MATERIALS 

 PROPERTIES OF INSULATING MATERIALS 



65 



Properties 



Power factor, at radio frequencies 



Dielectric constant, at radio fre- 

 quencies 



Dielectric strength (specimen l-s 

 in. thick. Step by step test at 

 25°C.) 



Tensile strength 



Water absorption, per cent in 24 hr. 



Specific gravity 



Coefficient of linear expansion, per 

 deg. C 



Effect of aging 



Effect of heat 



Effect of sunlight. 



Effect of ultraviolet light. 



Effect of moist air. 



Effect of steam. 



Solvents. 



Metallic inserts. 



Machining quahties . 



Hard rubber 



0.01-0.03 

 2.7-4.0 



500-1,000 volts per mil 



3,000-5,000 lb. per sq. in. 



0.02 



1.2-1.5 



60-80 X 10^6 

 Deteriorates slowly unless well 



vulcanized and protected from 



light 

 Softens at 50 to 65*C. Melts 



at 200°C. 



Discolors and disintegrates after 

 a few months. Sulphate films 

 formed on surface reduce sur- 

 face resistivity 



A few hours exposure is in its 

 effects equivalent to many 

 months exposure to sunlight 



No effect 



The only effect is that resulting 

 from^ the high temperature 



Affected by most organic solvents 

 and mineral oils; unaffected by 

 alkalies, weak acids, and certain 

 concentrated acids 



Hard rubber is rapidly deterio- 

 rated by contact with iron or 

 copper, the metals themselves 

 also corroding. Inserts should 

 be coated with tin, paper, unvul- 

 canized rubber, or other mutu- 

 ally protecting medium^ 



Admits of a high-polish but ma- 

 chines less accurately than would 

 be supposed, because of its great 

 resiliency. It has tendency to 

 warp, can be molded but not ac- 

 curately to size 



Vulcanized fiber 



0.05 

 5 



25-250 volts per mil 



9.000-16,000 lb. per sq. in. 



20-60 



1.2-1.4 



25 X 10-G 



Improves 



Will not melt; not readily inflam- 

 mable, but chars and becomes 

 brittle at high temperature. 

 Burns at about 340°C. 



No effect 



No data 



Absorbs water freely but without 

 permanent injury; while satu- 

 rated it becomes soft and flexible 

 and swells; warps and twists 

 upon drying 



Same as above, except absorptirfm 

 is more rapid 



Organic solvents have no perma- 

 nent effect; oils are sUghtly ab- 

 sorbed; affected by acids and 

 alkalies 



No effect 



Admits of a fine finish; may 

 be sawed, punched, drilled, 

 stamped, embossed, turned, 

 planed, bent, tapped 



Laminated phenolic 



0.03-0.07 

 4.5-6 



150-600 volts per mil 



6,000-20,000 lb. per sq. in. 



0.3-2.5 



1.3-1.4 



20-30 X 10- 



Improves 



Not readily inflammable. Tem- 

 peratures from BO-ISO^C. tend 

 to renew chemical reactions, 

 resulting in shrinkage and loss 

 in weight 



No visible effect 



Lowers surface resistivity 



Absorbs shght amount of water, 

 reducing dielectric properties 



Best grades not affected beyond 

 slight absorption of moisture ; 

 after a few days in steam the 

 cheaper grades will swell appre- 

 ciably and split ; superheated 

 steam tends to warp and blister 

 all grades 



Not affected by most organic 

 solvents, oils, or weak acids; at- 

 tacked by alkahes and strong 

 acids 



No effect 



Admits of a good pohsh; can be 

 sawed, punched, drilled, stamped, 

 turned, planed, knurled, em- 

 bossed, milled, tapped either 

 with or against the grain, though 

 not so easily as hard rubber and 

 vulcanized fiber 



