POWER TRANSMISSION BELT

Abstract: A toothed power transmission belt (10) is manufactured by an improved method to have substantially improved resistance to tooth root face cracking. The manufacture utilizes a modified rubber blend forming the teeth (15) and may utilize the same blend for embedding the load-carrying cords (14) to provide improved bonding of the teeth (15) to the cords (14) over a wide range of temperatures.

Description: This invention relates to power transmission belts and in particular to cogged, or toothed, transmission belts. One conventional form of power transmission belt comprises a cog belt wherein a plurality of teeth project from the body portion of the belt for engagement with suitable pulley teeth in providing a positive drive in the manner of a conventional chain drive. A serious problem arises in the conventional cog belts of the prior art in that the belts tend to crack at the junction of the tooth with the body of the belt in normal use of the belt. More specifically, the cracks form at the root face of the teeth. Such root face cracking is highly undesirable as it shortens the life of the belt. One attempted solution to the root face cracking problem has been to provide fabric on the face of the belt defining the teeth. In one conventional form, the cog belt is formed of a rubber blend. Tensile strength is provided in the belt by means of a plurality of longitudinally extending tensile cords embedded in a portion of the rubber outwardly of the teeth. Conventionally, the cords are provided in a layer of the belt comprising a cushion layer. It is desirable to provide a strong bond between the cords and the cushion layer rubber and to provide a strong bond between the cushion layer rubber and the material forming the teeth of the cog belt. It is known to form modified rubber blends including in the rubber silane coupling agents, silica and carbon black. Such blends have been used to provide improved characteristics in rubber structures, such as tyres and the like. Illustrative of prior art patents illustrating such modified rubber blends are British Patent Nos. 1 438 355, 1 439 247, 1 524 077 and 2 038 341, and U.S. Patent Nos. 3 350 345 and 3 957 718. Two conventional forms of cog belts are illustrated in U.S. Letters Patent Nos. 4 011 766 and 4 034 615. Another attempted solution to prevent root face cracking in such cog belts has been to use conventional carbon black material such as ISAF and SAF carbon black materials in the tooth rubber. Such formulated rubbers, however, have not been found to satisfactorily solve the problem because the strength of the rubber is substantially decreased at elevated temperatures, as may occur from high ambient temperatures and from the heat generated during the operation of the belt. Root face cracking is also found to occur in prior art belts as a result of the impositive bond of the tooth rubber through the load-carrying section rubber to the tensile cords. EP-A2-0 028 911 discloses a power transmission belt having a cushion section having longitudinally extending load-carrying cords therein, and a plurality of transverse, longitudinally spaced grooves extending inwardly of the cushion section, the cushion section being formed of a rubber blend comprising:- (a) about 100 parts by weight chloroprene rubber; (b) about 0.2 to 5.0 phr silane coupling agent; (c) about 10 to 60 phr silica; and (d) about 2 to 60 phr carbon black. According to the present invention there is provided a power transmission belt comprising:- a load-carrying section with longitudinally extending load-carrying cords therein; and a plurality of transverse, longitudinally spaced teeth extending from said load-carrying section and defining therebetween load-carrying root face portions, characterised in that:- the load-carrying cords are glass fibre ropes and in that the teeth and the load-carrying section are formed of a rubber blend which comprises:- (a) about 100 parts by weight chloroprene rubber; (b) 0.8 to 1.0 phr γ-mercaptopropyltrimethoxy silane coupling agent; (c) 25 to 30 phr silica; and (d) 15 to 20 phr carbon black. Thus, the present invention provides a power transmission belt with high resistance to such root face cracking as has occurred in the prior art belts. In the illustrated embodiment, the load-carrying section and teeth are formed as a monolithic structure. The teeth may be provided with a fabric cover of conventional construction. Thus, the power transmission belt, and manufacture thereof are extremely simple and economical while yet providing a highly improved