Belt

Abstract: A belt which prevents generation of cracks and noises at a joint part of a canvas. Tooth faces of tooth parts (4) of a synchronous belt are covered with the canvas (5). A warp yarn (6a,6b) of the canvas is such formed that a necessary number of spun yarns or filament yarns are gathered and given a final twist at many twisting times of 1000-3000 per meter. The warp yarns (6a,6b) of the canvas is so composed that a first pair of warp yarns made of an S twist yarn and a Z twist yarn and a second pair of warp yarns made of a Z twist yarn and an S twist yarn are arranged alternately in a belt-width direction. A weft yarn (7) of the canvas is composed of well known spun yarns or filament yarns. The canvas (5) is woven by the warp yarns and the weft yarns and shrunk in hot water so as to stretch in a belt-length direction. As compared with the conventional belt in which a canvas with high-stretchable crimp yarns for weft yarns is such used that the direction of the crimp yarns accords with a longitudinal direction of the belt, the number of joint parts of the canvas by which cracks are caused is reduced.

Description: BACKGROUND OF THE INVENTION The present invention relates to a belt such as a transmission belt, a synchronous belt or the like. Conventionally, there has been known a transmission belt such as a wrapped V belt, a raw-edged V belt, a V-ribbed belt or the like. For reinforcement of such a transmission belt, a canvas is used. In general, a woven fabric made of cotton fibers, a woven fabric made of chemical fibers (nylon 6, nylon 6,6, polyester, aramid) or a woven fabric made of blended yarns of cotton fibers with chemical fibers (cotton-nylon 6, cotton-nylon 6,6, cotton-polyester, cotton-aramid) is used as canvas for a belt. In a woven fabric used as canvas for a belt, warp yarns and weft yarns are small and approximately equal to each other in stretching. Therefore, the woven fabric is used in form of a commonly called bias canvas. In detail, the bias canvas is formed in such a manner that an original sized canvas is cut bias to incline the warp yarns and the weft yarns at 90-130 in a longitudinal direction of a belt. When such woven fabric is applied to a belt the length of which is longer than the width of the original sized canvas, it is required to form the canvas in such a manner as to join the woven fabrics to one another. In such a case, not only processes for forming the woven fabrics into a bias canvas are increased and complicated, but cracks easily generate in a joint part in which the woven fabrics are joined to one another, which shortens the belt life. In the case where such woven fabric is used as a covering canvas composing an outer portion of a V-ribbed belt or the like, noises easily generate at a joint part (a level difference part) in which the woven fabrics are joined to one another when the covering canvas receives a tension against the outer portion of the belt. In addition, since stretchings of the warp yarns and the weft yarns are unbalanced, the belt is apt to meander, i.e., move in a belt-width direction, or tumble. Further, in a synchronous belt, there has been known a reinforcing canvas which is used at tooth-bottom faces of tooth parts and is woven, using high-stretchable crimp yarns in a longitudinal direction, as disclosed in Japanese Utility-Model Open Gazette No.60-16037. More generally, there has been known a canvas in which high-stretchable crimp yarns are used in a lateral direction of the woven fabric and the lateral direction of the woven fabric is made to correspond with the longitudinal direction of the belt. In the case where such woven fabric is used as a canvas, two or more joint parts exist in the canvas when the length of the belt is longer than the width of the woven fabric. This presents a breakdown of the synchronous belt at the joint parts, thereby resulting in a shortened belt life. Further, since the woven fabric is so woven that the warp yarns in which all final twists are either S twists or Z twists are parallel with one another, the belt easily meanders, thereby further shortening the belt life. In EP-A-0 099 205 a woven fabric for use in a transmission belt is disclosed which comprises a warp of shrinkable yarns obtained by aligning and twisting individual shrinkable mixed yarns. The warps may alternatively be formed of more than two mixed twisted yarns