JP6474707B2 - Shaft seal mechanism - Google Patents

Description

  The present invention relates to a shaft seal mechanism that seals a reciprocating shaft that is inserted into a pressure-resistant structure such as a pump.

  In general, in a reciprocating pressure pump, a valve, a hydraulic cylinder, etc., a reciprocating shaft (for example, a piston, piston rod, or the like) inserted through a pressure-resistant structure that seals the generated pressure of an internal fluid (including gas) The plunger or the like has a shaft seal that forms a pressure boundary between the inside and the outside of the pressure-resistant structure, thereby sealing the leakage of the internal fluid when the reciprocating shaft is operating and when it is stationary.

  Normally, various gland packings and mechanical seals are used as the shaft seal of the reciprocating shaft. However, these seals enable sliding of the reciprocating shaft at the pressure boundary, so that a small amount of internal fluid leaks due to the necessity of holding an oil film on the sliding surface, wear of the sliding surface, and the characteristics of the sealing material. Is recognized.

  On the other hand, a diaphragm or a bellows type shaft seal (hereinafter referred to as a bellows seal) is a shaft seal that can completely seal an internal fluid because there is no sliding portion at the pressure boundary.

  As an example of the bellows seal, Patent Document 1 (Japanese Patent Laid-Open No. 2006-57610) discloses a bellows type shaft seal that can completely seal a high-pressure internal fluid leaking to the atmosphere in a shaft seal of a reciprocating pump. A shaft seal structure is disclosed. In this shaft seal structure, an auxiliary shaft seal is provided on the sliding side of the cylinder and the cylinder on the atmosphere side of the bellows type shaft seal, and the diameter of the shaft or cylinder in contact with the auxiliary shaft seal is equal to the effective diameter of the bellows. In addition, a primary seal is provided on the pump side shaft and the cylinder sliding portion from the bellows type shaft seal portion, and the diameter of the shaft or cylinder in contact with the primary seal is made equal to the effective diameter of the bellows. It is what.

  Patent Document 2 (Japanese Patent Laid-Open No. 2006-144741) discloses that a shaft seal of a reciprocating pump completely seals the leakage of fluid inside the pump into the atmosphere, and causes troubles due to freezing of the seal part or contamination of foreign matter. Disclosed is a pump shaft seal that prevents this. This reciprocating pump has a piston ring or packing on the piston, an auxiliary seal on the piston shaft, and a shaft that seals the cylinder chamber from the atmosphere side by a flexible member on the piston shaft on the atmosphere side of the auxiliary seal. A seal is provided, and the shaft seal is a bellows seal.

JP 2006-57610 A JP 2006-144741 A

  In a reciprocating shaft that requires a large stroke, the diaphragm may not be applied from the viewpoint of preventing excessive creep deformation and damage. On the other hand, the bellows seal will not break until a certain number of times if the bellows structure (plate thickness, pitch, amount of expansion / contraction per peak) is appropriately selected according to the reciprocating stroke and the internal / external pressure difference of the bellows. Repeated expansion and contraction following the reciprocating axis is possible.

  In general, the number of times of endurance of the bellows against repeated expansion and contraction can be obtained approximately by the bellows life calculation formula “M.W. Kellogg's formula” or “Hamada, Takezono's formula”. According to this, it can be seen that the sum of the bellows internal stress due to the reciprocating stroke (hereinafter referred to as stretching stress) and the bellows internal stress due to the variable pressure (hereinafter referred to as variable pressure stress) directly contributes to the durability. Therefore, as each stress component is smaller, the number of times of durability against expansion and contraction while receiving pressure can be improved.

  Further, according to the above-mentioned Kellogg equation, the stretching stress is proportional to the thickness of the bellows and the amount of stretching. The fluctuating pressure stress is proportional to the fluctuating pressure and inversely proportional to the square of the bellows plate thickness. For this reason, if the bellows plate thickness is reduced to reduce the expansion and contraction stress, the fluctuating pressure stress increases. In general, considering that the overall length of the bellows is limited to some extent in design and manufacturing, it is possible to reciprocate with a relatively long stroke. When a bellows seal is applied to the dynamic shaft seal, it is difficult to significantly improve the number of durability in a structure in which the bellows receives the pressure sealed by the pressure-resistant structure as it is.

