KR100479797B1 - Seals for Fluoropolymer Composition and Swivel Joints - Google Patents

Abstract

The present invention relates to 30-50% by weight light alloy powder, 0.5-5% by weight inorganic fibers, 1-5% by weight solid lubricant and / or hard powder, and residual proportions of tetrafluoroethylene and perfluoro (alkyl Fluororesin composition comprising a copolymer with vinyl ether), and a seal for a swivel joint prepared from the composition. The fluororesin composition of the present invention exhibits excellent wear resistance and creep resistance, in particular compression creep resistance, while maintaining excellent tensile strength and elongation rate, and thus, wear, bearing and other heavy loads of hydraulic and pneumatic cylinders. It is suitable as a sliding member, a fixing member, etc. which are added especially as a seal for a swivel joint.

Description

Fluorine Resin Composition and Seal for Swivel Joint

The present invention relates to a fluororesin composition. More specifically, the present invention relates to a fluororesin composition having improved abrasion resistance and creep resistance and a seal for a swivel joint made from the composition.

3 is a partial cross-sectional view of a swivel joint, such as a power shovel, wherein reference numeral 1 is a cylindrical housing, and reference numeral 2 is a rotating shaft which is in close contact with the inner wall 11 of the housing 1 to rotate. to be. Seal ring-shaped grooves 12 are formed on the inner wall 11 of the housing 1 at regular intervals, and in the grooves 12, ring-shaped elastic bodies 13 made of crosslinked elastomers and A ring-shaped fluororesin seal 14 is laminated thereon. The housing 1 and the rotating shaft 2 are hermetically sealed by the fluororesin seal 14.

When conventionally known fluororesins or compositions thereof are used to make the fluororesin seal 14, the sealing performance deteriorates and oil leakage may occur between the housing 1 and the rotating shaft 2 by the use of a short time. have. The fluororesin seal 14 is uniformly pressed against the rotating shaft 2 by the elastic body 13, and a high pressure P is applied to the interface between the housing 1 and the rotating shaft 2 while the swivel joint is operating. All. As a result of the researches of the present inventors, the fluororesin seal 14 is worn or deformed in contact with the rotating shaft 2 when it is operated for a long time due to external force applied during the swivel joint operation, and a part of the seal is the housing 1 and the rotating shaft. Invading between (2), it was found that the so-called extrusion phenomenon occurred as shown in Fig. 4, resulting in the oil leak mentioned above.

In-depth study newly revealed that a seal made of a fluororesin composition having improved abrasion resistance and creep resistance exhibits high performance as the seal 14 for the swivel joint.

An object of the present invention is to provide a fluororesin composition having improved wear resistance and creep resistance, and a seal for a swivel joint prepared from the composition.

The present invention provides a fluororesin composition and a seal for a swivel joint made of the composition as follows.

(1) 30-50 wt.% Light alloy alloy powder, 0.5-5 wt.% Inorganic fiber, 1-5 wt.% Solid lubricant and / or hard powder, and residual proportions of tetrafluoroethylene and perfluoro (alkyl Fluorine resin composition comprising a copolymer with vinyl ether).

When the composition of the present invention comprises any constituent in addition to the four constituents, the "remaining ratio" of the above-mentioned copolymer is a ratio including any constituent.

(2) The fluororesin composition of (1), wherein the copolymer of tetrafluoroethylene and perfluoro (alkylvinyl ether) comprises perfluoro (alkylvinyl ether) in a ratio of 0.1-10% by weight.

(3) The fluororesin composition of the above (1) or (2), comprising a solid lubricant and a hard powder in a ratio of 0.1-2 parts by weight of hard powder per 1 part by weight of solid lubricant.

(4) The fluororesin composition of any of the above (1) or (3), wherein the hard powder has a MOS hardness of 5 or more.

(5) The fluororesin composition of (4), wherein the hard powder is a composite oxide containing cobalt oxide and aluminum oxide.

(6) The fluororesin composition of any of the above (1) to (3), wherein the solid lubricant is a molybdenum compound.

(7) The fluororesin composition of (1) or (2), wherein the light alloy powder is bronze powder.

(8) The fluorine resin composition of (1) or (2), wherein the inorganic fiber is carbon fiber.

(9) A swivel joint seal made of the fluororesin composition as defined in any one of (1) to (8) above.

