JP2011247283A - Sealing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing system having improved pressure resistance without increasing the number of part items while maintaining superior sealing performance.SOLUTION: The sealing system seals an annular gap between a housing 50 which relatively reciprocates and a rod 60 inserted into an axial hole of the housing 50, and includes a rod packing 11 arranged in a first annular groove 51 which is formed at the internal periphery of the axial hole, and a backup ring 12 which is arranged at the lower-pressure side rather than the rod packing 11 being the inside of the first annular groove 51, and suppresses the internal peripheral end X of the rod packing 11 at a low-pressure side from being protruded to a fine gap Y between the rod 60 and the axial hole. A material of the rod packing 11 is nytril rubber, and a material of the backup ring 12 is polyamide whose Rockwell hardness is not lower than 90HRR and not higher than 110HRR.

Description

  The present invention relates to a sealing system including a rod packing and a backup ring.

  Conventionally, in a hydraulic cylinder or the like provided in various industrial machines (for example, construction machines), a sealing system in which a plurality of seals are combined is used. Such a sealing system is known to include a rod packing and a backup ring in order to seal an annular gap between a shaft hole of a cylinder (housing) and a rod. The rod packing and the backup ring are disposed in an annular groove provided on the inner periphery of the shaft hole.

  Here, the rod packing exhibits a function of preventing the sealing fluid (oil in the hydraulic cylinder) from leaking to the atmosphere side. As a material for the rod packing, nitrile rubber (NBR) which is excellent in flexibility and excellent in tracking with respect to shaft eccentricity is suitable.

  Further, the backup ring exerts a function of suppressing the inner peripheral end portion on the low pressure side of the rod packing from protruding into a minute gap between the rod and the shaft hole. As a material for the backup ring, a tetrafluoroethylene resin (PTFE) that has high strength and does not have a large difference in hardness from NBR is suitable. The backup ring is deformed by compression when subjected to pressure, and the above-described function is exhibited by the inner peripheral surface thereof being in close contact with the rod. That is, the low pressure side inner peripheral end portion of the rod packing is prevented from protruding into the minute gap between the inner peripheral surface of the backup ring and the rod. For this reason, if a material with a large hardness difference from NBR is used as the material for the backup ring, the inner peripheral end portion on the low pressure side of the rod packing is connected to the backup ring before the inner peripheral surface of the backup ring comes into close contact with the rod. There arises a problem that it protrudes into a minute gap between the inner peripheral surface and the rod.

  Here, when the hydraulic pressure is high, such as a hydraulic cylinder for a construction machine, the pressure resistance is enhanced by providing a buffering for buffering pressure on the high pressure side of the rod packing. However, when the buffering function is lowered due to deterioration with time, the backup ring protrudes into a minute gap between the rod and the shaft hole. Further, along with this, the inner peripheral end portion on the low pressure side of the rod packing protrudes into a minute gap between the inner peripheral surface of the backup ring and the rod. Thereby, the inner peripheral end portion on the low pressure side in the rod packing may be damaged, and the sealing function may be deteriorated.

  In order to solve such a problem, a technique using two backup rings is also known. That is, a technique is known in which a PTFE backup ring is disposed on the rod packing side, and a polyamide backup ring having a hardness higher than that of PTFE (Rockwell hardness of about 123 HRR) is disposed on the low pressure side. . However, in the case of such a technique, since two types of backup rings are required, the cost increases.

  In addition, in order to reduce the hardness difference between the rod packing and the backup ring by using only one polyamide backup ring with high hardness (Rockwell hardness of about 123 HRR), the material of the rod packing is made harder than NBR. The technology to make high urethane is also known. However, in this technique, although the pressure resistance is improved, since the hardness of the rod packing is high, there are disadvantages in that the followability to the shaft eccentricity is reduced and the sealing performance is lowered.

JP 2001-355739 A International Publication Number WO2005 / 121613

  An object of the present invention is to provide a sealing system in which pressure resistance is improved without increasing the number of parts and maintaining excellent sealing performance.

  The present invention employs the following means in order to solve the above problems.

