GB2208687A

GB2208687A - Pneumatic seal

Info

Publication number: GB2208687A
Application number: GB8819367A
Authority: GB
Inventors: Sture Persson
Original assignee: Skega AB
Current assignee: Skega AB
Priority date: 1987-08-14
Filing date: 1988-08-15
Publication date: 1989-04-12
Anticipated expiration: 2008-08-15
Also published as: SE8703168L; SE463632B; SE8703168D0; GB2208687B; DE3827483A1; GB8819367D0

Description

o' Pneumatic Seal r. fr) i_ /- 0 8 6 8 7 This invention relates to an

annular seal for sealing between two members which are movable relative to one another in a pneumatic device, e.g., between a piston or piston rod and a wall surrounding this.

Like in hydraulic cylinders, a seal between piston and cylinder wall ad between piston rod and a wall surrounding this in the end piece of the cylinder must be used in pneumatic cylinders. Lubrication in hydraulic cylinders is obtained through the hydraulic oil which reduces friction between seal and surrounding wall. As distinguished from this, the pressure medium used does not provide any lubrication in pneumatic cylinders but a lubricant must instead be added through so-called oil mist lubrication in order to establish a thin lubricant film on the cylinder wall and to embody the seal at the same time so that this does not damage the established lubricant film which, however, has appeared to be very difficult and is one of the great problems with seals for pneumatic devices. If the lubrication film is damaged, the friction will be increased directly and the seal is worn down rapidly and must be replaced and the risk of degradation of the lubricant film will also increase rapidly with increased pressure.

The present invention provides an annular seal for sealing between two members which are movable relative to one another in a pneumatic device, e.g., between a piston or piston rod and a wall surrounding this, which seal is arranged on or forms part of one of the members of the device and comprises a support member and at least one annular sealing lip projecting therefrom which functions dynamically and which is - 2 arranged to seal against the other member facing the pressure side of the device, wherein the dynamic sealing lip is provided with a low friction layer on its surface facing the other member of the device, which layer is intimately connected with and supported by a core of an elastic polymer material, of which the support member and each sealing lip are integrally formed.

One advantage of this seal is that in principle it does not require lubrication for its function, possibly initial lubrication as a one-time procedure at mounting or when putting into use, and that it does not require any oil mist lubrication, in any case after such a lubrication, but functions thereafter without addition of a friction decreasing lubricant even when pressurized.

Not the least in the food manufacturing industry and also in other fields with high demands on environment and hygiene this has been a long-felt want which has not been realised until now.

The core may preferably consist of EPDM, NBR or IIR and the low friction layer of ultrahigh molecular polyethylene.

It has also been found advantageous here to provide the dynamic sealing lip with a length in axial direction that is substantially shorter than the static sealing lip of the seal.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 shows a section of a seal the invention in its natural state and; Fig. 2 shows, partly in section, the seal applied to a piston of a pneumatic cylinder, its cylinder wall being indicated by dash-dot lines.

On the drawing 1 designates generally a seal according to according to the invention in a design intended to be arranged in an annular recess 4 in a piston 5 of a pneumatic cylinder, which recess is formed with end surfaces 2 and 3 located in a radial plane. The wall of the cylinder is indicated in Fig. 2 by dash-dot lines 6.

The inventive seal 1 comprises an annular base portion 7 serving as support and carrier and having a free end surface 8 for contact with the end surface 3 of the recess in order to absorb axial forces and having an inside diameter somewhat less than the outside diameter of the annular recess 4 in which the seal is to be arranged and which should have a depth somewhat greater than the thickness of the base portion 7 of the seal. Moreover, two annular sealing lips 9 and 10 are integral with this base portion, project divergently from the base portion 7 and form together with this a core consisting of an elastic polymer material, e.g. rubber and preferably EPDM, NBR or IIR rubber. The lip designated by 10 is the static sealing lip of the seal which is intended to be in contact with and seal against the bottom of the recess 4 while the lip designated by 9 is the dynamic sealing lip of the seal which is intended to seal against the cylinder wall 6 in the applied state of the seal.

In accordance with the invention the dynamic sealing lip 9 like the base portion 7 of the seal is covered with a low friction layer 11 of a low friction material, preferably ultrahigh molecular polyethylene, at its surface facing the cylinder wall 6. This layer is intimately connected, for example by vulcanization, with the elastic material in the core of the seal and may have the same thickness along the axial length of the seal but should preferably have a greater thickness along the axial length of the base portion than along the axial length of the dynamic sealing lip in accordance with the embodiment shown on the drawing.

The sealing lips 9 and 10 projecting divergently from the base portion 7 form in the natural state of the seal shown in Fig. 1 as essentially V-shaped gap 12 between themselves with a pointed or round bottom 13 and an angle 0(+ 0 on the side 14 of the dynamic sealing lip facing away from the low friction layer 11 and the side 15 of the static sealing lip facing the low friction layer 11, 4 representing the angle between a line 17 parrallel with the longitudinal axis 16 of the seal through the intersectional point 18 of the said sides 14 and 15 and the side 15 of the static sealing lip while the angle F represents the angle between the said line 17 and the side 14 of the dynamic sealing lip. The angle N should then be less than the angle E as shown in Fig. 1.

