WO2014083978A1

WO2014083978A1 - Sliding member

Info

Publication number: WO2014083978A1
Application number: PCT/JP2013/078817
Authority: WO
Inventors: 吉田　健太郎; 小菅　敏行; 一秋池田; 康範長岡
Original assignee: 住友電工焼結合金株式会社; 住友電工ファインポリマー株式会社
Priority date: 2012-11-30
Filing date: 2013-10-24
Publication date: 2014-06-05
Also published as: DE112013005750T5; US20150307800A1; JP2014109292A; CN104813048A

Abstract

The purpose of the present invention is to provide a sliding member having sufficient abrasion resistance and excellent adhesion to a sintered compact, which is a matrix. The sliding member has a surface layer composed of a cross-linked fluororesin and a matrix that adheres closely to the surface layer. The matrix is a sintered compact having a true density ratio of 0.75 to 0.96. The matrix is composed of a material having higher thermal conductivity than a fluororesin, and the thickness of the surface layer is 1 to 300 μm.

Description

Sliding member

The present invention relates to a sliding member that uses a fluororesin for a sliding portion of a base material made of a sintered body and has excellent wear resistance and is suitably used for a non-lubricated bearing, an oil pump rotor, a cam ring, or the like.

Fluoropolymers are extremely stable chemically and have excellent low adhesion and low friction (low friction coefficient). Due to their properties, industrial products such as seals and packing, and consumer products such as cooking utensils. Widely used in various applications.

Furthermore, since a sliding member such as a non-lubricated bearing is desired to have a low coefficient of friction, and in many cases heat resistance and chemical stability are desired, a sliding member made of a fluororesin is also expected. However, since the sliding member is required to have excellent wear resistance, the fluororesin has a problem that it is easily worn. Therefore, it is difficult to use the sliding member unless the wear resistance is improved. there were.

Incidentally, a method of adding a filler to the fluororesin is known as a method for improving the abrasion resistance of the fluororesin. However, this method has a problem that excellent properties inherent to the fluororesin, such as low friction, are easily impaired by the filler. On the other hand, Patent Document 1 proposes a method of improving wear resistance by irradiating ionizing radiation to a fluororesin, and discloses a sliding member made of fluororesin irradiated with ionizing radiation. ing.

Fluorine resin was once thought to have reduced mechanical properties due to irradiation. However, the mechanical properties can be improved by irradiation under specific conditions. For example, in Patent Document 2, with respect to polytetrafluoroethylene (PTFE), in the absence of oxygen, a dose of about 1 kGy to 10 MGy of ionizing radiation such as an electron beam at a temperature above the crystal melting point, preferably around 340 ° C. , It is disclosed that the elongation at break and the deterioration of the breaking strength due to irradiation are suppressed, and that the rubber elasticity is developed with low crystallinity and the yield strength is improved.

On the other hand, the sliding member has a problem that it becomes more easily worn when the temperature of the surface of the member rises due to heat generated during sliding. On the other hand, a method is known in which a fluororesin is brought into close contact with a radiator made of a metal material as a base material to form a sliding member (Patent Document 3). This sliding member can prevent the temperature of the fluororesin from rising due to heat generated during sliding because heat is radiated from the radiator. However, in this case, in addition to the feature of the excellent abrasion resistance of the fluororesin, the feature of good adhesion between the fluororesin film and the substrate is required.

Japanese Patent No. 3666805 Japanese Patent No. 3317452 JP 2011-208802 A

By the way, in the said patent document 3, the fluororesin is coat | covered to the metal material as a base material. However, in consideration of more efficient heat dissipation, a case where a sintered body is used as the base material can be considered. There is no mention in Patent Document 3 of the case where a sintered body is used as the base material. In addition, unlike the surface of the metal material, the surface of the sintered body is not smooth and has an uneven state. Therefore, even if the fluorine film is formed under the same conditions, the adhesion state is different.

