JP4115318B2 - Mechanical seal structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mechanical seal structure used under high pressure conditions such as a can water circulation pump.
[0002]
[Prior art]
For example, mechanical seals are conventionally used in shaft seals where high-temperature and high-pressure fluid pressure acts, such as a canned water circulation pump of a forced circulation boiler. Further, it is known that a general mechanical seal structure impairs the sealing performance because the contact surface between the seal ring and the stationary ring that become a seal surface cannot be kept parallel when used under high pressure. For this reason, under the conditions of high temperature and high pressure, a floating ring type mechanical seal provided with a floating ring divided from a stationary ring is employed.
[0003]
Therefore, a conventional floating ring type mechanical seal structure will be briefly described with reference to FIG. In FIG. 5, reference numeral 1 is a rotating shaft, 2 is a rotating ring, 3 is a seal ring, 4 is a seal casing, 5 is a stationary ring, 6 is a free ring, 7 is a spring retainer, 8 is a spring, 9 is a backup ring, Reference numeral 10 denotes an O-ring, and 11 denotes an adapter.
The rotary ring 2 and the seal ring 3 are components that rotate integrally with an impeller (not shown) attached to the rotary shaft 1, and the other seal casing 4, stationary ring 5, idle ring 6, spring retainer 7, etc. It becomes a component on the fixed side.
[0004]
The idle ring 6 is sandwiched and held between a seal ring 3 fixed to the rotary ring 2 and a stationary ring 5 slidably held in the axial direction by the seal casing 4 and biased in the direction of the rotary ring. These are annular members in which both end portions are substantially symmetrical. In this case, the relative rotational sliding of the seal surfaces 3a and 6a, which are the contact surfaces of the seal ring 3 and the idle ring 6, between the sealed fluid region H of high temperature and high pressure such as can water and the non-sealed fluid region L of atmospheric pressure. It is configured to shield and seal by contact action.
In a general conventional configuration, the idle ring 6 is made of a cobalt binder cemented carbide, and the backup ring 9 is made of polytetrafluoroethylene containing glass fiber.
Polytetrafluoroethylene is generally a fluororesin that is widely known under the trade name “Teflon (registered trademark)”.
As a publicly known document of a mechanical seal having such a floating ring, for example, there is Patent Document 1 below.
[0005]
[Patent Document 1]
JP-A-7-198042 (page 3-4, FIG. 1)
[0006]
[Problems to be solved by the invention]
By the way, in the above-mentioned conventional mechanical seal structure, for example, a leak occurs under a condition where a high pressure close to the pressure in the forced circulation boiler acts, and a sufficient sealing function cannot be exhibited. For this reason, in the canned water circulation pump, the pressure acting on the shaft seal portion is suppressed as low as possible by introducing sealed water to cope with high pressure, and the pressure resistance condition of the mechanical seal portion is relaxed and used.
Accordingly, there is a demand for a mechanical seal structure that does not leak even when exposed to high-temperature and high-pressure can water so that usable pressure resistance conditions can be set as high as possible.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a mechanical seal structure having excellent pressure resistance characteristics that can eliminate leakage from the shaft seal portion even when exposed to a high-temperature and high-pressure fluid. Is.
[0008]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
The mechanical seal structure according to claim 1 is configured such that a floating ring is sandwiched between a seal ring held by a rotary ring that rotates integrally with a rotary shaft side and a stationary ring held by a seal casing side. The space between the stationary ring and the spring retainer is sealed with an O-ring and a backup ring made of bronze-containing polytetrafluoroethylene.
[0009]
According to such a mechanical seal structure, by adopting a bronze-containing polytetrafluoroethylene backup ring that is excellent in compressibility and creep resistance, the backup ring protrudes from a predetermined position even under high pressure. There is nothing, and the followability of the seal surface is improved, and good sealability can be obtained.
[0010]
The mechanical seal structure according to claim 2 is a floating ring made of a nickel binder cemented carbide between a seal ring held by a rotary ring that rotates integrally with the rotary shaft side and a stationary ring held by the seal casing side. Is characterized by being held under pressure.
