GB2169671A

GB2169671A - Compound guide & sealing unit

Info

Publication number: GB2169671A
Application number: GB08529304A
Authority: GB
Inventors: Kurt Stoll
Original assignee: Festo SE and Co KG
Current assignee: Festo SE and Co KG
Priority date: 1984-11-30
Filing date: 1985-11-28
Publication date: 1986-07-16
Also published as: IT1200821B; GB2169671B; DE3443725A1; DE3443725C2; FR2574147A1; IT8522707A0; GB8529304D0; FR2574147B1

Abstract

The invention provides a guide and sealing unit for the piston rod of a pneumatic cylinder actuator, which is characterized by a high resistance to wear and by a very simple structure. The unit comprises a guide bush (5) made of synthetic resin forming an integral structure with a wiper ring (9) on the outer side of the cylinder actuator (2). There is a sealing ring (10) engaging the piston rod (4), while at the other end of the bush (5) there is a means for holding a sealing ring (8) in the bush. The strength of the sealing ring (9) and the surface integral therewith is greater than the strength of the sealing ring (8). <IMAGE>

Description

SPECIFICATION Compound guide & sealing Unit The invention relates to a guide and sealing unit more particularly but not exclusively for a piston rod in the housing of an actuator such as pneumatic one, consisting of a guide bush, an external wiper ring and a sealing ring on the internal end of the unit.

Normally a multi-component guide and sealing unit is employed for guiding and sealing a piston rod running through the end cover of a pneumatic cylinder actuator. Such a unit has a meet various requirements: on the one hand it has to reliably keep out foreign matter such as dirt, dust, shavings and the like from the interior of the cylinder actuator. On the other hand it has to ensure an air-tight sealing effect under all working pressures arising, so that the cylinder actuator is effectively sealed off from the outside. Finally, the arrangement is to have properties such as to guide the piston rod, and it should have a long working life.

Putting it succinctly, the unit has to guarantee a true guiding and sealing effect with a high efficacy of the supporting and hermetic functions. Furthermore, it has to exert the function of a wiper.

In order to fulfill these requirements it has so far been the practise in the art to provide a sealing ring of rubber in the cylinder actuator cover at one end which at the same time has the useful effect of covering over a guide bush (which is best made of fritted material) in the axial direction, such guide bush for its part holding a wiper ring (also made of rubber) as a protection against the outside atmosphere around the cylinder actuator, such wiper ring being axially supported on a molded element of the end cover of the cylinder actuator and serving less for sealing than for wiping off oil or the like. This unit has a shortcoming inasfar as the wear resistance leaves to be desired, more especially if the cylinder actuator is mounted where it is likely to be fouled by abrasive materials.A further disadvantage is that the assembly of the separate elements of the guiding and sealing unit is a relatively involved process. The design is complex and elaborate, since the unit generally comprises at least three main components.

Therefore one object of the present invention is to avoid these disadvantages of the prior art guide and sealing units.

A further aim of the invention is to devise a unit which, while not being elaborate in its design and having a simple structure, possesses a longer working life.

A still further object of the invention is to devise such a sealing and guide unit which offers advantages from the point of view of assembly.

In order to achieve these or other useful effects appearing in the course of the ensuing specification, a guide and support unit for a piston rod extending through the wall of a housing defining a space therein, is characterized in that it comprises a guide bush with internal and external ends, an external wiper ring, a sealing ring at said internal end of said bush, said guide bush forming an integral structure with said wiper ring and being adapted to retain said sealing ring in place, the strength of the material of said wiper ring being greater than that of the sealing ring, said sealing ring being soft and said wiper ring being made of a hard and rigid material.

Further useful developments of the invention are defined in the claims. The single-piece design of the guide bush and of the wiper ring gives rise to a distinct double effect inasfar as there is not only a reduction in the number of separate components of the guide and sealing unit, but furthermore a substantial enhancement in the strength of the wiper ring, since it is now made of the same material as the guide bush which combines a high degree of strength with running or sliding properties involving a low coefficient of friction. Preferably the guide bush, with the wiper ring part, is thus made of a hard and rigid synthetic resin, which may contain glass fibers to increase its strength. As the same time the guide bush forms the mount for the inner sealing ring which is best made of a soft and elastic material and preferably rubber.

The decrease in the costs of manufacture, occasioned by dispensing with expensive fritted metals and the combination of various functions in a single component, also involves the advantage of a long-lasting guide and sealing unit, this being due to an increasing strength or stiffness of the sealing members in the axial direction towards the outside and away from the interior of the cylinder.

The sealing of the cylinder from the outside may, in accordance with an advantageous further development of the invention, be increased inasfar as the sealing ring part of the guide bush possesses a resilient sealing lip that is radially biased towards the piston rod.

