JPH0791522A - Shaft-integrated gear made of thermoplastic resin - Google Patents

Abstract

PURPOSE:To obtain the excellent dimension accuracy, and to improve the productivity by specifying a ratio of the diameter of a root circle of a gear part to the diameter of a shaft part, and providing a hollow part inside of a shaft- integrated gear. CONSTITUTION:In a shaft-integrated gear to be used for a wide range as a mechanical part in each field of precision machine, electricity, electron or the like, a ratio of the diameter of a root circle of a gear part 2 to the diameter of a shaft part 1 is set at 1/1-5/1. This molding has a hollow part, and a hollow ratio is set in a range of 5-70%. Since this gear does not have a joint part and it can be molded by the injection at one time and a burr is hardly generated, it is molded by the hollow injection molding that gas is filled in a resin after injecting the thermoplastic resin into a mold cavity. As thermoplastic resin, polyacetal resin and polyamide resin are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear made of a thermoplastic resin, and more specifically to a shaft integral gear made of a thermoplastic resin having good dimensional accuracy and excellent productivity.

[0002]

Gears are widely used as mechanical parts in various fields such as automobiles, general machines, precision machines, and electric / electronic fields. In addition, gears made of various resins have been increasingly used in recent years because they have good formability, are lightweight, and do not rust. In many cases, a resin gear has a shaft hole at the center, and a shaft made of metal or the like is passed through the shaft hole to rotate and operate. At this time, when the rotations of the shaft and the gear are made to coincide with each other, (1) the shaft hole is formed in a shape other than a circle such as a D shape or a polygon, and the gear formed by injection molding or the like is fitted into the shaft made of metal or the like to assemble .

(2) Assembling is carried out in the same manner as (1), but the shaft hole is still circular and the shaft and the gear are fixed by screwing or the like. (3) A shaft-integrated gear shape is cut out by cutting a resin round bar or the like. The reason why such a method is used is that if the gear and the shaft are integrally molded at the same time by ordinary injection molding, the shaft portion becomes thick and the sink mark deteriorates the dimensional accuracy of the gear portion (the shaft portion is If you make it thinner, you can prevent sink marks to some extent, but the strength will decrease).

[0004]

However, in the above (1) and (2), the assembly process of the gear and the shaft is required. Further, in (3), since cutting is used, more time is required for manufacturing as compared with injection molding. As described above, the conventional method has a problem of poor productivity.

[0005]

As a result of intensive studies conducted by the present inventors in order to solve the above-mentioned problems, as a result, the ratio of the diameter of the root circle of the gear part to the diameter of the shaft part is within a certain range, and The present invention has been achieved by finding that the above problems can be solved when a hollow portion is provided inside. That is, according to the present invention, the ratio of the diameter of the tooth bottom circle 7 of the gear portion 2 to the diameter of the shaft portion 1 is 1/1 to 5.
/ 1, and is a shaft integrated gear made of thermoplastic resin having a hollow portion inside.

The present invention will be described in detail below. In the present invention, a shaft-integrated gear having a hollow portion is obtained, but any molding method can be used as long as it is a molding method that produces a hollow portion. However, the hollow portion here excludes a void (void) and a hollow portion formed by a foaming agent. As a molding method for carrying out the present invention, a hollow injection molding method is preferably used because it can be molded by a single injection without a joint portion and few burrs are generated.

The hollow injection molding method referred to in the present invention is a molding method for obtaining a hollow molded article by injecting a thermoplastic resin into a mold cavity and then injecting a gas into the resin in injection molding. The hollow injection molding method of the present invention is carried out by a combination of an ordinary injection molding machine and a gas injection device. The gas injection device is a device that injects a gas body into the resin through a pipe after the resin is injected and maintains this gas pressure for a set time. For this, the gas body to be injected is compressed to a high pressure in advance and stored in an accumulator, a method of introducing high pressure gas through a pipe at the time of gas injection, a method of continuously feeding a certain amount of gas body with a pump, and pressurizing it. Though conceivable, any method is possible as long as a gas body is sent into the resin after injection. At this time, the gas injection is performed by using the nozzle of the cylinder of the molding machine, the sprue of the mold,
A method of using a die runner or directly injecting into the product part is conceivable, but any method can be used as long as a high-pressure gas body can be injected into the resin. A representative method of the hollow injection molding method is disclosed in Japanese Patent Publication No. 57-14968.

