Abrasive products are used to shape and surface many building materials by grinding, lapping, polishing, and sandpapering. For construction purposes abrasive products are used in floors, ramps, steps. and stairways that are subject to slipping hazards. Abrasive grains or abrasive aggregates imbedded in the surface of walkways contribute nonslip qualities and may increase wear resistance. The imbedding material may be metal, vitrified clay mixtures. cement, asphalt, or rubber.
Abrasive Products in the Building Industry LOWELL H. MILLIGAN Norton Company Research Laboratories, Worcester, Mass.
IA?tlOSDS: (crystalline carbon) , garnet. [chiefly the crystalline mineral almandite, FesA12(SiO&], quartz sand (crydalline silicon dioxide), emery, and corundum (crystalline aluminum oxide) are the most important natural abrasives. Crystalline alumina and silicon carbide are the chief manufactured abrasives and are products of the high-temperature electric furnace. Most recently, molded boron carbide has been added to the list and is the hardest material ever produced by man for commercial use. Theqe materials are all extremely hard and are tough enough t o be usable commercially for grinding or abrading away other materials. To permit their sharp edges to function, they must be employed as grains of proper size for the purpose a t hand, either as loose granules or bonded with various binding agents into solid bodies that function successfully because they hold the abrasive grains while they are sharp but permit them to break out when they are dulled, thus exposing fresh sharp grains for -eri-ice.
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Cutting and Grinding Abrahive products enter the field of building construction to only a limited extent but nevertheless play an important part in their own way. Many materials of construction have to be shaped by mechanical methods, and the abrasive operations of grinding, lapping, polishing, and sandpapering are likely to be used where such materials are hard or tough, or where close tolerances or Emooth surfaces are required. For instance, marble and other natural stones are sawed into slab. with steel s a w that are without teeth, but are made to cut by means of a slurry of abrasive sand and water fed over them; the stones are surfaced on revolving iron rubbing beds fed with a mixture of ahraqive grains and water; grind1123
ing wheels and abrasive rubbing bricks serye to shape and smooth the stone products; and inscriptlons are cut upon them by means of abrasive blasts. Plate glass is ground and polished plane and smooth with abrasives. Bathtubs and terra cotta have certain surfaces ground for accurate fitting. In the lumber industry, the huge 5 a w of the lumber mills are kept sharp with abrasive wheels known as saw gummers; and everyone is familiar with sandpapering operation..
Construction
For construction purposes in the building industry abrasive products are used in floors, ramps, steps, and stairways that are subject to slipping hazards. Such hazards are present in many factories manufacturing chemical and other productq, in public buildings, and even to a limited extent in the shower bath and cellar >tainvays of the private home. Employee, customer, and home owner share the advantagf>s of safety underfoot. Abrasive products for these uses should posses adequate friction to eliminate dangerous falls and skidding, especially when the surfaces are wet, and must be wear-resisting. Manufactured electric-furnace abrasives have these properties to an ideal degree. The problem is to choose a method for incorporating them into floors that will utilize and preserve their inherently advantageous characteristics. One such method consists in casting molten nietal around the abrasive grains so that each grain is surrounded by the metal. The grains, with their points projecting above the metal surface, are thus present in metallic pockets, although there is little if any actual adhesion between metal and grains. A number of manufacturers make products of this type in which the metals may be iron, bronze, lead, aliiminuni, or
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INDUSTRIAL A I D ENGIKEERING CHEhIISTRY
nickel alloy, and the abrasive grains are either essentially crystalline aluminum oxide or silicon carbide. These products are advantageous for uses where the metals themselves are desirable but do not alone have sufficient nonslip characteristics.
CUTTING T E R R 4 COTT.4 M-ITH .iN A B R 4 S I V E W H E E L
Another class of nonslip products is of a ceramic nature and is particularly desirable where tile or other ceramic floors are normally used. Such floors may be highly decorative and are often placed in hotels, banks, public buildings, and schools. Ceramic nonslip products for these uses may be classified as: 1. Floor or stair tile, relatively large in size. 2. Mosaic tile, relatively small in size.
3. Nonslip ingredients of terrazzo floors and precast terrazzo stair treads. 4. Nonslip ingredients added to the wearing surface of cement or magnesite floors.
Nonslip tiles are manufactured by employing electric-furnace abrasives as the important ingredients of ceramic mixes that are molded to shape and then fired a t high temperatures in ceramic kilns to mature the bonding clays. The abrasive must be fine enough in grain size to prevent the production of too rough a surface; but if it is too fine, the nonslip properties will not be adequate. Similarly, some porosity is desirable in the finished tile t o prevent it from wearing smooth, but too much porosity makes the tile difficult t o clean.
VOL. 27, NO. 10
llarble terrazzo floors are decorative but are slippery when wet. If abrasive ingredients are included in the mixture with marble chips and cement, the final product may be just a s decorative and nonslip in addition. The best abrasive to use consists of crvstalline alumina grains prebonded with a glass-type ceramic bond into a strong but porous aggregate which is crushed to fragments of the proper sizing. These are incorporated in the terrazzo mixture so that the abrasive aggregates cover from 25 to 50 area per cent of the finished floor. The advantage of aggregates over straight abrasive grain additions is that the prebonded product is porous enough to permit penetration of the Portland cement and thus secure permanent anchorage and maximum nonslip characteristics. Each aggregate itself is strongly bonded together because of the nature of the ceramic bond glass that has united by surface reaction with the abrasive grains during firing in the ceramic kiln. After the cement in the finished floor has set, the floor is ground smooth with machines using abrasive bricks usually made of silicon carbide abrasive grains with a vitrified ceramic bond. In a similar m a n n e r a b r a s i v e g r a i n s or aggregates may be added to ordinary floors made with Portland cement, high-alumina quicksetting cement, magnesium oxychloride cement, or asphalt. However, the cost of manufactured abrasive is greater than that of many ordinary floor materials, and this feature prevents wide application in the cheaper floor field. Abrasive grains and aggregates are both acid- and alkaliresisting and hence may be used in combination with asphalt to make slip-proof, acid-proof floors. Recently a new nonslip product has been introduced consisting of abrasive aggregates bonded in the surface of rubber. A wire reinforcement is imbedded in the underside to aid in shock resistance. This product is strong, resilient, and slipproof, and is of particular value as a replacement on worn stair treads, and for factory applications such as floor inserts around dangerous machinery. Many laboratory tests have been made to show the improved nonslip properties and wear resistance obtained when abrasive materials are properly employed in the surfaces of walk ways. But service tests are perhaps more interesting and satisfactory. Many of these cover periods of from ten t o fifteen or more years and conclusively demonstrate the advantages of utilizing abrasives for these purposes.
CUTTINGGRANTEWITH
RECEIVEDa \ p r ~ l27, 1935
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