GB2043831A - Rolling Diaphragms - Google Patents

Abstract

A rolling diaphragm (2) comprises a tubular piece of fabric reinforced with an elastomeric material, the tubular piece of fabric being formed directly into the tubular shape and not by deformation of a first formed flat blank, so that the threads constituting the fabric experience minimal stress and deformation. The fabric may be woven or non-woven and the threads may be oriented at 5 DEG -15 DEG to the longitudinal axis of the diaphragm. <IMAGE>

Description

SPECIFICATION A Rolling Diaphragm I This invention relates to a rolling diaphragm device.

Rolling diaphragm devices are often unsatisfactory in that the diaphragm prematurely wears. This premature wear is often due to manufacturing imperfections in the diaphragm. It is believed that general wear and the significance of any minor manufacturing imperfections are increased due to the fact that the diaphragms are made by coating a tubular piece of fabric with an elastomeric material, this tubular piece of fabric having been deformed from an initially flat piece of fabric. The deformation may be, for example, by die drawing and the effect of this deformation of a flat piece of fabric into a tubular piece of fabric is to cause deformation and stresses in the individual threads forming the fabric.These deformations and stresses are not equal on all the threads and this leads to a variation in axial stiffness around the circumference of the formed diaphragm which can in turn lead to failures. In many instances it has been noticed that failure occurs where the threads cross at 450 to the axis of the diaphragm or at 450 to a radiai line for a shaliow diaphragm.

Diaphragm failures are also believed to occur as a result of the fabric being misplaced by as much as ten thousandths of an inch into the elastomeric material. For maximum flexibility of the diaphragms, the elastomeric coating has to be thin and provided on the side of the fabric that is subjected to the highest pressure in use of the rolling diaphragm device. The operating pressure difference then tends to hold the elastomer onto the fabric. It will be appreciated that it is very easy to misplace the fabric very slightly into the elastomer at various local points, causing possible failure to occur during the use of the rolling diaphragm devices.

It is an aim of the present invention to provide a rolling diaphragm device in which the above mentioned disadvantages are obviated or reduced.

Accordingly, this invention provides a rolling diaphragm device comprising a tubular piece of fabric which is reinforced with an elastomeric material, the tubular piece of fabric being such that it is formed directly into the tubular shape without being produced by deformation of a first formed flat shape.

The threads that constitute the fabric are thus not stressed or deformed, or at least these stresses and deformations are kept to a minimum.

If desired, the tubular piece of fabric may be formed of woven threads of the fabric.

Alternatively, the tubular piece of fabric may be formed of over-lying, non-woven threads of the fabric. In this latter case, the threads in each of the formed layers preferably run in different directions.

Preferably, the threads of the fabric run at an angle of 50 to 1 5" to the longitudinal axis of the diaphragm.

In other respects, the rolling diaphragm device of the present invention may be formed in the same manner and of the same materials as known rolling diaphragm devices. Thus, for example, the elastomeric material will usually be provided on the side of the fabric that is subjected to the highest pressure in use of the rolling diaphragm device.

The elastomeric material may be any of the known and used elastomeric materials such for example as synthetic and natural rubbers and silastic materials. A presently preferred material is a fluorosilicone rubber.

The fabrics may also be any of the presently known and used fabrics such for example as Nylon, Orlon (Registered Trade Mark), Dacron (Registered Trade Mark) and Terylene (Registered Trade Mark).

The diaphragm can be formed to various shapes and the elastomer can be applied to the fabric under various known conditions of heat and pressure as desired.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows a first method of manufacture of a diaphragm; Figure 2 shows the diaphragm formed in accordance with the illustrated method of Figure 1 in a rolling diaphragm device; Figure 3 shows a second method of forming a rolling diaphragm; Figure 4 shows a rolling diaphragm device employing the diaphragm device employing the diaphragm formed by the method illustrated in Figure 3; Figure 5 is a side view showing fabric threads being wound on a mandrel; and Figure 6 is an end view of the mandrel illustrated in Figure 5.

Referring to Figure 1, there is shown a tubular piece of fabric 2 made of woven threads such that it is formed as braiding. The fabric 2 is provided with beads 4, 6 for enabling the diaphragm to be located in a rolling diaphragm device. The fabric 2 is tensioned in the direction of the arrows 8, 10 and the fabric 2 may be supported on a mould for allowing the elastomeric material to be bonded to the fabric 2.