Moreover, in accordance with this invention the static sealing lip 10 of the seal, as seen in axial direction, is longer than the dynamic sealing lip in order to support and stablize the seal in its seat and to ensure that the dynamic sealing lip will be pressure activated.

The dynamic sealing lip 9 has such a length adapted to the angles V and F that the gap 12 in a radial plane through the end surfaces 19 of the dynamic sealing lip has a width measured perpendicularly to its surfaces 14 and 15, respectively, and consequently the thickness of the support portion 7, the static sealing lip 10 having a thickness which is equal to or somewhat greater than the dynamic sealing lip 9. Both sealing lips 9 and 10 have in principle the same thickness along the whole of their lengths. As to the static sealing lip 10 it can be somewhat narrower at its end section 20 as it can be formed with a surface 21 parallel with the T_.

longitudinal axis on its side facing away from the low-friction layer, see Fig.l.

At the seal 1 applied in its recess 4 its two sealing lips 9 and 10 should face the pressure side so that the pressure prevailing on the pressure side of the cylinder should be utilised to increase the contact pressure of the sealing lips against the respective surface in addition to the contact surface that the sealing lips 9 and 10 create themselves as they at the application of the seal in the recess 4 are pressed against each other thanks to their design to a substantially parallel position. Moreover the distance between the bottom of the recess and the wall 6 surrounding the seal 1 is somewhat greater than the total thickness of the seal at the base portion 7 so that no compression whatsoever will arise in the base portion 7 of the seal that has exclusively a guiding function.

In the low friction layer 11 surrounding the core a peripheral groove 23 is preferably arranged to be located more closely to the end surface 8 of the base portion than the part thereof passing onto the sealing lips 9 and 10.

As to a double-acting piston two seals according to the invention are used which are placed in each their recess with the end surfaces 8 facing each other. The piston shown on the drawing is made in one piece and the present seal is forced onto this type of piston and even if not shown on the drawing the piston to which a seal according to the invention is to belong should consist of two or more members that are combined to one unit after the seal has been applied, or be a so-called compact piston, of which the present seal is a part in a special design lacking the static sealing lip.

The seal according to the invention is also feasible as a piston rod seal, in which case the seal is applied in a recess in a wall through which a piston rod extends, in order to seal against the piston rod with its dynamic sealing lip located 5 internally therein.

This invention is not restricted to what has been describedabove and shown on the drawing but can be modified, changed and supplemented in many different ways within the scope of the inventive idea defined in the claims.

is 1

Claims

1. An annular seal for sealing between two members which are movable relative to one another in a pneumatic device, e.g., between a piston or piston rod and a wall surrounding this which seal is arranged on or forms part of one of the members of the device and comprises a support member and at least one annular sealing lip projecting therefrom which functions dynamically and which is arranged to seal against the other member facing the pressure side of the device, wherein the dynamic sealing lip is provided with a low friction layer on its surface facing the other -member of the device, which layer is intimately connected with and supported by a core of an elastic polymer material, of which the support member and each sealing lip are integrally formed.

2. The seal of claim 1, wherein the low friction layer is of ultrahigh molecular polyethylene and the core of rubber of the type EPDM, NBR or IIR or of another material having the corresponding properties.

3. The seal of claim 1 or 2, wherein the low friction layer has the same thickness along the whole of its axial length

4. The seal of claim 1 or 2, wherein the low friction layer has a greater thickness along its part extending across the support member. 30

5. The seal of any one of the preceding claims, wherein a peripheral groove is formed in the part of the low friction layer extending across the support member of the seal.

6. The seal of any one of the preceding claims, wherein the dynamic parts of the seal and the sealing lip supporting parts of the low friction layer are shorter in axial direction than the static sealing lip.

7. The seal of any one of the preceding claims, wherein the seal has a total thickness at its support member that is equal to or less than the distance between the bottom of the recess and the surface against which the dynamic sealing lip is to seal.

8. The seal of any one of the preceding claim, wherein the seal comprises a second annular sealing lip which projects from the support member and which functions statically.

9. The seal of claim 8 wherein the first and second sealing lips project divergently from the support member and face the pressure side of the device.

10. The seal of claim 8 or claim 9, wherein the seal is designed to be disposed with its support member and its static sealing lip in a recess in the one member of the device.

11. The seal of any one of the preceding claims, wherein the support member as well as the dynamic sealing lip is provided with the low friction layer on its surface facing the other member of the device.

12. An annular seal substantially as hereinbefore described with reference to the accompanying drawings.

Published 1988 at The Patent Office. State House. 66'71 High Holborn. London WCIR 4TP- Further copies may be obtaaned from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent Con 1181