j ALABAMA MICA DEPOSITS 33 



boiler coverings and fire-proof paints, has recently devel- 

 oped increasingly a new application to the rubber-tire 

 industry, as a tire ingredient, and as a powder for inner 

 tubes. It has long been utilized as a powder to prevent 

 adhesion in rolls of rubber belting, rubber or rubberoid 

 roofing and similar materials. For use in the rubber- 

 tire industry, new methods of grinding and of prepara- 

 tion were requisite in order to obtain the necessary fine- 

 ness and freedom from any deleterious admixture. I 



Limited information only is available as to the methods 

 little patented and largely kept secret, which have been 

 so far most successful in producing the required rubber 

 product. They mainly classify as first, disintegration by 

 heating ; second, abrasion with mill-stones or burrs ; and 

 third, by baking at intense heat followed by pulveriza- 

 tion under a steam or air blast. Products ranging from 

 8 to 200 mesh are subsequently made after grinding, on 

 vibrating screens. Ground mica so prepared, has been 

 marketed at prices which have been found very satisfac- 

 tory and profitable. 



Should ground mica so prepared become a fairly uni- 

 versally used material as a filler in the rubber tire pro- 

 duction of the United States, already estimated to have 

 reached a figure in excess of 50 million tires per year, a 

 very substantial increment in the value and use of what 

 is now largely as scrap, a low priced or altogether waste 

 product in mica production, is substantially indicated. 

 While for this purpose it has been found superior to 

 the filler hitherto in use, to which it has proved to be of 

 more value and utility by reason of its special qualities, 

 ground mica, for other and its ordinary uses, is the only 

 form of mica for which a satisfactory substitute has been 

 successfully found and commercially used. For electrical 

 mica in its special forms there is no known substitute. 



From its physical characteristics, the grinding of scrap 

 mica or its first preliminary disintegration, is a difficult 

 operation for reasons which are self-evident. Number- 

 less methods have been tried, and where successful, have 

 been as far as possible kept secret. The most satisfac- 

 tory results have apparently been obtained by the use 

 of various special forms of conical wooden rollers. The 



2 MB 



