JP5018303B2 - Sliding member and sealing device - Google Patents

Description

  The present invention constitutes a sealing device for sealing a fluid pressure between members that reciprocate or rotate relatively in a fluid pressure device, particularly a fluid pressure device such as a hydraulic power steering valve device for an automobile. The present invention relates to a sliding member suitable for the above.

  The sealing device comprising the sliding member of the present invention is less likely to wear this relatively soft counterpart material even when the relative motion surface (sliding counterpart material) of the seal device is a light alloy material such as an aluminum alloy, and It is durable enough for practical use even under actual use conditions at high temperature and high pressure.

  A sealing ring having a substantially rectangular cross section is used as a sealing device in a valve device for a power steering for an automobile which is a fluid pressure device. This type of valve device is composed of a cylinder that is a housing and a rotating or reciprocating moving body (for example, a rotating body or a piston) fitted to the inner peripheral surface thereof, and a seal ring is usually provided on the moving body. Mounted in the annular groove. Therefore, the sealing device performs a sealing function while sliding with respect to the housing under hydraulic action.

  As a sealing device for a fluid pressure device, particularly a power steering valve device for an automobile, which is used under severe conditions, various reinforcing materials and fillers such as polytetrafluoroethylene (hereinafter referred to as PTFE) or modified PTFE are used. In general, a seal ring made from a molded body made of a fluororesin composition blended with is used. Fluororesin has excellent electrical and chemical properties (especially good resistance to oils such as mineral oil, which is a working fluid), non-adhesiveness, heat resistance and low friction properties, but wear resistance, Since physical properties such as creep properties are insufficient, an appropriate amount of glass fiber, carbon fiber, bronze powder, solid lubricant or the like is blended in order to improve it.

  The housing of general fluid pressure equipment is made of iron-based materials such as steel and castings. However, in the case of a fluid pressure device such as a power steering valve device for an automobile, the device can be reduced in size and weight by using a light alloy material and increasing the pressure of the working fluid. Therefore, the housing (cylinder) is usually made of an aluminum alloy, and the sealing device is required to exhibit sealing performance while sliding against the housing under a high fluid pressure.

  Since the housing made of aluminum alloy is relatively soft, for example, when a sealing device is made from a material in which reinforcing fibers such as glass fiber and carbon fiber are blended with PTFE, the housing which is a sliding counterpart material is often worn. It is known that problems such as leakage occur early. On the other hand, a seal device made from a composition in which PTFE is mixed with a filler such as molybdenum disulfide, graphite, and aromatic heat-resistant resin has little wear on the sliding material, but the seal ring itself constituting the seal device As wear increases, protrusion damage progresses, and problems such as leakage also occur at an early stage.

  The present applicant has previously described a technique for filling PTFE with carbon fiber and aromatic synthetic resin powder as a sealing device with improved pressure resistance particularly suitable for use in a power steering valve device for automobiles. 1-13494) and a technique (Patent No. 2864848) in which modified PTFE is filled with carbon fiber together with graphite so that it can be used at higher pressure.

  Also, as a sealing device used for the same purpose, modified PTFE is filled with carbon fiber and bronze powder of metal powder (Patent No. 3673314), and modified PTFE is filled with carbon fiber and calcium sulfate or zinc oxide whisker. A technique (Japanese Patent No. 3660123) is disclosed. Further, as a fluororesin composition containing a filler corresponding to high pressure, a technique (Patent No. 3877506) is also disclosed in which modified PTFE is filled with carbon fiber and a granular inorganic compound (calcium sulfate or zinc oxide) having a Mohs hardness of 4 or less. Yes.

