JPH08312757A - Worm wheel made of resin and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a worm wheel made of resin to be suitable for mass production, shorten a mold cycle, provide a thread part with high shape precision, prevent lowering of strength due to the increase of temperature, have high rigidity and excellent slide properties and reduce a cost. CONSTITUTION: A work 10 made of resin is a worm wheel made of resin molded through injection molding method to manufacture an injection molded product having a hollow structure part in such a way that after molten resin is injected in a cavity by using an injection molding device having a mold in which a cavity is formed, pressure fluid is injected in molten resin in the cavity. A helical thread part 14 is formed in an outer peripheral part, a hollow structure part 16 is provided, and a reinforcing member 18 is formed at the interior.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin worm used as a drive part and a method for manufacturing the same.

[0002]

2. Description of the Related Art A worm gear is a worm (cylindrical worm gear), which is a cylindrical or drum-shaped screw gear having one or a plurality of threads, and a staggered shaft having a tooth surface meshing with the worm. It is composed of a worm wheel, which is a gear used for meshing, and is widely used in speed reducers because it has a relatively small size and a large reduction ratio, and it is quiet.

In recent years, with the development of synthetic resins having improved durability and the like, their uses have been diversified. One of the application examples thereof is a resin worm or a resin worm wheel. That is, when the required performance such as a small driving torque is low, a resin worm or a resin worm wheel is being actively used because of its productivity and other advantages. Usually, the resin worm is manufactured by cutting a resin round bar or by injection molding.

[0004]

However, there is a problem that mass productivity is difficult in cutting. On the other hand, in the injection molding method suitable for mass production, it takes a long time to cool and solidify the molten resin in the thick thread portion,
The molding cycle takes a long time, which is a major problem in cost reduction, and there is also a problem that volumetric shrinkage due to cooling and solidification of the resin and a decrease in shape accuracy of the screw thread portion are likely to occur due to sink marks.

Further, since the resin worm has a limitation such as a small driving torque and has a problem such as a decrease in elastic modulus due to temperature rise which is a fate of the synthetic resin, its application range is narrow. I also have problems.

Generally, in order to increase the rigidity of the synthetic resin and the elastic modulus when the temperature rises, a reinforcing filler such as glass fiber is added to the synthetic resin. However, the worm is
Since the speed is reduced and the power is transmitted while meshing with the worm wheel, the mesh surface of the worm with the worm wheel is constantly sliding. Therefore, it is often not preferable to add the reinforcing filler to the synthetic resin because of fear of abrasion of the thread portion due to abrasion.

Therefore, the object of the present invention is to be suitable for mass production, have a short molding cycle, have a high shape accuracy in the screw thread portion, have no strength reduction due to temperature rise, have high rigidity, and Inexpensive resin worm with excellent slidability,
And a method for manufacturing the same.

[0008]

The above object is to use an injection molding apparatus provided with a mold provided with a cavity,
It is a resin worm molded by the injection molding method to manufacture an injection molded product having a hollow structure by injecting a pressurized fluid into the molten resin inside the cavity after injecting the molten resin into the cavity. It is possible to achieve by the resin worm of the present invention, which has a spiral thread portion on the outer peripheral portion, a hollow structure portion, and a reinforcing member inside.

Further, the above object is a method for producing a resin worm having a hollow structure portion by using an injection molding apparatus provided with a mold provided with a cavity, in which a reinforcing member is arranged in the cavity. After that, while injecting the molten resin into the cavity, or after injecting it, a pressurized fluid is injected into the molten resin inside the cavity, thus having a spiral screw thread portion on the outer peripheral portion and having a hollow structure. This can be achieved by the method for producing a resin worm of the present invention, which is characterized by molding a resin worm having a portion and having a reinforcing member inside.

In the present invention, having a reinforcing member inside means that the reinforcing member is surrounded by the resin forming the resin worm, and that a part of the reinforcing member is surrounded by the resin forming the resin worm. And other parts are exposed to the hollow structure.

The amount of molten resin injected into the cavity is
The amount may be the amount that completely fills the cavity, but the amount that completely fills the cavity is preferable.
The injection timing of the pressurized fluid into the molten resin is after the molten resin has been introduced into the cavity in a considerable amount, at the same time as or after the introduction of the molten resin into the cavity is completed. The resin injection part for injecting the molten resin into the cavity and the pressurized fluid injection part for injecting the pressurized fluid into the molten resin may be provided at the same part of the mold or at different positions. Good. The number of resin injection parts and the number of pressurized fluid injection parts may each be one or more.

