Double walled metal tube, metal band and strip, and method of coating a metal strip

Abstract

The invention relates to a double walled metal tube comprising a tubular roll formed metal band having a brazing layer between the metal layers of the tubular roll formed metal band, wherein the brazing layer consists of a copper alloy. According to the invention, the copper alloy is a copper-tin alloy, wherein the copper-tin alloy contains 3-12 wt % tin. The invention also relates to a metal band for forming such a double walled metal tube and to a metal strip for producing such metal bands, and to a method of coating a metal band and strip.

1 . Double walled metal tube comprising a tubular roll formed metal band having a brazing layer between the metal layers of the tubular roll formed metal band, wherein the brazing layer consists of a copper alloy, the copper alloy being a copper-tin alloy, wherein the copper-tin alloy comprises 3-12 wt % tin.  
   
   
       2 . Double walled metal tube according to  claim 1 , wherein the copper-tin alloy comprises 6-8 wt % tin.  
   
   
       3 . Double walled metal tube according to  claim 1 , wherein the copper-tin alloy comprises about 7 wt % tin.  
   
   
       4 . Double walled metal tube according to  claim 1 , wherein the metal band is made of steel.  
   
   
       5 . Double walled metal tube according to  claim 1 , wherein the steel band is made of mild steel.  
   
   
       6 . Double walled metal tube according to  claim 1 , wherein the metal band from which the tube has been roll formed has a coating of a nickel layer on one side.  
   
   
       7 . Metal band for producing double walled metal tubes according  claim 1 , the metal band having a width of essentially 20-80 mm, wherein a coating layer is present on at least one side of the metal band for brazing the metal band, the coating layer being a copper-tin alloy, wherein the copper-tin alloy comprises 3-12 wt % tin.  
   
   
       8 . Metal band according to  claim 7 , wherein the copper-tin alloy comprises 6-8 wt % tin.  
   
   
       9 . Metal band according to  claim 7 , wherein the copper-tin alloy layer is present on both sides of the metal band.  
   
   
       10 . Metal band according to  claim 7 , wherein the metal band has a coating of a nickel layer on one side of the metal band.  
   
   
       11 . Metal band according to  claim 7 , wherein the metal band consists of steel.  
   
   
       12 . Metal strip for making metal bands for producing double walled metal tubes according to  claim 1 , wherein a coating layer for brazing purposes is present on at-least one side of the metal strip, the coating layer being a copper-tin alloy, wherein the copper-tin alloy comprises 3-12 wt % tin.  
   
   
       13 . Metal strip according to  claim 12 , wherein the copper-tin alloy comprises 6-8 wt % tin.  
   
   
       14 . Metal strip according to  claim 12 , wherein the copper-tin alloy layer is present on both sides of the metal strip.  
   
   
       15 . Metal strip according to  claim 12 , wherein the metal strip has a coating of a nickel layer on one side of the metal strip.  
   
   
       16 . Metal strip according to  claim 12 , wherein the metal strip consists of steel.  
   
   
       17 . Method of coating a metal strip with a coating layer consisting of a copper-tin alloy comprising the following steps: 
 cleaning the metal strip;    activating the surface of the metal strip;    continuously coating at least one side of the metal strip with a copper-tin alloy layer comprising 3-12 wt % tin;    posttreating the metal strip.    
   
   
       18 . Method according to  claim 17 , wherein the metal strip is coated with a copper-tin alloy layer comprising 6-8 wt % tin.  
   
   
       19 . Method according to  claim 17 , wherein the metal strip is continuously coated with a layer of nickel on one side of the metal strip.  
   
   
       20 . Method according to  claim 17 , wherein the metal band is coated using Physical Vapour Deposition (PVD), comprising the following steps: 
 cleaning the metal strip;    drying the metal strip;    activating the metal strip;    continuously coating at least one side of the metal strip with a copper-tin alloy layer comprising 3-12 wt % tin;    cooling of the coated strip;    applying an anti-oxidising agent.    
   
   
       21 . Method according to  claim 17 , wherein the metal band is coated using electroplating.  
   
   
       22 . Method according to  claim 17 , wherein the metal band is coated with a copper-tin alloy layer in a tin ion and copper ion containing cyanide bath.  
   