That is, the sealing system of the present invention is
A sealing system for sealing an annular gap between a relatively reciprocating housing and a rod inserted into a shaft hole of the housing,
A rod packing disposed in an annular groove provided on the inner periphery of the shaft hole;
A backup ring which is disposed in the annular groove and on the low pressure side of the rod packing, and suppresses the inner peripheral end portion on the low pressure side of the rod packing from protruding into a minute gap between the rod and the shaft hole; ,
In a sealing system comprising:
The material of the rod packing is nitrile rubber,
The material of the backup ring is a polyamide having a Rockwell hardness of 90 HRR or more and 110 HRR or less.

  In addition, regarding the material of the rod packing and the backup ring in the present invention, the case where other substances such as a filler are included to the extent that the basic material properties do not change is included.

  According to the present invention, as the material for the rod packing, the nitrile rubber that is excellent in flexibility and excellent in tracking with respect to the shaft eccentricity is adopted, so that excellent sealing performance can be maintained. In the present invention, as the material for the backup ring, a polyamide having a relatively low hardness and a Rockwell hardness of 90 HRR or more and 110 HRR or less is used. As a result, the hardness is higher than PTFE that is generally used as a material for the backup ring, and the hardness difference between the rod packing and the backup ring is not so high while improving the pressure resistance. Protrusion can be suitably suppressed. Thereby, it is possible to maintain excellent sealing performance without increasing the number of parts as in the case of using two backup rings.

  As described above, according to the present invention, it is possible to improve pressure resistance without increasing the number of components and maintaining excellent sealing performance.

It is typical sectional drawing which shows the use condition of the sealing system which concerns on the Example of this invention. It is a table | surface which shows the various results in case the hardness of a backup ring differs. It is a graph which shows the relationship between the hardness of a backup ring, the protrusion dimension of a backup ring, and the damage dimension of a rod packing.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. .

(Example)
With reference to FIGS. 1-3, the sealing system based on the Example of this invention is demonstrated. The sealing system according to the present embodiment can be suitably used for various hydraulic cylinders. In this case, the housing described below corresponds to a cylinder, the fluid to be sealed corresponds to oil, and the fluid pressure corresponds to hydraulic pressure.

<Sealing system>
In particular, with reference to FIG. 1, the configuration of the entire sealing system according to the embodiment of the present invention will be described. The sealing system according to this embodiment is used to seal an annular gap between the housing 50 and the rod 60 inserted into the shaft hole of the housing 50. The housing 50 and the rod 60 are configured to reciprocate relatively.

  The sealing system in the present embodiment includes a main seal portion 10, a pressure-resistant portion 20, and a dust seal portion 30. A first annular groove 51, a second annular groove 52, and an annular notch 53 are provided on the inner periphery of the shaft hole of the housing 50. A second annular groove 52 is provided on the side having the highest pressure, and an annular notch 53 is provided on the side having the lowest pressure (in the present embodiment, the atmosphere side). The main seal portion 10 is provided in the first annular groove 51, the pressure-resistant portion 20 is provided in the second annular groove 52, and the dust seal portion 30 is provided in the annular notch 53.

  The main seal part 10 mainly exhibits a function of preventing the fluid to be sealed on the high pressure side from leaking to the low pressure side (atmosphere side). The pressure-resistant part 20 mainly exhibits a function of buffering the fluid pressure of the fluid to be sealed against the main seal part 10. The dust seal part 30 mainly exhibits a function of preventing foreign matters (dust, dust, etc.) from entering the main seal part 10 side.

  The main seal portion 10 is disposed on the low pressure side of the rod packing 11 and the rod packing 11, and the inner peripheral end portion X on the low pressure side of the rod packing 11 protrudes into the minute gap Y between the rod 60 and the shaft hole. It is comprised from the backup ring 12 which suppresses this. In this embodiment, a U-packing having a U-shaped cross section is adopted as the rod packing 11, but various other packings can be adopted. The rod packing 11 includes a first seal lip 11 a that is slidably provided on the surface of the rod 60, and a second seal lip 11 b that is in close contact with the bottom surface of the first annular groove 51.

