Seal ring

Abstract

To improve air sealing performance and suppress vibration in a swivel joint for a construction machine or a general industrial machine.SOLUTION: A seal ring for sealing an annular gap between a housing and a stem of a swivel joint for a construction machine or a general industrial machine, the seal ring being composed of a resin composition containing a base material and a filler, wherein the base material is composed of a polyamide-based resin, and the filler is composed of a low-friction resin that is a resin having compatibility with the polyamide-based resin and having a lower static friction coefficient with respect to the stem than the polyamide-based resin.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a seal ring. [Background technology]

[0002] BACKGROUND ART Conventionally, a seal ring is known that seals an annular gap formed between a housing and a stem of a swivel joint for construction machinery or general industrial machinery.

[0003] For example, Patent Document 1 describes a seal ring made of urethane resin. Patent Document 1 also describes that the seal ring is made of an inner ring made of polyamide resin and an outer ring made of an elastic material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-14884 Summary of the Invention [Problem to be solved by the invention]

[0005] Seal rings made solely of urethane resin suffer from wear due to high temperatures and poor lubrication, resulting in sporadic oil leaks. When air leak tests are conducted on the aforementioned seal rings made up of an inner and outer ring to check for problems such as blowholes in the stem, the hard inner ring's ability to return to its original shape after installation is impaired, resulting in poor adhesion to the stem, resulting in poor air sealing (low-pressure sealing). Furthermore, the high coefficient of friction between the inner ring and the stem raises concerns about vibration due to stick-slip. [Means for solving the problem]

[0006] In order to solve the above problems, a seal ring according to one embodiment of the present disclosure is a seal ring that seals an annular gap between a housing and a stem of a swivel joint for construction machinery or general industrial machinery, and is made of a resin composition including a base material and a filler material, wherein the base material is made of a polyamide-based resin, and the filler material is made of a low-friction resin that is compatible with the polyamide-based resin and has a lower static friction coefficient with respect to the stem than the polyamide-based resin. [Effects of the Invention]

[0007] The present disclosure makes it possible to improve air sealing performance and suppress vibration in a swivel joint for construction machinery or general industrial machinery. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a swivel joint using a seal ring according to an embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the seal ring shown in FIG. [Figure 3] FIG. 1 is an image diagram showing the state of a filler in a seal ring using a filler that is not compatible with polyamide-based resin. [Figure 4] FIG. 1 is an image diagram showing the state of a filler in a seal ring using a filler that is compatible with polyamide-based resin. [Figure 5] FIG. 10 is a diagram showing the relationship between the constituent material of the seal ring and the starting torque and sliding torque. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present disclosure will be described below with reference to the accompanying drawings. The dimensions and scale of each part in the drawings may differ from those of the actual parts, and some parts are shown schematically to facilitate understanding. The scope of the present disclosure is not limited to these embodiments unless otherwise specified in the following description to the effect that the present disclosure is limited.

[0010] 1. Embodiment 1-1. Overview of swivel joint 100 using seal ring 10

[0011] Figure 1 is a cross-sectional view of a swivel joint 100 using a seal ring 10 according to an embodiment. The swivel joint 100 is a swivel joint for use in construction machinery or general industrial machinery, and is connected to a hydraulic system (not shown). The swivel joint 100 includes a housing 110, a stem 120, and a plurality of seal rings 10.

[0012] The housing 110 is a cylindrical member. The housing 110 is made of a metal material such as iron, stainless steel, or an aluminum alloy. A plurality of grooves 111 and 112 are provided on the inner circumferential surface of the housing 110. The housing 110 also has ports 113 and 114 that open to the outer circumferential surface of the housing 110. The ports 113 and 114 are connected to the grooves 111 and 112, respectively.

[0013] The stem 120 is a cylindrical member rotatably inserted into the housing 110. The stem 120 is made of a metal material such as iron, stainless steel, or an aluminum alloy. The stem 120 is provided with a plurality of oil supply passages 121 and a plurality of oil supply passages 122. Each of the plurality of oil supply passages 121 is a pipe extending along the longitudinal direction of the stem 120, and transfers hydraulic oil from the bottom to the top in the figure. Each of the plurality of oil supply passages 122 is a pipe extending along the longitudinal direction of the stem 120, and transfers hydraulic oil from the top to the bottom in the figure.