  For this reason, an object of the present invention is to provide a technology for improving the durability of a bellows seal that can completely seal an internal fluid, and provides a shaft seal mechanism that combines a bellow seal and a pressurizing mechanism for the bellow seal. Is.

Therefore, the present invention provides a shaft seal mechanism in which a reciprocating shaft that reciprocates in a cylinder by a drive mechanism is provided in a holding member that slidably holds in the cylinder. A bellows connected between the projecting tip and the holding member; a pressurizing cylinder which is provided on the opposite side of the bellows of the holding member and defines a pressurizing space; and an axial end of the pressurizing cylinder A pressurizing piston that moves with the reciprocating shaft, and the pressurizing space and the internal space of the bellows are connected via a communication passage, and the pressurizing space, the communication passage, and the bellows In the internal space, incompressible fluid is accommodated. The holding member constitutes a part of a so-called pressure-resistant structure, and the pressurization space defined by the pressurization cylinder and the pressurization piston communicates with the internal space of the bellows through a communication passage. A mechanism is formed.

As described above, the fixed end of the bellows is fixed to the holding member, and the free end of the bellows is fixed to one end of the reciprocating motion, and the bellows expands and contracts as the reciprocating shaft moves. As the bellows expands and contracts, the volume of the inner space of the bellows varies, but the incompressible fluid that is the working fluid accommodated in the pressurized space, the communication path, and the inner space of the bellows varies in the volume of the inner space of the bellows. Therefore, since the pressure in the inner space of the bellows is maintained, the bellows pressure deformation (cross-sectional deformation) is restricted, and the fluctuating pressure stress is suppressed. In addition, it is desirable that the shape of the pressurizing space and the bellows is set so that the volume change of the pressurizing space when the reciprocating shaft moves by a unit length is equal to the volume change of the internal space of the bellows.

  Furthermore, it is preferable that the communication passage is a communication hole formed in the holding member. Thereby, since the pressurizing space and the internal space of the bellows are directly connected, the working fluid can be easily moved. Further, the moving speed of the working fluid can be adjusted by adjusting the diameter of the communication hole.

  Furthermore, an inner tube is provided between one end of the reciprocating shaft and the pressurizing piston so as to define a predetermined communication space around the reciprocating shaft along the reciprocating shaft. The inner tube is formed with a first communication hole that communicates the pressurized space and the communication space, and a second communication hole that communicates the communication space and the internal space of the bellows, Is formed by the first communication hole, the communication space, and the second communication hole.

  In this case, an internal intubation tube is disposed so as to form a predetermined communication space between the reciprocating shaft and the reciprocating shaft, and the pressurized space and the internal space are communicated with each other via the communication space. It has become. Furthermore, the shape of the pressurizing space and the bellows is set so that the volume change of the pressurizing space when the reciprocating shaft moves a unit length is equal to the volume change of the inner space of the bellows intubation tube and the bellows. Is desirable.

  As described above, according to the present invention, since the pressure boundary integrated with the pressure-resistant structure is formed, the internal fluid can be completely sealed and the fluctuation pressure stress amplitude can be suppressed. The number of bellows durability determined by superimposing stress and fluctuating pressure stress can be improved.

It is explanatory drawing which showed the state by which the reciprocating shaft was pulled out from the cylinder in the shaft seal mechanism which concerns on Example 1 of this invention. It is explanatory drawing which showed the state in which the reciprocating shaft was pushed in in the cylinder in the shaft seal mechanism which concerns on Example 1 of this invention. It is explanatory drawing which showed the state by which the reciprocating shaft was pulled out from the cylinder in the shaft seal mechanism which concerns on Example 2 of this invention. It is explanatory drawing which showed the state by which the reciprocating shaft was pushed in in the cylinder in the shaft seal mechanism which concerns on Example 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  A shaft seal mechanism 1 according to the first embodiment shown in FIGS. 1 and 2 is provided in a plunger pump 3 that uses a piston rod 2 as a reciprocating shaft. One end of the plunger pump 3 is connected to a double-acting drive mechanism such as an air cylinder (not shown).

