JPH0790272B2 - Method for manufacturing U-shaped tube made of stainless steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a stainless steel U-shaped tube used for a high-purity gas supply device in the semiconductor manufacturing industry.

[Conventional technology]

With the rapid development of the semiconductor manufacturing industry in recent years, the purity of the high-purity gas used in this field is required to be extremely strict. For example, one of the specifications of high-purity nitrogen gas for semiconductor manufacturing factories is that the number of dust particles contained in high-purity nitrogen is less than 0.1 μm and less than 1 in 1 cu · ft. . Therefore, this high-purity nitrogen gas production apparatus and supply equipment are provided with measures to prevent such dust from entering everywhere.

The present invention also relates to the above-mentioned apparatus, and more particularly to a U-shaped tube whose inner surface used for an evaporator or the like is finished by electrolytic polishing.

U-shaped pipes that connect the evaporation pipes of evaporators that vaporize high-purity liquefied nitrogen into high-purity nitrogen gas have been manufactured by various conventional manufacturing methods, but the inner surface roughness of each of them is several μm to several μm. In order to manufacture a U-shaped tube having a surface roughness of 10 μm, which recently satisfies the specification of 1 μm or less, it is necessary to perform mechanical polishing or fluidized polishing after molding and then electrolytically polish the inner surface, which is complicated. It requires various processes and is a factor of high cost. For example, in order to manufacture an inner surface with a maximum surface roughness of 1 μm or less (see Fig. 1) using a 180 ° elbow (a U-shaped pipe without a straight pipe section) of the dimensions specified by the conventional JIS standard, It is performed by such a process. Hot-extrusion Seamless stainless steel tube made of raw material, cold-drawn using a specified jig, coating agent, and lubricant, and subjected to degreasing, pickling, etc. The maximum surface roughness of the inner surface is 4.5 μm, but this is molded into a U shape by heat treatment, and then the inner surface is mechanically polished to an apparent maximum surface roughness of about 1 μm, and then electrolytically polished. 180 ° elbow 1 (U with maximum surface roughness of 1 μm)
Character pipe) (shown in FIG. 1) is obtained.

However, as described above, recently, strict values are required for the surface roughness after the device is manufactured. For example, since the welding portion 3 between the evaporation pipe 2 and the U-shaped pipe 1 shown in FIG. 2 has conventionally been made by manual welding, a weld back bead is formed to be considerably rough, resulting in providing a bed for adhering dust particles. Therefore, the U-shaped pipe 1 and the evaporation pipe 2 may be welded by a dedicated pipe welding machine so that the surface roughness of the back bead of the welded portion is minimized. 4 (return vent in JIS standard) (shown in Fig. 3) must be used. Therefore, an attempt was made to minimize the weld back bead on the inner surface of the final product device by manufacturing a U-shaped tube having a long straight tube portion and electrolytically polished the inner surface and using it. However, when manufacturing a U-shaped pipe having a long straight pipe portion, it is difficult to perform mechanical polishing work in the manufacturing process. That is, the mechanical polishing is to polish the inner surface of the U-shaped tube by a polishing machine using a grindstone or cloth as an abrasive, but the inner portion of the bent R portion cannot be polished (non-shaded portions in FIGS. 4 and 5). . Although visual confirmation is an important check point for more reliable polishing, the inner portion of the bent R portion cannot be confirmed as described above, and the degree becomes larger as the straight pipe portion becomes longer.

There is also a method of fluidized polishing instead of mechanical polishing. Fluidized polishing is a method of polishing the surface of a work piece, that is, a U-shaped tube, by passing an abrasive material in which abrasive grains are encased in a viscoelastic polymer medium several times. However, when performing normal fluidized polishing, it is necessary to raise the surface roughness to some extent by mechanical polishing as the underlying polishing.

[Problems to be solved by the invention]

As described above, when mechanical polishing is performed to increase the surface roughness of the inner surface of a U-shaped tube having a long straight section, it is difficult or impossible to polish the inner section of the curved section (R section). It is difficult to confirm the surface roughness.

Further, the polishing by the fluidized polishing is usually performed as the finishing of the polishing by the mechanical polishing, so that it is meaningless if the polishing by the mechanical polishing is uncertain. In order to obtain the desired surface roughness only by fluidized polishing, it is necessary to prepare several kinds of abrasives with adjusted grain size and pass these abrasives over and over to perform polishing work. Is low and the cost is considerably high, which is difficult for practical use.

Therefore, as a method of finishing the maximum surface roughness of the inner surface of a U-shaped tube with a long straight tube made of stainless steel to 1 μm or less, either mechanical polishing or fluidized polishing is inconvenient in practice, and other methods have been developed. Was required.

The present invention eliminates the mechanical polishing or fluidized polishing step which is complicated in the manufacturing process of the U-shaped tube for performing the electrolytic polishing of the inner surface with the long straight tube portion as described above, and the stainless steel of which the surface roughness of the inner surface is extremely small. The purpose is to manufacture a steel U-tube.

[Means for solving problems]

The present invention repeats the step of brightly annealing a stainless steel tube having a predetermined size by drawing a stainless steel raw tube, and then bending it to make a U-shape and electrolytically polishing the inner surface to form the inside of the tube. Maximum wall roughness of 0.3 μm
It is a method for manufacturing a U-shaped tube made of stainless steel, characterized in that the thickness is about 0.7 μm.

[Action]

Bright annealing that eliminates the residual stress in the drawing process by eliminating the mechanical polishing or fluidized polishing process, which is complicated and costly during the manufacturing process of the U-shaped tube that has a long straight pipe and electrolytically polishes the inner surface. Then, the maximum surface roughness of the inner surface of the tube can be reached to 0.7 μm or less to about 0.3 μm simply by performing electrolytic polishing.

