Sealing devices and backup rings

Abstract

A sealing device for sealing an annular gap between a housing and a shaft of a hydraulic cylinder is provided, comprising an annular gasket which is disposed along the space and is composed of an elastic material, and a back-up ring in contact with the gasket. The back-up ring has a contact surface which contacts the shaft, and a part of the back-up ring including at least the contact surface is composed of a resin composition including a base material and a filling material. The base material is a polyamide-based resin, and the filling material is a polyolefin-based resin having compatibility with the polyamide-based resin.

Description

[Technical Field]

[0001] The present disclosure relates to a sealing device and a backup ring. [Background technology]

[0002] BACKGROUND ART Conventionally, a sealing device that seals an annular gap between a housing and a shaft in a hydraulic cylinder for construction machinery has been known.

[0003] For example, Patent Document 1 discloses a configuration in which a buffer ring, a rod packing, and a dust seal are arranged in this order from the inside to the outside of the housing in the direction along the axis of the shaft. Here, the buffer ring is a member for mitigating the hydraulic pressure applied to the rod packing. The buffer ring has a packing made of an elastic material such as urethane resin and a backup ring made of a hard resin such as polyamide resin, which are fitted together. The backup ring prevents the packing from deforming due to excessive pressure from inside the housing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-8088 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration described in Patent Document 1, abnormal noise may occur during low-speed operation of the hydraulic cylinder due to insufficient sliding of the backup ring against the shaft. [Means for solving the problem]

[0006] In order to solve the above problems, a sealing device according to one aspect of the present disclosure is a sealing device having a rod packing that seals an annular gap between a housing and a shaft of a hydraulic cylinder for construction machinery, and a buffer ring that relieves hydraulic pressure applied to the rod packing, wherein the buffer ring is arranged along the gap and comprises an annular packing made of an elastic material, and a backup ring that contacts the packing, the backup ring has a contact surface that contacts the shaft, and at least a portion of the backup ring, including the contact surface, is made of a resin composition that includes a base material and a filler, 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 shaft than the polyamide-based resin.

[0007] A backup ring according to one aspect of the present disclosure is a backup ring for mitigating hydraulic pressure applied to a rod packing that seals an annular gap between a housing and a shaft of a hydraulic cylinder for construction 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 is made of a low-friction resin that is compatible with the polyamide-based resin and has a lower coefficient of static friction with respect to the shaft than the polyamide-based resin. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a hydraulic cylinder using a sealing device according to an embodiment. [Figure 2] FIG. 2 is a partially enlarged cross-sectional view of the hydraulic cylinder shown in FIG. 1. [Figure 3] FIG. 10 is an explanatory diagram of buffering of the sealing device according to the embodiment. [Figure 4] FIG. 1 is an image diagram showing the state of a filler in a backup ring that uses a filler that is incompatible with polyamide-based resin. [Figure 5]FIG. 1 is an image diagram showing the state of a filler in a backup ring that uses a filler that is compatible with polyamide-based resin. [Figure 6] FIG. 10 is a diagram showing an apparatus for measuring the sliding resistance of a backup ring. [Figure 7] FIG. 10 is a diagram showing a sliding resistance waveform during low-speed operation of the backup ring according to Comparative Example 1. [Figure 8] FIG. 10 is a diagram showing a sliding resistance waveform during high-speed operation of the backup ring according to Comparative Example 1. [Figure 9] FIG. 4 is a diagram showing a sliding resistance waveform during low-speed operation of the backup ring according to the first embodiment. 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. First embodiment 1-1. Overview of the hydraulic cylinder 100 using the sealing device 10 1 is a perspective view of a hydraulic cylinder 100 using a sealing device 10 according to an embodiment. The hydraulic cylinder 100 is an extension / contraction mechanism that hydraulically expands and contracts in a direction along an axis AX, and is used as a power source for machinery such as construction machinery or general industrial machinery, for example.

