Patent Application
20140302975
1. Field of the Invention
The present invention relates to a manufacturing method for manufacturing a resin shaft member by injecting a resin material into a mold, a molding mold, and a roller shaft.
2. Description of the Related Art
Conventionally, a roller shaft used to convey paper in a copying machine or printer is manufactured by press-fitting and joining a rubber roller on a metal shaft. At a portion of the shaft at which the requested rigidity is low, a resin shaft is used.
A shape such as a key groove is added to a metal shaft by processing part of the end face later. As a rust prevention measure for a post-processed portion, plating is performed.
A resin shaft needs to have a rib structure because it is difficult to manufacture a columnar round shaft, in order to ensure the shaft accuracy and prevent a sink mark or the like. When rubber is press-fitted and joined to the rib portion, the outer shape accuracy of the rubber degrades and the surface needs to be polished.
Further, a mold for molding a shaft has a parting between the stationary side and the movable side. Even a step or a small flash at the parting line affects the accuracy of the rubber surface after press-fitting the rubber.
As a method of forming a resin shaft into a columnar shape, there is proposed a method of filling the inside of a mold with a gas to form a hollow structure when filling the inside of the mold with a resin (see Japanese Patent Application Laid-Open No. H08-132467).
As a method of removing a parting line on the end face, there is proposed a method of arranging a piece on the end face in a direction perpendicular to the mold opening/closing direction (see Japanese Patent Application Laid-Open No. 2001-18226).
Further, there is proposed a method of forming a shape such as a gear on the end face (see Japanese Patent Application Laid-Open No. H10-281139).
A conventional method has problems in the weight of a finished piece and the manufacturing cost of a roller shaft because the weight of a metal shaft is heavy, the end portion requires fabrication, and the surface needs to undergo rust prevention plating.
A resin shaft needs to have a rib structure because it is difficult to manufacture a columnar round shaft, in order to ensure the shaft accuracy and prevent a sink mark or the like. When rubber is press-fitted and joined to the rib portion, the outer shape accuracy of the rubber degrades and the surface needs to be polished.
Further, a mold for molding a shaft has a parting between the stationary side and the movable side. Even a step or a small flash at the parting line affects the accuracy of the rubber surface after press-fitting the rubber.
According to the present invention, there is provided a mold used to mold a resin shaft member including a shaft portion and a roller joint portion configured to join a roller, comprising a plurality of cavities of different shapes, wherein at least one of the plurality of cavities includes an insert having a space portion which is surrounded by a parting-free surface and used to mold the roller joint portion, and a gate configured to inject a resin into the space portion, the space portion is larger in diameter than the shaft portion, and the insert is movable by an ejector in an opening/closing direction of the mold.
According to the present invention, there is provided a method of manufacturing a resin shaft member including a shaft portion and a roller joint portion configured to join a roller, comprising: molding, by using a mold including at least a first cavity and a second cavity, a first part on which the shaft portion is molded by the first cavity, and molding a second part on which the roller joint portion is molded on the first part by the second cavity in which the first part is inserted.
According to the present invention, there is provided a roller shaft which is obtained by joining rollers to a plurality of roller joint portions of a resin shaft member on which a shaft portion and the plurality of roller joint portions are integrally molded, wherein the roller joint portion has a seamless shape.
A shaft member with a large shaft diameter requiring high shaft rigidity is molded using a foaming resin material, thereby molding a high-accuracy cylindrical resin shaft member free from any sink mark.
In a mold for molding a resin shaft member according to the present invention, a plurality of parting-free inserts is arranged at portions to each of which a roller is press-fitted and joined. In addition, a plurality of cavities are arranged in accordance with the number of roller joints.
When molding a resin shaft member according to the present invention, a molded article molded by the first cavity is inserted in the second cavity to mold a rubber roller joint portion. Sequentially, the next roller joint portion is molded by the third cavity.
In the present invention, a plurality of parting-free inserts were arranged in the mold in accordance with the number of roller joint portions, and roller joint portions were sequentially molded in the mold. Thus, the roller joint portions for press-fitting and joining a roller could have a parting-free seamless shape.
