EFFECT OF GRINDING TONE LENGTH IN WOOD GRINDING

To investigate the effect oi grinding zone-length in wood grinding, a laboratory study has been done. The grinding zone length was tested at three levels. Spruce (Picea abies) wood was used. Both unpressurized (GW) and pressurized (PGW)grindings were made and only sapwood was used in the GW series. The inlet and outlet temperatures oi the grinding zone were measured along with other Common process variables. Grinding zone temperature increased, from inlet to outlet, by 5-10 degrees C in the GW grinding trials depending on the grinding zone length. Shower water temperature was 75 degrees C. In PGW grinding, shower water 105 degrees C, temperature increased-less. Specific load Was higher using the two-longest grinding zones during both GW and PGW grinding when operating at a given shoe speed. Specific energy was lowest for-the shortest grinding zone. Irrespective Of grinding zone length,the GW pulps ail had about the same long fibre fraction and hence the-same paper strength, whereas the PGW pulps developed more long fibres with an increase in grinding zone length and hence pulp strength increased.