“Ideally, we tend not to exceed 1,600 degrees F as a general rule,” Frick said,
adding that many times the company heats to even lower temperatures.
Uniform heating is critical, and heating the plate only where rolling will take
place often isn’t an option. The same holds true when forming hot on the press
For instance, when rolling a grade like 4140 plate, “we need to make sure the
plate is heated evenly through the thickness,” Frick said. “If localized heating
were used, it would be too hard to control and possibly create hard spots in the
material, possibly creating cracking and fracturing.”
Once heated, the plate is transported with care. Musil added that this includes
specific chains and other pieces of material handling equipment. “We have ded-
icated pieces of workholding equipment that we use only for holding and form-
ing hot plates. Those chains are inspected periodically, and we have a routine
Some operations dedicate certain roll machines for the hot rolling process.
These rolls have bearings and components designed, placed, and/or protected
in such a way so they can withstand the intense heat from the workpiece. Ulti-
mately, roll shops consult with their plate rolling machine vendors about which
machines are capable of hot rolling and which aren’t.
At Halvorsen, operators perform hot rolling on the shop’s mechanical rolls but
not on the company’s hydraulic machine. “It isn’t designed with heat shields,
and it has rubber hydraulic lines that aren’t far away from the action of the roll,”
This isn’t to say hydraulic plate rolls can’t perform hot rolling; many certainly
have the capability. Modern rolls, including variable-geometry plate rolls, are
customized to meet requirements for the hot rolling and cold rolling of various
materials. (Unlike other plate roll types where the top roll is fixed, the variable-geometry, three-roll machine has a top roll that moves up and down, a little like
a large round punch on a press brake.)
For instance, a combination of hot rolling as well as cold rolling high-strength
material could call for rolls to have a specific balance of hardness and toughness. The right combination would allow the machine to roll high-strength material effectively while at the same time handle the transfer of heat from the
workpiece during hot rolling.
What Makes Plate Rolling Unique
When the roll operation starts, hot plate rolling looks very much like conventional cold plate rolling. But hot plate rolling does introduce a few unique variables. The most obvious is the operator’s heat-shielded personal protective
equipment. Getting close to hot plate requires well-thought-out procedures and
continual caution. The heat from a very hot plate can melt nearby objects.
Depending on the job, the hot rolling process also can require additional labor. “When we hot roll, we dedicate three people to the job, considering the
additional material handling required,” Frick said.
A 6.5-in.-thick plate glows red as it’s being hot rolled. Because of a lengthy backlog
at the mill, hot rolling in this case allowed the plate roller to reduce the customer’s
required lead time. The project would have been delayed if the customer had waited
for heat-treated plate from the mill. Photo courtesy of Uni-Form Components Inc.
A 6.5-in.-thick hot-rolled plate is rolled up and ready to be welded. Photo courtesy of
Uni-Form Components Inc.
Hot plate can emerge from the oven with a slight bow in it, “but once you pass
it through the roll, the bowing really isn’t an issue,” Musil said.
Once rolling commences, plate rolling basics remain the same, “though you’ll
be able to roll it in fewer passes because it’s hot,” Frick said. “And you don’t have
to deal with the kind of springback that you’d have if you were rolling cold.”
With fewer rolling passes, the overall rolling cycle can be much faster; plates
spend less time on the rolls themselves. In many cases, working quicker is im-
portant for safety and operator comfort. Sliding the finished workpiece off the
end of the plate roll requires care, and the workpiece may need to sit on the
floor for a day to cool.
“You do work a little faster,” Musil said, “so you don’t spend a lot of time next
to the hot plate. But again, other than the personal protective equipment, it’s
fundamentally the same process as when rolling cold.”
Sources emphasize that a shorter rolling cycle time (thanks to fewer rolling
passes) alone isn’t a good reason to perform hot plate rolling. It takes time for
plates to heat, and it may require extra personnel to monitor the operation. And
there’s no getting around the fact that heating changes a plate’s properties.
As Moscrip explained, though heating steel does alter the material ever so
slightly, the change usually is so small that the metallurgical properties are still
well within the material specification range for the application. All the same, the
effect of the heating and cooling cycle involved in hot rolling remains a factor to
Can You Roll This?
Sources agree that if a job can be cold rolled with available plate rolling equipment, it should be. “I’d say that cold rolling is always the preferred method,”
It’s one reason behind some of the massive plate rolls now appearing in the
heavy plate rolling market. Some plate rollers of the world now are capable of
cold- olling 11-in.-thick plate—though thickness capacity depends on the material grade, width of the workpiece (in relation to the width of the plate roll machine, analogous to the bend length on the press brake), radius being formed,
and other application variables.
For this reason, many roll shops hesitate when describing their “maximum
rolling capacity,” be it rolled cold or hot. Capacity depends on so many factors.
The question to ask roll shops isn’t necessarily about maximum thickness or the
tightest diameters; it’s instead about showing a job’s requirements and asking,
“Can you roll this?”
After asking this question, you occasionally may find that hot plate rolling is
the only viable option. The trick is considering the options available, then mov-
ing forward on the most cost-effective path.
Senior Editor Tim Heston can be reached at firstname.lastname@example.org.
The Halvorsen Co., 800-423-7080, www.halvorsenusa.com
Paramount Roll & Forming Inc., 888-400-3883, www.paramount-roll.com
Uni-Form Components Co., 800-231-3272, www.uniformcomponents.com