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.
