US 5,732,874 A · Method of forming seamed metal tube

Abstract

The method of forming a seamed metal tube having a metal coating of this invention includes applying a metal coating to the upper face of a metal strip prior to welding. The strip is then formed into an open seam tube and welded, preferably in a non-oxidizing atmosphere with the seam preferably located in the lower portion of the tube. Finally, at least a lower portion of said tube is reheated with the seam located in the lower portion of the tube, thereby causing the metal coating to flow downwardly over the seam, coating the seam. In one embodiment, the strip is preformed into an arcuate shape and coated, wherein the metal coating increases in thickness toward the lateral strip edges, such that the coating will flow over the seam following welding. The inside coated seamed tube may also be immersed in a galvanizing or metal coating bath to coat the outside of the tube. In a preferred embodiment, the inside and outside coatings comprise substantially the same metal and a single galvanizing bath apparatus is used to coat the inside and outside surfaces of the seamed tube. In another embodiment, the coating on the inner surface of the seamed tube has a melting temperature substantially below the melting temperature of the metal strip, but higher than the melting temperature of the outside metal coating. In another embodiment, a lance is provided having a free end which extends through the adjacent lateral edges of a tube-shaped strip and a nozzle which applies metal coating material over the seam. A control loop is also disclosed for improved reflow of the metal coating over the seam.

Claims62

Dependent claims

A method of forming a seamed metal tube having a metal coating on at least an inside surface of said tube from a continuously moving, relatively flat metal strip, said method comprising:

a) applying a metal coating to a top surface of said metal strip, said coating having a melting temperature substantially below the melting temperature of said metal strip;
b) forming said strip into a tube-shaped strip having opposed adjacent spaced lateral edges and said coating on an inner surface of said tube-shaped strip;
c) heating and integrally welding said adjacent edges of said tube-shaped strip to form a tube having a welded seam;
d) locating said seam in a lower portion of said tube and blanketing at least an inner surface of said seam with a non-oxidizing gas;
e) reheating at least said lower portion of said tube to the melting temperature of said metal coating, said metal coating then flowing downwardly over and coating said inner surface of said seam.

2 more elements

A method of forming a seamed metal tube having a metal coating on at least an inside or outside surface of said tube from a continuously moving, relatively flat metal strip, said method comprising:

a) forming a metal strip having a metal coating material on at least one side of said strip into a tube-shaped strip having opposed adjacent spaced lateral edges and said metal coating material on an inner or outer surface of said tube-shaped strip, said metal material having a melting temperature substantially below the melting temperature of said metal strip;
b) heating said adjacent edges of said strip to at least about the forging temperature of said strip and integrally welding said adjacent edges to form a tube having a welded seam;
c) cooling said adjacent edges of said strip to below about the vaporization temperature of said metal coating material;
d) reheating at least a lower portion of said tube to at least about the melting temperature of said metal coating material, with said welded seam in a lower portion of said tube;
and
e) melting said metal coating material over said inner or outer surface of said seam in said lower portion of said tube, thereby forming a tube with said metal coating material over an entire inside or outside surface of said tube including said inner or outer surface of said seam.

3 more elements

A method of forming a seamed metal tube having a metal coating on an inner and outer surface of said tube from a continuously moving metal strip, said coating having a melting temperature substantially below the melting temperature of said metal strip, said method comprising the following steps performed in sequence:

a) running said strip through a molten metal coating bath apparatus comprising:
a sealed housing assembly having a lower reservoir of molten metal and an upper chamber, a sealed tank located within said housing assembly, a pump means pumping molten metal from said reservoir into said tank and said tank having an upper chamber spaced above said molten metal,
wherein said strip passes over said molten metal through said molten metal coating tank upper chamber;
b) pouring molten metal over a top surface of said metal strip in said upper chamber of said tank;
c) forming said metal strip into a tube-shaped strip having opposed adjacent spaced lateral edges and said coated surface on an inner surface thereof;
d) heating and integrally welding said adjacent edges of said tube-shaped strip to form a tube having a welded seam;
and
e) coating said outer surface of said tube with said molten metal by passing said seamed tube through said molten metal bath apparatus below the level of said molten metal in said galvanizing tank with said welded seam in a lower portion of said tube, said molten metal flowing downwardly over said seam and coating said seam at the outer surface of said tube and reflowing said coating on said inner surface downwardly over and coating said seam on the inner surface of said tube.

5 more elements

A method of forming a seamed metal tube having a metal coating on at least an inner or outer surface thereof from a continuous moving metal strip, said method comprising:

a) applying a metal coating to at least one surface of said strip, said coating comprising a first metal coating material having a melting temperature substantially below the melting temperature of said strip;
b) rolling and forming said metal strip into a tube-shaped strip having an inner and outer surface with said one coated surface located on one of said inner or outer surface of said tube-shaped strip and spaced adjacent lateral edges;
c) heating and integrally welding said lateral edges of said tube-shaped strip together to form a tube having a welded seam;
d) reheating at least a lower portion of said tube with said seam in said lower portion of said tuber to at least the melting temperature of said coating;
e) coating said inner or outer surface of said seam with said first metal coating material or a second metal coating material while said seam remains at a temperature at least equal to the melting temperature of said metal coating material;
f) providing a control loop for controlling flow of said metal coating material over said seam and limiting the amount of heat supplied to said lower portion of said tube during reheating and localizing said heat to an area adjacent said seam and confining the area having a temperature above the melting temperature of said metal coating material to said area adjacent said seam, thereby providing a smooth, uniform coating over said seam without stripping said coating from the remainder of said inner surface of said tube.

3 more elements

Dependencies are inferred from the claim text.

Method of forming seamed metal tube

Life of this patent

Method of forming seamed metal tube

Life of this patent

Abstract

Claims62