There is no particular limitation on the material of the resin worm of the present invention or the reinforcing member in the manufacturing method thereof, and it may be made of metal (including alloy) or synthetic resin. When the reinforcing member is made of metal, examples of such metal include spring steel. When the reinforcing member is made of synthetic resin,
Such a synthetic resin may be appropriately selected from a thermoplastic resin, a thermoplastic elastomer, an alloy of these resins, or a thermosetting resin. Above all, it is desirable to use engineering plastics, for example, crystalline resins such as polyacetal resins, nylon-based resins, polybutylene terephthalate resins, and amorphous resins such as polycarbonate resins and modified PPE resins, and resin worms are required to have high rigidity. In such a case, it is preferable to use a rigidity-improving grade in which these resins are filled with a reinforcing filler. When molding the reinforcing member from a thermoplastic resin, it is necessary to pay attention to the melting point. That is, when molding a resin worm, if a resin having a melting point higher than that of the thermoplastic resin forming the reinforcing member placed (inserted) in the cavity of the mold is injected into the cavity, the reinforcing member will melt. The shape may not be retained. Therefore,
The reinforcing member is preferably made of synthetic resin having a melting point higher than that of the resin forming the worm.
If the reinforcing member is made of synthetic resin, there are advantages that mass productivity is excellent, weight reduction can be achieved, and a desired elastic modulus is easily obtained.

The shape of the reinforcing member can be arranged (inserted) in the cavity, and does not prevent formation of the hollow structure inside the molten resin during injection of the molten resin and injection of the pressurized fluid. There is no particular limitation as long as it has a shape.
A preferable shape is a spiral shape or a cylindrical shape provided with a through hole.

There is no particular limitation on the synthetic resin that can be applied to the resin worm of the present invention or the method for producing the same, and injection-moldable synthetic resins, more specifically, thermoplastic resins, thermoplastic elastomers, alloys of these resins, and It may be appropriately selected from thermosetting resins. Among them, engineering plastics, for example, crystalline resins such as polyacetal resins, nylon resins, polybutylene terephthalate resins, and amorphous resins such as polycarbonate resins and modified PPE resins can be used.

In molding the resin worm of the present invention, the amount, temperature, pressure or injection speed of the molten resin during injection molding, the amount of pressurized fluid to be injected, the pressure or speed,
Various conditions such as mold temperature and cooling time must be appropriately selected and controlled depending on the type of resin used, the shape of the mold, etc. and cannot be uniquely determined.

As the pressurized fluid to be injected, substances such as nitrogen gas, carbon dioxide gas, air and helium gas which are gaseous at room temperature and liquids such as water can be used, but gas liquefied under high pressure may also be included.

[0017]

Since the resin worm of the present invention is manufactured by the injection molding method, it is suitable for mass production and the manufacturing cost can be reduced. Further, since the pressurized fluid is injected into the molten resin in the cavity, the time required for cooling and solidifying the resin can be shortened and the molding cycle can be shortened.
Moreover, while the resin in the cavity is cooled and solidified, the pressurized fluid injected into the resin continues to press the resin toward the mold surface of the cavity. As a result, it is possible to effectively prevent sink marks and volume shrinkage from occurring particularly in the thick thread portion of the resin worm, and it is possible to form the thread portion having high shape accuracy. Further, since the resin worm of the present invention has the hollow structure portion, the weight can be reduced.

Moreover, since the resin worm of the present invention has the reinforcing member, it has high rigidity. Furthermore, since the resin worm that meshes with the worm wheel does not contain a reinforcing filler such as glass fiber, it has excellent slidability.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The resin worm of the present invention and the method for producing the same will be described below with reference to the accompanying drawings.

Example 1 FIG. 1A shows a schematic sectional view of a resin worm of Example 1. A spiral screw thread portion 14 is formed on the outer peripheral portion of the shaft portion 12 of the resin worm 10. In addition, the shaft portion 12 of the resin worm 10
A hollow structure portion 16 is formed in the. Further, the shaft portion 12
Is provided with a reinforcing member 18. A schematic front view of the reinforcing member 18 in Example 1 is shown in FIG.
A schematic sectional view is shown in FIG. Note that FIG. 1C is a schematic cross-sectional view taken along the line CC of FIG. 1B. The shape of the reinforcing member 18 in the first embodiment is
It has a cylindrical shape provided with a plurality of through holes 18A. FIG.
The resin worm 10 of the present invention that constitutes the speed reducer used in Examples and Comparative Examples, and the resin worm 1
A worm gear including a gear (worm wheel) 20 meshing with 0 is schematically shown.

