WO1997038256A1 - Clamping method - Google Patents

Abstract

The invention discloses a method of clamping or sealing a sleeve (12) to a shaft or pipe (10). The method includes the steps of providing a cavity (14) between the outer surface of shaft or pipe (10) and the inner surface of sleeve (12). An elastomeric member (16) is inserted into cavity (14) and is compressed by a piston member (20) to form a closed chamber (14) to such an extent to compress the elastomeric member (16) into firm contact with shaft or pipe (10) and locking piston member (20) in that position to prevent opening of closed chamber (14).

Description

CLAMPING METHOD This invention relates to a method of application of pressure to a surface, or surfaces, such as to or across an interface between two bodies that are to be clamped or bonded against relative movement across the line of pressure, and/or which are required to form a seal against flow over the interface, or where a seal or packing is required between two relatively movable bodies such as a shaft in a bearing or housing.

The invention also relates to members clamped by the method. An object of the invention is to distribute interfacial forces between two bodies so as to reduce localised and potentially damaging pressures.

Another object is to enhance the effective friction and/or sealing effect between the bodies.

Another object is to enable predetermination of an effective interface over which frictional and/or sealing pressures are to act. A further object is to provide apparatus fitted with clamps, seals, bonding, packing etc. representing various applications for the principles of the invention.

The above and other objects and advantages will become apparent hereinafter. In one aspect of the invention there is provided a method of clamping or sealing a sleeve to a shaft or pipe, said method including the steps of providing a cavity between the outer surface of said shaft or pipe and the inner surface of said sleeve, inserting an elastomeric member into said cavity, compressing said elastomeric member with a piston member to form a closed chamber in said cavity to such an extent to compress the elastomeric member into firm contact with said shaft or pipe and locking said piston member in that position to prevent opening of said closed chamber.

For the purposes of this specification "elastomeric" and "rubber" include rubber and other natural and synthetic (or partly synthetic) substances having properties akin to rubber, including a hardening under sufficient pressure to what is substantially a solid, and possibly returning to, or substantially to, its former state upon release of the pressure.

The chamber is advantageously formed so as to direct on to an appropriate surface or surfaces at least a substantial part of the total forces due to compression of the elastomeric member.

In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, in which:- Fig. 1 is a crocs-sectional view of a part of a shaft with a sleeve to be secured thereto by the method according to the invention and showing the initial assembly of components;

Fig. 2 is a similar view to that of Fig. 1 showing the first stage of compression of the elastomeric member; Fig. 3 is a similar view to that of Fig. 2 showing the second stage of compression of the elastomeric member;

Fig. 4 is a similar view to that of Fig. 3 showing the third stage of compression of the elastomeric member; and

Fig. 5 is a similar view to that of Fig. 4 showing the final stage of compression of the elastomeric member and locking thereof;

Referring to Figs. 1 to 5 in more detail there is shown a cylindrical shaft or pipe 10 or first body (only a portion of which is shown) and a cylindrical sleeve 12 or second body which is to be permanently secured thereto using the method of the invention. A chamber or cavity 14 is formed between shaft 10 and sleeve 12 in which a ring-like elastomeric member 16 is inserted. In this embodiment a recess in sleeve 1 2 forms cavity 14 but a recess coul¹"^* be formed in shaft or pipe 10 or both. Member 16 in this embodiment hds a rounded end 22 or D-shaped cross-section. Chamber 14 is preferably tapered at one end by conical section 1 8. An annular piston or thrust ring 20 is inserted in the chamber 14 to complete the assembly. Components 10, 12 and 20 are solid and preferably formed of metal or metallic alloy but the compositions thereof may vary depending on requirements. Suitable plastics materials or resin based materials may also be used. Turning to Fig. 1 it is seen that piston 20, in the first part of its travel to the left indicated by distance 24, pushes the insert 1 6 to the position shown in Fig. 2 . Insert 16 abuts conical section 18 and has gone as far as it can without deformation. The next part of the movement of piston 20, ie over the distance shown as 26, causes the insert material 1 6 to deform and eventually to fill chamber 14, as shown in Fig. 3. Thereafter piston 20 may, under sufficient pressure, move further to the left by the distance shown as 28, compressing the elastomeric material 1 6 and causing it to harden effectively to a solid. At the point shown in Fig. 4 piston 20 may be locked by pins 30,32 and the external force removed, as shown in Fig. 5. Pin 32 is optional as only one pin is needed to hold insert 16 in place. Pin 30 may, for example, be a grub screw which is inserted through a drill hole in outer wall of sleeve 12. Pin 30 may be replaced by a circlip at the end of piston 20 or substituted by any other form of locking means. The type of locking means is not critical to the operation of the invention. The insert 1 6 remains solid in the pressure chamber 14, although it may revert to its normal rubbery state if the chamber 14 is allowed to expand eg by unlocking the piston 20 by removal of pins 30,32.

