Work Index Wi Research Articles

A New Approach to the Calculation of Work Index and the Potential Energy of a Particulate Material

The work index Wi was defined by F. Bond as the specific energy (kWh/ton) required to reduce a particulate material from infinite grain size to 100 microns. The calculation is based on the size-energy relationship e1,2=C.(1/x2n–1/x1n ) , which for n = 0.5, x1 = ∞ and x2 =100, by definition gives e∞, 100 = Wi and consequently C=10Wi. In theory, for a given material the value found for Wi.should be constant regardless of the measured sizes x1 and x2 used to calculate the constant C by measuring the energy e. In practice this is not so due to the fact that n ≠ 0.5 and many correction factors have been proposed to overcome this inadequacy experienced by accepting n= 0.5. The present paper proposes a simple way to calculate the appropriate exponent n using conventional grinding procedures. The same calculation can be used to calculate the true value of Wi and attribute a potential energy state to a material at any size.

Grindability soft-sensors based on lithological composition and on-line measurements

The grinding efficiency evaluation can be performed through the comparison of the operational work index with the ore work index Wi. In this work, the development of an ore grindability soft-sensor (ESTMOL) is presented. The ore work index is estimated on the basis of its lithological composition. Also addressed is the experimental development of a lithological composition sensor (ACOLITO) for ores on a conveyor belt. The lithological composition is determined from image analysis on samples obtained by a color video camera. Finally, a global operational work index for a complete grinding section is defined here, and its on-line estimation (PREDIMOL) is addressed, including the required soft-sensors to overcome the measurement problems. The experimental work is done with samples obtained from the CODELCO - Andina grinding plant. All the sensors have given up to now good results.

Ｗｏｒｋ Ｉｎｄｅｘの測定が不可能な微粒子の微粉砕性の評価法

In a previous paper, the authors proposed a corresponding Work Index Wi , c which is proportional to the Work Index Wi . Wi , c can be determined from the zero-order increasing rate constant of the mass fraction finer than a cut size in a ball mill grinding.In this paper, the authors proposed an application of Wi , c to the fine particles such as fly ash of which the Work Index was not defined in JIS. The grinding experiments were carried out using the mill made of alumina with a diameter 144 mm and the grinding balls of alumina with a diameter 20 mm. The maximum size of fly ash used is about 75μm. The relationship between Wi , c of fly ash and the cut size was studied. As the results, Wi , c is approximately constant to a certain cut size but increases below it. Wi , c can be useful for evaluating a grindability of fine particles.

Ｗｏｒｋ Ｉｎｄｅｘに基づく乾式，湿式粉砕の微粉砕性の比較

In our previous paper, we proposed a corresponding Work Index Wi. c which is proportional to the Work Index Wi. Wi. c can be determined from the zero-order increasing rate constant in a ball mill grinding.In this paper, we propose an application of Wi. c to compare fine grindability in dry and wet grinding. The grinding tests were carried out by using a mill made of alumina with a diameter 144mm and grinding balls of alumina with a diameter 20mm. The feed sample was silica glass with density of 2, 150kg·m-3 and vickers hardness of 465kgf·mm-2. In the case of wet grinding, the volume of water added was twice of the feed sample.The relationship between Wi. c and the particle size was studied in dry and wet grinding. As a result, Wi. c in wet grinding was smaller than Wi. c in dry grinding. It was suggested that Wi. c could be useful for evaluating a fine grindability in dry and wet grinding.

Ｗｏｒｋ Ｉｎｄｅｘｉに基づく砕料の微粉砕性評価

The demand for fine particles is increasing in many industries, thus, it is important to evaluate the fine grindability of solid materials. The Work Index proposed by Bond is an important factor in designing a grinding process and has been widely used.In this paper, the authors proposed a corresponding Work Index Wi, c. which is proportional to the Work Index. Wi, c could be estimated by the examination of the zero-order increasing rate constant of the mass fraction less than a sieving size. Ball mill grinding was carried out on silica glass to measure the rate constant. The mill used was made of alumina with a diameter of 144mm and an inner length of 130mm. Its volume was about 2.1 liters. The grinding balls were also alumina with a diameter of 20mm. The relationship between Wi, c and the sieving size was studied.As the results, it was presumed that the Work Index could be approximately constant to a sieving size of 20μm and increased in the range of a size less than 20μm.