Therefore, an object of the present invention is to provide a sliding member having sufficient wear resistance and excellent adhesion to a sintered body of a base material.

As a result of intensive investigations to solve the above problems, the inventors have sufficient wear resistance and low wear resistance by setting the true density ratio of the sintered body used as the base material within a predetermined range. And it discovered that the adhesiveness with the sintered compact of a base material was improved.

That is, the gist of the present invention resides in the following [1] to [4].
[1] A surface layer composed of a cross-linked fluororesin and a base material in close contact with the surface layer, wherein the base material is a sintered body having a true density ratio of 0.75 to 0.96, Is a sliding member made of a material having a higher thermal conductivity than that of fluororesin and having a surface layer thickness of 1 to 300 μm.
[2] The sliding member according to [1], wherein the base material is an iron-based sintered body.
[3] The sliding member according to [1] or [2], wherein the thickness of the surface layer is 10 to 100 μm.
[4] Any one of [1] to [3], wherein the fluororesin is polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. The sliding member according to 1.

According to this invention, it is possible to obtain a sliding member having sufficient wear resistance and improved adhesion to the sintered base material.

The perspective view which shows notionally the thrust wear test (ring-on-disk type wear evaluation) performed in the Example and the comparative example.

Next, a mode for carrying out the present invention will be described. In addition, this invention is not limited to this form and an Example, As long as the meaning of this invention is not impaired, it can change into another form.

The sliding member according to the present invention is a member having a surface layer made of a cross-linked fluororesin and a base material in close contact with the surface layer.

The fluororesin is a fluorine-containing resin, and the fluororesin forming the surface layer is polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene in that it has excellent mechanical strength and chemical resistance. A copolymer (FEP), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or the like is preferable, and among them, PTFE having particularly excellent mechanical strength, chemical resistance, and heat resistance is more preferable. Further, other components may be included in the fluororesin as long as the gist of the present invention is not impaired. For example, PTFE may contain a trace amount of polymerized units based on a copolymerizable monomer such as perfluoro (alkyl vinyl ether), hexafluoropropylene, (perfluoroalkyl) ethylene, or chlorotrifluoroethylene. Moreover, the mixture of 2 or more types of fluororesins may be sufficient.

The surface layer made of this fluororesin must adhere to the base material. If the surface layer is peeled off and the base material is exposed, the function as a sliding member is not achieved.

For this reason, in order to improve the adhesion to the base material, the fluororesin and the base material are simultaneously irradiated with ionizing radiation. When the crosslinking is not performed or when the crosslinking is insufficient, the wear resistance is low, and the mechanical strength of the fluororesin is lowered, so that it cannot be used as a sliding member. Irradiation is usually performed at a dose of about 1 kGy to 1500 kGy.

The thickness of the surface layer made of the fluororesin is preferably 1 μm or more, and preferably 10 μm or more. When the thickness of the surface layer is too thin, the convex portion of the substrate protrudes from the surface layer, which is not preferable. On the other hand, the upper limit of the thickness of the surface layer is preferably 300 μm, and preferably 100 μm. If the thickness is too thick, heat generated on the surface of the member at the time of sliding becomes difficult to conduct to the base material, and it becomes difficult to prevent the temperature of the surface of the member from being increased, and wear resistance tends to be insufficient. By making it within these ranges, it is easier to effectively conduct heat generated on the sliding surface of the surface during sliding from the surface layer to the base material to dissipate heat, and increase the temperature of the surface of the sliding member. As a result, the wear resistance can be improved.

For this wear resistance, a thrust wear test (ring-on-disk wear evaluation) is often performed in which a cylinder is placed on a sample and rotated while pressure is applied to measure the degree of wear. In particular, in this test method, wear resistance and dynamic friction coefficient (μ) are often evaluated by a multiplier (limit PV value) of pressure (P) and rotational speed (V) at which rapid wear occurs. The sliding member of the present invention has a very high limit PV value, good sliding properties, excellent wear resistance and a low dynamic friction coefficient.

