... “double vertical ring-die pellet mill”, Research,Design,Produced by ourselves,With alone shape,more reasonable structure and ... rollers materials are alloy steel,Heat treatment made by ourselves,Hardness more than 52,In this ... same time assure hardness and density,The special design is 4 to 8 rollers working,Increase ... .18500 CE Approved Bioenergy New design FD series double vertical wood pellet mill