cog belt manufacture having high resistance to root face cracking. For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:- Fig. 1 is a fragmentary side elevation of a power transmission system utilising a power transmission belt embodying the invention; and Fig. 2 is a fragmentary longitudinal section of the power transmission belt of the invention. In the exemplary embodiment of the invention as disclosed in the drawing, a power transmission belt generally designated 10 is shown to comprise a cog, or toothed, belt adapted to be driven by a toothed pulley 11 and drive a complementary toothed pulley 12. As seen in Fig. 2, the belt defines a longitudinally extending, outer load-carrying section 13 having embedded therein a plurality of longitudinally extending glass fibre ropes 14 acting as tensile cords. Belt 10 further defines a plurality of transversely extending longitudinally spaced teeth, or cogs, 15. As shown, the cogs are spaced longitudinally by lands 16. The lands define the root face of the belt. In the illustrated embodiment, the root face and teeth are joined to the load-carrying section monolithically, as at 17. A cover fabric 18 may be provided on the bottom surface of the teeth and root faces. The invention comprehends forming the cog teeth of the improved modified rubber blend so as to have improved bonding to tensile cords 14 for extended belt life. The use of the improved modified rubber blend further provides improved strength in the cog teeth, providing further improved extended belt life. Thus, the invention comprehends the forming of such a belt by forming the teeth of the modified rubber blend including a silane coupling agent, silica and carbon black. Further, the invention comprehends forming the cushion, or load-carrying section 13 in which the tensile cords are embedded similarly of the improved modified rubber blend so as to provide improved bond strength between the teeth and the tensile cords. The use of the silane coupling agent in the disclosed range provides an improved reinforcing of the rubber without early vulcanisation defined by a short scorch time. Such vulcanisation prevention is particularly desirable in view of the fact that the rubber comprises chloroprene rubber. The use of silica in the indicated range provides the desirable adhesive and tear strength characteristic without excessively raising the Mooney viscosity so as to avoid faulty tooth molding and the like. The use of carbon black in the indicated range provides the desirable reinforcing effect while again maintaining the Mooney viscosity suitable to prevent molding problems and shortened useful life. The silane coupling agent is γ-mercaptopropyltrimethoxy silane. It has been found that the use of the improved modified rubber blend provides a long, troublefree life to the belt. The rubber may include additives such as softeners, antioxidants, processing agents, tackifiers, accelerators, sulfurs, etc. The formation of the rubber blend may be effected by conventional mixing steps such as by using Banbury mixers, kneaders, calender rolls, etc. The silica may be kneaded with the silane coupling agent by means of a kneader. The invention comprehends the forming of the belt with the improved modified rubber blend in each of the load-carrying and tooth sections. Where the improved rubber blend is utilised in the load-carrying section, improved bond strength between the load-carrying rubber and the tensile cords is obtained. It has been found that the improved belt manufacture utilising the modified rubber blend hereof may be effected with other steps in the manufacturing process being of conventional characteristics. EXAMPLE I 100 parts of chloroprene rubber was blended with 2 phr stearic acid, 4 phr magnesium oxide, 3 phr antioxidant, 5 phr process oil, 15 phr HAF carbon black, 30 phr silica, 1 phr silane coupling agent (γ-mercaptopropyltrimethoxy silane), 5 phr zinc oxide, and 0.5 phr Na-22. The materials were kneaded in a Banbury mixer and vulcanised under conventional vulcanising conditions at 150°C for 30 minutes. The physical properties of the vulcanised modified rubber blend were as follows:- The modified rubber blend was utilised in forming a cog belt of the L-type, having the teeth 15 at 9.525 mm pitch, 800 mm (31.5") length, and 19 mm (0.75") width. The tensile cords were composed of glass fibre ropes. The belts thus manufactured exhibited the following characteristics:- In conducting the load-carrying cord adhesion test, a determination was made of the force required to pull out two ropes from the belt having a