Relationships Between Log Size and Volume Throughput for Types of Sawmill Headrigs

Studies of cubic volume throughput related to log size were conducted in sawmills in British Columbia. Mill types studied included conventional band and circular headrigs, log-gang mills, chipper headrigs, and scrags, that were producing mainly 2-inch thick lumber from the various commercial species of British Columbia. Logs were scaled for the cubic volume content and throughput was expressed as cubic feet of log processed per minute at each of the head-rigs. In five chipper headrigs and three scrag mills, where log top diameter ranged from 4 to 15 inches, R-squared values for regression equations incorporating the linear form of log top diameter, length and taper ranged from 0.66 to 0.99. In four log-gang mills, where log top diameters ranged from 5 to 20 inches, the inclusion of the quadratic function of diameter significantly improved the proportion of variation in throughput explained using the linear form of diameter with log length and taper. R-squared values were generally lower than for chipper headrigs and scrags and ranged from 0.47 to 0.90. For the log-gang mills, throughput was a maximum in the top diameter range from 15 to 20 inches. Log top diameters in five band and five circular headrigs studied ranged from 9 to 45 inches, with the bulk of the observations concentrated between 15 and 30 inches. For the ranges encountered, the relationships between log size and throughput were erratic and generally extremely poor, with R-squared values ranging from 0.04 to 0.43. The inclusion of number of turns and cuts performed on a log while on the carriage, as additional explanatory variables, significantly improved R-squared values to levels from 0.57 to 0.79, indicating that incorporation of a cutting strategy, where it can be predetermined, would be helpful in obtaining more acceptable estimates of through put in the band and circular mills studied. Throughput, being defined as cubic volume processed per minute at the headrig, means that the relationships defined apply to sawmills where throughput is controlled by the headrig.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member