266 BELL SYSTEM TECHNICAL JOURNAL 



factory results could be obtained with 10-24-mesh material and a 

 12.75 per cent ± .75 per cent moisture content. This moisture content 

 was sufficient to give a compact part and body mix still could be fed 

 satisfactorily to the dies. Methods ofjprocessing the body mix were 

 then worked out to hold it within these limits. 



The use of material within these close size limitations involved 

 considerable effort to establish economical methods of production. 

 Common practice consisted of slaking the clay in water, adding the 

 other body ingredients, mixing thoroughly with water, filter pressing, 

 complete drying, addition of water to obtain the desired moisture 

 content, aging and screening. The effect of aging was investigated 

 and found negligible with the moisture content to be used and it was 

 therefore decided to dry the material after filter pressing to the 

 required approximate twelve per cent moisture content before the 

 disintegrating and sizing operations. Methods of handling were 

 evolved to obtain a maximum percentage of material between 10 and 

 24-mesh and to regranulate the fines without again mixing them with 

 excess water. 



Various methods of economically removing fins after forming were 

 investigated and initially the fired parts were tumbled with small 

 porcelain balls. This method removed fins and produced smooth 

 surfaces. Another advantage of the method was the automatic 

 elimination of any weak or flawed parts by breakage during the 

 tumbling. Later, further developments in methods of firing described 

 hereafter made it more economical to remove the fins in the raw state 

 by vacuum brushing the parts in multiple after they were arranged on 

 trays at the pressing machines. 



Initially the parts were fired using the practice then commonly 

 followed in the industry. With this method, the parts were placed 

 in saggers and fired in an intermittent kiln. This method involved 

 costly handling, heat losses due to heating and cooling the furnace at 

 each firing, and considerable expense from sagger replacements. A 

 small continuous kiln was therefore installed in which the parts were 

 carried in layers on top of cars through successive preheating, firing, 

 and cooling zones which were continuously maintained at definite 

 temperatures, the heat from the cooling fired ware being used to heat 

 the incoming ware. 



Summarizing, the method of manufacture finally developed for 

 porcelain blocks consisted in mixing feldspar, clay and flint with water 

 to get an intimate mixture, filter pressing, drying to proper moisture 

 content, sizing, automatically molding the parts, removing fins in 

 multiple, and firing in a continuous kiln. This method resulted in a 



