232 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



INCOMPATIBLE WITH ORGANIC PLASTICS 



Another useful property inherent in the fact that silicones are high- 

 polymer molecules is their incompatibility with other plastic materials. 

 A silicone fluid applied as a very dilute water emulsion spreads over the 

 metal surface of dies to form an extremely thin film to which hot 

 plastics and synthetic rubbers do not adhere. This property is of gieat 

 value in the manufacture of tires and other molded-rubber articles. 

 It is also useful in the molding of other plastic materials. 



In the silicone fluids, various combinations of properties often lead 

 to unexpected uses. For example, their incompatibility together with 

 their surface effects at the interfaces of oil-air systems has been utilized 

 to prevent the foaming of crankcase oils. Traces of silicone oil in 

 petroleum oil are sufficient to prevent foaming. 



Similarly, in aqueous systems foaming is often a serious and costly 

 problem. A new silicone compound has recently been developed to 

 prevent the foaming of aqueous systems or to kill foams once they have 

 been formed. This product is effective at very high dilutions, varying 

 from 1 to 100 parts per million. 



In England the natural compressibility of certain silicon fluids has 

 been utilized in a "liquid spring" hydraulic shock absorber that has 

 been developed for use in aircraft landing gear. As the compressibil- 

 ity of the silicone fluids is 15 to 25 percent greater than petroleum fluids, 

 the makers believe that the landing of heavier aircraft on present 

 fields may be possible without increasing the size or weight of the 

 landing gear. 



The flat viscosity-temperature slope of silicone fluids together with 

 their high flash point has led to an extensive study of their use as hy- 

 draulic fluids in aircraft by the Naval Research Laboratory, Wash- 

 ington, D. C. 



This same flat viscosity-temperature slope of silicone fluids together 

 with their shear resistance has led to the development of a torsional 

 vibration damper for automotive crankshafts. In this device a free- 

 wheeling flywheel floats in a film of silicone oil which damj)s any 

 torsional vibration in the crankshaft. 



In these applications some well-known engineering principles have 

 been made practical for the first time. Correct in theory, these prin- 

 ciples were not practicable until silicones were developed and proved 

 to have the properties necessary to reduce theory to practice. 



ECONOMY 



There are very few established uses for silicone products which do 

 not result in a considerable saving of time and money. An example 

 is the speeding up of production and the reduction of rejects through 

 the use of a silicone mold release in rubber molding. Silicone resins 



