JPS62137435A - Piston for hydraulic cylinder - Google Patents

Abstract

PURPOSE:To obtain a piston for hydraulic cylinder consisting of a phenol resin molding excellent in heat resistance by mixing a resol type phenol resin having a different structure with a resin system, and using a filler such as reinforced fibers. CONSTITUTION:All the phenol resins used in the piston 1 are solid resol type phenol resins, whose composition is such that the weight ratio of the solid resol type phenol resin, in which the free phenol exceptional number average molecular weight is 800-1,200 and the dimethylene ether group constituent ratio in a phenol nucleus combining function group is 40-60% in mol, and the resin, in which the free phenol exceptional number average molecular weight is 600-1,000 and the dimethylene ether group constituent ratio in the phenol nucleus combining function group is 0-20% in mol, is 3:7-7:3. The fillers are made of inorganic fibers such as glass fibers, carbon fibers, graphite fibers, or the like, and glass powder, clay, mica, graphite powder, or the like may be partially used in combination. By using these materials, molding is carried out by means of an injection molding machine, and after molding post cure is carried out to enhance the heat resistance and dimensional stability.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to carino Z-pistons for disc brakes, wheel cylinder pistons for drum brakes, and O-R pistons for clutches, which are made of a phenolic resin molding with excellent heat resistance.
This invention relates to a piston for a hydraulic cylinder such as a ration cylinder piston. [Prior Art] The following will mainly describe the carriage chimney piston of a disc brake.

In recent automobiles, the use of disc brakes has become commonplace for the purpose of improving braking performance. This is because disc brakes are easier to maintain braking performance, especially instantaneous braking force and continuous braking force, than other systems. FIG. 1 is a sectional view showing the configuration of a disc brake. (1) is a carino piston, (2) is a seal, (
3) is a disk play kinozorad, (4) is a disk,
(5) is brake fluid.

Conventionally, chrome-plated steel is often used for the carry/1° piston (1). Disc brakes generate frictional heat when braking. Since kinetic energy is converted into thermal energy, the amount of heat generated increases as the vehicle speed at the start of braking increases and as the vehicle weight increases. This heat travels through the brake pedal and the brake piston, raising the temperature of the brake fluid. It is well known that repeated sudden braking or continuous braking on long downhill slopes can cause the brake fluid to boil, a so-called paper lock phenomenon, which can reduce the effectiveness of the brakes. Improving braking performance requires heat countermeasures, that is, heat radiation into the air and insulation into the brake fluid. Recent trends include the use of asbestos as the main compounding material and molded products with binders such as phenolic resin, which have been used for a long time for the purpose of improving friction properties, and the use of steel wool and other materials as the main compounding material. The molded bodies used are undergoing major changes. Furthermore, the use of sintered bodies made of various metal powders, mainly copper, called sintered molds, has begun to be seen in some car models. This tendency increases the amount of heat transferred to the brake fluid and increases the likelihood of paper lock development if the conventional design is used. In order to solve this problem, the carry chisel piston was made of resin,
Insulating the brake fluid is effective in preventing the temperature of the brake fluid from rising, and the carrier piston is constructed of phenolic resin and has been put into practical use to some extent. Since the carry ε-piston locally reaches over 200°C during braking, it is required to have strength when hot, a small coefficient of thermal expansion, and small dimensional change over a wide temperature range. It is necessary that the dimensions and strength do not change significantly in the coexistence of It is difficult for phenolic resin carrying pistons to meet the above requirements, especially heat resistance above 200℃ and small dimensional change rate over a wide temperature range, and its application is limited to low heat generation during braking. It can be said that it was limited to certain car models. However, with the exception of special heat-resistant resins such as polyimide, phenolic resin has high heat resistance and is highly practical as a resin for carry IJ/ε-pistons, and its application as a carry-go piston will be expanded. There has been a strong desire to improve heat resistance by this method. Improvements in heat resistance and dimensional stability were also desired for drum brake wheel cylinder pistons and clutch operation cylinder pistons.

