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EP-4739933-A1 - GAS SPRING AND CORRESPONDING PRODUCTION METHOD

EP4739933A1EP 4739933 A1EP4739933 A1EP 4739933A1EP-4739933-A1

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 material transparent oorr semi-transparent to visible light.

Inventors

  • CAPPELLER, AUGUSTO
  • FIORESE, MASSIMO
  • GUSELLA, Giovanni

Assignees

  • Special Springs S.r.l.

Dates

Publication Date
20260513
Application Date
20240704

Claims (14)

  1. 1. A gas spring (1) comprising: an outer casing (2) having internally a closed cavity (3) ; a piston-rod (4) , which is inserted 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 distinct pieces (5, 6) of the outer casing (2) ; said gas spring (1) being characterized in that at least one of said annular gaskets (7, 10, 11) is an annular gasket made of transparent or semi-transparent polymeric material.
  2. 2. The gas spring according to Claim 1, wherein said transparent or semi-transparent polymeric material is an elastomer .
  3. 3. The gas spring according to Claim 1 or 2, wherein said transparent or semi-transparent polymeric material is polyurethane .
  4. 4. The gas spring according to any one of the preceding claims, wherein said annular gasket made of transparent or semi-transparent polymeric material has a surface hardness greater than or equal to 90 ShoreA.
  5. 5. The gas spring according to any one of the preceding claims, wherein said annular gasket made of transparent or semi-transparent polymeric material is an annular sealing gasket or an annular protective gasket.
  6. 6. The gas spring according to any one of the preceding claims, wherein said annular gasket made of transparent or semi-transparent polymeric material is a lip or double lip gasket .
  7. 7. 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) , and is coupled in a fluid-tight manner to said cupshaped body (5) via the interposition of at least a first annular sealing gasket (7) ; said first annular sealing gasket (7) being made of transparent or semi-transparent polymeric material .
  8. 8. The gas spring according to any one of the preceding claims, wherein the piston-rod (4) is coupled in a fluid- tight manner to the outer casing (2) via the interposition of at least a second annular sealing gasket (10) ; said second annular sealing gasket (10) being made of transparent or semi-transparent polymeric material.
  9. 9. A production method of a gas spring (1) comprising: an outer casing (2) having internally a closed cavity (3) ; a piston-rod (4) which is inserted 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 distinct pieces (5, 6) of the outer casing (2) ; said production method being characterised by comprising the steps of: - realizing at least one of said annular gaskets (7, 10, 11) in a transparent or semi-transparent polymeric material ; - checking, via optical and/or visual inspection, the structure of said annular gasket made of transparent or semi-transparent polymeric material to detect the presence of any bubbles inside said annular gasket; and - using said annular gasket made of transparent or semitransparent polymeric material in the assembly of said gas spring (1) , if said annular gasket made of transparent or semi-transparent polymeric material is without bubbles or has, inside itself, bubbles with nominal volume below a first predefined maximum threshold and/or with overall volume below a second predefined maximum threshold.
  10. 10. The production method of a gas spring according to Claim 9, wherein said at least one annular gasket (7, 10, 11) made of transparent or semi-transparent polymeric material is produced by injection moulding.
  11. 11. The production method of a gas spring according to Claim 9 or 10, wherein said at least one annular gasket (7, 10, 11) made of transparent or semi-transparent polymeric material is made of transparent or semi-transparent polyurethane .
  12. 12. The production method of a gas spring according to any one of Claims 9-11, wherein said first predefined maximum threshold is equal to 0,01% of the overall volume of the annular gasket and/or is equal to approximately 0,3 mm 3 .
  13. 13. The production method of a gas spring according to any one of Claims 9-12, wherein said second predefined maximum threshold is equal to 0,02% of the overall volume of the annular gasket and/or is equal to approximately 0, 6 mm 3 .
  14. 14. The production method of a gas spring according to any one of Claims 9-13, wherein the checking of the structure of said annular gasket made of transparent or semi-transparent polymeric material is carried out by an optical inspection electronic device 100 that comprises: at least one videocamera or camera (101) adapted to acquire one or more images of said at least one annular gasket (7, 10, 11) made of transparent or semi-transparent polymeric material; and a data processing unit (102) which is programmed/ conf igured so as to process the images acquired from said video-camera/s or camera/s (101) , to detect the presence of any bubbles inside said annular gasket.

Description

"GAS SPRING AND CORRESPONDING PRODUCTION METHOD" Cross-Reference to Related Applications This Patent Application claims priority from Italian Patent Application No . 102023000014262 filed on July 7 , 2023 , the entire disclosure of which is incorporated herein by reference . Technical Field The present invention relates to a gas spring and to the corresponding production method . 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 . Background of the Invention As is known, the gas springs which are used in the moulds for sheet metal moulding generally comprise : a cup-shaped body substantially cylindrical in shape ; a bushing substantially cylindrical in shape , separate and distinct from the cup-shaped body, which f luid-tightly closes the mouth of the cup-shaped body via the interposition of at least one annular sealing gasket ; and a substantially cylindrical-shaped, piston-rod which is fitted in pass-through and axially slidable manner in the hole at centre of the 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 bushing with the interposition of at least one annular sealing gasket , so as to form/delimit , together with the cup-shaped body and the bushing, a variable-volume closed chamber that is filled up with a high-pressure gas . The pressuri zed gas thus 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 body of the bushing, until the piston-rod undergoes an axial force capable of overcoming the thrust of the gas . 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 . As a result , during the movement of the piston-rod, the pressure of the gas inside the variable-volume closed chamber can rise up to easily reach values above 500- 600 bar, with the sealing problems that this entails . Problems that unfortunately directly af fect the reliability of the device . The Applicant , in fact , has carefully examined a statistically signi ficant sample of the gas springs that highlighted mal functions during the first year of li fe , and has found that most of these mal functions are caused by an abnormal under-pressure deformation and/or early rupture of one of the annular sealing gaskets of the gas spring . By analysing the defective composite , the Applicant has furthermore found that the early rupture and the abnormal under-pressure deformation are both due , in almost all cases , to the presence of small bubbles of air or other gas not necessarily globoidal in shape , that are hidden inside the body of the annular sealing gasket . The annular sealing gaskets used in the gas springs , in fact , are commercial type annular gaskets , and are made of polymeric material filled with carbon black and/or other additives , via inj ection moulding . The bubbles of air or other gas occasionally form inside the body of the annular sealing gasket during inj ection moulding of the piece . Unfortunately, to date there are no economic and reliable quality control systems that are capable to detect , in a non-destructive manner, when there are bubbles of air or other gases hidden inside the annular sealing gaskets . The low production cost of the annular sealing gaskets made of polymeric material , in fact , makes this type of structural checks economically non-af fordable . For the same reasons it is economically unthinkable to use ultrasonic equipment , X-ray equipment or similar machinery to detect bubbles or other structural discontinuities within the opaque body of the annular sealing gaskets that are used on assembly of the gas springs . This type of equipment , in fact , has economically unsustainable costs . Summary of the Invention Aim of the present invention is to overcome the problems connected with the defectivity of the annular sealing gaskets without excessively increasing the production costs of the gas springs . 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 . Moreover, according to the present invention there is provided a production method of a gas spring as defined in Claim 9 and preferably, though not necessarily, in any one of the claims depending on it . Brief Description of the Drawings The present invention will now be described with reference to the attached drawings , which show a non-limiting embodiment thereof , wherein : - Figure 1 is a