Investigations into the quality of mill plate wear using attrition mills in Ghana.
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Date
AUGUST 2016
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Abstract
Attrition mills are machines used for size reduction (grinding) of fibrous material especially agro-food produce such as maize, millet sorghum, cassava chips, pepper etc., into a desirable flour sieve size. In the Attrition mill, two roughened disc with teeth or grooves, which are made from cast iron are mainly engaged for the grinding. Observation has proven that the teeth wear out rampantly during milling. Hence the objective of the work was to investigate, identify the causes of wear and develop a solution technique to rectify the problem. The method used for the study included the purchased of grinding disc samples from known foundries at Suame Magazine Industrial Area in Kumasi. The samples were prepared and their elemental compositions were determined at Tema Steel Works (TSW). The specimen was compared to ascertain the correlation between the elemental composition, and the foundry practices. The dial indicator was used to determine the parallelism and concentricity of the mill plates. Soaked maize was milled using the grinding disc samples. The resulting flour sample was taken to GAEC laboratory and analyzed to determine the amount of iron particles present.
Results indicated that hardness of the grinding mill plates was deduced from the depth of penetration using Brinell hardness method and there was a moderately strong correlation between wear and hardness. The hardness values obtained ranged between 429 BHN and 534 BHN and the penetration values were between 2.65 mm and 2.95 mm. It was established that, the lesser penetration the greater the value of the hardness and the lesser the wear. It was shown that, the wear rates ranges from 1.5×〖10〗^(-3) kg/min to 5.167×〖10〗^(-3) kg/min.
From the analysis, it was established that significant metals particles existed in the milled flour. The study revealed that heavy metal particle was found in the mill flour with values ranging from 14.71 mg/kg to 21.55 mg/kg of flour. For the limit of contaminants levels, Asare and Nulux indicated an average value of 50 %. Abudia and Atanga were 100 % below the contaminant limits, suggesting a good standard. Navin and Babawala having 75 % above the contaminants limits indicating poor standard.
It could be concluded that the relationship between wear rate of 1.5×〖10〗^(-3) kg/min to 5.167×〖10〗^(-3) kg/min, hardness value of 429 BHN and 601 BHN, 2.65 mm to 2.5 mm penetration and 2.41 kg and 3.00 kg concentricity mass has been established.
It could be recommended that, the result could be used to improve the general performance of the foundries while the redesigned version could be recommended for adaptation.
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A thesis submitted to The Department of Mechanical Engineering, Kwame Nkrumah University of Science and Technology, KNUST, in partial fulfillment of the requirements for the degree of Master of Science, Mechanical Engineering,