The leading portion 22 of insert 16 may be convexly-shaped as shown in order to facilitate entry into a forward part of the chamber 14 so shaped as to deflect the rubber into firm contact with the relevant surface portion of shaft 10. The shape illustrated is a converging or wedge-shaped, and the "horizontal" movement of the rubber is converted into a "vertically downward" movement by the inclined plane effect of the conical section 1 8 of sleeve 12 as shown in Fig. 2. It will be understood that though the preferred embodiment is described with reference to circular components the shaft 10 and sleeve 12 is not so limited. These components may be square or any other desired cross-section. Although it is not certain at this stage, it is believed that by the use of the physical properties of rubber to impress or enhance a clamping and/or sealing or other force applied to a surface, the effective friction between the relevant bodies may tend to increase as the tensile forces increase, as if the solidified rubber were "hooking" into the first body. This could be due to increase in effective co-efficient of friction, or increase in effective inter-body "normal reaction" forces, or a combination of the two.

The invention may find application to many forms of apparatus wherein clamping, sealing, bonding or other interaction is required between two bodies or surfaces. Examples are tube expanders, couplings and other fittings, pipe swaging, pipe plugs, couplings and the like, bearing/seal assemblies, valve stem assemblies, bolt seals, wall anchors, and vessel closures.

It is to be understood that in not all situations must the rubber be compressed to absolute solidification. In some applications, such as where merely sealing pressures are required or suffice, it may be desirable to reduce or even minimise rubber compression. In this regard the invention can provide an efficient seal or packing between two relatively movable surfaces. Thus in the accompanying drawings the first body 10 may be regarded as moving toward the viewer, relatively to the second body 12 and/or insert 16, the latter being potentially a seal - after the manner of an "O-ring". For this purpose the rubber could be left, and the system locked, in the condition shown in Fig. 3, or very slightly compressed to a condition between those represented by Figs. 3 and 4. Further compression/solidification of the rubber could act as a brake upon the bodies' relative movement. However in other applications higher interfacial forces may be required. Our invention provides a ready means of adjusting the rubber compression as required, and of making full use of the propensity of rubber progressively to harden or "energise", as compression increases. At the low energy end of the spectrum a relatively small amount of rubber may suffice eg for sealing purposes. At the high energy end (eg for clamping, mechanical bonding, braking etc.), it may be desirable to have a relatively large body of rubber.

For specific purposes the insert 16 may be provided with a cover or lining, such as of Teflon (Registered Trade Mark) or asbestos. The shape of the pressure chamber 14 need not be critical, however it is preferable for the opposite walls to converge gradually in the direction in which the piston 20 advances. In this way an "inclined plane" effect may give a substantial mechanical advantage, so that a relatively small force on the piston 20 will force the rubber over a relatively large surface area where its effect will be greatest.

A movable piston 20 is only one way of providing a variable-volume pressure chamber. Referring to Fig. 1 of the drawings, it will be apparent that the "piston" might be an integral part of eg the first body, and the volume of the pressure chamber reduced by a relative movement of the second body to the right.

Although the embodiment has been described with reference to circular articles it is to be understood that by "surface" or "surface portion" we include all shapes and do not mean necessarily a plane. It could, for example, be an annular portion of a pipe or tube of circular (as shown), square or any other cross-sectional form when viewed axially. Figs. 1 to 5 are quite general in illustrating the invention whether applied to a flat or curved surface, endless or otherwise. Flat members may be joined together by applying compression forces as shown by arrows 34,36. In all cases the form of the pressure chamber must be such as to direct a substantial component of the rubber's compression normally on to the relevant surface or surfaces, which may mean that the chamber must be sufficiently retentive of pressure to avoid substantial lateral extrusion of the rubber ie in the direction of viewing Figs. 1 to 5.

Various additions and modifications may be incorporated into the foregoing without departing from the ambit of the invention.

Claims

1 . A method of clamping or sealing a sleeve to a shaft or pipe, said method including the steps of providing a cavity between the outer surface of said shaft or pipe and the inner surface of said sleeve, inserting an elastomeric member into said cavity, compressing said elastomeric member with a piston member to form a closed chamber in said cavity to such an extent to compress the elastomeric member into firm contact with said shaft or pipe and locking said piston member in that position to prevent opening of said closed chamber.

2. The method of claim 1 , wherein said cavity has a tapered or conical end.

3. The method of claim 1 or 2, wherein said elastomeric member has a ring-like shape.

4. The method of claim 2, wherein said elastomeric member has a converging end which cooperates with said tapered end of said cavity to deflect elastomeric member into said firm contact with said shaft or pipe.

5. The method of any one of the preceding claims, wherein locking of said piston member is by a fastener inserted into said sleeve and also entering said elastomeric member.

6. The method of any one of the preceding claims, wherein the amount of compression of said elastomeric member controls the pressure rating of the clamping between said shaft or pipe and said sleeve.

7. The method of any one of the preceding claims, wherein a recess is formed in either or both of said shaft or pipe or said sleeve to form said cavity.

8. In combination a sleeve and shaft or pipe when clamped or sealed together using the method of any one of the preceding claims.