Although the use is different, sliding members with improved lubricity, heat resistance, friction wear resistance and compression creep resistance such as bearings for precision equipment, PTFE zinc oxide whisker and carbon fiber, coke powder, graphite powder, There is also a proposal to prepare a composition containing a filler selected from bronze powder, copper powder, zinc oxide powder, talc, glass fiber, and the like (Japanese Patent Application Laid-Open No. 2004-2108395).
Japanese Examined Patent Publication No. 1-13494 Japanese Patent No. 2864848 Japanese Patent No. 3673314 Japanese Patent No. 3660123 Japanese Patent No. 3871506 JP 2004-210839 A

  In recent years, with the higher output and smaller size of the steering force in power steering devices for large vehicles and off-road vehicles, the temperature and pressure specifications for the seal device have become higher and higher than the conventional 120 ° C x 12 MPa. Specifications such as 135 ° C. × 13 MPa have been adopted.

  The conventional sealing device made of a filled fluororesin-based material with improved pressure resistance, wear resistance, and creep resistance as proposed in the above Patent Documents 1 to 5 is sufficient for a test condition of 120 ° C. × 12 MPa. However, when it was tested at 135 ° C. × 13 MPa, it was found that the durability performance was insufficient and the target of operation 200,000 times without leakage could not be achieved.

  The object of the present invention is to reduce the wear of the counterpart light alloy material and the wear of the sealing device itself to the same degree or more as the conventional sealing device made of fluororesin material with filler, and under high temperature and high pressure conditions. To provide a sealing device excellent in durability under high-temperature and high-pressure conditions that can prevent functional deterioration such as protrusion damage of the sealing device that easily occurs, and a sliding member suitable for manufacturing this sealing device. is there.

  The “extrusion damage” of a sealing device means that the sealing device (seal ring) installed in the groove is pushed out of the groove into the gap between two members (eg, cylinder and rotating body) that move relatively under high pressure. This refers to a phenomenon in which the protruding portion and the protruding portion are peeled off and damaged, and the sealing performance cannot be exhibited (see FIG. 3). It is considered that the creep resistance of the fluororesin material constituting the sealing device is affected. In FIG. 3, 12 is a seal ring fitted in the annular groove 26, 24 is a cylinder, and 32 is a piston. Reference numeral 36 denotes a damaged portion of the seal ring that protrudes into the gap 34, and fluid leakage occurs as shown in the figure as the protrusion damage progresses.

  As described above, sliding members in which various fillers (including fiber reinforcing materials) are blended alone or in combination in accordance with applications and purposes have been used for sealing devices. These fillers are selected from glass-based, metal-based, carbon-based, sulfide, oxide, nitride, heat-resistant organic material, etc. having a melting point of about 330 ° C. or higher, which is the melting point of fluororesin, and the form thereof Examples include fiber, particle, sphere, flake, and powder.

  Among these various fillers, the inventors have a high effect of improving the wear resistance and protrusion resistance of fluororesin at high pressure and high temperature, and 135 ° C. in a light alloy valve device for automotive power steering. An evaluation test was conducted to obtain a combination of fillers that can withstand 200,000 operations under the condition of × 13 MPa, and it was found that the above object can be achieved by blending a specific combination of fillers with PTFE or modified PTFE. It was.

  In one aspect, the present invention provides at least one fluorine resin 50 to 85 mass selected from polytetrafluoroethylene (PTFE) and a tetrafluoroethylene copolymer (modified PTFE) with 1 mass% or less of a fluorine-containing comonomer. %, Carbon fiber 5 to 10% by mass, copper-zinc alloy powder 5 to 20% by mass, and a zinc oxide whisker 5 to 20% by mass having a three-dimensional acicular crystal structure. It is a sliding member.

  From another aspect, the present invention is a sealing device for sealing a fluid pressure between relatively reciprocating and / or rotating members in a fluid pressure device, comprising the sliding member. It is the sealing device characterized by this. This fluid pressure device is preferably an automotive power steering valve device.

The findings obtained up to the completion of the present invention are outlined below.
When an aluminum alloy was used for the sliding material (cylinder) and an evaluation test was performed under the condition of 135 ° C. × 13 MPa, the material modified with carbon fiber and graphite in the modified PTFE proposed in Patent Document 2 is sliding. The wear of the counterpart cylinder was not so great, but the thickness of the seal device itself was greatly changed due to wear and protrusion damage, the durability was low, and the amount of leakage was large. On the other hand, as proposed in Patent Document 3, in the material in which the modified PTFE is filled with carbon fiber and bronze powder, wear of the cylinder, which is a sliding counterpart, is increased, and the amount of leakage is large.