As a result, in the present invention, the roller surface accuracy upon press-fitting and joining a rubber roller at a roller joint portion became high, and conventional roller surface polishing could be omitted.
A shaft requiring high rigidity was molded by the mold and molding method according to the present invention using a foamed material as the resin material. Hence, a cylindrical shaft member with high rigidity and high accuracy of a roller joint portion without any sink mark could be manufactured, and a metal shaft could be replaced with a resin shaft.
Therefore, a resin shaft member according to the present invention could have high accuracy and high functionality at low cost, and could improve the productivity and quality.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. The same reference numerals denote the same parts throughout the drawings.
To the contrary, roller joint portions 7 are molded and integrated with the shaft portion 1 after molding the shaft member 10. A non-foam layer 8 molded using a non-foaming resin is formed at the boundary between each roller joint portion 7 and the shaft portion 1.
The roller joint portion 7 has a parting-free seamless shape.
A roller is press-fitted and joined at the roller joint portion, forming a roller shaft. Since the roller joint portion has a parting-free seamless shape, the roller surface accuracy upon press-fitting and joining a roller at the roller joint portion 2 is high, and conventional roller surface polishing can be omitted. The roller preferably uses, e.g., rubber, but a roller made of a substance other than rubber is also available.
The shaft member 10 can use a resin material such as high-impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), modified polyphenylene ether (PRO), polystyrene (PS), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), a liquid crystal polymer (LCP), or polyacetal (POM).
It is also possible to increase the strengths of the shaft portion and shaft member 10 by filling one of a glass filler, carbon fiber, talc, and plate-like filler in the resin material at the shaft portion 1. A combination of these fillers can also be used.
By manufacturing the shaft member 10 according to the present invention by using a foaming resin, as shown in
Since a sink mark and warping, which appear in a thick shaft member, change depending on the maximum diameter of the shaft member and the molding cycle, the resin material is not always limited to a foaming resin material. A non-foaming resin is also usable in accordance with a desired shape or the type of resin material.
At least one of the plurality of cavities, at a portion thereof, includes a space portion (shape serving as a roller joint portion) which is surrounded by a parting-free surface formed by an insert 9. And the insert 9 is used to mold a roller joint portion. Further, the mold 40 includes gate 41 for injecting a resin into the space portion of the insert 9, a runner 11 to which a resin material is supplied from the outside, ejector rod 12, and an ejector plate 13. The diameter of the space portion of the insert 9 is larger than the inner diameter of the shaft portion 1. The insert 9 does not have a parting, so no parting line is generated on a roller joint portion molded by the insert 9.
One of the plurality of cavities is a cavity for molding a shaft portion, and has a gate for injecting a resin into the shaft portion.
In
After a dwell step and cooling step upon filling the resin material, the mold 40 is opened, and the ejector plate 13 and the ejector rod 12 coupled to the ejector plate 13 are pushed out to move the insert 9 coupled to the ejector rod 12 in the die opening/closing direction.
Although the molded article (part) of a shaft member is temporarily extracted from each cavity, a molded article (part) which has not had a final shape yet is inserted again into the mold 40.
After inserting the molded article (part) which has not had a final shape yet, the roller joint portion 6 is molded again, as needed. A molded article (part) on which molding of the necessary roller joint portions 6 has ended is extracted as a final molded article (resin shaft member) without returning it to the mold 40.
In
When the mold 40 is opened to push out the ejector plate 13, as shown in
Holding portions (for supporting a part serving as a molded article) are formed at the two end portions of each cavity to support the shaft center of a shaft portion on one end face in the shaft direction. One of the holding portions includes a slide member 18 movable in a direction perpendicular to the mold opening/closing direction, and the other includes a block 19. In molding, the first part 15 and second part 16 serving as molded articles are held at the two ends in the shaft direction in the respective cavities.