   
       23 . Double walled metal tube according to  claim 1 , wherein the steel band is made of mild steel having a composition of 0.03-0.07% C, ≦0.02% P, ≦0.015% S, ≦0.06% Si, 0.05-0.4% Mn, 0.02-0.07% Al (all percentage in weight), the remainder Fe and unavoidable impurities.  
   
   
       24 . Metal band according to  claim 7 , wherein the copper-tin alloy comprises about 7 wt % tin.  
   
   
       25 . Metal band according to  claim 7 , wherein the copper-tin alloy layer is present on both sides of the metal band, the copper-tin alloy layer having a thickness of 0.5-5 μm on each side  
   
   
       26 . Metal band according to  claim 7 , wherein the copper-tin alloy layer is present on both sides of the metal band, the copper-tin alloy layer having a thickness of 3-5 μm on one side and 0.5-1.5 μm on the other side  
   
   
       27 . Metal band according to  claim 7 , wherein the copper-tin alloy layer is present on both sides of the metal band, the copper-tin alloy layer having a thickness of about 4 μm on one side and about 1 μm on the other side.  
   
   
       28 . Metal band according to  claim 7 , wherein the metal band has a coating of a nickel layer on one side of the metal band having a thickness of 0.5-2 μm on one side of the metal band and a copper-tin alloy layer having a thickness of 3-5 μm on the other side of the metal band.  
   
   
       29 . Metal band according to  claim 7 , wherein the metal band consists of mild steel.  
   
   
       30 . Metal band according to  claim 7 , wherein the metal band consists of mild steel having a composition of 0.03-0.07% C, ≦0.02% P, ≦0.015% S, ≦0.06% Si, 0.05-0.4% Mn, 0.02-0.07% Al (all percentage in weight), the remainder Fe and unavoidable impurities.  
   
   
       31 . Metal strip according to  claim 12 , wherein the copper-tin alloy comprises about 7wt % tin.  
   
   
       32 . Metal strip according to  claim 12 , wherein the copper-tin alloy layer is present on both sides of the metal strip, the copper-tin alloy layer having a thickness of 0.5-5 μm on each side.  
   
   
       33 . Metal strip according to  claim 12 , wherein the copper-tin alloy layer is present on both sides of the metal strip, the copper-tin alloy layer having a thickness of on one side and 0.5-1.5 μm on the other side  
   
   
       34 . Metal strip according to  claim 12 , wherein the copper-tin alloy layer is present on both sides of the metal strip, the copper-tin alloy layer having a thickness of about 4 μm on one side and about 1 μm on the other side.  
   
   
       35 . Metal strip according to  claim 12 , wherein the metal strip has a coating of a nickel layer on one side of the metal strip, the nickel layer having a thickness of 0.5-2 μm on one side of the metal strip and a copper-tin alloy layer having a thickness of 3-5 μm on the other side of the metal strip.  
   
   
       36 . Metal strip according to  claim 12 , wherein the metal strip consists of mild steel.  
   
   
       37 . Metal strip according to  claim 12 , wherein the metal strip consists of mild steel having a composition of 0.03-0.07% C, ≦0.02% P, ≦0.015% S, ≦0.06% Si, 0.05-0.4% Mn, 0.02-0.07% Al (all percentage in weight), the remainder Fe and unavoidable impurities.  
   
   
       38 . Method of coating a metal strip with a coating layer consisting of a copper-tin alloy comprising the following steps: 
 cleaning the metal strip;    activating the surface of the metal strip;    continuously coating at least one side of the metal strip with a copper-tin alloy layer comprising 3-12 wt % tin;    posttreating the metal strip comprising applying an anti-oxidising agent.    
   
   
       39 . Method according to  claim 17 , wherein the metal strip is coated with a copper-tin alloy layer comprising about 7 wt % tin.  
   
   
       40 . Method according to  claim 17 , wherein the metal strip is continuously coated with a layer of nickel on one side of the metal strip before the coating of the copper-tin alloy layer.  
   
   
       41 . Method according to  claim 17 , wherein the metal band is coated using electroplating, using a copper plated layer and a tin plated layer, the coated metal being subsequently annealed to produce a copper-tin alloy.