[0014] A port 113 of the housing 110 supplies hydraulic oil to an oil supply passage 121 of the stem 120 via the groove 111. On the other hand, a port 114 of the housing 110 discharges hydraulic oil from an oil supply passage 122 of the stem 120 via the groove 112.

[0015] A plurality of seal rings 10 are disposed in the gap between the inner peripheral surface of the housing 110 and the outer peripheral surface of the stem 120. In the example shown in Fig. 1, a seal ring 10 is disposed in each of a plurality of grooves provided on the inner peripheral surface of the housing 110.

[0016] Each seal ring 10 is an annular elastic member that seals the gap, preventing the hydraulic oil in the gap from leaking to the outside or preventing the hydraulic oil from entering from one of grooves 111 and 112 to the other.

[0017] 1-2.Details of Seal Ring 10 Fig. 2 is an enlarged cross-sectional view of the seal ring 10 shown in Fig. 1. Fig. 2 shows an example of the shape of the seal ring 10. Note that the shape of the seal ring 10 is not limited to the example shown in Fig. 2 and is arbitrary.

[0018] 2, a groove 115 is provided on the inner peripheral surface of the housing 110, and the seal ring 10 is fitted into the groove 115. Here, the outer peripheral surface of the seal ring 10 is in close contact with the housing 110, and the circumferential position of the seal ring 10 relative to the housing 110 is fixed. In contrast, the inner peripheral surface of the seal ring 10 is in close contact with the outer peripheral surface of the stem 120 so as to be slidable.

[0019] The seal ring 10 has a plurality of recesses 12 provided on one side surface 11, a plurality of recesses 14 provided on the other side surface 13, and a groove 15 provided on the inner peripheral surface of the seal ring 10.

[0020] The recesses 12 are spaced apart from one another in the circumferential direction of the seal ring 10. Similarly, the recesses 14 are spaced apart from one another in the circumferential direction of the seal ring 10. The arrangement, shape, number, and other aspects of the recesses 12 and recesses 14 are not limited to the illustrated example and are arbitrary. Furthermore, the recesses 12 and recesses 14 may be provided as needed or may be omitted.

[0021] Groove 15 is an annular groove provided around the entire circumference of seal ring 10. Groove 15 is located at the center in the width direction of the inner peripheral surface of seal ring 10. As a result, the inner peripheral surface of seal ring 10 has surfaces 16 and 17 divided by groove 15. Each of surfaces 16 and 17 is a contact surface that slidably contacts the outer peripheral surface of stem 120. The shape, arrangement, etc. of groove 15 are not limited to the example shown in the figure and are arbitrary.

[0022] The seal ring 10 is made of a resin composition in which a base material and a filler material are mutually dissolved. Here, the base material is made of a polyamide resin. Meanwhile, the filler is made of a low-friction resin that is compatible with the polyamide resin and has a lower coefficient of static friction with the stem 120 than the polyamide resin. Therefore, the resin composition is a polymer alloy in which the polyamide resin and the low-friction resin are mutually dissolved. This allows the advantages of both the polyamide resin and the low-friction resin to be optimally utilized.

[0023] Here, polyamide-based resins have excellent properties such as heat resistance, mechanical properties, and chemical resistance. Furthermore, polyamide-based resins have extremely low dynamic friction resistance. However, polyamide-based resins have relatively high static friction resistance. Therefore, when a seal ring made solely of polyamide-based resin is subjected to an air leak test to check for problems such as blowholes in the stem 120 after being incorporated into the swivel joint 100, the seal ring's ability to return to its original shape after installation is reduced, resulting in a decrease in adhesion to the stem 120, resulting in a decrease in air sealing (low-pressure sealing). Furthermore, a seal ring made solely of polyamide-based resin has a high coefficient of friction with the stem 120, raising concerns about vibration due to stick-slip.

[0024] Therefore, by using a filler made of a low-friction resin, which has a lower coefficient of static friction with respect to the stem 120 than polyamide resin, in the seal ring 10, it is possible to reduce the coefficient of static friction of the seal ring 10 with respect to the stem 120. As a result, it is possible to solve the problems of seal rings made only of polyamide resin. In other words, it is possible to improve the air sealing performance of the swivel joint 100 and suppress vibrations.