〔Example〕

Example 1 A hot-extruded seamless stainless steel element tube was used as a material,
This is subjected to cold drawing using a predetermined jig, coating agent and lubricant, degreasing, pickling, etc., followed by cutting and chamfering to obtain a raw pipe of a predetermined size. At this time, the size can be appropriately determined according to the product specifications, or the length of the straight pipe portion is set to about 0.5 to 5 times the pipe diameter. The maximum surface roughness of the inner surface of the pipe at the end of the process is about 4.5 μm. Then, this raw tube is subjected to bright annealing to eliminate the residual stress generated in the cold drawing step. The condition of this bright annealing treatment is to put the above-mentioned raw tube in an annealing furnace, and set it at 1100 ° C ± 30 in an annealing gas atmosphere of a predetermined composition and concentration.
After keeping the temperature condition of ℃ for 4 minutes, it is cooled by air cooling by natural cooling. The steps of cold drawing and bright annealing are repeated a plurality of times. Then, it is formed into a U shape by cold bending. The maximum surface roughness of the inner surface at this time is about 6 μm. By electropolishing the U-shaped tube after molding to finish the inner surface, a U-shaped tube having a maximum inner surface roughness of about 0.7 μm can be obtained. The electrolytic polishing process is performed in the following steps.

A plurality of U-shaped tubes to be treated are set with their openings facing upward, and the electrode rods are set so that eccentricity of the pole rod does not occur in the U-shaped tubes. A liquid sending pipe is connected to the opening, and liquid is circulated from the electrolytic solution tank by a liquid sending pump. Electrolytic polishing is performed by setting voltage and current to predetermined values and energizing for a certain period of time. During this process, carefully check the temperature of the polishing liquid and whether gas is generated. After performing electrolytic polishing treatment for a certain period of time, the electrolytic solution is drained and rinsed with washing water.
The maximum inner surface roughness of the U-shaped tube after this process is 0.7μ
Although it is less than or equal to m, all the products are visually inspected, and the maximum surface roughness is checked by a surface roughness meter by a sampling inspection.

Example 2 A hot or cold extruded seamless stainless steel element tube is used as a raw material, which is subjected to cold drawing processing, degreasing, pickling, etc., and cut into a predetermined size to obtain a raw tube. This is annealed in the air according to the usual method, and the maximum surface roughness of the inner surface of the pipe is 6μ.
m is obtained. Then, cold drawing is performed again and bright annealing is performed. The cold drawing and bright annealing steps are repeated a plurality of times. The greater the number of repetitions, the higher the value of the maximum surface roughness of the obtained inner surface of the pipe. That is, by increasing the number of times, the maximum surface roughness after bright annealing can be improved to about 3 μm. Next, a U-shape is bent, and the maximum surface roughness at this time is about 4.5 μm. The U-shaped tube after molding is subjected to electrolytic polishing treatment to obtain a U-shaped tube having a maximum inner surface roughness of about 0.3 μm. It should be noted that performing the atmospheric annealing in the first step is that the atmospheric annealing does not require an atmospheric gas having a particularly adjusted composition as compared to the bright annealing, so that the processing operation becomes easy in terms of both material and labor, and the processing cost This is because In this embodiment, the cold drawing process and the atmospheric annealing process are performed once, but it goes without saying that these processes may be repeated. In that case, the number of times of repeating the steps of cold drawing and bright annealing may be small.

〔The invention's effect〕

According to the present invention, a stainless steel pipe having a predetermined size drawn as described above is bright-annealed, and then bent to a U shape, and the inner surface is electrolytically polished to obtain the maximum surface roughness of the inner wall of the pipe. Is 0.7 μm or less, which is a method for manufacturing a U-shaped pipe made of stainless steel, which requires complicated mechanical polishing or flow required to make the surface roughness of the inner surface of the pipe extremely small. By eliminating the polishing process and performing a simple bright annealing process, the residual stress required after the drawing process is eliminated and at the same time the rough surface of the inner surface of the pipe is pre-processed for electrolytic polishing. It became possible to easily obtain a maximum surface roughness of 0.7 μm or less. Therefore, the manufacturing cost is sufficiently reduced as compared with the conventional stainless steel U-shaped tube subjected to the inner surface electrolytic polishing, and the equipment cost for mechanical polishing or fluidized polishing becomes unnecessary in the case of new installation.

[Brief description of drawings]

FIG. 1 is a front view of a U-shaped pipe without a straight pipe portion, FIG. 2 is a front view showing a state in which the U-shaped pipe shown in FIG. 1 is connected to an evaporation pipe, and FIG. 3 is a U having a straight pipe portion. FIG. 4 is a front view of the U-shaped pipe, FIG. 4 is a view for explaining the state of mechanical polishing in the U-shaped pipe shown in FIG. 1, and FIG. 5 is a mechanical polishing state in the U-shaped pipe shown in FIG. It is a figure for explaining a state. 1,4 …… U-tube, 2 …… Evaporation pipe, 3 …… Welded part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-50-7085 (JP, A) JP-A-61-257420 (JP, A)

Claims (1)

[Claims] 1. A step of drawing a stainless steel raw tube to a predetermined size and performing bright annealing is repeated a plurality of times, then bending is performed to make a U-shape, and the inner surface of the tube is finished by electrolytic polishing. A method for manufacturing a U-shaped tube made of stainless steel, characterized in that the inner surface roughness of the tube is 0.7 μm or less.