As part of a further advantageous outgrowth of the invention the guide and sealing unit is only locked in the housing axially in order to prevent it slipping out of place, whereas adjacent to the inner sealing ring there is a retainer sleeve supported peripherally on the guide bush, such sleeve extending in the annular space between the guide bush and the housing so that an elastic and yielding supporting action is ensured for locating the guide bush in place, such bush for example leading to the advantage of compensating for inaccuracies in manufacture and substantially relieving the guide bush from undesired lateral stresses. In this respect it is possible to utilize a self-aligning, yielding and elastic means for supporting the guide bush in place.

A more detailed account of the invention will now follow referring to the accompanying drawings.

Figure 1 is a radial section taken through a guide and sealing unit in accordance with the invention.

Figure 2 shows a unit as in Fig. 1 but with a modified sealing element.

Figure 3 shows a further possible modification of the invention in the same manner of representation.

Fig. 1 diagrammatically shows a radial section through a component of a housing cover 1 of a pneumatic cylinder actuator 2 with a piston 3 attached to a piston rod 4 for the actuation of means constituting a load, which is not shown.

The sealing and guide means for the piston rod 4 extending through the cylinder cover 1 has as its main part a guide bush 5 that is fashioned on a wear-resistant hard or rigid synthetic resin, preferably reinforced by glass fiber, with good running properties, that is to say with a low coefficient of friction. When moved towards the interior of the cylinder actuator 2 this guide bush 5 will be checked by a radial projection 6 as it is inserted into the cylinder cover 1. This projection 6 may naturally be placed further towards the outer side of the cylinder actuator if the guide bush 5 is suitably offset.In the form of the invention shown in Fig. 1 the guide bush 5 has a recess 7 adjacent the interior of the cylinder actuator 2 for a sealing ring 8 of soft, elastic material for radially sealing off the piston rod 4 against the internal pneumatic pressure obtaining in the cylinder actuator 2 in the space between the piston 3 and the cylinder end cover 1. At its opposite axial end the guide bush 5 has a wiper ring 9 for sealing off the piston rod 4 against materials from the outside and more specifically against the penetration of dust or dirt particles and foreign matter of all sorts, such ring 9 being made integrally with the guide bush. In order to perform the wiping function the guide bush 5 has a sealing lip 10 formed on it, which surrounds the piston rod 4 like a cuff and it is radially pretensioned or biased onto it.In order to locate the guide bush 5 in place in the axial direction there is an abutment 11 which was able to be adjusted in relation to the cylinder before being fixed in place on the cylinder actuator end cover. This abutment may more particularly be removed from the position shown when the guide bush 5 with the sealing ring 8 is to be renewed. The sealing ring 8 may have a form differing from that shown in Fig. 1, as for example one with a crescentlike cross section. To make possible such renewal itfis possible to provide the section, forming the wiper ring 9 of the guide bush 5 with recesses (not illustrated) against which suitable tools may be applied. It is also possible to dispense with the abutment.

In accordance with a further form of the invention, it is possible to facilitate assembly of the guide bush 5 by having it made in two parts with an axial parting plane therebetween, the axial parting faces being coated with a sealant film prior to assembly, just as the inner cylinder face, corresponding to the outerface of the piston rod 5, of the guide bush 5 may be provided with a lubricant for reducing friction.

Fig. 2 shows a further working example of the invention in the case of which the inner sealing ring 8, made of a soft elastic rubber material, is widened out in the form of a rubber sleeve or a retainer sleeve 12, which in the form of a molding, surrounds the guide bush 5 like a pipe. The guide bush 5 and the rubber sleeve 12 are in this case retained in place by annular projections 13 on the guide bush 5, which fit into corresponding grooves in the rubber sleeve 12, and locked joined so that they may be placed jointly in the cylinder actuator cover 1. In-other respects the guide bush 5 is designed like that of Fig. 1.In addition to a very powerful sealing action this unit possesses the advantage of an elastomeric, self-aligning supporting effect for the guide bush 5 so that it is practically possible to prevent undesired radial stressing thereof, and at least however this elastic retaining stystem for the guide bush 5, which to a certain degree is able to follow the axial angular motion of the piston rod, will enable such stressing to be reduced substantially. This unit offers the advantage of allowing for inaccuracies in manufacture. If the tolerances are less tight production costs will ultimately be lower.

It is naturally possible to employ other designs for the rubber supporting means of the guide bush 5, as for example by the use of a respective external coaxial sealing ring adjacent to the internal and external faces of the cylinder actuator cover 1.

