Injection Molded Parts

Abstract

To provide an injection molded body that has high dimensional accuracy in shape and excellent quietness.SOLUTION: An injection molded body includes a central part, a body part and an outer peripheral part, where the body part connects the central part to the outer peripheral part. The body part includes: a gate mark generated at the time of injection molding; and a groove part that is provided while extending in a circumferential direction in a position different from the gate mark in a radial direction and has a depth that varies in the circumferential direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an injection-molded article such as a gear. [Background technology]

[0002] Plastic gears, manufactured by injection molding or insert molding and having teeth on their outer peripheries, have been known as gears used in various mechanical devices. Compared to metal gears, plastic gears have the advantages of being quieter, more wear-resistant, and more chemical-resistant. Furthermore, they are lighter than metal gears and can be mass-produced through precision molding.

[0003] In order to improve the dimensional accuracy of the shape, such as the roundness, which affects the rotation transmission accuracy, resin gears are devised to control the flow of molten resin material in the cavity.

[0004] For example, Patent Document 1 discloses a resin gear in which a circular rim on the outer periphery of a molded product is connected to a shaft portion in the center of the molded product by a disk-shaped web, and a rib is erected on the outer periphery of the web, more peripherally than a gate provided on the web, to control the flow of molten resin material.

[0005] In Patent Document 1, the volume of resin flowing into the space that defines the rib is increased, delaying the timing at which the flow of molten resin material reaches the rim on the outer periphery of the resin gear. This allows the resin to be filled evenly from the gate to the rim on the outer periphery, improving the roundness of the molded resin gear. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5443089 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the resin gear of Patent Document 1, the ribs are erected in the axial direction on the outer periphery of the web gate to adjust the flow of molten resin, which increases the overall external dimensions of the resin gear in the axial direction, which may cause interference with the mating resin gear, and therefore requires changing the external dimensions of the mating resin gear depending on the installation position of the resin gear.

[0008] Furthermore, since the ribs are formed by collecting resin in the direction of their extension, there is a problem in that the resin tends to flow in the circumferential direction, making it difficult to fill the resin uniformly with high precision in the radial direction.

[0009] In particular, when molding a plastic gear, if a weld is formed on the outer tooth portion when molten resin is filled into the outer periphery, noise is generated during rotation transmission due to the influence of rotation transmission accuracy, particularly a single pitch error.

[0010] For these reasons, there is a demand for gears that are quieter and less susceptible to single pitch errors, by filling molding materials such as resin more precisely and uniformly all the way to the outer periphery.

[0011] The present invention has been made in view of the above points, and an object of the present invention is to provide an injection molded article having high dimensional accuracy in shape and excellent quietness. [Means for solving the problem]

[0012] One embodiment of the injection molded article of the present invention is An injection molded article having a main body portion having an axial hole in the center and a rim portion provided on the outer periphery of the main body portion, One surface of the main body has a gate mark formed during injection molding, a groove portion that is provided radially outward of the gate mark and at a position different from the gate mark, extending in a circumferential direction, and has a deepest portion and a shallowest portion with different depths in the circumferential direction, The rim portion extends from the outer periphery toward the other surface of the main body. only The structure is such that it is provided protrudingly. [Effects of the Invention]

[0013] As described above, according to the present invention, an injection molded article having high dimensional accuracy and excellent quietness can be realized. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing a gear as an injection molded article according to one embodiment of the present invention. FIG. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3. [Figure 5] FIG. 4 is a cross-sectional view taken along line BB in FIG. 3. [Figure 6] FIG. 4 is a cross-sectional view taken along line CC in FIG. 3. [Figure 7] FIG. 1 is a diagram illustrating the dimensional accuracy of a gear as an injection-molded article according to an embodiment of the present invention. [Figure 8] FIG. 1 is a diagram illustrating the dimensional accuracy of a gear as an injection-molded article according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0016] FIG. 1 is a perspective view showing a gear as an injection-molded article according to one embodiment of the present invention, and FIG. 2 is a bottom view of the gear.

[0017] The injection-molded gear 1 shown in FIGS. 1 and 2 has, for example, a disk-shaped gear body 3 having a shaft portion 2 in the center, and an annular rim portion 4 provided on the outer periphery of the gear body 3.

[0018] An injection-molded article is formed by injecting a molding material into a mold for a product to fill the space that will become the product, and is rotatable. The injection-molded article is, for example, a rotation transmission member that rotates and transmits its rotational force or an external driving force to another rotating body. The injection-molded article may be formed, for example, by insert molding, in which a member is placed in a mold in advance and the molding material is filled around the member.