length equal to three teeth thereof. The pulsation test was conducted by applying sine wave pulsation to the belts under an average axial load of 48 kg. In the running test, the drive pulley was an 18-tooth pulley and was driven at 7,200 rpm, the driven pulley was a 36-tooth pulley and placed a 7 hp load on the belt. A 62 mm diameter hydropulley was used to maintain tension in the belt. The cog belts of Example I exhibited a reduced modulus variation over the range of 25 to 90°C as compared with similar belts utilising carbon black alone in lieu of the disclosed formulation utilising the silane coupling agent, silica, and carbon black. As indicated above, the cog belts of the present invention provide an improved bonding of the teeth to the load-carrying cords so as to produce an increased useful life of one and one-half to four times the conventional belts utilizing only the carbon black additive. The improved belts exhibited high strength to root face cracking which, as indicated above, has been a serious and perplexing problem in the prior art belts. EXAMPLE II 100 parts of chloroprene rubber was blended with 2 phr stearic acid, 4 phr magnesium oxide, 3 phr antioxidant, 5 phr process oil, 20 phr HAF carbon black, 25 phr silica, 0.8 phr silane coupling agent (γ-mercaptopropyltrimethoxy silane), 5 phr zinc oxide, and 0.5 phr Na-22. The materials were kneaded in a Banbury mixer and vulcanised under conventional vulcanising conditions at 150°C for 30 minutes. The physical properties of the vulcanised modified rubber blend were as follows:- The modified rubber blend was utilised in forming a cog belt of the L-type, having the teeth 15 at 9.525 mm pitch, 800 mm (31.5") length, and 19 mm (0.75") width. The tensile cords were composed of glass fibre ropes. The belts thus manufactured exhibited the following characteristics:- In conducting the load-carrying cord adhesion test, a determination was made of the force required to pull out two ropes from the belt having a length equal to three teeth thereof. The pulsation test was conducted by applying sine wave pulsation to the belts under an average axial load of 48 kg. In the running test, the drive pulley was an 18-tooth pulley and was driven at 7,200 rpm, the driven pulley was a 36-tooth pulley and placed a 7 hp load on the belt. A 62 mm diameter hydropulley was used to maintain tension in the belt. The cog belts of Example II exhibited a reduced modulus variation over the range of 25 to 90°C as compared with similar belts utilising carbon black alone in lieu of the disclosed formulation utilising the silane coupling agent, silica, and carbon black. As indicated above, the cog belts of the present invention provide an improved bonding of the teeth to the load-carrying cords so as to produce an increased useful life of one and one-half to four times the conventional belts utilising only the carbon black additive. The improved belts exhibited high strength to root face cracking which, as indicated above, has been a serious and perplexing problem in the prior art belts. The improved characteristics of the blends of Examples I and II are shown with reference to a conventional rubber blend having a similar composition except for the use of 35 phr HAF carbon black instead of the indicated carbon black, silica and silane coupling agent constituents of the above-discussed examples. The prior art blend exhibited the following physical properties:- Thus, the invention broadly comprehends an improved power transmission belt manufacture having high resistance to root face cracking and thereby providing extended useful life of the transmission belt.

Claims: A power transmission belt comprising:- a load-carrying section with longitudinally extending load-carrying cords therein; and a plurality of transverse, longitudinally spaced teeth extending from said load-carrying section and defining therebetween load-carrying root face portions, characterised in that:- the load-carrying cords are glass fibre ropes and in that the teeth and the load-carrying section are formed of a rubber blend which comprises:- (a) 100 parts by weight chloroprene rubber; (b) 0.8 to 1 phr γ₋mercaptopropyltrimethoxy silane coupling agent; (c) 25 to 30 phr silica; and (d) 15 to 20 phr carbon black. A power transmission belt as claimed in claim 1, wherein the root face portions are provided with a fabric cover.

Inventors: KAKIUCHI, HAJIME, MASHIMO, SATOSHI, NAKAJIMA, MASAYOSHI
Applicants: MITSUBOSHI BELTING LTD.
Application year: 1981
Main classification: F16G5
IPC codes: C08L7, C08L21, C08K3, B29D29, F16G5, C08K5, F16G1