mixed in a ratio of greater than 1:15 of elastic yarns formed of polyurethane fibrous yarns oriented at more than 10 %, or rubber yarns and other fibrous yarns. The weft is made alternatively of twisted yarns or monofilament yarns. The fabric is presented to having excellent shrinkability, wear resistance and crack resistance. In EP-A-0 271 587 a toothed belt having a woven cloth sticked on its surface which is in contact with a pulley is disclosed. For providing a high wear resistance of this one surface and for hindering the development of cracks those yarns among the yarns forming such cloth which are intended to run in the longitudinal direction of the belt are comprised of crimped raw nylon threads of a relative viscosity in sulfuric acid of about 2.5, a fineness of monofilament of not more than 2.5 d and a strength of raw thread of not less than 7.5 g/d. Summary of the invention According to the present invention there is provided a belt comprising a belt body and a shrunk woven canvas having warp yarns and weft yarns of different characteristics and covering the belt body in such a manner that the warp yarns extend in a longitudinal direction of the belt. A belt of this general kind is believed to be known from EP-A-0 271 587. The present invention has for its object the provision of a belt in which generation of cracks and noises caused at a joint part of the canvas are prevented. With the belt according to the present invention, the direction of the warp yarns corresponds with the longitudinal direction of the belt, whereby the warp yarns of the canvas comprise a necessary number of spun yarns or filament yarns gathered and given a final twist at 1500-3000 times per meter, and the canvas is woven in such manner that a first pair of warp yarns made of a S twist yarn and a Z twist yarn and a second pair of warp yarns made of a Z twist yarn and a S twist yarn are arranged alternately in a belt-width direction. Thereby, the stretchability in the longitudinal direction of the canvas (i.e., the belt-length direction) can be enhanced, and the number of joint parts of the canvas is reduced as compared with the conventional belt, so that generation of cracks and noises caused at the joint part can be prevented. In particular, since a first pair of warp yarns made of a S twist yarn and a Z twist yarn and a second pair of warp yarns made of a Z twist yarn and a S twist yarn are arranged alternately in the belt-width direction, any meandering motion and lateral tumble of the belt can be restrained. The belt of the present invention is applied to a synchronous belt having tension cords provided inside of a belt body thereof and tooth parts formed at regular intervals at a lower part thereof. The belt is as well applied to a V-ribbed belt having tension cords provided inside of the belt body and plural ribs formed at a lower part thereof. In case of the V-ribbed belt, the warp yarns are formed of spun yarns of 60-10 yarn number gathered and given a final twist at 1500-2500 times per meter, and twisting times of S twist warp yarn are approximately 10-20 percent more than that of Z twist warp yarn. The weft yarns are formed of spun yarns of 40-7 yarn number gathered and given a final twist at 1600 to 8000 times per meter (40-200 times per inch). The invention is set out in Claim 1. Further preferred embodiments are set out in Claims 2-5. BRIEF DESCRIPTION OF THE DRAWINGS Accompanying drawings show preferred embodiments of the present invention. In the drawings, Fig.1 is a front view showing a part of a synchronous belt, Fig.2 is an explanatory diagram of a canvas, Fig.3 is a schematic diagram of a testing apparatus, Fig.4 is a schematic diagram of another testing apparatus, Fig.5 is a front view showing a part of a V-ribbed belt, Fig.6 is a perspective view of a raw-edged V belt, Fig.7 is a schematic view of another testing apparatus, Fig.8 is a schematic view of still another testing apparatus, and Fig.9 is a schematic view of still another testing apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS Detailed description is made below about embodiments of the present invention with reference to the accompanying drawings. (FIRST EMBODIMENT) A belt of the present embodiment is applied to a synchronous belt. In Fig.1 showing a schematic structure of a synchronous belt, reference numeral 1 designates the synchronous belt, wherein a belt