JPH0343503B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to gears manufactured by injection molding using composite plastics, and in particular to manufacturing gears for small precision measuring instruments using high-strength composite plastics reinforced with two types of reinforcing fibers: fine reinforcing fibers and relatively large-sized reinforcing fibers. Regarding the method. Recently, plastics have been widely used as industrial materials for functional parts, structural parts, etc. that are subject to loads. Plastics used in such areas are generally referred to as engineering plastics, and are distinguished from plastics used in relatively light-duty applications, so-called general-purpose plastics. However, even engineering plastics alone are far inferior to metal materials in terms of mechanical strength, thermal properties, dimensional accuracy, etc., and for this reason, they are only used for parts with relatively large dimensions and small loads. Ta.
Therefore, in order to improve the properties of engineering plastics, composite technology using reinforcing materials, especially short fibers, was investigated. Due to these advances in materials, plastics have a greater degree of freedom in product design, can be easily molded, almost no post-finishing is required, and can be assembled into one piece, while still taking advantage of the advantages of plastics. Composite plastics are being used increasingly in the field of high-load precision mechanical parts, which have been difficult to use. Therefore, the object of the present invention is to manufacture a gear for a small precision measuring instrument that enables a gear for a small precision measuring instrument to be used in, for example, a portable watch, etc., which has high dimensional accuracy, strength suitable for occasions, and excellent long-term durability. It's about providing a method. The manufacturing method of the gear for small precision measuring instruments of the present invention has a tooth thickness of 0.1 to 1.0 mm, a tooth width of 0.05 to 0.4 mm, and a pitch circle diameter of 0.4 to 0.4 mm.
5mm, module 0.05~0.5mm, gear shaft diameter 0.1~0.5
mm gear is made of a composite plastic material made of a thermoplastic resin with two types of reinforcing fibers: potassium titanate single crystal fibers and carbon fibers whose average fiber length is longer than the average fiber length of the potassium titanate single crystal fibers. It is characterized by being molded using an injection molding method. The present invention will be explained below using a wristwatch gear as an example. Watch gears have dimensional accuracy, mechanical strength,
One of the most demanding fields in terms of long-term durability
It is one. Regarding dimensional accuracy, the tolerance is 1/100mm
At least the base is required, and the gear dimension is the tooth thickness.
0.1mm to 1.0mm, tooth width 0.05mm to 0.4mm, pitch circle diameter 0.4
mm~5mm, module 0.05~0.5, gear shaft diameter 0.1mm
Very small at ~0.5mm. Processing such minute gears using plastic injection molding has become possible through the development of advanced injection molding technology and ultra-precision mold processing technology. On the other hand, in terms of mechanical strength, wristwatch gears are driven with low torque, but because their absolute dimensions are small, the stress per unit area is extremely large. In particular, the load when adjusting the needle is large, and the bending strength
15Kg/mm3 or ^more is required. The present inventor used the third wheel having the shape shown in FIG. 1 as the above-mentioned wristwatch gear to measure the moldability and strength of various composite plastics. As a result, it was found that the size of the reinforcing fibers greatly influences the formability and strength reinforcement efficiency of small precision gears such as gears for wristwatches. Based on this, the present inventor had previously applied for a patent to discover the optimal size of reinforcing fibers when applying composite plastic to small precision gears, but upon further progressing this research, By using a combination of two types of reinforcing fibers with different fiber sizes, the present invention was completed by further improving molding accuracy and strength, and improving long-term wear resistance. To explain the present invention in detail, the size of the third wheel in Fig. 1 used for material evaluation is that the thickness of the gear 2 is 0.12 mm, the pitch circle diameter is 3.5 mm, the module is 0.058,
Thickness of pinion 3 0.4mm, pitch circle diameter 0.50mm, module 0.63, shaft diameter of gear shafts 1 and 4 0.2mm, shaft length
It is 2.5mm. Gate 5 when molding this third wheel by injection molding is a pinpoint gate with a diameter of 0.25 mm. After forming a third wheel of such a size from various composite plastics, the strength was measured using the method shown in FIG. That is, the destructive bending strength of the teeth 6 of the pinion 3 of the third wheel is determined by fixing the pinion 3, rotating the metal gear 7, and measuring the rotational torque when the tooth 6 of the pinion 3 breaks using a U-gauge. It was calculated by measuring. In addition to the bending strength of the teeth, the bending strength of the gear shafts 1 and 4 shown in FIG. 1 was tested using the method shown in FIG. 3. That is, the third wheel was installed on the fixed base 8, and the load P was applied to the third wheel while increasing at a constant speed, and the bending strength was determined from the load P when the gear shaft 1 or 4 broke. The relationship between the type of reinforcing fiber and the relative fracture bending strength of the teeth 6 is shown in FIG. The materials used here are polyacetal (copolymer type) as plastic, potassium titanate single crystal fiber A with an average fiber diameter of 0.2 μm and average fiber length of 30 μm as reinforcing fibers, and carbon fiber B with an average fiber diameter of 8 μm and average fiber length of 400 μm. and average fiber diameter 10μm, average fiber length
Each contains 30wt% of 400μm glass fiber C. As shown in FIG. 4, when looking at the relative strength to the bending strength determined by the ASTM method, the bending strength decreases as the fiber size increases. On the other hand, FIG. 5 shows the relative bending strength of gears 1 and 4 using similar materials. The bending fractures in this test were all near the roots of gear shaft 1 and gear 2. As shown in FIG. 5, with respect to gear shafts, there is not as much difference in strength depending on fiber size as there is with teeth, and carbon fibers have the highest efficiency. According to the bending strength measurement method, the direction of the bending stress on the teeth 6 is parallel to the orientation direction of the reinforcing fibers, and the direction of the bending stress on the gear shafts 1 and 4 appears to be perpendicular to the fiber orientation direction. From this, the results shown in FIGS. 4 and 5 indicate that the potassium titanate single crystal fibers are relatively uniformly dispersed and are not strongly oriented. This is a desirable characteristic for molding small precision parts. Further, although carbon fibers have insufficient dispersibility into small parts such as the teeth 6, they have an excellent reinforcing effect on gear shafts. On the other hand, glass fiber has poor filling and dispersion properties due to its large fiber size, making it unsuitable for small precision parts. Carbon fiber also shows the best properties in terms of wear resistance and lubricity.
