Synchronous belt

Abstract: A woven fabric (5) for covering a tooth part formed on a belt body of a synchronous belt is woven with a lengthwise yarn (6) and a widthwise yarn (7). The lengthwise yarn (6) is made of a crimped yarn of synthetic fiber or a covering yarn in which a crimped yarn of synthetic fiber is wound around an elastic cord yarn. The widthwise yarn (7) is made of a spun yarn of synthetic fiber or meta-linked type aromatic polyamide fiber. The widthwise yarn expose more to the woven fabric surface than the lengthwise yarn. Thus, the belt life is lengthened and the noise reduced.

Description: This invention relates to a synchronous belt in which a tooth part formed on a belt body is covered with a woven fabric, and particularly relates to an improvement of the woven fabric. A synchronous belt in which a tooth part formed on a belt body is covered with a woven fabric has been used in variable fields and, in its turn, has been used under severe conditions such as high rotation, high loading, high temperature, etc. Under such conditions, increase in durability thereof is desired since the belt life is shortened because of a degradation of the materials of the belt, chip-out of the tooth part and breakage of the tension member in a short period. In addition, with machine tools for automobiles and home appliance high graded, noise at belt driving is desired to be reduced. In order to enhance the durability of a synchronous belt, it is proposed in Japanese Patent Application Laying Open Gazette No.60-81536 and corresponding to EP-A-0 138 466 that a synchronous belt is covered with a woven fabric having woolly yarns of high viscosity polyamide fiber. Also proposed in Japanese Patent Application Laying Open Gazette No.55-40319 is that a heat-resisting synthetic fiber of more than 90% of a strength remaining ratio after 400 hours passed under 120° atomospheric temperature is used as one of weft yarn and warp yarn, a synthetic fiber including nylon 6 or nylon 6,6 is used as the other yarn, and the one yarn exposes more to a surface of the woven fabric than the other yarn and vice versa. In order to reduce the noise, it is proposed in Japanese Utility Model Registration Application Laying Open Gazette No.62-87238 that at least one ply of a rough woven fabric is embedded in the belt body and at least one ply of surface woven fabric is adhered to the surface of the belt body. Also proposed in Japanese Utility Model Registration Application Open Gazette No.63-11949 is a synchronous belt having a canvas on which only RFL (resorcin formaldehyde latex) adhesion treatment is provided and in which at least the contact surface with a pulley is uncoated with rubber. However, instead of the durability ensured, the noise is not reduced in the former two synchronous belts, and vice versa in the latter two synchronous belts. In other words, both the high durability and the low noise are not obtainable in any of the known synchronous belts. With the synchronous belt of the kind as referred to in EP-A-0 138 466 and corresponding to the belt in accordance with the preamble of claim 1 the lenghtwise or weft yarns and the widthwise or warp yarns of the woven fabric are formed of polyamide synthetic resin having an ultimate viscosity of greater than approximately 1.30 whereby either of the weft or warp yarns may also be fully woolly processed yarns. With the use of such a specifically designed woven fabric for covering the tooth part of such a synchronous belt an improved resistance to cracking and shearing of the teeth in use of the belt is aimed. It is an object of the present invention to enhance in general the durability of such toothed synchronous belts and to reduce their noise developing characteristics at meshing by particularly specifying the kind and structures of the yarns and combinations thereof composing the woven fabric and to also enhance in general the abrasion resistance of the tooth part as well as to lessen in general their capability of failure. In accordance with the present invention a synchronous belt in which a tooth part formed on a belt body is covered with a woven fabric comprises a yarn in a longitudinal direction of the belt and made of a covered yarn and a yarn in a widthwise direction of the belt and made of a spun yarn of synthetic fiber. The covered yarn is so composed that a crimped yarn of synthetic fiber is wound around a core yarn of elastic yarn. The spun yarn in the belt width direction may be made of meta-linked type aromatic polyamide and is preferably exposed more to the surface of the woven fabric than the crimped yarn of the lengthwise directed yarn. The invention is claimed in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a perspective view of a synchronous belt. Fig.2 is a view showing the structure of a yarn of a woven fabric extending in the longitudinal direction of the belt. Fig.3 is a graph showing a relation between strength and elongation of the woven fabric in a stretching direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig.1 shows a synchronous belt 1 having a belt body 2 