A study of the performance of a band sawmill

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A band sawmill system has been studied for lumber recovery, productivity, quality control, and forecasting and budgeting. A total of 78 mill-run logs (comprising of 70 Iroko Maclura excelsa) and eight Obeche (Triplochiton scluoxylon K. Schum) ranging from diameters of 57cm to ,154cm were studied under the normal industrial conditions prevailing at the mill. Lumber recovery was 43%. Solid residue and sawdust together constitute 57% of the log throughput. Factors contributing to the low recovery have been identified as excessive slabbing, edging and trimming, and persistent quarter sawing of logs. The effects of log diameter and log length on lumber recovery, sawing time and productivity have also been investigated and regression equations developed to quantify the relationships. The effect of log diameter on lumber recovery, sawing time and productivity were significant whereas only that of the log length on sawing time was significant. Productivity studies have shown that the mill was not being utilized to capacity. The proportion of productive time lost due to delays for a variety of reasons varied from 0.5 to 11%. Saw changing had an exceptional amount of 40% of the total non-productive time i.e. 10.8% of the total working time. Control charts showed that there was general lack of control at the machine centres. Thickness variations both within - and between boards were greater than similar variations in width of boards. The break-even point for the planned period would occur 3 at (81,520,000 and at an output of 3836m . It is considered that the most effective ways to improve the performance of the study mill would be through live-sawing of logs, initiation of proper preventive maintenance schedules and quality control programmes and adequate supervision.
A thesis submitted to the Department of Wood Technology and Industrial Management, University of Science and Technology. In partial fulfilment of the requirements for the degree of Master of Science, 1979