  In contrast, when both graphite and bronze powder were blended with the modified PTFE, the wear of the cylinder was reduced, but the wear and sticking damage of the seal device was still quick and the durability was still insufficient. The same test was conducted using brass (copper-zinc alloy) powder, which is a higher-strength copper alloy in place of bronze, and as a result, wear and protrusion damage of the sealing device was reduced and the amount of leakage was reduced. However, the wear of the light alloy cylinder was slightly increased, and the target durability could not be obtained.

  From this result, by using brass powder with higher thermal conductivity than bronze (about twice), the frictional heat generated in the sealing device can be efficiently released to the aluminum alloy cylinder with higher thermal conductivity. It was speculated that by suppressing the heat storage of the sealing device to be low, a decrease in strength of the fluororesin, which is the main component of the sealing material, could be suppressed.

  According to the science chronology (2005 edition, page 401, edited by National Astronomical Observatory), alloys such as brass and bronze increase in thermal conductivity as the temperature rises, but simple metals such as copper, zinc, tin, and nickel When the temperature is high, the thermal conductivity decreases. Therefore, when a test similar to the above was carried out using zinc powder, which is a raw material of brass (tin-zinc alloy) and has a thermal conductivity at 0 ° C. slightly higher than that of brass instead of brass powder, aluminum was used. The wear of both the alloy cylinder and the seal device was large (about 1.5 times that of brass), and the leakage amount was inferior to that of brass. Also from this, it is presumed that blending of powder having high thermal conductivity at high temperature is suitable as a blending material for fluororesin.

  Heat-resistant synthetic resins, graphite, nitrides, sulfides, oxides, etc. with solid lubricants or similar effects to prevent wear of mating light alloy housing materials with fluororesin reinforcing fillers (carbon fibers, etc.) It is known that attacking the opponent's face can be mitigated by filling the proper amount.

  In the above evaluation test, graphite, which is a typical solid lubricant, was used as such a material. However, as described above, not only the wear of the counterpart material is not sufficiently improved by graphite, but also the sealing device. There was also a tendency for the wear and protrusion damage to increase.

  As a result of further studies, the inventors have found that when an appropriate amount of zinc oxide whisker having a three-dimensional needle crystal structure (hereinafter referred to as “three-dimensional zinc oxide whisker”) is blended instead of graphite, the counterpart material and the sealing device are combined. It was found that both wear and protrusion damage can be significantly reduced.

  The three-dimensional zinc oxide whisker is a zinc oxide whisker having a unique three-dimensional needle-like crystal structure in which needle-like crystals extend in all directions from the center of a regular tetrahedron toward each vertex, like a tetrapot. Ordinary whiskers are one-dimensional linear and tend to cause anisotropy when compounded as a reinforcing material in a molded product, whereas needle crystals have a three-dimensional structure extending in a tetrapot shape. Zinc oxide whiskers exhibit a needle-like reinforcing effect without imparting anisotropy. In addition, since it has slipperiness due to the smoothness of the crystal surface, good thermal conductivity, and the Mohs hardness is relatively soft at 4, the strength of the fluororesin does not increase the wear of the mating material and the sealing device itself. It is speculated that it can be increased.

  That is, in the sliding member of the present invention, brass powder, which is a copper alloy having high heat conductivity and high strength at high temperature, in addition to carbon fiber having a high reinforcing effect, which has been conventionally used as a filler for fluororesin. In combination with three-dimensional zinc oxide whisker, the strength of the fluororesin is prevented from lowering when sliding at high temperature and pressure, and the friction and wear between the sliding mating member and the seal device are reduced. Therefore, it is possible to realize a sealing device with excellent durability.

