Milling is the process of mechanically removing excess material from the inside of a sewer pipe; it is performed remotely in trenchless operations, usually by a specialized hydraulic milling robot.
Milling forms a smooth surface on the interior of the pipe, necessary in pipe relining and continuous sliplining. The smooth surface provides foldable liners a smooth surface to which they may adhere. In continuous slip lining, the smooth interior surface of the host pipe ensures no obstruction to the insertion of the carrier pipes.
Trenchlesspedia Explains Milling
Milling removes persistent deposits, root intrusions or pipe edges, as well as excess metal or plastic from a pipe's interior. The hydraulic milling robot used in this process is a low-profile, wheeled or tracked crawler.
The milling robot is operated remotely and is equipped with interchangeable grinding wheels, cutters and filling tools that allow it to mill and grout the interior of the pipe, as well as remove root invasions to prevent failed repairs.