GB2223824A - Piston seal - Google Patents

Description

Piston Seal 2223B24 The invention relates to a piston seal according to

the preamble of claim 1.

In these known piston seals, the static and the-dynamic sealing parts are made from the same material. Such piston seals are used in hydraulic cylinders. The materials ued for the sealing parts are, for instance, nitrile butadiene rubber, silicon caoutchouc and suchlike, which operate optimally when used in hydraulic media. In certain fields, however, especially in the foodstuffs industry, the use of pneumatic cylinders is

10. laid down. In this case, however, materials of much higher quality have to be used which have a lower coefficient of friction, since hydraulic oil is no longer present for lubrication. Such materials are however relatively expensive. This means that piston seals with such sealing parts are very costly. Furthermore, there is the fact that these 15. high-quality materials, such as polytetrafluor ethylene, are extremely sensitive to improper uses, so that the unavoidable reject ratios in the " such piston seals increase costs still further.

production of The underlying task of the invention is to design a piston seal of this 20. kind in such a way that it can be produced at the lowest material cost.

In the case of a piston seal of the generic kind, this task is solved according to the invention by the characteristic features of claim 1.

25. In the case of the piston seal according to the invention, the highquality expensive material is provided only at those points where it is really required. Since the sealing and sliding surface of the dynamic sealing part is moved along the cylinder wall, the high-.quality material is also only provided in this area, whereas the remaining part 30. of the seal can be made from less expensive material. Savings can thus be made on a large amount of expensive material, which has a favourable effect on the manufacturing costs of the piston seal according to the invention. The waste in the manufacture of the piston seal then has only f a small effect on cost. In particular, there is also the possibility o.

35. adapting the various areas of the piston seal to their given case of application in an optimum fashion as regards the choice of material. Thus, the high-quality material is selected, for exarrple, for---the sealing and sliding surface of the dynamic sealing part taking into account the desired sealing effect and the losh coefficient of friction, whereas for the static sealing part a material can be used for which in-portance is attached not so much to low friction, but rather to a good fit of the piston seal on the piston rod.

Further features of the invention are given in the further claims. the 10. description and the drawing.

The invention is described below in greater detail with the aid of an f embodiment shown in the drawing.

example o

15. The drawing shows a piston seal according to the invention in a perspective view and through an axial cross-section.

The seal 1 is positioned in the known manner in a pneumatic cylinder (not shown) on its piston rod. The guidance in the cylinder is achieved 20. by a central section 16, the lateral cylindrical surface of which lies against the cylinder wall. When the piston rod moves back and forth, the buffer or cushion part 3, 3' of the seal strikes against the cylinder stops in the end positions.

25. As the drawing shows, the piston seal has a disc-shaped carrier 4 which is preferably made of metal, especially steel. The carrier 4 is encased.

The casing 5 has a sealing part provided on the radially outer edge 8 of the carrier 4, said sealing part together with two sealing lips 7, 7' 30. being made from a high-quality material, such as preferably fluorine polymer, especiallly polytetrafluor ethylene, or a combination of polytetrafluor ethylene with fluorine polymer, which has a low sliding friction and a high abrasive resistance. The sealing part 6 can, however, also be made from a cheaper material, for example from the same 35. material as the static sealing part 2; however, the sealing lips 7, 7', 1 5.

which extend around the periphery of the piston seal, are then provided in their sliding and sealing areas 7a, 7b with a layer made from a highquality material, preferably poly- tetrafluor ethylene or a combination of polytetrafluor ethylene and fluorine polymer. In this case, the whole of the remaining casing 5 can be made from an inexpensive material. The layer 7a, 7b made from high-quality material ensures an excellent seal with a low rate of wear and an extremely favourable manufacturing cost.

10. In order to be adapted to the particular conditions of use, the piston seal can also have sealing edges (not shown) on its external periphery to inprove the sealing effect still further. These additional sealing edges can be designed in the same way as in the forms of embodiment described above.

15. The sealing lips 7, 7' and the layers 7a, 7b can be made frort different materials so as provide sealing against different media on the two sides of the piston seal. In this way it becomes a very easy matter to adapt the piston seal in the cLolimum manner to the different media to be 20. sealed from one another. Particularly when the piston seal has the layers 7a, 7b, a very favourably priced piston seal can be produced which fulfils its purpose excellently.