In
As shown in
Similar to the operation of setting the first part 15 in the second cavity 102 to mold the second part 16 on which the roller joint portion 23 is molded, when the mold 40 is opened, the second part 16 on which the roller joint portion 23 is molded by the second cavity 102 is extracted and set in a third cavity 103 to mold the third part 17 on which a roller joint portion 25 is molded. A roller joint portion 22, a roller joint portion 24, and the roller joint portion 25 are molded at different positions.
In
As described above, the parts 10 are simultaneously molded by the respective cavities. After the mold 40 is opened, the molded parts are sequentially inserted in adjacent cavities of different shapes and then the mold 40 is closed to perform the next molding operations. By repeating this operation, the shaft member of the finished piece is molded.
Although
As described above, a shaft member having two roller joint portions may be molded by the first and second cavities.
The shaft member may be a shaft member on which one roller joint portion is molded by molding only a shaft portion by the first cavity and molding a roller joint portion by the second cavity.
In
In
Each slide 30 and each insert 32 incorporate center pins (not shown) which hold a shaft member serving as a molded article as the shaft center of each cavity. Simultaneously when the mold is opened, each slide 30 moves and is released from the molded article of a shaft member. Each insert 31 having the shape of a roller joint portion, and each insert 32 for forming the shape of a molded article on the end face in the shaft direction in each cavity move in the mold opening direction in conjunction with the operation of the ejector plate.
In the embodiment, the molded articles (parts) molded by the respective cavities 26 to 29 move in a direction (direction perpendicular to the mold opening/closing direction) in which each slide 30 is set in the shaft direction. Then, the molded articles (parts) are released from the mold.
In the embodiment, the molded article 291 molded by the fourth cavity is a completed shaft member on which all roller joint portions are molded.
The mold having four cavities has been described above, but the present invention is not limited to this. When the mold has two, first and second cavities, the second part on which one roller joint portion is formed serves as a completed shaft member.
When the mold has the first, second, and third cavities, the third part on which two roller joint portions are formed serves as a completed shaft member.
As described above, roller joint portions can be sequentially formed by repeating the steps in
The mold according to each of the above-described embodiments includes a maximum of four cavities. However, to mold a shaft member shown in
Tables 1 to 4 show resin materials each used for the shaft member 10 molded using the mold 40 shown in
Table 1 shows the results of molding using the mold (mold shown in
In Table 1, the related art represents the results obtained by molding the shapes of all the shaft member and roller joint portions by one cavity. Examples 1 to 4 represent the results of molding using the mold and molding method according to the present invention.
In the related art, since the portions of the shaft member and roller joint portions having different diameters were molded at once, the molding cycle became long, and a sink mark was generated at the roller joint portion, degrading the circularity. Further, since the parting line (PL) existed even at the roller joint portion, a parting step was generated at the roller joint portion.
To the contrary, in Examples 1 to 4 according to the present invention, only a φ8-mm shaft portion was molded by the first cavity, and φ10-mm roller joint portions were molded sequentially by the second and subsequent cavities. This was substantially the same as molding at a thickness of 2 mm.
For molded articles molded according to Examples 1 to 4, the molding cycle was greatly shortened. In addition, since no sink mark was generated at the roller joint portion, the circularity and run-out accuracy were improved. Further, since no parting line existed at the roller joint portion, no step was generated.
From Table 1, it was verified that a shaft member molded using the mold and molding method in each example of the present invention was superior in all productivity, part accuracy, and part function to the related art.
Table 2 shows the results of molding using the mold (mold shown in
In Table 2, the types of all resin materials are different in Examples 5 to 9. To increase the rigidity of the shaft member, a glass filler reinforcement is filled in all the resin materials.
As a result of molding each resin material by using the mold and molding method according to each example of the present invention, resin materials reinforced by various glass fillers improved the molding cycle and part accuracy, compared to glass fiber-free resin materials shown in Table 1.
Especially in Example 6, the same quality as that of a conventional part obtained by joining rollers to a metal shaft was achieved in all the straightness of the shaft member, the circularity of the roller joint portion, run-out of the roller portion, and the step of the roller joint portion.
