Pulp Paper & Logistics
HEIMBACH 21 One single nozzle of the high-
Fig. 25 Comparison of on-machine vs lab mesurement PRIMOBOND from Heimbach
were made on one of the fabrics, after it had been taken out (Figure 24). This showed a significant reduction in the water permeability at the exact position of the decreased caliper (compare to Figure 23). To confirm these findings, a
comparison with a Primobond fabric was made between the results of Wire-Perm- Measurements that were taken on machine during day 27 of the fabric’s lifetime and a set of caliper measurements taken in the Heimbach lab after the fabric was removed three days later. The form of the graphs was nearly identical and led to the same conclusion (Figure 25): the caliper had been significantly reduced through internal wear and compression, the dewatering channels had been compacted accordingly and the resistance to flow had been significantly increased. Interestingly, the air permeability profile of
the problem area did not vary to the same extent, which could be regarded as significant. Subsequent measurements taken from other fabrics showed the same results. This comparison had provided a
direct cause for the development of the cross direction profile peaks. However, there was as yet no identification of the cause of the fabric damage.
4.2 Cause of the fabric damage The cause could only be found from inside the machine, as it had to be a mechanical issue. After an intensive and very
detailed inspection of all possible areas, conducted both with the machine stopped and running, the experienced Heimbach-specialists with practical support from the customer, finally managed to solve the problem. The cause of the fabric damage was of such a simple nature, that it initially seemed unbelievable:
pressure shower pipe in a position that was difficult to reach and to inspect had been damaged in such a way that it was producing an extremely turbulent, pulsed water jet. The photos illustrate this effect (Figure 26). As a result of this malfunctioning, the water jet had been battering the fabrics in a continuous hammering action. The fabrics had been literally ‘beaten into a pulp’. In addition to the fabric damage in the small strip of the problem area, hardly any fabric cleaning had taken place at all. Consequently, the dewatering channels were significantly reduced in their efficiency not only through being mechanically compacted, but by being highly contaminated as well. (By the way, only one of the other jets shown in the photo in Figure 26 is in a satisfactory condition). The damaged nozzle was
replaced and the whole length of the shower pipe was overhauled. Fabric life times increased from 3-4 to 8-10 weeks. Significantly
better fabric cleaning and improved cross direction moisture profiles were also achieved.
Summary The discrepancy between cause and effect in our case study had truly disproportional effects: The financial loss due to fabric
costs, machine stops, loss of production, rejects, complaints by customers (printers) and extremely high additional loss of time added up to several hundred thousand euros. The new nozzle, its installation and the overhaul of the shower pipe amounted to an investment of approximately 1,000 euros. This demonstrates very clearly
the totality of technological relevance in the paper making process. The high-pressure shower system is but a minute part of all this.
* More information from Chris
Kershaw, Vice President Corporate Marketing, Heimbach UK Ltd, email:
chris.kershaw@heimbach. com and Hans J Struck, PMS GmbH, Offenburg, email: pms-
struck@rubynozzle.com
Fig. 26 Water jet hammering against the fabric May 2013
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