Document g2a9EnVXD83nzDLVbpXOZ78aa

-39- VI. GRINDING OPERATIONS Power grinders are perhaps the most universally used of the small powers driven tools. The usual power grinder, oommonly known as the emery vdieel, oonsists of a cast metal stand and two abrasive wheels mounted on a- through shaft vhich is either belt or motor driven. There are also several grinding wheels, such as are found on machine tool equipment where grinding takes the place of lathe and planer work. All grinding operations produoe dust to a greater or lesser degree, depending oq the composition and construction of the wheel, the- material being ground and the ventilation or exhaust hoods provided. What is the Composition of Grinding Wheels? Grinding wheels are made of either bauxite which is mined, or silicon oarbide whioh is made by heating a mix ture of quarts sand, coke and conrnon salt in an electric furnaoe. The bauxite or silicon carbide are crushed to the desired grain size, mixed with an adhesive sub stance called a bond, and formed into wheels, discs, oones or.cylinders. There are many wheels in which the binder is shellac, rubber, bakelite and other organic com pounds. Bauxite wheels are known in the shop as "Alundum" and "Aloxite", while silicon carbide wheels are known as "Crystolon" and "Carborundum". Alundum wheels should be used on material of low tensile strengths such as cast iron, brass, alumi num, copper and marble. Is Abrasive Dust Harmful? According to Dr. W. Irving Clark in a paper read at a meeting of Government Officials in Industry (Boston - May 21, 1931) the artifical abrasives, aluminum oxide and silicon carbide do not contain free silica and their dust cannot produoe silicosis. The dust, like any other inorganic dust, can, however, if breathed for a long period of time in large quantities, produoe an X-ray picture similar to that of early silicosis. This picture ohanges very slightly as years of exposure increase, and at no time are the nodules, characteristic of sili cosis, evident. Unlike silicosis, there is no progress in the process after expo sure ceases and there appears to be no marked physical disability. Although there is no silicosis, the X-rays do show signs of pneumoooniosis. Carborundum dust, chemically, is silicon carbide. According to Miller and Sayers (U.S. Pub. Health Rep. Vol. 49 $3 of Jan. 19, 1934) carborundum dust when in jected into the peritoneal cavity of guinea pigs produoed no reaction and was termed "inert". Dusts such es quartz and flint - silicosis producing dusts - produoed a proliferative reaction. Leroy U. Gardner (U. S. Pub. Health Rep. Vol. 60 #21 of May 24, 1935) reports that carborundum produces practically no reaction when inhaled by guinea pigs in high concentrations over a period of time. Quoting from Dr, Gardner's article, the part pertaining to carborundum dust: "The dust which does reach the tracheobronchial lymph nodes.apparent ly lacks the proper physiochemioal properties to stimulate any but a very slight proliferation of connective tissue. In the lungs, there is praotically no fibrosis." The Journal of the American Medioal Association (Notes and Queries 103, 1472, 1934) makes this statement regarding the health hazard of breathing dusj: from arti ficial abrasives: "Only silica (Si02) is capable of inducing silicosis, but any other mineral dust under conditions of prolonged and gross exposure may cause some increase in pulmonary fibrosis. If the relative potential harm of silica is rated as 100, these other non-toxic mineral dusts may be rated E*001529