body 2 has tension cords 3 therein and tooth parts 4 formed at regular intervals at a lower part thereof. Tooth faces of the tooth parts 4 are covered with a canvas 5. The canvas 5 is woven by warp yarns 6a, 6b and weft yarns 7, wherein each warp yarn 6a, 6b has an excellent stretchability and is oriented in accordance with a belt-length direction. As shown in Fig.2, the warp yarns 6a, 6b of the canvas 5 comprise a necessary number of spun yarns or filament yarns gathered and given a final twist at twisting times of 1500 to 3000 per meter. A first pair of warp yarns 6A made of a S twist yarn 6a and a Z twist yarn 6b and a second pair of warp yarns 6B made of a Z twist yarn 6b and a S twist yarn 6a are arranged alternately in the belt-width direction. The weft yarns 7 comprise spun yarns or filament yarns which have less stretchability. The warp yarns 6a, 6b and the weft yarns 7 are woven by a power loom or a high-speed loom as it is well known for being formed into a woven fabric. The woven fabric is shrunk in hot water to make the plane weave canvas 5 further stretching in a longitudinal direction of the belt. Then, the canvas 5 undergoes a well known treatment, i.e., a dip treatment by an adhesive in which resorcin, formaldehyde and latex are condensed thus serving as a canvas for belt. The following Table 1 shows an example of a canvas according to a belt of the present invention together with an example of a conventional canvas. example of the present invention conventional example Construction warp yarn 70d/2 × 2 70d/3 weft yarn 210d/1 140d/2 Twisting times (times/10cm) warp yarn S twist: 2200 S twist: 40 Z twist: 2000 weft yarn S twist: 40 S twist: 20 Density (number/2.54 cms (inch) warp yarn 65 95 weft yarn 110 72 Strength (kgf/3cm) warp yarn 75 120 weft yarn 220 100 Elongation (%) warp yarn 160 35 weft yarn 40 140 50% Modulus (kgf/3cm) 0.2 (longitudinal direction of canvas) 0.5 (lateral direction of canvas) As material of the canvas, spun yarns or filament yarns made of chemical fibers such as cotton, nylon 6, nylon 6,6, polyester or aramid, or blended yarns of such chemical fibers can be used. For a method of weaving, a plain weave, a twill weave, a satin weave or the like is available. In accordance with conventional fabricating process of the canvas, filament fibers are given a false twist, heated in the vicinity of the melting point, woven into a canvas and then shrunk. Unlike the conventional process, however, in a fabricating process of the canvas according to the present invention, the final twist time of spun yarns or filament yarns comprising the warp yarns 6a, 6b is more than that of the conventional process. A woven fabric is further formed in such a manner that the first pair of warp yarns 6A made of a S twist yarn 6a and a Z twist yarn 6b and a second pair of warp yarns 6B made of a Z twist yarn 6b and a S twist yarn 6a are arranged alternately in a belt-width direction, and the woven fabric is shrunk in hot water. This prevents the belt from meandering and presents a stretchability capable of sufficiently standing the use of the belt. Accordingly, it is not required that a canvas having high-stretchable crimp yarns as weft yarns is used in such a manner that the direction of the crimp yarns corresponds with the longitudinal direction of the belt as in a conventional belt. When a synchronous belt is made by using the canvas of the present embodiment, the canvas to be used as a covering canvas is wound on a toothed cylindrical mold such that the warp yarns can be oriented in a peripheral direction of the mold, tension-resistance codes are spur therearound, an unvulcanized rubber sheet of a set thickness is wound thereon, and a rubber is formed into tooth grooves of the cylindrical mold together with stretching the canvas (or warp yarns thereof) by applying pressure and heating from outside. The belt fabricated in such a manner decreases the number of joint parts thereby lessening the generation of cracks at the joint parts. This leads to a considerable, stable elongation of belt life. Further, since the warp yarns are so designed that the first pair of warp yarns 6A made of the S twist yarn 6a and the Z twist yarn 6b and the second pair of warp yarns 6B made of the Z twist yarn 6b and the S twist yarn 6a are arranged alternately in the belt-width direction, this prevents the belt from meandering thereby resulting