Sometimes, advancements in
manufacturing are industry-specific and take years to be
commercially licensed for general use. That was the case 30
years ago when bearing manufacturers in the United States,
Europe and Japan began designing large thrust roller bearings
for mini-mill customers seeking to reduce friction and stress
in rolling mills. What started as designs for specific
customers is today standard equipment for rolling mills all
over the world.
So when an aluminum producer
asked Siemens Corp. three years ago to create a simple,
reliable and inexpensive method to measure the thickness of
stationary plates on a hot-mill roller table without the use of
X-rays, the global engineering and manufacturing behemoth
accepted the challenge.
Andrew Frampton, new product
manager for aluminum in the Metal Technology Group at Siemens
Industries in Canonsburg, Pa., fielded the request in late
2007. "I was on a visit to the plant," he said. "I was talking
to the operations and engineering people, and they described
the problem to me."
The problem was operator error
in measuring the thickness of plates coming off the rolling
mill. Operators had to use a micrometer to measure the
thickness of the plates, which often were very hot and
difficult to move, creating a safety hazard if the sheet
shifted while the operator was measuring it. And the mill was
getting inconsistent readings, caused mainly by the different
strengths of the operators screwing down the micrometer.
"It was a usable system, but it
certainly wasnt satisfactory," Frampton said.
The customer told Frampton that
the device needed to be able to operate fully automatically and
measure thickness to within plus or minus 0.025 millimeter
across a wide range of thicknesses. "Right there and then," he
said, "I had a reasonable idea of what we could do."
Frampton, a 30-year veteran of
the industry who went to work for Siemens when his former
employer was acquired in 2006, went back to the shop, assembled
his team and put together a conceptual design. "We went back to
the customer and they said, OK, lets build it. But
it cant interfere with any of the existing equipment on
Frampton and the crew from
Siemens worked with the customer to install the new equipment
in 2008. It was designed to fit in and around existing roller
table drives with a minimum of disruption to existing equipment
location and operations. The device consists of two pneumatic
cylinders mounted above and below the mill roller table. The
cylinders are equipped with position transducers that measure
the displacement of the cylinder pistons when activated. The
displacement measures are used to calculate the thickness of
the plate. Because of varying product widths and tapered table
rollers, the device covers the range of vertical location of
the plate as it sits on the table.
The top cylinder can be
retracted away from the table when not in use to protect the
device and ensure the operator has a clear view down the line.
"The top of the roller table is about 30 to 36 inches above the
floor," Frampton said, "and that retraction has to be
consistent. It has to pretty much come to the same place every
Fully automatic and with an air
panel for control, the unit is air- or water-cooled, depending
on the severity of the heat environment. That proved to be a
problem Siemens engineers had to address more fully in the
start-up phase of the project. "We did have a few issues with
heat," Frampton said. "It turned out the cylinder seals were a
little bit tight. We went back to the shop and made them with a
The cylinders and seals as
originally designed had a very tight tolerance and tended to
stick in the heat of rolling operations. When that happened,
measurements could get erratic in a very short time frame.
Siemens went back to the manufacturer, specified a low-friction
seal and a tighter bore for the cylinders, and modified it to
eliminate the problem.
Siemens designed the unit so it
could be supplied with a small pneumatic logic control (PLC)
device to interface with the equipment, or a local PLC already
in place that also will work with the device. If needed, the
bottom measuring head can be equipped with a small automatic
cleaning device before it contacts the bottom of the plate.
Another unique feature of the
product is that it offers an automatic zero-setting sequence.
"We specifically designed the equipment so that they can zero
it out periodically," Frampton said. "Thats all done with
The operators at the mill
calibrate the equipment about once a month. "Other than that,"
a mill engineer said, "you dont hear much about it. And
thats a good thing."
The equipment was installed in
2008 and, with the exception of the debugging of the cylinders,
has worked flawlessly ever since. The customer is happy, and
Frampton said measurement consistency and safety considerations
have more than lived up to expectations. "The accuracy of the
transducers and the location of the heads always in the same
place is the biggest selling point."