Die casting machine with piston positioning control

A cylinder and reciprocating piston combination, comprising:

• a. a cylinder body defining a chamber and having an open end;
• b. a piston movable in said chamber in response to a supply of pressurized fluid to said chamber;
• c. a piston rod connected to said piston for movement therewith relative to said body and extending through said open end;
• d. said piston rod having a substantially cylindrical core formed from a ferrous metal having a circumferentially grooved peripheral surface, said peripheral surface being covered by a substantially non-ferrous metal coating which extends at least part way into the grooves of said peripheral surface and which extends across peripheral core portions between such grooves to define a smooth, substantially cylindrical outer wear surface extending coaxially of said core;
• e. packing means carried by said body and forming a seal circumferential of said wear surface to inhibit the escape of pressurized fluid through said open end;
• and
• f. transducer means positioned near said wear surface, said ferrous metal core and said non-ferrous metal coating cooperating to define a magnetic discontinuity means for cooperating with said transducer means for providing a variation in an electrical signal indicative of the passage past said transducer means of one of the grooves in said peripheral surface.