Method of coating a substrate

Abstract

A method of coating a metal substrate with a protective metal coating by melting the coating, heating the surface only of the substrate with a high frequency induction heater to the melting temperature of the coating or greater and substantially immediately applying the molten metal coating to the heated substrate prior to penetrate of the heat through the substrate.

The invention is claimed as follows: 
     
         1 . A method of coating a metal substrate having a first outer surface and a second inner surface, said method comprising the following steps performed in a continuous inline process:
 melting an adherent metal coating in a coating chamber and maintaining said melted metal coating in a melted form such that the melted metal coating is maintained directly adjacent to an induction heating coil exit end of an induction coil, said metal coating having a melting temperature substantially less than a melting temperature of the metal substrate;   applying a paint to the second inner surface of the metal substrate, said paint having a burning temperature, said burning temperature of the paint being less than said melting temperature of the metal coating;   thereafter, heating the first outer surface of the metal substrate with the induction heating coil at a frequency of at least 10,000 Hertz to a temperature equal to or greater than the melting temperature of the metal coating, and without actively heating the second inner surface of the metal substrate and without adversely affecting the paint on the second inner surface of the metal substrate;   immediately after heating the first outer surface of the metal substrate with the induction heating coil, moving the heated first outer surface of the metal substrate out of the induction coil exit end and directly into the directly adjacent melted metal coating in the coating chamber and applying the molten metal coating on the heated first outer surface of the metal substrate prior to penetration of the heat through the metal substrate to the second inner surface of the metal substrate by moving the metal substrate through the molten metal coating; and   immediately after applying the molten metal coating to the heated first outer surface of the metal substrate, quenching the molten metal coating on the first outer surface of the metal substrate with a fluid coolant having a temperature substantially below the melting temperature of the metal coating, thereby freezing the molten metal coating on the first outer surface of the metal substrate to have a predetermined thickness.   
     
     
         2 . The method of  claim 1 , which includes using the induction coil to heat the first outer surface of the metal substrate with the induction heating coil at a frequency of at least 50,000 Hertz. 
     
     
         3 . The method of  claim 1 , which includes applying the molten metal coating on the heated first outer surface of the metal substrate prior to fifty percent penetration of the heat through the metal substrate toward the second inner surface of the metal substrate. 
     
     
         4 . The method of  claim 1 , which includes applying the molten metal coating on the heated first outer surface of the metal substrate prior to thirty percent penetration of the heat through the metal substrate toward the second inner surface of the metal substrate. 
     
     
         5 . The method of  claim 1 , wherein the metal substrate is a ferrous metal substrate. 
     
     
         6 . The method of  claim 1 , wherein the metal coating includes zinc. 
     
     
         7 . The method of  claim 1 , which includes applying molten metal coating on the heated first outer surface of the metal substrate within 0.2 seconds following heating of the first outer surface of the metal substrate. 
     
     
         8 . The method of  claim 1 , which includes applying molten metal coating on the heated first outer surface of the metal substrate within 0.1 second following heating of the first outer surface of the metal substrate. 
     
     
         9 . The method of  claim 1 , wherein the metal substrate is tubular, the first outer surface is an outer surface of the tubular metal substrate, and the second inner surface is an inner surface of the tubular metal substrate, and which includes heating the first outer surface of the metal substrate with the induction heating coil at a frequency of at least 50,000 Hertz, applying the molten metal coating on the first outer surface of the metal substrate prior to fifty percent penetration of the heat through the metal substrate toward the second inner surface of the metal substrate, and applying molten metal coating on the heated first outer surface of the metal substrate within 0.1 seconds following heating of the first outer surface of the metal substrate. 
     
     
         10 . A method of coating a metal substrate having a first outer surface and a second inner surface, said method comprising the following steps performed in a continuous inline process:
 melting an adherent metal coating in a coating chamber and maintaining said melted metal coating in a melted form such that the melted metal coating is maintained directly adjacent to an induction heating coil exit end of an induction coil, said metal coating having a melting temperature substantially less than a melting temperature of the metal substrate;   applying a polytetrafluoroethylene to the second inner surface of the metal substrate, said polytetrafluoroethylene having a burning temperature, said burning temperature of the polytetrafluoroethylene being less than said melting temperature of the metal coating;   thereafter, heating the first outer surface of the metal substrate with the induction heating coil at a frequency of at least 10,000 Hertz to a temperature equal to or greater than the melting temperature of the metal coating, and without actively heating the second inner surface of the metal substrate and without adversely affecting the polytetrafluoroethylene on the second inner surface of the metal substrate;   immediately after heating the first outer surface of the metal substrate with the induction heating coil, moving the heated first outer surface of the metal substrate out of the induction coil exit end and directly into the directly adjacent melted metal coating in the coating chamber and applying the molten metal coating on the heated first outer surface of the metal substrate prior to penetration of the heat through the metal substrate to the second inner surface of the metal substrate by moving the metal substrate through the molten metal coating; and   immediately after applying the molten metal coating to the heated first outer surface of the metal substrate, quenching the molten metal coating on the first outer surface of the metal substrate with a fluid coolant having a temperature substantially below the melting temperature of the metal coating, thereby freezing the molten metal coating on the first outer surface of the metal substrate to have a predetermined thickness.   
     
     
         11 . The method of  claim 10 , which includes using the induction coil to heat the first outer surface of the metal substrate with the induction heating coil at a frequency of at least 50,000 Hertz. 
     
     
         12 . The method of  claim 10 , which includes applying the molten metal coating on the heated first outer surface of the metal substrate prior to fifty percent penetration of the heat through the metal substrate toward the second inner surface of the metal substrate. 
     
     
         13 . The method of  claim 10 , which includes applying the molten metal coating on the heated first outer surface of the metal substrate prior to thirty percent penetration of the heat through the metal substrate toward the second inner surface of the metal substrate. 
     
     
         14 . The method of  claim 10 , wherein the metal substrate is a ferrous metal substrate. 
     
     
         15 . The method of  claim 10 , wherein the metal coating includes zinc. 
     
     
         16 . The method of  claim 10 , which includes applying molten metal coating on the heated first outer surface of the metal substrate within 0.2 seconds following heating of the first outer surface of the metal substrate. 
     
     
         17 . The method of  claim 10 , which includes applying molten metal coating on the heated first outer surface of the metal substrate within 0.1 seconds following heating of the first outer surface of the metal substrate. 
     
     
         18 . The method of  claim 10 , wherein the metal substrate is tubular, the first outer surface is an outer surface of the tubular metal substrate, and the second inner surface is an inner surface of the tubular metal substrate, and which includes heating the first outer surface of the metal substrate with the induction heating coil at a frequency of at least 50,000 Hertz, applying the molten metal coating on the first outer surface of the metal substrate prior to fifty percent penetration of the heat through the metal substrate toward the second inner surface of the metal substrate, and applying molten metal coating on the heated first outer surface of the metal substrate within 0.1 seconds following heating of the first outer surface of the metal substrate.