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Sunday, 24 November 2013

Classification of Natural Abrasives

Classification of Natural Abrasives Points : Classification of Natural Abrasives, Flint, Garnet, Emery, Crocus, Diamond The following are some common natural abrasive: 1. Flint: It comes from the mineral quartz a crystalline rocklike material. It is used, in making the familiar yellowish coloured abrasive paper called Sandpaper. It is one of the oldest kinds of abrasive paper and is used in woodworking. 2. Garnet It is radish coloured glasslike mineral which is crushed into fin abrasive grains. It is harder and sharper than flint and is widely used for woodworking. 3. Emery Emery is one of the oldest kinds of natural abrasives used for metalworking. It is black in colour and is composed of a combination of corundum and iron oxide. Corundum is aluminum oxide, A1203. Emery, used for making an emery cloth for polishing metals, is about 60 % corundum. Emery grains are not as sharp as artificial abrasives. The cutting action of emery is slight; therefore, it is used largely as a polishing abrasive. 4. Crocus It is a fine, soft, red abrasive of iron oxide, or iron rust. It may be produced artificially or naturally and is used to clean and polish metal surfaces to a high glass. It is available in the form of Crocus Cloth or as a polishing compound. 5. Diamond It is the hardest substance known. It is used in the form of abrasive grains which are bonded together to form a thin layer of abrasive. The layer of abrasive is bonded to a wheel, thus forming a grinding wheel. Diamond grinding wheels are used for grinding very hard materials, such as cemented-carbide cutting tools, ceramic cutting tools, glass, and stone. The diamonds used for this purpose are industrial diamonds in the form of chips or grains. They are much less expensive than the diamonds used for jewelry.
A diamonds chips may be brazed on the end of a soft steel bar to make tool for dressing or truing softer grinding wheels. Diamonds used in industry have been produced artificially during recent years. However, they are still almost as expensive as natural diamonds. Fine diamond dust is also used in lapping compound for lapping hardened steel and other very hard materials.

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