[0011] 1, the hydraulic cylinder 100 includes a housing 110, a piston 120, a shaft 130, a sealing system 140, and a sealing device 10. First, each part of the hydraulic cylinder 100 will be briefly described below in order based on FIG.

[0012] In the following, one direction along the axis AX is referred to as the "X1 direction," and the direction opposite to the X1 direction is referred to as the "X2 direction." However, the X1 direction and the X2 direction may be collectively referred to as the "axial direction." Furthermore, the direction along the axis AX may be referred to as the "circumferential direction." Furthermore, the direction perpendicular to the axis AX may be referred to as the "radial direction."

[0013] The housing 110 is a cylindrical tube with a bottom that extends in a direction along the axis AX. The housing 110 is made of a metal material such as iron, stainless steel, or an aluminum alloy.

[0014] In the example shown in FIG. 1 , the end of housing 110 in the X1 direction is open, and a boss B1 is provided at the end of housing 110 in the X2 direction. Housing 110 is also provided with port 112 and port 113. Port 112 is a hole used to introduce or discharge hydraulic oil to or from a space within housing 110 that is positioned in the X1 direction relative to piston 120. Port 113 is a hole used to introduce or discharge hydraulic oil to or from a space within housing 110 that is positioned in the X2 direction relative to piston 120. The pressure of the hydraulic oil within housing 110 is adjusted via ports 112 and 113.

[0015] The shape of the housing 110 is not limited to the example shown in FIG. 1 and may be any shape as long as it allows a gap to be formed between the housing 110 and the shaft 130 that is sealed by the sealing device 10.

[0016] Piston 120 is a structure disposed within housing 110 so as to be reciprocatable in a direction along axis AX. Piston 120 divides the space within housing 110 into a space positioned in the X1 direction relative to piston 120 and a space positioned in the X2 direction relative to piston 120. Piston 120 is made of a metal material such as iron, stainless steel, or aluminum alloy. Piston 120 reciprocates in a direction along axis AX relative to housing 110 by adjusting the pressure of hydraulic oil within housing 110 through ports 112 and 113.

[0017] The shape of the piston 120 is not limited to the example shown in FIG. 1, and may be any shape.

[0018] The shaft 130 is a piston rod extending in a direction along the axis AX. The piston 120 is fixed to the end of the shaft 130 in the X2 direction or a portion thereof in the vicinity thereof. The shaft 130 moves in a direction along the axis AX relative to the housing 110 as the piston 120 moves in a direction along the axis AX relative to the housing 110. The shaft 130 is made of a metal material such as iron, stainless steel, or an aluminum alloy.

[0019] 1, a boss B2 is provided at the end in the X1 direction of the shaft 130. The distance between the boss B1 and the boss B2 changes as the piston 120 moves relative to the housing 110 in the direction along the axis AX.

[0020] The shape of the shaft 130 is not limited to the example shown in FIG. 1 and may be any shape as long as it allows a gap to be formed between the housing 110 and the shaft 130 that is sealed by the sealing device 10.

[0021] The sealing system 140 is a piston sealing system made up of a group of parts that seal the annular gap between the piston 120 and the housing 110. In the example shown in Fig. 1, the sealing system 140 has a wear ring 141, a piston packing 142, and a contamination seal 143. These are arranged in the X2 direction in the order of wear ring 141, piston packing 142, and contamination seal 143. Here, annular grooves (not shown) are provided on the outer circumferential surface of the piston 120 in correspondence with the wear ring 141, piston packing 142, and contamination seal 143, respectively, for arranging them.

[0022] The wear ring 141 is an annular member that functions as a sliding bearing to reduce eccentricity of the shaft 130 relative to the housing 110. This function improves the durability and sealing performance of the piston packing 142. The wear ring 141 is made of a resin such as PTFE (polytetrafluoroethylene), polyester resin, phenolic resin, or polyamide resin.

