94 



Table 70. 



MECHANICAL PROPERTIES. 

 TABLE 70. — Rubber and Leather. 



(a) Rubber, — Sheet.* 



The specific gravity of rubber averages from 0.95 to 1.25, corresponding to an average weight 

 of 60 to 80 Ib/ft^. 



Four-ply rubber belts show an average ultimate tensile strength of 0.63 to 0.65 kg/mm^ or 

 890 to 930 Ib./in^ (Benjamin), and a working tensile stress of 0.07 to o.ii kg/raxo? or 100 to 150 

 Ib./in^ is recommended (Bach). 



(b) Leather, — Belting. 

 Oak tanned leather from the center or back of the hide: 



Minimimi tensile strengths of belts f single 2.8 kg/mm^ or 4000 Ib./in' 

 (Marks, p. 622) \ double 2.5 kg/mm^ or 3600 Ib./in^ 



Maximum elongation for one hour application of f single 13.5 per cent 

 1.6 kg/mm^ or 2250 Ib./in^ stress \ double 12.5 percent. 



Modulus of elasticity of leather varies from an average value of 12.5 kg/mm^ or 17,800 Ib/in^ 

 (new) to 22.5 kg/mm^ or 32,000 Ib./in^ (old). 



Chrome leather has a tensile strength of 6.0 to 9.1 kg/mm^ or 8500 to 12,900 Ib/in^. 



The specific gravity of leather varies from 0.86 to 1.02, corresponding to a weight of 53.6 

 to 63.6 Ib./ft^. 



Smithsonian Tables. , 



