SOME CERAMIC MANUFACTURING DEVELOPMENTS 277 



fired parts to the desired thickness of 0.030 inch. This operation was 

 costly and losses from breakage were high. The narrow dimensional 

 limits of ±.002 inch on thickness were also hard to maintain because 

 of the difficulty of keeping the lapping surfaces parallel. In view of 

 this, it was decided to machine the parts from natural talc rod or lava. 



The mineral talc or lava, being soft, was easy to machine and the 

 firing shrinkage was only one per cent as compared to about ten per 

 cent with dry pressed porcelain. While less difficulty with warpage 

 and dimensional variations was experienced, the machined surfaces, 

 while reasonably smooth and accurate, were not equal in quality to 

 surfaces obtainable with molded parts. The chief difficulty with the 

 process was in obtaining a satisfactory raw material free from flaws 

 and fissures. The first work was done with domestic lava which was 

 somewhat granular in structure but large rejections resulted from pitted 

 surfaces and chipped edges. A survey of domestic lavas showed that 

 only a small percentage was sufficiently dense. Chinese white lava 

 was found to be homogeneous and fine grained but of uneven shrinkage. 

 Best results were obtained with Italian green lava and this material 

 was used in commercial production. Due to breakage because of 

 fissures, the number of good insulators per foot of rod was very low and 

 the manufacturing cost was therefore excessive. 



In view of this, various domestic manufacturers of glass, porcelain, 

 lava and other types of ceramic parts were canvassed but no source 

 of supply that could meet the required quality limits could be located. 

 It was therefore decided to make a thorough investigation of new 

 molding compositions for the job. As a first step in this study, it 

 was necessary to do away with drying shrinkage which required 

 a binder which would give sufficient strength in the raw state to 

 withstand the various finning and handling operations prior to firing. 

 It was also desirable that such a binder should not affect the fired 

 structure of the parts. "V^arious organic substances such as pitches, 

 phenolic resins, asphalts, paraffins, and waxes were tried in both 

 hot and cold molded bodies. It was found that a large percentage 

 of these binders could be incorporated into a body without defor- 

 mation during firing.^ As a mixture of paraffin and carnauba wax 

 was found satisfactory for cold molding and in addition possessed 

 sufficient hardness to furnish the necessary molded strength, this 

 combination of materials was chosen for the binder.^" 



8 W. J. Scott Patent 1,847,102, "Ceramic Material," March 1, 1932. W. J. Scott 

 Patent 1,977,698, "Ceramic Material and Method of Making the Same," October 23, 

 1934. 



1" L. I. Shaw and W. J. Scott Patent 1,847,197, "Ceramic Material and Method of 

 Making the Same," March 1, 1932. 