[0019] The injection-molded article may not have teeth on its outer periphery, and the outer periphery of the rim portion 4 may be configured to slide against the outer periphery of another injection-molded article. The injection-molded article may also be formed into a pulley by providing a circumferentially extending recess on its outer periphery. The injection-molded article preferably has a circumferentially extending portion with high dimensional accuracy, and is preferably an injection-molded article such as a gear or pulley formed in a disk or columnar shape (which may be hollow) that rotates around a shaft. In this embodiment, a gear 1 is used as an example of an injection-molded article, and the main body will be referred to as a gear main body 3 for convenience in the following description.

[0020] The shaft portion 2 is provided in the center of the gear 1 and provides the central axis of rotation of the gear 1. The shaft portion 2 has a shaft hole 21 that penetrates the gear 1 in the axial direction (thickness direction), and the shaft portion that constitutes the rotation axis of the gear 1 is inserted into this shaft hole 21.

[0021] In this embodiment, injection-molded gear 1 has teeth 6, which require high dimensional accuracy, provided on the outer peripheral surface of rim 4, which is provided on the outer periphery of gear body 3. Teeth 6 is molded integrally with gear body 3, is provided at a radial position different from gate marks G1 to G3, and corresponds to the outer periphery that engages with another mechanical component (e.g., another gear) during use.

[0022] The gear body 3 has gate marks G and grooves 5 on one surface (top surface) that are spaced apart in the axial direction. That is, the gear body 3 has gate marks G1 to G3 and grooves 5 on the same end surface. The gear body 3 has a flat inner surface (surface on the bottom side) and a shape with a different height on the other surface (top surface in the figure).

[0023] The gear main body 3 has a first web 31, a second web 32, a groove portion 5, and a third web 33 arranged in order from the axial hole 21 side as the shaft portion 2 toward the outer periphery, and a rim portion 4 is connected to the outer periphery of the third web 33.

[0024] In this embodiment, the rim portion 4 is provided so as to protrude perpendicularly from the outer periphery of the gear body, that is, from the outer periphery of the third web 33 which is the outer periphery web.

[0025] The gate marks G1 to G3 are marks formed when the gear 1 is molded by injection molding or the like. A gate is a resin injection port into the space formed by the core and cavity of a mold. Specifically, when the gear 1 is molded using a mold (core and cavity), the gate marks G1 to G3 are marks formed when a molding material (e.g., molten resin) is filled through the gate to form a molded product (gear 1), and then the molded product (gear 1) is removed from the cavity. The gate marks G1 to G3 are preferably positioned in a way that allows the molding material to flow appropriately throughout the entire molded product that will become the final product.

[0026] The molten resin, which is the molding material for forming the injection-molded gear 1, may be, for example, a thermoplastic resin suitable for injection molding, such as a general-purpose synthetic resin such as polyethylene resin, polypropylene resin, or polyamide resin (e.g., polyamide 66), or an engineering plastic such as polyacetal resin (POM) or polybutylene terephthalate resin. Furthermore, these resin materials may be mixed with fillers or reinforcing fibers (glass fiber, carbon fiber), or metal powder may also be used as the molding material. In this embodiment, for example, POM containing reinforcing fibers such as glass fiber as a reinforced resin is used as the molten resin.

[0027] In this embodiment, the gate marks G1 to G3 are provided on the second web 32 at equal intervals in the circumferential direction.

[0028] Fig. 3 is a plan view of the gear according to one embodiment of the present invention, and Fig. 4, Fig. 5, and Fig. 6 are cross-sectional views taken along lines A-A, B-B, and C-C in Fig. 3, respectively. As shown in Fig. 1 and Figs. 3 to 6, groove 5 is provided adjacent to and radially outward from gate marks G1 to G3.

[0029] The portion of the core that becomes groove 5 has the function of temporarily blocking the radial flow of molten resin that is injected through gate marks G1 to G3 and poured into the cavity during molding of gear 1. Groove 5 adjusts the molten resin flowing radially from the gates, allowing it to flow in evenly and fill the cavity.

[0030] The portions of the core that will become grooves 5 block the molten resin from the gate marks G1 to G3 and allow it to flow radially, for example, toward the outer periphery, beyond the portions that will become grooves 5. Grooves 5 extend in the circumferential direction and have different depths in the circumferential direction.

[0031] The portions of the core that become grooves 5 control the molten resin flowing uniformly over the entire gear 1. By varying the depth of grooves 5, the time it takes for the molten resin flowing in the radial direction (e.g., radial direction) from the gate inside the cavity during molding to pass over grooves 5 and flow radially outward to the outer periphery is adjusted according to the depth of grooves 5. This allows the molten resin to flow uniformly over the entire outer periphery, and over the entire injection-molded product.

