Method of making British porcelain insulators at Taylor, Tunnicliff & Co.

The Insulator in the Making.

A description is given here of the factory of Taylor, Tunnicliff & Company, Hanley, England, where, in addition to many other kinds of pottery, insulators for electrical purposes are manufactured. As compared with ordinary pottery, the business of insulator making is highly technical, necessitating the use of specially prepared clay, special machinery and most accurate workmanship. In fact, a large staff of skilled mechanics is constantly employed in constructing and renewing machinery. The raw material is first calcined and given a preliminary crushing. It is then water-ground in large circular pans, lined with chert pavers, over which heavy stones or runners are driven. The material is thus reduced to the consistency of cream, and is fine enough to pass through silk lawns of ninety to 120 strands to the inch, through which it is forced by special machinery. It is then passed to large store arks, from which it is drawn for mixing with the various components that go to make up the “body” or clay. From these arks the material is pumped through conduits to the mixing room, where the proper blending takes place. This is an important part of the manufacture. Much depends upon the skill of the mixer to produce the proper blending of the necessary components. In some cases six or seven different materials are added together for this purpose. After the mixing, the components are again passed through silk lawns. The old process next took this material and evaporated it to the proper consistency: today the process consists of pumping the fluid clay through a filter press, which separates the clay from the water, leaving material of the proper consistency for forming the insulators. The first stage in the forming is to take a lump of clay which has been weighed out so as to be of the proper size place it on the wheel, and give it by hand the proper shape. From here the soft form is taken to a drying room, where it is left until sufficiently dry to be turned up in a lathe. Here it is given its final shape and proper size, each part being complete, with the exception of the glaze.

The insulators are then placed in saggars (coarse clay boxes) and stacked up in the kiln, which is gradually brought up to the proper temperature. The firing process requires about one week. Only those insulators which have dried properly without cracking are fired, and after firing they are again examined for faults and tested. After the test they are dipped in the glazing liquid, which usually contains lead, as this seems to unite the glaze more firmly with the clay and not simply give a coating of glaze over the surface of the clay. As there is some danger of lead poisoning, due to this kind of glaze, and particularly to those operators who wipe off the excess of glaze and put the insulator into final shape for the last firing, every precaution is taken at this stage to prevent this trouble. The operators are all required to wear long aprons, completely covering the clothes, and a covering over the head, and in front of each is a ventilating duct through which air is drawn constantly. The excess of glaze, as it is cut off, falls into a porcelain pan containing water. These precautions seem to be ample, as there has not been a single serious case of lead poisoning during the last five years.—Abstracted from the Electrical Review (London), March 6.