Factors affecting sawmill residue chip quality
A study was conducted to determine the effects of knife angle, wood temperature, disk speed, anvil condition, and residue type, on loblolly pine sawmill residue chip quality. A 152-cm, six-knife, horizontal infeed, top-discharge chipper restored to factory specifications was used as the test machine. Chips were recovered after being blown 4m vertically through a cyclone settler onto a screen pack with the top screen blinded. OVersize chips were not re-chipped. Material types included cants as controls, slabs, edgings, and trim blocks. Chipper rim speeds included the manufacturerJs recommended 3,385 meters per minute along with 2,370 meters per minute and 1,693 meters per minute achieved by the drift-down method. Knife angles included 30, 31, 32, and 33 degree straight grinds. Wood temperatures ranged from ambient temperatures of over 21 degrees C. through chilled (approximately +2 degrees C.) and frozen (-4 degrees C.). The chip distributions from chipping slabs and edgings were not significantly different from those of the cants. Less than 50 percent of the weight of the trim blocks was returned as acceptable chips in most trials. Reducing disk speed resulted in a major reduction in pin chips and fines. Knife angles had less effect on chip size distributions than any of the other variables tested. The percentage of pin chips and fines was greater for chilled and frozen wood than for wood at ambient summer temperature.