GB2315820A

GB2315820A - Improvements in diaphragms

Info

Publication number: GB2315820A
Application number: GB9712968A
Authority: GB
Inventors: Lewis Hunt Norris
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-07-29
Filing date: 1997-06-19
Publication date: 1998-02-11
Also published as: DE19729682A1; GB9712968D0; GB9615900D0

Abstract

A fibre-reinforced flexible diaphragm for use in positive displacement diaphragm pumps comprises a generally planar elastomeric diaphragm body (1) having an array of at least substantially radially extending reinforcing fibres (4,6-variant C or 2-variant B) embedded therein. The array of radial reinforcing fibres (2) may be fabricated as part of a 'spiders web' pattern in which they are interwoven with a second series of circumferentially extending fibres (3). Alternatively the array of reinforcing fibres comprise a first series of fibres (4) extending tangentially in a first sense from a centrally located circle and a second series of fibres (6) extending tangentially in the opposite sense from the centrally located circle, the two series being interwoven. The angle between each successive fibre in each series is substantially uniform. The centrally located circle may include at least one further concentric circle whereby the fibres progress from the innermost circle via any intermediate circles to the outer circle. The central area of the diaphragm is reinforced by a rigid annular plate having a central aperture and the central area immediately outside the periphery of the plate comprises a conic shaped portion. Preferred materials for the fibres are specified.

Description

2315820 IMPROVEMENTS IN DIAPHRAGMS This invention relates flexible

diaphragms and particularly to improved fibre-reinforced flexible diaphragms for use in positive displacement pumps or like machines.

Diaphragms for use in positive displacement pumps., also known as diaphragm pumps, require great strength at their central area, particularly when the rear face of the diaphragm is pulled outwardly to create suction in the pumping chamber. Conventionally the diaphragms for use in such pumps are constructed from flexible materials, such as rubber, with reinforcing fibres embedded therein. In manufacture a woven mat of reinforcing fibres is cut to the shape of the diaphragm and is moulded into the diaphragm by casting or laminating the flexible material around the mat by a combination of heat and pressure. The surface of the diaphragm facing the pumping chamber often carries a further laminated layer of a flexible chemically resistant material such as polytetrafluoroethylene (PTFE).

When a woven sheet is used to form the reinforcing mat in which the warp threads are orthogonal to the weft threads a generally circular diaphragm will have areas where either the warp or the weft thread extends radially with respect to the centre of the diaphragm are other areas spaced at 45 degrees to these regions where the reinforcing threads extend at 45 degrees to a radial direction. The effect of this type of reinforcement is to produce variation of the radial elasticity of the diaphragm when measured at various points around its circumference. In the regions where the warp or weft threads extend radially the radial elasticity is a minimum and between each two regions of minimum elasticity there lies a region of higher radial elasticity.

As a result on this variation in radial elasticity uneven strains exist within the diaphragm during use which may ultimately lead to rupture. The present invention provides improved diaphragms with even radial elasticity 5 leading to an extended life in use.

According to the present invention there is provided a fibre-reinforced flexible diaphragm comprising a generally planar diaphragm body formed from an elastomer and having an array of reinforcing fibres embedded therein, characterised in that the array of fibres includes fibres which extend generally radially in all radial directions from the centre of the diaphragm.

is In a first embodiment an array of reinforcing fibres is fabricated as a 'spiders web' pattern in which a first series of fibres extend radially from the central area of the diaphragm and asecond series of fibres extend circumferentially interwoven between the first series of fibres.

In a second embodiment the array of reinforcing fibres is fabricated with a first series of fibres extending tangentially in a first sense from from a centrally located ring, the angle between each successive fibre in the array being substantially uniform. A second series of fibres extend tangentially in the opposite sense from from the centrally located ring and are interwoven with the first series of fibres. The effect is to produce a reinforcing fibre array in which the interstitial spaces are generally rhomboid in form.

In the central area of the diaphragm the surface is preferably reintorced by means of a rigid annular plate, preferably of metal, having a central aperture for a joining member fitted between the pair of diaphragms.

3 In twin diaphragm pumps, such as those sold under the trade mark "Plotronics", fluids are sucked into the in the central pumping chamber and driven out by air pressure applied to and exhausted from a pair of chambers formed around the outer surfaces of the diaphragms. A joining member between the two diaphragms under normal operating conditions acts as a thrust tube. In order to stabilise each diaphragm during the axial transition and roll through, smoothly the diaphragm is coned inwardly in the central area immediately outside the periphery of any central reinforcing plate. Reinforcing plates may be formed as a flat annulus having a diameter less than that of the conic shaped portion of the diaphragm. The stability of the cone is provided by the material from which the diaphragm is formed; an elastomer containing reinforcing fibres. In a preferred form of the present invention the diameter of the central reinforcing plate is increased and given a conic profile at its periphery which matches the mean of the deflected shape of the conic part of the diaphragm in its pressure and suction modes. This enables a larger than customary diameter to be used for the reinforcing plate. This provides a greater peripheral length for the reinforcing plate to support the diaphragm and reduce any shearing and other uneven tensional loads caused by out of balance pressures between the diaphragm faces in either direction.

