Painting on previous pages from Frauenthal Keramik, Austria. These images from Norsk Teknsik Porselen in Norway( top) and Ifö Ceramics in Sweden.
Electrical porcelain has a rich history going back over a century and a half to the time when small-scale pottery firms first began making telegraph insulators. These were crude, threadless pieces – produced in much smaller volumes than alternatives made from glass, which were cheaper and also typically regarded as better.
As electrical distribution began to develop in the 1880s, larger and better quality insulators were needed to carry the voltages of overhead power lines. Industry pioneers all over the globe soon began to experiment with various mixtures of clay that would yield insulators with better electrical and mechanical characteristics. Soon, porcelain began to replace glass for most electrical distribution, even at low voltages, due to perceived superior insulation quality and strength.
As voltages continued to increase and insulators of ever-larger dimensions became necessary, the attributes required of clays became even more demanding. Increasingly,
focus was placed on strength as well as on high plasticity and good drying behavior, with minimal presence of organic matter. Other key parameters included fine grain size and low residue content, together allowing the porcelain not only to be shaped into huge pieces without deformation but also to be fired with no release of gases that might result in porosity in the body.
Today, the ceramic bodies of porcelain insulators are prepared according to strictly followed recipes which involve a compromise in the relative amounts of different ingredients to meet goals of long service life, ease of production or some optimal combination of low cost with sufficient required performance.
For example, a typical formulation for the porcelain mass will contain varying proportions of ball clay, kaolin( for strength and plasticity), feldspar( a flux that helps sintering in the kiln), and fillers such as quartz, alumina or calcined bauxite( intended to impart additional mechanical strength). A variety of secondary materials are also used to facilitate processing including water and additives such as binders – all of which are burned off in the kiln during firing at temperatures of from 1200 to 1300 ° C.
At the same time, growing attention has been placed over the years on‘ micro-structure’ of raw materials in order to avoid development of unwanted microscopic interfaces. In particular, experts believe that quartz crystallites found in some ceramic aggregates may feature critically
Improved body compositions allow even very large pieces to be shaped with no deformation.
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Photos: INMR ©