in an elongation of the belt life and also enhances the quality of the belt. Explanation is made next about a test conducted with reference to a relation between the number of joint parts of a canvas and belt life. As shown in Fig.3, a belt 13 of 280cm belt length is wound between a driving toothed pulley 11 having 20 teeth and rotating at 8000rpm and a driven toothed pulley 12 having 20 teeth. The belt 13 is run under a temperature of 100°C and an initial tension of 20kg/cm 2 . For the pulley, an H-shaped pulley with 25.4mm pulley width, 80.85mm pitch diameter and 79.48mm outside diameter is used. The result of the test is shown in below-mentioned Table 2. In an example of a conventional belt, a crimp yarn of 70d/3 is so used as to fit a stretching direction thereof to a longitudinal direction of the belt. In Table 2, "Belt life" indicates the period of time till a crack generates at a joint part. example of the present invention conventional example Canvas width 1.4m 0.85m 1.25m 1.45m Number of tested belt 20 50 50 50 Number of joint part 1 4 3 2 Belt life (Hr) 200 110 130 170 Dispersion of belt life (σn-1) 25 43 40 36 The belt according to the example of the present invention has only one joint part even in case of a long-length belt thereby elongating belt life as compared with the belt of the conventional example. Further, explanation is made below about a test conducted with reference to a meandering motion of a belt. As shown in Fig.4, a synchronous belt 12A is wound between a driving toothed pulley 11A and a driven toothed pulley 11B each having same construction as used in the above-mentioned test about a relation between the number of joint parts of a canvas and belt life. The synchronous belt 12A is run with the driven toothed pulley 11B tensed at load of F1 = 63.5 Kg (140LBS) in direction A. For the synchronous belt 12A, a belt having 122 cm (48 inches) belt length and 1.9 cm (0.75 inches) belt width is used. The result of the test is shown in the following Table 3. conventional example example of the present invention Number of tested belt 20 20 meandering motion of belt 1.0 0-0.5 It is understood that the example of the present invention shows a high efficiency of preventing a meandering motion as compared with the example of the conventional belt. An amount of meandering motion of the example of the present invention is a half or less than it as compared with that of the conventional example. In the example of the present invention, the amount is approximately 0. The value of 0.5 is caused by non-uniformity of cord arrangement. (SECOND EMBODIMENT) A belt of the present embodiment is applied to a transmission belt. In Fig.5 showing a schematic structure of a V-ribbed belt, reference numeral 21 designates a V-ribbed belt as a transmission belt, wherein a belt body 22 has tension cords 23 therein and plural ribs 24 formed at a lower part thereof and an outer periphery of the belt body 22 is covered with a canvas 25. The canvas 25 is woven by warp yarns and weft yarns, wherein the warp yarns are oriented in accordance with a longitudinal direction of the belt and have an excellent stretchability as in case of the canvas 5 of the first embodiment. The warp yarns of the canvas 25 comprise spun yarns of yarn number 60-10 gathered and given a final twist at 1500 to 2500 times per meter. A first pair of warp yarns 6A made of an S twist yarn 6a and a Z twist yarn 6b and a second pair of warp yarns 6B made of a Z twist yarn 6b and an S twist yarn 6a are arranged alternately in the belt-width direction. The twisting number of the S twist warp yarn 6a is 10-20 percent more than that of the Z twist warp yarn 6b. The weft yarns 7 comprise spun yarns (yarn number 40-7) with less stretchability gathered and given a final twist at 1600 to 8000 times per meter (40 to 200 times per inch). The other construction excluding the above construction in the canvas 25 is the same as in the canvas 5 of the first embodiment. Further, material and a weaving method of the canvas 25 is also same as in the canvas 5 of the first embodiment. The following Table 4 shows an example of the canvas 25 of the present invention together with an example of a conventional canvas. example of the present invention conventional example Warp yarn Yarn No. 30S/2 × 2 20S/2 Denier 354d × 2 = 709d 531.5d Twist S twist:2400 times/m S. twist:600 times/in Z twist:2000 