Cup seals for compressors

Abstract

To provide a cup seal for a compressor that is excellent in mechanical properties such as frictional wear properties and tensile elongation at break.SOLUTION: A cup seal 1 for a compressor is used in a reciprocating compressor that has a piston and a cylinder and that compresses gas by reciprocating motion of the piston. The cup seal is fixed to the piston and press-fitted to the inside diameter of the cylinder to create an airtight seal between the piston and the cylinder, and the cup seal is composed of a resin composition. The resin composition contains polytetrafluoroethylene resin as the main component, and contains aromatic polyester resin powder and carbon fibers having an aspect ratio of 3-15.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present invention relates to a cup seal used in a reciprocating compressor that compresses gases such as air. 【Background Art】 【0002】 A reciprocating compressor includes a cylinder and a piston that defines a compression chamber within the cylinder, and is a device that reciprocates the piston to perform gas intake, compression, and discharge. The piston in a reciprocating compressor is attached to a crankshaft via, for example, ball bearings, and due to the eccentric rotational movement of the crankshaft, the piston reciprocates while oscillating within the cylinder. In this reciprocating compressor, a cup seal is provided to hermetically seal between the piston and the cylinder in order to ensure the airtightness of the compression chamber. 【0003】 As a cup seal for a reciprocating compressor, for example, a cup seal in the form of an annular dish-shaped member as disclosed in Patent Document 1 is known. This cup seal is made of a resin composition based on polytetrafluoroethylene resin and blended with spherical graphite or the like, and has an annular flat portion provided on the inner peripheral side and an annular lip portion provided on the outer peripheral side and curved so as to project from the flat portion to one side in the axial direction. In a state where it is attached to a reciprocating compressor, the outer peripheral surface of the curved lip portion abuts against the inner peripheral surface of the cylinder and slides on the inner peripheral surface of the cylinder as the piston reciprocates. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2019-190584 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 Incidentally, cup seals are generally manufactured by deforming a washer-shaped sheet material made of a resin composition into a dish shape, for example, by drawing. Therefore, if the tensile elongation at break of the resin composition is insufficient, the sheet material may break during the drawing process. Furthermore, even if complete breakage does not occur, if minute cracks appear on the surface of the sheet material, the wear resistance of the cup seal may decrease. In this regard, the cup seal described in Patent Document 1 is made of a resin composition that does not contain anisotropic fillers, and therefore has excellent tensile elongation at break. When the sheet material is processed into a dish shape by drawing, localized stress concentration is suppressed, and the occurrence of minute cracks on the surface of the sheet material caused by this can be suppressed. 【0006】 Furthermore, since cup seals used in reciprocating compressors are operated under unlubricated conditions, the resin composition itself is required to have excellent friction and wear characteristics. The cup seal described in Patent Document 1 improves friction and wear characteristics by incorporating spheroidal graphite and the like into the resin composition, but there is room for improvement in terms of wear resistance. 【0007】 This invention has been made in view of these circumstances, and aims to provide a cup seal for compressors that is excellent in mechanical properties such as frictional wear characteristics and tensile elongation at fracture. [Means for solving the problem] 【0008】 The present invention relates to a compressor cup seal used in a reciprocating compressor having a piston and a cylinder, which compresses gas by the reciprocating motion of the piston, and is fixed to the piston and press-fitted into the inner diameter of the cylinder to airtightly seal the space between the piston and the cylinder. The compressor cup seal is made of a resin composition, the resin composition mainly composed of polytetrafluoroethylene (PTFE) resin, and is characterized by containing aromatic polyester resin powder and carbon fibers with an aspect ratio of 3 to 15. 