  The use of a three-dimensional zinc oxide whisker as zinc oxide to be blended in a fluorine resin used for a sliding member is also described in Patent Document 6, but in Patent Document 6, copper powder and bronze are used as metal powder. Only the powder is listed. However, when copper powder or bronze powder is used instead of brass powder, high durability as achieved in the present invention cannot be obtained under high temperature and high pressure fluid pressure conditions. By the way, in the material proposed by Patent Document 6 in which PTFE is filled with carbon fiber, three-dimensional zinc oxide whisker and bronze powder, the durability is different from that using brass, but it is a cylinder that is a sliding counterpart. Wear, sealing device wear, and overhang damage were all large, and the amount of leakage was large.

  The sliding member and the sealing device of the present invention have low aggression against the mating material (wear of the mating material) even when sliding against a mating material made of a relatively soft light alloy, and the sealing device itself is resistant to damage. It has excellent wear resistance and high durability that satisfies the performance required for a valve device of a power steering because it suppresses protrusion damage of fluororesin when sliding under high temperature and high pressure fluid pressure conditions.

  Since the sliding member and the sealing device of the present invention show superior pressure resistance and wear resistance not only against soft light metal but also against other materials made of general iron-based materials, It is not limited to a valve device for hydraulic power steering for automobiles used at high temperatures and high pressures, but is useful as a sealing device for fluid pressure equipment in general and a sliding member for light metal materials.

  Further, the sliding member and the sealing device of the present invention are not limited to a sealing device having a substantially rectangular cross section, but a sealing device combined with a sealing device having a lip-shaped cross section such as an oil seal or a rubber ring having only a contact surface made of a fluororesin. The present invention can also be applied as a seal ring for a device, a fluid pressure cylinder including a light alloy or other fluid pressure devices, or a bearing member. Needless to say, the sealing device of the present invention can be applied not only to rotation but also to reciprocating motion or motion combining rotation and reciprocating motion.

  The main material of the sliding member according to the present invention is a fluororesin. The fluororesin is either a tetrafluoroethylene copolymer (modified PTFE) of polytetrafluoroethylene (PTFE), which is a homopolymer of tetrafluoroethylene, and a fluorine-containing comonomer of 1% by mass or less, or its Both can be used.

The fluorine-containing comonomer used for the synthesis of the modified PTFE can naturally be copolymerized with tetrafluoroethylene. Examples of such a fluorine-containing comonomer include a compound represented by the general formula CFX═CF ₂ . Here, X is preferably a fluorine-containing alkyl group or alkyloxy group having 6 or less carbon atoms, or a halogen other than fluorine. Examples of such comonomers include perfluoroalkenes having 3 to 6 carbon atoms (for example, hexafluoropropylene), perfluoro (alkyl vinyl ethers) having a perfluoroalkyl group having 1 to 6 carbon atoms [for example, perfluoro ( Propyl vinyl ether)] and chlorotrifluoroethylene.

  The amount of the comonomer in the modified PTFE is a small amount of 1% by mass or less. Therefore, the modified PTFE substantially maintains the basic performance of PTFE and has similar thermal properties. However, when the molecular structure of the modified portion protrudes from the molecular structure of PTFE, the protrusions catch each other, so that there is less slip between molecules compared to PTFE, and the strength, elastic modulus, and creep resistance are improved.

  If the amount of comonomer exceeds 1% by mass, the slidability of PTFE is remarkably impaired and fluidity is obtained at a temperature higher than the melting point. Therefore, a compression-molded material similar to PTFE, which will be described later, exceeds the melting point. It becomes difficult to produce a material by a so-called free baking method that is heated and fired. The amount of comonomer is preferably 0.01 to 0.5% by weight. Such modified PTFE is commercially available. An example of a commercially available product is Teflon (registered trademark) 70J manufactured by Mitsui DuPont Fluorochemicals.

  Both PTFE and modified PTFE are formed by compression molding the raw material powder using a mold, and then heating and baking at about 330 to 390 ° C., so-called free baking and then cooling the molded body. It is processed into various products by cutting. In PTFE and modified PTFE, the resin itself is thermoplastic, but since it does not become a melt having fluidity even when heated to the above temperature, ordinary molding methods for thermoplastic resins such as injection molding cannot be applied. .

