JP3049911U - Plastic piston - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the condition of the surface of the seal groove bottom surface. SOLUTION: There is provided one or a plurality of piston parts 5, 6 formed integrally with a rod part 4, and a seal groove is formed on the outer periphery of the piston part.
A molded part 2 which is a plastic piston having a hollow part 9 which is open along a central axis to one end inside the rod part and the piston part;
A filling part 3 filling the hollow part. The hollow portion is a circular hole. The molded part is a reinforced plastic mixed with reinforcing fibers such as glass fiber and carbon fiber.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to an improvement of a plastic piston having a seal groove for mounting a seal on an outer periphery.

[0002]

[Prior art]

 This type of plastic piston, which is formed by injection molding a thermoplastic plastic reinforced with glass fiber, is used for brakes and clutches of automobiles. The general shape of this piston is a solid part in which one or more shaft-shaped rod parts have a piston part integral with the enlarged rod part, and a seal groove is formed along the outer peripheral surface of the piston part. Body. A seal is mounted in this seal groove so that the piston inserted into the cylinder slides in a fluid-tight manner. The molding die for such a piston is formed in a divided manner in order to take out the molded piston, and the position of the dividing surface of the die becomes a dividing line of the die and appears as a flash on the piston surface. Due to the shape of the piston, the split surface of the mold is inevitably located at a position crossing the seal groove, and burrs appear in the molded piston so as to cross the seal groove. The projection amount of the burrs can be reduced to some extent by changing molding conditions (material injection speed, etc.) even for the same plastic material. However, molding conditions that reduce this burr tend to worsen surface roughness. Therefore, a balance between the two is necessary. At present, for example, with a certain material, the protrusion amount of the burrs is reduced to about 0.03 mm and the surface roughness (center line average roughness Ra) is reduced to about 1.0 μm. However, it is extremely difficult to reduce this.

[0003]

[Problems to be solved by the invention]

 Naturally, this piston is required to have rigidity, reliability, and durability. In particular, the condition of the bottom surface of the seal groove affects the sealing performance, so it must be good. It is rare. An object of the present invention is to provide a plastic piston that can improve the condition of the surface of the bottom surface of the seal groove while maintaining other requirements for the piston.

[0004]

[Means for Solving the Problems]

 Means of the present invention is a plastic piston having one or a plurality of piston parts integrally formed with a rod part and having a seal groove on an outer periphery of the piston part, wherein a center axis is provided inside the rod part and the piston part. And a filling portion having a hollow portion that opens to reach one end along the edge of the hollow portion, and a filling portion that fills the hollow portion. 3).

[0005] In the means of the present invention, since the molded portion has a hollow portion, the thickness of the groove bottom of the seal groove can be appropriately reduced. The reduced thickness improves the flow state of the plastic material during injection molding of the molded part.In other words, a favorable rectification state is obtained, so that flow marks are less likely to occur and the surface roughness is lower than before. Be improved. Further, since the volume of the mold space is reduced by the amount of forming the hollow part, the degree of temperature rise when the internal gas is compressed is small by that much, and the burned black stripes on the surface of the molded product (high temperature due to the compression of the internal gas Therefore, plastic deterioration (so-called gas burning) is less likely to occur than before. Accordingly, the injection conditions are eased, the burrs at the bottom of the seal groove are reduced, and the molding conditions for reducing the surface roughness are also relaxed. Can be reduced. The decrease in strength due to the provision of the hollow part can be reduced by forming the filling part with an appropriate one after molding the molded part, for example, a plastic of the same material as the molded part or a material with higher strength. I can make up for it.

[0006] In the above means, it is preferable that the hollow portion is a circular hole. In general, the seal groove is annular, and by forming the hollow portion as a circular hole, the thickness of the portion forming the seal groove bottom is constant over the entire circumference, so that moldability is improved, surface roughness is reduced, and Equalize in the lap.

[0007] It is preferable that the molded part is a reinforced plastic in which reinforcing fibers such as glass fiber and carbon fiber are mixed (claim 3). Reinforced plastics mixed with reinforcing fibers generally have a large surface roughness on the molding surface and may reduce the sealing performance at the bottom of the seal groove. A strong plastic piston is obtained.

[0008]

[Embodiment of the invention]

 One embodiment of the present invention will be described with reference to FIG. The plastic piston 1 of this embodiment is a piston for a brake cylinder of an automobile, and is composed of a molded part 2 and a filling part 3, and the molded part 2 is made of, for example, glass fiber for reinforcement. It is formed by injection molding using a mixed thermoplastic reinforced resin, and has a shaft-shaped rod portion 4, a first piston portion 5 provided at one end of the rod portion 4, and a second piston portion provided in the middle of the rod portion 4. It comprises a two-piston part 6 and a hollow part 9. The first piston portion 5 has a seal groove 7 on the outer periphery, and the second piston portion 6 has a seal groove 8 on the outer periphery. The seal grooves 7 and 8 are provided with seals, and the seals and the seal groove bottom surfaces 7a and 8a are in close contact with each other to maintain fluid tightness. The hollow part 9 is a circular hole extending from one end of the molded part 2 to the inside of the first piston part 5 at the other end, and is provided along the same axis as the common axis of the rod part 4, the first and second pistons 5, 6. There is a dead end near the inside of the seal groove 7. The filling section 3 is made of, for example, the same material as that of the molding section 2 and is fixed in a state in which the hollow section 9 is filled.

