GB2099522A - Sliding seal system - Google Patents

Abstract

A sliding seal system for pistons and piston rods of power cylinders and for floating pistons of pressure reservoirs, which consists of a combination of sealing and lubricating rings 11, 12 respectively and with which a high partial pressure can be generated to obtain practically complete dry-running of the combination seal system is described. The lubricating ring 12 is of plastically deformable material which is non self- lubricating but contains a high proportion of dry mineral lubricant, and the sealing ring 11 has reinforcing means which are distributed evenly in a portion 11b thereof to produce additional pressure at sealing edge or sealing portion 14. The reinforcing means may comprise fibre ends distributed evenly and with random orientation within the portion 11b. The fibre end reinforcement may be of cotton, synthetic material, asbestos, cellulose or combinations of such substances, or the reinforcement may be of carboxylated nitrile rubber. <IMAGE>

Description

SPECIFICATION Sliding seal system The invention relates to a sliding seal system for piston rods of power cylinders and for floating pistons of pressure reservoirs particularly those comprising a combination of sealing and lubricating rings, with which a high partial pressure may be generated to obtain substantially complete dry-running of the seal system and in which the lubricating ring is made of plastically deformable material which is not self-lubricating but contains a high proportion of mineral dry lubricant.

In this kind of combination seal system the lubricating rings are made of pure, plastically deformable material which is non-self-lubricating but acts as a supporting framework for a high proportion of solid lubricant in the form of molybdenum disulphide (MoS2) or similar substances. However, lubricating rings of this kind only realise their full efficiency when sliding friction is obtained on substantially dry sliding surfaces and the lubricating ring itself (or the detached particles of solid iubricant) are subjected to such high shear loadings that corresponding layer lattice segments of singlecrystal plates are detached.

It has been proposed to provide a combination seal system which reliably excludes the formation of a liquid film, emanating from the working medium, both in the high-pressure range and when the working medium is at very low pressure, without being subject to any notable wear, and such that, in operation, an incompressible, continuous and firmly anchored coating of dry lubricant is formed between the metallic sliding surface of the cylinder or the piston rod and the seal system; rectangular slot being provided for the combination seal system and conventional seal materials used. With the known proposal the sealing ring has fabric reinforcement which acts to generate additional pressure at the sealing edge in operation.

Tests have shown that known fabric reinforcements for sealing rings wear unevenly.

The seal materials have a heterogeneous structure because of the fabric reinforcement and preferably incorporate a textile fabric. It can happen, particularly in extreme operating conditions, that the wear at the sealing edge, or the sealing portion, also occurs unevenly in line with the heterogeneous structure of the seal materials.

Moreover, it is also possible, that the textile fabric inserts may separate from the rubber, presenting the danger of premature failure of the seal.

Consequently, the present invention is based on the knowledge that the seal materials of the sealing ring must have as homogeneous a structure as is possible in order that uniform wear is ensured.

In accordance with the invention there is provided a sliding seal system for pistons and piston rods of power cylinders and for floating pistons of pressure reservoirs, the seal comprising a combination of sealing and lubricating rings, with which a high partial pressure may be generated to obtain substantially complete dryrunning of the seal system and in which the lubricating ring is of a plastically deformable non self-lubricating material containing a high proportion of mineral dry lubricant, the sealing ring having reinforcing means distributed evenly in partial zones within its rubber substance and produce additional pressure at its sealing edge or sealing portion.

The reinforcing means are preferably made of fibre ends distributed evenly and with random orientation and, with the rubber form a homogeneous mass. The fibre ends maybe of cotton, synthetic materials, asbestos, cellulose or combinations of these substances.

In one embodiment the reinforcing means are of a carboxylated nitrile rubber.

The proposed reinforcing means which are distributed evenly in partial zones of the sealing ring within the rubber substance guarantee uniform wear and thus longer life for the seal system.

In addition, the production of a rubber substance having an evenly distributed reinforcing means is simpler and less costly than the production of fabric reinforcement inside the rubber substance.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figures 1 and 2 illustrate axial sections through various embodiments of single acting forms of seal.

Figures 3 and 4 are diagrammatic axial-section views of two piston seals, one being single-acting and the other double-acting.

Figures 5 and 6 are similar sectional views of two piston-rod seals.

Figure 7 is an axial-section view of a so-called "axially braced cup seal", but with the number of entirely elastic and reinforced sealing rings reduced, and Figures 8, 9 and 10 are axial sections through various embodiments of single-acting and doubleacting forms of seal.

Figures 1 and 2 show axial sections through a single-acting seal 11 for a piston and a piston-rod respectively with a ring 1 2 containing a high proportion of dry lubricant. A line 13 indicates the position of the moving surface of a piston rod and a cylinder respectively (not shown) in relation to the position of the seal when fully assembled, the seal itself being shown in the position it adopts prior to insertion of the piston rod and prior to being fitted in the associated cylinder respectively. The seals 11 are formed in one piece and consist of an entirely elastic section 1 a and a section 116 having reinforcing means distributed evenly within its rubber substance.In one embodiment the reinforcing means takes the form of fibre ends are distributed uniformly and with random orientation and they form with the rubber a homogeneous mass. Cotton, synthetic materials, asbestos, cellulose or a combination of these substances may be used to form the fibre ends. Carboxylated nitrile rubber may also be used as the reinforcing means. The reinforced section 1 b is designed so that, by extension toward the sealing edge 14 and by appropriate shaping, the entirely elastic section of the seal is reinforced, supported and stiffened such that when fully assembled there is still sufficient elasticity, but the pressure levels between the sealing edge and 14 and the "moving surface" 13 remain at least twice as high as with conventional seals.In this way the desired objective is obtained with regard to dry-running and the formation of a lubricating film on the moving surface.