  The PTFE and / or modified PTFE powder used as the fluororesin in the present invention has an average particle size of 100 μm or less, preferably 5 to 100 μm, more preferably 10 to 50 μm, from the viewpoint of uniform mixing with the filler to be blended. Good thing. The resin powder may be synthesized directly in powder form by employing suspension polymerization or emulsion polymerization, or may be obtained by pulverizing a bulk polymer.

  Carbon fiber has been conventionally blended in fluororesin-based sliding members in order to improve the wear resistance and compression creep characteristics of the fluororesin. In the present invention, both pitch-based and PAN-based carbon fibers can be used. Carbonized fibers fired at about 1000 ° C. are preferable to fibers that are at least partially graphitized by raising the firing temperature to 2000 ° C. or more because wear of the sliding counterpart material is reduced.

  Although carbon fibers have different diameters and lengths, various types are commercially available, but those having an average diameter of 5 to 15 μm and an average length of 50 to 1000 μm are preferable, with an average diameter of 8 to 12 μm and an average length of 100 to 500 μm. More preferred.

  In the present invention, as a metal powder, a copper-zinc alloy powder represented by brass is used instead of a conventional bronze powder or copper powder. Brass is an alloy having copper and zinc as main components and a zinc content of 10 to 40% by mass. In addition to copper and zinc, trace amounts of iron and lead may be included. In general, a copper-zinc alloy having a zinc content of 30 to 40% by mass is called brass and is widely used. In the present invention, for example, a zinc content of around 30% by mass can be advantageously used.

  Further, a copper-zinc alloy powder called Western silver made of Ni: 9 to 19%, Cu: 54 to 75% in mass%, and zinc: used instead of brass powder or together with brass powder. You can also

  Brass and other copper-zinc alloys are used in powder form. As the powder, in addition to a powder formed by an atomizing method or the like, a foil piece powder formed by a quenching roll method or a powder formed by pulverization can be used. From the viewpoint of uniform dispersibility in the composition, a substantially spherical powder obtained by the gas atomization method is advantageous, but other powders can also be used. It is preferable to use powder that has been sieved to 250 mesh pass and 500 mesh on with a Tyler sieve.

  As described above, the three-dimensional zinc oxide whisker is a needle-like zinc oxide crystal having a unique three-dimensional shape in which a needle-like crystal extends from the center of a regular tetrahedron to each vertex in a tetrapot shape. As described in Patent Document 6, for example, the three-dimensional zinc oxide whisker can be manufactured by heat-treating metal zinc powder having an oxide film formed on the surface in an atmosphere containing oxygen. The length of each acicular portion extending in the four directions from the center is preferably 3 to 200 μm, and the diameter of the tapered acicular portion is preferably 0.1 to 10 μm at the base (center position).

  Three-dimensional zinc oxide whisker improves the creep properties and wear resistance of PTFE, and when used in combination with carbon fiber, it exhibits the effect of a solid lubricant, and further improves surface smoothness. Contributes to the mitigation of the aggressiveness of carbon fiber or copper-zinc alloy powder to the mating housing material. In addition, 3D zinc oxide whiskers can be used for final molded body lubrication, wear resistance, compression creep resistance, etc. It has the feature that there is almost no influence on the physical properties of

  The surface of the three-dimensional zinc oxide whisker may be treated with a silane-based, chromium, or titanium-based coupling agent. In particular, a three-dimensional zinc oxide whisker surface-treated with a silane coupling agent is preferable because dispersibility in a fluororesin is improved. As an example of a commercial product of the surface-treated three-dimensional zinc oxide whisker, Panatetra (registered trademark) manufactured by Amtec Corporation can be given.

  In the present invention, each of the above components is, in mass%, fluorine resin (PTFE and / or modified PTFE) 50 to 85%, carbon fiber 5 to 10%, copper-zinc alloy powder 5 to 20%, three-dimensional zinc oxide. It mix | blends in the ratio of 5-20% of whisker.

