Method and device for thermal spraying

Abstract

A thermal spraying method is provided, wherein spray particles of a powdered spray material are introduced into a hot carrier gas stream, heated by the carrier gas stream and then sprayed onto the surface of a substrate by a spray nozzle, wherein the temperature of the spray particles upon impact onto the substrate is below the melting temperature of the spray material. The spray particles are heated in the hot carrier gas stream upstream of the nozzle throat to a temperature that causes at least partial melting of the spray particles in that location.

What we claim is: 
     
         1 . A thermal spraying method, wherein spray particles of a powdered spray material are introduced into a hot carrier gas stream, heated by the carrier gas stream and then sprayed onto the surface of a substrate by means of a spray nozzle, wherein the temperature of the spray particles upon impact onto the substrate is below the melting temperature of the spray material, characterized in that the spray particles are heated in the hot carrier gas stream upstream of the nozzle throat to a temperature that causes at least partial melting of the spray particles in that location. 
     
     
         2 . The method as claimed in  claim 1 , wherein the temperature to which the spray particles are heated upstream of the nozzle throat is adjusted by controlling a temperature of the carrier gas stream and/or a pressure at which the carrier gas stream is supplied to the spray nozzle. 
     
     
         3 . The method as claimed in  claim 1 , wherein the temperature to which the spray particles are heated upstream of the nozzle throat is adjusted such that the temperature of at least a portion of the spray particles upon impact onto the substrate is more than 60% of the melting temperature of the appropriate spray material in Kelvin. 
     
     
         4 . The method as claimed in  claim 3  wherein said temperature is more than 70% of the melting temperature of the appropriate spray material in Kelvin. 
     
     
         5 . The method as claimed in  claim 3  wherein said temperature is more than 80% of the melting temperature of the appropriate spray material in Kelvin. 
     
     
         6 . The method as claimed in  claim 1 , wherein spray particles formed from metallic materials are used and said metallic materials are selected from the group consisting of heat resistant iron-, nickel- and cobalt-based alloys. 
     
     
         7 . The method as claimed in  claim 6  wherein said metallic materials are selected from the group consisting of a MCrAlY alloy, aluminum, iron, copper, nickel, zinc and tin and alloys that contain at least one of these elements. 
     
     
         8 . The method as claimed in  claim 1 , wherein spray particles formed from composite materials are used. 
     
     
         9 . The method as claimed in  claim 1 , wherein spray particles formed from materials with a vitreous structure are used. 
     
     
         10 . The method as claimed in  claim 9  wherein said vitreous structure materials are selected from the group consisting of synthetic glass and metallic glass. 
     
     
         11 . The method as claimed in  claim 1 , wherein the carrier gas stream containing the spray particles is initially introduced into a convergent nozzle section and then expanded in a divergent nozzle section of the spray nozzle. 
     
     
         12 . The method as claimed in  claim 1 , wherein a spray nozzle is used that has a graphite material and/or a ceramic material at least in a region of its inner wall in a zone of contact with the spray particles 
     
     
         13 . The method as claimed in  claim 1  wherein a spray nozzle is used that consists of a graphite material and/or a ceramic material. 
     
     
         14 . The method as claimed in  claim 1 , wherein a spray nozzle is used that has an ante-chamber and/or an elongated convergent section for heating the spray particles. 
     
     
         15 . The method as claimed in  claim 1 , wherein at least one external gas heat supply is provided to heat the carrier gas stream via which the spray particles are heated. 
     
     
         16 . The method as claimed in  claim 1 , wherein the carrier gas stream is selected from the group consisting of nitrogen, helium, air and a mixture thereof. 
     
     
         17 . A thermal spraying device, characterized by means for introducing spray particles of a powdered spray material into a hot carrier gas stream that heats them up and for spraying them onto a surface of a substrate by means of a spray nozzle, wherein the temperature of the spray particles upon impact onto the substrate is below the melting temperature of the spray material and wherein the spray particles can be heated to a temperature upstream of the nozzle throat that causes at least partial melting of the spray particles in that location. 
     
     
         18 . The device as claimed in  claim 17 , wherein the spray nozzle has a graphite material and/or a ceramic material in at least a region of its inner wall and/or consists of a graphite material and/or a ceramic material. 
     
     
         19 . The device as claimed in  claim 17 , comprising a spray nozzle that has an ante-chamber and/or an elongated convergent section of the spray nozzle in order to heat the spray particles. 
     
     
         20 . The device as claimed in  claim 17 , comprising an external gas heating supply in order to heat the carrier gas stream.