Electric porcelains

The slime, consisting of kaolin, fine quart2, and feldspar, is sometimes used as is after being dewatered. This material may be used in the manufacture of light-colored brick or may be further processed to produce a high grade ceramic kaolin used in the manufacture of dinnerware, electrical porcelain, or sanitary-ware (see Ceramics). Floes of kaolin may be sold in bulk from the drier or pulveri2ed and sold in a powdered form. 

Ceramics. In ceramics, talc is widely used in wall tile and hobbyware bodies, in electrical porcelains, and in cordierite formulations. Wall tile and hobbyware ate talc—clay bodies that ate pressed and fast-fired to a high porosity (bisque) and then glazed and tefired to produce the final product. Talc containing tremolite and carbonate is preferred to ensure good porosity. 

In electrical porcelains (often called steatite bodies), high purity talc products with low levels of alkali metals ate preferred. A typical steatite is made from 85% talc, 10% plastic kaolin, and 5% BaCO. Steatites ate used as insulators on high voltage equipment such as automotive starters, microwave oven generators, and laser generators. 

The last brown pigment to be considered is the Hon manganese brown. This is the deep brown associated with electrical porcelain insulators and with artware and bean pots. In many gla2es the presence of manganese wiH cause poor surface and unstable color. Hence, the use of this pigment is limited to dark colors on products where gla2e surface quaHty requHements are modest. 

China clay or kmlin, which is predominantly kaolinite, is particularly valuable because it is essentially free from iron impurities (and therefore colourless). World production in 1991 was 24.7M1 (USA 39%, UK 13%, Colombia, Korea and USSR 7% each). In the USA over half of this vast tonnage is used for paper filling or paper coating and only 130000 tonnes was used for china, crockery, and earthenware, which is now usually made from ball clay, a particularly fine-grained, highly plastic material which is predominantly kaolinite together with clay-mica and quartz. Some 800000 tonnes of ball clay is used annually in the USA for white ware, table ware, wall and floor tiles, sanitary ware, and electrical porcelain. 

A borosilicate glass for sealing to alloys of the Kovar type (p. Ill) l Clso seals to some electrical porcelains. It is made by the British phomson Houston Co., and is often referred to as BTH C,40 or as The linear expansion coefficient is 4-85 x 10 from 50 to... 

With the possible exception of common line insulators, electrical porcelain is especially formulated and may contain varying percentages of zirconia and beryllia. These ingredients increase both strength (mechanical) and resistance to high temperatures. Hard porcelains are especially formulated to resist thermal shock as well. 

As part of the characterization of an electrical porcelain the following weighings were made at 25 °C using a balance which was accurate to the third decimal place ... 

The electrical porcelain used for such insulators is chosen because of its excellent durability in outdoor conditions, its low cost, its adequate mechanical strength (insulators rated to safely withstand tensile loading up to 90 tonnes are produced) and the ability to produce large monolithic units (the largest produced to date is 12 m long and nearly 2 m in diameter). The dielectric strength (see Section 5.2) is less critical, since the insulators are normally used in air, which limits the electrical stress which can be applied. 

Typical physical properties of the two main types of high voltage electrical porcelain are listed in Table 5.2. 

Fig. 5.20 Microstructures of (a) 99.9% A1203 (Courtesy of E.W. Roberts), (b) 95% A1203 (Courtesy of R. Morrell), (c) chemically etched electrical porcelain note the partially dissolved quartz grains and mullite precipitates (Courtesy of S.T. Lundin).

Low-permittivity ceramics are widely used for their insulative properties. The major requirements are good mechanical, thermal, and chemical stability good thermal shock resistance low-cost raw materials and low fabrication costs. These include the clay- and talc-based ceramics also known as electrical porcelains. A large-volume use of these materials is as insulators to support high tension cables that distribute electric power. Other applications include lead-feedthroughs and substrates for some types of circuits, terminal connecting blocks, supports for high-power fuse holders, and wire-wound resistors. 

A gigantic combined de-airing extmsion machine with a barrel diameter as wide as 850 mm and the capacity for putting out 12 columns of brick at once has little in common with a tiny, 20 mm-diameter micro-extmder. Or, compare a vertical extmder for clay pipes with diameters up to 1.50 m with an intermittent-action piston extmder that can work vertically as well as horizontally. Or how about a twin-screw extruder or piston extmder sporting extmsion pressures up to 400 bar in contrast with a huge vacuum extmder for forming electrical porcelain slugs at relatively low pressure ... 

In 1840 the first electric porcelain insulator was produced at KPM in Berlin... 

Price DB, Reed JS (1983) Boundary conditions in electrical porcelain extrusion. J Ceramic Bulletin vol 62 No 12 pp 1348-1350... 

Refractory alumina High alumina Electrical porcelain ... 

Engineering structural ceramics (32%) Electrical and electronic ceramics (21%) Capacitors, substrates, and packages (20%) Electrical porcelain (5%)... 

Technical Ceramics Electrical porcelains Low-frequency insulators... 

Industrial applications. Filler for paper and board, coating clays, ceramics, bone china, hard porcelain, fine earthenware, porous wall tiles, electrical porcelain, semivitreous china, glazes, porcelain, enamels, filler for plastics, rubbers and paints, cosmetics, insecticides, dusting and medicine, textiles, and white cement. 

The fin of excess body formed during the plastic-pressing of ceramic ware, e.g. electrical porcelain it is removed by an auxiliary process. 

Sand-gritting. The process of roughening those parts of the glaze of an electrical porcelain insulator where cement will be applied in the final assembly. The sand (a specially-prepared mixture of coarse-graded porcelain together with powdered glaze) is applied to areas of the glazed insulator before it is fired. 

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