JPH06182821A - Gear made of thermoplastic resin - Google Patents

Abstract

PURPOSE:To obtain a gear excellent in dimensional accuracy within a short period by providing a hollow structure to the entire peripheries or a part of the root parts of the teeth of a gear made of a thermoplastic resin. CONSTITUTION:Hollow parts 6 are provided to the entire peripheries or a part of the root parts of teeth by introducing gas into the root parts 3 of teeth by a gas assist molding method. The gas assist molding method is a molding method injecting a thermoplastic resin into a mold cavity in injection molding and subsequently injecting gas in the resin to obtain a hollow molded product. The gas assist molding method is performed by the combination of an injection molding machine and a gas injection device. The root parts 3 of the teeth are parts having the same thickness as the tooth width present between the web part 4 usually applied in a gear made of a thermoplastic resin and a tooth bottom circle 2. By this constitution, the shape error due to the shrinkage of tooth parts is suppressed and the gear having excellent accuracy is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear by a gas assist molding method, and more particularly to a gear made of a thermoplastic resin having excellent dimensional accuracy.

[0002]

Gears are widely used as mechanical parts in various fields such as automobiles, general machines, precision machines, and electric / electronic fields. Further, in recent years, the use of gears made of thermoplastic resin has been expanding more and more because of its good moldability, light weight, and rust-free property. Further, with the recent increase in technology in each field, the demand for dimensional accuracy of the parts has become more sophisticated, and it is a technical subject to meet this demand.

[0003] However, when injection molding is performed, the thermoplastic resin largely contracts when it is solidified from the molten state in the mold, so that a molded product cannot be obtained according to the size of the mold, and the product is manufactured accurately. Very hard to get. Therefore, conventionally,
Various improvements have been made in terms of molding conditions, resin characteristics, mold design, etc. For example, a mold design is designed in consideration of mold shrinkage, and the mold is designed mainly using the following three methods.

(1) The cavity module is made the same as the product, and molding shrinkage is expected by the pressure angle and the dislocation coefficient. (2) The cavity pressure angle is the same as the product, and the module is expected to shrink. (3) Expect molding shrinkage in both module and pressure angle.

With such a mold design, it has become possible to obtain a certain degree of accuracy.

[0006]

However, none of the above methods (1), (2) and (3) takes into consideration the deviation of the involute tooth profile itself due to contraction and the contraction in the tooth streak direction, and it is more advanced. It was necessary to correct the mold by trial and error when high dimensional accuracy was required. For this reason, a lot of labor and time are required for development and manufacturing, so that it is very difficult to obtain an accurate gear in a short period of time.

As described above, the conventional injection molding method has a problem that the error of the gear becomes large because the shrinkage of the thermoplastic resin when it solidifies is large.

[0008]

As a result of intensive studies conducted by the present inventors to solve the above problems, a thermoplastic resin gear having a hollow structure at the root of the tooth solves the above problems. The inventors have found that and reached the present invention. In other words, it was found that by introducing gas into the root of the tooth by using the gas assisted molding method, it is possible to suppress the shape error due to the contraction of the tooth and to obtain a highly accurate gear.

That is, the present invention is a thermoplastic resin gear having a hollow portion 6 at the entire circumference or a part of the tooth root portion 3. The present invention will be described below. The gas-assisted molding method 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 body into the resin in injection molding.

The gas-assisted 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 injecting the resin 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 method of introducing the gas into the nozzle of the cylinder, the sprue of the mold, the runner, and the product portion can be considered directly, but any method can be used as long as a high-pressure gas can be injected into the resin.

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, polyacetal resin (hereinafter referred to as POM
And a polyamide resin (hereinafter abbreviated as PA) have high heat resistance, excellent mechanical properties, and excellent sliding characteristics, and thus are often used as resins for gears.
It is also preferably used in the present invention.

In the present invention, since the root of the tooth has a hollow portion, an inorganic and / or organic filler may be added to the thermoplastic resin, if necessary, for the purpose of improving heat resistance, mechanical strength and the like. Can be done. 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,
Reinforcement of ferrite, calcium silicate, calcium carbonate, magnesium carbonate, dolomite, zinc oxide, titanium oxide, magnesium oxide, iron oxide, molybdenum disulfide, graphite, gypsum, glass beads, glass powder, glass balloon, quartz, quartz glass, etc. Fillers may be mentioned, which may be hollow. Further, two or more kinds of these reinforcing fillers can be used in combination, and if necessary, they can be pretreated with a coupling agent such as a silane type or titanium type and used.