The resin used for molding the resin worm 10 of Example 1 was a polyacetal resin (manufactured by Mitsubishi Engineering Plastics Co., Ltd., trade name: Iupital F1).
0, natural color, melting point: 165 ° C). The material of the reinforcing member 18 used in Example 1 is polyamide MXD.
6 resin (manufactured by Mitsubishi Engineering Plastics Co., Ltd., trade name: Lenny 1022F, glass fiber 50% reinforced grade, natural color, melting point: 243 ° C).

The preformed reinforcing member 18 is attached to the mold 30.
After being placed in the cavity 32 provided in the mold, the mold is closed. This state is shown in the schematic sectional view of FIG. The arrangement of the reinforcing member 18 in the cavity 32 is
It can be performed by attaching to a holder 34 made of a metal rod arranged in the mold 30.

On the other hand, the resin composed of the above polyacetal resin was previously plasticized and melted at a resin temperature of 200 ° C. in a cylinder (not shown) of an ordinary injection molding apparatus. Then, the molten resin 40 was injected from the cylinder into the cavity 32 through the gate portion 36 which is a resin injection portion. The amount of the injected molten resin 40 was set so as not to completely fill the cavity 32. Immediately after the injection of the molten resin 40 is completed, a pressurized fluid composed of compressed nitrogen gas is
It was injected into the molten resin 40 in the cavity 32 via the pressurized fluid injection part 38. This causes the cavity 32
The hollow structure portion 16 was formed in the molten resin 40 inside. This state is shown in a schematic cross-sectional view in FIG.

While maintaining the pressure of the pressurized fluid at a predetermined value, the resin in the cavity 32 is cooled and solidified for a predetermined cooling time, and then the pressurized fluid in the hollow structure portion 16 is injected. It was opened to the atmosphere through the portion 38, and then the mold was opened, and the resin worm as a molded product was taken out from the mold 30. Thus, the resin worm shown in FIG. 1 (A) could be molded.

(Embodiment 2) In Embodiment 2, the reinforcing member 18 is made of metal and has a spiral shape. Specifically, a coil spring made of spring steel was used as the reinforcing member. The resin used for molding the resin worm 10 was the same as in Example 1. Furthermore, a resin worm was molded under the same conditions and method as in Example 1. A schematic sectional view of the obtained resin worm is shown in FIG.

(Comparative Example) A resin worm having no reinforcing member was molded. The resin used for molding such a resin worm was the same as in Example 1. And Example 1
A resin worm was molded under the same conditions and method as in.

The resin worms obtained in Examples 1 and 2 and the comparative example were incorporated into a speed reducer using the worm gear shown in FIG. 3, an endurance test was conducted, and the resin worms after the test were tested. The appearance was inspected. The test conditions were as follows. The test results are shown in Table 1 below. Shaft torque: 50kg ・ cm Temperature inside speed reducer: 80 ° C Operating time: 6000 hours Lubricant: Grease application

[0028]

[Table 1] Material test result of reinforcing member Example 1 Polyamide MXD6 No abnormality Example 2 Metal No abnormality No Comparative Example No reinforcing member Twist occurred in worm

As a result of the durability test, no abnormality was found in the resin worms of Examples 1 and 2. On the other hand, since the resin worm of the comparative example lacks rigidity,
There was a twist.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to these embodiments. The injection molding conditions and the materials used in the examples are mere examples and can be changed as appropriate. In the embodiment, the shaft portion 12 has a cylindrical shape exclusively, but may have a drum shape. The number and pitch of the teeth of the screw thread portion can be appropriately changed according to design specifications. In the molding of the resin worm in the embodiment, the pressurized fluid was injected into the molten resin from the direction parallel to the axis of the shaft portion 12. However, the pressurized fluid was injected from the direction perpendicular to the axis of the shaft portion 12 and at the end of the shaft portion 12. The pressurized fluid may be injected into the molten resin from a position slightly apart from the part. The reinforcing member 18 may be embedded in the shaft portion 12, or even if a part of the reinforcing member 18 is exposed in the hollow structure portion 16, there is no problem in terms of characteristics.