【0009】 The above resin composition is characterized by containing 3% to 20% by volume of the aromatic polyester resin powder and 1% to 20% by volume of the carbon fibers, relative to the entire resin composition. 【0010】 The above resin composition is characterized in that the content of the aromatic polyester resin powder is greater than the content of the carbon fibers. 【0011】 The above aromatic polyester resin powder has the chemical structure shown in formula (1) below, and is characterized in that the 50% particle size is 3 μm to 30 μm in particle size distribution measurements using laser light scattering. [ka] 【0012】 It is characterized by having a tensile strength of 15 MPa or more and a tensile elongation at break of 200% or more. [Effects of the Invention] 【0013】 The compressor cup seal of the present invention is made of a resin composition in which PTFE resin is used as the base resin and aromatic polyester resin powder and carbon fibers with an aspect ratio of 3 to 15 are blended therein, so the resin composition itself has excellent friction and wear properties. Furthermore, the carbon fibers are carbon fibers with a predetermined aspect ratio, and by blending them in combination with aromatic polyester resin powder, wear resistance is improved while the tensile strength and tensile elongation at break of the sheet material are also improved. As a result, for example, localized stress concentration during deep drawing is suppressed, and the occurrence of minute cracks on the surface of the sheet material caused by this can be suppressed. Consequently, it is possible to achieve both friction and wear properties and mechanical properties such as tensile elongation at break in the compressor cup seal. 【0014】 The resin composition contains 3% to 20% by volume of aromatic polyester resin powder and 1% to 20% by volume of carbon fibers, and furthermore, the content of aromatic polyester resin powder in the resin composition is greater than the content of carbon fibers, so that the friction and wear characteristics can be suitably exhibited while suppressing the anisotropy caused by carbon fibers. 【0015】 Since the aromatic polyester resin powder has the chemical structure shown in formula (1) above and a 50% particle size of 3 μm to 30 μm, it is easy to improve abrasion resistance and tensile properties, and because it exhibits a granular shape of a predetermined size, it particularly leads to an improvement in tensile elongation at break. 【0016】 Since the sheet material has a tensile strength of 15 MPa or more and a tensile elongation at break of 200% or more, it is possible to manufacture cup seals that do not break or crack even during deep drawing. [Brief explanation of the drawing] 【0017】 [Figure 1] This is a cross-sectional view showing an example of the cup seal of the present invention. [Figure 2] This is a partial cross-sectional view of a reciprocating compressor to which the cup seal of the present invention is applied. [Figure 3] This is a schematic diagram of a wear test using a 3-pin on-disk method. [Modes for carrying out the invention] 【0018】 An example of the structure of a reciprocating compressor to which the cup seal for a compressor of the present invention is applied will be described based on FIG. 2. FIG. 2 is a partial cross-sectional view of the reciprocating compressor. The compressor 11 is a reciprocating compressor that compresses the gas in the pressure chamber by the reciprocating motion of the piston. The compressor 11 includes a substantially cylindrical cylinder 12 having a hollow portion, a substantially cylindrical piston 13 provided in the cylinder 12 so as to be reciprocally movable while swinging, a cup seal 1 fixed to the piston 13, a suction valve 14, and a discharge valve 15. A pressure chamber 16 is formed between the cylinder head 12a located at the upper end of the cylinder 12 and one end of the piston 13. The compressor 11 includes driving means (not shown) on the other end side of the piston 13 for reciprocating the piston 13 in the axial direction while swinging the piston 13. The driving means is, for example, a crankshaft that eccentrically rotates with the rotation of a rotating shaft. By this driving means, the piston 13 reciprocates in the directions indicated by the arrows X and Y in FIG. 2. 【0019】 The piston 13 is composed of a connecting rod 17 provided with a mounting flange 17a and a disc-shaped retainer 18. The mounting flange 17a of the connecting rod 17 has a concave portion 17b at the central axis portion and is fitted with a convex portion at the central axis portion of the retainer 18. The cup seal 1 is sandwiched in a piston groove formed by the connecting rod 17 and the retainer 18 and is fastened and fixed by a coupling tool 19. 