according to a first embodiment. Embedded in parallel at a pitch line of the belt body 2 are a plurality of tensile cords 3 of low elongation and high strength made of glass fiber, carbon fiber, aromatic polyamide fiber and the like. A tooth part 4 is integrally formed with one of the surfaces of the belt body 2 and is covered with a woven fabric 5. A single or blended component among NR (natural rubber), SBR (styrene-butadiene rubber), CR (chloroprene rubber), NBR (acrylonitrile-butadiene rubber), CSM (chlorosulfonated polyethylene rubber), H-NBR (hydrogenated nitrile rubber) and the like, or single urethane elastomer is used for the rubber of the belt body 2 and its tooth part 4. The woven fabric 5 is woven with a lengthwise yarn 6 made of a crimped yarn of synthetic fiber and a widthwise yarn 7 made of a spun yarn of synthetic fiber. The spun yarn is composed of short fibers gathered into tows and has many giggings on its surface. The materials of the yarns 6 and 7 are nylon fiber, polyester fiber, aromatic polyamide fiber, aromatic polyester fiber and the like. Particularly, the prefered material for the lengthwise yarn 6 is an aliphatic synthetic fiber which is easy to be crimped and the melting point of which is comparatively low, such as nylon fiber, polyester fiber. The spun yarn is suitable for the widthwise yarn 7, because the giggins of the spun yarn cushions a shock owing to a contact with a pulley at belt driving. This enhances the durability of the synchronous belt 1 and decreases the noise. Since the spun yarn has a lower strength than a continuous fiber yarn, the spun yarn is used as the widthwise yarn 7 to which load is not applied and the stretch yarn composed of the crimped yarn of continuous fiber is used as the lengthwise yarn 6 to which load is applied. Thus, the general strength of the woven fabric is maintained, while displaying the cushion property. Further, the widthwise yarns 7 are exposed more to the surface of the woven fabric 5 than the lengthwise yarns 6 in order to enhance the cushion property. As weave design, satin weave, modified twill weave, and the like are prefered. Such weave designs restrain fatigue owing to a shock received by the woven fabric 5 and cushion the shock to the tensile cords 3. As a result, life of the woven fabric 5 and the tensile cords 3 remarkably increases. In addition, the noise at the shock generated at an engagement of the synchronous belt 1 with a pulley is reduced thanks to the cushion property. In case where the woven fabric 5 is permeated thoroughly with an adhesion containing much rubber cement or rubber component, for example, RFL, the spun yarn is appropriately gathered into tows without decreasing the cushion property and abrasion is hard to occur. Even without the adhesion treatment, the above property would not be lost as far as the spun yarn is used. A performance test has been exemplified to two synchronous belts A-I and A-II according to this embodiment, a comparative example B-I, and a conventional example X. Respective woven fabrics are prepared for the respective belts A-I, A-II, B-I, X. Each structure thereof and thereof and property results are respectively indicated in Table 1 and Table 2. In each belt, a warp yarn and a weft yarn are respectively the widthwise yarn 7 and the lengthwise yarn 6. After a conventional rubber-cement treatment is conducted on each woven fabric in Table 1, the tooth part of the belt body is covered with the woven fabric to obtain the synchronous belt as shown in Fig.1. In detail, the synchronous belt of 0.656mm PLD (pitch line differential) and 19mm belt width with 125 teeth is obtained by a conventional method in which the rubber-cement-treated woven fabric is wound on a toothed cylindrical mold, the tensile cords are spun therearound, an unvulcanized rubber sheet of a set thickness is wound thereon, and rubber is formed to tooth grooves of a drum, applying pressure and heating from outside. Thereafter, the synchronous belt is trained between driving and driven pulleys both with 18 teeth, with 20kg tension applied. Then the belt is run under the conditions of 4 PS load, 1000 rpm and atmospheric temperature of 100°. Running time of the belt at which the tooth part is chipped out or broken is shown in Table 3. As indicated in Table 3, it is clear that each running time (corresponding to the belt life) of the belts A-I, A-II of the present invention is remarkably long, compared with the comparative example B-I and conventional example X. Particularly, the synchronous belt with the woven fabric of satin weave is superior to that of twill weave in its belt life. The same running test is conducted for measuring a remaining strength of the belt after 100-hour running. The results are indicated in Table 4. As a result, the belts A-I and A-II of the above first embodiment are superior to the conventional example X in the remaining strength, and particularly the belt A-1 is also superior to the comparative one B-I therein. Further, the noise caused at belt running is measured in the same running test. The results are indicated in Table 