Continuous chromate-free fluidized-bed pipe coating

Abstract

A continuous process for the chromate-free coating of pipes by fluidized-bed coating that includes application of a primer layer, immersion in a fusible polymer coating material and heating by induction.

1 . A process comprising 
 coating a pipe with a coating material comprising one or more pulverulent fusible polymers to form a coated pipe having a polymer coating,    melting the polymer coating to form a pipe having smooth melt coating, and    cooling to form a pipe having a hardened coating,    wherein the pipe is not treated with chromate and    wherein melting comprises heating with a medium frequency induction coil.    
     
     
         2 . The process as claimed in  claim 1 , wherein the coating material comprises a polyamide.  
     
     
         3 . The process as claimed in  claim 1 , wherein the coating material comprises at least one of nylon-11 or nylon-12.  
     
     
         4 . The process as claimed in  claim 1 , wherein the coating material comprises nylon-12 in the form of a precipitated powder.  
     
     
         5 . The process as claimed in  claim 1 , wherein the hardened coating has a thickness of from 50 to 1,000 μm and a mean deviation of thickness does not exceed 30%.  
     
     
         6 . The process as claimed in  claim 1 , wherein the hardened coating has a thickness of from 50 to 300 μm and a mean deviation of thickness does not exceed 30%.  
     
     
         7 . The process as claimed in  claim 1 , wherein the hardened coating has a thickness of from 50 to 300 μm and a mean deviation of thickness does not exceed 20%.  
     
     
         8 . The process as claimed in  claim 1 , further comprising 
 applying a primer to a pipe to form a primed pipe and baking the primed pipe.    
     
     
         9 . The process as claimed in  claim 8 , wherein the primed pipe is baked with a medium-frequency induction coil.  
     
     
         10 . The process as claimed in  claim 8 , wherein the primer comprises a solvent, and baking comprises evaporating the solvent.  
     
     
         11 . The process as claimed in  claim 10 , further comprising 
 dissipating the evaporated solvent with a radial fan.    
     
     
         12 . The process as claimed in  claim 1 , wherein the pipe is coated with the coating material in a fluidized-bed coating basin comprising a medium-frequency induction coil incorporated in said fluidized-bed coating basin.  
     
     
         13 . The process as claimed in  claim 12 , wherein the fluidized-bed coating basin further comprises an air flush system positioned above the pipe and one or more metal flow-guide panels positioned below the pipe.  
     
     
         14 . The process as claimed in  claim 1 , further comprising 
 preheating the pipe with a medium-frequency induction coil before coating the pipe with the coating material.    
     
     
         15 . The process as claimed in  claim 1 , further comprising 
 smoothing the coated pipe having a polymer coating by heating with a medium-frequency induction coil before melting the polymer coating.    
     
     
         16 . The process as claimed in  claim 1 , further comprising 
 applying an adhesion promoter to the pipe, where the adhesion promoter is in the form of a suspension, a solution or a powder.    
     
     
         17 . The process as claimed in  claim 1 , further comprising 
 pre-cooling the pipe having a smooth melt coating with an air flush system before cooling with water to form the pipe having a hardened coating.    
     
     
         18 . The process as claimed in  claim 8 , further comprising 
 cleaning the pipe before applying the primer.    
     
     
         19 . The process as claimed in  claim 1 , wherein only the external surface of the pipe is coated.  
     
     
         20 . A pipe coated by the process as claimed in  claim 1 , comprising a primer layer and a polymer coating layer comprising a fusible polymer.  
     
     
         21 . A pipe coated by a chromate-free process, comprising a primer layer and a polymer coating layer applied in a fluidized-bed coating process.