69:'s axis. The rollers are on opposite sides of the billet, and the surface of their largest cross sections are separated by a distance slightly smaller than the outside diameter (OD) of the original billet. The load imparted by the rollers compresses the material and the 6° skew provides both rotation and translation to the billet. The friction between the rollers and the billet is intentionally high, and is sometimes increased by using
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is set inside and a short distance from the start of the central void. This mandrel forces the material outward and compresses the material against the back side of the tapered rollers. This compressive loading fuses the circumferential fissures and sets the initial internal and external diameter
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A heated cylindrical billet workpiece is fed between two convex-tapered rollers, which are rotating in the same direction. The rollers are usually 6° askew from parallel with the
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The
Stiefel process is very similar to the Mannesmann process, except that the convex rollers are replaced with large conical disks. This allows for larger tubes to be formed.
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of the billet and causes circumferential fissures to propagate at various radii near the outer surface, and a central longitudinal void to form at the axis. A tapered
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values. The formed tube is then cooled and can be cold worked to refine the diameters and to achieve the desired yield strengths.
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varying radially through the billet, with the highest stresses at the outer surface and the central axis. The stress exceeds the
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115:"The Development History of Seamless Steel Pipe | CSCMP's Supply Chain Quarterly"
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process, invented in the 1880s, and the
Stiefel process, developed two decades later.
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Mannesmann mills can produce tubes as large as 300 mm (12 in) in diameter.
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Finally, the rolls push the blank over the mandrel to form a uniform inner diameter.
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The stresses induced by the rolls causes the center of the blank to fracture.
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process for forming thick-walled seamless tubing. There are two types: the
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Hot working metalworking process for forming thick-walled seamless tubing
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131:… , vol. 6 (New York, New York: The Industrial Press, 1917),
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Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003),
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The process starts with the blank fed in from the left.
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152:Materials and Processes in Manufacturing
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101:References
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75:stresses
83:mandrel
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67:billet
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