[0025] FIG. 3 is an image diagram showing the state of the filler PO in a seal ring 10X that uses a filler PO that is incompatible with the polyamide-based resin PA. In the seal ring 10X, as shown in FIG. 3, the filler PO is simply mixed with the polyamide-based resin PA. Therefore, in the seal ring 10X, there are areas where only the filler PO is present and areas where only the polyamide-based resin PA is present. Therefore, the filler PO is unlikely to be exposed on the surface of the seal ring 10X. Furthermore, the filler PO is likely to be covered by the polyamide-based resin PA.

[0026] For this reason, a skin layer LS of approximately 10 μm to 20 μm thick and made only of polyamide resin PA is formed on the surface of seal ring 10X. Therefore, even if filler material PO has self-lubricating properties, seal ring 10X cannot fully utilize these properties. Therefore, seal ring 10X suffers from the same problems as seal rings made only of polyamide resin.

[0027] FIG. 4 is an image diagram showing the state of the filler in a seal ring 10 using a filler PO that is compatible with polyamide resin PA. In the seal ring 10, as shown in FIG. 4, the filler PO is dissolved in the polyamide resin PA. Therefore, the filler PO is uniformly present in the seal ring 10. Accordingly, the filler PO is uniformly present on the surface of the seal ring 10. As a result, the self-lubricating properties of the filler PO are suitably exhibited on the surface of the seal ring 10, even in the portion corresponding to the skin layer LS described above.

[0028] The polyamide resin used in the resin composition constituting the seal ring 10 may be any resin having an acid amide bond (-CONH-) in the molecule, but aliphatic polyamides are preferred.

[0029] Examples of aliphatic polyamides include polycaproamide (polyamide 6), polypentamethylene adipamide (polyamide 56), polyhexamethylene adipamide (polyamide 66), polyundecaneamide (polyamide 11), polylauryl lactam (polyamide 12), polytetramethylene adipamide (polyamide 46), polytetramethylene sebacamide (polyamide 410), polypentamethylene sebacamide (polyamide 510), polyhexamethylene sebacamide (polyamide 610), polyhexamethylene dodecamide (polyamide 612), polydecamethylene adipamide (polyamide 106), and polydecamethylene sebacamide (polyamide 1010).

[0030] In particular, from the viewpoint of mechanical strength, etc., the polyamide-based resin used in the resin composition constituting the seal ring 10 preferably contains at least one of polycaproamide (polyamide 6), polyundecaneamide (polyamide 11), polylauryllactam (polyamide 12), polyamide 46 (PA46), and polyamide 66 (PA66), and it is particularly preferable that it contains polyundecaneamide (polyamide 11).

[0031] On the other hand, the low-friction resin used in the resin composition constituting the seal ring 10 is not particularly limited as long as it is compatible with polyamide-based resins and has a lower static friction coefficient with respect to the stem 120 than polyamide-based resins, but is preferably a polyolefin-based resin. The static friction coefficient of polyolefin-based resins is lower than the static friction resistance of polyamide-based resins. Furthermore, the dynamic friction coefficient of polyolefin-based resins is relatively small, although it is higher than the dynamic friction resistance of polyamide-based resins. By constituting the seal ring 10 with a resin composition in which such a polyolefin-based resin is compatible with a polyamide-based resin, it is possible to realize a seal ring 10 having both a low dynamic friction coefficient and a low static friction coefficient while taking advantage of the excellent properties of polyamide-based resins, such as heat resistance, mechanical properties, and chemical resistance.

[0032] The polyolefin resin used in the resin composition constituting the seal ring 10 is a modified resin in which a reactive functional group such as a carboxylic acid, an acid anhydride, or an epoxy group has been introduced into a polyolefin such as a polyethylene resin, a polypropylene resin, or an ethylene-propylene copolymer so as to have compatibility with the polyamide resin used in the resin composition constituting the seal ring 10. In particular, because of its excellent compatibility with polyamide resins, the polyolefin resin used in the resin composition constituting the seal ring 10 is preferably a maleic acid-modified polyolefin resin, and more preferably a maleic acid-modified polyethylene resin.

[0033] Here, the polyolefin resin is preferably a polyethylene resin because it has a smaller static friction coefficient than polypropylene resin, etc. This allows the static friction coefficient of the seal ring to be smaller than in an embodiment using a polypropylene resin, etc.