[0032] In this embodiment, as shown in FIGS. 1, 3 and 4, the groove portion 5 is formed in a ring shape in a plan view surrounding the shaft hole 21 serving as the shaft portion 2.

[0033] The deepest parts 52 of the grooves 5 are adjacent to the gate marks G1 to G3 on the outer circumferential side of the gear body 3 and are arranged on radial lines passing through the gate marks G1 to G3. In addition, the grooves 5 are formed to extend circumferentially from the deepest parts 52 (52-1, 52-2, 52-3).

[0034] Further, the shallowest portion 54 of the groove 5 is disposed in the middle of the deepest portions 52-1, 52-2, and 52-3 that are disposed apart from each other in the circumferential direction of the groove 5.

[0035] In this embodiment, the bottom of groove 5 is sloped so that the depth gradually decreases from deepest portions 52-1, 52-2, 52-3 to shallowest portions 54-1, 54-2, 54-3. In this configuration, as shown in Figures 3 and 6, intermediate portions 56-1, 56-2, 56-3 between adjacent deepest portions 52-1, 52-2, 52-3 and shallowest portions 54-1, 54-2, 54-3 in groove 5 are at the same height.

[0036] The injection-molded article has a disk-shaped or cylindrical main body, for example, a web portion, on which a gate mark is provided, and a portion requiring high dimensional accuracy as an outer periphery that is spaced apart radially from the gate mark and engages with another mechanical part during use. The outer periphery is molded integrally with the main body and is located at a different radial position from the gate mark.

[0037] The injection molded article may have a groove portion provided in the main body portion, extending in the circumferential direction at a position between the outer periphery and the gate mark in the radial direction, and having a depth that varies in the circumferential direction. The groove portion may be disposed adjacent to the gate mark in the radial direction on the outer periphery side.

[0038] In addition, the grooves have portions with varying depths in the circumferential direction so that the molten resin, which is the molding material, can be uniformly filled in the outer periphery. For example, the injection-molded article may have a portion in the outer periphery (rim portion 4) of the main body (gear main body 3) that requires dimensional accuracy, such as the tooth portion 6 of the gear 1. In this case, the grooves 5 in the injection-molded article may be formed in an arc-like shape in plan view, extending circumferentially, with the deepest portion being adjacent to the gate marks G1 to G3 on the radially outer side.

[0039] That is, in an injection-molded article, as long as the molten resin is allowed to flow uniformly inside the cavity to prevent welds from occurring in areas requiring high dimensional accuracy, such as the teeth 6, the groove 5 does not have to be ring-shaped and surround the shaft adjacent to the gate mark G. Furthermore, the groove 5 may have a flat inclined surface whose depth varies gradually in the circumferential direction, a stepped bottom surface, or a curved inclined surface.

[0040] According to the configuration of the gear 1 of this embodiment, the gear 1 has a groove portion 5 that is provided radially between the gate marks G1 to G3 and the tooth portion (outer periphery) 6, extending circumferentially, and has a depth that varies circumferentially.

[0041] As a result, when molding gear 1, the molten resin as the molding material injected from the gate is blocked depending on the height of the portion of the core that will become groove 5, allowing the flow rate of the molten resin to be adjusted. The flow is controlled so that it flows circumferentially along the portion that forms groove 5 of the cavity. For example, if groove 5 is formed adjacent to gate mark G, this control can be performed immediately after injecting the molten resin into the mold through the gate. Therefore, by controlling the flow of molten resin, which normally fills portions closer to the gate faster than portions farther from the gate, the molten resin can be uniformly filled into tooth portion 6, which requires high dimensional accuracy.

[0042] This makes it difficult for welds to occur in areas requiring high dimensional accuracy, such as the tooth portion 6, reducing the occurrence of single pitch errors in the tooth portion 6 and ensuring quietness when the injection-molded body rotates and transmits its rotational force to other parts by meshing. Furthermore, because the occurrence of welds is suppressed in the tooth portion 6, a decrease in strength due to welds is less likely to occur.

[0043] 7 and 8 are diagrams illustrating the dimensional accuracy of a gear as an injection-molded article according to one embodiment of the present invention. In FIG. 7, FIG. 7A shows gear 1 according to this embodiment, and FIG. 7B shows gear 100, which is manufactured by injection molding like gear 1 but does not have grooves 5 like gear 1, and the locations where the single pitch error of each gear was measured are shown. FIG. 8 shows the single pitch error measured at the same location on each tooth of gear 1 according to this embodiment and gear 100 as a comparative example. In FIG. 8, the numbers arranged in the circumferential direction are the numbers of the teeth, and the numbers arranged in the radial direction indicate the error for each tooth, with 0 (no error) as the reference.

