CSR of coke , called coke strength after reaction is determined as below In the test a 200g sample of –21mm +19mm square hole coke (usually prepared by crushing 10kg of +25mm coke) is heated at 1100 C under 1atm pressure of carbon dioxide for 2 hours. The coke is cooled under nitrogen .The reacted coke is placed in an I drum (no lifters) and subjected to 600 revolutions. The percent of material removed from the drum that is +10mm square hole (sieve) is known as the coke strength after reaction (CSR). the minimum value of CSR is 62% Micum index M 40 indicates the strength of coke against both impact The micum drum is made of mild steel and is 1m in internal diameter. 50kg sample of coke above 63mm size is rotated for 4 minutes at the rate of 25 revolutions/min. After rotation, the coke is taken out and screened through standard round holes. The percentage coke retained on 40mm ais designated as M40 inde. the min value is 80%. so the CSR takes a reaction into account , and then determines the strength of coke , a case that is likely to occur in the process of blast furnace hot metal making ,but M 40 index accounts for the strength of the coke that can support the charge(feed like iron ore ,flux etc) put into the blast furnace.