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The Manufacturing Process for As-Welded Mechanical Tubing |
In the manufacturing process, flat steel strip is slit to the proper width and then passes through a series of rolls that progressively cold-form it into a tubular shape. The formed tube then enters the welding unit, where heat is generated by the natural resistance of the steel to an electric current.
When this heat, which is confined to a narrow band along both edges of the strip, reaches the proper temperature, the two edges are forced together by pressure rolls to create the weld. No extraneous metal is added during the process, so the weld has the same composition as the body of the tube. As a result, the weld is as strong as, or stronger than, the tube itself.
The pressure used to force the edges together creates a small amount of outside and inside weld flash. In most cases this is removed from the outside surface to maintain OD tolerances and give a smooth contour. The inside weld flash may be treated in a number of ways depending on customer requirements.
When the ID is non-functional, or an inside fit is relatively unimportant, the specific application will determine the appropriate ID flash condition.
When the ID is functional, the flash is controlled to within a specified height from the tube’s inside surface. There are several degrees of flash control available. They are discussed in detail in the as-welded specifications brochure.
Following the flash control process, the tube is cooled and sized to the specified dimensions by a series of finishing rolls and is then cut to the length ordered.
A number of our tube mills are equipped with state-of-the-art, double-action, flying cut-offs that produce a dimple-free tube, cut to length, to a tolerance of ±.032” in the 1/2” through 4” OD size range. Off-line tube cutting facilities are used for other sizes. Chamfering, reaming and deburring of the OD and ID are also available for the entire round size range. Wire brush deburring is available for shapes and round sizes.
Tubing to be used in severe fabrication applications exceeding the capabilities of as-welded tubing is then annealed in a furnace equipped with an exothermic gas atmosphere that protects it from oxidation and scaling. The resultant metallurgical structure combines optimum hardness with ductility.
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