Abstract The invention relates to the production of plasma-sprayed coatings at low surface speeds and long stand off distances e.g. more than 7.5 cm. A zone of sub-atmospheric pressure is maintained through which the hot gas effluent and entrained coating powder produced by a plasma torch is caused to pass on its way to the substrate being coated. The sub-atmospheric zone preferably extends over the whole path of hot gas effluent and entrained coating powder. Apparatus is provided which comprises a plasma torch and a chamber preferably a tube together with means for maintaining a zone of sub-atmospheric pressure in the chamber. In the case of the tube this may be a spiral passage mounted in said tube which injects a sheath of gas moving along the inner surface of the tube in a spiral path.
A METHOD FOR PRODUCING PLASMA SPRAYED COATINGS COMPRISING MAINTAINING AN ARC BETWEEN A FIRST AND SECOND ELECTRODE, PASSING A GAS INTO SAID ARC TO PRODUCE A HOT GAS EFFLUENT, INTRODUCING A COATING POWDER INTO SAID HOT GAS EFFLUENT, PASSING SAID COATING POWDER ENTRAINED HOT GAS EFFLUENT THROUGH AN ARC CNSTRICTNG NOZZLE, SURROUNDING SAID COATING ENTRAINED HOT GAS EFFLUENT BY A VORTICAL FLOW OF GAS MOVING IN THE SAME DIRECTION AS SAID HOT GAS EFFLUENT TO PROVIDE A ZON OF SUB-ATMOSPHRIC PRESSURE FROM SAID NOZZLE SUBSTANTIALLY TO A SUBSTRATE TO BE COATED, MAINTAINING SAID COATING POWDER ENTRAINED HOT GAS EFFLUENT WITHIN SAID ZONE OF SUB-ATMOSPHERIC PRESSURE UNTIL IT STRIKES SAID SUBSTRATE.
Claim 4
Independent Claim
110 words
A METHOD FOR PRODUCING PLASMA SPRAYED COATINGS COMPRISING MAINTAINING AN ARC BETWEEN A FIRST AND SECOND ELECTRODE, PASSING A GAS INTO SAID ARC TO PRODUCE A HOT GAS EFFLUENT, INTRODUCING A COATING POWDER INTO SAID HOT GAS EFFLUENT, PASSING SAID COATING POWDER ENTRAINED HOT GAS EFFLUENT THROUGH AN ARC CNSTRICTNG NOZZLE, SURROUNDING SAID COATING ENTRAINED HOT GAS EFFLUENT BY A VORTICAL FLOW OF GAS MOVING IN THE SAME DIRECTION AS SAID HOT GAS EFFLUENT TO PROVIDE A ZON OF SUB-ATMOSPHRIC PRESSURE FROM SAID NOZZLE SUBSTANTIALLY TO A SUBSTRATE TO BE COATED, MAINTAINING SAID COATING POWDER ENTRAINED HOT GAS EFFLUENT WITHIN SAID ZONE OF SUB-ATMOSPHERIC PRESSURE UNTIL IT STRIKES SAID SUBSTRATE.
Claim 5
Dependent Claim
27 words
A method according to claim 1 wherein said vortical flow of gas is established in a nozzle connected in gas tight relationship with said arc constricting nozzle.