In the case of the embodiment of the invention to be seen in Fig. 3 the guide bush 20 on the piston rod 21 is made integrally with the wiper ring 23 which extends away from the interior of the cylinders 22. The arrangement consists of hard synthetic resin material, whose properties replace the properties of fritted material as so far used for guide bushes. The recess 24 in the cylinder actuator end cover 25 also accepts the sealing ring 26 on the side nearest the piston 27. This sealing ring serves to seal off the interior 22 of the cylinder from the outside and is made of soft synthetic resin, rubber or the like, and in order to improve assembly is made integrally with the retainer sleeve 28, same also being fashioned of soft synthetic resin material, rubber or the like. In this illustrated working example of the invention the guide bush and the retainer bush are concentrically cylindrical, the retainer sleeve surrounding the guide bush and gripping it elastically. 29 denotes a sealing lip engaging the piston rod, 30 denotes a wiper lip on the wiper ring which prevents the ingress of dirt into the space within the cylinder.

The invention will thus be seen to provide a guide and sealing arrangement as a compact component for guiding and sealing a piston rod running through a cylinder end cover. The component is designed with a careful choice of the sealing materials having different strength characteristics at the interfaces with the housing member so as to ensure a high resistance to wear. The component is made up Of a smaller number of parts, fully profits from the properties of the materials utilized and simplifies manufacture inasmuch as greater tolerances are possible. A further important advantage is that fitting the component and removing it are very much simpler and less time consuming.

The invention will be consequently seen to relate to a sealing and guide system for producing a wiping action using a relatively hard material and for the sealing action on the inside uses a soft material as has so far been the practise. In addition the supporting or guiding function is assumed by a synthetic resin bush, which is made integrally with the wiper ring.

A further advantage that is produced is that the softness of the groove ring is used for sealing in an inward direction with the possibility of elastically supporting the guide bush by means of a rubber support so that it is possible to avoid an undesired lateral displacement of the guide bush, this increasing the length of service of the overall sealing and guiding system.

The manufacturing costs of the soft sealing and bearing part and also for the hard wiper and guide part are better than the design used so far, which consisted of a greater number of separate parts. The guide bush with the wiper ring is able to be extracted from the outside for replacement. On inserting the replacement component into the recess, grease is used to be able to slip the component into position more readily.

Claims

1. A guide and support assembly for a piston rod extending through the wall of a housing defining a space therein, the assembly comprising a guide bush with internal and external ends relative to the piston rod location, an external wiper ring, and a sealing ring at the internal end of the bush, the guide bush forming an integral structure with the wiper ring and being adapted to retain the sealing ring in place, the strength of the material of the wiper ring being greater than that of the sealing ring, the sealing ring being formed of a relatively soft, and the wiper ring being formed of a relatively hard and rigid, material.

2. A guide and sealing assembly according to claim 1, wherein the guide bush is formed of a material selected from the group consisting of synthetic resin, hard synthetic resin, and synthetic resin reinforced with glass fibres.

3. A guide and sealing assembly according to claim 1 or 2, wherein the wiper ring is formed of a hard synthetic resin material.

4. A guide and sealing assembly according to any of the preceding claims, wherein the sealing ring is formed of soft elastic rubber.

5. A guide and sealing assembly according to any of the preceding claims, wherein the wiper ring has a sealing lip adapted to rest against the piston rod with a radial loading effect thereon.

6. A guide and sealing assembly according to any of the preceding claims, wherein the sealing ring is retained in an axial recess in the guide bush.

7. A guide and sealing assembly according to any of claims 1 to 5, comprising a retainer sleeve adjacent to the sealing ring, the sleeve being drawn onto the guide bush and surrounding same at least partly round its circumference so as to allow for radial loading of the guide bush.

8. A guide and sealing assembly according to claim 7, wherein the sealing ring is made integrally with the retainer sleeve.

9. A guide and sealing assembly according to claim 8, wherein the guide bush is elastically and self-aligningly supported in the retainer sleeve to allow for manufacturing tolerances.

10. A guide and sealing assembly according to any of claims 7 to 9, wherein the guide bush has at least one annular projection and the retainer sleeve has an annular groove, the guide bush being interlocked with the retainer sleeve.

11. A guide and sealing assembly according to any of claims 7 to 10, wherein the sealing ring and the retainer sleeve are made of a material selected from the group comprising soft synthetic resin material and rubber.

12. A guide and sealing assembly according to any of the preceding claims, wherein on its peripheral face the guide bush has at least two sealing rings for supporting same on the housing.

13. A guide and sealing assembly according to any of the preceding claims, wherein the housing wall has a first abutment and a movable abutment adapted to be locked in a given setting thereof for axially positioning the guide bush, the movable abutment being arranged on a side of the housing wall remote from the space therein.

14. A guide and sealing assembly according to any of the preceding claims, wherein the housing is in the form of a pneumatic cylinder actuator.

15. A guide and sealing assembly substantially as described herein before with reference to Fig. 1 of the accompanying drawings.

16. A guide and sealing assembly substantially as described hereinbefore with reference to Fig. 2 of the accompanying drawings.

17. A guide and sealing assembly substantially as described hereinbefore with reference to Fig. 3 of the accompanying drawings.

18. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.