[0023] The piston packing 142 is an annular structure that seals the annular gap between the housing 110 and the piston 120. Although not shown, the piston packing 142 has a seal ring and a backup ring. The seal ring is made of a hard material such as polyamide resin. The piston packing 142 contacts the inner circumferential surface of the hole 111 of the housing 110. The backup ring is disposed between the seal ring and the piston 120 and is made of an elastic material such as urethane resin. In an elastically deformed state, the backup ring presses the seal ring against the inner circumferential surface of the hole 111 of the housing 110.

[0024] The contamination seal 143 is an annular member that prevents foreign matter from entering the space in the housing 110 in the X2 direction from the piston 120, from reaching the piston packing 142. The contamination seal 143 is made of a resin such as PTFE. The contamination seal 143 comes into contact with both the housing 110 and the piston 120 in an elastically deformed state.

[0025] The configuration of the sealing system 140 described above is not limited to the example shown in FIG. 1 and may be any configuration as long as it seals the annular gap between the housing 110 and the piston 120.

[0026] The sealing device 10 is a rod sealing system made up of a group of parts that seal the annular gap between the housing 110 and the shaft 130 .

[0027] 1-2. Details of the sealing device 10 FIG. 2 is a partially enlarged cross-sectional view of the hydraulic cylinder 100 shown in FIG. 2 shows a cross-section of a portion of the hydraulic cylinder 100 cut along a plane including the axis AX. As shown in FIG. 2, the sealing device 10 has a dust seal 20, a rod packing 30, and a buffer ring 40. These are arranged in the X2 direction in the following order: dust seal 20, rod packing 30, buffer ring 40. Here, annular grooves 111a, 111b, and 111c are provided on the inner circumferential surface of the hole 111 of the housing 110. The dust seal 20 is arranged in groove 111a. The rod packing 30 is arranged in groove 111b. The buffer ring 40 is arranged in groove 111c.

[0028] The dust seal 20 is an annular member for preventing foreign matter such as muddy water or dust from the external space of the housing 110 from reaching the rod packing 30. The dust seal 20 has a reinforcing ring 21 and a seal member 22.

[0029] The reinforcing ring 21 is an annular member that reinforces the sealing member 22 around the axis AX. In the example shown in FIG. 2, the reinforcing ring 21 is substantially L-shaped in a cross section cut along a plane including the axis AX. The reinforcing ring 21 is made of a metal material such as stainless steel. The sealing member 22 is an annular elastic member fixed to the reinforcing ring 21 and in contact with the wall surface of the groove 111a and the outer peripheral surface of the shaft 130. In the example shown in FIG. 2, the sealing member 22 has a shape having two portions that extend obliquely in the X1 and X2 directions from near the inner peripheral edge of the reinforcing ring 21 toward the shaft 130 in a cross section cut along a plane including the axis AX. The sealing member 22 is made of an elastic material such as urethane resin. The sealing member 22 contacts both the housing 110 and the shaft 130 in an elastically deformed state. The configuration of the dust seal 20 is not limited to the example shown in FIG. 1 and may be any configuration. Moreover, the dust seal 20 is provided as needed and may be omitted.

[0030] The rod packing 30 is an annular member that functions as a main seal for preventing leakage of hydraulic oil from inside the housing 110 to the external space. The rod packing 30 includes a packing 31 and a backup ring 32.

[0031] The packing 31 is an annular elastic member that contacts both the wall surface of the groove 111b and the outer circumferential surface of the shaft 130. In the example shown in FIG. 2, the packing 31 has a substantially U-shape when viewed in cross section cut along a plane including the axis AX. The packing 31 is made of an elastic material such as urethane resin. The packing 31 contacts both the housing 110 and the shaft 130 in an elastically deformed state.

[0032] The backup ring 32 is a flat washer-shaped member that comes into close contact with the surface of the packing 31 facing the X1 direction. The backup ring 32 is made of a resin such as PTFE (polytetrafluoroethylene), polyester resin, phenolic resin, or polyamide resin. The backup ring 32 functions as a sliding bearing for reducing eccentricity of the shaft 130 relative to the housing 110. This function improves the durability and sealing performance of the rod packing 30. The configuration of the rod packing 30 is not limited to the example shown in FIG. 1 and is arbitrary.

