A machine consisting of two (2) adjacent, heavy, chilled iron rolls set horizontally, and which revolve in opposite directions (i.e., upper surfaces rotate), used for the mechanical working of rubber Mills are of different types. For masticating, and mixing compounds the rolls are smooth and revolve with differential speed. For crepeing and washing rubber, mills have scored or fluted rolls and differential speeds and may be equipped to spray the rubber with water. Mills with even-speed rolls are occasionally used for different purposes. Mills are corridor hollow and equipped for internal heating with steam or cooling with water.