Description of how electrical porcelain is made at Thomas

[Trade Journal]

Publication: Chemical and Metallurgical Engineering

New York, NY, United States
vol. 26, no. 10, p. 438-442, col. 1-2

Electrical Porcelain Manufacture

Description of the Plant and Operations of R. Thomas & Sons at East Liverpool, Ohio — Production of Ware for High- and Low-Voltage Uses—Raw Glazes Employed-Body Similar to Chemical Stoneware-Ceramic Control



THE 12-kiln plant of the R. Thomas & Sons, manufacturers of electrical porcelains, is well located in East Liverpool, Ohio, for while the ultimate product and markets are different from tableware, the operations in the plant are essentially those belonging to the white ware pottery. The labor market is also best at this point. The plant produces a general line of insulators for low- and high-voltage electrical construction, while the 10-kiln plant at Lisbon, Ohio, is devoted to the manufacture of the patented Hewlett insulator. The Lisbon plant was originally built to manufacture tableware.

R. Thomas, together with his son, the late George W. Thomas, organized the present company in 1873, building the first plant in East Liverpool. - It was the first firm in the United States established for making high-voltage porcelains. Low-voltage porcelains are made by the dry process, where the dried cake from the filter press is ground to powder and compressed in heavy molding machines. High-voltage porcelains follow the method of molding the plastic clay employed in chinaware plants.


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The raw materials used are kaolin or English china clay, English ball clay, flint or ground silica, feldspar, barium carbonate, magnesium carbonate and calcium carbonate. Raw white glazes are made up of these materials, no frits being used. Colored glazes are made from Albany slip, feldspar and flint. The top of the raw storage piles and blunger house is on a level with the incoming railroad tracks. The materials are delivered from cars to storage by an endless belt and-tripper to four of the seven concrete bins and direct by shovel to the remaining three. Fig. 1 is a view in the aisle of the blunger house. On the left are the blungers with feed openings nearly on a level with the Fairbanks transfer table scales appearing in the center. This weighing outfit is so arranged that the scale car can be wheeled into each concrete raw material bin for loading. The doors of two of these bins are seen on the right. A blunger charge for the wet process slip weighs 5,400 lbs. and for the dry process 6,500 lb. There are four blungers, consisting of steel tanks lined with vitrified brick and equipped with double agitators. The line shaft driving the blungers through bevel gears is in turn driven by a 20-hp., 220-v., two phase motor.


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Three blungers operate on the wet-process slip, the remaining one on the dry-process. The charge is blunged 1 hour to give the necessary creamy slip. Three agitated storage cisterns below the floor receive the slip from the blungers. The three blungers deliver into two of these, while the third receives the dry process slip from one blunger.

Fig. 2 is a view on the delivery side of the blungers with the wet-process double-acting slip pump in the foreground. This pump delivers wet-process slip from the two cisterns to the lawn room in the main buildings located up hill from the railroad. A similar pump likewise handles the dry-process slip from the third cistern to a second lawn room. These pumps are also equipped with 20-hp. Westinghouse motors.




The saggers for holding insulators while burning in the kilns are made as usual in a separate department raw materials used for making these saggers are Kentucky ball clay, Pennsylvania sandy clay, wad clay and grog. The equipment here consists of a small dry pan, grinder, vertical pug mill, small wad mill and a 28-ton steam press having a pressure of 250 lb. per for forming the sagger. The wad mill is a small affair extruding a plastic clay string about a} in. diameter. This is used between the top edge and the lid of the complete sagger for sealing in the ware, thus preventing the entrance of kiln gases and resultant contamination of the ware.

The formed sagger from the steam press is dried thoroughly by placing over a gas flue. It is not necessary to burn the saggers in separate kilns, as often practiced. The “green” product from the drying flue may be filled and burned at the same time as the ware it contains.




The slip for dry body or low-voltage porcelain is delivered from the blunger house as mentioned above to a cistern in the low-voltage lawn room. Thence it is pumped onto a 120-mesh lawn shaker screen and returns to a second cistern, where it is agitated until delivered by a second pump at 80 lbs. pressure to the filter room.


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The larger or high-voltage lawn room is equipped with two units, each consisting of a cistern receiving slip from the blunger house, a 120-mesh shaker lawn, a second cistern and a pump delivering the finished slip to the filters. Fig. 3 shows one of the double-acting pumps in the high-voltage lawn room driven by two-phase electric motor, and Fig. 4 shows the switchboard, carrying oil switches, fuses and knife switches controlling the pump motor circuits and shaker lawn motor. The shaker lawn appears in Fig. 5.


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The glazes made from white ingredients or Albany slip without frits are ground in three 1,000-lb. pebble mills adjoining the high-voltage lawn room. Fig. 6 shows a portion of one of these arranged with belt drive.




Production of the plastic cake from the slips as they are pumped in from the lawn rooms is carried on in one location with a battery of seven 80-lb. leaf type, Patterson filter presses. One press is used on low-voltage and six on high-voltage body. For dry-process low-voltage porcelains, the cakes from the filter press are elevated to a drying room located over the kilns and after thorough drying are pulverized and tempered for pressing to shape.

For wet-process, high-voltage porcelain the plastic cakes are piled in a heap, beaten with mallets into a solid mass and permitted to age for a period varying from 1 to 3 days. During this time the moisture becomes evenly distributed throughout the mass. Just before it is sent on to the shaping department it passes a vertical type pug mill. This operation consolidates the clay, works out any air bubbles and forms it to suitable slabs for working.




The pug mill consists of a vertical hollow cylinder, in the middle of which revolves a shaft carrying projecting blades. The blades, being set at an angle, gradually force the clay downward, at the same time kneading and mixing it. At the bottom of the cylinder it is forced through an opening in the side, coming out as a continuous bar from 4 to 6 in. in diameter. From this bar slabs are cut of suitable length for subsequent processes. Pugging is an important operation in the manufacture of insulators, for upon it depends the freedom of an insulator from checks and air bubbles and the consequent ratio of dielectric strength.