[0033] The buffer ring 40 is an annular member for mitigating the hydraulic pressure applied to the rod packing 30. This mitigation improves the durability of the rod packing 30. The buffer ring 40 has a packing 41 and a backup ring 42.

[0034] The packing 41 is an annular elastic member disposed along the gap between the housing 110 and the shaft 130. Here, the packing 41 contacts both the wall surface of the groove 111c and the outer peripheral surface of the shaft 130. In the example shown in FIG. 2, the packing 41 has a substantially U-shape when viewed in cross section cut along a plane including the axis AX. The packing 41 is made of an elastic material such as urethane resin. The packing 41 contacts both the housing 110 and the shaft 130 in an elastically deformed state. Since the elastic material constituting the packing 41 contains urethane resin, it is possible to effectively prevent hydraulic oil from reaching the rod packing 30.

[0035] The backup ring 42 is an annular member that is disposed along the gap between the housing 110 and the shaft 130 and that comes into contact with the packing 41. Here, the backup ring 42 is in close contact with the inner peripheral surface of the packing 41. The backup ring 42 suppresses deformation of the packing 41 due to excessive pressure from inside the housing 110. This allows the buffer ring 40 to more effectively receive hydraulic pressure from a position in the X2 direction than the buffer ring 40. As a result, the hydraulic pressure applied to the rod packing 30 can be more effectively alleviated by the buffer ring 40.

[0036] 3 is an explanatory diagram of the buffer ring 40 of the sealing device 10 according to the embodiment. As shown in FIG. 3, a groove 41a is provided on the inner circumferential surface of the packing 41. A backup ring 42 is fitted into the groove 41a. The backup ring 42 has a surface 42a that comes into close contact with the groove 41a and an inner circumferential surface 42b. Here, the inner circumferential surface 42b is a contact surface that comes into contact with the outer circumferential surface of the shaft 130.

[0037] At least a portion of the backup ring 42, including the inner peripheral surface 42b, 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 shaft 130 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 makes it possible to optimally utilize the advantages of both the polyamide resin and the low-friction resin.

[0038] Here, polyamide-based resin has excellent properties such as heat resistance, mechanical properties, and chemical resistance. Furthermore, the dynamic friction resistance of polyamide-based resin is extremely small. However, the static friction resistance of polyamide-based resin is relatively large. Therefore, if the backup ring 42 is made solely of polyamide-based resin, abnormal noise may occur during low-speed operation of the hydraulic cylinder 100 due to insufficient sliding of the backup ring 42 against the shaft 130.

[0039] Therefore, by using a filler made of a low-friction resin, which is a resin that has a lower coefficient of static friction with respect to the shaft 130 than polyamide resin, the coefficient of static friction of the backup ring 42 with respect to the shaft 130 can be reduced.

[0040] FIG. 4 is an image diagram showing the state of the filler PO in a backup ring 42X that uses a filler PO that is incompatible with polyamide-based resin PA. In the backup ring 42X, as shown in FIG. 4, the filler PO is simply mixed with the polyamide-based resin PA. As a result, the backup ring 42X has 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 backup ring 42X. Furthermore, the filler PO is likely to be covered by the polyamide-based resin PA.

[0041] For this reason, a skin layer LS of approximately 10 μm to 20 μm in thickness, made only of polyamide resin PA, is formed on the surface of backup ring 42X, and as a result, even if filler material PO has self-lubricating properties, backup ring 42X is unable to fully utilize these properties.