5. The noise test is conducted under the atomospheric room temperature. Each noise volume at 300 Hz (primary meshing frequency) and 600Hz (secondary meshing frequency) is measured at fixed 100rpm. Table 5 teaches that each noise volume of the belts A-1 and A-11 are almost the same as that of the comparative example B-I but is much lower than that of the conventional one X. In addition, the woven fabric of satin weave displays more noise reducing feature than that of twill weave. A synchronous belt 1 according to a second embodiment is the same as in the first embodiment except for the woven fabric 5. In detail, the synchronous belt is so composed that the tensile cords 3 are embedded in the belt body 2 and the tooth part 4 formed on the belt body 2 is covered with the woven fabric 5. (see Fig.1) In the woven fabric 5, the yarn 7 in the widthwise direction of the belt is made of a spun yarn of meta-linked type aromatic polyamide fiber and the yarn 6 in the longitudinal direction thereof is made of a crimped yarn of synthetic fiber as in the above first embodiment. The widthwise yarn 7 is exposed more to the surface of the woven fabric 5 than the lengthwise yarn 6. Since the spun yarn of meta-linked type aromatic polyamide fiber is used as the widthwise yarn 7 of the woven fabric 5, sufficient cushion property is obtained. The aromatic polyamide fiber is therefore the most preferable fiber since a greater cushion property is obtained with a synthetic fiber of high elasticity. The para-linked type aromatic polyamide fiber, however, causes fibrillary breakage because of high fiber orientation ratio and low abrasion resistance. Thus, the para-linked type aromatic polyamide fiber is unsuitable for the abrasion resistance material. Since the meta-linked type aromatic polyamide fiber has sufficient elasticity and low fiber orientation ratio (compared with the para-linked type), the abrasion resistance is superior. Consequently, the meta-linked type aromatic polyamide fiber with high elasticity and high abrasion resistance is used as the yarn 7 in the widthwise direction of the belt. With this embodiment the same effects as in the above first embodiment are obtainable, namely that the durability of the synchronous belt 1 is enhanced and that the noise is reduced thanks to the cushion property of the widthwise yarn 7 of the woven fabric 5 (giggings on the surface of the spun yarn). In addition, since the meta-linked type aromatic polyamide fiber is used for the widthwise yarn 7, the abrasion resistance is greatly enhanced. The performance test is continued to a synchronous belt A-III of this second embodiment comparative examples B-II, B-III, B-IV and a conventional example X. Respective woven fabrics are prepared for the respective belts A-III, B-II, B-III, B-IV, X. Each structure thereof and property results are respectively indicated in Table 6 and Table 7. In each belt, the warp yarn and the weft yarn in Table 6 are used as the widthwise yarn and the lengthwise yarn respectively. After a conventional rubber-cement treatment is conducted on the woven fabric in Table 6, the tooth part of the belt body is covered with the woven fabric to obtain the synchronous belt, as shown in Fig.1, of 0.656mm PLD and 19mm belt width with 125 teeth. The method of making the belt is the same as in the above first embodiment. Thereafter, the running test under the conditions as in the first embodiment is conducted. Running time of the belt at which the tooth part is chipped out or broken is shown in Table 8. According to Table 8, it is found that the running time (corresponding to the belt life) is long when the spun yarn is used as the warp yarn (widthwise yarn). Further, the spun yarn of meta-linked type aromatic polyamide spun fiber as in the present invention is the most suitable yarn in view of the belt life. The remaining strength of the belt after 100-hour running is measured in the same running test. The results are indicated in Table 9. As result, it is clear that the remaining strength after running of the belt is not so reduced. In this point, there is only little difference between meta-linked type and para-linked type. Further measured is the noise volume at the belt running in the same running test. The results are indicated in Table 10. The testing method is the same as in the above first embodiment. In Table 10, it is found that the noise volume of the belt A-III is lower than that of the comparative examples B-III, B-IV and the conventional one X. The synchronous belt of a third embodiment which finally was produced in accordnce with the present invention is the same as the above first embodiment except for the woven fabric 5. In detail, the synchronous belt 1 is so composed that the tensile cords 3 are embedded in the belt body 2 and the tooth part 4 formed on the belt body 2 is covered with the woven fabric 5 (see Fig.1). In the woven fabric 5, the lengthwise yarn 6, as shown in Fig.2 in enlarged scale, is made of a covered yarn composed of a core yarn 8 of elastic yarn such as polyurethane, and a crimped yarn 9 of synthetic fiber wound