Suitable for sliding parts such as gear shafts. From the above results, the present inventor has come to the conclusion that the combined use of potassium titanate fibers and carbon fibers is appropriate as reinforcing fibers for composite plastics for small precision gears. In addition to polyacetal, the plastics used include nylon 6, 6, nylon 6, 12, nylon metaxylene diamine 6, nylon 11, and nylon.
12 Engineering plastics such as polyamide, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, modified polyphenylene oxide polyarylate, polysulfon, polyether sulfon, polyphenylene sulfide, polyoxybenzylene, etc.
It can be used singly or as a mixture of general-purpose plastics such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, ABS, and acrylic resin. EXAMPLES The present invention will be explained in detail with reference to Examples below. Examples 1 to 5, Comparative Examples 1 to 5 The third wheel, which is a wristwatch gear shown in FIG. 1, was molded from various composite plastics, and its moldability and strength were measured. At the same time, a test piece for bending strength test specified in ASTM D790-66 was molded and the strength was measured. Wt% of reinforcing agent of plastic material, potassium titanate single crystal fiber, carbon fiber and glass fiber of each test piece of Examples 1 to 5 and Comparative Examples 1 to 5 and tooth bending strength of each example and each comparative example, The first measurement result of gear shaft bending strength and ASTM bending strength
Shown in the table. In Examples 1 and 5, each of which contains potassium titanate single crystal fiber and carbon fiber as reinforcing agents at 20 wt% or more, each of the teeth, gear shaft, and ASTM bending strength is 20.
Kg/m ³ or more, ensuring excellent mechanical strength. Furthermore, Comparative Examples 1 to 3, in which the reinforcing agent is either potassium titanate single crystal fiber or carbon fiber, are inferior in either of the bending strengths, and Comparative Example 4, in which glass fiber is used as the reinforcing agent, No. 5 has poor filling properties and dispersibility during injection molding and cannot be molded. As described above, the method for manufacturing a gear for a small precision measuring instrument according to the present invention has a tooth thickness of 0.1 to 1.0 mm, a tooth width of 0.05 to 0.4 mm,
Pitch circle diameter 0.4~5mm, module 0.05~0.5mm,
A gear with a gear shaft diameter of 0.1 to 0.5 mm is made of thermoplastic resin with two types of reinforcing fibers: potassium titanate single crystal fiber and carbon fiber whose average fiber length is longer than the average fiber length of the potassium titanate single crystal fiber. By injection-molding a composite plastic material with added carbon dioxide, it has become possible to manufacture gears for small precision measuring instruments made of plastic with high strength and excellent dimensional accuracy comparable to metal gears. That is, the method for manufacturing a small gear of the present invention includes 2
The potassium titanate single crystal fiber used as one of the two reinforcing materials has a short average fiber length of 30 μm, so
Small gears with excellent dimensional accuracy while maintaining high strength, suitable for forming ultra-small gears with face widths of 0.05 to 0.4 mm, pitch diameters of 0.4 to 5 mm, and modules of 0.05 to 0.5 mm. Furthermore, since the carbon fiber used for the other of the two reinforcing materials had a longer average fiber length than the average fiber length of the potassium titanate single crystal fiber, it was possible to produce a carbon fiber with higher strength. This makes it possible to provide small gears, and the synergistic effect of these two results in a small precision measuring instrument gear made of plastic that has high strength and excellent dimensional accuracy comparable to metal gears. Although only the gears for watches were described in the examples, cameras,
We believe that the present invention will also make a significant contribution to the use of plastic gears for other small precision measuring instruments such as VTRs and micro printers.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a plan view of the third wheel, which is a gear for a wristwatch, and 1 and 4 are gear shafts, 2 is a gear, 3 is a pinion, and 5 is a pinpoint gate. Figure 2 shows the third wheel in kana 3.
Enlarged view of a part of and the metal gear 7 that meshes with it
It is an enlarged view of a part of. 6 indicates the tooth of Kana 3.
FIG. 3 is a diagram showing measurement of the bending strength of the gear shafts 1 and 4 of the third wheel, where 8 is a fixed base and P is a continuously changing load. FIG. 4 shows the relationship between the type of reinforcing fiber and the relative fracture bending strength of the tooth 6 of the third wheel pinion 3 after molding. A is potassium titanate fiber, B is carbon fiber, and C is glass fiber. Figure 5 shows
Type of reinforcing fiber and third wheel gear shaft 1 after molding
The relationship between the relative fracture bending strength of No. 4 is shown.

Claims (1)

[Claims] 1 Tooth thickness 0.1~1.0mm, tooth width 0.05~0.4mm, pitch circle diameter 0.4~5mm, module 0.05~0.5mm, gear shaft diameter
A gear of 0.1 to 0.5 mm was prepared by adding two types of reinforcing fibers to a thermoplastic resin: potassium titanate single crystal fibers and carbon fibers whose average fiber length was longer than the average fiber length of the potassium titanate single crystal fibers. A method for manufacturing a gear for a small precision measuring instrument, characterized in that the gear is molded from a composite plastic material using an injection molding method.