Tube Straightening: Straight
tubes or pre-stressed tubes – both can be accomplished at the same time!
The tube, pipe and wire
industries all utilize straighteners both in-line and off-line with regard to
the main manufacturing process.
Straightening these products involve “stressing” the tube in a
particular plane(s) to counter-act forming, internal material or welding heat
stresses. All of which can be removed or
balanced by using straighteners.
Figure 1: Multi-roll
straightener or stressing unit (prior to wire forming)
There are many types of straighteners used in today’s
manufacturing environment: multi-roll or
multi-plane, Turkshead and cross-roll.
Cross-roll straighteners tend to be used as an off-line processing
action, as typically the tube or pipe is cut to a finite length and the tube or
pipe is rolling radially as it is processed.
Turkshead straighteners are used on tube and pipe mills in-line and use
either 2 or 4 roll designs to encompass the tube and impart a force (or stress)
in up to 2-axis of direction. Multi-roll
or multi-plane straighteners, as shown in Figure 1 above, tend to be used to
counteract forces within a tube, pipe or wire that are variable and
multi-direction as the product moves through the straightener.
Turkshead straighteners involve an operator to adjust the
unit to counteract the internal stresses, but as these stresses change, the
Turkshead must also be changed. This is
not entirely true with a multi-roll or multi-plane straightener. This unit is more robust to small changes as
it stresses the tube multiple times to achieve straightness. In essence, you “beat” the product up to
achieve your desired goals. More rolls
can be added to achieve a state that almost does not require an operator for
all but the most stubborn material characteristics.
Figure
2: Multi-roll straightener or stressing
unit (post wire forming)
Straighteners can be used before special forming units or
after them, depending on the specific manufacturing method.
These units have been recently used in specialty
applications where manufacturers want to “raise the level of work hardening”
within their product without adding specialty heat treat processes or specialty
materials. Since these straightening
devices work by imparting stresses to counter-act already present stresses,
they are a viable choice to add percentage points to the work hardness of a
product without imposing other damage, like, ovality changes. Too much straightening can damage the OD
characteristics of a tube, pipe or wire so as always, there are side effects
that you must monitor to achieve the highest level of quality within a process.
