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 the line."
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 time."
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 bigger clearance."
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 software."
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."