Pulp Paper & Logistics
HEIMBACH 13
the vacuum system of the wire section. Heimbach-TASK looked at everything that affects the wire section: each pump, the pressure screens, even the rotation frequency of the propeller in the pulper. The cause remained undiscovered.
On the track of barring To be certain that the barring frequency stayed at a constant 12.56Hz for a longer period of time, a 30-minute continuous measurement was carried out – with exactly the same results. The tension of the forming
fabric was modified and still the same barring frequency was seen. What surprised most of the team, however, was that the frequency disturbance of 12.56Hz remained unchanged even when the jet velocity was varied. Thus it could be ruled out that the cause of the disturbance was directly related to the fan pump. If this had been the case, one would have recorded a different frequency after changing the jet speed. Could the mass variation ultimately be related to machine speed? When the speed was lowered
by 10 m/min this was a direct hit: The frequency of the barring changed from 12.56Hz to 12.31Hz (as shown in Figure 2). As the
Figure 2: Barring frequency is directly influenced by the machine speed.
team proceeded to increase the speed again, the frequency changed proportionately. Now it was clear that the barring originated from the machine and was therefore influenced by the
machine speed. But where was the cause for this?
Heavy vibrations Heimbach-TASK noticed very strong vibration in the press
Photo 2: Vibration measuring equipment. Data transmitted by telemetric system
section. Could it be possible that these were the cause of the barring in the sheet? Vibration measurements on both presses showed that, while the first press vibrated, it did not exhibit any serious abnormalities. So, the equipment was transferred to the second press (as in Photos 2 and 3). The counter (CC) roll of the shoe press, as it were a deflection- compensating roll, was generating five beats per rotation. It was causing the entire press to oscillate (as in Figure 3) and these oscillations transmitted through the frame and machine foundation to the wire section. It was possible to feel the vibration in the whole body.
4 May/June 2019
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