|WHAT IS HEAT STRAIGHTENING?
The practice of heat straightening steel has been used for
decades. Early ironworkers and welders discovered that when
heat was applied to small areas of a steel member, the member
was distorted. Taking this observation further, they began
to experiment on their own, trying to discover how to use
this concept on their jobs. Over the years, the practice was
used to camber beams, when mechanical cambering was insufficient
for the task. Since then, the process has been applied to
steel beams and girders, trusses and columns, in an effort
to repair damaged members.
Scientifically, heat straightening is a relatively simple
process to understand. When a steel member is heated, the
heated area expands. Upon cooling, the area will contract.
This is the principle upon which heat straightening is based.
However, it is the application of this principle which produces
the desired results, and which requires experience and expertise
to be successful.
Over the years, true heat straighteners have learned the
proper application of heat and restraining forces necessary
to conduct real heat straightening repairs. Some "heat
straighteners" believe all that is necessary to conduct
these repairs is to heat the damaged area and push it back
into place. In order to do this, the steel must be heated
above the phase transformation temperature, thus changing
the steel's molecular structure and it's strength and ductility
characteristics. This is known as mechanical or "hot"
working. It used to be known as blacksmithing. Call it what
you will, IT IS NOT HEAT STRAIGHTENING.
During proper repairs, the repeated heating and cooling of
the damaged area will move the member back to it's original
shape. It is never forced back into position. The heat is
controlled and kept below the phase transformation temperature,
thus retaining the steel's original molecular characteristics.
Only by carefully controlling the amount and location of the
heat and restraining forces can true heat straightening repairs
WHAT TYPES OF MEMBERS CAN BE HEAT STRAIGHTENED?
Any steel member can be repaired by heat straightening. The
most common repairs are to highway bridge beams that have
been impacted by over-height loads. However, repairs have
also been performed on columns of multi-level bridges, crane
rails in steel plants and trusses and columns in automotive
plants. In addition, many different sizes of members have
been repaired, from a 12' deep crane rail with a 4" flange,
down to a 3x3x5/16 angle.
WHAT ARE THE ADVANTAGES OF HEAT STRAIGHTENING?
There are several advantages to using heat straightening,
but as we all know, it all comes down to money. This is the
biggest advantage of heat straightening.
IT COSTS LESS. An average repair of a highway bridge
beam takes just FOUR DAYS.
Even the most severe damage can usually be repaired in two
weeks or less. In addition, traffic on the bridge does not
have to be detoured (unless the damage is extremely severe).
Also, lane closures under the structure can be removed at
the end of each day, no permanent closures are necessary.
Finally, repairs can be conducted during night and weekend
hours, whenever traffic volumes are at their lowest, thus
significantly reducing the impact to the public. Compare this
to the long and expensive process of replacing a beam; long
traffic closures, both on and under the bridge, cost of materials
and labor, public frustration, it all adds up, quickly. Over
the years, heat straightening costs have generally been about
25% OR LESS of the cost
of replacement. It's easy to see why heat straightening is
an attractive alternative.