[0042] FIG. 5 is an image diagram showing the state of the filler PO in a backup ring 42 that uses a filler PO that is compatible with polyamide resin PA. As shown in FIG. 5, in the backup ring 42, the filler PO is dissolved in the polyamide resin PA. Therefore, the filler PO is uniformly distributed in the backup ring 42. Therefore, the filler PO is uniformly distributed on the surface of the backup ring 42. As a result, the self-lubricating properties of the filler PO are suitably exhibited on the surface of the backup ring 42, even in the portion that corresponds to the skin layer LS described above.

[0043] The polyamide resin used in the resin composition that constitutes the backup ring 42 may be any resin that has an acid amide bond (-CONH-) in the molecule, but aliphatic polyamides are preferred.

[0044] 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).

[0045] In particular, from the viewpoint of mechanical strength, etc., it is preferable that the polyamide-based resin used in the resin composition constituting the backup ring 42 contains at least one of polyamide 46 (PA46), polyamide 66 (PA66), and polyamide 11 (PA11), and it is particularly preferable that it contains polyamide 46.

[0046] On the other hand, the low-friction resin used in the resin composition constituting backup ring 42 is not particularly limited as long as it is compatible with polyamide-based resin and has a lower coefficient of static friction with shaft 130 than polyamide-based resin, but is preferably a polyolefin-based resin. The static friction coefficient of polyolefin-based resin is smaller than the static friction resistance of polyamide-based resin. Furthermore, the dynamic friction coefficient of polyolefin-based resin, while larger than the dynamic friction resistance of polyamide-based resin, is relatively small. By constituting backup ring 42 from a resin composition in which such polyolefin-based resin is compatible with polyamide-based resin, it is possible to realize a backup ring 42 with a low coefficient of both dynamic and static friction while taking advantage of the excellent properties of polyamide-based resin, such as heat resistance, mechanical properties, and chemical resistance.

[0047] The polyolefin resin used in the resin composition that constitutes backup ring 42 is a modified resin in which a reactive functional group such as a carboxylic acid, acid anhydride, or epoxy group has been introduced into a polyolefin such as a polyethylene resin, polypropylene resin, or ethylene-propylene copolymer, so that the polyolefin resin has compatibility with the polyamide resin that constitutes the resin composition that constitutes backup ring 42. In particular, because of its excellent compatibility with polyamide resins, the polyolefin resin used in the resin composition that constitutes backup ring 42 is preferably a maleic acid-modified polyolefin resin, and more preferably a maleic acid-modified polyethylene resin.

[0048] Here, the polyolefin resin is preferably a polyethylene resin, since it has a smaller coefficient of static friction than polypropylene resins and the like.

[0049] The density of polyolefin resin is 0.85 g / cm 3 Over 0.90 g / cm 3 The following is preferable. That is, the polyolefin resin is preferably a low-density polyolefin resin. In this case, there is an advantage that the compatibility with the polyamide resin is superior to the case where a high-density polyolefin resin is used.

[0050] Furthermore, the filler content in the resin composition constituting the backup ring 42 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 backup ring 42 while reducing the coefficient of static friction. 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. [Example]

[0051] Examples of the present invention will be described below in detail, but the present invention is not limited to the following examples.

[0052] A.Backup ring manufacturing A-1. Example 1 The backup ring of Example 1 was manufactured using polyamide 46 as the base material and maleic acid-modified low-density polyethylene as the filler material.

[0053] Specifically, first, polyamide 46 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 %.

[0054] The weighed polyamide 46 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 backup rings. The cylinder temperature of the injection molding machine was 285°C to 295°C, and the mold temperature was 120°C.

[0055] A-2. Example 2 A backup ring of Example 2 was manufactured in the same manner as in Example 1, except that polyamide 11 was used instead of polyamide 46 as the base material.

[0056] A-3. Example 3 A backup ring of Example 3 was manufactured in the same manner as in Example 1, except that polyamide 66 was used instead of polyamide 46 as the base material.

[0057] A-4. Example 4 A backup ring of Example 4 was produced in the same manner as in Example 1, except that the content of maleic acid-modified low-density polyethylene in the resin composition constituting the backup ring was set to 5 vol %.

