Browsing by Author "Mitchual, Stephen Jobson"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Densification of Sawdust of Tropical Hardwoods and Maize Cobs at Room Temperature Using Low Compacting Pressure Without a Binder
    (2015-05-22) Mitchual, Stephen Jobson
    This dissertation reports the findings of densifying maize cobs and sawdust of six selected tropical hardwood timber species at room temperature (25oC) using low compacting pressure (CP) varied from 10 MPa to 50 MPa, without a binder. The maize cobs was crushed using a hammer mill. Particle size 1mm or less of the maize cobs was used for the study. Sawdust of the six timber species were sun dried and graded into particle sizes (P): P ≤ 1 mm, 1 mm < P ≤ 2 mm and 2 mm < P ≤ 3.35 mm. Briquettes were produced using a laboratory hydraulic press and a piston. Physical and mechanical characteristics of briquettes determined were briquettes' stability, relaxed density, compressive strength (CS) in cleft, impact resistance index (IRI) and water resistance (WR) quality. Additionally, some physico-chemical and thermal properties of the biomass materials used for the study were determined. The study revealed that at 5% level of significance the density of timber species used for the study had significant negative correlation with CS in cleft, IRI and WR quality of briquettes produced. Furthermore, species density significantly and positively correlated with relaxed density of briquettes produced. Generally, species, particle size and CP had significant effect on stability in length and diameter, relaxed density, CS in cleft, IRI and WR quality of briquettes produced (p-value < 5%). Linear regression models established between the research factors and dependent variables suggested that species density, particle size and CP were good predictors of stability in length and diameter, relaxed density, CS in cleft, IRI and WR quality of briquettes produced. The multiple correlation coefficient (R) and adjusted R2 for the regression models ranged from 0.74 - 0.93 and 0.54 - 0.87 respectively with p-values less than 5%. The result further indicated that mixing sawdust of C. pentandra with P. africana or T. superba significantly improved upon the CS in cleft, IRI and WR quality of briquettes 6 produced. The mixing ratio of the sawdust also had significant effect on the mechanical and physical properties of the briquettes produced. The study further revealed that briquettes produced from maize cobs at low CP and room temperature had low CS in cleft, IRI and WR quality. However, these properties were significantly improved when maize cobs was combined with sawdust of C. pentandra, T. superba and P. africana. The gross calorific values of the six hardwood timber species were adequate and they ranged from 20.16 to 22.22 MJ/kg. The biomass materials used for the study were also found to be environmentally friendly since they contained low amount of nitrogen, sulphur and ash content. From this study it could be concluded that briquettes with adequate physical and mechanical properties could be produced from sawdust of tropical hardwood species and their mixture at room temperature using low CP. Additionally, briquettes with adequate physical and mechanical characteristics could be produced from maize cobs at room temperature using low CP when maize cobs particles are combined with sawdust of Ceiba pentandra. These findings could enhance the existing technology for densifying sawdust and maize cobs, especially in the rural communities.
  • Thumbnail Image
    Item
    Densification of sawdust of tropical hardwoods and maize cobs at room temperature using low compacting pressurewithout a binder
    (2015-02-23) Mitchual, Stephen Jobson
    This dissertation reports the findings of densifying maize cobs and sawdust of six selected tropical hardwood timber species at room temperature (25oC) using low compacting pressure (CP) varied from 10MPa to 50MPa, without a binder. The maize cobs was crushed using a hammer mill. Particle size 1mm or less of the maize cobs was used for the study. Sawdust of the six timber species were sun dried and graded into particle sizes (P): P ≤ 1mm, 1mm < P ≤ 2mm and 2mm < P ≤ 3.35mm. Briquettes were produced using a laboratory hydraulic press and a piston. Physical and mechanical characteristics of briquettes determined were briquettes' stability, relaxed density, compressive strength (CS) in cleft, impact resistance index (IRI) and water resistance (WR) quality. Additionally, some physico-chemical and thermal properties of the biomass materials used for the study were determined.The study revealed that at 5% level of significance the density of timber species used for the study had significant negative correlation with CS in cleft, IRI and WR quality of briquettes produced. Furthermore, species density significantly and positively correlated with relaxed density of briquettes produced. Generally, species, particle size and CP had significant effect on stability in length and diameter, relaxed density, CS in cleft, IRI and WR quality of briquettes produced (p-value < 5%). Linear regression models established between the research factors and dependent variables suggested that species density, particle size and CP were good predictors of stability in length and diameter, relaxed density, CS in cleft, IRI and WR quality of briquettes produced. The multiple correlation coefficient (R) and adjusted R2 for the regression models ranged from 0.74 - 0.93 and 0.54 - 0.87 respectively with p-values less than 5%. The result further indicated that mixing sawdust of C. pentandra with P. africana or T. superba significantly improved upon the CS in cleft, IRI and WR quality of briquettes produced. The mixing ratio of the sawdust also had significant effect on the mechanical and physical properties of the briquettes produced. The study further revealed that briquettes produced from maize cobs at low CP and room temperature had low CS in cleft, IRI and WR quality. However, these properties were significantly improved when maize cobswas combined withsawdust of C. pentandra, T. superba and P. africana.The gross calorific values of the six hardwood timber species were adequate and they ranged from 20.16 to 22.22 MJ/kg. The biomass materials used for the study were also found to be environmentally friendly since they contained low amount of nitrogen, sulphur and ash content. From this study it could be concluded that briquettes with adequate physical and mechanical properties could be produced from sawdust of tropical hardwood species and their mixture at room temperature using low CP. Additionally, briquettes with adequate physical and mechanical characteristics could be produced from maize cobs at room temperature using low CP when maize cobsparticles are combined with sawdust of Ceiba pentandra. These findings could enhance the existing technology for densifying sawdust and maize cobs, especially in the rural communities.
  • Thumbnail Image
    Item
    Performance of bandsaw blades used in rip-sawing wawa, (triplochiton scleroxylon) at a Ghanaian sawmill
    (2002-12-11) Mitchual, Stephen Jobson
    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.