[0034] The density of the polyolefin resin is preferably 0.85 or more and 0.90 or less. That is, the polyolefin resin is preferably a low-density polyolefin resin. In this case, there is an advantage that the polyolefin resin has better compatibility with the polyamide resin than when a high-density polyolefin resin is used.

[0035] Furthermore, the filler content in the resin composition constituting the seal ring 10 is preferably 1 vol% or more and 50 vol% or less, more preferably 5 vol% or more and 40 vol% or less, and even more preferably 5 vol% or more and 20 vol% or less. Having this content within this range has the advantage of making it easier to utilize the mutual advantages of the polyamide-based resin and the low-friction resin. For example, this has the advantage of making it easier to increase the mechanical strength of the seal ring 10 while reducing the static friction coefficient. On the other hand, if this content is too low, it may be difficult to utilize the advantages of the low-friction resin. On the other hand, if this content is too high, the advantages of the polyamide-based resin may be lost.

[0036] The flexural modulus of the resin composition constituting the seal ring 10 is preferably 1.2 GPa or less, which provides good flexibility to the seal ring 10. As a result, deterioration in the return to normal deformation of the seal ring 10 when it is mounted can be suitably reduced when an air leak test is performed.

[0037] 2. Working Example Examples of the present invention will be described below in detail, but the present invention is not limited to the following examples.

[0038] A. Seal ring manufacturing A-1. Example The seal ring of Example 1 was manufactured using polyamide 11 as the base material and maleic acid-modified low-density polyethylene as the filler material.

[0039] Specifically, first, polyamide 11 and maleic acid-modified low-density polyethylene were weighed out so that the content of maleic acid-modified low-density polyethylene in the resin composition was 20 vol %.

[0040] The weighed polyamide 11 and maleic acid-modified low-density polyethylene were mixed in a tumbler, and the mixture was kneaded in a twin-screw extruder at a temperature of 260°C to 310°C to form pellets of the resin composition. The pellets were then molded in an injection molding machine to obtain seal rings. The cylinder temperature of the injection molding machine was 285°C to 295°C, and the mold temperature was 120°C.

[0041] A-2. Comparative example 1 As the seal ring of Comparative Example 1, a seal ring made of urethane resin was manufactured.

[0042] A-3. Comparative example 2 A seal ring of Comparative Example 2 was produced in the same manner as in Example 1, except that only polyamide 11 was used without using maleic acid-modified low-density polyethylene, which is a low-friction resin.

[0043] B. Seal ring evaluation The starting torque and sliding torque under no pressure were measured for each of the seal rings of the example and comparative examples 1 and 2 when they were installed in a swivel joint. The measurement results are shown in FIG.

[0044] As shown in Figure 5, the seal ring of the example can reduce both the starting torque and the sliding torque compared to the seal rings of comparative examples 1 and 2. In particular, the reel ring of the example can reduce the sliding torque by approximately 81% compared to the seal ring of comparative example 1. This shows that the seal ring of the example can reduce vibration due to stick-slip.

[0045] Furthermore, when the seal rings of the Example and Comparative Examples 1 and 2 were assembled into a swivel joint and subjected to an air leak evaluation, it was found that the air sealing properties (low pressure sealing properties) were reduced in Comparative Examples 1 and 2, whereas no such problem was observed in the Example.

[0046] In addition, seal rings were manufactured using polyamide 6, polyamide 12, polyamide 46, and polyamide 66 instead of polyamide 11 as the base material in the examples, and similarly, better results were obtained compared to comparative examples 1 and 2.

[0047] 3. Notes From the above embodiments and examples, the following aspects can be understood, for example.

[0048] (Appendix 1) A first embodiment, which is a suitable example of the seal ring of the present disclosure, is a seal ring that seals an annular gap between a housing and a stem of a swivel joint for construction machinery or general industrial machinery, and is made of a resin composition containing a base material and a filler material, the base material being made of a polyamide-based resin, and the filler being made of a low-friction resin that is compatible with the polyamide-based resin and has a lower static friction coefficient with respect to the stem than the polyamide-based resin.

[0049] In the above aspect, the air sealing performance of the swivel joint can be improved and vibration can be suppressed.