【0020】 As shown in FIG. 1, the cup seal 1 is a dish-shaped annular member having a through hole in the central axis portion. The cup seal 1 has an annular flat portion 2 provided on the inner peripheral side and a lip portion 3 provided on the outer peripheral side and curved so as to project from the flat portion 2 to one side in the axial direction. In a state where the cup seal 1 is attached to the compressor 11 (see FIG. 2), the flat portion 2 is fixed to the piston groove, and the lip portion 3 is bent and abuts against the inner peripheral surface of the cylinder 12. When the piston 13 reciprocates, the outer peripheral surface of the lip portion 3 slides on the inner peripheral surface of the cylinder 12. 【0021】 The cup seal 1 is made of a resin composition described later, in which aromatic polyester resin powder (particles) and carbon fibers with a predetermined aspect ratio are dispersed in a PTFE resin base material. This makes the cup seal 1 a self-lubricating resin material with excellent sliding properties while exhibiting excellent wear resistance. Although there are concerns that the inclusion of carbon fibers in the cup seal 1 may cause damage to the inner surface of the cylinder 12, this damage can be reduced by setting the aspect ratio of the carbon fibers within a predetermined range and adjusting the amount of carbon fibers used. Furthermore, although the carbon fibers acting as an anisotropic filler may cause minute cracks during the manufacturing of the cup seal 1 (for example, during the sheet material drawing process), the tensile properties are improved by setting the aspect ratio of the carbon fibers within a predetermined range and incorporating granular aromatic polyester resin powder. 【0022】 The operation of the compressor 11 described above will now be explained. The compressor 11 compresses external air and supplies it to a storage tank or the like by repeating an intake process and a compression process. In the intake process, the piston 13 moves while oscillating away from the cylinder head 12a (direction X shown in Figure 2), drawing in air from the outside. In this process, the intake valve 14 provided in the cylinder head 12a opens, and air flows into the compression chamber 16. In the compression process, the piston 13 moves while oscillating towards the cylinder head 12a (direction Y shown in Figure 2), compressing the air in the compression chamber 16. In this process, the intake valve 14 provided in the cylinder head 12a closes, and at a predetermined timing, the discharge valve 15 opens, causing the compressed air to be discharged to the outside of the cylinder 12. 【0023】 The resin composition used in the compressor cup seal of the present invention can be formed into a cylindrical material by, for example, pre-molding a mixed powder consisting of a PTFE resin as a base resin and various fillers, and then firing the pre-molded body. Alternatively, a long cylindrical material may be obtained by extrusion molding using the above mixed powder. The cup seal of the present invention shown in Figure 1 is formed, for example, by drawing a hollow disc-shaped sheet material (washer material) obtained by machining such a cylindrical material. In the drawing process, the outer circumference of the sheet material is bent toward one side in the axial direction to form the lip portion. During this drawing process, it is necessary to bend the sheet material uniformly, and if the bending is uneven, there is a risk that minute cracks may occur on the surface of the sheet material. Also, if the tensile elongation at break is insufficient, there is a risk that the sheet material may break. 【0024】 Conventionally, resin compositions for cup seals have been known that use PTFE resin, which has self-lubricating properties, as the base resin, with various fillers added to provide properties such as wear resistance. However, adding fillers to PTFE resin reduces the tensile elongation at break. 【0025】 The inventors have discovered that by incorporating carbon fibers with a small aspect ratio and aromatic polyester resin powder, it is possible to achieve both excellent tensile elongation at break and frictional wear characteristics. This invention is based on these findings. 