Particleboard Quality as Affected By Planer Shaving Geometry

This research study concerns the redesigning of planer heads in order to produce more flake-like shavings and permit particleboards to be produced which have characteristics more nearly like flakeboards. Two special planer heads, both identical except for diameter, one 8 inches in diameter and the other 12 inches in diameter, were used in the study. Four knives were used with the following characteristics: 1) a 30? rake angle and a shallow throat, 2) a 40? rake angle with a deep rounded throat, 3) a 30? rake angle with a deep rounded throat, and 4) a 50? rake angle with a deep rounded throat. A cabinet planer with a 5-inch head was also used to provide shavings for particleboard fabrication for the research study. Observations were made of the effect on board quality of the variables 1) head diameter, 2) rake angle, 3) head angle, 4) cuts per inch, 5) depth of cut, 6) knife jointing, 7) knife face beveling, 8) depth of throat at cutting knife, 9) percent moisture content, and 10) effect of steaming Douglas-fir wood before cutting shavings. Modulus of rupture and modulus of elasticity values were determined and dimensional changes were measured for thickness and length of board specimens. The ratio of modulus of elasticity to modulus of rupture was practically constant for all particleboard test pieces, averaging about 140. Modulus of elasticity differences were not large and were not considered in the results. Dimensional movements in thickness were relatively large in all instances, averaging between 20 and 30 percent swelling. There were no differences found between three Douglas-fir lumber groups or between batches of urea resin adhesives. Linear dimensional movement values were determined by averaging five measurements from each board (linear movement index). A “quality index” was calculated for each board result by dividing modulus of rupture by the, linear movement index multiplied by 100. Increasing cutter head size from 5 to 8 inches in diameter more than doubled the quality index; increasing to a 12-inch head size did not improve the quality index significantly. Increasing the rake angle of the knife from 30? to 50? improved results. A head angle of 45? was found to be best. Twelve cuts per inch was best but only slightly better than 8 and 18. A depth of cut of 1/32 inch apparently gave particles which produced the best boards. Jointing the knife, beveling the knife face, or changing knife throat depth apparently made little difference. Steaming planing stock just before cutting particles did not improve the boards made from them, but cutting green stock produced particles from which high quality boards were made. The highest quality board made from planer shavings produced in the study was one produced with green cut shavings using a 12-inch diameter cutter head at a head angle of 45?, with a knife having a 30? rake angle and deep throat, cutting at 8 cuts per inch at a depth of 1/16 inch.

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