Oct 31 2005
Soft paper hankies are produced on huge rollers at a speed of up to two kilometers per minute. The roller surface has to be very flat and smooth. A new grinding machine works with micrometer accuracy and cuts downtime by more than half.
Atishoo! A sneeze into a handkerchief has a speed of up to 160 km/h. To withstand this force the paper layers have to be strong, but they also have to be soft on the nose. The central element in the manufacture of tissue paper is the drying cylinder. This is heated from the inside with high-pressure steam and located under a huge hood. The production process – particularly creping, in which a steel blade scrapes the paper off the cylinder – take their toll of the roller surface and it has to be ground flat every two years. Ulrich Priber and Jürgen Schönitz from the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz have developed an easy-to-handle, high-precision grinding unit. Their work on an “intelligent polish-grinding system for the paper industry” has earned them the Joseph-von-Fraunhofer Prize.
Drying cylinders have hitherto been ground with machines weighing several tons and requiring parts of the paper machine to be dismantled. This costs production time. “We had an idea for a smaller and faster machine but we didn’t have the experience to translate it into reality,” explains Sjaak Melkert, head of Voith Paper Service GmbH, who ordered the new grinding system. The development was assigned to the Chemnitz-based research engineers. “The basic idea made sense: to use a grinding device directly suspended in the machine,” relates Priber. But how would the device know where to grind and what grinding force to apply? The key factor is precise measurement of the cylinder, performed by a laser system that scans the rotating roller. A thin steel wire stretched and aligned across each machine serves as the reference point for the cylinder axis. After the measurements have been taken, the computer produces a detailed elevation map of the surface. This is used to control the grinding process, as reflected in the name given to it: Virtual Reference Grinding VRG.
The new system functions on the basis of force, so the grinding force is finely proportioned with pinpoint accuracy. The higher the elevation, the greater the contact pressure, which is automatically and hydraulically set. This results in an accuracy of below 50 micrometers – on a surface of up to 100 m². In addition, the machine is much faster than conventional systems: grinding now takes just one and a half days compared with three days by conventional means. This saves thousands of euros for each service interval and allows soft and strong tissue paper to be produced faster than ever.
This prize has been awarded by the Fraunhofer-Gesellschaft every year since 1978, in recognition of outstanding scientific work by members of its staff leading to the solution of application-oriented problems. Over 200 researchers have meanwhile seen their work honored in this way. This year, three prizes were awarded – each valued at € 10,000. The silver lapel pin bearing the effigy of the man for whom the award is named is an additional trophy.
http://www.fraunhofer.de