[0050] (Appendix 2) In a second aspect, which is a preferred example of the first aspect, the low-friction resin is a polyolefin-based resin. In the above aspect, the static friction coefficient of the polyolefin-based resin is smaller than the static friction resistance of the polyamide-based resin. Furthermore, the dynamic friction coefficient of the polyolefin-based resin is relatively small, although it is larger than the dynamic friction resistance of the polyamide-based resin. By forming a seal ring from a resin composition in which such a polyolefin-based resin is compatible with the polyamide-based resin, it is possible to realize a seal ring with a small dynamic friction coefficient and a small static friction coefficient while taking advantage of the excellent properties of the polyamide-based resin, such as heat resistance, mechanical properties, and chemical resistance.

[0051] (Appendix 3) In a third embodiment, which is a preferred example of the second embodiment, the polyolefin resin is a maleic acid-modified polyolefin resin. In this embodiment, the compatibility of the low-friction resin with the polyamide resin can be improved compared to an embodiment using a polyamide resin. This allows the advantages of both the polyamide resin and the low-friction resin to be optimally utilized.

[0052] (Appendix 4) In a fourth aspect, which is a preferred example of the second or third aspect, the polyolefin resin is a polyethylene resin. In this aspect, the static friction coefficient of the seal ring can be made smaller than in an aspect using a polypropylene resin or the like.

[0053] (Appendix 5) In a fifth aspect, which is a suitable example of any of the second to fourth aspects, the density of the polyolefin resin is 0.85 or more and 0.90 or less. This aspect has the advantage that the compatibility of the low-friction resin with the polyamide resin is excellent compared to when a high-density polyolefin resin is used.

[0054] (Note 6) In a sixth embodiment, which is a preferred example of any one of the first to fifth embodiments, the content of the filler in the resin composition is 1 vol% or more and 50 vol% or less. This embodiment has the advantage of easily utilizing the mutual advantages of the polyamide resin and the low-friction resin. For example, this has the advantage of easily increasing the mechanical strength of the seal ring while reducing the static friction coefficient.

[0055] (Appendix 7) In a seventh aspect which is a suitable example of any of the first to sixth aspects, the polyamide resin includes at least one of polyamide 6, polyamide 11, polyamide 12, polyamide 46, and polyamide 66. The above aspect has the advantage that the mechanical strength of the seal ring can be easily increased.

[0056] (Appendix 8) In an eighth aspect, which is a preferred example of any one of the first to seventh aspects, the flexural modulus of the resin composition is 1.2 GPa or less. In this aspect, the seal ring has good flexibility. As a result, deterioration in the return property of the seal ring when it is mounted can be suitably reduced when an air leak test is performed. [Explanation of symbols]

[0057] 10...seal ring, 10X...seal ring, 11...side surface, 12...recess, 13...side surface, 14...recess, 15...groove, 16...surface, 17...surface, 100...swivel joint, 110...housing, 111...groove, 112...groove, 113...port, 114...port, 115...groove, 120...stem, 121...oil supply passage, 122...oil supply passage, LS...skin layer, PA...polyamide resin, PO...filler.

Claims

1. A seal ring for sealing an annular gap between a housing and a stem of a swivel joint for construction machinery or general industrial machinery, The resin composition includes a base material and a filler material. the base material is made of a polyamide resin, the filler is made of a low-friction resin that is compatible with the polyamide resin and has a lower coefficient of static friction with respect to the stem than the polyamide resin; Seal ring.

2. The low-friction resin is a polyolefin resin. The seal ring according to claim 1 .

3. The polyolefin resin is a maleic acid-modified polyolefin resin. The seal ring according to claim 2 .

4. The polyolefin resin is a polyethylene resin. The seal ring according to claim 2 .

5. The density of the polyolefin resin is 0.85 or more and 0.90 or less. The seal ring according to claim 2 .

6. The content of the filler in the resin composition is 1 vol% or more and 50 vol% or less. The seal ring according to claim 1 or 2.

7. The polyamide-based resin includes at least one of polyamide 6, polyamide 11, polyamide 12, polyamide 46, and polyamide 66. The seal ring according to claim 1 or 2.

8. The flexural modulus of the resin composition is 1.2 GPa or less. The seal ring according to claim 1 or 2.

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