【0026】 The resin composition used in the present invention preferably contains 1% to 20% by volume, more preferably 3% to 15% by volume, and even more preferably 3% to 10% by volume, of carbon fibers with an aspect ratio of 3 to 15 relative to the total resin composition. In this specification, "aspect ratio" is the value obtained by dividing the "average fiber length" of the carbon fiber by the "average fiber diameter". Here, both "average fiber length" and "average fiber diameter" are number averages, and can be obtained by measuring, for example, 200 samples using a scanning electron microscope and taking the average value. By using carbon fibers with a small aspect ratio, localized stress concentration during processes such as deep drawing during the manufacture of cup seals can be suppressed, and the occurrence of minute cracks on the surface of the sheet material caused by this can be suppressed. In this specification, "anisotropy" refers to the fact that the shape, expansion rate, strength, etc., differ depending on the direction. 【0027】 As the carbon fiber mentioned above, milled fibers with a short average fiber length can be used. The average fiber length is preferably 20 μm to 300 μm, and more preferably 20 μm to 200 μm. Examples of commercially available milled fibers that can be used in this invention include PAN-based carbon fibers such as Teijin Limited: HT M100 40MU and Toray Industries, Inc.: Torayca MLD-30. Examples of pitch-based carbon fibers include Kureha Corporation: Kureca M-101S, M-101T, M-201F, M-201S and Mitsubishi Chemical Corporation: Dialead K223HM-50 μm. 【0028】 Furthermore, the average fiber diameter of the carbon fibers is preferably 5 μm to 30 μm, and more preferably 5 μm to 20 μm. 【0029】 The carbon fibers used in this invention have an aspect ratio of 3 to 15, with an aspect ratio of 3 to 12 being more preferred, and an aspect ratio of 3 to 8 being even more preferred. If the aspect ratio exceeds 15, for example, localized stress concentration during the drawing process of cup seals may cause minute cracks to occur on the surface of the sheet material. 【0030】 The aromatic polyester resin used in the present invention preferably has the chemical structure shown in formula (1) below. This resin is a fully aromatic polyester resin consisting of a homopolymer of 4-hydroxybenzoic acid and has excellent abrasion resistance and heat resistance. Specific commercially available products with the following chemical structure include Sumitomo Chemical Co., Ltd.: Sumika Super E101-S, E101-S2, E101-P, E101-M, and Egene Optoelectronic Materials Co., Ltd.: Supernol S101Plus, S101B, S101P, etc. [ka] 【0031】 Furthermore, the 50% particle size (D50) of the aromatic polyester resin is not particularly limited, but is preferably 3 μm to 50 μm, more preferably 3 μm to 30 μm, and even more preferably 5 μm to 15 μm. By keeping it within this range, it is easier to obtain a good effect on improving abrasion resistance. On the other hand, if D50 exceeds 50 μm, the tensile elongation at break of the resin composition may decrease. Note that D50 is the particle size at the point where the cumulative value of the particle size distribution reaches 50%, and in this invention, it is measured using a particle size distribution measuring device that utilizes laser light scattering. 【0032】 The amount of aromatic polyester resin powder blended is preferably 3% to 20% by volume, more preferably 3% to 15% by volume, and even more preferably 3% to 10% by volume, relative to the total resin composition. Furthermore, it is preferable that the content (by volume) of aromatic polyester resin powder in the resin composition is greater than the content (by volume) of carbon fibers. 【0033】 In the present invention, the PTFE resin used as the base resin of the resin composition can be a general PTFE resin represented by -(CF2-CF2)n-, or a general PTFE resin can be made to contain a perfluoroalkyl ether group (-C p F 2p-O-)(p is an integer between 1 and 4) or polyfluoroalkyl group (H(CF2) q Modified PTFE resins incorporating elements such as -)(q being an integer between 1 and 20) can also be used. These PTFE resins and modified PTFE resins may be obtained using either the suspension polymerization method to obtain general molding powder or the emulsion polymerization method to obtain fine powder. From the viewpoint of abrasion resistance, it is preferable to use molding powder with a higher molecular weight than fine powder. Examples of commercially available PTFE resins that can be used in this invention include Mitsui Chemours Fluoroproducts Co., Ltd.: Teflon® 7J, 7A, 7AJ, 70J; Daikin Industries, Ltd.: Polyflon M-12, M-18, M-18F, M-111, M-112; AGC Inc.: Fluon G163, G190, G192, etc. 