The above-mentioned purpose is to use a copolymer of tetrafluoroethylene and perfluoro (alkylvinyl ether) (hereinafter abbreviated as PFA modified PTFE) as the fluororesin, and the above-mentioned large amount of light alloy powder, a small amount By the addition of inorganic fibers and solid lubricants and / or hard powders. The addition of large amounts of hard alloy alloy powder alone to the PFA modified PTFE can significantly improve the physical properties, but adding the powder in an excessive amount lowers the mechanical properties of the PFA modified PTFE composition, specifically the tensile strength and elongation. When the content of the light alloy is set within the above-mentioned range, and addition of a small amount of inorganic fibers and solid lubricants and / or hard powders, wear resistance and creep resistance can be improved without degrading the mechanical properties of the PFA modified PTFE composition. have. Adding small amounts of inorganic fibers is effective to improve the overall physical properties of the composition. Solid lubricants serve to reduce the wear and creep properties of articles obtained from the composition by imparting lubricity to the composition, and hard powders are effective in improving the hardness of the composition.

As the PFA modified PTFE, for example, a copolymer of at least one perfluoro (alkylvinyl ether) component represented by the following formula (1) with tetrafluoroethylene may be used:

[Formula 1]

RO-CF = CF ₂

Wherein R is perfluoroalkyl.

Preferred examples of perfluoro (alkylvinyl ether) include three R compounds such as perfluoro (propylvinyl ether), perfluoro (butylvinyl ether) and the like. Or perfluoroalkyl having four carbon atoms. Preferred examples of PFA modified PTFE include copolymers comprising perfluoro (alkylvinyl ether) in a ratio of 0.1-10% by weight, specifically 0.5-5% by weight.

Examples of the hard copper alloy powder include various copper alloy powders such as bronze, brass, phosphor bronze, German silver, and soft bronze. Particularly, bronze powder is preferred in consideration of load resistance deformation.

The inorganic fibers can be used as long as the tensile strength is not very low. Examples of such inorganic fibers include glass fibers such as soda glass fibers, alkali free glass fibers, silica glass fibers, and the like; Ceramic fibers such as rock wool fibers; Metal fibers such as steel fibers, iron fibers, aluminum fibers, nickel fibers, copper fibers and the like; Whiskers, such as potassium titanate, carbon fiber, etc. are mentioned. Of these, glass fibers such as alkali-free glass fibers and carbon fibers are preferable, and carbon fibers are particularly preferable because they significantly improve the load resistance deformation of the composition of the present invention.

In general, inorganic fibers have a tensile strength of at least 200 kgf / mm ² , in particular at least 300 kgf / mm ² , in a single fiber, and preferably have an average fiber diameter of at most 50 μm, in particular at most 10 μm. The average length of the inorganic fibers is 10-1000 μm, in particular 50-150 μm, and their aspect ratio is 1-80, in particular 5-50, more specifically 5-15. Carbon fibers have an average fiber diameter of 30 μm or less, in particular 10-20 μm, an average length of 0.05-2 mm, in particular 0.1-0.8 mm and an aspect ratio of 1-80, in particular 5-50. In the present invention, in order to further improve creep resistance, it is preferable to use inorganic fibers made of glass fibers and carbon fibers, and various kinds of carbon fibers can be used.

Examples of solid lubricants include those generally known as solid lubricants, such as graphite, mica, soapstone, zincated (zinc oxide), molybdenum-based compounds and other inorganic compounds. It is preferable to use a molybdenum type compound among these. Examples of molybdenum-based compounds include molybdenum disulfides and organic molybdenum compounds, for example, molybdenum disulfides are natural hexagonal and trigonal. Hexagonal crystals include high grade concrete for lubrication with a purity of 99% or more obtained from minerals produced in the United States, Chile, Canada, and other countries, and iron alloys with a purity of about 85%. Other molybdenum disulfides can be exemplified by synthetic tetragonal materials, which are obtained by heating the tetragonal materials. The organic molybdenum compound may be, for example, molybdenum dialkyl diphosphate, molybdenum dialkyl dithiocarbamate and the like.

It is preferred that the hard powder has a mohs hardness of at least about 5, in particular at least 6. Examples of hard powders include various inorganic powders commonly known as abrasives, such as composite oxides including aluminium, cobalt oxide and aluminum oxide, alumina, silicon carbide, boron carbide, natural or synthetic diamonds, emeralds, spinels, garnets, flints and the like. Can be mentioned. Examples of the composite oxide composed of cobalt oxide and aluminum oxide include 4CoO-3Al ₂ O ₃ , CoO-nAl ₂ O ₃ (1 ≦ n ≦ 5), and include cobalt oxide, aluminum oxide and at least one other inorganic oxide, For example, the composite oxide including chromium oxide and magnesium oxide may be CoO-Al ₂ O ₃ -Cr ₂ O ₃ , CoO-Al ₂ O ₃ -MgO, or the like. Various cobalt blues are preferred as examples of complex oxides.

