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Accurate to the Micrometre

Accurate to the Micrometre

Accurate to the Micrometre

Here’s how readychain energy chains help Friedrich Vollmer Feinmessgerätebau GmbH achieve micrometre-accuracy in its measurement devices. Article by igus.

With the VLTG, Vollmer has developed the new “standard” for strip thickness measurement in cold rolling mills. (Source: Friedrich Vollmer Feinmessgerätebau GmbH)

Cold rolling mills operate at speeds of up to 2,000 metres per minute. A uniform strip thickness is a very decisive quality criterion, wherein the micrometre really matters. The more valuable the material is, the more precisely it must be rolled. This is because precious metals are cold-rolled and an oversize in this case is not only a quality defect, but also expensive from the manufacturer’s point of view. 

More than 50 years ago, Friedrich Vollmer Feinmessgerätebau GmbH developed a method for micrometre-accurate tactile strip thickness measurement of cold strip. The devices quickly became the worldwide standard in rolling mill technology and were subsequently expanded to include control units that can readjust the process at high speed.

The company has retained this unique selling proposition over the decades and has carried out intensive research work to develop a contactless measuring method with extreme accuracy to the point where it is ready for series production, thereby again gaining a development lead for the coming years. The Vollmer design engineers have chosen laser measurement as the measuring method. Since conventional lasers do not yield exact results under the ambient conditions of the rolling process with high temperatures, steam, humidity and oil mist, a proprietary laser technology was developed, and launched in 2014: the VTLG .

The VTLG has two laser distance sensors arranged opposite each other. The laser beams are in a common axis. A cumulative distance measurement enables the recording of the thickness of a material positioned in the beam path. The measuring rate is up to 80 kHz. This works with a resolution of 0.05 µm, whereby a measuring accuracy of +0.5 µm is achieved. This opens up completely new possibilities for the rolling mill operator to produce strip and foil with reproducible thickness. According to Elke Roller, sales manager at Vollmer, the VTLG became the new standard for strip thickness measurement. In fact, since its market launch, Vollmer has already sold around 90 units of this design in 17 countries. 

The mechanical structure of the C-frame in which the sensors are located must also meet the highest standards. The frame is made of Invar, a special steel with a minimum coefficient of thermal expansion. The sensor units move within the frame by means of a precision linear drive. The Sales Manager says: “For most users, a measurement of the strip thickness at the centre line position is sufficient to control the thickness. The sensor system then moves to the centre line position and is thereby adjusted. Other users continuously move the measuring device across the width of the strip to measure the thickness at different positions.” For this reason the energy and signal supply must be movable in the C-frame.

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