  The plunger pump 3 is fixed to the discharge port block portion 5 in which the discharge port 4 is formed, the cylinder 6 fixed to the discharge port block 5 and defining the cylinder space 7 therein, and the discharge port block portion 5. And a base flange 8 as a holding member that closes one end of the cylinder 6 and slidably holds the piston rod 2, and a pressurizing cylinder 9 is disposed in the discharge port block portion 5. The

  The pressurizing cylinder 9 has a pressurizing cylinder chamber 10 as a pressurizing space, and one end thereof is closed by a pressurizing piston 11.

  A free end 12a of a bellows 12 is fixedly connected to a tip 2a of the piston rod 2 extending into the cylinder space 7, and a fixed end 12b of the bellows 12 is fixedly connected to the base flange 8, and the piston rod 2 In between, an internal space 13 of the bellows 12 is defined. The internal space 13 communicates with the pressurizing cylinder chamber 10 through a communication hole 14 formed in the base flange 8.

The pressurizing cylinder chamber 10, the communication hole 14, and the internal space 13 contain incompressible fluid such as hydraulic fluid .

As shown in FIG. 2, when the piston rod 2 is driven by the drive mechanism in the direction in which the piston rod 2 is inserted into the discharge port block portion 5, the cylinder space 7 surrounded by the discharge port block portion 5, the base flange 8 and the cylinder 6 is formed. A part of the pumped fluid to be accommodated is excluded and discharged from the discharge port 4. Pressure is generated by the viscous resistance, and this pressure acts on the outer surface of the bellows 12 as a fluctuating pressure load. At this time, the incompressible fluid in the pressurized cylinder chamber 10 flows into the internal space 13 of the bellows 12 through the communication hole 14 and balances with the variable pressure load from the outer surface of the bellows 12, thereby generating bellows variable pressure stress. Such a restraining action against cross-sectional deformation can be obtained.

On the other hand, as shown in FIG. 1, when the piston rod 2 is driven by the drive mechanism in the direction in which it is pulled out from the discharge port block 5, the incompressible fluid in the inner space 13 of the bellows 12 By flowing into the pressurizing cylinder chamber 10 via 14 and balancing, a constraining effect can be obtained against cross-sectional deformation that causes the fluctuating pressure stress of the bellows 12 in the same manner as described above.

  From the above, since the bellows fluctuation pressure stress is suppressed or alleviated, the number of times of durability until the bellows 12 is damaged due to repeated plunger reciprocation can be improved.

  The shaft seal mechanism 1 according to the second embodiment shown in FIGS. 3 and 4 is mounted on the plunger pump 3 that uses the piston rod 2 as a reciprocating shaft, as in the first embodiment. One end of the plunger pump 3 is connected to a double-acting drive mechanism such as an air cylinder (not shown).

  The plunger pump 3 is fixed to the discharge port block portion 5 in which the discharge port 4 is formed, the cylinder 6 fixed to the discharge port block 5 and defining the cylinder space 7 therein, and the discharge port block portion 5. And a base flange 8 as a holding member for closing one end of the cylinder 6 and indirectly holding the piston rod 2 slidably, and a pressure cylinder 9 in the discharge port block 5. Is placed. Further, an intubation tube 15 is arranged along the piston rod 2 so as to define a communication space 16 around the piston rod 2. Note that the base flange 8 directly and slidably holds the inner tube 15 that is sheathed on the piston rod 2.

  The pressurizing cylinder 9 has a pressurizing cylinder chamber 10 as a pressurizing space, and one end thereof is closed by a pressurizing piston 11. Further, the inner insertion tube 15 is disposed between the tip 2 a of the piston rod 2 and the pressurizing piston 11.

