JPS6151180B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a timing belt and a method for manufacturing the same. Lately, timing belts with shallow grooves formed at a constant pitch in the width direction on the back side of an endless belt have been used quite often. Since the transmission is carried out by the belt, there is no slippage between the belt and the pulley, and therefore the speed ratio can be kept constant, no initial tension is required, the speed ratio can be increased, and the speed ratio can be increased at low speeds. However, it has the advantage of being able to drive at high speeds. The properties required of a timing belt are flexibility, flexibility, and no elongation, as well as abrasion resistance, oil resistance, heat resistance,
It is important to have cold resistance and ozone resistance, but conventional products did not completely meet the above requirements. In many cases, chloroprene rubber is used as a molding material, and cords made of cotton, synthetic fibers, or steel wire are embedded in the rubber and then vulcanized and molded to meet these requirements. In order to suppress belt elongation, increase tensile strength, and improve abrasion resistance, measures such as attaching nylon cloth to the outer surface of the belt have been used. The above-mentioned conventional timing belts have drawbacks such as the use of many types of molding materials, the manufacturing process being complex and time consuming, and the quality of the belts being highly variable. As a result of intensive research to eliminate the above-mentioned drawbacks of conventional timing belts, the inventor found that by using a thermoplastic synthetic resin as a molding material, and by stretching the thermoplastic synthetic resin and orienting its molecules, the strength can be improved. This invention was achieved by focusing on the fact that heat setting eliminates elongation. That is, the first invention of this application is a timing belt characterized in that the concave portions of the uneven portion formed on one side of an endless belt made of a thermoplastic synthetic resin are molecularly oriented in the circumferential direction, and the convex portions are not molecularly oriented. In the second invention, a molded belt made of thermoplastic synthetic resin and injection molded into an annular shape having unevenness on one side is stretched around a pair of rotating rolls, and then the distance between the axes of the rotating rolls is adjusted. By increasing the size, only the recessed part of the formed belt is stretched in the circumferential direction,
This is a method for manufacturing a timing belt, which is characterized in that the belt is then heat-set. The thermoplastic synthetic resin used in this invention has crystallinity and has the property of molecular orientation upon stretching. The melting point of the resin is 120° C. or higher, preferably 150° C. or higher, and a lower glass transition point is preferable because stretching can be performed at a relatively low temperature. In addition, the tensile elastic modulus before stretching is 500~20000Kg/
cm ² , preferably 1000 to 10000 Kg/cm ² . Examples of thermoplastic synthetic resins having such physical properties include polyester rubber, copolymerized nylon, and thermoplastic polyurethane, and in particular, synthetic resins synthesized from terephthalic acid, isophthalic acid, 1,4-butanediol, and polytetramethylene glycol. Polyester polyether copolymer with tensile modulus of 1000~
5000Kg/cm ² is suitable. These polyester polyether copolymers include, for example, pelprene.
It is commercially available under trade names such as P150B, P150M, P70B (manufactured by Toyobo Co., Ltd.), Hytrel 5556, and 6365 (manufactured by DuPont). Incidentally, some amount of organic or inorganic filler material may be added to the thermoplastic synthetic resin. The structure of the timing belt according to the present invention will be explained with reference to FIG. 1. A is a timing belt, B is a belt wheel, and the back surface of the timing belt A has a recess 1 and a protrusion 2 at regular pitch intervals. Concave and convex portions 2b, which are formed alternately and are formed on the outer peripheral surface of the belt pulley B in correspondence with the concave and convex portions 1 and 2;
The uneven portions 1 and 2 of the timing belt A are engaged with 1b, and the timing belt A is rotated endlessly. The thin wall portion 3 forming the concave portion 1 of the timing belt A is molecularly oriented in the circumferential direction by stretching, and the thick wall portion forming the convex portion 2 is not stretched and molecularly oriented. . Although the length L ₁ of the concave portion 1 and the length L ₂ of the convex portion 2 of the timing belt A are shown to be the same, it goes without saying that L ₁ and L ₂ may be different. Next, a method for manufacturing the timing belt will be explained with reference to FIG. 2 and the following drawings. In FIG. 2, Aa is a molded belt that is injection molded into an annular shape, and the length La of the recess 1a formed on the outer peripheral surface of this molded belt Aa, and
The thickness Ta of a is shorter than the length L ₁ of the recess 1 of the timing belt A and larger than the thickness T ₁ of the recess 1, and the length L 2 and the thickness T _{2 of the protrusion 2 are the length L 1} of the recess ₁ of the timing belt A. It is formed in the same way as that of . As shown in FIG. 3, the forming belt Aa is passed around a pair of rotating rollers C, C, and in an atmosphere having a temperature higher than the glass transition point, the forming belt Aa is rotated as the rotating roller C rotates. While rotating and traveling, change the distance between the axes of rotating rollers C and C from D ₁ to D ₂
The molded belt Aa is stretched in the circumferential direction by spreading it out. By stretching the formed belt Aa, the thinner recess 2 is stretched, the length La of the recess 2 is changed to the length L ₁ of the recess 1 of the timing belt A, and the thickness Ta is reduced to the desired thickness. A thin part 3 with a thickness T ₁ is formed, but the convex part 2 has a thickness T ₂
is larger than the thickness Ta of the recess 1a, so it is not stretched and the length L ₂ of the protrusion 2 of the timing belt A is
The thickness is maintained at _T2 . Next, the rotating rollers C and C are heated at a temperature of 100°C or higher and approximately 10°C lower than the melting point while maintaining the distance D ₂ between the axes as is or reducing the distance D ₂ between the axes by approximately 50% or less. The timing belt A is heat-set for 2 minutes or more, and as a result of this heat-setting, the timing belt A no longer stretches in the circumferential direction. The magnification at which the concave portion of the formed belt is stretched is 1.2 times or more, preferably 3 to 10 times, and the stretching magnification is
If it is less than 1.2 times, molecular orientation in the thin portion will not be sufficient, resulting in low strength and elongation cannot be eliminated by heat setting. And the length La and thickness Ta of the recessed part of the above molded belt
is set by the stretching ratio. The molded belt shown in FIG. 2 above has uneven parts formed on the outer peripheral surface, but as shown in FIG. Either one of them may be turned over and stretched so that the uneven portion becomes the outer peripheral surface. However, the above-mentioned rotating rollers C and C with the uneven parts 1a and 2 as the inner peripheral surfaces
When stretching is carried out over a period of time, it is inevitable that the convex portions will be slightly compressed and deformed. Since the molded belt in the above manufacturing method is molded by ordinary injection molding, its shape has good precision and is easily manufactured. However, the production of a molded belt is not limited to the above method; for example, after extrusion molding into a cylinder having the same cross-sectional shape as shown in FIGS. 2 and 4, this cylinder is cut into rounds to a desired width. It may be a method. In addition, in order to stretch and heat-set the above-mentioned formed belt, a cylinder made of a combination of a number of small pieces with a fan-shaped cross section that expands in the diametrical direction is inserted into the inside of the above-mentioned formed belt, and the small pieces are expanded in the diametrical direction. You can read it. The timing belt according to the present invention has sufficient tensile strength as a belt because the recessed portion is stretched, and because it is heat-set, the belt does not stretch during use. Therefore, there is no need to use reinforcing cords that are embedded in conventional timing belts. Molded products such as films made of thermoplastic synthetic resin and stretched in a uniaxial direction have the property of tearing in the direction of stretching, but the thin portions of the timing belt of the present invention alternate with convex portions that are not stretched. This arrangement prevents tearing in the stretching direction. Furthermore, since the timing belt of the present invention is molded from thermoplastic synthetic resin, it satisfies various properties required for a belt, such as heat resistance, aging resistance, and abrasion resistance. Furthermore, according to the present invention, there is no need for reinforcing cords in the molding material or various additives added to the rubber compound, and there is no need for the molding of the molded belt.
Since it is produced by stretching and heat setting, its production is simple. Examples of the present invention will be described below. Example Polyester ether copolymer (trade name Pelprene P150B, melting point 212℃, tensile modulus 3000Kg/
cm ² ) with 80 teeth and the dimensions shown below, this formed belt was passed around a pair of rotating rollers with a diameter of 5 cm and a distance between their axes of 5.2 cm, and at an ambient temperature of 50°C. While rotating a rotary roller at 60 rpm, the above-mentioned distance between the axes was expanded to 30 cm and stretched, and then heat-set in that state at 190° C. for 10 minutes to obtain a timing belt with the following dimensions.

