Pulp Paper & Logistics


HEIMBACH 15


Fig. 7 Various types of water jets Fig. 6 Potential fabric damage


section is to continuously remove contamination from the surfaces and within the weave of the forming fabric while it is running. To achieve this, use is made of the kinetic energy of the water jets from the high-pressure shower nozzles. For efficient functioning, the


shower system needs to be of a solid construction and to be installed at an appropriate position in the forming section and at the correct angle to the fabric. The shower should have an appropriate number of nozzles


spaced at distances from each other that relate to the width of the oscillation stroke. Effective mist removal should also be considered because foreign matter that has been flushed out of the fabric could otherwise be returned into the fabric weave.


1.1 Influence of fabric design on the function of conditioning systems For choosing the correct angle of the shower jets and the appropriate water pressure, the structures of different fabric


designs need to be taken into consideration. • Single Layers have relatively large openings. The water jets can penetrate the fabric weave directly (Figure 1). • Double Layers have typically small openings (high count of yarns in machine direction). Therefore the path of the water through the weave is hindered and significantly slowed down (Figure 2). • Triple Layers with integrated support structures (SSB-fabrics), are available in a variety of mesh sizes and internal structures and generally can be penetrated by water jets in a relatively unhindered way (Figure 3). The paper side construction of


many modern fabric designs is extremely fine, in that diameters of machine and cross direction yarns are often as low as 0.11 mm. This makes the paper side surface


of these fabrics quite sensitive to showering. In contrast the machine side of many modern fabric designs is relatively robust, with cross direction yarn diameters ranging from 0.18 to 0.45 mm.


1.2 Properties of water jets Each water jet must be presented to the fabric surface with laminar flow for the purpose of efficient coverage and cleaning of the fabric. The ideal needle jet should be fine, with well-defined lateral boundaries, no air pockets, a constant diameter (Figure 4) and should meet the fabric surface with sufficient pressure. A turbulent jet, i.e. one that disintegrates into single droplets before impinging the fabric surface (Figure 5), is much less efficient at cleaning the fabric and could – depending on the amount of


4


Fig. 8 Uneven coverage


Fig. 9 Volume flow in needle jet nozzles [I/min] May 2013


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