Method for the production of tubes for heat exchangers from precipitation-hardened alloys by high-frequency induction welding

Abstract

Described herein is an embodiment of a method for the production of tubes for heat exchangers, including the steps of: a) producing an ingot with rectangular cross section (plate) b) hot-rolling said plate so as to form a blank c) rapidly cooling said blank by spraying water inside a purposely designed cooling tunnel d) cold-rolling said blank until a strip or skelp is obtained e) forming the tube starting from the skelp to pass from the plane geometry of the skelp to the cylindrical geometry of the tube and welding the tube; in which the ingot is formed starting from an alloy that can undergo precipitation hardening, and the tube is welded by high-frequency induction welding.

1 . A method for the production of tubes, in particular tubes for heat exchangers, starting from a plane skelp made of a metal alloy, in which respective opposite longitudinal edges of the skelp are bent towards one another until they are brought into mutual contact and butt welded against one another, wherein: 
 i) the metal alloy with which the skelp is obtained is chosen in the group of alloys that can undergo precipitation hardening; and    ii) the welding step is performed by a process of high-frequency induction welding.    
     
     
         2 . The method according to  claim 1 , comprising the steps of: 
 a) producing an ingot with rectangular cross section (plate);    b) hot-rolling said ingot so as to form a blank;    c) rapidly cooling said blank;    d) cold-rolling said blank until a skelp is obtained; and    forming the tube starting from said skelp to pass from the plane geometry of said skelp to the cylindrical geometry of the tube and welding said tube,    said ingot being formed starting from said alloy that can undergo precipitation hardening and said tube being welded by means of said process of high-frequency induction welding.    
     
     
         3 . The method according to  claim 2 , wherein said step of rapid cooling of the blank is performed by spraying water within a purposely designed cooling tunnel.  
     
     
         4 . The method according to  claim 2 , wherein immediately after step d) said skelp is subjected to a thermal treatment of annealing and ageing at a temperature of between 350° C. and 600° C.  
     
     
         5 . The method according to  claim 2 , wherein immediately prior to step e) there is envisaged the step of subjecting said skelp to an operation of embossing.  
     
     
         6 . The method according to  claim 1 , wherein said alloy is an alloy belonging to the systems Cu—Fe—P and/or Cu—Fe—Ni—P.  
     
     
         7 . The method according to  claim 1 , wherein the alloy used has a composition expressed in weight percentages of: Fe 0.101 wt %; P 0.0348 wt %, the remainder Cu; or else: Fe 0.056 wt %, P 0.0362 wt %, Ni 0.0613 wt %, the remainder Cu.  
     
     
         8 . The method according to  claim 1 , wherein said blank is rolled until it has a thickness of approximately between 0.2 and 1.0 mm.  
     
     
         9 . The method according to  claim 1 , wherein said skelp is subjected to a thermal treatment of annealing and ageing at a temperature of approximately between 350° C. and 600° C.  
     
     
         10 . The method according to  claim 1 , wherein said tube is welded by high-frequency induction welding using a generator frequency of 600 kHz.  
     
     
         11 . The method according to  claim 10 , wherein said high-frequency welding is carried out by operating at a welding rate of approximately between 50 m/min and 200 m/min.  
     
     
         12 . The method according to  claim 10 , wherein said tube is welded by high-frequency induction welding so as to have an absorbed power of approximately between 20 kW and 60 kW.  
     
     
         13 . The method according to  claim 10 , wherein said tube is welded by high-frequency induction welding using a tightening force on said edges, applied via said tightening rollers of approximately between 50 kg and 300 kg.  
     
     
         14 . The method according to  claim 1 , wherein said tube is welded by high-frequency induction welding operating with an angle of the “welding vee” of approximately between 2° and 20°.