Many customers who produce round austenitic stainless steel tubing often wonder how much reshaping can be performed while not harming the material integrity due to cold working and how they orient that section for their mill system.
Taking round product and reshaping, or reforming, into complex shapes is common among carbon steel tube producers but not common to austenitic stainless steel producers. The term complex shape does not necessarily require various sharp angles, which has no purpose in fluid or Heat Transfer applications. Instead, it complexity can encompass very thin, tall elliptical shapes that are not easily produced on standard, reshaping capable, tube mills.
Depending on the application, five, six, seven or more stands are required to reshape the round product into elliptical shapes. It essentially depends on how much material must be physically moved. A well-engineered tooling arrangement will design around a specific amount of material movement that can be accomplished per pass, per horizontal center (center between driven stands), etc. Unlike more common tubing applications, the manufacture of complex stainless steel tubing requires an integrated tooling and mill design to truly optimize the forming process. Most tube mill system producers do not have this expertise in house and must work with their tooling suppliers externally to determine the correct material flow patterns that yield satisfactory results.
Yoder Manufacturing, a long time supplier of tube & pipe mill systems, is unique in the industry. As part of the Formtek Group, Yoder is able to supply tube mills, roll tooling and cutoff equipment, in conjunction with Hill Engineering, another Formtek company. As a whole, they are able to look at the complete manufacturing system and apply appropriate disciplines to yield a system that reshapes round, fusion welded tubing into an ellipse. Based on recent installations, Yoder installed an elliptical tube system that produces a finished product that is 73% thinner than the incoming round tube diameter (as shown below).
Due to the reshaping tooling designs, the final product had minimal surface marking, typically caused by speed mismatch, which was accomplished by considering the profile orientation through the mill: the tall axis of the ellipse is horizontal, taking advantage of the natural forming state of the driven stands, while reducing the effects of rotational speed differences, due to changes in tool-to-section radii.
Orienting a section like this would normally cause headaches for cutoff manufacturers because the system requires a horizontal flow to shear the ellipse to length. Again, Yoder and the intercompany expertise of Hill Engineering were able to look at the big picture and determine that designing a cutoff with a complete horizontal cutting motion yielded far more advantage to the reshaping process.
In summary, reshaping of austenitic tubing is possible but you must consider the overall manufacturing solution with the forming, tooling and cutoff as an integrated system. Allowing ample amount of stands to perform the reshaping, and orienting the product so that it is aligned to the strengths of your mill system is crucial in producing a complex shape successfully.
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