  In this embodiment, a washer-shaped backup ring 12 is used. The backup ring 12 is disposed so as to be in close contact with the low-pressure side wall surface of the first annular groove 51. When the backup ring 12 receives pressure, it is deformed by compression, and its inner peripheral surface is in close contact with the rod 60. As a result, the low pressure side inner peripheral end portion X of the rod packing 11 is suppressed from protruding into the minute gap between the inner peripheral surface of the backup ring 12 and the rod 60.

The pressure-resistant portion 20 includes a buffer ring 21 and a backup ring 22 that suppresses the inner peripheral end portion on the low pressure side of the buffer ring 21 from protruding into a minute gap between the rod 60 and the shaft hole. In the present embodiment, an annular notch 21b is provided near the inner peripheral end of the buffer ring 21 on the low pressure side, and a backup ring 22 is attached to the notch 21b.

  The dust seal portion 30 is a dust seal including a reinforcing ring 31 having a substantially L-shaped cross section that is fitted and fixed to the inner peripheral surface of the annular notch 53 and a rubber seal portion 32 that is integrally fixed to the reinforcing ring 31. Composed. The rubber seal portion 32 includes a first lip 32a extending to the high pressure side and a second lip 32b extending to the low pressure side (atmosphere side).

<Main seal part>
The main seal portion will be described in more detail. As described above, the main seal portion 10 includes the rod packing 11 and the backup ring 12.

  Nitrile rubber (NBR) is used as the material for the rod packing 11. Thus, in this embodiment, as the material of the rod packing 11, NBR excellent in flexibility and excellent in tracking with respect to shaft eccentricity is adopted, so that excellent sealing performance can be maintained. Note that urethane may be used as a material for the rod packing. However, since urethane has a higher hardness than NBR, the followability to shaft eccentricity is inferior. Also. Since urethane has a property of being hydrolyzed, there is a problem that it deteriorates in an environment of high temperature and high humidity. Furthermore, NBR is superior to urethane in terms of life due to “sag”. Thus, NBR is superior to urethane in terms of sealing performance.

  In this embodiment, a polyamide having a Rockwell hardness of 90 HRR or more and 110 HRR or less is used as a material for the backup ring 12. Hereinafter, the reason why a Rockwell hardness of 90 HRR or more and 110 HRR or less is adopted in polyamide will be described in detail.

  As explained in the background art, when a polyamide having a Rockwell hardness of about 123 HRR is used as the material for the backup ring, urethane having a hardness higher than NBR must be used as the material for the rod packing. I must. In this case, the pressure resistance is increased, but the deterioration of the sealing performance is inevitable.

  Therefore, in this embodiment, a polyamide having a Rockwell hardness of 90 HRR or more and 110 HRR or less is used as a material for the backup ring 12. Thereby, the strength of the backup ring 12 is higher than that of the PTFE backup ring, and the pressure resistance is improved. Moreover, since the hardness difference between the backup ring 12 and the NBR rod packing 11 is not so high, the protrusion of the rod packing 11 can be suitably suppressed. As a result, the pressure resistance can be increased with only one backup ring 12, so that the number of parts does not increase as in the case of using two backup rings, and the cost does not increase.

  Here, FIG. 2 shows various test results when PTFE is used as the material for the backup ring and when plural types of polyamides having different Rockwell hardness are used. The hardness (durometer) of PTFE is D70. Moreover, the test result about the thing made from 85HRR (R85), 109HRR (R109), 120HRR (120R), 123HRR (R123) is shown as a back-up ring made of polyamide. Here, the diameter of the rod 60 used for the test is 75 mm. The fluid pressure (hydraulic pressure) is 35 MPa. The dimensions of the backup ring 12 are an inner diameter of 75 mm, an outer diameter of 88 mm, and a height (axial width) of 3 mm. The stroke for reciprocating the rod 60 was 1000 mm, the speed was 400 mm / sec, and the rod 60 was reciprocated for 100 km. The environmental temperature was set to 120 ° C. Further, the minute gap between the rod 60 and the inner periphery of the shaft hole of the housing 50 was set to 0.25 mm.

  As the test results, as shown in the table, “tensile strength”, “elongation”, “comb” and “extrusion” are shown. In addition, the test method of a tensile strength test and an elongation test is performed according to ASTM (American Society for Testing and Materials) D638 (JIS K 7113).

