JP2000283059A - Cryogenic liquid pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pump capable of being assembled at ordinary temperature and usable at an ultra-low temperature without causing a seizure in a sliding part by forming a cylinder and a piston base material by use of the same material, subjecting the surface of the piston to a self-lubricating composite plating, and setting the space between the piston and the cylinder to a prescribed precision. SOLUTION: A liquid hydrogen pump has a suction opening 2 formed on the bottom of a bottomed cylindrical pump housing 1, and the upper part of the housing 1 is fixed to a liquid hydrogen storage vessel. A piston 10 fitted to a cylinder 11 within the housing 1 is reciprocated through a connection rod 15 by the operation of a pump driving mechanism arranged in the upper part of the housing 1. In this case, the circumferential surface of the piston 10 is nickeled by use of a suspension obtained by dispersing a material having self- lubricating function such as polytetrafluoroethylene or molybdenum disulfide in a metal matrix, and the plating layer is polished, whereby the clearance between the cylinder 11 and the piston 12 is set to 1-3 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid pump for extracting and supplying a liquefied gas such as liquid hydrogen liquefied at an extremely low temperature in a liquid state.

[0002]

2. Description of the Related Art As such a liquid pump for discharging and supplying a liquefied gas in an extremely low temperature state, there is known a liquid pump disclosed in Japanese Patent Application Laid-Open No. 7-4350 previously proposed by the present inventors. In this liquid pump, a suction port formed in the pump housing is opened at the bottom of a tank containing liquid hydrogen,
The cylinder is connected to the pump drive unit arranged at the top of the pump housing so that the cylinder can reciprocate.The piston that moves relative to the cylinder is connected to the bottom of the pump housing, and the piston is fixed. Has become.

[0003] A liquefied gas represented by liquid hydrogen has properties such as low viscosity, low latent heat, and extremely low temperature. For this reason, a liquid pump that handles such a liquid must adjust its clearance to about 1 to 3 μm so that the liquid does not leak from the gap between the cylinder and the piston at the time of compression. And the cylinder must be formed of the same material.

Therefore, in the above-described conventional apparatus, the peripheral surface of the piston is lined with a nickel alloy having a linear expansion coefficient smaller than that of the cylinder, and a self-lubricating synthetic resin is disposed on the outer peripheral surface of the lining surface. With a structure, the shrinkage of the self-lubricating synthetic resin is suppressed with a nickel alloy,
The self-lubricating synthetic resin prevents seizure between the piston and the cylinder.

[0005]

However, the coefficient of linear expansion of each material has a temperature dependency, and each material has a delicate difference in composition depending on the production lot. Is difficult to set accurately to a predetermined dimension, and the fact is that it is experimentally determined. For this reason, there was a problem that it was difficult to mass-produce industrially.

The present invention has been proposed in view of the above points, and can be assembled at room temperature, does not require high-precision manufacturing technology, and can be used at extremely low temperatures where seizure does not occur on sliding parts. It is an object to provide a simple liquid pump.

[0007]

In order to achieve the above-mentioned object, the present invention is to form a cylinder and a piston base which are relatively slidable from the same material, and perform self-lubricating composite plating on the surface of the piston. A gap between the piston peripheral surface and the cylinder inner peripheral surface is formed with a clearance of a predetermined accuracy.

[0008]

According to the present invention, the outer peripheral surface of the piston formed of the same material as the cylinder is subjected to the self-lubricating composite plating, and the self-lubricating composite plated portion is polished to form the piston peripheral surface and the cylinder inner peripheral surface. The gap of the specified accuracy (1-3
μm) clearance.
With a simple operation, the gap between the piston circumferential surface and the cylinder inner circumferential surface can be accurately set. In addition, the peripheral surface of the piston is self-lubricating composite plating, but since this plating thickness is much thinner than the thickness of the piston,
The contraction amount of the plating layer is extremely small, which is negligible compared to the contraction amount of the metal part of the piston, so that the gap between the piston and the cylinder can be kept constant.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of a liquid hydrogen pressure pump showing one example of a liquid pump to which the present invention is applied, and FIG. 2 is a sectional view of a main part thereof. In this liquid hydrogen pump, a suction port (2) is radially opened at the bottom of a pump housing (1) formed in a bottomed cylindrical shape. A mounting flange (3) for fixing to a liquid hydrogen storage container (not shown) is fixed to an upper part of the pump housing (1), and a pump head (4) is provided above the mounting flange (3). It is attached.