The thermoplastic resin used in the present invention includes polyethylene, polypropylene, polystyrene and ABS.
Resin, polyvinyl chloride, polyamide, polyacetal,
Polycarbonate, modified polyphenylene ether, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyimide, polyamideimide, polyetherimide, polyarylate, polysulfone, polyethersulfone, polyetheretherketone, liquid crystal polymer, polytetrafluoroethylene, Examples include thermoplastic elastomers, but any thermoplastic resin can be used as long as ordinary injection molding is possible. In particular, the polyacetal resin and the polyamide resin have high heat resistance, are excellent in mechanical properties, and are also excellent in sliding properties, and are therefore often used as resins for gears, and are preferably used in the present invention.

Since the present invention has a hollow portion inside, an inorganic or organic filler can be blended with the thermoplastic resin, if necessary, for the purpose of improving heat resistance, mechanical strength and the like. Suitable fillers include glass fibers, carbon fibers, metal fibers, aramid fibers, potassium titanate, asbestos, silicon carbide, ceramics, silicon nitride, barium sulfate, calcium sulfate, kaolin, clay, pyrophyllite, bentonite, and seri. Site, zeolite, mica, mica, nepheline sinite, talc, attarpulgite, wollastonite, PMF, ferrite, calcium silicate, calcium carbonate, magnesium carbonate,
Reinforcing fillers such as dolomite, zinc oxide, titanium oxide, magnesium oxide, iron oxide, molybdenum disulfide, graphite, gypsum, glass beads, glass powder, glass balloons, quartz, quartz glass can be mentioned, and these are hollow. It may be. Further, these reinforcing fillers can be used in combination of two or more kinds, and if necessary, they can be used after being pretreated with a coupling agent such as a silane-based or titanium-based coupling agent.

Examples of the gas body used in the present invention include nitrogen, helium, neon, an inert gas such as argon, steam and the like, but any gas body can be used as long as it is inert to the resin. Further, when these gas bodies are used, impurities are usually contained, but if the amount of impurities is too large, the resin may be decomposed or burned during molding, which is not preferable. Nitrogen gas is more preferably used industrially in consideration of economy.

The "shaft" in the present invention means that the product rotates,
It is a part that is supported by other parts (bearing parts) so as to stabilize the rotation during operation. The shaft portion 1 is shown in FIG. By making the diameter of the shaft portion 1 thin, it is possible to prevent sink marks caused by the shrinkage of the resin at this portion to some extent. Therefore, the present invention is particularly effective when the shaft diameter is 5 mm or more.

In the present invention, it is necessary that the ratio of the diameter of the root circle 7 of the gear part 2 to the diameter of the shaft part 1 is 1/1 to 5/1. When the value of this ratio exceeds 5, the dimensional accuracy of the gear portion 2 is deteriorated, which is not preferable, and when it is less than 1, it is not practical. Preferably, the ratio of the diameter of the root circle 7 of the gear part 2 to the diameter of the shaft part 1 is 1/1 to 4/1. The molded product of the present invention is required to have a hollow portion, but the preferred hollow ratio is 5 to 70%, more preferably 10 to 60.
%. This is because when the hollow rate is high, the surface appearance is deteriorated due to hesitation marks or the like, and when the hollow rate is low, the dimensional accuracy, which is the object of the present invention, is impaired. The hollow ratio is defined by the following equation.

Hollow ratio (%) = {(V × ρ-M) / (V ×
ρ)} × 100 where V is the volume when the hollow part is filled with the same resin, ρ is the specific gravity of the resin used, and M is the mass of the hollow molded product. In the present invention, it is effective to provide an auxiliary cavity (also referred to as an auxiliary chamber or a discarding cavity) in the mold in order to increase the hollow ratio. This auxiliary cavity is a cavity for allowing the resin in the product cavity to escape when injecting a gas body.
The details are disclosed in JP-A-20.

The present invention makes it possible to integrate the shaft and the gear, but it is useful to further integrate the roller part and the pulley part at the same time, because the parts can be made more functional.

[0015]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the present invention.

[0016]

Examples 1 to 11 Various spur gears having the following gear specifications and shapes were produced, and were used as Togitsu City Examples 1 to 11. Examples of cross-sectional views of product aspects are shown in FIGS. Module: 1.0 Number of teeth: 11 to 42 Diameter of root circle 7: 8.5 to 39.5 mm Diameter of tip circle 8: 13 to 44 mm Tooth width: 20 mm Standard pressure angle: 20 ° Diameter of shaft portion 1 : 8 mm Length of shaft part 1: 20 mm on both sides of the gear, using polyacetal resin and polyamide resin as the thermoplastic resin, the mold temperature is 80 ° C., the preset temperature of the cylinder is 200 ° C., 290 ° C. Hollow injection molding was performed. Moreover, the hollow value of each Example was obtained by changing the measured value of the resin.