  If the carbon fiber content is less than 5% by mass, wear resistance cannot be expected. If the carbon fiber content exceeds 10% by mass, the aggressiveness to a soft mating material such as an aluminum alloy (abrasion of the mating material) increases. If the amount of the copper-zinc alloy powder such as brass is less than 5% by mass, pressure resistance and protrusion damage resistance cannot be expected, and if it exceeds 20% by mass, the wear of the mating material increases. If the three-dimensional zinc oxide whisker is less than 5% by mass, the lubrication effect cannot be expected, and if it exceeds 20% by mass, the wear of the sealing device increases and the balance with other fillers deteriorates. It is done.

  A preferable blending ratio is, by mass%, 85 to 50% by mass of a fluorine resin, 6 to 10% of carbon fibers, 5 to 20% of a copper-zinc alloy powder, and 5 to 20% of a three-dimensional zinc oxide whisker. In addition, the three-dimensional zinc oxide whisker has a high specific gravity of about 5.8, and is effective as a solid lubricant that mitigates the attack of the copper-zinc alloy powder such as carbon fiber and brass against the counterpart material. In order to make full use, from the balance with other fillers, the blending amount of the three-dimensional zinc oxide whisker is equal to or more than the carbon fiber and within the total amount of the carbon fiber and the copper-zinc alloy powder. It is preferable.

  In the present invention, the above-mentioned fillers are blended in a well-balanced manner, compressive strength / thermal conductivity by copper-zinc alloy powder such as brass, wear resistance / creep resistance by carbon fiber, and resistance by three-dimensional zinc oxide whisker. Creep characteristics, thermal conductivity, friction characteristics, lubrication effects, etc. complement each other, and the effect is demonstrated. The durability of sliding members, especially sealing devices, at high temperatures and high pressures is significantly improved, and their practical use is improved. It is possible.

  After each filler is added to the powdered fluororesin, it is uniformly mixed with a suitable mixer such as a Henschel mixer to obtain a powder mixture that can be called a filled fluororesin material composition. In the powder mixture, one or two or more kinds of additives such as a solid lubricant, an oxidation stabilizer, a heat stabilizer, a weather stabilizer, a flame retardant, and a pigment are added without departing from the object of the present invention. You may contain.

  Further, in order to improve the fluidity of this powder mixture and improve the handleability such as filling into the mold, the fluororesin has an average particle size of 250 to 250 by a granulation method conventionally performed with a fluororesin. It is also good as a granulated powder of 800 μm.

  The powder mixture can be molded by a compression molding method or an extrusion molding method, similarly to the conventional molding of a fluororesin. For example, a primary molded body is obtained by preforming by compression molding and heating the resulting preform to a temperature not lower than the melting point of the fluororesin (usually 330 to 390 ° C.) and firing. After cooling, the primary molded body is processed into a desired sliding member or seal device shape by cutting or the like using the primary molded body as a processing material.

In the examples, the following materials were used.
PTFE: Teflon (registered trademark) 7-J (average particle size: 35 μm) manufactured by Mitsui DuPont Fluorochemical Co., Ltd.
Modified PTFE: Teflon (registered trademark) 70-J (average particle size 35 μm) manufactured by the same company,
Carbon fiber: Type M-101S (average fiber diameter 14.5 μm, average length 120 μm) manufactured by Kureha Chemical Industry Co., Ltd.
Graphite: Synthetic graphite powder (average particle size 18 μm) manufactured by Oriental Sangyo Co., Ltd.
Brass powder: Bra-At-100 (Cu70-Zn30) manufactured by Fukuda Metal Foil Industry Co., Ltd.
Bronze powder: Bro-At-100 (Cu90-Sn10) manufactured by the same company,
Zinc oxide whisker: Silane coupling agent surface treatment type three-dimensional zinc oxide whisker manufactured by Amtec Co., Ltd .: Panatetra (registered trademark) (needle base diameter: 0.2 to 3 μm, needle part length: 2 50 μm).

