Process for hardfacing a progressing cavity pump/motor rotor

Abstract

A method of hardfacing a metal body, including the steps of flame spraying a metallic material onto a surface of the metal body to produce a layer of the metallic material on the metal body and fusing the layer of metallic material to provide a hardfacing layer, is improved by roughening the surface of the metal body prior to the step of flame spraying to provide a mechanical bond between the metal body and the hardfacing layer. The roughening is carried out to achieve a surface roughness adjusted to the thickness of the hardcoating. The surface roughness is preferably 40%-90% of the thickness of the hardfacing layer. A rotor for a progressing cavity pump/motor, including a metallic rotor body having a surface, and a layer of hardfacing on the surface, the hardfacing comprising of fused flame sprayed metallic material, the surface of the rotor body having an average surface roughness of at least substantially 6 mils with irregular protrusions for providing a mechanical bond between the rotor body and the hardfacing.

1 . In a method of hardfacing a metal body, including the steps of flame spraying a metallic coating material onto a surface of the metal body to produce a metallic coating having a coating thickness and fusing the metallic coating to provide a hardfacing layer, the improvement comprising the step of roughening the surface of the metal body prior to the flame spraying for generating a surface roughness equal to at least 40% and at most 90% of the coating thickness.  
   
   
       2 . The method of  claim 1 , wherein the step of roughening the surface of the metal body comprises the step of forming a multiplicity of jagged irregular projections and indentations, substantially covering the surface of the metal body.  
   
   
       3 . The method of  claim 1 , wherein the step of roughening the surface of the metal body comprises grit blasting.  
   
   
       4 . The method of  claim 3 , wherein the grit blasting comprises blasting with steel grit having a hardness at least equal to a hardness of the metal body.  
   
   
       5 . The method of  claim 4 , wherein the grit blasting comprises blasting with steel grit having a hardness between about 20 and about 50 Rockwell.  
   
   
       6 . The method of  claim 3 , wherein the grit blasting comprises blasting with grit at an air pressure of between about 80 psi and about 150 psi.  
   
   
       7 . The method of  claim 1 , wherein the minimum surface roughness is 8 mil.  
   
   
       8 . The method of  claim 1 , wherein the metallic material is selected from the group consisting of chromium, molybdenum and nickel and alloys thereof.  
   
   
       9 . The method of  claim 7 , wherein the thickness of the layer of metallic material is substantially uniform.  
   
   
       10 . The method of  claim 1 , wherein the metallic material comprises between about 30 wt. % and 80 wt. % metal carbide powder.  
   
   
       11 . The method of  claim 10 , wherein the metal carbide powder is selected from the group consisting of the carbides of tungsten, titanium, tantalum, columbium, vanadium and molybdenum.  
   
   
       12 . The method of  claim 11 , further comprising, prior to the step of flame spraying the metallic material onto the metal body, the steps of: 
 (a) predicting the approximate expected grain size of an abrading substance to be encountered by the metal body when the metal body is placed into service; and    (b) selecting a grain size for the metal carbide powder that is finer than the grain size of the abrading substance.    
   
   
       13 . The method of  claim 1 , wherein the step of fusing the layer of hardfacing comprises heating by inductive heating.  
   
   
       14 . The method of  claim 1 , wherein the metal body is a rotor for a progressing cavity pump/motor.  
   
   
       15 . A rotor for a progressing cavity pump/motor, comprising: 
 (a) a metallic rotor body having a surface; and    (b) a layer of hardfacing on the surface, the hardfacing consisting of flame sprayed and fused metallic material applied at a coating thickness, the surface of the rotor body having a surface roughness with irregular protrusions for providing a mechanical bond between the rotor body and the hardfacing, the surface roughness having a depth equal to 40-90% of the coating thickness.    
   
   
       16 . The rotor of  claim 15 , wherein the flame sprayed metallic material is selected from the group consisting of chromium, molybdenum and nickel and alloys thereof.  
   
   
       17 . The rotor of  claim 15 , wherein the irregular protrusions are formed by a multiplicity of jagged irregular projections and indentations in the surface of the rotor body.  
   
   
       18 . The rotor of  claim 15 , wherein the surface of the metal body has a surface roughness of 60-90% of the coating thickness.  
   
   
       19 . The rotor of  claim 15 , wherein the surface of the metal body has a surface roughness of 70-90% of the coating thickness.