The base material is made of a sintered body having a higher thermal conductivity than the fluororesin. This sintered body is obtained by heating an aggregate of raw material powders at a temperature lower than the melting point. Specifically, the raw material powders are inserted into a product-shaped mold, and pressed and compressed at a predetermined pressure. Next, the obtained molded body is obtained by heating and sintering.

This raw material powder includes metal powder and non-metal powder. Examples of the metal powder include iron-based powder and non-ferrous metal powder. Examples of the iron-based powder include pure iron powder, iron-based alloy powder such as carbon steel, and iron-based partially sintered powder. Examples of the non-ferrous metal powder include metals such as copper, nickel, manganese, chromium, and aluminum, and powders of various alloys not containing iron. The non-metallic powder refers to a powder other than metal, such as graphite powder and ceramic powder.

The true density ratio of the base material, that is, the density of the sintered body constituting the base material with respect to the density of the metal itself constituting the base material is preferably 0.75 or more, and preferably 0.80 or more. If it is smaller than 0.75, the strength as a sliding member may be insufficient. On the other hand, the upper limit of the true density ratio is preferably 0.96 and preferably 0.89. If it is larger than 0.96, there will be less surface vacancies and there will be a tendency for the adhesion to the surface layer made of the fluororesin to be insufficient.

The base material has a larger volume than the surface layer made of the fluororesin. Moreover, in order to endure the heat | fever by the heat_generation | fever etc. at the time of sliding, the thing excellent in heat resistance is used. When the thermal conductivity of the sintered body constituting the base material is lower than that of the fluororesin on the surface layer, the heat generated on the surface of the member during sliding is difficult to dissipate and it is difficult to prevent the temperature of the member surface from rising. Further, when the volume of the base material is small, the heat capacity of the base material is small, so that similarly generated heat is difficult to dissipate and it is difficult to prevent the temperature of the member surface from rising.

The substrate preferably has a thermal conductivity of 0.001 Cal / ° C. · cm · second or more, preferably 0.01 Cal / ° C. · cm · second or more, and more preferably 0.1 Cal / ° C. · cm · second or more.
This base material is composed of a material having a higher thermal conductivity than that of the fluororesin, but the thermal conductivity of the fluororesin to which no filler is added is about 0.0005 Cal / ° C. · cm · sec (PTFE is 0.0005 Cal / ° C. · cm · second), if less than 0.001 Cal / ° C. · cm · second, heat transfer from the surface layer made of the fluororesin to the substrate may not be sufficiently generated. On the other hand, the higher the thermal conductivity of the substrate, the better.

As described above, the base material has a larger volume than the surface layer made of a fluororesin, and a larger volume is preferable for heat dissipation. Specifically, the value of the thermal conductivity of the substrate when expressed in Cal / ° C. · cm · second is X, and the value of (volume of the substrate) / (volume of the surface layer made of fluororesin) is Y. In this case, X · Y is preferably 0.005 or more, more preferably 0.05 or more, and still more preferably 0.5 or more.

By the way, examples of materials used as the base material and their thermal conductivity include the following. Iron: 0.18 Cal / ° C. · cm · sec. Aluminum: 0.53 Cal / ° C. · cm · sec. Ceramic (brick): 0.07 Cal / ° C. · cm · sec.

Next, the manufacturing process of the sliding member of the present invention will be described.
First, a base material having a predetermined shape is formed. This shape is flat, convex, hollow, cylindrical or tubular and has a sliding part on the outer surface of the cylinder, and is cylindrical and has a sliding part on the inner surface. And various other shapes.

