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(A) GRINDING WHEEL CONSTRUCTION
thismorningA grinding wheel is compod of millions of extremely hard particles of abrasive grit or grain, bonded together with a suitable material. The orientation of the individual grains is completely random, which explains why they may be expod at the surface of the wheel with virtually any effective rake angle. The abrasive material can be either manufactured or natural but the latter has very limited u and the vast majority of wheels in u are made with manufactured abrasives. The natural abrasives include sandstone such as this . Corundum and emery are oxides of aluminium (AL2O3), which have to be crushed into granules, but sandstone exists as granules of mainly quartz and silica(SiO2)
汽车培训 The discontinuance of the natural abrasives is not due to any lack of abrasive ability, but to the prence of impurities and non-uniformity of cutting action. In fact the two most common abrasives in general u are manufactured from the two naturally occurring compounds .
honoluluManufactured abrasives can be given the most desirable crystalline structure and grain sha
pe,which make them superior for modern grinding applications.
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Aluminium-oxide abrasive is produced in electric-arc furnaces by fusing bauxite with finely crushed coke and iron particles. Bauxite is a fine clay compod of almost pure aluminium oxide.
钦佩when the product has cooled and solidified,it forms a crystalline abrasive which can be crushed to the size range required for grinding wheel constuction. The are then graded into the respective grain sizes ud. Aluminium-oxide abrasives are manufactured and marketed under the names "Aloxite","Alundum"and"Bauxilite".Silicon-carbide abrasive is produced in electrical-resistance furnaces from the chemical reaction of silica and finely crushed coke in the prence of sawdust and sodium chloride. The coke supplies the carbon needed to combine with the silica to from the compound,the two other constituents help to bring about the reaction. The heated mixture gives off a vapour which crystalli around the conductor in the furance. After the process is finished the crystals are easily removed and can then be crushed and graded into the respective grai
n sizes. Silicon carbide is manufactured and marketed under the trade names "Crystolon" and "Unirundum"
The grading operation entails passing the grains through a ries of mesh screens,each subquent sreen having a finer mesh than the previous one. The grains which do not pass through the mesh are of a particular grain size. The very small grains which pass through the final mesh are then graded by a floation technique in hydraulic tanks.The grains are then ready for moulding into a grinding wheel using a bonding material or binder.
The bonding material must have three characteristics for it to perform efficiently:
It must be capable of holding the grains in the moulded wheel shape.
It must be able to support the grains during the grinding operation.
It must relea the grains when they have become dulled,before the pressure becomes too great.bullet train
The bonding material is is clasd as soft,medium or hard,which is a measure of how easily it will relea the grains. Soft binders will relea the grain more readily than hard ones, which retain them for a longer period of operation.
deem是什么意思About 80 per cent of all grinding wheels are bonded with vitrified glass as this can be controlled to give a wide range of strengths. The grains are moulded under pressure to the required shape after being thoroughly mixed with the correct amount of mi-dry ceramic clay. The wheels are then dried prior to being fired over a long period, during which time the clay fus to form the vitrified glass bond. Silicate-bonded wheels are made in the same way.火锅 英文>孔子英文
