Help: How to translate a passage related to the rolling of heat exchangers, especially what comes after the comma.

http://www.chinastjx.com/news/hynews/2011_11_16_160.htm 1. Expansion of tubes in shell-and-tube heat exchangers: One end of the tube is annealed, and surface contaminants and rust are removed using sandpaper. The tube is then inserted into the hole in the tube sheet, while the other end is fixed. An expansion tool is used to force the tube into the hole in the tube sheet; under the pressure exerted by the rollers of this tool, the diameter of the tube increases. Since this end has been annealed, it undergoes plastic deformation； The diameter of the tube sheet holes also increases at the same time, but due to plastic deformation, once the expander is removed, the tube sheet holes attempt to contract back to their original diameter as a result of elastic deformation. However, the pipe end has undergone plastic deformation and can no longer return to its original diameter, thereby pressing the outer surface of the pipe end tightly against the inner surface of the tube sheet hole, achieving the purpose of securing and sealing the shell-and-tube heat exchanger. It seems that “roll” refers to the roller of a tube expander, or something with a similar function. The roller should extend only beyond the thickness of the tube sheet, with no more than 5 mm at either end. How to translate the first sentence? In the case of re-rolling, meaning rolling again? ? ?