[Purpose of the invention]

Based on the above background, the present invention has obtained the knowledge that heat resistance can be improved by mixing resol type phenolic resins with different structures in the resin system and using fillers such as reinforcing fibers, and based on this knowledge. The present invention has been completed through various studies. The purpose is to provide a piston for a hydraulic cylinder such as a carino piston for a disc brake, which is made of a phenolic resin molding having excellent heat resistance.

[Structure of the invention]

The present invention is free phenol excluded number average molecule! (below,
800-1200. A solid resol-type phenol resin with a dimethyl ether group composition ratio of phenol core-binding functional groups of 40 to 60 moles, and a number average molecular weight (M) excluding free phenol of 600 to 1000, and a dimethylene ether group composition ratio of phenol core-binding functional groups. is 0
A molded body of a composition comprising 100 parts by weight of a phenolic resin whose mixing ratio (CMu ratio) with a solid resol type phenolic resin of ~20 molar ratio is 3 to 7:3 and 100 to 250 parts by weight of a filler. The present invention relates to a characteristic piston for a hydraulic cylinder.

Note that the ratio of functional groups is NM after acetylating the resin.
It was determined by R measurement. The piston for a hydraulic cylinder of the present invention can be obtained by injection molding using a screw injection molding machine or by plasticizing a molding material using a screw extruder and heating and compression molding the plasticized material in a predetermined mold. Therefore, the composition of the present invention must have a structure that allows plasticization using a screw.

This is because a molded product obtained by plasticizing powder or a preformed powder using high frequency, infrared rays, etc. and then heating and compression molding in a mold has poor heat resistance, particularly thermal shock resistance.

The present invention will be explained in detail below. All of the phenolic resins used in the present invention are solid resol type phenolic resins. In liquid form, the process of turning it into a molding material is complicated;
Industrially disadvantageous. In addition, novolak-type phenolic resins that use hexamethylenetetramine or noraformaldehyde as a curing agent have high heat resistance because, due to their reaction mechanism, the crosslinking density does not increase, and gas is generated from a small amount of remaining curing agent. It has drawbacks such as not being able to obtain the desired chemical resistance, being inferior in chemical resistance compared to the resol type, and easily being attacked by brake fluid, etc., and is therefore not suitable for use in pistons for hydraulic silling.

The composition of the solid resol type phenolic resin is that M is 800~
1200, a solid resol type phenol resin (hereinafter referred to as dimethylene ether type resol) in which the dimethylene ether group composition ratio of the phenol core-binding functional group is 40 to 60 moles, and The ratio (weight ratio) to a solid resol type phenol resin (hereinafter referred to as methylol type resol) having a dimethylene ether group composition ratio of 0 to 20 moles is 3 = 7 to 7.
3. Dimethylene ether type resol has a large activation energy of approximately 30 kcal/mol.
The reaction is difficult to proceed at relatively low temperatures, and on the contrary, the reaction proceeds easily at high temperatures, making it suitable for injection molding, whereas methylol-type resols have an activation energy of approximately 10 kc.
Since the at/mot is small and the reaction proceeds at a relatively low temperature, the thermal stability of the preplasticized product in the screw during molding is poor.

Cured products of dimethylene ether type resols have a considerable amount of remaining dimethylene ether groups due to their curing mechanism, and because the distance between phenol nuclei is relatively long, crosslinking density is less likely to increase than cured products of methylol type resols, making them more heat resistant. is inferior. Therefore, in order to obtain a resin composition that has high heat resistance and excellent thermal stability of the pre-plasticized material in the screw, the blending ratio of dimethylene ether type resol and methylol type resol is 3.
Near to 7:3. If the ratio of dimethylene type resol is less than 3:3, preplasticization with a screw becomes difficult, and conversely, if the ratio of methylol type resol is less than 7:3, heat resistance becomes insufficient. It is appropriate that the filler used in the present invention is mainly inorganic. Organic materials such as wood flour and lubricant have poor heat resistance. In order to obtain heat resistance as a piston for a hydraulic cylinder, K needs to have high strength against distortion during heating and a small coefficient of thermal expansion. Desirable fillers for this purpose are inorganic reinforcing fibers, such as glass fibers, carbon fibers, graphite fibers, etc., and it is optional to partially use glass powder, clay, mica, graphite powder, etc. in combination.