  The materials selected from the above were blended in the proportions shown in Table 1, and mixed uniformly with a Henschel mixer to obtain a filled fluororesin composition. This was compression molded under a pressure of 70 MPa, and the obtained preform was fired at 370 ° C. for 2 hours to obtain a sleeve-like molded body having an outer diameter of 45 mm, an inner diameter of 30 mm, and a height of 60 mm.

  A ring-shaped main body 12 having a substantially rectangular cross-sectional shape shown in FIG. The seal ring 12 has an outer diameter of 36.0 mm, an inner diameter of 33.0 mm, and a width of 1.8 mm. The seal ring 15 in FIG. 1B is a seal ring that does not have a chamfered corner (R chamfering or C chamfering), and has a cross-sectional shape before chamfering the seal ring 12.

The seal ring 12 obtained in this way is provided on the outer peripheral surface of the rotary body 22 of the hydraulic operation test apparatus 20 which is composed of the rotary body 22 and the cylinder 24 shown in FIG. The sample was mounted in the annular groove 26 and subjected to 200,000 rotation sliding tests. The material of the cylinder 24 that is the sliding partner of the seal ring was JISH5302 aluminum alloy die-cast ADC-5. To maintain the temperature of the test equipment by applying oil temperature of 135 ° C and pressure of 12.7 MPa from the A port on one side of the equipment circumference, a band heater is attached to the outer circumference of the test equipment, and a sensor embedded in the cylinder section is used. The temperature in the cylinder was maintained. The rotation speed was 60 min ⁻¹ .

  Since the friction / wear characteristics of the fluororesin-based material with filler are generally evaluated in a dry state, a friction effect is obtained by the relative motion surface of PTFE-PTFE by transfer of the fluororesin material to the mating surface. However, in a sealing device of a fluid pressure device such as a hydraulic device, a PTFE transfer film is difficult to be formed by a fluid such as oil. It is considered that the seal performance cannot be evaluated correctly.

  In this test, the hydraulic oil for power steering pressurized from the A port is sealed (sealed) by the ring-shaped seal ring 12, but as the number of rotations increases, the seal ring 12 is subject to its own wear and cylinder. The thickness is reduced by repeated protrusion (see FIG. 3) of the gap 24 between the rotor 24 and the rotating body 22 (see FIG. 3) and peeling (protrusion damage) of the protruding portion, and wear due to the light alloy cylinder 24 and the like. The hydraulic oil leaks from the sealing device 10 to the adjacent B and C ports. Collect the leaked hydraulic fluid in a container.

  Measure the amount of leakage from the B and C ports at regular intervals. If the amount of leakage exceeds 100 ml / min before the target number of 200,000, the test is interrupted at that point as the use limit. The number of rotations was regarded as the durability number, and the amount of leakage until that time was measured. About what achieved 200,000 endurance times, the leak amount at that time was measured. In addition, both the one where the test was interrupted and the one where 200,000 times were achieved showed the wear amount of the sliding portion between the thickness dimension of the seal ring 12 and the seal ring of the counterpart light alloy cylinder 24 after the test was completed. It was measured. The amount of wear and protrusion damage of the seal ring 12 was evaluated by the change (%) in the thickness dimension of the seal ring.

  About the sealing apparatus shape | molded from the fluorine resin with a filler of the mixing | blending of an Example shown in the following, an Example, a comparative example, and a prior art example, comparative evaluation was performed on the same test apparatus and conditions. These comparative evaluations are also shown in Table 1. In the following formulations, all percentages are% by mass.

(Examples 1-7)
In Examples 1 to 3, PTFE was used, and in Examples 4 to 6, modified PTFE was used, and a sealing device was produced from a filled fluororesin composition having the following composition.

Example 1: A composition comprising 60% PTFE and 10% carbon fiber, 15% brass powder and 15% zinc oxide whisker;
Example 2: A composition containing PTFE 55%, carbon fiber 10%, brass powder 20%, and zinc oxide whisker 15%;
Example 3: A composition containing 10% carbon fiber, 20% brass powder and 20% zinc oxide whisker in 50% PTFE;
Example 4: Composition obtained by blending 80% modified PTFE with 5% carbon fiber, 5% brass powder, and 10% zinc oxide whisker;
Example 5: A composition comprising 75% modified PTFE and 5% carbon fiber, 10% brass powder and 10% zinc oxide whisker;
Example 6: A composition in which 10% carbon fiber, 10% brass powder and 10% zinc oxide whisker are blended with 70% modified PTFE;
Example 7: A composition obtained by blending 10% carbon fiber, 15% brass powder and 10% zinc oxide whisker with 65% modified PTFE.