The piston 1 is completed, for example, by first forming the molded part 2 by injection molding and providing the filling part 3 in the hollow part 9 of the molded part 2. When the molding part 2 is injection-molded, the mold 10 is as shown in FIG. In other words, in FIG. 2, the mold 10 accepts portions at both ends in the longitudinal direction of the molding portion 2 and opens portions 11 and 12 outward in the axial direction at the time of taking out the product. The upper and lower portions 13 and 14 are opened. The boundaries of these portions are mold separation surfaces 15, 16 and 17, and the gate position is one end indicated by 18 when considering that there is no warp with respect to the axis. It is the position of the center axis of. The portion forming the hollow portion 9 is provided in the portion 11 as a cylindrical body. In addition, the mold used as a conventional solid body has a configuration in which there is no cylindrical body forming the hollow portion 9 in the mold part 11, and the other parts are the same.

In general, burrs are formed on the product surface at the positions of the mold separation surfaces 15, 16, and 17, although there are differences in size depending on the situation. Since the mold separating surfaces 17 of the mold portions 13 and 14 are located at positions crossing the first and second seal grooves 7 and 8, linear seals extending in the direction crossing the groove bottoms 7a and 8a of the seal grooves 7 and 8 are formed. I can do it. However, as compared with the conventional solid body, the presence of the hollow portion 9 makes the thickness of the portion forming the groove bottom thinner and uniform over the entire circumference. It is thought that the uniformity of the flow state of the material is improved, and if the injection conditions are changed and appropriate conditions are determined, the state of the groove bottom surface is greatly improved as a result. That is, the size of the burrs on the groove bottom surface can be made smaller and the surface roughness can be made smaller than before. The strength of the piston can be satisfied by providing the filling portion 3 in the hollow portion 9.

Although the above embodiment has shown the case where the piston portion is provided at two places, the present invention can be applied to the case where the piston portion is provided at one place or at two or more places.

As a modified example of the embodiment, the hollow portion 9 may have an end opposite to the above, that is, an end on the first piston 3 side, and a dead end at the other end. In that case, a mold gate should be provided at the center of the dead end.

[0013]

【Example】

 In FIG. 1, when the thickness of the groove bottom 7a of the molded portion 2 is about 1 mm and the thickness of the groove bottom 8a is about 1.5 mm, the height of the burr at the bottom of the groove is 0.01 mm or less. A surface roughness (center line average roughness Ra) of 0.6 μm or less was achieved. In addition, in the solid body of the comparative example (the same except that there is no filling portion 3), the height of the groove bottom is 0.03 mm, and the surface roughness of the groove bottom (center line average roughness Ra) is about 1.0 μm. Is the limit.

[0014]

[Effect of the invention]

 According to the first, second and third aspects of the present invention, since the burrs at the bottom of the seal groove can be reduced and the surface roughness can be reduced, the sealing performance of the piston portion is improved. The invention according to claim 2 has the effect of reducing the surface roughness and equalizing it over the entire circumference in addition to the above effects. According to the third aspect of the present invention, in addition to the above-described effects, there is an effect that the sealing performance can be ensured and a high-strength plastic piston can be obtained.

[Brief description of the drawings]

1A and 1B show an embodiment of the present invention, wherein FIG. 1A is a partial cross-sectional front view, and FIG. 1B is a left side view.

FIG. 2 is a front view showing a divided configuration of an injection mold for forming a molding section of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plastic piston 2 Molding part 3 Filling part 4 Rod part 5 1st piston part 6 2nd piston part 7 Seal groove 8 Seal groove 9 Hollow part 10 Injection mold 11 Mold part 12 Mold part 13 Mold part 14 Mold part 15 Mold separation surface 16 Mold separation surface 17 Mold separation surface 18 Gate position

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 08 B29L 31:16 31:26

Claims (3)

[Utility model registration claims] 1. A plastic piston having one or more piston portions formed integrally with a rod portion and having a seal groove on an outer periphery of the piston portion, wherein the plastic piston is provided along a central axis inside the rod portion and the piston portion. A plastic piston comprising: a molded portion having a hollow portion reaching one end and opening; and a filling portion filling the hollow portion. 2. A plastic piston having one or a plurality of piston portions formed integrally with a rod portion and having a seal groove on an outer periphery of the piston portion, wherein the plastic piston is provided along a center axis inside the rod portion and the piston portion. A plastic piston comprising: a molded part having a hollow portion reaching one end and having an opening; and a filling portion filling the hollow portion, wherein the hollow portion is a circular hole. 3. A plastic piston having one or a plurality of piston portions formed integrally with a rod portion and having a seal groove on an outer periphery of the piston portion, the plastic piston being provided along a central axis inside the rod portion and the piston portion. It consists of a molded part having a hollow part that reaches one end and opens, and a filling part that fills the hollow part, and the molded part is mixed with reinforcing fibers such as glass fiber and carbon fiber. A plastic piston characterized by a reinforced plastic construction.