[0058] A-5. Comparative example 1 A backup ring of Comparative Example 1 was manufactured in the same manner as in Example 1, except that only polyamide 46 was used without using maleic acid-modified low-density polyethylene, which is a low-friction resin.

[0059] A-6. Comparative example 2 A backup ring of Comparative Example 2 was produced in the same manner as in Example 2, except that only polyamide 11 was used without using maleic acid-modified low-density polyethylene, which is a low-friction resin.

[0060] A-7. Comparative example 3 A backup ring of Comparative Example 3 was manufactured in the same manner as in Example 3, except that only polyamide 66 was used without using maleic acid-modified low-density polyethylene, which is a low-friction resin.

[0061] A-8. Reference example 1 A backup ring of Reference Example 1 was manufactured in the same manner as in Example 1, except that PTFE having an average particle size of 50 μm was used as the filler instead of the maleic acid-modified low-density polyethylene. The PTFE content in the resin composition was set to 7 vol %.

[0062] A-9. Reference example 2 A backup ring of Reference Example 2 was manufactured in the same manner as in Example 1, except that polyamide 66 was used as the base material instead of polyamide 46, oil was used instead of maleic acid-modified low-density polyethylene, and the oil content in the resin composition constituting the backup ring was set to 10 vol %.

[0063] A-10.Reference example 3 A backup ring of Reference Example 3 was manufactured in the same manner as in Example 1, except that polyamide 11 was used as the base material instead of polyamide 46, and molybdenum disulfide having an average particle size of 5 μm was used instead of maleic acid-modified low-density polyethylene. The molybdenum disulfide content in the resin composition was set to 0.5 vol%.

[0064] B. Backup Ring Evaluation B-1.Measuring device 6 is a diagram showing an apparatus 200 for measuring the sliding resistance of a backup ring. The apparatus 200 has a shaft 210, a housing 220, and a pair of thermocouples 230. The shaft 210 is an iron cylinder that reciprocates along an axis AX. The housing 220 is an iron cylinder tube that has a hole 221, a pair of grooves 222, a hole 223, and a pair of holes 224.

[0065] The shaft 210 is inserted into the hole 221. Buffer rings 40_1 and 40_2, each having a backup ring to be measured, are disposed in a pair of grooves 222, respectively. The buffer rings 40_1 and 40_2 have the same configuration. However, the buffer rings 40_1 and 40_2 are disposed symmetrically with each other so that the backup ring contacts the side of the pair of side surfaces of the groove 222 that is farther from the hole 223. The hole 223 penetrates the housing 220 so as to open onto the inner circumferential surface of the hole 221. A device (not shown) is connected to the hole 223 for introducing hydraulic oil toward the hole 221 at a predetermined pressure. The pair of holes 224 each penetrates the housing 220 so as to open onto the inner circumferential surface of the hole 221 near the groove 222. A pair of thermocouples 230 are inserted into the pair of holes 224, respectively.

[0066] B-2. Evaluation Using the above-mentioned device 200, the sliding resistance of the backup rings of each Example, Comparative Example, and Reference Example was measured under the following measurement conditions. The presence or absence of abnormal noise during the measurement was then checked for evaluation. Furthermore, for each Example and Comparative Example, the sliding resistance range, which is the range of variation in sliding resistance, was measured.

[0067] <Measurement conditions> Hydraulic oil pressure: 35MPa Shaft 210 movement speed: 25 mm / s Shaft 210 stroke: 200mm Temperature: 80℃ Hydraulic oil: Daphne Super Hydro 46A (manufactured by Idemitsu Kosan)

[0068] The evaluation results are shown in Table 1. In addition to the evaluation results, Table 1 also lists the types, contents, and compatibility of the base material and filler used in the backup ring.

[0069] [Table 1]

[0070] In Table 1, "PA46" indicates polyamide 46. "PA11" indicates polyamide 11. "PA66" indicates polyamide 66. "PE" indicates maleic acid-modified low-density polyethylene. "MoS" indicates molybdenum disulfide.