Next, a fluororesin layer is formed by covering the surface, that is, the portion to be the sliding portion with a fluororesin. As a method of coating the fluororesin, a method of covering a fluororesin film, a method of powder coating, for example, a method of electrostatic coating of fluororesin powder, a method of spraying fluororesin powder, a fluororesin dispersion ( And a method in which the dispersion medium is dried and removed by applying a liquid in which a fluororesin powder is uniformly dispersed in a dispersion medium.

Above all, the method of applying a fluororesin dispersion is a preferable method in that a fluororesin layer having a uniform thickness can be easily formed. In the case of a fluororesin that is soluble in a solvent, a method in which a fluororesin solution is applied and the solvent is dried and removed may be employed, but this is not applicable to a resin that is insoluble in a solvent such as PTFE.

In the case of applying a fluororesin dispersion, water and an emulsifier, water and alcohol, water and acetone, or a mixed solvent of water, alcohol and acetone can be used as the dispersion medium. After applying the fluororesin dispersion, the dispersion medium is dried and removed by air drying or hot air drying. A film made of fluororesin powder is formed by drying and removing the dispersion medium.

After the coating film of the fluororesin is formed by the above-described coating or the like, baking is performed by heating to a melting point or higher of the fluororesin, the fluororesin powder is fused, and a fluororesin layer is formed. Firing is preferably performed in a temperature range of 350 to 400 ° C. It is also possible to remove the dispersion medium in the baking step without providing a drying step.

Subsequently, the surface of the fluororesin layer thus formed is irradiated with ionizing radiation to crosslink the fluororesin. When an appropriate combination of the fluororesin and the base material is selected, the adhesion between the fluororesin layer and the base material is improved during this crosslinking.

When crosslinking is performed, it is placed in an oxygen-free atmosphere, specifically in an atmosphere having an oxygen concentration of 1000 ppm or less, preferably 10 ppm or less, and a temperature range of the fluororesin crystal melting point to about 400 ° C., preferably 0 to 0 from the crystal melting point. Irradiating the surface of the fluororesin film with ionizing radiation while keeping the temperature range 30 ° C higher. The range of irradiation dose is usually 1 kGy to 1500 kGy, preferably 100 kGy to 1000 kGy.

At this time, the above baking and ionizing radiation irradiation may be performed simultaneously. If the temperature of the atmosphere is too low, the crosslinking reaction of the fluororesin is unlikely to occur, and if the atmosphere temperature is too high, especially when the temperature exceeds 400 ° C., thermal decomposition of the fluororesin is promoted and the material properties are deteriorated. Further, if the irradiation dose is less than 1 kGy, the crosslinking reaction is insufficient and improvement in characteristics cannot be expected, and if it exceeds 1500 kGy, decomposition of the fluororesin tends to occur, which is not preferable.

Examples of ionizing radiation used for crosslinking of fluororesins include electron beam, charged particle beam such as high energy ion beam, high energy electromagnetic wave such as gamma ray and X-ray, neutron beam, etc. An electron beam is preferably used because it is inexpensive and can provide a high-power electron beam and can easily control the degree of crosslinking.

The adhesion of the surface layer of the sliding member obtained by the above method can be measured by a cross cut test. This cross-cut test is a test method described in JIS-K-5400 (1998 edition). Specifically, 100 cross-cuts are scratched on the surface layer, and a tape is applied thereon. It is a test method that repeats the test of peeling after attaching and counting the number of grids remaining without being peeled. 99/100 or more means that 99 or more of 100 grids are not peeled off. Means it remains.

If the adhesion between the surface layer and the substrate is low, contact (adhesion) between the surface layer and the substrate tends to be insufficient, and problems such as voids are likely to occur especially during sliding. If the contact becomes insufficient and voids or the like are generated, heat generated in the surface layer is hardly conducted to the base material, and it is difficult to prevent a temperature rise on the surface of the member. As a result, the abrasion resistance tends to be insufficient, and therefore, it is preferable that the surface layer and the base material are not peeled at all by 100 times or more by a cross-cut test.