therearound. The widthwise yarn 7 is made of a spun yarn of meta-linked type aromatic polyamide fiber, as in the above second embodiment. The widthwise yarn 7 is exposed more to the surface of the woven fabric 5 than the lengthwise yarn 6. Since the lengthwise yarn 6 is composed of the elastic core yarn 8 and the crimped yarn 8 of synthetic fiber wound therearound, the inside core yarn 8 wound by the crimped yarn 9 can display the elastic function without a contact with the giggings, though the gigging of the widthwise yarn 7 (spun yarn) restrains the crimped yarn 9 for stretching. Thus, a great elongation of the yarn 6 is obtained, ensuring the stretchability by the elastic function of the core yarn 8. This enables a sufficient shrinking treatment, high elongation upon low loading at forming the belt. and a stable formation of the tooth part, reducing the defective tooth part. With this inventive embodiment, the same effects as in the above first embodiment are obtainable, namely, that the durability of the synchronous belt 1 is enhanced and the noise is reduced by the cushion property of the widthwise yarn 7 (giggings of the surface of the spun yarn) of the woven fabric 5. The abrasion resistance is otherwise remarkably enhanced, as in the above second embodiment, by using meta-linked type aromatic polyamide fiber as the widthwise yarn 7. Finally, a stable formation and less defective tooth part can be realized because of the double structure of the lengthwise yarn 6. A performance test is conducted to the inventive belts A-IV, A-V, and A-VI, a comparative example B-V and a conventional example X. The structure and property results of the respective woven fabrics used for each belt are indicated in Table 11 and Table 12 respectively. A relation between strength and elongation (SS) of the woven fabric in a stretching direction is shown in Fig.3. In each belt, the widthwise yarn and the lengthwise yarn are respectively the warp yarn and the weft yarn in Table 11. After the rubber-cement treatment is conducted on the woven fabric in Table 11, the tooth part of the belt body is covered with the woven fabric to obtain a synchronous belt, as shown in Fig.1, of 0.686mm PLD and 19mm belt width with 125 teeth. The method of making the belt is the same as in the above first embodiment. Thereafter, the running test under the conditions as in the first embodiment is conducted. Running time of the belt at which the tooth part is chipped out or broken is shown in Table 13. According to Table 13, it is found that each running time (corresponding to the belt life) of the belts A-IV, A-V, A-VI of the present invention is much longer than the comparative example B-V and the conventional one X, wherein the belt A-VI of the present invention is remarkable. The remaining strength of the belt after 100-hour running is measured in the same running test. The results are indicated in Table 14. From the results, it is clear that the belts A-IV, A-V, A-VI of the present invention are superior to that of the comparative example B-V and the conventional example X in the remaining strength. Further measured is the noise volume at the belt running in the same running test. The results are indicated in Table 15. The testing method is the same as in the above first embodiment. In Table 15, it is found that the noise volume of the belts A-IV, A-V, A-VI of the present invention is lower than that of conventional examples X, though the belts IV, V, VI IV are not so different in the noise volume from the comparative example B-V. A number of belts with defective tooth per 500 belts is indicated in Table 16. Table 16 teaches that the defective tooth is hard to occur in the belts A-IV, A-V, A-VI of the present invention, compared with the comparative example B-V.

Claims: A synchronous belt (1) having a toothed part (4) formed on the belt body (2) and covered with a woven fabric (5), the woven fabric comprising lengthwise yarns (6) and widthwise yarns (7) made of synthetic fibres, characterized in that said lengthwise yarns (6) are each composed of a covered yarn comprising an elastic core yarn (8) around which a crimped yarn (9) is wound, said widthwise yarns (7) being each composed of a spun yarn. A synchronous belt (1) according to claim 1, wherein said spun yarn of each of said widthwise yarns (7) comprises a meta-linked type aromatic polyamide fibre. A synchronous belt (1) according to claim 1 or claim 2, wherein said widthwise yarns (7) are exposed more to a surface of said woven fabric (5) than said lengthwise yarns (6).

Inventors: FUJIWARA AKINORI C O BANDO CHE, MATSUOKA HIROSHI C O BANDO CHE, ONOE SUSUMU C O BANDO CHEMICAL, SHIOYAMA TSUTOMU C O BANDO CHE, TANAKA MICHIO C O BANDO CHEMIC, FUJIWARA, AKINORI, C/O BANDO CHEMICAL IND., LTD., MATSUOKA, HIROSHI, C/O BANDO CHEMICAL IND., LTD., ONOE, SUSUMU, C/O BANDO CHEMICAL IND., LTD., SHIOYAMA, TSUTOMU, C/O BANDO CHEMICAL IND., LTD., TANAKA, MICHIO, C/O BANDO CHEMICAL IND., LTD.
Applicants: BANDO CHEMICAL IND, BANDO CHEMICAL INDUSTRIES, LIMITED
Application year: 1992
Main classification: F16G1
IPC codes: F16G1