Grading of fines

The particle size distribution of fines should be determined in case their content in the mixture of aggregates is greater than 10%. In the case where a filler has been used, its particle size distribution should be determined regardless of the percentage added. 

The grading of the fines is determined in accordance with CEN EN 933-10 (2009), using an air jet sieving apparatus. 

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Fig. 233. Schematic view of an installation for the mechanical grading of fine-grain powder (vibrating screen), according to Yegorov [11].

Sbot-ftort er. A frame witli a series of sieves of diHerent grades of fineness, to sort shot into... 

Powdered tin can be commercially obtained in various grades of fineness. To prepare smaller quantities in the laboratory, pure tin is melted in a porcelain dish and heating is continued until the mass glows dark red. Liquid tin is poured off from the surface oxide scum into a preheated porcelain mortar and is vigorously pounded immediately after hardenii. Since the metal cools down quickly to temperatures at which brittleness disappears, the mortar should be kept at about 200°C. If this is not done, the larger unbroken pieces must be heat treated again. 

The result indicated that optimum reduction temperature was 1375°C, the optimum percentage of CaO was 12%, and the optimum atomic ratio of C/O was 1.2, resulting in the grade of fine ore of 5.71%. At the same time, the recovery rate of nickel was 96.35%. 

It is important to use recently-prepared pure sodamide, which must be of fine granular form. Old material of irregular lumpy form, even if ground gives poor results, and should not be employed. The sodamide may be prepared as detailed in Section 11,50,j. A satisfactory grade is marketed by May and Baker Ltd. 

Sandstone. Sandstone wheels were once quarried extensively for farm and industrial use, and special grades of stone for precision honing, sharpening, and lapping are a small but important portion of today s abrasive industry. Production of honing and sharpening stones from deposits of dense, fine grain sandstone in Arkansas account for 76% of the value (about 2 million in 1987) and 88% of the total quantity of such stones in the United States (4). 

Bulk Density. Bulk density of fine mica is deterrnined with a Scott-Schaeffer-White volumeter using a 2.54-cm cube. A 7.6-cm diameter cylinder x 12.7-cm long is used to determine the bulk density of coarse mica, eg, oil-weU-grade mica. 

For free-flow agents, water-insoluble, finely divided adsorbents such as sodium siUcoalurninate, tricalcium phosphate, calcium siUcate, magnesium carbonate, and siUcon dioxide are used. Concentrations between 0.5 and 2% are typically added to table salt and some industrial grades of salt for use in apphcations where caking may occur. 

In ancient India, a steel called wootz was made by placing very pure kon ore and wood or other carbonaceous material in a tightly sealed pot or cmcible heated to high temperature for a considerable time. Some of the carbon in the cmcible reduced the kon ore to metallic kon, which absorbed any excess carbon. The resulting kon—carbon alloy was an excellent grade of steel. In a similar way, pieces of low carbon wrought kon were placed in a pot along with a form of carbon and melted to make a fine steel. A variation of this method, in which bars that had been carburized by the cementation process were melted in a sealed pot to make steel of the best quaUty, became known as the cmcible process. 

Uses. Hiere are several different grades of barium carbonate manufactured to fit the specific needs of a wide variety of applications very fine, highly reactive grades are made for the chemical industry coarser and more readily haridleable grades are mainly supplied to the glass industry ... 

Much effort has been made by catalyst manufacturers to improve catalyst atttition resistance and thus reduce the formation of fines (see Catalysts, supported). In the 10-year petiod from 1980 to 1990, most catalyst manufacturers improved the atttition resistance of their catalyst by a factor of at least 3—4. This improvement was achieved even though the catalyst zeoHte content duting this petiod was continually increasing, a factor that makes achieving catalyst hardness more difficult. As an example of the type of atttition improvement that has been achieved, the catalyst atttition index, which is directiy related to catalyst loss rate in a laboratory attrition test, decreased from 1.0 to 0.35 for one constant catalyst grade during 1989—1990 (37). 

FIG. 19-68 The schematic diagram showing the relationship between the physical and chemical properties of fine particles and their behavior in flotation. (G) and (R) refer to whether the phenomena affects grade and/or recovery. The arrows indicate the various factors contributing to a particular phenomena observed in flotation of fine particles (Fiierstenaii, 1980). 

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