The sliding member of the present invention has a low coefficient of friction similar to that of a conventional sliding member made of a fluororesin, and further has wear resistance superior to that of the conventional sliding member. It is suitably used for non-lubricated bearings used in products such as those requiring high wear resistance.

The present invention will be described below with reference to examples. First, the evaluation method will be described.
<Evaluation method>
[Abrasion resistance measurement]
The abrasion resistance of the fluororesin coating was evaluated by a thrust abrasion test (ring-on-disk abrasion evaluation, Suzuki abrasion evaluation). Specifically, as shown in FIG. 1, a metal cylinder (mating shaft) is placed on the test sample, and a predetermined load (surface pressure: P) is applied to the test sample at a predetermined speed (rotational speed). : V) and measure the wear state of the test sample.
Using an S45C cylinder with an outer diameter / inner diameter of 11.5 / 7.4 as the counter shaft, wear was measured under dry (greaseless) lubrication conditions, the rotational speed (V) was kept constant at 1800 rpm, and surface pressure ( P) was changed, and the limit PV value (P · V value at which rapid wear occurs) was determined. When the limit PV value is 100 MPa · m / min or more, ○ (high), 1 to 100 MPa · m / min is indicated by Δ (medium), and less than 1 MPa · m / min is indicated by x (low). It was shown in 1. As for the slipping property, the dynamic friction coefficient (μ) is shown in Table 1 as ◯ (good) when less than 0.5, and x (bad) when 0.5 or more.

[Adhesion measurement]
The peel resistance of the fluororesin coating was measured by a cross cut test. Specifically, 100 samples of a grid-like scratch were made on the fluororesin coating of the sample, and the test of peeling after applying the tape was repeated, and the number of grids remaining without being peeled was counted. . In 10 repetition tests, the case where all 100 grids were peeled off was evaluated as x (low), and the case where 1 to 99 grids were stripped out of 100 was evaluated as △ (medium), 100 Table 1 shows the case where none of the pieces were peeled off.

[Strength measurement]
A tensile test was conducted based on JIS Z 2241. Table 1 shows the case where the tensile strength is 300 MPa or more as ◯ (high), and the measurement impossible as-. When the tensile strength is 300 MPa or more, it can be used as a structural member such as an automobile.

(Examples 1 to 3, Comparative Examples 1 to 6)
On an iron-based sintered material (2.0% Cu-0.8% C-Fe) having a density shown in Table 1 and having a thickness of 20 mm, a fluororesin dispersion (manufactured by Daikin Corporation: D10-FE) (Resin name: PTFE) was applied and dried, followed by baking in a nitrogen atmosphere at 380 ° C. for 10 minutes to coat a fluororesin film having a thickness of 15 μm on the iron-based sintered material. Thereafter, the sample was heated to 330 ° C. in a nitrogen atmosphere (oxygen concentration: 5 ppm), and irradiated with 300 kGy with an irradiation apparatus (Sagatron: acceleration voltage 1.13 MeV) manufactured by Nissin Electric Co., Ltd., to prepare a test sample.
The above tests were performed on the obtained test samples. The results are shown in Table 1.
In addition, as steel used in Comparative Example 2, SNCM630 steel was used, a fluororesin film was formed in the same manner as described above, and an electron beam irradiation treatment was performed.

The configurations of the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to the scope of these descriptions. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

Claims

Having a surface layer composed of a cross-linked fluororesin and a base material in close contact with the surface layer;
The base material is a sintered body having a true density ratio of 0.75 to 0.96,
The sliding member, wherein the base material is made of a material having a higher thermal conductivity than fluororesin, and the thickness of the surface layer is 1 to 300 μm.
The sliding member according to claim 1, wherein the base material is an iron-based sintered body.
The sliding member according to claim 1 or 2, wherein the surface layer has a thickness of 10 to 100 µm.
The fluororesin is at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. The sliding member according to any one of claims.