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Flat film and sheet processors have a new way to measure thickness. A patent-pending system developed by Mikros LLC, Las Vegas, Nevada, utilizes electromagnetic field (EMF) technology to directly measure both web thickness and temperature, and provides processors with an alternative to beta/X-ray gauges in a much lighter and smaller package, as it requires no shielding to guard against radiation.

Mikros was formed about two years ago by industry veterans with experience in web-thickness measurement. Bruce Johnson, the company’s vice president, was formerly the president of Indev as well as Automation and Control, which Indev purchased in 2017. Johnson also owned Mikros’ predecessor company Microspec, which was also in the ����ý of in-line control and measurement. However, Microspec’s markets were far more varied — not only plastics but paper, steel, nonwovens, roofing shingles and more— whereas Mikros focuses specifically on web or coiled products.

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Much of the technology is the brainchild of Wim Muller, who for more than 20 years was a senior development engineer for ABB Ltd.’s paper division in Europe. Muller is now the president/owner of MCS Engineering in the Netherlands, and supplies Mikros the EMF sensor technology.

Mikros EMF system installed on a sheet line. The system uses no belts or vector drives and instead relies on an independent linear drive system on each head. The technology is nonnuclear, so no shielding is required. Source: Mikros LLC

Johnson reports Mikros has 15 EMF systems up and running in the U.S. and Europe. In addition to the Mikros system being lighter than typical beta gauges, it uses independent linear drives, eliminating the larger AC drives and all the belts typically used in other scanners. This is said to expedite field installation to a few days and greatly minimize maintenance. “Maintenance personnel love the fact that there are no belts,” Johnson says.

Johnson explains the setup, “We scrap the entire belt system and vector drive approach, and instead have independent linear drive systems on each head. So essentially there is a precision linear roll on the top, a precision linear roll on the bottom of the frame, with a motor attached. These heads are about one-third the weight of all those in typical beta and X-ray systems because they require so much shielding. The heads not connected with belts or shafts; they're independent, but because of the encoders, the aligned is much more consistent that what would be possible with a belt because there are no slippages. If the heads ever do get out of alignment, you can basically send them both ‘home,’ where they auto align.”

The control algorithm is said by Johnson to be simpler as well, as the EMF system measures thickness directly and requires no basis-weight conversions or concerns about refractive indices. The system can measure webs in a thickness range from 6µm to 0.7 inches and widths from 12 to 280 inches at ±0.02% repeatability and is set up to communicate with cast film and sheet lines that feature automatic die-bolt adjustment.

“This is a new idea in thickness measurement,” Johnson says. “It’s direct thickness measurement. We're using an electromagnetic field that we pass throughout the material itself. Beta or X-ray gauging systems do not measure film thickness directly. They measure basis weight and then the algorithm in the controls extrapolates thickness based on that. EMF technology is also impervious to density variations in the material being measured.

“That is why it does well with regrind and high loadings calcium carbonate,” Johnson says. “You could put 100% calcium carbonate and it doesn't care.” One of its first installations involved sheet that was filled with metal for an undisclosed government project. Johnson recalls, “When you have metal inside of plastics, your densities will be all over the place. Our system didn't care. It was able to get more than enough data to have very accurate thicknesses even with a large volume of metal inside.”

“This is a new idea in thickness measurement,” Johnson says. “It's direct thickness measurement.” 

The fact that Mikros EMF technology measures web temperature at the same time is an added and critical benefit, Johnson says. At one installation, he says the ability of the EMF scanner to map film “hot spots” and identify film quality defects helped to significantly reduce to ROI at one installation.

He elaborates, “The first problem they solved using EMF technology measurement was hot spots on their chill rolls. This was happening intermittently and was being caused by small amounts of dust flake that was slowly dripping above the line and building up on the rolls. They were chasing this problem for a long time. They were seeing thickness variations that came and went. Once they installed the EMF system and started measuring thickness and temperature across the web, they realized that these variations were not caused by process fluctuations or anything related to the die bolts. So, in short order, through process of elimination, they investigated the chill rolls.”

One reportedly novel feature of the EMF scanner is that it can measure both web thickness and temperature.

During operation, a solid continuous gap of 5 mils is maintained between the web and each sensor head. A controlled stream of air is used to make sure that the distance from the surface of the web to the bottom of the EMF sensor stays stable. This provides what Mikros says is an extremely accurate and fast response to thickness changes within the sheet.

Sensors remain noncontact, and with an independent sensor-servo control along with high sensitivity of the sensor heads, the slightest variation in electrical-magnetic field strength, thickness, temperature and even metal presence is detected quickly and accurately. According to Mikros, this data is then relayed typically via OPC to PLCs, PCs and plant networks for data analysis and closed-loop process control.

Operator interface of Mikros EMF scanning system.

Profile measurements and trends are continuously mapped and displayed on the operator screens along with process system adjustments. Utilizing the cross-direction profile controller, Mikros can also provide a high level of extrusion die, nip roll and other process automation, Johnson says.

In terms of pricing, Johnson says the Mikron MF technology runs about 5-10% above conventional systems.