[0011]
According to such a mechanical seal structure, since the nickel binder cemented carbide having excellent corrosion resistance is adopted, it is possible to suppress the occurrence of erosion due to corrosion on the seal surface of the idle ring and to improve the sealing performance and durability. .
[0012]
The mechanical seal structure according to claim 3 is configured such that a floating ring is held between a seal ring held by a rotary ring that rotates integrally with the rotary shaft side and a stationary ring held by the seal casing side. The hydro ring portion is provided in the idle ring.
[0013]
According to such a mechanical seal structure, lubricating water (using injection water) can be supplied to the sealing surface through a hydro-cut portion provided for the purpose of taking lubricating water into the sealing surface.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a mechanical seal structure according to the present invention will be described with reference to the drawings.
FIG. 3 shows an outline of the can water circulation pump 200, in which a drive motor 230 located in the upper part and an impeller 201 provided in the lower part are connected by a single rotating shaft 1. A space between the drive motor 230 and the impeller 201 is referred to as a prime mover base 202, a bearing 203 is provided in the upper part of the prime mover base 202, and a free ring type mechanical seal (to be described later) 20) is incorporated.
[0015]
As a method for sealing the canned water in the idle ring type mechanical seal 20, since the feed water pump (not shown) is also operated during the boiler operation, the injection water into which a part of the feed water is introduced is passed between the upper and lower floating rings 204, 205. It is possible to prevent the can water from rising from the impeller 201 by sealing with the injection water.
The injection water introduced between the floating rings 204 and 205 (indicated by a thick arrow in the figure) partly joins the can water and is sent to a water drum (not shown), and the rest is degassed (not shown). Guided to a vessel.
The introduced injection water is depressurized to, for example, about 98 Pa (10 kg / cm ² ) with the floating rings 204 and 205, and finally sealed with the mechanical seal 20.
[0016]
However, during hot banking when the boiler operation is stopped, the operation of the water supply pump is also stopped, and as shown in FIG. 4, the supply of injection water is lost and sealing becomes impossible. For this reason, for example, canned water having a high pressure of about 1960 Pa (200 kg / cm ² ) and approximately the same high pressure as that in the boiler body rises along the rotary shaft 1 as indicated by a thick arrow in the figure. It is necessary to seal the water pressure only with the mechanical seal 20.
[0017]
As shown in FIG. 1, the idle ring type mechanical seal 20 used here includes a rotary ring 2 and a seal ring 3 as main components on the rotary side that operate integrally with the rotary shaft 1 of the pump. As main components on the stationary side, there are a spring retainer 7, an adapter 11, a stationary ring 5, a floating ring 6, and the like.
In this mechanical seal 20, a sealed fluid region H on the high-pressure fluid side is obtained by a relative rotational sliding action on a contact surface between the seal surface 6 a of the idle ring 6 on the stationary side and the seal surface 3 a of the seal ring 3 on the rotation side. And a non-sealed fluid region L at atmospheric pressure.
The spring 8 held by the spring retainer 7 has a function of urging the stationary ring 5 and the idle ring 6 to press from the top to the bottom toward the seal ring 3, and is arranged via the backup ring 9. The O-ring 10 seals between the stationary ring 5 and the spring retainer 7 so that the can water does not leak from the sealed fluid region H on the high-pressure fluid side to the non-sealed fluid region L at atmospheric pressure.
[0018]
The idle ring 6 is a member having a convex section in the shape of an annular pressing portion 61 and a sealing portion 62 having substantially the same shape protruding from both end surfaces of the annular main body portion, and the end surface of the pressing portion 61. Comes into contact with the end surface 5 a of the stationary ring 5, and the seal surface 6 a serving as the end surface of the seal portion 62 is in sliding contact with the seal surface 3 a serving as the end surface of the seal ring 3.
Further, as shown in FIG. 2, the idle ring 6 is provided with a hydrocut portion 6b by partially cutting the seal surface 6a. The hydrocut portion 6b is configured such that lubricating water for cooling or the like is supplied between the seal surfaces 3a and 6a that are in sliding contact with each other by relative rotation. In the illustrated example, the hydrocut portions 6b are provided at eight positions at a 45-degree pitch. In addition, the number and arrangement | positioning of the hydrocut part 6b are not limited to the example of illustration.