【0034】 The resin composition used in the present invention preferably has PTFE resin as its main component, and more preferably contains 3% to 20% by volume of aromatic polyester resin powder and 1% to 20% by volume of carbon fibers with an aspect ratio of 3 to 15 relative to the entire resin composition. A particularly preferred form is a resin composition that has PTFE resin as its main component, and more preferably contains 3% to 15% by volume of aromatic polyester resin powder and 3% to 15% by volume of carbon fibers with an aspect ratio of 3 to 8 relative to the entire resin composition. The amount of PTFE resin is preferably 70% to 96% by volume relative to the entire resin composition. If the amount of PTFE resin is less than 70% by volume, it is relatively difficult to maintain low friction, and if the amount of PTFE resin exceeds 96% by volume, the abrasion resistance may decrease. The amount of PTFE resin may be 80% or more by volume, or 85% or more by volume. 【0035】 The above resin composition may contain well-known resin additives other than aromatic polyester resin powder and carbon fibers with an aspect ratio of 3 to 15, to the extent that they do not impair the effects of the present invention. Preferred resin additives that can be added include those with a low degree of anisotropy, such as spheroidal graphite, coke powder, and resin powders (polyphenylene sulfide resin, polyether ether ketone resin, polyimide resin, etc.). The resin composition does not need to contain graphite such as spheroidal graphite, flake graphite, or scale graphite. In addition, colorants (carbon black, iron oxide, titanium oxide, etc.) may be added as needed. 【0036】 The tensile strength (according to ASTM D1708) of molded articles (such as sheet materials and cup seals) made from the above resin composition is preferably 15 MPa or higher, and more preferably 18 MPa or higher. Furthermore, the tensile elongation at break (according to ASTM D1708) is preferably 200% or higher, and more preferably 250% or higher. By using sheet materials with such excellent tensile properties, the material can be stretched uniformly even during deep drawing processes, thereby suppressing the occurrence of defects. 【0037】 Because the cup seal of the present invention has excellent tensile properties, its drawability is ensured even when the thickness of the cup seal itself is increased. Therefore, the tolerance range for the thickness of the cup seal is wide, for example, it can be 0.3 mm to 3 mm thick. Increasing the thickness can be expected to extend the lifespan. 【0038】 The gas compressed in a reciprocating compressor to which the cup seal of the present invention is applied is not particularly limited. When used in a compressor that compresses air, it can be used even in environments where moisture due to condensation adheres to the sliding surface between the cup seal and the cylinder. [Examples] 【0039】 The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples. 【0040】 The raw materials used in the resin compositions of Examples 1 and 2 and Comparative Example 1 are listed below. As shown in Table 1, the resin compositions of Examples 1 and 2 consist only of PTFE resin, aromatic polyester resin powder, and carbon fibers with an aspect ratio of 3 to 15. 【0041】 (1)PTFE resin Mitsui Chemours Fluoroproducts Co., Ltd.: Teflon (registered trademark) 7J (2) Aromatic polyester resin D50: 13μm (3) Carbon Fiber-1 Average fiber length 150 μm, average fiber diameter 14.5 μm, aspect ratio 10.3 (4) Carbon Fiber-2 Average fiber length 40 μm, average fiber diameter 7 μm, aspect ratio 5.7 (5) Scale-like graphite Imerys GC Japan Co., Ltd.: TIMREX KS25 【0042】 The D50 of aromatic polyester resin powder was measured using a particle size distribution analyzer that utilizes laser light scattering. The average fiber length and average fiber diameter of carbon fiber-1 and carbon fiber-2 were calculated as the average values ​​of 200 samples using a scanning electron microscope. 【0043】 <Tensile strength and tensile elongation at fracture> Using resin compositions made from the raw materials described in (1) to (5) above, dumbbell test specimens (dimensions: thickness 1 mm, parallel section width 4.7 mm, grip distance 22 mm) were prepared in accordance with ASTM D1708, and the tests were conducted. Tensile conditions were 23°C and a tensile speed of 100 mm / min. The results are shown in Table 1. 