47.3 SHAPE ROLLING
· In sheet rolling we are only attempting to reduce the cross section thickness of a material. If instead we selectively reduced the thickness we could form complex section easily. This technique is called shape rolling.
· In practice we can make complex cross sections by rolling materials in multiple passes. We can't do this in one pass because we would overwork the material, and it would crack.
· Some of the types of shape rolling are listed below,
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ring rolling - a ring shaped part is rolled between two rollers.
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thread rolling - a round shaft is placed between two flat surfaces having flattened screw thread projections. The surfaces are compressed and moved tangentially to produce threads on the shaft.
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cross section - a billet or bloom is passed through a set of rollers that slowly transform it to the final shape.
· We may also use rolling to make seamless tube with the Mannesmann process,
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1. A bar (cylinder) is rolled radially between two rollers.
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2. The force applied by the rollers creates a stress concentration at the center of the bar which may or may not lead to a central crack in the bar.
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3. A mandrel is forced into the center where it pierces the hole, and ensures a desired size.
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4. The rollers are oriented so that they slowly pass the bar through and onto the mandrel.
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5. The finished tube is removed from the mandrel.
