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 use
d 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 i
n 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 o
perating at a given shoe speed. Specific energy was lowest for-the sho
rtest grinding zone. Irrespective Of grinding zone length,the GW pulps
ail had about the same long fibre fraction and hence the-same paper s
trength, whereas the PGW pulps developed more long fibres with an incr
ease in grinding zone length and hence pulp strength increased.