[Table] The timing belt obtained as described above was passed around a pair of belt wheels, and the initial tension was 2 kg/cm.
Although it was rotated for 168 hours at a linear speed of 5 m/sec, no abrasion powder was generated and no deformation due to permanent elongation was observed.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the timing belt of the present invention hung on a belt pulley, Fig. 2 is a side view of an endless injection molded belt, and Fig. 3 is an example of a means for stretching the formed belt. FIG. 4 is a side view of another shape of the endless molded belt. A: Timing belt, Aa: Molded belt,
1, 1a: concave portion, 2: convex portion, C: rotating roller,
D ₁ , D ₂ : Distance between axes.

Claims (1)

[Scope of Claims] 1. A timing belt characterized in that the concave portions of the uneven portion formed on one side of an endless belt made of a thermoplastic synthetic resin are molecularly oriented in the circumferential direction, and the convex portions are not molecularly oriented. 2 The tensile modulus of thermoplastic synthetic resin is 500~
The timing belt according to claim 1, which has a weight of 20000 Kg/cm ² . 3. A molded belt made of thermoplastic synthetic resin and injection molded into an annular shape with uneven portions on one side is passed around a pair of rotating rolls, and then the molded belt is made by increasing the distance between the axes of the rotating rolls. A method for manufacturing a timing belt, which comprises stretching only the concave portion of the belt in the circumferential direction and then heat-setting the belt. 4. The method for manufacturing a timing belt according to claim 3, wherein the formed belt is passed around a pair of rotating rolls with the uneven portions as the outer peripheral surface.