YANKEE SURFACE MANAGEMENT WORLD PULP&PAPER 28 for accurate fines determination of the various samples. The relative merits of the different techniques have been described elsewhere 4, now let us turn to how we use these measurements. One approach, shown in Figure 5, is to develop some generic indices which we can use to benchmark one system against another. The four indices described in this study are as follows: • Calculated net solids addition to system as percent of production • Solids in clarfied water shower, kg/hr/m • Percent trash in short loop • Percent silo fines in coating Please note that these are arbitrary indices, not necessarily absolute values to be interpreted rigidly per machine. However, the indices do allow machine to machine comparison, and thus some patterns start to emerge. This study was carried out over a 12 month period by BTG in the EMEA area. The results are summarised in Table 2. The Sankey diagram allows us to visualise the quantity of fines, ash and short fibre as they circulate around the system. One key point to understand in the context of this article is how much of this material ends up in the silo loop. This is important as any material here ends up diluting the forward flow of thickstock and will be present in the wet sheet as it is transferred from the press felt to the Yankee. Any anionic material here is pressed into a hot, cationic polymer plasma on the Yankee and thus, the anionic material – if unfixed and mobile – readily transfers into the coating. We must also be aware of a secondary factor: the Dreshfield effect.3 This describes how particulate matter in the wet sheet matrix will migrate to the sheet surfaces when it is heated. This further exacerbates the fines and ash incorporation into the coating film. Realising that the Sankey diagram can visualise this equilibrium, the next step is to quantify it by making suitable measurements. Depending upon the time available, various techniques can be used from a simple total solids through to lab instruments Figure 5. Typical tissue machine fines and ash audit. Table 2. Comparison of fines audit KPI’s over 5 European tissue machines.