[0019]
The above-mentioned idle ring type mechanical seal is known to be excellent in high-pressure characteristics. For example, even in canned water (high-pressure fluid of about 1960 Pa) under operating conditions in which the sealed water disappears in the canned water circulation pump. In order to prevent leakage, it is necessary to further improve the breakdown voltage characteristics.
Therefore, the inventors have conducted various tests and studies in order to investigate the cause of leakage at high pressure.
[0020]
As a result, as a first result, when the backup ring 9 made of glass fiber-containing polytetrafluoroethylene is subjected to a high pressure action, a failure to follow the seal surface due to protrusion from a predetermined position may occur. It was found that a leak occurred as a cause. That is, a defective seal portion is generated between the stationary ring 5 and the spring retainer 7, and high-pressure fluid leaks from the defective seal portion.
Therefore, the backup ring 9 was tested by changing various materials, and it was found that the use of the bronze-containing polytetrafluoroethylene backup ring 9 yielded the most excellent results. This is presumably because the backup ring 9 made of bronze-containing polytetrafluoroethylene is excellent in terms of compression resistance and creep resistance necessary for high-pressure specifications.
[0021]
As a second result, when the mechanical seal 20 in which a leak occurred due to high pressure was disassembled and inspected, generation of erosion due to corrosion was observed on the seal surface 6a of the idle ring 6. This is presumed to be due to a problem with the material of the idle ring 6 (cobalt binder cemented carbide). When various tests were conducted on corrosion resistance using various materials, nickel binder cemented carbide had the most excellent corrosion resistance. showed that. Therefore, in this invention, it decided to employ | adopt the idle ring 6 made from a nickel binder cemented carbide.
[0022]
Needless to say, the mechanical seal structure described so far is not limited to the shaft seal portion of the canned water circulation pump of the forced circulation boiler, and can be widely applied as a shaft seal structure for pumps that handle high-temperature and high-pressure fluids. .
And the structure of this invention is not limited to embodiment mentioned above, In the range which does not deviate from the summary of this invention, it is possible to combine and change suitably.
[0023]
【The invention's effect】
The mechanical seal structure of the present invention has the following effects.
(1) Since the backup ring is made of bronze-containing polytetrafluoroethylene, it is possible to prevent leakage due to protrusion of the backup ring between the stationary ring and the spring retainer, and to improve durability and reliability against high pressure. be able to.
(2) Since the idle ring is made of a nickel binder cemented carbide, erosion due to corrosion can be prevented from occurring on the seal surface of the idle ring, and durability and reliability against high pressure can be improved.
(3) The lubricity of the seal surface can be improved by providing the hydrocut portion on the idle ring.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an essential part showing an embodiment of a floating ring type mechanical seal structure according to the present invention.
2A and 2B are diagrams showing a floating ring of the floating ring type mechanical seal shown in FIG. 1, wherein FIG. 2A is an enlarged view showing a hydrocut portion, and FIG. 2B is a bottom view.
FIG. 3 is a cross-sectional view showing an outline of a can water circulation pump, showing a path in the pump of injection water.
FIG. 4 is a diagram showing a path through which injection water supply to the can water circulation pump shown in FIG. 3 is stopped and can water flows to the shaft seal portion.
FIG. 5 is a cross-sectional view showing a conventional floating ring type mechanical seal structure.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rotating shaft 2 Rotating ring 3 Seal ring 3a Seal surface 5 Stationary ring 6 Free ring 6a Seal surface 6b Hydro cut part 7 Spring retainer 9 Backup ring 10 O-ring 20 Free ring type mechanical seal

Claims (3)

  A floating ring is sandwiched and held between a seal ring held on a rotary ring that rotates integrally with the rotary shaft side and a stationary ring held on the seal casing side, and the gap between the stationary ring and the spring retainer is maintained. A mechanical seal structure characterized by being sealed with an O-ring and a backup ring made of bronze-containing polytetrafluoroethylene. Mechanical seal structure according to claim 1, wherein between the seal ring and said stationary ring, characterized by comprising to clamp holds the floating ring made of nickel binder cemented carbide. The mechanical seal structure according to claim 1, wherein a hydrocut portion is provided in the idle ring.

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