Patent ID: 7425295

Claim:
A production method for a tone wheel made of elastic material to be fixed to a rotating member in which a magnetic encoder is assembled in combination with said tone wheel and a magnetic sensor provided at a fixed member, said method comprising the steps of: charging an elastic raw material mixed with magnetic powders into an annular cavity of an assembled molding die, said assembled molding die comprising a non-magnetic die member and a magnetic die member which constitutes magnetic pass; generating a magnetic field in one predetermined direction and molding an annular molded body out of said elastic raw material mixed with magnetic powders, with said assembled molding die in said magnetic field, in which said magnetic field is applied to said elastic raw material in said annular cavity via said magnetic die member, thereby aligning said magnetic powder in said elastic raw material in one direction corresponding to said magnetic field; and magnetizing the surface of said annular molded body thus produced, with a magnetizing apparatus a pattern according to which the N poles and the S poles are alternately arranged along its circumference, wherein; said assembled molding die has one die block and another die block which are detachably engaged with each other, and a flash groove at matching surfaces where the distal end of said one die block and that of said another die block are matched, and wherein said one die block has an annular molding surface formed on the magnetic die member side of said die, and said another die block has a non-magnetic annular molding receiving surface part which is formed with an annular molding surface to be interposed between said elastic raw material and said magnetic die member in such a manner that said elastic raw material and said magnetic die member do not contact each other.