Performance of bandsaw blades used in rip-sawing wawa, (triplochiton scleroxylon) at a Ghanaian sawmill

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An optimum side clearance and kerf width of bandsaw blade is required by the wood industry for efficient lumber production from tropical hardwoods. However, little or no work has been done on the influence of kerf width and side clearance of bandsaw blade on sawing accuracy when processing tropical hardwoods. It is the object of this study to determine the accuracy of kerf width of stellite-tipped and swage-sets saw when Sawing Wawa (Triplochiton Scleroxylon) at a Ghanaian sawmills. It is also the object of this study to examine the influence of kerf width and side clearance of bandsaw blades on sawing accuracy of Wawa (Triplochiton Scleroxylon) The research work was carried out at the FABI timbers limited in Kumasi. Eight 152mm (6 inches) bandsaw blades with similar specifications were randomly sampled from a total of ten bandsaw blades for the study. A complete randomized design and Student’s T-test were used to assess the significant difference between the kerf width of stellite-tipped saws and swage-set saws and the outer and inner side clearance of stellite-tipped saws respectively. At 5% level of significance the mean kerf width of the stellite-tipped saws which was 4.20mm was found to be significantly bigger than the kerf width of the swage-set saws which was 3.06mm. The main contributing factor to thickness variation of sawn lumber was excessive kerf width of the bandsaw blades used. A quadratic relationship between side clearance and sawing variation was established. As the side clearance increased the sawing variation decreased until an average minimum value of 0.42mm, 0.33mm and 0.59mm standard deviation within boards, standard deviation between boards and total standard deviation respectively were obtained for a mean optimal side clearance value of 0.69mm. Thereafter the sawing variation began to increase with increasing side clearance. It was also established that when the side clearance varied from 0.8319mm to 0.4336mm for stellites saws the sawing variation was generally low having an average minimum value of 0.3485mm. A quadratic relationship was also established between the surface smoothness of sawn lumber and the standard deviation of the side clearance. It was established that the surface smoothness of the sawn lumber was good, very good or excellent when the standard deviation of the side clearance was 0.1700mm or low and was poor or very poor when the standard deviation of the side clearance was 0.2100mm or more. The thickness variation of sawn lumber was also found to increase with increasing depth of cut. It was observed that the ratio of the wheel diameter to the saw blade thickness ranges between 1030 and 1066. Nevertheless- the ratio of the tooth pitch to the tooth height, which was 2.74 on the average, was significantly less than the recommended value of 3. Lastly, lumber thickness at the mill used for the study was found to be out of control. The mean thickness of boards produced was 42.42m as against a nominal thickness of 41.00mm. This resulted in a loss of 3.46m3 of lumber for every l00m3 of lumber produced, which was a great financial loss to the company.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of Master of Science degree in Wood Technology and Industrial Management, 2002