Table 3 shows the results of foam molding using the mold (mold shown in
Table 3 represents the results obtained by mixing a foaming agent in various resin materials and performing foam molding by using the mold and molding method according to the present invention. As for the method of injecting and filling the foamed material, nitrogen gas is guided to the plasticating cylinder of an injection molding apparatus at high pressure and mixed with a resin in a high-temperature molten state in the cylinder, and the resultant mixture is injected into a mold to fill it.
In all the examples, the molding cycle and part accuracy were improved, compared to the results shown in Tables 1 and 2.
In all the examples, the same quality as that of a conventional part obtained by joining rollers to a metal shaft was achieved.
This result reveals that a conventional metal part could be replaced with a resin part, abruptly improving the productivity.
Table 4 shows the results obtained by integrally forming a gear shape on the end face shown in
In Table 4, each material is the result of foam molding, similar to Table 3.
In Example 16, a two-color molding apparatus was used. In Examples 17 to 19, in addition to the two-color molding apparatus, a compact injection unit was attached to a mold to perform three-color molding.
In all the examples in Table 4, the above-mentioned nitrogen gas was mixed in a resin to perform foam molding using only a plasticator configured to mold a shaft member.
In Example 15 in Table 4, all parts were molded using a POM material. Since the POM resin is higher in mold shrinkage factor than other resins, the accuracies of the shaft member and roller joint portion became poorer.
Example 16 exhibits the result of using resin materials among which only the material of the shaft portion was reinforced by a glass filler. Since the resin material reinforced by the glass filler was used for only the shaft portion, the accuracies of both the shaft portion and roller joint portion were improved, compared to Example 15.
In Examples 17 to 19, a resin material reinforced by a glass filler was used for the shaft portion, and the roller joint portion was molded using a resin material (unreinforced resin material) of the same type that was not reinforced by a glass filler.
In Examples 17 to 19, the accuracies of the shaft portion and roller joint portion substantially satisfied the standards.
In all Examples 15 to 19, the shape accuracy of the gear portion was almost the same and satisfied the standard.
Among the resin materials listed in Tables 1 to 4, HIPS stands for high-impact polystyrene, ABS stands for acrylonitrile butadiene styrene, and PC stands for polycarbonate. PPO stands for modified polyphenylene ether, PS stands for polystyrene, PBT stands for polybutylene terephthalate, PPS stands for polyphenylene sulfide, LCP stands for liquid crystal polymer, and POM stands for polyacetal. GF30 and GF50 indicate mixing ratios (%) of the glass filler, respectively.
Although the above-described examples used the glass filler as a filler for reinforcing a resin material, a carbon fiber, talc, or plate-like filler may be filled to reinforce a resin material. Also, a combination of these fillers can be used.
In the aforementioned examples, a roller joined to a shaft member was made of rubber. However, even a roller made of a substance other than rubber is also available.
In the mold for molding a resin shaft member according to the present invention, a plurality of parting-free insert can be arranged at portions to each of which a roller is press-fitted and joined. A plurality of cavities can be arranged in accordance with the number of roller joints.
Since a plurality of parting-free insert were arranged in the mold in accordance with the number of roller joint portions, the roller joint portions to each of which a roller was press-fitted and joined could be formed into a parting-free seamless shape.
In the present invention, therefore, the roller surface accuracy after press-fitting and joining, e.g., a rubber roller to a roller joint portion became high, and conventional roller surface polishing could be omitted.
A shaft requiring high rigidity was molded by the mold and molding method according to the present invention using a foamed material as the resin material. Hence, a cylindrical shaft member with high rigidity and high accuracy of a roller joint portion without any sink mark could be manufactured, and a metal shaft could be replaced with a resin shaft.
The resin shaft member according to the present invention could have high accuracy and high functionality at low cost, and could improve the productivity and quality.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-078494, filed Apr. 4, 2013, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-078494 | Apr 2013 | JP | national |
