Pulp Paper & Logistics
HEIMBACH 17
Fig. 17 Even water jet spacing through pipe reinforcement
Fig. 18 Distance between nozzle FS to nozzle BS: fabric width minus 1 nozzle spacing
loosened contamination particles. This water is diffused by the fabric structure and movement and can create a water mist on the inside of the return loop (Figure 12). The high concentration of
Fig. 19 Distance between nozzle FS to nozzle BS: fabric width plus 2 nozzle spacings
shutdown it may be necessary to temporarily connect an alternative water supply to the shower pipe. When assessing the cleaning
performance of the jet (refer to the table in Figure 9 for nozzle diameter and water pressure values), the elastic response of the fabric should be considered. On the one hand this will counteract the jet impact but it will also cause a small movement of the fabric strands. This movement will loosen contamination particles, which are mainly deposited around the cross-over points of the fabric strands, making them much easier to flush out. Care should be taken to ensure
that the water pressure does not exceed the above limits as this can lead to fabric damage with a loss in performance and lifetime. As a general rule the pressure should be as high as necessary in
order to achieve good cleaning, and it should be kept as low as possible in order to avoid damage to the fabric (Figure 10), and in the interest of energy efficiency.
1.3 Configuration of the high- pressure showers, cleaning process and removal of contamination particles High-pressure needle jet showers are often installed between two rolls on the return loop and are directed onto the paper side of the fabric (Figure 11). The shower should be positioned as early as possible on the return run to avoid contaminants being pressed into the fabric by the return rolls. Typically the needle jets are positioned perpendicular to the fabric surface. The fabric will carry part of the water with it with the remainder penetrating the fabric and taking with it any
contaminant material in this mist can cause problems with deposit build up in the forming section especially on high-speed machines. Suction boxes are often installed to take up and remove this water mist. It is becoming increasingly
common to direct the shower onto the fabric as it passes over a return roll (Figure 13). The water jet penetrates the fabric body and hits the roll surface, which
causes a pressure pulse to pass back through the fabric. This mechanism loosens fibre, filler and other contaminants from the fabric and they are flushed out (Figure 14). Part of the flushed out
contamination will deposit on the roll surface and so good doctoring is required. The doctor blade itself should be showered to keep it clean and lubricated (Figure 14). The advantage of this shower
layout is that there is no misting on the inner return loop and therefore none of the associated deposit problems described previously. It is also possible to run two high
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Fig. 20 Example: Wrong oscillation stroke set-up May 2013
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