In Figures 3 to 6, when the assembly is complete, a piston 1 slides in a cylinder (not shown) and a piston rod (not shown) slides in an end cover 2. The working medium in the respective cases exerts a pressure on the sliding seal system 4 in the direction of the arrows 3 or alternately in the direction of arrows 3a and 3b.

The seal system 4 is located in a seal slot 5 and comprises an actual sealing ring 4a with a partial zone 4b (or two partial zones as shown in figure 4) provided with a reinforcing means of the kind described above and disposed on a low pressurize side of the seal system. The seal system 4 further comprises a ring 4c which is located in a corresponding recess, the ring 4c contains a high proportion of dry mineral lubricant and is of a plastically deformable material which is non-self lubricating.

A support ring 6 of wear-resistant material may be provided, together with a supporting shoulder 7 at the back of the seal if necessary, so that the ring 4c is completely supported when very high working pressures are involved.

The way in which the desired conversion is achieved within the seal combination is described for the sake of clarity with reference to Fig. 3, but is achieved in the same way in the seals of Figs.

4, 5 and 6. The forces acting in use, on the seal combination 4 are determined by the prevailing service pressure, the dimensions of the surface area on which the service pressure acts (D:--D)76/4, the pre-stressing at the sealing edge 4d and the magnitude of the frictional forces at the seal during operation, whereas the seal is supported merely over a surface area of (D21-D32)/4 and the surface area (D32-D22),t/4 of the seal is unsupported (or possibly supported only by the return pressure of the low pressure side).The annular space 8 (which has an area (D32-D22)/4 facing toward the high pressure side) cannot be pressurized by the prevailing operating pressure, or by the seal itself under the operating pressure, as any pressurized fluid in the annular space 8 may escape therefrom via the slotted supporting ring 6, or across the relatively rough end face of ring 4c on the low pressure side.

This combination of forces acting in use on the seal combination presses the ring 4c more strongly than in conventional seal combinations against its corresponding metallic sliding surface (not shown) which produces an extremely smooth, pressure-resistant lubricating layer on the metallic sliding surface.

Figure 7 shows a combination seal system 11 for sealing the moving surface of a piston rod (not shown). An entirely elastic sealing ring 1 5' is located between the parts of a seal provided with a reinforcing means of the kind discussed above, namely a thrust ring 16, sealing ring 13' and supporting ring 14'. A ring 12 of plastically deformable material which is non-self-lubricating and contains a high proportion of dry lubricant, is located between the face of the supporting ring 14' on the low pressurise side of the system and the flank 1 7 of the slot which is also on the low pressurise side.Lengthwise, the entire seal system 11 is designed so that, once it has been fitted into the seal slot, powerful axial pressure is guaranteed by the flanks 1 7 and 1 8 of the slot by means of a projection 1 9 of thrust ring 1 6 which may be provided with pressure equalising notches; as a result, when a piston rod is inserted, complete support is provided for the individual parts of the seal and these seal parts are made to exert an additional pressure on the moving surface of the piston rod at a level that would usually be unacceptable.

The magnitude of this additional pressure is determined simply by axial compression using the deformation brought about at the projection 19 by virtue of the distance between the flanks 1 7 and 1 8 of the slot so that, when sliding movements are made in operation, the ring 12 immediately produces a smooth and incompressible film of lubricant on the moving surface of the piston rod and at the same time the elastic sealing ring 15' ensures dry-running at all operating speeds arising. A corresponding axial compression may also be produced by a compression or disk spring acting in the axial direction or by a compression gland design for example instead of the projection 1 9.

The reference numerals in figures 8, 9 and 10 refer to corresponding parts shown in figures 1 and 2. These figures show so-called "compact seals" exerting the usual minimal pressure at the sealing edge 14 or sealing portion 1 5. The high contact pressure needed against the moving surface represented by the line 1 3 for reliable operation of the ring 1 2 is produced by the ring 12 itself being embedded in the stiff reinforced section 1 b in that the radial height of the ring 12 is greater than.the corresponding height of the recess provided in section 1 b for embedding the ring, consequently the result is direct radial pressure of the ring 12 between the associated moving surface and the base of the embedding slot and the magnitude of this radial pressure may be determined by the rigidity of the fabric section.

The displaced oversize part of the ring 12 produces a corresponding displacement or deflection of the lateral web of the section 1 1 b provided with a reinforcing means, which section, including this web, is for its part resiliently supported by the elastic section 1 a of the seal.

Claims (5)

Claims

1. A sliding seal system for pistons and piston rods of power cylinders and for floating pistons of pressure reservoirs, the seal comprising a combination of sealing and lubricating rings, with which a high partial pressure may be generated to obtain substantially complete dry-running of the seal system and in which the lubricating ring is of a plastically deformable non self-lubricating material containing a high proportion of mineral dry lubricant, wherein the sealing ring has reinforcing means distributed evenly in partial zones within its rubber substance and produce additional pressure at its sealing edge or sealing portion. ~~~~~~~~~~~~~~~~

2. A system according to claim 1, wherein the reinforcing means comprise of fibre ends distributed evenly and with random orientation within the rubber with which they form a homogeneous mass.

3. A seal system according to claim 2, wherein the fibre ends are of cotton, synthetic materials, asbestos, cellulose or combinations of these substances.

4. A seal system according to anyone of the preceding claims, wherein the reinforcing means are of carboxylated nitrile rubber.

5. A sliding seal system according to claim 1 and substantially as herein described with reference to the accompanying drawings.