[0044] As shown in Figures 7A and 7B, multiple gears (six each) were produced, including gear 1 according to the present embodiment and gear 100 as a comparative example. In both the manufacturing methods for gear 1 and gear 100, the same molding material (e.g., POM containing reinforcing fibers such as glass fiber as a reinforced resin) was used. In both manufacturing methods, the same mold was used, in which a groove forming die for forming the grooves could be attached and detached. Furthermore, in both manufacturing methods, gear 1 and gear 100 were manufactured under the same conditions, including the temperature of the molding material and environmental conditions.

[0045] The single pitches of the right and left tooth flanks of the tooth portions 6A and 60 of the gears 1 and 100 shown in FIG. 7 were measured and are shown in FIG.

[0046] Figures 8A and 8B show the results of measuring a single pitch on the right and left tooth flanks of the tooth portion 6A (see Figure 7A) of multiple gears 1. Figures 8C and 8D show the results of measuring a single pitch on the right and left tooth flanks of the tooth portion 60 (see Figure 7B) of multiple gears 100.

[0047] As shown in Figures 7 and 8, when comparing the gear 1 of this embodiment with the gear 100 of the comparative example, dimensional errors occur on both the left and right tooth flanks of the tooth portion 60 of the gear 100, and in particular, a single pitch error occurs due to the weld.

[0048] In contrast, in the gear 1 of this embodiment having the groove portion 5, the tooth portion 6A of the gear 1 has little dimensional error on the left and right tooth flanks, and the single pitch error due to the weld is small or absent.

[0049] This shows that in an injection molded product such as gear 1, by providing groove portion 5 that is radially adjacent to the gate mark and extends circumferentially, and that has a depth that varies circumferentially, the gear has higher dimensional accuracy of shape and is quieter than the comparative example.

[0050] In this embodiment, there are three gates (i.e., gate marks G1 to G3), but this is not limiting, and a single gate may be used as long as the depth of groove 5 can be controlled so that the molten resin is uniformly filled in the cavity of the injection molded body. In this case, there will be one gate mark. There may also be two or four or more gates, in which case there will be two or four or more gate marks.

[0051] Furthermore, although the groove portion 5 is provided adjacent to the outer periphery of the gate mark G, this is not limited to this. If there is a portion requiring high dimensional accuracy, such as a tooth portion, on the inner periphery (inside in the radial direction) of the gate mark G, the groove portion may be provided adjacent to the inner periphery of the gate mark.

[0052] In this embodiment, the gear body 3 has the gate marks G1 to G3 and the groove 5 on the same end face. This makes it easier to remove the core from the cavity and allows for accurate molding when forming the injection-molded article by injection molding or the like, but the body may also have the groove on the side opposite to the gate marks.

[0053] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. In other words, the above description of the configuration and the shape of each part is merely an example, and it is clear that various modifications and additions to these examples are possible within the scope of the present invention. [Industrial Applicability]

[0054] The injection molded article according to the present invention has high dimensional accuracy in shape and excellent quietness, and is useful as a gear. [Explanation of symbols]

[0055] 1. Gears 2 Shaft 3 Gear body (body) 4 Rim section 5 Groove 6 Teeth (outer periphery) 21 Shaft hole 31 First Web 32 Second Web 33 Third Web 52, 52-1, 52-2, 52-3 Deepest 54, 54-1, 54-2, 54-3 Shallowest part 56-1, 56-2, 56-3 middle part G1, G2, G3 gate marks

Claims

1. An injection molded article having a main body portion having an axial hole in the center and a rim portion provided on the outer periphery of the main body portion, One surface of the main body has a gate mark formed during injection molding, a groove portion that is provided radially outward of the gate mark and at a position different from the gate mark, extending in a circumferential direction, and has a deepest portion and a shallowest portion with different depths in the circumferential direction, The rim portion is provided so as to protrude from the outer circumferential portion only toward the other surface side of the main body portion. Injection molded body.

2. the deepest part of the groove is disposed at a radial position passing through the gate mark, The injection molded article according to claim 1.

3. The depth of the groove portion gradually decreases from the deepest portion in the circumferential direction. The injection molded article according to claim 2.

4. The groove portion has a ring shape surrounding the shaft hole. The injection molded article according to any one of claims 1 to 3.

5. The groove portion is provided adjacent to the gate mark on the outer circumferential side of the gate mark. The injection molded article according to any one of claims 1 to 4.

6. The outer peripheral surface of the rim portion is provided with gear teeth. The injection molded article according to claim 5.

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