Alignment of Cylinders with Space Technology
The alignment of rolls and cylinders plays a bigger role in the quality of the end product and even in the whole production line than is often thought.
Fig.1. Aligning rolls with PARALIGN®
Fig.2. A dehumidifying machine.
VTT Technical Research Centre of Finland Ltd, the leading research and technology company in the Nordic countries, tested a unique gyroscope-based technology used to align rolls primarily in the pulp & paper, converting, printing and steel industries, and reports.
Usually the alignment of cylinders and rolls is performed with optical measuring devices and, in its simplest form with spirit levels and measuring tape. The challenge with the latter is the inaccuracy and poor reliability of the measuring.
Optical measuring also has its own limitations: visual contact is needed and other disturbances like heat radiation and external vibration have their effect on the quality of the measurement. Furthermore, the alignment measurement of a whole line of machines takes time, and may even be impossible during a short stoppage.
The technique designed by the German manufacturer PRUFTECHNIK and patented in 2005 is based on ring laser gyroscopes that measure according to a gyroscope principle every angular change in three perpendicular directions. There are no spinning parts within the device, but the angle measurement of X, Y, and Z-axes takes place with the help of ring lasers and the device recognizes its own position in space at any particular moment. The same gyroscope technology is used for the navigation of space shuttles and missiles. The resolution of the laser gyroscopes is 0.004 mm/m and the measurement accuracy for the cylinder alignment is 0.05 mm/m.
Fast and Accurate
A PARALIGN® measurement is performed by two engineers. One technician swipes the surface of the roll with PARALIGN® (Figure 1) and the other follows the measurement on the computer in real time. During the sweep (minimum 20 degree angle) the device gathers hundreds of measuring points from the surface of the roll, and the programme calculates the angular position of the rotation axis of the roll.
The measurement of a single roll takes only a few minutes and when the desired elements have been measured, the alignment results can be displayed in a single view (Figure 6) directly on your computer screen. Advantages of PARALIGN® include fast and always reliable measurement results, which allow the measurement of dozens of rolls within one stoppage day. There are no physical limitations to the measurement as long as the measured element is within reach. The gyroscopic measurement method has been successfully applied in paper and printing machines as well as in the steel industry, everywhere where rolls or cylinders are used. Hundreds of gyroscopic alignments have been carried out during the past years all over the world.
Test Measurement on Dehumidifier
The VTT group uses their research and knowledge to provide expert services to their domestic and international customers and partners, serving both the private and public sectors.
Fig.3: Gyroscopic principle.
Fig.4: PARALIGN® device with laser gyroscopes.
Fig.5: Measurement directions (Roll, Pitch, Yaw), wherefrom the cylinder alignment is calculated.
A test measurement was performed on a pilot dehumidifier. The fourcylinder steam heated dehumidifier is used in paper and cardboard manufacturing for the drying of rolls made with a pilot paper machine in a study setting and at various customer sites. The largest track width is 600 mm, the largest diameter of roll 1200 mm and rotational speed 10–70 m/min.
There were 21 measured rolls and 4 cylinders. The preliminary preparations took an hour and the measuring two hours. The measurement results read as follows; the green circle represents the operator side of the roll or cylinder and the red one the machine side.
The more red can be seen, the more misalignment there is between the roll measured and the chosen reference roll (in the figure 6, roll 3). The guide rolls are clearly visible in the report. Both rolls were measured twice in maximum positions. The table above shows the rolls with the biggest alignment errors.
"PARALIGN® is very fast and easier to use than optical measuring devices. It measures at a pace four times faster than traditional optical methods. In addition to the swiftness, a clear advantage is that measuring can be done when other optical measuring devices fail due to obstacles in the line of sight." VTT, Technical Research Centre of Finland Ltd.
Fig.6: PARALIGN® report showing misaligned rolls in red colour.
Roope Siilasto
Research Scientist,
VTT,
Technical Research Centre of Finland Ltd,
A Heat Pump Plant Turns the Carbon Footprint of Textile Fibre Production Negative