The internally formed bead parts 4A, 6A can be omitted if desired and the bead 4A can be inclined at a greater angle than is illustrated in the main part of Figure 1, a greater angle being illustrated in the scrap part of Figure 1 which is indicated by the reference numeral 12.

In Figure 2, the elastomeric coated fabric 2 is shown formed in a rolling diaphragm device 14.

This device comprises a first member 1 6 and a second member 1 8 which are secured together by a bolt 20 and a nut 22 and which trap the bead 4 in the circular recess 24 as is illustrated. The bead 6 is trapped in a circular recess 26 of a main body part of a device 28 as is also illustrated in Figure 2. In operation of the rolling diaphragm device 14 higher pressure will exist on the side 30 of the fabric 2 than on the side 32.

Referring now to Figure 2, there is shown woven tubular braiding 34 having beads 36, 38 being tensioned through a hollow core 40 in the direction of arrows 42, 44. The individual threads of the fabric, as shown, lie along the surface of the core or are pulled inwards towards a centre line of the core. Referring to both Figures 1 and 3, it will be appreciated that the taper of the fabric 2, 34 and therefore the taper of the resulting diaphragm is dictated simply by the need to connect the differing diameters of the retaining beads 4, 6 and 36, 38. These tapers are effectively straightened out in the working sections of the diaphragm by an acceptable degree of radial tension and compression during use of the rolling diaphragm devices of the invention.

Referring now to Figure 4, it will be seen that a diaphragm 46 formed by the method illustrated in Figure 3 is provided in a rolling diaphragm device 48. The device 48 comprises a first part 50 and a second part 52 which trap a retaining bead 54 of the diaphragm 46 into the illustrated recess 56. A retaining bead 58 of the diaphragm 46 is trapped in the illustrated recess 60.

In Figure 5, there is illustrated a mandrel 62 having a handle 64. Individual threads 66 are wound as shown in Figure 5. A layer of the thread 66 is first laid one way and then another layer of the thread 66 is then laid at an opposing angle over the top of the first laid layer of threads 66.

Only two layers of threads 66 are illustrated but more than two layers could be employed if desired. It will thus be appreciated than in Figure 5, the threads are not woven into brading. Also shown in Figure 5 in dotted lines are portions 68, 70 of a mould 72, the portions 68, 70 being used for moulding retaining beads on the diaphragm to be formed. In Figure 6, the crossing of the threads 66 in the two layers is clearly illustrated. By using the mandrel 62 first to receive the threads 66 and then as a core for the mould 72, it will be appreciated that the elastomeric material can be provided on and around the threads 66 without disturbing them. The winding angle of the threads 66 illustrated in Figures 5 and 6 can be reduced to 50 or less to the longitudinal axis of the mandrel 62. The fact that the threads 66 are not interwoven does not constitute a disadvantage because the elastomer is effective to bind the threads together. When the moulding in the mould 72 has been finished, the rounded ends of the product can be cut off to form the completed diaphragm.

Advantageously, the diaphragms illustrated in the drawings are made from a fluorosilicone rubber on a Terylene (Registered Trade Mark) fabric. Such diaphragms are advantageously used in fuel systems.

It is to be appreciated that the embodiments of the invention described above have been given by way of example only and that modifications may be effected. Thus, for example, different shapes of diaphragms to those illustrated can be manufactured and the angle of inclination of the various threads of the fabric can be varied from those shown.

Claims (6)

Claims

1. A rolling diaphragm device comprising a tubular piece of fabric which is reinforced with an elastomeric material, the tubular piece of fabric being such that it is formed directly into the tubular shape without being produced by deformation of a first formed flat shape.

2. A rolling diaphragm according to claim 1 in which the tubular piece of fabric is formed of woven threads of the fabric.

3. A rolling diaphragm according to claim 1 in which the tubular piece of fabric is formed of over-lying, non-woven threads of the fabric.

4. A rolling diaphragm according to any one of the preceding claims in which the threads of the fabric run at an angle of 5 to 150 to the longitudinal axis of the diaphragm.

5. A rolling diaphragm according to any one of the preceding claims in which the elastomeric material is a fluorosilicone rubber.

6. A rolling diaphragm substantially as herein described with reference to the accompanying drawings.