The above-mentioned copper alloys, solid lubricants and hard powders usable in the present invention are used in the fine powder state or the ultra fine powder state. These pass completely through the 100 mesh (particle size) Tyler standard screen, in particular through the same screen of 200 mesh and through the same screen of 300 mesh completely.

The hard metal powder is included in the proportion of 30-50% by weight of the fluororesin composition. If the content is less than 30% by weight, the creep resistance cannot be significantly improved, while if it is more than 50% by weight, the tensile strength and the elongation may be degraded. The content of the hard alloy powder is preferably 35-45% by weight.

The inorganic fiber is added at a ratio of 0.5-5% by weight of the fluororesin composition. When the content is less than 0.5% by weight, the wear resistance cannot be significantly improved, while when the content is more than 5% by weight, the elongation is reduced to a problem. The content of the inorganic fibers is preferably 1-4% by weight, in particular 1-3% by weight.

In the present invention, the solid lubricant and the hard powder are preferably used together at the same time, but may be used independently of each other. These contents, when used alone or in combination (total amount of solid lubricant and hard powder), are 1-5% by weight of the fluororesin composition. If the content is less than 1% by weight, wear resistance cannot be significantly improved, whereas if it is more than 5% by weight, tensile strength and elongation may deteriorate. The content of solid lubricants and / or hard powders is preferably 2-4% by weight, in particular 2.5-3.5% by weight. When used in combination, the solid lubricant and the hard powder are preferably used in a ratio of 0.1-2 parts by weight, in particular 0.2-1 parts by weight, per 1 part by weight of the solid lubricant.

According to the present invention, in addition to the constituents described above, various additives added to the fluororesin, for example, antioxidants, pigments, molding aids and the like, may be added as necessary. When the total amount of the other components except the PFA modified PTFE in the fluororesin composition of the present invention is in the range of 40-68.5 wt%, deterioration of tensile strength may be reduced.

The composition of the present invention can be prepared by a conventional method by mixing PFA modified PTFE, hard alloy alloy powder, inorganic fiber, solid lubricant, hard powder, and other components added as needed. The composition thus obtained can be molded into a desired shape by conventional methods used for molding the fluororesin composition, for example, compression molding, sintering, ram extrusion, or the like.

The seal for the swivel joint of the present invention can be produced by molding the composition of the present invention by the above-described method, and the shape and size of the seal may be conventional.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1-5 and Comparative Example 1-5

PFA modified PTFE (trade name: POLYFLON M112, manufactured by DAIKIN INDUSTRIES, LTD), PTFE resin (trade name: Fluon G163, manufactured by Ashai Glass Co, Ltd.), brass powder (particle size: 100% passed through 350 mesh Tyler standard screens) ), Carbon fibers (average fiber diameter: 14.5 μm, average length: 0.20 mm), molybdenum disulfide (average particle size: 100% passed through a 400 mesh Tyler standard screen), and cobalt blue (Moss hardness: 6-7 , Particle size: 100% through a 400 mesh Tyler standard screen) were mixed in the kind and content as described in Table 1 and dry mixed with a Henschel mixer. After preforming in a mold under a pressure of 600 kgf / cm ² , the raw material was obtained by sintering at 365 ° C. for 3 hours. The raw material was machined to obtain a sample having a predetermined size for testing physical properties.

The samples obtained in each example were subjected to load deformation in accordance with ASTM D621 and tensile strength and elongation in accordance with ASTM D1457 under conditions of 14 MPa × 24 hr. The results are shown in Table 1.

Table 1 shows that the compositions of the present invention have excellent resistance in terms of load strain, tensile strength and elongation. In contrast, the compositions of Comparative Examples 1 and 2 using PTFE resin instead of PFA modified PTFE exhibited inferior load strains, and even when PFA modified PTFE resin was used, the amount of the other constituents was kept outside the compounding range of the present invention. The compositions of Comparative Examples 3-5 exhibited inferior elongation.

TABLE 1

Example 6

The seal for a swivel joint (thickness 2.1 mm, inner diameter 100 mm, outer diameter 105 mm) was manufactured with the composition of Example 1.