The reinforcing plate must be securely bonded to the flexible laminate forming the diaphragm. Such bohding may be increased by perforating the reinforcing plate. Where the centre of the reinforcing plate engages the thrust tube it may be raised above the general surface on the side. facing the pumping chamber to reduce the local thickness of the material forming the diaphragm at this point and provide a more positive engagement with the thrust tube.

4 The engaging surface of the plate may optionally be corrugated, serrated, knurled or otherwise roughened to provide additional retention and sealing with the material forming the diaphragm. This arrangement also provides greater security for the central termination of the reinforcing material.

The fabrication of the reinforcing fibre mat may be carried out by means of a frame carrying circular arrays of pins around which hold the fibre filaments in position as a web or other pattern is created by manual or mechanical laying. The fibre mat may be formed from a single filament of fibre held rigidly between the central and circumferential pins. In this manner of construction the is axial load on the fibres is deflected from the central core. The completed mat may be held in shape for removal from the frame by application of an adhesive which is compatible with the elastomer into which the mat is incorporated. Photosensitive adhesives which are cured by ultra violet radiation are particularly suited for this purpose as no toxic curing agents are required and there is no release of liquid during hardening.

When laying the fibres in the frame it will be realised that the fibres forming the mat will be closer together around the central area than at the periphery and due to space fewer pins will be present. To overcome this problem the central array of pins may comprise a plurality of concentric rings so that total number of pins is increased and fewer filaments are held by each pin.

In order that the invention may be clearly understood it will now be described with reference to the accompanying drawings in which:

Figure 1 shows in schematic form of a diaphragm with three different types of reinforcing mat.

Figure 2 shows in schematic form the layout of a frame for forming a mat for use in one embodiment of the invention, Figure 3 shows in schematic form a plan view of a preferred form of diaphragm in accordance with the invention, Figures 4a, 4b and 4c show variations on the structure of the reinforcing plate in the embodiment of Figure 3, and Figure 5 shows in schematic cross section a diaphragm incorporating a preferred form of reinforcing plate.

A diaphragm for a pump, see Figure 1, consists of a substantially flexible circular disc 1 which comprising an elastomeric material reinforced with a fibre mat. In the prior art, see quadrant A, a woven mat comprises orthogonal threads of which some warp and some weft threads are radial or substantially radial while others are at an angle of 45 degrees to these threads. As a result the stiffness and elasticity of the diaphragm comprising these threads it not isotropic. In use such diaphragms become distorted and eventually fail. In accordance with one form of the invention, see quadrant B, an array of reinforcing fibres is shown having a first set of fibres 2 arranged to extend generally radially from the central point of the diaphragm 1. A second set of fibres 3 is arranged to extend circumferentially in a series of rings. The fibres 3 are interwoven with the fibres 2. The interstitial spaces between the fibres are substantially rectangular. Such an arrangement of fibres forms a mat having uniform radial stiffness. In accordance with an alternative form of the invention, see quadrant C, an array of reinf orcing f ib:i:es is shown having a first set of fibres 4 arranged to extend generally tangentially from a central circle 5 in a generally clockwise direction. A second set of fibres 6 is arranged to extend generally tangentially from the central circle 5 in a generally anti-clockwise direction. The fibres 4 and 6 may be interwoven. In this embodiment the concentration of fibres at the ring 5 causes thickening 5 of the mat.

In a further embodiment, see Figure 2, a modification of the arrangement of fibres shown in quadrant C reduces the concentration of fibres at the central ring causing thickening of the mat. An array of reinforcing fibres is shown having a first set of fibres 11 arranged to extend generally tangentially from a central circle 12 in a generally clockwise direction. A second set of fibres 13 is arranged to extend generally tangentially from the central circle 12 in a generally anti-clockwise direction. Within the central 12 there are two further concentric circles 14 and 15. The fibres forming the mat progress from the innermost circle 15 via the intermediate circle 14 to the outer circle 12. By splitting the reversal of direction of the fibres 11 and 13 among the three sets of circles the central thickening of the reinforcing fibre mat is reduced. This is important as it ensures better bonding within the elastomeric lamina forming the diaphragm. The continuity of the fibres around the central pins provides useful load distribution.

A preferred form of diaphragm according to the invention, see Figure 3, consists of a reinforced elastomer body 20 having a central reinforcing plate 21. The upper surface of the plate 21, facing the pumping chamber and in contact with the fluid being pumped, is treated so as to provide positive engagement with the thrust tube. Thetreatment may consist of knurling 22 or corrugations 23 on the surface. The treatment of the upper surface by knurling is shown in cross section on an enlarged scale in 7 The reinforcing plate 30 in a preferred form, see Figure 5, has an increased diameter. The increased peripheral portion 31 is given a conic profile which matches the profile of the diaphragm 32, 33 at this portion. The main portion of the diaphragm 34 is reinforced elastomer ending in a peripheral increase in diameter 35 used to form a fluid seal when the diaphragm is fitted to a pump.

