JPS583454B2 - Stepped pipe drawing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for accurately manufacturing a stepped tube consisting of a concentric large-diameter portion and a small-diameter portion by drawing.

Stepped tubes that require strict precision in terms of concentricity, straightness, roundness, wall thickness uniformity, etc. include, for example, nuclear reactor sheath tubes.

The object of the present invention is to provide a method for producing such a precise stepped tube that requires high precision by drawing.

Conventionally, in the production of stepped pipes by drawing, the entire length of the pipe is first drawn to the dimensions of the large diameter part of the product, then passed through a die with the dimensions of the small diameter part, and once the required length has been drawn, the pipe is drawn out of the drawing machine. In this case, drawing, especially when finishing the small diameter part of the finished product, is done by the so-called dry drawing method, or by inserting a mandrel with a floating plug attached to the tip into the pipe. Since this method uses the so-called floating core method, in which the other end of the mandrel is held cantilevered and the plug at the tip is pulled out while holding it in a floating state from around the die hole, bending is likely to occur, especially in stepped pipes. Since the central axes of the large-diameter part and the small-diameter part may be misaligned, it is extremely difficult to obtain highly accurate drawings using such conventional drawing methods.

This invention provides a new method that combines the advantages of both the mandrel drawing method and the floating core drawing method, especially for drawing the small diameter part of the product after drawing the large diameter part of the product in the production of stepped pipes. By adopting this method, it is possible to easily mass-produce stepped tubes with extremely high precision.

In manufacturing precision stepped pipes, which is the object of the present invention, it is first necessary to precisely finish the entire length of the pipe to the dimensions of the large diameter part of the finished product, for example by drawing. For example, the invention "Method for preventing deformation of pipe during drawing process" (1977) filed by the same person
(Patent Application Publication No. 9705), other methods have been proposed or have already been implemented, and it is not difficult to obtain a straight pipe with high precision.

The present invention provides a pipe whose entire length is finished to the dimensions of the large diameter part of the finished product.
Next, the product is drawn through a die that draws the small diameter part. At this time, a hollow plug is slidably fitted to the outer periphery of the mandrel, and the mandrel with the slidable plug is inserted into the tube. Then, the plug is placed in a position opposite to the introduction part of the drawing die hole, and as the tube is drawn, the mandrel is propelled in the drawing direction at the same speed as the drawing of the tube.

This method of drawing causes the hollow plug that fits into the mandrel to slide relative to the mandrel and always maintain its normal relative position relative to the die.

The hollow floating plug is finished with precise dimensions and has the smallest possible clearance (3/100~5/100
), the tube is pulled out straight together with the mandrel, and the center axes of the large diameter and small diameter sections coincide, providing excellent concentricity as well as straightness.

In addition, as drawing begins, a force acts on the hollow plug to maintain its correct position in relation to the die, keeping the distance between the die hole and the mandrel equal all around the circumference, ensuring uniform thickness of the drawn pipe, and the characteristics of mandrel drawing. The effects of roundness, high dimensional accuracy, etc. are combined, making it possible to easily obtain a precise stepped tube.

The partially longitudinal side views shown in FIGS. 1 and 2 are explanatory views showing one embodiment of the present invention, and the structure and operation of the present invention will be further explained with reference to both figures.

As shown in Figure 1, the pipe 1 whose entire length has been precisely drawn to the dimensions of the large diameter part of the finished product has a drawing part 1 at the tip for drawing the small diameter part.
' is formed and then inserted into a die 2 having a small diameter section.

It is a common practice to lubricate the inner and outer surfaces of the tube 1 before drawing it out.

3 is a mandrel into which a hollow plug 4 is fitted, and the outer diameter D of the mandrel is determined by the inner diameter of the small diameter portion.

The front part of the hollow plug 4 is formed into an appropriate curved or inclined surface corresponding to the introduction part of the die 2 hole.

The clearance between the inner circumference of the plug and the outer circumference of the mandrel is 3
/100 to 5/100 mm, and the width l of the inner periphery is appropriately set to l=D to 2D with respect to the diameter D of the mandrel.

When inserting the mandrel 3 into the pipe 1, as shown in FIG. 1, by temporarily fixing the hollow plug 4 to the tip of the mandrel with a split ring 5, etc., the hollow plug can be easily placed in the position of the die 2. can be reached.

FIG. 2 shows the state in which the pipe 1 is being drawn, with the pinched portion 1l of the pipe being gripped by the scissors wheel 6 of the drawing machine.

This drawing is similar to so-called mandrel drawing, in which the mandrel 3 is drawn together with the tube 1 and propelled through the die.

Therefore, the hollow plug 4 slides on the outer circumference of the mandrel,
Due to the frictional force of the wedge action, the floating plug acts as a floating plug while always maintaining its normal relative position with respect to the die 2, and the center of the plug always coincides with the center of the mandrel, that is, the drawing center axis.

When the small diameter portion of the finished product has been drawn out to a predetermined length, the drawing is stopped and the tube is removed from the drawing machine.

The stepped tube obtained as described above has excellent roundness and wall uniformity in both the large diameter part and the small diameter part, and the centers of the large diameter part and the small diameter part are coincident, and there is no step part that tends to occur with conventional methods. It is straight with no bends, and the stepped portions are beautifully formed.

As described above, the method of the present invention uses a combination of mandrel drawing and a "floating" plug that fits and slides on the mandrel to obtain a stepped pipe with excellent straightness, concentricity, etc. As shown by the broken line in Figure 2, by attaching to the mandrel 3 an auxiliary ring 7 with a spherical outer circumference that is loosely inscribed in the large-diameter pipe, the straightness of the mandrel is improved, and therefore the straightness of the pipe is further improved. is valid above.

In the present invention, the diameter of the mandrel 3 is determined so that there is a clearance of about 5/100 to 10/100 mm between the inner periphery of the small diameter part of the pipe, and the mandrel is propelled at a constant speed in synchronization with the drawing of the pipe. By providing an interlocking drive device, the mandrel may be directly pulled out of the product after drawing, and in this case as well, a product with higher precision can be obtained compared to the conventional method.

As described above, according to the present invention, the mandrel drawing and the floating core drawing are performed simultaneously, and the synergistic effect allows for good concentricity and straightness when drawing a stepped pipe that requires stopping the drawing in the middle. Therefore, the present invention has the effect of making it possible to mass-produce stepped tubes for use in nuclear reactor sheath tubes and other applications requiring precision at low cost.

[Brief explanation of drawings]

FIGS. 1 and 2 are explanatory diagrams illustrating embodiments of the present invention, and are side views showing main parts in longitudinal section. 1: Pipe, 1l: Diaphragm part, 2: Die for drawing small diameter part, 3
: Mandrel, 4: Hollow plug, 5: Temporary split ring,
6: Scissors wheel.

Claims (1)

[Claims] 1. In manufacturing stepped pipes consisting of a large diameter part and a small diameter part, a drawing part is formed at the tip of the pipe whose entire length is finished to the dimensions of the finished large diameter part, and the pipe is inserted into a drawing die with the dimensions of the small diameter part. At the same time, a mandrel with a hollow plug slidably fitted around the outer periphery is inserted into the pipe, and the hollow plug is brought into a position facing the introduction part of the drawing die hole, and the mandrel is inserted into the pipe while the pipe is drawn. A method for drawing a stepped pipe, characterized in that a small diameter portion over a required length is drawn while maintaining the relative position of the hollow plug normally by propelling the pipe in the same direction at the same speed as when the pipe is being drawn. .