Examples of the gas body used in the present invention include inert gases such as nitrogen, helium, neon and argon, 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 root portion 3 of the tooth in the present invention has the same thickness as the tooth width between the web portion 4 (thinned portion) and the root circle 2 formed in a normal thermoplastic resin gear. Part (see FIGS. 1-2). Further, in the present invention, the gas is introduced to the entire circumference or a part of the root portion 3 of the tooth and the hollow portion 6 is provided to suppress the shrinkage of the resin. In the gas assist molding method, a gas body is supplied into the resin to compensate for the shrinkage of the resin,
Furthermore, since the resin can be effectively adhered to the mold, it is expected that the dimensional accuracy will be improved. Even with a normal injection molding method, the shrinkage of the resin can be compensated by applying a holding pressure, but since the resin is solidified at the gate portion after the gate sealing, the pressure cannot be transmitted. However, in the gas-assisted molding method, it is considered that good results can be obtained because pressure is applied to the inside of the cavity by the gas body even after the gate sealing. Further, it is difficult to reduce the tooth error by simply introducing the gas into an arbitrary part.

In the present invention, the tooth 5 such as the tooth root portion 3 is used.
It is conceivable that the contraction of the tooth portion including the tooth 5 could be effectively suppressed by passing the gas through the portion close to. Therefore, it is preferable to provide the hollow portion 6 in the root portion 3 of the tooth in a range as close to the entire circumference as possible. INDUSTRIAL APPLICABILITY The present invention is particularly effective for large-width gears having large influence of shrinkage, and large-module gears such as module 2 or more.

The gear according to the present invention has good dimensional accuracy, and is useful as a mechanical component in various fields such as automobiles, general machines, precision machines, and electric / electronics.

[0017]

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.

[0018]

Examples 1 and 2 A module 1 having 60 teeth, a tooth tip diameter of 62 mm, a tooth width of 6 mm, a standard pressure angle of 20 °, and a web thickness of 1.5 mm was used as an involute gear (flat tooth) mold. 2A and 2B are cross-sectional views of the product form using this mold. There was only one gate, which was provided at the base of the tooth.

Polyacetal resin and polyamide resin are used as the thermoplastic resin, the mold temperature is 80 ° C., the set temperature of the cylinder is 200 ° C., respectively.
Gas-assisted molding was performed at 290 ° C. In addition, the measured value of the resin was a value that gives a short shot. In the gas-assisted molding method, it is also possible to use a measured value of a full shot and introduce the gas only in the resin contraction amount. However, since the resin gear is a relatively small molded product, the entire shrinkage volume is small, and if a full shot measurement value is used, the injected gas body may not pass through the gate. For this reason, the short shot weights were used this time.

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. 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 the accumulator, and after injection of the resin, it was injected into the resin through a pipe. The gas body was introduced from the nozzle through the sprue and runner into the cavity of the gear. The conditions at this time were: gas injection delay time (time from injection of resin to injection of gas) 0.5 seconds, gas injection time (time to inject gas) 40 seconds, pressure holding time (stop gas injection) The time of holding the gas system in the closed state and the time of adding the gas pressure) was set to 50 seconds. Mold opening was performed 10 seconds after the pressure holding time was completed, and the molded product was taken out.

Molded articles having a hollow structure were obtained by the above methods. One of the embodiments of the hollow portion is shown in FIG.
It is shown in (B). For the accuracy measurement of the obtained gear, the tooth profile error and the tooth trace direction error of JIS gear accuracy standard (JIS 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 results obtained are shown in Table 1.
It was shown to.

[0022]

[Comparative Examples 1 and 2] Using the molds of Examples 1 and 2, ordinary injection molding such as resin injection, resin pressure holding, and cooling was performed without injecting a gas. Cylinder set temperature, mold temperature, etc. are the same as those in Examples 1 and 2, the holding pressure is 500 kg / cm ² ,
The pressure holding time was 15 seconds and the cooling time was 50 seconds.

The results obtained are shown in Table 1.

[0024]

[Table 1]

[0025]

As shown in Table 1, the gear according to the present invention has a shape closer to the mold because the resin shrinkage is suppressed.
It can be seen that the error is small as an involute gear.
As described above, since the gear of the present invention has good dimensional accuracy with little error, it accurately moves as a mechanical component and is very useful industrially.

[Brief description of drawings]

FIG. 1 (A) is one of the cross-sectional views of the hollow-molded gears obtained in Examples 1 and 2, in which a tooth mold is partially omitted. FIG. 1B is one of cross-sectional views in the tooth width direction of the hollow-molded gears obtained in Examples 1 and 2.

FIG. 2 (A) is a cross-sectional view of a gear obtained by a mold used in Examples, in which a tooth profile is partially omitted.
FIG. 2B is one of cross-sectional views in the tooth width direction of the gear obtained by the mold used in the example.

[Explanation of symbols]

 1 Tip circle 2 Bottom circle 3 Base of tooth 4 Web part 5 Tooth 6 Hollow part

Claims (1)

[Claims] 1. A thermoplastic resin gear having a hollow portion 6 on the entire circumference or a part of the root portion 3 of the tooth.