47.3 SHAPE ROLLING

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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,

ring rolling - a ring shaped part is rolled between two rollers.

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.

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,

1. A bar (cylinder) is rolled radially between two rollers.

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.

3. A mandrel is forced into the center where it pierces the hole, and ensures a desired size.

4. The rollers are oriented so that they slowly pass the bar through and onto the mandrel.

5. The finished tube is removed from the mandrel.