Roy, Ronald Keith (6 Morley Crescent, Box Hill North, VIC 3129, AU)
| 1. | A sealing bearing assembly for an elongate reciprocable member, including: a housing defining a passage which extends through the housing and in which said member is reciprocable along an axis; seal means disposed in said passage for extending about and engaging the reciprocable member so as to fluid seal said passage in the presence of a pressure differential between respective ends of the passage; and pressure reduction means between said seal means and one end of said passage which in situ is the end exposed to a fluid pressure higher than the other end; said pressure reduction means including a plurality of lips which extend about said passage so as to project inwardly of said passage with an inclination towards said one end, whereby each lip if exposed to said higher fluid pressure varies in its inclination as it bends and is pressed against the reciprocable member. |
| 2. | A sealing bearing assembly according to claim 1 wherein said lips are formed integrally in sleeve means which also defines a bearing surface for the reciprocable member. |
| 3. | A sealing bearing assembly according to claim 2 wherein said sleeve means is part of a cartridge adapted to be mounted in an opening of an end cover of a fluid powered cylinder assembly, the cartridge also including the seal means. |
| 4. | A sealing bearing assembly according to claim 2 or 3 wherein said housing includes the sleeve means. |
| 5. | A sealing bearing assembly according to claim 1 wherein the reciprocable member is a rod eg. a piston rod and the assembly is correspondingly of generally annular configuration. |
| 6. | A sealing bearing assembly according to any one of claims 2 to 4 wherein the reciprocable member is a rod eg. a piston rod and the assembly is correspondingly of generally annular configuration. |
| 7. | A sealing bearing assembly according to claim 6 wherein the pressure reduction means further includes a plurality of annular grooves formed in the inner surface of the bearing sleeve, between said lips and the seal means. |
| 8. | A sealing bearing assembly according to claim 6 or 7 wherein the lips are defined by a plurality of spaced right angular grooves formed in the bearing sleeve so as to be inclined, in axial cross section, to said axis. |
| 9. | A sealing bearing assembly according to any preceding claim wherein the seal means is an annular mechanical seal. |
| 10. | A sealing bearing assembly according to claim 9 wherein there are two such seals. |
| 11. | A sealing bearing assembly according to claim 9 or 10 wherein the housing includes respective interior annular grooves for the respective seals. |
Background Art Fluid powered actuators such as hydraulic and pneumatic piston and cylinder devices are often required for reliable operation in somewhat adverse environments. The sealing and bearing assembly for supporting the reciprocating piston rod where it projects through the end of the cylinder is expected to provide a reliable long term seal against fluid leakage from within the cylinder, which fluid may often be at very high pressure.
The assembly may also have to cope over time with high temperatures and/or with a dirty, dusty or oily external environment which may contaminate the piston rod externally of the cylinder but should not traverse the sealing and bearing assembly to affect the interior of the cylinder. In some cases, for example crust breaker actuators in aluminium smelters, it may be specified that the sealing and bearing assembly for the piston rod must be electrically insulating without arcing at the very high currents present.
All of these requirements may be additionally complicated in some circumstances by significant side loadings on the piston rod.
It is known to provide combination sealing bearing assemblies for piston rods which contain both a bush or sleeve providing an axially extending bearing surface, together with multiple annular seals of various configurations and, at the outside of the assembly, an annular wiper lip for cleaning the piston rod on its return stroke. All or some of these components are typically retained in an integral, generally tubular housing as a unitary sealing and/or bearing cartridge. An exemplary configuration is disclosed in Australian patent 584738. Selected components such as the bush and/or cartridge housing may be formed in an electrically insulating material.
The present applicant's prior Australian patent 675884 proposes a modification of these cartridges in which the bearing sleeve is formed with plural annular grooves in its internal bearing surface as a means for reducing the actual fluid pressure communicated to the sealing units.
United States patent 4744571 discloses a self compensating sealing configuration for reciprocable rods in which the rod substantially deforms a set of spaced annular wipers which extend about the rod. The wipers have an internal diameter substantially less than the external diameter of the rod to ensure their deformation, and the sealing function is augmented by 0-rings located in the grooves between the wipers.
Summary of the Invention It is an object of the invention to provide a further improvement in the performance and/or functional life of a sealing bearing assembly for a reciprocable member.
The invention accordingly provides a sealing bearing assembly for an elongate reciprocable member, including: a housing defining a passage which extends through the housing and in which said member is reciprocable along an axis;
seal means disposed in said passage for extending about and engaging the reciprocable member so as to fluid seal said passage in the presence of a pressure differential between respective ends of the passage; and pressure reduction means between said seal means and one end of said passage which in situ is the end exposed to a fluid pressure higher than the other end; said pressure reduction means including a plurality of lips which extend about said passage so as to project inwardly of said passage with an inclination towards said one end, whereby each lip if exposed to said higher fluid pressure varies in its inclination as it bends and is pressed against the reciprocable member.
