 12, which are placed inside the straight through hole of plug body 6 on opposite sides of the annular sealing gasket 10.

[0062] With reference to Figure 2, in the example shown, in particular, the plug body 6 preferably substantially consists of a bushing roughly cylindrical in shape, which preferably has a monolithic structure, is preferably made of metallic material, and has a shape substantially complementary to the mouth of cup-shaped body 5. The bushing is moreover provided with a substantially circular-shaped, central through hole having a diameter roughly complementary to that of piston-rod 4 .

[0063] Similarly, the annular gasket 10 is preferably a lip gasket and is preferably accommodated inside an annular groove made inside the central through hole of the bushing .

[0064] The annular gasket 11 is preferably a lip gasket and is preferably accommodated inside an annular groove made at the mouth of the central through hole of the bushing .

[0065] The guide and / or centring rings 12 , on the other hand, are preferably accommodated inside respective annular grooves made inside the central through hole of the bushing, respectively above and below the annular groove accommodating the annular sealing gasket 10 .

[0066] The annular sealing gasket 7 , in turn, is preferably a double-lip gasket , and is preferably accommodated inside an annular groove made on the outer periphery of the bushing .

[0067] The locking member 8 , on the other hand, preferably includes a Seeger elastic ring or the like , advantageously made of metallic material , which is preferably adapted to removably engage an annular groove made in the cavity of cup-shaped body 5 , close to the mouth of the latter .

[0068] With reference to Figures 1 and 2 , in turn, the piston- rod 4 preferably consists of a cup-shaped body substantially cylindrical in shape , which is made of metallic material , and is fitted in axially slidable manner into the plug body 6 , or rather into the bushing, with the concavity facing the inside of cup-shaped body 5 .

[0069] In addition, said cup-shaped body advantageously has , at the mouth, also a protruding annular flange , which is adapted to prevent the complete extraction of the cup-shaped body from the plug body 6 , or rather from the bushing .

[0070] With reference to Figures 1 and 2 , finally the gas spring 1 is preferably provided with a one-way valve 13 and / or with a safety plug 14 , both advantageously located on the bottom of the cup-shaped body 5 .

[0071] Through the one-way valve 13 it is possible to introduce the pressuri zed gas into the inner cavity 3 of casing 2 , or rather into the variable-volume closed chamber .

[0072] The safety plug 14 , on the other hand, is structured so as to automatical ly discharge , outside of gas spring 1 , the pressuri zed gas present in the inner cavity 3 of casing 2 , or rather in the variable-volume closed chamber, when the pressure of the gas present in the same inner cavity 3 exceeds a predetermined maximum limit , and / or when the piston-rod 4 performs an "overtravel" , i . e . when the piston- rod 4 re-enters inside the casing 2 exceeding the maximum stroke allowed by the dimensions of the gas spring 1 .

[0073] More in detail , the bottom wall of casing 2 , or rather of cup-shaped body 5 , which contributes to delimiting the variable-volume closed chamber, is preferably provided with two through ducts that connect the variable-volume closed chamber with the outside .

[0074] The first through duct accommodates the one-way valve 13 , while the second through duct is f luid-tightly closed by the safety plug 14 .

[0075] Preferably, the mouth of the first through duct is also f luid-tightly closed by an additional closure cap 15 , preferably with a mushroom structure .

[0076] More in detail , the first through duct is preferably L- shaped, and preferably ends inside the cavity 3 on the top of a protuberance 16 that rises from the bottom of the same cavity .

[0077] Preferably, the protuberance 16 and / or the final section of the first through duct is / are substantially coaxial to the longitudinal / central axis A of the same casing 2 .

[0078] The protuberance 16 allows the lubricating oil that should reach the inner cavity 3 to accumulate at the bottom of the cavity without reaching and / or damaging the one-way valve 13 .

[0079] The second through duct , on the other hand, is preferably substantially straight and advantageously also parallel to and spaced from the longitudinal / central axis A of the casing .

[0080] The safety plug 14 , moreover, is preferably structured so as to protrude cantilevered ins ide the inner cavity 3 of casing 2 , so as to be hit by the pi ston-rod 4 when it performs an "overtravel" , i . e . when the piston-rod 4 re-enters inside the cavity 3 exceeding the maximum stroke allowed by the dimensions of the gas spring 1 .

[0081] The one-way valve 13 and the safety plug 14 are already known components easily available on the market , so they won' t be further described .

[0082] Operation of gas spring 1 is similar to that of the gas springs currently present on the market , and therefore does not need any further clari fications .

[0083] The advantages connected with the particular structure of annular gaskets 7 and / or 10 and / or 11 are remarkable .

[0084] The use of a graphite- filled and / or carbon fibre- filled polymeric material , or rather of a graphite- filled and / or carbon fibre- filled polyurethane , signi ficantly increases the resistance of the annular gasket to mechanical stresses such as scrapping and bending, without however af fecting its elastic properties , and therefore increases the average li fe of the gas spring . Furthermore , the use of a graphite- filled and / or carbon fibre- filled polymeric material allows to increase the thermal conductivity of the annular gasket 7 and / or 10 and / or 11 , thus improving the heat dispersion resulting from normal operation of the gas spring .