times/m (150 times/10in). Weft yarn Yarn No. 20S/2 20S/2 Denier 531.5d 531.5d Twist S twist: 200 times/in (50 times/10in). S twist:600 times/in (150 times/10in). twist yarn canvas twist yarn canvas Strength (kgf) warp 0.52 21.5 0.70 37.0 weft 0.763 32.6 0.74 41.0 Elongation (%) warp 171.0 159.5 11.1 26.5 weft 12.6 17.0 10.8 19.0 Thickness (mm) 0.88-0.92 0.55 Construction (number/5cm) 30S/2 ×2 × 20S/2 50 × 80 20S/2 × 20S/2 76 × 85 In the above Table 4, the strength of twist yarn shows a value per one yarn of yarn number 30S/2 with reference to the example of the present invention and a value per one yarn of yarn number 20S/2 with reference to the conventional example. The strength of canvas shows a value per 3cm. A numerator and a denominator in the "Construction" indicate yarn numbers of the warp and weft yarns (and the numbers thereof), and feeding numbers of the warp and weft yarns, respectively. When a V-ribbed belt 21 is made by using the canvas 25 of the present embodiment, the canvas 25 is wound on a toothed cylindrical mold such that the warp yarns can be oriented in a peripheral direction of the mold, an adhesive rubber sheet is wound thereon, tension-resistance codes are spur therearound, a bottom rubber sheet is wound thereon, and pressure and heating are applied from outside. After the application of pressure and heating, ribs are formed by scraping the bottom rubber, and then a V-ribbed belt is obtained by cutting at a set width dimension. The belt 21 made in such a manner decreases the number of joint parts as compared with the case using a conventional bias canvas, thereby lessening the generation of cracks and noises at the joint parts. This leads to a considerable elongation of belt life. Further, since the warp yarns are so designed that the first pair of warp yarns 6A made of the S twist yarn 6a and the Z twist yarn 6b and the second pair of warp yarns 6B made of the Z twist yarn 6b and the S twist yarn 6a are arranged alternately in the belt-width direction, this prevents the belt from meandering and tumbling thereby resulting in an elongation of the belt life and also enhances the quality of the belt. In addition, since the canvas 25 of the present embodiment is not required to be a bias canvas, this makes fabricating process of the canvas simplified and presents an advantage of reducing fabrication costs. Explanation is made below about each testing method conducted with reference to the following five points: the adhesive strength of a joint part (Point 1), the meandering motion performance of the belt (Point 2), the level difference of a joint part (Point 3), a crack of the belt bottom (Point 4), and a lateral tumble (Point 5). Each test with reference to the Points 1-3 is conducted by using a V-ribbed belt (with three ribs, 1000mm belt length and 20mm belt width) as a transmission belt and each test with reference to the Points 4 and 5 is conducted by using a raw-edged V belt with 890 cm (35 inches) belt length as a transmission belt shown in Fig.6. In Fig.6, reference numeral 26 indicates the raw-edged V belt, and 27 indicates a belt body having tension cords 28. The raw-edged V belt 26 has upper and lower canvas layers 29A, 29B which are provided at an upper side and a lower side of the belt body 27 respectively. A testing method in respect to the adhesive strength of a joint part is as follows. A canvas undergoes an adhesion treatment by an unvulcanized adhesive rubber to be attached to another canvas, and vulcanized under a temperature of 148°C for 30 minutes. Thereafter, peeling resistance is measured when the attached canvases are peeled. For belts, peeling resistance is measured when a canvas of 1cm width is peeled from a belt body. A testing method in respect to a meandering motion performance of the belt is as follows. As shown in Fig.7, a belt 33 is wound between a driving ribbed pulley 31 with 95.5mm diameter and a driven plain pulley 32 with 75mm diameter and 40mm pulley length, and is located at a center in a width direction of the driven plain pulley 32. (Under this situation, a distance between a belt edge and a pulley edge in a width direction of the driven plain pulley 32 is 10mm.) Lateral moving width from the center of the belt 33 and the period of time till the lateral moving begins are measured. A testing method in respect to a level difference of a joint part is as follows. After the