  A free end 12a of a bellows 12 is fixedly connected to a tip 2a of the piston rod 2 extending into the cylinder space 7, and a fixed end 12b of the bellows 12 is fixedly connected to the base flange 8, and the piston rod 2 In between, an internal space 13 of the bellows 12 is defined. The internal space 13 is communicated with the pressurizing cylinder chamber 10 via first and second communication holes 14 a and 14 b formed in the inner insertion tube 15 and further through the communication space 16.

The pressurizing cylinder chamber 10, the first communication hole 14 a, the communication space 16, the second communication hole 14 b, and the internal space 13 contain an incompressible fluid such as hydraulic fluid .

As shown in FIG. 4, when the piston rod 2 is driven by the drive mechanism in the direction in which the piston rod 2 is inserted into the discharge port block portion 5, the cylinder space 7 surrounded by the discharge port block portion 5, the base flange 8 and the cylinder 6 is formed. A part of the pumped fluid to be accommodated is excluded and discharged from the discharge port 4. Pressure is generated by the viscous resistance, and this pressure acts on the outer surface of the bellows 12 as a fluctuating pressure load. At this time, the incompressible fluid in the pressurized cylinder chamber 10 flows into the internal space 13 of the bellows 12 through the first communication hole 14 a, the communication space 16, and the second communication hole 14 b, and from the outer surface of the bellows 12. By balancing with the fluctuating pressure load, it becomes possible to obtain a restraining action against cross-sectional deformation that causes a bellows fluctuating pressure stress.

On the other hand, as shown in FIG. 3, when the piston rod 2 is driven by the drive mechanism in a direction in which the piston rod 2 is pulled out from the discharge port block portion 5, the incompressible fluid in the inner space 13 of the bellows 12 is The cross-sectional deformation that causes the fluctuating stress of the bellows 12 to flow into the pressurized cylinder chamber 10 through the communication hole 14b, the communication space 16, and the first communication hole 14a and balance them, as described above. A constraining effect can be obtained.

  From the above, since the bellows fluctuation pressure stress is suppressed or alleviated, the number of times of durability until the bellows 12 is damaged due to repeated plunger reciprocation can be improved.

DESCRIPTION OF SYMBOLS 1 Shaft seal mechanism 2 Piston rod 2a Tip 3 Plunger pump 4 Discharge port 5 Discharge block part 6 Cylinder 7 Cylinder space 8 Base flange 9 Pressurizing cylinder 10 Pressurizing cylinder chamber 11 Pressurizing piston 12 Bellows 12a Free end 12b Fixed end 13 Inside Space 14 Communication hole 14a First communication hole 14b Second communication hole 15 Inner intubation 16 Communication space

Claims (3)

In the shaft seal mechanism provided on the holding member that slidably holds the reciprocating shaft that reciprocates in the cylinder by the drive mechanism,
A bellows provided between one end of the reciprocating shaft and projecting into the cylinder and the holding member;
A pressurizing cylinder provided on a side opposite to the bellows of the holding member and defining a pressurization space;
A pressurizing piston that closes the axial end of the pressurizing cylinder and moves with the reciprocating shaft;
The pressurized space and the internal space of the bellows are connected via a communication passage,
An incompressible fluid is accommodated in the pressurizing space, the communication passage, and the inner space of the bellows.   The shaft sealing mechanism according to claim 1, wherein the communication passage is a communication hole formed in the holding member. It said to define a predetermined communication space around the reciprocating shaft along the reciprocating shaft, comprising an inner intubation disposed between one of the tip and the pressurizing piston of the reciprocating shaft,
The internal intubation is formed with a first communication hole that communicates the pressurized space and the communication space, and a second communication hole that communicates the communication space and the internal space of the bellows.
The shaft seal mechanism according to claim 1, wherein the communication passage is formed by the first communication hole, the communication space, and the second communication hole.

Images