Preferably, said lips are formed integrally in sleeve means which also defines a bearing surface for the reciprocable member.
Advantageously, said sleeve means is part of a cartridge adapted to be mounted in an opening of an end cover of a fluid-powered cylinder assembly, the cartridge also including the seal means. Said housing may comprise the sleeve means.
Preferably, the reciprocable member is a rod such as a piston rod and the assembly is correspondingly of generally annular configuration.
Preferably, the pressure reduction means further includes a plurality of annular grooves formed in the inner surface of the bearing sleeve, between said lips and the seal means.
Preferably, the lips are defined by a plurality of spaced right angular grooves formed in the bearing sleeve so as to be inclined, in axial cross section, to said axis.
The seal means is preferably an annular mechanical seal and any of a variety of conventional seals may be used. There are preferably two such seals. The housing preferably includes respective interior annular grooves for the respective seals.
Brief Description of Drawings The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side elevation, half-sectioned, of an end assembly of a pneumatic piston and cylinder actuator, showing the piston rod in situ; and Figure 2 is an enlargement of the portion X in Figure 1.
Description of Preferred Embodiments The illustrated end assembly 10 comprises a generally cylindrical housing formed by an outer metal housing 12 and an inner annular housing in the form of a sleeve 23 of a sealing bearing cartridge 15. Housing 12 has an axial bore 11 which receives and retains cartridge 15, and an inner peripheral flange 13 by which it may be fitted, by bolts 14, to the cylinder (not shown) of a fluid-powered piston and cylinder actuator, e. g. a hydraulic or pneumatic actuator. Cartridge 15 defines a passage or bore 20 that extends through the cartridge and in which piston rod 8 is reciprocable along axis 7. Cartridge 15 is held between a fine shoulder 21 in bore 11 and a retainer ring assembly 22.
Sleeve 23 is an integral generally tubular body adapted to fit about piston rod 8 of the fluid powered actuator. The sleeve is provided with a number of formations to be further described such as to define an axially inner end 24 and an axially outer end 25.
These designations refer to the correct disposition of the assembly in bore 11 with respect to the actuator cylinder. In situ, inner end 24 thus faces the interior of the cylinder and outer end 25 the exterior, although, of course, other components may actually lie between these ends and the respective interior and exterior.
The interior cylindrical surface 20a of bore 20 of sleeve 23 includes an intermediate portion 28 characterised by six equispaced grooves 30. The cross-section of each of these grooves is depicted as rectangular but may be rectangular, angled, V, sawtooth or any other suitable form. Surface 20a defines a bearing surface for the piston rod and grooves 30 provide a labyrinth seal formation in this surface.
Outwardly of intermediate sleeve portion 28 are a pair of axially spaced relatively larger similar grooves 32,33 which mount respective annular mechanical seals 34,35.
Seals 34,35 extend about and engage piston rod 8 so as to fluid seal passage 20 in the presence of a pressure differential between the ends of the passage. Midway between these seals is a fine peripheral groove 36 to which grease or other lubricant for the seals may be delivered from a reservoir 38 via one or more radial orifices 37 in sleeve 23.
Adjacent the outer end 25 of sleeve 12 is a still further interior groove 40 which is of similar size to grooves 32,33 and which mounts a rod wiper 42. Outer sleeve end 25 further includes an inner tapered rim 44 providing an auxiliary wiping function (with retainer ring assembly 22) adjacent rod wiper 42.
Cartridge 15 includes sleeve 23, seals 34,35, and rod wiper 42. The external cylindrical surface of sleeve 23 has a pair of rectangular grooves to receive O-ring or other type of seals 45 to prevent bypass of fluid between the sleeve and the cylinder end housing bore 11.
As described in Australian patent 675884, the labyrinth seal formation provided by grooves 30 serves to create turbulence in the flow of fluid between the piston rod and bearing surface 20. Each groove itself thereby creates local turbulence and reduces the pressure and flow of fluid on to the next groove. This effect is cumulative so that at the axially outer end of the labyrinth seal formation, the pressure of fluid transmitted to the seals 34,35 has been substantially reduced, in consequence minimising the risk of leakage.