The sealing part 6 forms a dynamic sealing part, because the sealing 25. lips 7, 7' become elastically deformed and slide along the cylinder wall when the piston rod moves back and forth. The piston seal also has a static sealing part 2 with the sealing area 2a which forms a seal against the piston rod. Since the static sealing part 2 does not move relative to the piston rod during operation, it can be made from a lower 30. quality material than the dynamic sealing part 6, for example rubber, nitrile butadiene rubber and suchlike.

The casing 5 has at leas'. one cushion part 3, 3' on each of the faces 9, 9' of the carrier 4. They are rings with a preferably rectangular cross35. section. The cushion parts 3, 3' are positioned at a small radial distance from the neighbouring insides 10, 10' of the dynamic sealing part 6, so that a groove 11, ll' is formed between the latter and the cushion parts or buffers 3, 3'. Each cushion part 3, 3' has axial openings 12, 12' which preferably lie at the same peripheral distance 5. one after the other and which form air ducts like the grooves 11, 11'. They effect a uniform conpressive stressing of the whole piston area at the end stop and thus a pressure-free impact of the piston rod. The cushion parts 3, 3' are made from a cheaper material than the dynamic sealing part 6 or its layer. The cushion parts 3, 3' are preferably made 10. from nitrile butadiene rubber which is more elastic and softer than the material from which the dynamic sealing part is produced. The cushion parts 3, 3' cushion the impact of the piston seal against the respective cylinder stops in the two end positions of the piston rod. The radially- inner edges 13, 13' of the cushion parts 3, 3' lie roughly ove-r half the radial width of the carrier 4.

A cover 14, 14' is attached to the static sealing part 2 on the two sides 9, 9' of the carrier 4, said cover extending to a point close to the cushion part 3, 3'. Grooves 15, 15' are located respectively between 20. the covers 14. 14' and the cushion parts 3, 3'. The carrier 4 can obviously be coirpletely covered, so that the grooves 11, 11', 15, 15' are not present. The cover 14, 14' and the static sealing part 2 are preferably made from the same material, particularly of elastic material such as nitrile butadiene rubber. The cushion parts 3, 3' can also consist of separate areas which are arranged distributed around the periphery of carrier 4. The cushion parts 3, 3' are at all events thicker than the cover 14, 14', so that the piston seal meets its end position with its cushion parts 3, 3'.

30. it is an advantage for the different materials of the dynamic and static sealing parts 6 and 2 and, if necessary, the cushion part 3, 3' to have different colours, such that the different colours make it possible to detect inmediately if any errors have occurred during assembly. The different colouring makes it possible, for example, to detect in an 35. optically simple and reliable way whether, for instance, the dynamic sealing part 6 is made from the desired high-quality material or whether it is made inadvertently from the lower quality material of the static sealing part 2 and/or the cushion parts 3, 3,, as a result of which the piston seal would wear prematurely in service. This allows a simple 5. check to be made so that it is ensured that only correctly manufactured piston seals are supplied.

The static sealing part 2, preferably together with the cover 14, 14', and the cushion parts 3, 3' can be made from materials with different 10. Shore hardnesses. Thus, a more elastic softer material with good cushioning properties can be selected for the cushion parts 3, 3' than for the static sealing part 2 in which good sealing properties are sought. The cushion parts 3, 3' and the static sealing part 2, preferably together with the cover 14, 14', can thus be made from different materials, so that the piston seal can be specifically adapted to the sealing conditions and the cushioning conditions. Preferably, in this case, the materials for the static sealing part 2 and the cushion parts 3, 3' can be differently coloured or have a different coloration, so that manufacturing faults are immediately detected.

20. The piston seal, especially its dynamic and static sealing part 6, 2, as well as the cushion parts 3, 3' can be produced with different materials in a single operation and can be intimately bonded to one another. This allows the seal to be manufactured at a favourable cost, whilst giving 25. it a long service life as a result of the secure bonding of the piston seal parts to one another and to the carrier.

The static sealing part 2 with the sealing surface 2a can be made from a more elastic material than the dynamic sealing part 6 with the sealing 30. and sliding surfaces 7a, 7b. In order to achieve a firmer bonding between the carrier 4 and the casing 5, the carrier can have any suitable crosssectional shape. Thus, for example, it can have recesses or cut- outs into which the material of the casing penetrates during manufacture and thus ensures a firm anchouring between the carrier and 35. the casing. A bonding of this kind is advisable especially in those 71 areas of the casing 5 in which shear forces or shear stresses act during assembly and/or in service. Moreover, the carrier 4 can be provided with suitable adhesive agents which ensure an intimate bond between the carrier and the material. Roughening of the carrier surface can also be 5. carried out for a better adhesion of the material.