A pump drive mechanism (5) is housed in the pump head (4). The pump drive mechanism (5) includes a crankshaft (6) that is rotationally driven in conjunction with a rotary drive source such as a DC electric motor (not shown), and a connecting rod (7) connected to the crankshaft (6). And a crosshead (8) connected to the pump head (4) via a liner (9). The crosshead (8) is slidably inserted into the pump head (4).

[0011] Inside the pump housing (1), SUS
A piston (10) formed of 304L and a cylinder (11) formed of SUS304L slidably inserted into the piston (10) are mounted, and the piston (10) is mounted on the pump housing (1). Is fixed to the inside of a piston holder (14) which is held on a bottom wall (12) via a universal joint (13). The cylinder (11) is fixed to the lower end of a cylinder holder (17) supported by the crosshead (8) via a connecting rod (15) and a universal joint (16).

The cylinder (11) has a suction valve (18) and a piston.
A discharge valve (19) is formed in (10), and the cylinder is
When the lowering operation of (11) is performed, the suction valve (18) opens and the discharge valve (19) closes, and when the cylinder (11) moves upward, the discharge valve (1) is opened.
9) is opened and the suction valve (18) is closed. When the cylinder (11) is lowered by the operation of the pump drive mechanism (5), liquid hydrogen is taken into the pressurized chamber (20) formed in the piston (10), and the pressurized chamber is raised when the cylinder (11) is raised. Liquid hydrogen is sent from (20).

In the liquid pump having such a basic structure, the clearance between the peripheral surface of the piston (10) and the inner peripheral surface of the cylinder (11) greatly affects the pump efficiency.
Therefore, in the present invention, the outer peripheral surface of the piston (10) polytetrafluoroethylene, molybdenum disulfide, tungsten disulfide, boron nitride, particles of a material having a self-lubricating function such as graphite metal matrix (surfactant) Nickel plating to a thickness of 15 μm using a suspension uniformly dispersed in
The clearance between the inner peripheral surface of (11) and the outer peripheral surface of the piston (10) is formed to be 1 to 3 μm.

The piston (10) and the cylinder (11) are SUS3
When the outer diameter of the piston (10) is Dp, the thickness of the plating layer (21) is t, and the clearance between the piston (10) and the cylinder (11) is h, the cylinder diameter (Dc) is: Dc = Dp + 2t + 2h. When the piston (10) and the cylinder (11) are assembled at normal temperature (300K) and cooled to the liquid hydrogen temperature (20K), the piston diameter (D _P1 ) becomes the linear expansion coefficient of SUS304L as α ₁ , Assuming that the linear expansion coefficient is α ₂ , D _P1 = D _P (1−α ₁ × (300-20)) + 2t (1−α ₂ × (300-20)). In this case, the cylinder diameter (D _C1 ) is D _c1 = D _c ((1−α ₁ × (300-20)) = (Dp + 2t + 2h) ((1−α ₁ × (3
00-20)).

Here, the piston diameter D at 300K_p1
8 mm, thickness t of the plating layer (21) is 10 μm, clearance
h is 1 μm, linear expansion coefficient α of SUS304L₁Is 11 × 10
^-6, Linear expansion coefficient α of plating material_TwoIs 3.5 × 10^-6Place
The piston diameter D at 20K _P1Is 17.96434 mm,
Cylinder diameter D at 20K_c1Becomes 17.96649.
Therefore, the clearance at 20K is (D_c1-D_P1) /
2, h = 0.000976 (mm), and
For 0.001mm clearance at 300K (0.
(001-0.00000976) /0.001 = 0.024
Only 2.4% for 1 μm clearance
No change will occur.