Initial pressure reduction in advance of grooves 30 is provided in a region axially adjacent the inner end 24 of sleeve 23. Here, on the interior surface 20a of the sleeve, are formed several peripherally extending square or rectangular grooves 50 which differ from grooves 30 by being deeper and by being inclined, in any axial cross section, at about 45° to axis 7, oriented so that the floor of each groove is axially further than its mouth from sleeve inner end 24. This angle is of course not critical but it is thought that the angle is
preferably in the region of 45°. Grooves 50 define between them respective lips 52 of substantially uniform width which project inwardly of passage 20 while being inclined towards the inner end 24 of the sleeve. The drawings illustrate five grooves 50 and four lips 52, but these numbers may of course vary to suit the structural context and/or the application.
It is important to appreciate that the radially innermost annular edge face 54 of lips 52 remains, under relaxed conditions, a diameter slightly larger than that of piston rod 8 since this edge face 54 is co-cylindrical with the main bearing surface 20a of the bearing sleeve. However, these lips perform a pressure reduction or pre-sealing function, additional to that of grooves 30, by which the internal pressure in the cylinder chamber is not fully communicated to seals 34,35, thereby enhancing the performance and effective life of the seals.
The functioning of the lips 52 will now be explained, with reference to Figure 2.
In the event that the internal pressure in the cylinder chamber is communicated to the axially innermost of grooves 50, say groove 50a, so that this groove 50a is at a higher pressure than the groove 50b next in sequence, the pressure differential, as indicated by arrows 55 in Figure 2, distorts the first lip 52a by bending it about a fulcrum region 57 at the root of the lip. Because of its inclination, the lip is thereby pressed against the outer cylindrical surface 8a of the reciprocable rod to perform a sealing function.
In the event that lip 52a is deformed to the position indicated in Figure 2 by broken lines 60, the lip will further deform over-centre and the pressure is likely to be partially communicated past the lip to the next groove 50b. The process now repeats, and indeed is repeated even where the overcentre deformation of the lip does not occur and there is simply a degree of leakage of fluid pressure past the first lip to the second groove.
It will be appreciated that if sleeve 23 is formed in very low friction material such as PTFE, the deformation and compression of lips 52 does not cause a substantial drag force on the piston rod.
Seals 34,35 may be any suitable ordinary mechanical seal, for example a U-type seal, an expanded U-type seal also known as a polypak, or a glide ring type. The seal may be formed in a suitable material for the temperature or pressure range of the intended application. Suitable materials include teflon (PTFE), nitrile or viton. There may be an annular expander element within the seal or under the seal in the groove 32,33. A particularly preferred seal, that depicted in Figure 1, is a glide-ring type seal comprising a U-section contact component 39a of PTFE-based composition, and an underlying close fitting expander component 39b of viton elastomer, of generally rectangular section. The inner corners of grooves 32,33 may be stepped to locate the underlying components of the mechanical seals.
Wiper 42, assisted by retainer ring 22 and sleeve rim 44, are designed to wipe or scrape off contaminating foreign matter from the piston rod and thereby serve to protect seals 34,35 and the labyrinth seal formation provided by grooves 30 substantially against contaminant incursion along the external surface of the piston rod from the exterior of the cylinder. Each wiper may be one of a variety of known conventional wipers and may be formed in a metallic or other suitable material according to the application.
The material of sleeve 23 is preferred to be very low friction as mentioned but would depend upon intended application and might be metallic e. g. cast iron, stainless steel, brass, bronze or some other copper based alloy. Other possibly suitable materials include nylon, ultra high molecular weight polyethylene, teflon (PTFE) based materials, other polymers, and ceramics.
It will be understood that the inclined deformable lips 52 and the following shallower labyrinth grooves 30 combine to provide a highly effective pressure reduction or pre-seal function in advance of seals 34,35. This further facilitates the performance and effective life of the seals, and hence of the whole sealing bearing cartridge and end assembly.
Possible applications for the sealing bearing assembly include normal industrial cylinders, heavy duty side loading applications, or high temperature applications such as crust-breaker actuators in aluminium smelters.
It is emphasised that the assembly need not be provided in an integral sleeve as illustrated, although it is advantageous to provide such a one piece cartridge assembly.
The assembly could, however, be in, e. g. two or three pieces. For instance, there could be a bearing or bush section, then a seal and wiper cartridge, or even separate seal and wiper sections.
For optimum performance in situ, it is expected that the clearance between the piston rod 8 and bearing surface 20a would need to be quite fine, for example in the range 0.002-0.003". The exterior diameter of the sleeve 23 would be calculated in relation to the intended application to provide sufficient clearance for expansion to avoid seizure of the piston rod, particularly in the case of high temperature conditions where teflon and some materials of relatively greater co-efficient of expansion are being used.
The invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings.
All of these different combinations constitute various alternative aspects of the invention.
The term"comprises"or its grammatical variants as used herein is equivalent to the term"includes"and is not to be taken as excluding the presence of other elements or features.