[0085] It is finally clear that modi fications and variations may be made to the gas spring 1 without , however, departing from the scope of the present invention .

[0086] For example , in a first embodiment variation, instead of engaging in axially slidable manner the plug body 6 , the piston-rod 4 is f itted in pass-through and axially slidable manner into the bottom of the cup-shaped body 5 .

[0087] In this alternative embodiment , therefore , the piston- rod 4 is f luid-tightly coupled to the bottom of cup-shaped body 5 via the interposition of at least one annular sealing gasket , which is adapted to prevent the leakage / passage of the pressuri zed gas in the interstitial space between the piston-rod 4 and the cup-shaped body 5 .

[0088] Clearly also in this case the annular sealing gasket 7 that is interposed between the piston-rod 4 and the cupshaped body 5 , is preferably made of graphite- filled and / or carbon fibre- filled polyurethane or other graphite- filled and / or carbon fibre- filled elastomeric polymer .

[0089] With reference to Figure 3 , moreover, in a second embodiment variation the piston-rod 4 engages in axially slidable manner the plug body 6 , but it is f luid-tightly coupled directly to the cup-shaped body 5 .

[0090] In other words , instead of being placed inside the plug body 6 , the annular sealing gasket 10 is preferably fitted directly on the piston-rod 4 , or rather on the protruding perimeter flange of piston-rod 4 , so as to slide directly on the lateral surface of the inner cavity 3 , or rather on the inner surface of the cup-shaped body 5 , and is adapted to prevent the leakage / passage of the pressuri zed gas in the interstitial space between the piston-rod 4 and the cupshaped body 5 .

[0091] More in detail , the annular sealing gasket 10 is preferably a lip gasket and is pre ferably accommodated inside an annular groove made on the periphery of the protruding annular flange of the cup-shaped body forming the piston-rod 4 .

[0092] Clearly also in this embodiment the annular sealing gasket 10 is preferably made of a graphite- filled and / or carbon fibre- filled elastomeric polymer, or more in detail of graphite- filled and / or carbon fibre- filled polyurethane .

[0093] In this embodiment , moreover, the gas spring 1 is advantageously provided with a single guide and / or centring ring 12 , clearly located inside the through hole of the plug body 6 , or rather inside the central through hole of the bushing .

[0094] Since the annular sealing gasket 10 is interposed between the piston-rod 4 and the cup-shaped body 5 beneath the plug body 6 , the gas spring 1 may optionally also be devoid of the annular sealing gasket 7 .

[0095] Finally, in a less sophisticated embodiment , only some of the annular gaskets 7 and / or 10 and / or 11 may be made of graphite- filled and / or carbon fibre- filled polyurethane or other graphite- filled and / or carbon fibre- filled thermoplastic elastomer . The remaining gaskets , on the other hand, are made of not- filled polyurethane or other not- filled polymeric material .

Claims

C L A I M S1. A gas spring (1) comprising: an outer casing (2) internally provided with a closed cavity (3) ; a piston-rod (4) , which is fitted in the outer casing (2) in axially slidable manner and is structured so as to form / delimit , inside said closed cavity (3) , a variable-volume closed chamber adapted to contain a pressurized gas; and one or more annular gaskets (7, 10, 11) that are interposed between the piston-rod (4) and the outer casing (2) and / or between separate pieces (5, 6) of the outer casing (2) ; said gas spring (1) being characterised in that at least one of said annular gaskets (7, 10, 11) is made of a graphite- filled and / or carbon fibre-filled polymeric material.

2. The gas spring according to Claim 1, wherein said polymeric material is an elastomer.

3. The gas spring according to Claim 1 or 2, wherein said polymeric material is a polyurethane.

4. The gas spring according to any one of the preceding claims, wherein the amount of graphite and / or carbon fibre is lower than 20% by weight of the polymeric material.

5. The gas spring according to any one of the preceding claims, wherein the amount of graphite and / or carbon fibre is lower than 10% by weight of the polymeric material.

6. The gas spring according to any one of the preceding claims, wherein the amount of graphite and / or carbon fibre is higher than 0,5% by weight of the polymeric material.

7. The gas spring according to any one of the preceding claims, wherein the quantity of graphite and / or carbon fibre is higher than 1% by weight of the polymeric material.

8. The gas spring according to any one of the preceding claims, wherein said annular gasket or gaskets (7, 10, 11)has / have a surface hardness higher than or equal to 90 ShoreA.

9. The gas spring according to any one of the preceding claims, wherein said annular gasket or gaskets (7, 10, 11) is / are annular sealing gaskets and / or protective annular gaskets .

10. The gas spring according to any one of the preceding claims, wherein said annular gasket or gaskets (7, 10, 11) is / are single lip or double lip annular gasket (s) .

11. The gas spring according to any one of the preceding claims, wherein the outer casing (2) comprises a cup-shaped body (5) and a plug body (6) , separate and distinct from the cup-shaped body (5) , which is at least partially fitted into the cup-shaped body (5) , so as to delimit said closed cavity (3) ; said plug body (6) being coupled f luid-tightly to said cup-shaped body (5) via the interposition of at least one of said annular gaskets (7) .

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