attached canvases are vulcanized in the above-mentioned testing method in respect to an adhesive strength of a joint part, the joint part is taken apart and the level difference of the joint part is directly measured with a scale. A testing method in respect to a crack of a belt bottom is as follows. As shown in Fig.8, a belt 44 is wound about a driving pulley 41 which has 125mm diameter and rotates at 4900rpm, a driven pulley 42 with 125mm diameter and an idler pulley 43 with 70mm diameter, thereby forming three shafts. With a load of F2 = 85kgf applied to the idler pulley 43 in a direction B, the period of time till a crack generates at a joint part of a canvas is measured. A testing method in respect to a lateral tumble is as follows. As shown in Fig.9, a belt 53 is wound between a pulley 51 with 140mm diameter and a pulley 52 with 60mm diameter. With the peripheral velocity of the pulley 51 varied, the peripheral velocity at which a lateral tumble of the belt 53 generates is measured. Results of the above tests are shown in the following Table 5. In a conventional example, a bias canvas composed of warp yarns and weft yarns each yarn number of which is 20S/2 is so used as to fit a stretching direction thereof to a longitudinal direction of the belt. example of the present invention conventional example Adhesive strength of joint part Canvas (kg/in.) more than 8.0 (canvas break) 6.0 Belt (kg/cm) yarn break (complete adhesion) 3.5 Meandering motion performance of belt Lateral moving width small large Lateral moving beginning time (second) 0 0-50 Level difference of joint part (cord going-down) (mm) 0 0.2-0.4 Crack of belt bottom 1.5 (one joint part) 1.0 (two joint parts) Lateral tumble (m/minute) 1.3 1.0 In the "Crack of belt bottom" of the above Table 5, the value of the example of the present invention is exponentially displayed based on that the period of time till a crack generates at a joint part of the conventional example is set to a standard value of 1.0. In the "Lateral tumble" of the Table 5, the value of the example of the present invention is exponentially displayed based on that the peripheral velocity at which the lateral tumble generates at the conventional example is set to a standard value of 1.0.

Claims: A belt (1; 21) comprising a belt body (2; 22) and a shrunk woven canvas (5; 25) having warp yarns (6A, 6B) and weft yarns (7) of different characteristics and covering the belt body (2; 22) in such a manner that the warp yarns (6A, 6B) extend in a longitudinal direction of the belt; characterized in that the warp yarns (6A, 6B) comprise spun yarns or filament yarns gathered and given a final twist at 1500 to 3000 times per meter, and the weft yarns (7) comprise spun yarns or filament yarns, the canvas (5; 25) being woven in such a manner that a first pair of warp yarns (6A) made of a S twist yarn (6a) and a Z twist yarn (6b) and a second pair of warp yarns (6B) made of a Z twist yarn (6b) and a S twist yarn (6a) are arranged alternately in the belt-width direction, and being shrunk in hot water so as to have a large stretchability in the longitudinal direction of the belt. The belt according to claim 1, wherein the belt is a synchronous belt (1) having tension cords (3) provided inside of the belt body (2) and tooth parts (4) formed at regular intervals at a lower part of the belt body and covered by the canvas (5). The belt according to claim 1, wherein the belt is a V-ribbed belt (21) having tension cords (23) provided inside of the belt body (22) and plural ribs (24) formed at a lower part of the belt body, said canvas (25) covering the belt body (22) and comprising warp yarns (6A, 6B) having spun yarns of 60 to 10 yarn number gathered and given a final twist at 1500 to 2500 times per meter. The belt according to claim 3, wherein the warp yarns (6A, 6B) comprise S twist yarns (6a) that are twisted approximately 10 to 20 percent more than the Z twist yarns (6b). The belt according to claim 4, wherein the weft yarns (7) of the canvas (25) comprise spun yarns of 40 to 7 yarn number gathered and given a final twist at 1600 to 8000 times per meter (40 to 200 times per inch).

Inventors: KIMOTO KANJI, KIMOTO, KANJI, Kimoto, Kanji, c/o BANDO CHEMICAL INDUSTRIES, LTD.
Applicants: BANDO CHEMICAL IND, BANDO CHEMICAL INDUSTRIES, LIMITED
Application year: 1993
Main classification: F16G1
IPC codes: F16G5, D03D1, F16G1