  Here, “combination” means a phenomenon in which the inner peripheral end portion on the low pressure side of the rod packing 11 protrudes into a minute gap between the inner peripheral surface of the backup ring 12 and the rod 60 and is damaged. ing. The circles in the table indicate that no damage has occurred or that the damage does not affect the sealing performance even if it is damaged. Moreover, x in the table indicates that damage has occurred and has an adverse effect on the sealing performance.

  “Extruding” means a phenomenon in which the inner peripheral end portion on the low pressure side of the backup ring 12 protrudes into the minute gap Y between the rod 60 and the shaft hole. The numerical values in the table indicate the axial length of the portion of the first annular groove 51 that protrudes further to the low pressure side than the low pressure side wall surface. In the table, ◎ indicates that no protrusion occurs, and ◯ indicates that the protrusion does not affect the sealing performance even if the protrusion occurs. Moreover, x in the table indicates that protrusion has occurred and the sealing performance is adversely affected.

  FIG. 3 shows the relationship between the polyimide Rockwell hardness [HRR] and the protrusion of the backup ring [mm], and the polyimide Rockwell hardness [HRR] and the rod packing damage in the polyimide backup ring. The relationship with [mm] is shown. Note that “the protrusion of the backup ring [mm]” is the axial direction of the portion of the inner peripheral end portion on the low pressure side of the backup ring 12 that protrudes further to the low pressure side than the side wall surface on the low pressure side of the first annular groove 51. Indicates the length. “Rod packing damage [mm]” indicates the axial length of the above-mentioned “comb”.

  As can be seen from FIGS. 2 and 3, as the material of the backup ring 12, by adopting a polyamide having a Rockwell hardness of 90 HRR or more and 110 HRR or less, the backup ring 12 protrudes and the rod packing 11 is broken (combination). ) Can be prevented from affecting the sealing performance.

  The reason why the polyamide having a Rockwell hardness of 90 HRR or more and 110 HRR or less is adopted as the material of the backup ring 12 will be further described. When the maximum fluid pressure (maximum hydraulic pressure) is 35 [MPa], the Rockwell hardness of the backup ring 12 is preferably 90 [HRR] or more. Thereby, the protrusion of the backup ring can be eliminated, or even if it protrudes, the influence on the sealing performance can be eliminated. A major reason for this is that the life of the backup ring is taken as a guide until it reaches 1/3 of its height (axial width).

  However, as described above, if the hardness of the backup ring is too high, the hardness difference from the rod packing becomes large, and the possibility of damage to the rod packing increases. Therefore, from this point of view, the hardness of the backup ring should be as low as possible.

  Therefore, in this embodiment, taking into account tolerances and the like, the reference is set to 100 HRR, and 100 HRR ± 10 HRR, that is, the lower limit is set to 90 [HRR] and the upper limit is set to 110 [HRR]. As a result, as apparent from the above test results, it is possible to suppress the protrusion of the backup ring and to prevent the rod packing from being damaged.

DESCRIPTION OF SYMBOLS 10 Main seal part 11 Rod packing 11a 1st seal lip 11b 2nd seal lip 12 Backup ring 20 Pressure-resistant part 21 Buffer ring 21b Notch 22 Backup ring 30 Dust seal part 31 Reinforcement ring 32 Rubber seal part 32a 1st lip 32b 2nd lip 50 Housing 51 1st annular groove 52 2nd annular groove 53 Annular notch 60 Rod

Claims (1)

A sealing system for sealing an annular gap between a relatively reciprocating housing and a rod inserted into a shaft hole of the housing,
A rod packing disposed in an annular groove provided on the inner periphery of the shaft hole;
A backup ring which is disposed in the annular groove and on the low pressure side of the rod packing, and suppresses the inner peripheral end portion on the low pressure side of the rod packing from protruding into a minute gap between the rod and the shaft hole; ,
In a sealing system comprising:
The material of the rod packing is nitrile rubber,
The sealing system according to claim 1, wherein the material of the backup ring is a polyamide having a Rockwell hardness of 90 HRR to 110 HRR.

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