TPT July 2009

In the second region the billet is pierced and elongated. The high- toe-angle and high-expansion piercer decreases circumferential shear strain and reduces piercing elongation, so that with the newly developed piercer the hollow shell has fewer inside defects than with a conventional piercer. To pierce a thin walled stainless hollow shell another technique, the skewing mechanism of the disc guide, is provided. The skewing mechanism of the disc guide is illustrated in figure 3. When piercing the thinner wall, the hollow shell is elongated along the pass line, expanded to the circumference, and tends to be extruded from the clearance between the main roll and disc guide (peeling). To prevent this peeling, the skewing mechanism of the disc guide is provided to minimise the clearance between the disc and the roll at the outlet side of the piercer. As mentioned above, with the high-toe-angle and high-expansion piercer and the skewing mechanism of the disc guide, ultra-thin stainless hollow shells are pierced without inside defects. Sumitomo Metals has many patents concerning this piercing technology, for example, patent DE3844802 “Method of piercing and manufacturing seamless tubes” was published 11 May 1995. Measuring and controlling hot wall thickness of tubes The method of measuring and controlling hot wall thickness of tubes is illustrated in figure 5. The production line comprises a 5-stand mandrel mill and 12-stand sizer and hot wall thickness meter. No 4 and 5 stand of the mandrel mill are final reduction rolls. Figure 6-a is an illustration of No 4 stand and figure 6-b shows No 5 stand. Figure 6-c shows the channel directions of a hot wall thickness meter. Figure 7-a gives the typical results of measurement using the hot wall thickness meter.

 Figure 6-a :

Schematic illustration of mandrel mill No 4 stand

 Figure 6-b :

Schematic illustration of mandrel mill No 5 stand

 Figure 6-c :

Directions of the channels of hot wall thickness meter

Figure 7-a is a representation of such results of an example in which the new method isn’t carried out and figure 7-b is a representation of the results of an example in which the new method is carried out. Figure 8 is a graphic representation of the changes in deviation in thickness by starting the control of wall thickness. Figure 9 is a graphic representation of the distribution of the deviation in thickness before and after controlling wall thickness. In figure 6-a cylinders 4a and 4b are positioned on both sides of an upper roll of No 4 stand. The extent of groove closure caused by cylinder 4a and 4b is controlled by feeding back the results of the thickness measurements in the directions of channels 3, 4 and 5, among channels 1 through 8 as shown in Figure 6-c. Cylinders 4c and 4d are placed on both sides of a lower roll of No 4 stand.  Figure 7 : Results of hot wall thickness measurement (a) Representation of results in an example in which the new method is not carried out (b) Representation of results in an example in which the new method is carried out (a) (b)

 Figure 4 : View of piercer  Figure 5 : Schematic illustration of the method of measuring and controlling hot wall thickness of tubes

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J uly 2009

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