JPH0373367B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a plug for drawing a ribbed tube.

(Prior Art) A ribbed tube is a tube in which ribs 2 are processed into a spiral shape on the inner surface of a tube 1, as shown in FIGS. 3 and 5. Ribbed tubes are mainly used for evaporation tubes in power generation boilers. In addition, ribbed tubes do not cause film boiling compared to smooth tubes even under operating conditions with extremely high heat loads, so burnout is less likely to occur. Typically, ribbed tubes are manufactured by cold drawing using a grooved plug.

FIG. 5 shows a conventional plug for withdrawing a multi-ribbed tube. A multi-filament groove 23 is cut into the plug body 22, and a mandrel (not shown) is attached to the screw 27. Groove side 24
is inclined so that the groove 23 opens toward the outer diameter side of the plug. When the processed tube is squeezed using a die (not shown), material protrudes into the groove 23 of the plug 21 to form a rib.

(Problems to be Solved by the Invention) Conventionally, the groove width and the slope of the groove side surface 24 were constant from the rib machining start position A of the plug 21 to the rib machining end position B of the groove 23. When machining is performed using the conventional plug 21, the material does not fill the groove 23, so the corners 3 and 4 of the rib 1 are rounded and smooth as shown in FIG. 6A.

On the other hand, it is known that in a ribbed tube, if the corners of the ribs have a radius as described above, the heat exchange rate decreases. This tendency is particularly noticeable when the ribbed tube is used under supercritical temperature conditions.
Therefore, there has been a strong desire for a ribbed tube in which the corners of the ribs are not gentle and the cross-sectional shape of the ribs is sharp.

(Means for Solving the Problems) In the plug for ribbed tube drawing of the present invention, the groove bottom width at the rib machining start position of the plug is greater than or equal to the groove bottom width at the rib machining end position, and the groove extends from the rib machining start position. The slope of the groove side surface becomes steeper toward the end position of the rib machining. Further, the groove cross-sectional shape is equal to the desired rib cross-sectional shape at and near the rib machining end position.

At the rib machining start position, the line where the groove side surface and the groove cross section intersect is a straight line, and the line where the groove bottom surface and the groove cross section intersect is either a straight line or a curved line protruding toward the center of the plug. Furthermore, at and in the vicinity of the rib machining end position, the line where the groove bottom surface intersects with the groove cross section forms a curved line that projects toward the outer diameter side of the plug. The grooves may be single or multi-threaded.

(Function) During the drawing process, the material first protrudes into the groove at the starting position of the rib process of the plug, and a wide initial peak is formed. At the rib machining start position, the angle of inclination of the groove sides is small (therefore, the opening at the top of the groove is wide), and the bottom of the groove is linear or concave, so there is a lot of material in the groove. This ensures that there is sufficient material to form the ribs. The initially formed peak follows a groove that gradually becomes narrower as the machining tube advances, and progresses to the rib machining end position while narrowing the width. At and near the rib machining end position, the peaks are finished in the desired rib cross-sectional shape. During the above processing, the groove width of the plug gradually becomes narrower, and the slope of the groove side surface becomes steeper from the rib processing start position to the rib processing end position along the groove. always deforms smoothly and fills the groove. Therefore, the cross-sectional shape of the rib is equal to the cross-sectional shape of the groove.

(Embodiment) FIGS. 1 and 2 show an embodiment of the present invention.

Eight spiral grooves 13 are cut in the plug body 12 of the plug 11, and a screw 17 for attaching a mandrel (not shown) projects from the rear end of the plug body 12. The groove side surface 14 is inclined so that the groove 13 opens toward the outer diameter side of the plug. FIG. 2C shows the cross section of the groove at the rib machining start position, and FIG. 2C shows the groove cross section at the rib machining end positions B and B'. As shown in FIG. 2, the slope of the groove side surface 14 is from the rib machining start position A to the rib machining end position B.
Point B is about 15 degrees gentler than the rib machining end position B, and gradually becomes steeper toward the rib machining end position B, and the slope of the groove side surface 14 is the same as the rib machining end position B (Fig. 1). ' is formed into a rib-processed shape approximately 5 mm before the rib-processing end position, point B, toward point A. Further, the groove bottoms 15, 15', 15'' have shapes to obtain the required rib dimensions, and the groove bottoms 15, 15', 15''
is the same as the final target rib shape. At the rib machining start position A, the line intersecting the cross section of the groove at the groove bottom 15' is a straight line, and at the groove bottom 15'' it is a curved line protruding toward the center of the plug.
Therefore, the plug is designed so that the rib machining starts from the rib machining start position A and is gradually machined toward the point B' or B where the desired rib shape is obtained. The width of the groove bottoms 15, 15', and 15'' is constant from the rib machining start position A to the rib machining end positions B and B', or is greater at A than B and B'. (However, B = B 6B shows a cross section of the rib 2 of the ribbed tube 1 processed using the plug 11. The corners 3 and 4 of the rib 2 are not rounded and have a sharp shape.

(Effects of the Invention) According to the plug of the present invention, a ribbed tube having a rib with a sharp cross-sectional shape can be manufactured. In addition, this invention simply requires the groove width of the plug,
Since only the slope of the groove side surface and the shape of the groove bottom surface are changed, the existing equipment can be used as is, and the process can be carried out easily. Furthermore, it helps improve the critical heat load of the boiler evaporator tube.

[Brief explanation of drawings]

Fig. 1 is a plan view showing an example of the plug of the present invention, Fig. 2 A, B and C are partial sectional views of the plug, respectively, and Figs. 3 and 4 are a front view and a partial sectional view of the ribbed tube, respectively. Fig. 5 is a plan view showing an example of a conventional plug, and Figs. 6A and 6B are cross-sectional views of ribs of ribbed tubes processed by the conventional plug and the plug of the present invention, respectively. 1...Ribbed tube, 2...Rib, 3, 4...
...Rib corner, 11, 21...Plug, 13, 23
...Groove, 14, 24...Groove side surface.

Claims (1)

[Claims] 1 Spiral groove 1 in which the groove bottom width at the rib machining start position A of the plug 11 is greater than or equal to the groove bottom width at the rib machining end position B
3 is cut into the plug body 12, and the groove 13 is cut into the plug body 12.
In the plug 11, the groove side surface 14 is inclined so that the groove opens toward the outside diameter of the plug, and the slope of the groove side surface 14 becomes steeper as it goes from the rib machining start position A to the rib machining end position B along the groove 13. , the line where the groove bottom surfaces 15', 15'' and the groove cross section intersect at the rib machining start position A is a straight line or a curved line protruding toward the center of the plug, and the groove is formed at the rib machining end position B and its vicinity B'. A plug for ribbed tube drawing processing, characterized in that its cross-sectional shape is equal to the required rib cross-sectional shape.