As described above, the outer peripheral surface of the piston (10) is subjected to self-lubricating composite plating, and the plating layer (21) is polished to adjust the gap between the cylinder (11) and the piston (10). If the thickness of the plating layer (21) is
Since it is extremely small with respect to the thickness of (10), the plating layer (2
Even if the coefficient of linear expansion of the material constituting 1) is slightly different from the coefficient of linear expansion of the piston components, the amount of contraction in the plating layer (21) is ignored compared to the amount of contraction of the piston (10). Small enough to do. For this reason, even if the pump is operated in a temperature range of, for example, 20 K, the cylinder (11) and the piston (10) formed of the same material contract in the same manner. , The change in the order of a few percent in the order of microns on the micron order, so that the clearance at the time of assembly can be maintained even in an extremely low temperature range of 20K.

[0017]

According to the present invention, the outer peripheral surface of a piston formed of the same material as the cylinder is subjected to self-lubricating composite plating, and the plating layer is polished to form a gap between the piston peripheral surface and the cylinder inner peripheral surface. Since the clearance is formed with a predetermined accuracy (1 to 3 μm), the gap between the piston peripheral surface and the cylinder inner peripheral surface can be accurately set by a simple operation. In addition, the peripheral surface of the piston is self-lubricating composite plating, but since the plating thickness is much smaller than the piston thickness, the contraction amount of the plating layer is smaller than that of the metal part of the piston. Since the amount is extremely small to a negligible amount, the gap between the piston and the cylinder can be kept constant.

In order to maintain the clearance between the normal temperature range and the extremely low temperature range substantially constant, the peripheral surface of the piston is subjected to self-lubricating composite plating, and the plated layer is polished and formed to a predetermined size. Therefore, high-precision machining can be performed relatively easily, and it is practical for mass production.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a liquid hydrogen pressure pump showing an example of a liquid pump to which the present invention is applied.

FIG. 2 is a sectional view of a main part of FIG.

FIG. 3 is a conceptual diagram of a main part.

[Explanation of symbols]

 10 ... piston, 11 ... cylinder, 21 ... plating layer.

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 000158312 Iwatani Corporation 3-4-8 Honcho, Chuo-ku, Osaka-shi, Osaka (71) Applicant 000120386 Ebara Ujilight Co., Ltd. 4--19, Taito, Taito-ku, Tokyo No. 9 (72) Inventor Kimiko Yamane 377-2 Miyamae, Fujisawa-shi, Kanagawa Prefecture (72) Inventor Masaru Hiruma 2-31-13, Shishigaya, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Masaomi Matsumoto Yokohama, Kanagawa Prefecture 43-20 Enokaoka, Aoba-ku, A-shi F-term (reference) 3H070 AA07 BB00 CC37 DD01 DD11 EE02 EE03 EE15 3H071 AA15 BB01 CC05 CC32 DD01 DD06 EE02 EE03 EE15 3H075 AA15 BB03 CC14 DA03 DA04

Claims (3)

[Claims] A cryogenic liquid pump provided in a tank containing a liquid in a cryogenic state such as a liquefied gas, wherein a relatively sliding cylinder and a piston base are formed of the same material, A cryogenic liquid pump characterized in that the surface is self-lubricating composite plating and a clearance between a piston peripheral surface and a cylinder inner peripheral surface is formed with a predetermined precision clearance. 2. The cryogenic liquid pump according to claim 1, wherein a gap between the piston peripheral surface and the cylinder inner peripheral surface is set to 1 to 3 μm. 3. The cryogenic liquid pump according to claim 1, wherein the liquid in the cryogenic state is liquid hydrogen.