Pressure control system for a grinding machine and actuating unit therefor

Claim 1

In a grinding machine for conditioning the upper surface of an elongated workpiece such as a billet, in combination, a reciprocable carriage selectively movable in opposite directions in the vicinity of said workpiece, a grinding wheel boom pivoted on said carriage for swinging movement toward and away from the workpiece, a rotatable grinding wheel carried on said boom in workpiece-traversing relationship, and pressure control means effective between the carriage and the boom for regulably applying down pressure to the boom to force the grinding wheel against the surface of the workpiece, said pressure control means comprising an hydraulic boom cylinder operatively interposed between the boom and the carriage and effective when fluid under pressure is applied to one end of the cylinder to apply such down pressure to the boom, a pump effective to supply fluid under pressure to said one end of the cylinder, a bleeder valve interposed between said pump and said one end of the cylinder, said valve having a variable valve orifice in communication with said cylinder and a movable valve element effective to vary the size of said orifice, an actuating unit for said bleeder valve including a manually operable control element movable between a fully retracted position and a fully advanced position and effective when progressively shifted from such retracted position to such advanced position progressively to decrease the size of said valve orifice, a solenoid-actuated directional valve interposed between said pump and said cylinder and having a solenoid winding, said directional valve being effective in one position to direct pressure fluid from said pump to said one end of the cylinder and to bleed pressure fluid from the other end of the cylinder, said directional valve being effective in another position to direct pressure fluid from the pump to said other end of the cylinder and to bleed pressure fluid from said one end of the cylinder, means yieldingly biasing said directional valve to said one position, said winding being effective upon energization thereof to shift said directional valve to its other position, an electric circuit for said winding, and a control normally open switch disposed in said circuit, said manually operable control element being effective when moved from its fully retracted position to close said control switch and energize said circuit for the solenoid winding.