GB2208089A - Diaphragm piston - Google Patents

Abstract

A dish shaped moulded rubber pneumatic actuator diaphragm has a moulded in premoulded reinforcement comprising radially extending main members 14 connected one to the next by joining elements 15 which lie along arcs of concentric circles. <IMAGE>

Description

This invention relates to diaphragm manufacture and relates more especially to the manufacture of diaphragms for pneumatic pressure operable actuators.

It is normal for pneumatic pressure operable actuators to be provided with a pressure responsive member which forms a movable wall of a pressure chamber. The pressure responsive member may comprise a sealingly slideable piston or, alternatively, a dish-shaped reinforced diaphragm arranged to act against a suitable push-plate. The diaphragm is typically sealingly clamped at its periphery between a pressure plate and a non-pressure plate to thereby define the necessary pressure chamber Typically, such diaphragms are moulded of rubber and incorporate reinforcing fabric embedded in the rubber. The positioning of the reinforcing fabric within the thickness of the diaphragm is critical to the extent that incomplete penetration of the fibres of the reforcing fabric can result in leakage along the fibres if they emerge at the surface within the pressure chamber.Additionally, since the fibres of the fabric run in accoi-aance w~cI, particular weave pattern, (weft and warp), the rolling characteristic of the diaphragm and also its strength may not normally be uniform by distributed over angular positions around the diaphragm.

The present inventionXas an object to remove or substantially reduce the above shortcomings of a moulded diaphragm.

According to the present invention there is provided a diaphragm moulded of flexible material such as rubber or plastics with an embedded reinforcement said reinforcement comprising spaced outwardly extending main members which lie substantially along radial roll sections of the flexible material.

In the case of a diaphragm in the shape of a surface of revolution, particularly a generally circular dish-shaped diaphragm the main members of the reinforcement preferably extend generally outwards from the centre of rotation along spaced generators.

The reinforcements may further comprise spaced elements joining the main members, one to the next, and in a particular embodiment these spaced elements may lie along circular arcs to form spaced circular members traversing the main members. Alternatively, sue spaced elements joining the main members may lie along chords of such circular arcs.

In order to facilitate positioning the reinforcement between the surfaces of a moulded diaphragm, the reinforcements may be provided with suitably located projections (pips) at suitably chosen positions of the members or elements the lengths of such projectioins preventing the main members lying too close to either surface of the roulded flexible material @nd thereby assisting handling and position or the reinforcements in relation to a mould and affording reliable manufacture.

In order to maximise possible leakage paths between such projections appearing near one surface and projections appearing near the other surface, the projections (pips) may be arranged to be blaggered so that they do not be immediately opposite one another on the sides of the reinforcement.

The reinforcements may be moulded in one piece and the material thereof may be chosen to be such that whilst it may be appreciably harder than the material of the diaphragm it has a particular affinity for the diaphragm material. The material from which the reinforcements are moulded may, for example, be a harder derivitive of the same polymer or other material which is used for injection moulding the finished diaphragm.

In order that the invention may be more clearly understood and readily carried into effect, the same will be further describved with reference to the accompanying drawings of which; Fig. 1 illustrates a sectional view of a dish-shape flexible circular diaphragm and, Fig. 2 illustrates a plan view of a moulded rein forcement for the diaphragm of Fig. 1.

Referring to Fig. 1, the diaphragm shown in section therein is a diaphragm having a typical well known circular shape which is used for diaphragms of actators employed in compressed air braking systems. The diaphragm comprises a peripheral bead 1, a generally 'S'-shaped curved portion 2 and a central flat portion 3 which in operation bears against a push-plate denoted by the broken outline 4, for operating a push rod denoted by the broken outline 5. Actuation therefore takes place in the direction of the arrow 6 in response to the fluid pressure applied as represented by arrows 7. Hitherto, such diaphragms have been manufactured as indicated above by conventional rubber mould techniques and incorporating a woven fabric reinforcement.In accordance with the present invention the diaphragm of Fig. 1 is formed by injection moulding of synthetic rubber or other material into a mould, the mould now being provided with a moulded plastics reinforcement having main members extending radially outwads from the centre. Furthermore, the reinforcement is provided with projections or pips such as 8 which facilitate positioninspf the reinforcement within the mould such as to ensure consistent spacing of the reinforcement between the diaphragm surface 10 and 11 during moulding.

The reinforcement is more clearly to be seen in Fig. 2 wherein it is to be seen that a circular bead reinforcement 12 is joined to a central portion 13 by radially extending main members 14. The main members are further joined by elements 15 which are generally bara'lc' to the circumference and inte:tcCrn- adjacent main members 14 to provide further strengthening against circumferential stretching at spaced radial positions.

The members 15 may be in the form of arcs of a circle or, alternatively, they may simply be straight as shown, i.e., chords of such arcs. In that case it will be appreciated that having regard for the distinct shape, the spacing of the main members is close enough to permit straight line joining thereof by the elements 15 within the thickness of the non-planar regions of the portion 2. Furthermore, the intersections of element 15 and members 14 are provided with outwardly and inwardly extending projections 8, which provide for positioning of the reinforcement within the mould as mentioned above.

Although in the embodiment of the reinforcement as shown in Figs. 1 and 2, the pips 9 are located immediately opposite one ancther, in an alternative, pips on one side may be arranged to not coincide with pipes on the other side. In that way the remote possibility of leakage between one side of the diaphragm and the other in operation may be substantially reduced.

The materials of the pre-moulded reinforcement on the one hand and the injection moulding material of the diaphragm are chosen to provide good material bonding. For example, the material of the rein orecement may be chosen to be a harder deri-ative of the trial of the diaphragm itself to afford mutual bonding during moulding and curing. However, the method and materials of the moulding do not form part of this particular invention.

By virtue of the invention wherein a pre-moulded reinforcement is provided for a moulded diaphragm and having main radial reinforcement members, a relatively uniform strength and roll-flexibility can be provided around the diaphragm and the range of materials such as polymers which can now be employed for diaphragms may be extended. Furthermore, by providing moulded projections on the reinforcement the positioning of the reinforcement within a two-part mould for manufacture can be such as to maintain the main members and elements thereof at desired depths beneath the diaphram surface.

Claims (9)

1. A diaphragm moulded of flexible material such as rubber or plastics with an embedded reiinforcement said reinforcement comprising spaced outwardly extending main members which lie substantially along radial roll sections of the flexible material.

2. A diaphragm moulded of flexible material as claimed in claim 1 wherein said diaphragm is of generally circular dish shaped surface of revolution and the main members extend generally outwards from the centre of rotation along angularly spaced generators.

3. A diaphragm as claimed in claim 1 or claim 2 said main members being joined one to the next by spaced joining elements.

4. A diaphragm as claimed in claim 2 or 2 and 3 wherein said joining elements lie along circular arcs which join at the main members to form spaced concentric circles of such members.

5. A diaphragm as claimed in claim 4 wherein said joining elements lie along chords of concentric circles which tranverse the main members.

6. A diaphragm as claimed in any preceeding claim wherein the reinfrocements have projections which ensure that said main members or main members and joining elements are located beneath the respective diaphragm surface or surfaces.

7. A diaphragm as claimed in claim 6 said projections being provided on both sides of the reinforcement.

8. A diaphragm as claimed in claim 7 said projections being provided by locally thickened points on each side.

9. A diaphragm substantially as described herein with reference to Figs. 1 and 2 of the accompanying drawing.