2858 Chapter 23 



Table 23-9. — Classification of hardboard in the Commercial Standard for 

 Basic Hardboard — abbreviated^ (U.S. Department of Commerce 1973a) 



Class and surface Thickness 



Inches 



1. Tempered 



SIS Vi 



SIS and S2S 1/10 to 3/8 



2. Standard 



SIS and S2S 1/12 to Ys 



3. Service tempered 



SIS and S2S '/h to Ys ~ 



4. Service 



SIS and S2S '/s to V2 



S2S 78 to 1 '/« 



5. Industriaiite 



SIS and S2S Yh to Vi 



S2S Yh to 1 '/s 



'See table 23-10 for thickness, water resistance, and mechanical properties. 



LOW TEMP. 



MAX. STRENGTH 



TIME (HRS.) 

 HEAT TREATING OVEN 



^AX. BOND 

 QUALITY 



Figure 23-86. — Hypothetical development of board strength as affected by changing 

 bond strength and fiber strength during pressing and heat treating. (Drawing from 

 Suchsland and Woodson 1985.) 