(Comparative Examples 1-6)
Comparative Example 1: A composition containing a large amount of brass powder in which 50% of modified PTFE is blended with 10% carbon fiber, 30% brass powder and 10% zinc oxide whisker;
Comparative Example 2: A composition containing a large amount of zinc oxide whisker in which PTFE 55% is blended with carbon fiber 10%, brass powder 10%, and zinc oxide whisker 25%.

Comparative Example 3: A composition containing a large amount of carbon fiber in which PTFE 65% is blended with 15% carbon fiber, 10% brass powder, and zinc oxide whisker 10.
Comparative Example 4: A composition in which brass powder is added to a conventional composition in which 5% carbon fiber, 10% graphite, and 10% brass powder are blended with 75% modified PTFE.

Comparative Example 5: A composition obtained by adding bronze powder to a conventional composition in which 5% carbon fiber, 10% graphite, and 10% bronze powder were blended with 75% modified PTFE.
Comparative Example 6: A composition in which zinc powder is added to a conventional composition in which 5% carbon fiber, 10% graphite, and 10% zinc powder are blended with 75% modified PTFE.

(Conventional example)
Conventional Example 1: A composition proposed in Patent Document 2 in which 85% modified PTFE is blended with 5% carbon fiber and 10% graphite.
Conventional Example 2: A composition proposed in Patent Document 3 in which 60% modified PTFE is blended with 10% carbon fiber and 30% bronze powder.

  Conventional Example 3: A composition proposed in Patent Document 6 in which 60% PTFE is mixed with 10% carbon fiber, 15% zinc oxide whisker and 15% bronze powder.

  As can be seen from Table 1, all of the sealing devices produced from the filled fluororesin composition according to the present invention can be rotated and rotated 200,000 times, and the seal ring has a thickness change of 45 after the test. % Or less, the wear of the sealing device and the protrusion damage are small, and the cylinder wear amount is 40 μm or less, and the attacking property to the cylinder is low. Therefore, the amount of leakage after 200,000 rotations / sliding was as good as 100 cc / min or less, and the durability was very excellent even under high-temperature and high-pressure fluid pressure conditions of 135 ° C. × about 13 MPa.

  On the other hand, each of the filled fluororesin compositions shown in the conventional examples and comparative examples has a leak rate of 100 cc / min or more before reaching the target number of 200,000 times, and is durable under high-temperature and high-pressure fluid pressure conditions. Was insufficient.

1A and 1B are cross-sectional views of a seal ring constituting a seal device according to the present invention. It is explanatory drawing of the apparatus used by the rotation sliding test in the Example of this invention. It is a typical explanatory view showing the situation of overhang damage.

Explanation of symbols

10: sealing device, 12, 15: sealing ring, 20: valve device, 22: rotating body, 24: cylinder, 26: annular groove, 32: piston, 34: gap, 36: protruding state, A: pressure port, B, C: Leak check port

Claims (3)

  50 to 85% by mass of at least one fluorine resin selected from a tetrafluoroethylene copolymer with polytetrafluoroethylene and 1% by mass or less of a fluorine-containing comonomer, 5 to 10% by mass of carbon fiber, and a copper-zinc alloy A sliding member produced from a molded body of a composition comprising 5 to 20% by mass of powder and 5 to 20% by mass of zinc oxide whisker having a three-dimensional acicular crystal structure.   A sealing device for sealing a fluid pressure between members that reciprocate and / or rotate relatively in a fluid pressure device, comprising the sliding member according to claim 1. .   The sealing device according to claim 2, wherein the fluid pressure device is a valve device of an automotive power steering.

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