The filler used in the present invention is phenolic resin 10
The range is 100 to 250 parts by weight relative to 0 parts by weight,
If it is less than 100 itt parts, the properties such as heat resistance, strength, and dimensional stability will be poor, and if it is more than 250 parts by weight, problems such as poor fluidity during molding will occur. Generally, a curing aid, a mold release agent, a pigment, etc. are added and mixed to these compositions, and then a molding material is obtained by heating and mixing. The piston for a hydraulic cylinder of the present invention is produced by injection molding the molding material using a complete screw set injection molding machine, or by fully plasticizing the molding material using a screw set extruder, and then heating and compression molding the plasticized product in a predetermined mold. can be obtained. It is desirable to perform dust curing after molding in order to improve heat resistance and dimensional stability.

〔Effect of the invention〕

Since the piston for a hydraulic cylinder of the present invention has an improved crosslinking density of the molded product due to the resin composition, it has excellent heat resistance, such as a small reduction rate of heavy sound and a small decrease in strength under high temperature conditions.

〔Example〕

A dimethylene ether type resol having an Mn of 1000 and a composition ratio of dimethylene needle groups of 41 moles;
Mn is 800, composition ratio of dimethylene ether group is 20
A phenol resin having a ratio of 1:1 to a methylol type resol, which is a mortar, was mixed with glass fiber and others in the composition shown in Table 1, and then kneaded with hot rolls to obtain a molding material.

Comparative Example 1 Dimethylene ether type resol only k84 After mixing glass fiber and others with the composition shown in Table 1 as a fat component, the mixture was kneaded with hot rolls to obtain a molding material.

Comparative Example 2 Glass Ia, ? After mixing everything including a, the mixture was kneaded with hot rolls to obtain a molding material.

A complete comparison test of physical properties of -C and below was conducted for these molding materials. +11 specific gravity, (2) surface strength (Ronokuwell M scale), +3+ bending strength, (4) bending modulus, (5
) compressive strength, (6) coefficient of linear expansion, (7) thermal shock resistance, (
8) Dimensional stability For items (1) to (6), test pieces were obtained by injection molding,
Measured according to JISK6911. (7) and (8)
The term is the carino-piston model (6) shown in Figure 2.
was obtained by injection molding and evaluated by the following method.

Thermal shock resistance: Approximately 30
After heating at 0°C, cool with water.

This was repeated to evaluate thermal shock resistance.

Dimensional stability: A carry chisel piston model was immersed in brake fluid, air, grease, etc. at 150°C for 400 hours to evaluate its dimensional stability.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of a disc brake. FIG. 2 is a partially sectional front view of the carry/ξ-piston model of the embodiment.

Claims (1)

[Claims] Free phenol excluded number average molecular weight is 800-1200
, a solid resol type phenol resin in which the dimethylene ether group composition ratio of the phenol core-binding functional group is 40 to 60 mol%, and a number average molecular weight excluding free phenol of 600.
~1000, and the mixing ratio (weight ratio) of the solid resol type phenol resin in which the dimethylene ether group composition ratio of the phenol core-binding functional group is 0 to 20 mol% is 3:7 to 7:
100 parts by weight of phenolic resin and 100 parts by weight of filler
A piston for a hydraulic cylinder, characterized in that it is made of a molded body of a composition having a weight of 250 parts.