[0071] As shown in Table 1, no abnormal noise was generated in each of the Examples. In contrast, abnormal noise was generated in each of the Comparative Examples and Reference Examples.

[0072] Fig. 7 is a diagram showing the sliding resistance waveform during low-speed operation of the backup ring according to Comparative Example 1. Fig. 7 shows the change in sliding resistance over time when the movement speed of shaft 210 is 25 mm / s. As shown in Fig. 7, in Comparative Example 1, the sliding resistance range ΔFr, which is the range of fluctuation in sliding resistance, is relatively large. Furthermore, in Comparative Example 1, abnormal noise was generated during measurement.

[0073] Fig. 8 is a diagram showing the sliding resistance waveform during high-speed operation of the backup ring according to Comparative Example 1. Fig. 8 shows the change in sliding resistance over time when the movement speed of shaft 210 is 400 mm / s. As shown in Fig. 8, in Comparative Example 1, when the movement speed of shaft 210 was increased, the sliding resistance width ΔFr was relatively small, and no abnormal noise was generated during measurement.

[0074] Fig. 9 is a diagram showing the sliding resistance waveform during low-speed operation of the backup ring according to Example 1. Fig. 9 shows the change in sliding resistance over time when the movement speed of shaft 210 is 25 mm / s. As shown in Fig. 9, in Example 1, the sliding resistance range ΔFr, which is the range of fluctuation in sliding resistance, was extremely small, and no abnormal noise was generated during measurement.

[0075] As can be seen from the above, in each example, the base material and the filler are compatible with each other, so that the generation of abnormal noise can be reduced even when the hydraulic cylinder is operating at low speed. [Explanation of symbols]

[0076] 10... sealing device, 20... dust seal, 21... reinforcing ring, 22... sealing member, 30... rod packing, 31... packing, 32... backup ring, 40... buffer ring, 40_1... buffer ring, 40_2... buffer ring, 41... packing, 41a... groove, 42... backup ring, 42X... backup ring, 42a... surface, 42b... inner peripheral surface, 100... hydraulic cylinder, 110... housing, 111... hole, 111a... groove, 111b... groove, 111c ...groove, 112...port, 113...port, 120...piston, 130...shaft, 140...sealing system, 141...wear ring, 142...piston packing, 143...contamination seal, 200...device, 210...shaft, 220...housing, 221...hole, 222...groove, 223...hole, 224...hole, 230...thermocouple, AX...axial line, B1...boss, B2...boss, LS...skin layer, PA...polyamide resin, PO...filler, ΔFr...sliding resistance width.

Claims

1. a rod packing that seals an annular gap between a housing and a shaft of a hydraulic cylinder for construction machinery; A sealing device having a buffer ring for mitigating hydraulic pressure applied to the rod packing, The buffering an annular packing made of an elastic material and disposed along the gap; a backup ring in contact with the packing, the backup ring has a contact surface that contacts the shaft, At least a portion of the backup ring, including the contact surface, is made of a resin composition including a base material and a filler, 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 shaft than the polyamide resin; Sealing device.

2. The low-friction resin is a polyolefin resin. The sealing device according to claim 1 .

3. The polyolefin resin is a maleic acid-modified polyolefin resin. The sealing device according to claim 2 .

4. The polyolefin resin is a polyethylene resin. The sealing device according to claim 2 or 3.

5. The density of the polyolefin resin is 0.85 g / cm or more and 0.90 g / cm or less. The sealing device 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 sealing device according to claim 1 .

7. The polyamide-based resin includes at least one of polyamide 11, polyamide 46, and polyamide 66. The sealing device according to claim 1 .

8. The elastic material includes a urethane resin. The sealing device according to claim 1 .

9. A backup ring for alleviating hydraulic pressure applied to a rod packing that seals an annular gap between a housing and a shaft of a hydraulic cylinder for construction 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 shaft than the polyamide resin; Backup ring.

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