To manufacture diaphragms in accordance with the invention a circular mat comprising an array of fibres having fibres which extend generally radially in all radial directions from the centre is sandwiched between two layers of curable elastomer together with, optionally, a reinforcing plate. The sandwich is heated under conditions which cure the elastomer and ensure that the mat is fully bonded within a homogeneous layer. Curable rubber is the preferred elastomer. Although only a single layer of reinforcing mat is described two layers may be embedded in the elastomer forming the diaphragm. Each layer may have the same spacing between its radially extending fibres and the two layers may be angularly displaced so that the fibres of one layer overlie the interstitial spaces of the other layer. Such an arrangement may be adopted in the absence of a central reinforcing plate.

The fibres used must be chemically and physically compatible with the elestomeric material within which they are embedded as reinforcement. Suitable materials include glass fibres, carbon fibres, steel filaments, cotton f ibres, synthetic polymer f ibres such as PTFE f ibres, nylon fibres, polyester fibres such as polyethylene terephthalane fibres, kevlar fibres. The fibres may be monofilament or multifilament in structure. In the case of synthetic polymer fibres they are preferably axially oriented.

8 compatible with the elastomeric material within which they are embedded as reinforcement. Suitable materials include glass fibres, carbon fibres, steel filaments, cotton fibres, synthetic polymer fibres such as PTFE fibres, nylon fibres, polyester fibres such as polyethylene terephthalane fibres, kevlar fibres. The fibres may be monofilament or multifilament in structure. In the case of synthetic polymer fibres they are preferably axially oriented.

The improved method of construction of pump diaphragms provides a minimum number of fibres bonded to the central plate and provides variable flexure radially so as to enhance the life of the diaphragm in use.

9

Claims

CLAIMS.

A fibre-reinforced flexible diaphragm comprising a generally planar elastomeric diaphragm body having an array of reinforcing fibres embedded therein, characterised in that the array of fibres includes fibres which extend generally radially in all radial directions from the centre of the diaphragm.
2. A flexible diaphragm in accordance with claim 1, characterised in that the array of reinforcing fibres is fabricated as a 'spiders web' pattern in which a first series of fibres extend radially from the central area of the diaphragm and a second series of fibres extend circumferentially interwoven between the first series of f ibres.
3. A flexible diaphragm in accordance with claim 1, characterised in that the array of reinforcing fibres is fabricated with a first series of fibres extending tangentially in a first sense from from a centrally located circle, the angle between each successive fibre in the array being substantially uniform, and a second series of fibres extend tangentially in the opposite sense from from the centrally located circle and are interwoven with the first series of fibres.
4. A flexible diaphragm in accordance with claim 3, characterised in that within the centrally located circle there is at least one further concentric circle whereby the fibres forming the mat progress from the innermost circle via any intermediate circles to the outer circle.
5. A flexible diaphragm in accordance with any of the 35 preceding claims, characterised in that the central area of the diaphragm is reinforced by means of a rigid annular plate having a central aperture.
6. A flexible diaphragm in accordance with claim 5, characterised in that the diaphragm is coned inwardly in the central area immediately outside the periphery of the central reinforcing plate and in that the reinforcing plate is formed as a flat annulus having a diameter less than that of the conic shaped portion of the diaphragm.
7. A flexible diaphragm in accordance with claim 6, characterised in that the diameter of the central reinforcing plate is increased and given a conic profile at its periphery which matches the mean of the deflected shape of the conic part of the diaphragm in its pressure and suction modes.
8. A flexible diaphragm in accordance with any of the claims 5 to 7, characterised in that the bonding of the reinforcing plate to the elastomer forming the diaphragm is increased by perforating the reinforcing plate.
9. A flexible diaphragm in accordance with any of the claims 5 to 7, characterised in that the central edge of the reinforcing plate is raised above the general surface on the side facing the pumping chamber.
10. A flexible diaphragm in accordance with any of the claims 5 to 7, characterised in that the surf ace of the plate is corrugated, serrated, knurled or otherwise roughened to provide additional retention and sealing with the material forming the diaphragm.
11. A flexible diaphragm in accordance with any of the preceding claims, characterised in that the f ibres are a axially oriented polyester.
12. Fibre-reinforced flexible diaphragms in accordance with claim 1 and as herein described. 5
13. Fibre-reinforced flexible diaphragms as herein described and illustrated with reference to the accompanying drawings.
14. The method of making a fibre-reinforced flexible diaphragm as claimed in any of the claims 1 to 13, comprising a forming an array of reinforcing fibres which includes fibres which extend generally radially in all radial directions from the centre of a fibre mat, laminating the fibre mat between at least two layers of curable elastomer and, optionally, a central reinforcing plate, and thereafter pressing and heating the laminate to form a generally planar elastomeric diaphragm body.