The carrier 4 can be made not only from a suitable metal, but also from a non-metallic material; for example, it can be manufactured from plastic.

10.

In the case of smaller piston seals, the carrier 4 can preferably be punched out of a fairly thin steel band. This allows simple manufacture at a favourable cost. In the case of smaller piston seals, the thickness of the carrier 4 can be under 0.5 nun.

15.

The described piston seal 1 is eminently suited for installation in pneumatic cylinders which operate at high ambient temperature and which cannot be operated in the hydraulic medium on safety and/or health grounds, such as exist, for example, in the foodstuffs sector.

t

Claims (23)

Claims

1. A piston seal with at least one static and at least one dynamic sealing part, which has a sealing and a sliding-surface, characterised in that at least the sealing and sliding surface (7a, 7b) of the dynamic sealing part (6) is made from a high quality material with a low 5. friction coefficient which is different from the material of the static sealing part (2).

2. A seal according to claim 1, characterised in that the high-quality material is fluorine polymer.

10.

3. A seal according to claim 1 or 2, characterised in that the highquality material is polytetrafluor ethylene.

4. A seal according to any one of claim 1 to 3, characterised in that 15. the material is made from a combination of fluorine polymer and polytetrafluor ethylene.

5. A seal according to any one of claim 1 to 4, characterised in that the whole dynamic sealing part (6) is made from the high-quality 20. material.

6. A seal according to any one of claims 1 to 5, characterised in that it a produced in one operation.

25.

7. A seal according to any one of claims 1 to 6, characterised in that the different materials of the seal (1) are intimately bonded together.

8. A seal according to any one of claim 1 to 7, characterised in that the sealing and sliding surface (7a, 7b) of the dynamic sealing part (6) 30. is provided on a layer made from a high-quality material.

9. A seal according to any one of claims 1 to 8, characterised in that, at least apart from the sealing and sliding surface (7a, 7b), it is made from a lower quality material, and preferably the same material.

10. A seal according to any one of claims 1 to 9, characterised in that the materials of the static and dynamic sealing parts (2, 6) have a different shade of colour.

11. A seal according to any one of claim 1 to 10, characterised in that the sealing surface (2a) of the static sealing part is made from a softer, more elastic material than the sealing and sliding surface (7a, 7b) of the dynamic sealing part (6).

10.

12. A seal according to any one of claims 1 to 11, in which the static sealing part has at least one cushion part, characterised in that the cushion part (3, 3') is made from a more elastic material, preferably nitrile butadiene rubber, than the dynamic sealing part (6).

15.

13. A seal according to any one of claims 1 to 12, in which the dynamic sealing part has two radially-sealing sealing lips, characterised in that the sealing lips (7, 7') and/or their sealing and sliding surfaces (7a, 7b) are made from a different material.

20.

14. A seal according to claim 13, characterised in that at least one and preferably both sealing lips (7, 7') have the layer, and preferably a tetrafluor ethylene layer.

15. A seal according to any one of claims 1 to 14, characterised in that 25. it has additional sealing edges on the outer periphery.

16. A seal according to any one of claim 1 to 15, characterised in that the cushion part (3, 3') and the static sealing part (2) are made from materials with different Shore hardnesses.

30.

17. A seal according to any one of claim 1 to 16, characterised in that the cushion part (3, 3') and the static sealing part (2) are made from different materials.

35.

18. A seal according to any one of claims 1 to 17, characterised in thal, the cushion part (3, 3') and the static sealing part (2) have a different shade of colour.

10.

19. A seal according to any one of claim 1 to 18, in which a carrier is 5. provided which carries the sealing parts, characterised in that the carrier (4) is made of metal.

20. A seal according to any one of claim 1 to 19, characterised in that the carrier (4) is punched out of a fairly thin steel band.

21. A seal according to any one of claims 1 to 20, characterised in that the carrier (4) in the case of a small piston seal has a thickness which is smaller than 0.5 mm.

15.

22. A seal according to any one of claim; 1 to 18 or 21, characterised in that the carrier (4) is made of a non-meta-1lic material.

23. A seal substantially as hereinbefore described with reference to and as illustrated in the acccnpanying drawing.

Published].990 at The Patent Office. State House. 66 71 High Holborn. London WCIR4TP Further copies maybe obtamedfroni The Patent Office Sales Branch, St Mary Cray. Orpington. Kent BR5 3RD Printed by Multiplex techniques ltd- St Mary Cra.,,-. Kent. Con. 187,