Method for making a three-dimensional diaphragm

Abstract: A diaphragm comprises a base fabric (1) formed of warp yarns (1a) radially extending in centrally convex form from the central region and weft yarns (1b) helically interwoven with the warp yarns (1a), and a rubber member (2) of centrally convex membrane form molded integrally with the base fabric (1).

Description: The present invention relates to a method for making a three-dimensional diaphragm of centrally convex form used where pressure resistance is required. Diaphragms are usually moulded out of rubber in membrane form and, where pressure resistance is required, they are reinforced by a base fabric of plain weave disposed in the rubber member. In the case where the diaphragm is of centrally convex form, it has been common practice to mould such diaphragm of centrally convex form by setting a base fabric of plain weave and rubber in a press die or the like, and pressing the assembly as disclosed in US-A-5031720. EP-A-0332899 relates to a method as defined in the first part of current claim 1 and discloses a diaphragm formed by preforming a lattice-shape base fabric into a centrally convex form and moulding integrally therewith a rubber member using an injection moulding process. In the above, since the fabric is of plain weave, the warp and weft yarns constituting the portion of the base fabric in and around the centrally convex region are drawn towards the centrally convex region during the press moulding operation, resulting in variations in the density of the warp and weft yarns, wrinkles, overlaps and the like, thus making the pressure-resisting strength nonuniform. As a result, some of the yarns constituting the base fabric are broken prematurely owing to repetitive vibrations, thus degrading the durability. In DD-A-106451, a fabric reinforced plastic membrane is disclosed having a fabric inlay with radial and concentric or spiral shaped arrangement of the fabric threads. This results in a flat membrane which when annularly clamped is subjected to clamping forces evenly across the membrane. The present invention provides a method of making a three dimensional diaphragm having a centrally convex region, comprising forming a base fabric having a centrally convex region, and moulding a rubber member integrally with the base in a press die conforming to the intended shape of the diaphragm, characterised in that the three dimensional base fabric is formed of warp yarns radially extending in centrally convex form from the central region and weft yarns helically interwoven with the warp yarns. Since the warp yarns in the base fabric are radially disposed in centrally convex form and the weft yarns are helically interwoven with the warp yarns, the base fabric has a three dimensional construction of centrally convex form, and the yarn density does not become varied even in the state where the yarns are moulded with rubber, making it possible to eliminate wrinkles or overlaps and maintain a uniform pressure resisting strength, thus improving the durability. According to the present invention, the warp yarns of the base fabric radially extend in centrally convex form from the central region and the weft yarns are helically interwoven with warp yarns, thereby forming a three dimensional base fabric of centrally convex form. Even when this base fabric is moulded with rubber, the yarns remain in regular equi-spaced disposition. And there is no danger of producing wrinkles or overlaps, so that the pressure-resisting strength in the various regions can be made uniform. It has been found that the durability can be greatly increased (about 50 - 100 times). The density of yarn disposition becomes rational and, as compared with the conventional plain weave, it becomes possible to decrease the number of yarns used by about 10%. Further, since the warp yarns of the base fabric are radially disposed and the weft yarns are helically interwoven with the warp yarns, it becomes possible to construct such base fabrics in three-dimensional form and to mold this type of diaphragm of centrally convex form to have any desired shape which suits the intended purpose. DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view in longitudinal section showing a diaphragm according to an embodiment of the present invention; Fig. 2 is a schematic perspective view showing an example of the weave construction of a base fabric to be used in the diaphragm of the invention; and Fig. 3 is a schematic perspective view showing by way of example the tying of the weft yarns in the top of the centrally convex region of the base fabric to be used in the diaphragm of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to an embodiment shown in the drawings. Fig. 1 is a sectional view in longitudinal section showing a diaphragm according to an embodiment of the present invention. The numeral 1 denotes a base fabric, and 2 denotes a rubber member. In addition, in Fig. 1, the base fabric 1 is shown embedded in the central region of the rubber member 2 in sandwich form. However, it may be disposed on either the front surface or the back surface of the rubber member 2. The base fabric 1 consists of warp yarns 1a and weft yarns 1b, wherein said warp yarns 1a radially extend in centrally convex form from the central region said weft yarns 1b being helically interwoven with said warp yarns 1a. In addition, the warp yarns 1a may be arranged so that they increase in number as they extend from the intermediate region to the lower outward skirt region. Further, as shown in Fig. 3, they may be tied together in the middle region by a tying string 1c. Further, some of the warp yarns 1a may radially extend in centrally convex form from the central region as shown in Fig. 2 and the others may be tied together in the middle region as shown in Fig. 3. There is no limitation on the fiber used for the warp and weft yarns 1a, 1b; any fiber may be used. As for the thickness of yarns and weave density, they may be suitably selected according to uses. The means for making the base fabric 1 forms no portion of the present invention, and it may be formed radially disposing the warp yarns 1a in centrally convex form, winding the weft yarns 1b helically from the upper middle region to the lower outward skirt region, during which every other or few weft yarns 1a are moved in the warp direction so as to effect the shedding motion as in the case of plain weave. The shape and size of the base fabric 1 are selected according to the intended shape of the diaphragm. The base fabric 1 together with a rubber material is set in a press die or the like which suits the intended shape and then press-molded to provide a diaphragm of Intended shape. In the diaphragm of the present invention thus produced, the warp yarns 1a of the base fabric 1 are radially regularly disposed at equal intervals and the weft yarns 1b are helically interwoven with the warp yarns 1a; therefore, in contrast to the membrane form of the diaphragm, the pressure-resisting strength in the various circumferential regions is uniform.

Claims: A method for making a three-dimensional diaphragm having a centrally convex region, comprising forming a base fabric (1) having a centrally convex region, and moulding a rubber member (2) integrally with the base fabric in a press die conforming to the intended shape of the diaphragm, characterised in that the three-dimensional base fabric is formed of warp yarns (1a) radially extending in centrally convex form from the central region and weft yarns (1b) helically interwoven with said warp yarns.

Inventors: SOWA NOBUHIRO, SOWA, NOBUHIRO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES, CO. LTD
Application year: 1993
Main classification: F16J3
IPC codes: F16J3