What's the material and thickness of your tube sheet(s)? What's the wall thickness of your tubes?
Do you have a torque-control motor and drive? Do you have any operators experienced with rolling small diameter tubes? Are you roller expanding only, or will you be doing a strength or seal weld in addition?
Do you have a torque-control motor and drive? Do you have any operators experienced with rolling small diameter tubes? Are you roller expanding only, or will you be doing a strength or seal weld in addition?
It's been a while since we did any 3/8" tubes, but for small diameter ferrous materials, you usually want about 8% wall reduction in the expanded area (I'm assuming your application is low pressure with that tube sheet thickness). Use a micrometer to check your first couple tubes.
Make sure your mandrel is inserted no more than 1/2" from the front face of the tube sheet. Get an extra set of rollers. The manufacturer/distributor of your expander can give more advice about what you want to use to drive it.
Expand the tubes one hemisphere at a time, and start with the largest bend radius. Don't expand one leg of the u-tube, then it's other leg. Just expand one whole half, then move to the next half.
We always used parallel rollers instead of tapered rollers for such applications.
For such applications our shop people like to use petroleum jelly, either alone or with a little kerosene, for the lubricant. We have also seal welded tubes of your size in thin tubesheets. We did this by trimming the tube ends to the shortest length possible and randomly welding the tubes with the smallest weld possible so there is no straight lines in the weld pattern.