In some cases, the hollow member is formed in the resin worm by injecting the molten resin into the cavity and injecting the pressurized fluid into the molten resin without disposing the reinforcing member in the cavity. After that, the resin worm can be manufactured by releasing the resin worm from the mold and then inserting the reinforcing member into the hollow structure portion. Alternatively, in some cases, a core for forming a hollow structure is arranged in the cavity of the mold, and molten resin is injected between the core and the mold surface of the cavity.
In this way, after forming the hollow structure part in the resin worm,
It can also be manufactured by releasing the resin worm from the mold and then inserting a reinforcing member into the hollow structure portion. In this case, by providing a spiral convex portion or a linear convex portion on the surface of the core, a spiral concave portion or a linear concave portion is formed on the inner surface of the hollow structure portion of the resin worm. It If the convex portion that engages with the concave portion is formed on the surface of the reinforcing member, the reinforcing member can be reliably engaged with the hollow structure portion of the resin worm. Incidentally, the method for producing a resin worm of the present invention can be applied to the molding of a hollow pipe-shaped molded product, whereby
The strength of the hollow pipe-shaped molded product can be improved.

[0032]

The resin worm of the present invention is suitable for mass productivity, can shorten the molding cycle, and can reduce the manufacturing cost. Further, while the resin in the cavity cools and solidifies, the pressurized fluid injected into the resin continues to press the resin toward the mold surface of the cavity,
In particular, it is possible to effectively suppress the occurrence of sink marks in the thick thread portion of the resin worm, and it is possible to form the thread portion having high shape accuracy. Moreover, since the resin worm of the present invention has the reinforcing member, it has a high rigidity, and since the worm in the portion that meshes with the worm wheel does not contain a reinforcing filler such as glass fiber, it does not slide. A resin worm having excellent durability and durability can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a resin worm of Example 1,
Moreover, it is a schematic front view and a cross-sectional view of the reinforcing member.

FIG. 2 is a schematic cross-sectional view of a resin worm of Example 2.

FIG. 3 is a schematic configuration diagram of a worm gear used for evaluation.

FIG. 4 is a schematic cross-sectional view of a mold or the like for explaining the method of manufacturing the resin worm of Example 1.

[Explanation of symbols]

 10 Worm 12 Worm Shaft Part 14 Screw Thread Part 16 Hollow Structure Part 18 Reinforcing Member 18A Through Hole 20 Worm Wheel 30 Mold 32 Cavity 34 Retainer 36 Gate Part 38 Pressurized Fluid Injection Part 40 Molten Resin

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akinasa Kaneishi 5-6-2 Higashi-Hachiman, Hiratsuka-shi, Kanagawa Sanryo Engineering Plastics Co., Ltd. Technical Center (72) Toshiaki Izumida 5 Higashi-Hachiman, Hiratsuka-shi, Kanagawa 6-2, Sanryo Engineering Plastics Co., Ltd. Technical Center

Claims (6)

[Claims] 1. A hollow structure is provided by injecting a molten resin into a cavity using an injection molding apparatus equipped with a mold having a cavity and then injecting a pressurized fluid into the molten resin in the cavity. A resin worm molded by an injection molding method for producing an injection-molded article having a structure part, having a spiral thread part on the outer peripheral part, having a hollow structure part, and
A resin worm having a reinforcing member inside. 2. The resin worm according to claim 1, wherein the reinforcing member is made of metal or synthetic resin. 3. The resin worm according to claim 1, wherein the reinforcing member is made of a synthetic resin having a melting point higher than that of the resin forming the worm. 4. The resin worm according to any one of claims 1 to 3, wherein the reinforcing member has a spiral shape. 5. The resin worm according to claim 1, wherein the reinforcing member has a cylindrical shape provided with a through hole. 6. A method for producing a resin worm having a hollow structure part, which uses an injection molding device equipped with a mold having a cavity, wherein a reinforcing member is placed in the cavity and then the worm is placed in the cavity. While or after injecting the molten resin, a pressurized fluid is injected into the inside of the molten resin in the cavity, thereby having a spiral thread portion on the outer peripheral portion and a hollow structure portion, A method for producing a resin worm, which comprises molding a resin worm having a reinforcing member inside.