Nitrogen gas was used as the gas body to be injected into the resin, and the gas injection port was provided in the nozzle portion of the cylinder of the molding machine. At this time, a shut-off valve was provided on the screw side (hopper side) of the gas injection port for the purpose of preventing gas from entering the cylinder (in the direction opposite to the mold). Nitrogen gas was introduced into the gas injection device, the pressure was raised to 100 kg / cm ² and stored in an accumulator, and after the resin was injected, it was injected into the resin through a pipe. The gas body was introduced from the nozzle through the sprue, runner, and gate into the product cavity. The gate was provided at one point on the shaft on one side of the product as shown in FIGS. The condition at this time is that the gas injection delay time (the time until the gas is injected after the resin is injected) is 1.0.
Seconds, gas injection time (gas injection time) was 5 seconds, and pressure holding time (time to stop gas injection and keep the gas system closed and the time of gas injection) was 50 seconds.
Mold opening was performed 5 seconds after the pressure holding time was completed, and the molded product was taken out.

Further, in this embodiment, when the hollow ratio was 35% or more, the auxiliary cavity was used on the side opposite to the gate. Molded articles having hollow structures were obtained by the above methods. Examples of the form of the hollow portion are shown in FIGS.
JIS gear accuracy standard (JI
The tooth profile error and the tooth trace direction error of S B 1702) were used. Any error is a deviation in dimension from an ideal involute gear, and it can be said that the smaller the error value, the more accurately the gear operates. The obtained results are shown in Tables 1 and 2.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Comparative Examples 1 to 5 and 7 to 8] Using the molds used in Examples 1 to 11, without injecting a gas body, resin injection, resin pressure holding,
Normal injection molding such as cooling was performed. (Since it is a normal molding method, an auxiliary cavity was not used.) Cylinder set temperature, mold temperature, etc. were the same as in the example, the resin holding pressure was 800 kg / cm ² , the holding pressure time was 51 seconds, and the cooling time was 5 seconds. Seconds were set so that the cycle time was the same as that in the example.

The results obtained are shown in Tables 1 and 2.

[0023]

[Comparative Example 6] A spur gear having the following gear specifications and shapes was produced, but the same method as in Examples 1 to 9 was used for other conditions. A cross-sectional view of the product mode is shown in FIG. Module: 1.0 Number of teeth: 50 Diameter of root circle 7: 47.5 mm Diameter of tip circle 8: 52 mm Tooth width: 20 mm Standard pressure angle: 20 ° Diameter of shaft 1: 8 mm Length of shaft 1 Table 2 shows the results obtained by 20 mm on both sides of the gear.

[0024]

As shown in Tables 1 and 2, it can be seen that the shaft-integrated gear according to the present invention has few errors, has good dimensional accuracy, and has an excellent shape as a gear. Also,
Since the hollow injection molding method is used, molded products can be obtained in a short time,
It can be said that the gear has excellent productivity. In Comparative Examples 1 to 8, the gear part has a large error.

Since the shaft-integrated gear according to the present invention has good dimensional accuracy and excellent productivity, it is useful as a mechanical component in various fields such as automobiles, general machinery, precision machinery, electric / electronics, etc. Very useful. It is particularly useful for gear parts such as facsimiles and copiers.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a gear according to a fifth exemplary embodiment, showing a cross section passing through a shaft center.

FIG. 2 is a cross-sectional view of a gear according to a fifth exemplary embodiment, showing a cross section taken along plane AB of FIG. Part of the involute tooth profile is omitted.

FIG. 3 is a cross-sectional view of a gear according to a fifth exemplary embodiment, showing a cross section taken along the CD plane of FIG.

FIG. 4 is a cross-sectional view of a gear according to a ninth exemplary embodiment, showing a cross section passing through a shaft center.

FIG. 5 is a cross-sectional view of the gear of Comparative Example 6, showing a cross section passing through the center of the shaft.

[Explanation of symbols]

 1 Shaft part 2 Gear part 3 Tooth root 4 Tooth tip 5 Hollow part (hatched part) 6 Gate 7 Tooth root circle 8 Tooth tip circle

Claims (1)

[Claims] 1. A shaft-integrated type made of a thermoplastic resin, in which a ratio of a diameter of a root circle 7 of a gear part 2 to a diameter of a shaft part 1 is 1/1 to 5/1 and which has a hollow portion inside. gear.