Pipes and tubular conduits – Structure
Patent
1996-10-10
2000-02-29
Hook, James F.
Pipes and tubular conduits
Structure
138178, 138DIG11, 294321, F16L 902
Patent
active
06029714&
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a stainless steel pipe of the bright annealing finish type (BA type), having a highly-smoothed inner surface, suitable as a clean pipe for use in an apparatus for the production of semiconductors, and as a method for producing the same.
BACKGROUND ART
Clean pipes are classified, according to the method of the production thereof, into the bright annealing finish type in which a stainless steel pipe after being cold drawn is subjected to bright annealing treatment; the electric polishing finish type (EP type) in which the inner surface of a stainless steel pipe of a bright annealing finish is further smoothed by means of electrochemical polishing; and like method.
It is well known that the inner surface roughness of a clean pipe is closely related to the production of impurities or fine particles and the discharge of water vapor from the inner surface of the pipe. In an apparatus which is required to have a high degree of cleanliness, clean pipes of the electrolytic polishing finish type whose inner surface roughness becomes lower and are expensive, are used.
In the production of a pipe having a smooth inner surface, there has been a conventional method employed in which a tubing material is subjected to cold plug drawing. Cold plug drawing is a method of processing in which a tubing material 85 is cold drawn with the outer and inner surfaces thereof constrained, as shown in FIG. 10, by a fixing die 86 having a round hole and a plug 81, and the outlet-side end of the tubing material 85 chucked (not illustrated). A chemical conversion treatment lubrication and oil lubrication are the general methods of lubrication between the tools (the die 86 and the plug 81) and the tubing material 85, and oil lubrication capable of forming a thin lubricating film is employed in order to obtain highly-smoothed inner and outer surfaces.
A material for a pipe such as a clean pipe which is required to have a more highly-smoothed inner surface is subjected to a highly-smoothing treatment such as electrochemical polishing after it is cold drawn by the above-described method.
Typically, there are two types of methods for cold drawing in which different plugs are used as shown in FIG. 10.
FIG. 10(a) shows a method in which a cylindrical plug 81 whose outside diameter is uniform is used. The cylindrical plug 81 is connected with a plug-supporting rod 87. This method is used for producing pipes of relatively large dimensions.
FIG. 10(b) shows a method in which a floating plug 82 is used. This method is characterized by the shape of the plug and by the method for supporting the plug. As illustrated in this figure, the floating plug 82 is tapered, and the cone angle 2.beta. of the plug is smaller than the facial angle 2.alpha. of the die.
For this reason, those forces which act on the floating plug 82 are the frictional force which acts in the direction of drawing, and, in addition to this, the pushing-back force which acts on the tapered surface of the plug in the direction reverse to the direction of drawing. The frictional force and the pushing-back force are canceled and balanced with each other. Therefore, such a plug-supporting rod 87 as is used in the method using a cylindrical plug shown in FIG. 10(a) is not needed, and even if a supporting rod is provided in consideration of operation, almost no force acts on the supporting rod.
Since the floating plug has the above-described characteristics, the method using this plug is commonly adopted to draw a tubing material to obtain, in particular, a pipe whose diameter is small. However, in the case where this plug is used, the balancing position of the plug varies depending upon the state of lubricating films provided on the inner and outer surfaces of the tubing material, or upon the force for drawing the tubing material. Since the change of the balancing position of the plug is extremely obstructive to the operation for drawing the tubing material, proposals for improvements for this change have been made. For instance, Japanese
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Choba Hajimu
Furugen Munekatsu
Imamura Yoichi
Hook James F.
Sumikin Stainless Steel Tube Co., Ltd.
Sumitomo Metal Industries Ltd.
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