Example 7 Comparative Examples 6 and 7

In Example 7, a seal for the swivel joint of the same size was prepared with the composition of Example 2 in the same manner as in Example 6, and likewise a seal for the swivel joint of Comparative Example 6 was prepared with the composition of Comparative Example 1 Similarly, a seal for the swivel joint of Comparative Example 7 was prepared from the composition of Comparative Example 2. The seal of Comparative Example 7 is commercially available.

Example 6, Example 7, and Comparative Example 6 were tested according to Tabletop Test 1 below, and the results are shown in FIG.

Tabletop Test 1: Each test seal is applied to a swivel joint as shown in FIG. 3 using turbine oil (turbine # 56) as working fluid, and the swivel joint is operated hydraulic pressure: 10.3 MPa, fluctuation range of swing angle: ( +) 120 °-(-) 120 °, rocking cycle: It was operated cyclically under the condition of 13 cpm, whereby the total leakage amount (cc) of the working liquid was measured with increasing rocking cycle.

1 shows that the service life of the seal for swivel joint of Comparative Example 6 ended within only 256 hours. In contrast, the seals of Examples 6 and 7 could still function sufficiently after 1280 hours. Further, as can be clearly seen from the performance of Examples 6 and 7, the composition of the present invention and the seal for the swivel joint were excellent in wear resistance.

The following tabletop test 2 was performed about the seal of Example 6 and the comparative example 7, and the result is shown in FIG.

Tabletop Test 2: Each test seal was applied to a swivel joint as shown in FIG. 3 using turbine oil (turbine # 56) as working fluid, and the swivel joint was operated hydraulic pressure: 0-34.3 MPa, pressure cycle: 18 cpm , Fluctuation range of swing angle: (+) 1080 °-(-) 1080 °, rocking cycle: cyclically operated under conditions of 13 cpm, whereby the total amount of leakage of the working fluid (cc) is Measured accordingly.

FIG. 2 shows that the seal for the swivel joint of Example 6 exhibits very good resistance to deterioration when compared to the seal of Comparative Example 7. FIG. After disassembling and examining the seal after 185 hours of operation, the seal of Example 6 exhibited no deformation, while the seal of Comparative Example 7 markedly destroyed a portion thereof.

The fluororesin composition of the present invention maintains excellent tensile strength and elongation while exhibiting excellent wear resistance and creep resistance, in particular compression creep resistance, so that hydraulic and pneumatic cylinders, bearings and other heavy loads can be applied for sliding. As a member and a member for fixing, it is especially suitable as a seal for swivel joints. The seal for a swivel joint of the present invention can be produced by a conventional method, has excellent wear resistance and creep resistance, and has a long life compared with a conventional product.

1 is a graph showing the results of bench testing 1 in Example 6, Example 7, and Comparative Example 6. FIG.

2 is a graph showing the results of the tabletop test 2 in Example 6 and Comparative Example 7. FIG.

3 is a partial cross-sectional view of a typical swivel joint of a power shovel.

4 is a view illustrating the extrusion phenomenon of the seal in the swivel joint.

Description of the main parts of the drawing

1: cylindrical housing

2: axis of rotation

3: seal ring groove

13: elastic body

14: fluorine resin seal

Claims (9)

30-50% by weight light alloy powder, 0.5-5% by weight inorganic fibers, 1-5% by weight solid lubricant and / or hard powder, and residual proportions of tetrafluoroethylene and perfluoro (alkylvinyl ether) A fluororesin composition comprising a copolymer with. The fluororesin composition according to claim 1, wherein the copolymer of tetrafluoroethylene and perfluoro (alkylvinyl ether) comprises 0.1 to 10% by weight of perfluoro (alkylvinyl ether). The fluororesin composition according to claim 1 or 2, comprising both the solid lubricant and the hard powder in a ratio of 0.1-2 parts by weight of the hard powder per 1 part by weight of the solid lubricant. The fluorine resin composition according to claim 1 or 2, wherein the hard powder has a MOS hardness of 5 or more. 5. The fluororesin composition of claim 4, wherein the hard powder is a composite oxide comprising cobalt oxide and aluminum oxide. The fluororesin composition according to claim 1 or 2, wherein the solid lubricant is a molybdenum-based compound. The fluororesin composition according to claim 1 or 2, wherein the light alloy powder is bronze powder. The fluororesin composition according to claim 1 or 2, wherein the inorganic fiber is carbon fiber. A swivel joint seal made of the fluororesin composition as defined in claim 1.

Images