【0044】 <Abrasion Test> Pin test specimens (φ5 × 10 mm) were prepared using resin compositions made from the raw materials (1) to (5) described above. The obtained pin test specimens were subjected to abrasion testing using a 3-pin on-disk type testing machine as shown in Figure 3. As shown in Figure 3, the test surfaces of the three pin test specimens 20 were pressed against the surface of the rotating disk 21 of the testing machine with the following surface pressure, and the rotating disk 21 was rotated. The specific test conditions are as follows. For the mating material, an anodized aluminum alloy disk was used, simulating the inner circumferential surface of a cylinder. The results are shown in Table 1. (Test conditions) Speed: 1.2m / s Surface pressure: 0.08 MPa Lubrication: No lubrication (dry) Temperature: 80℃ Duration: 50 hours 【0045】 [Table 1] 【0046】 As shown in Table 1, Examples 1 and 2, which used aromatic polyester resin powder and carbon fibers with an aspect ratio of 3 to 15, had a tensile strength of 15 MPa or more and a tensile elongation at break of 200% or more. In Comparative Example 1, which used flaky graphite with high anisotropy instead of granular aromatic polyester resin powder with sufficiently low anisotropy, the tensile elongation at break decreased to 95%. In other words, the resin compositions of Examples 1 and 2 are more stretchable than those of Comparative Example 1, and are less prone to breakage or microcracks during deep drawing. 【0047】 Furthermore, the wear amounts for Example 1 and Example 2 were 6 μm and 4 μm, respectively, which were superior to Comparative Example 1, which had a wear amount of 12 μm. In addition, the aggressiveness towards the mating material was also reduced. Comparing the results of Example 2 and Comparative Example 1 in Table 1, it can be seen that the aromatic polyester resin powder contributed not only to improved wear resistance but also to improved tensile properties (especially tensile elongation at break). 【0048】 Furthermore, cylindrical materials were prepared using the resin compositions of Examples 1 and 2 and Comparative Example 1. A hollow disc-shaped sheet material (1 mm thick) obtained by machining this cylindrical material was then drawn to produce a cup seal with the shape shown in Figure 1. In Examples 1 and 2, there was no breakage or minute cracks in the sheet material during the drawing process, but in Comparative Example 1, minute cracks were observed. [Industrial applicability] 【0049】 The cup seal of the present invention has excellent mechanical properties such as friction and wear characteristics and tensile elongation at break, and can therefore be widely used as a sealing material for reciprocating compressors. [Explanation of symbols] 【0050】 1. Compressor cup seal 2 Plane part 3. Lip section 11 Compressor 12 cylinders 13 pistons 14. Intake valve 15 Discharge valve 16 Compression Chamber 17 Connecting Rods 18 Retainer 19 Connectors 20-pin test specimen 21 RPM disc

Claims

[Claim 1] A compressor cup seal used in a reciprocating compressor having a piston and a cylinder, which compresses gas by the reciprocating motion of the piston, is fixed to the piston and press-fitted into the inner diameter of the cylinder to airtightly seal the space between the piston and the cylinder, The aforementioned compressor cup seal is made of a resin composition and has a lip portion in which the washer-shaped outer circumference is bent toward one side in the axial direction. The resin composition mainly consists of polytetrafluoroethylene resin, and includes aromatic polyester resin powder and carbon fibers with an aspect ratio of 3 to 15. A cup seal for compressors characterized by having a tensile elongation at break of 200% or more. [Claim 2] The cup seal for a compressor according to claim 1, characterized in that the resin composition contains 3% to 20% by volume of the aromatic polyester resin powder and 1% to 20% by volume of the carbon fiber, based on the entire resin composition. [Claim 3] The compressor cup seal according to claim 2, characterized in that the content of the aromatic polyester resin powder in the resin composition is greater than the content of the carbon fiber. [Claim 4] The cup seal for a compressor according to any one of claims 1 to 3, characterized in that the aromatic polyester resin powder has a chemical structure shown in the following formula (1), and the 50% particle size is 3 μm to 30 μm in particle size distribution measurement using laser light scattering method. 【Chemistry 1】 [Claim 5] A compressor cup seal according to any one of claims 1 to 4, characterized in that it has a tensile strength of 15 MPa or more.

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