Double roll crushers (DRC) have the highest throughputs among primary crushers. In the oil sands, the hourly capacity may exceed 14,000 tih. They are preferably used. to comminute medium-hard rock or sticky materials. An unusual tough particle or unbreakable object may effect substantial dynamic forces in a DRC. Considering the large amount of energy stored in the flywheels and the fact that the mass of the floating rolls of the largest machines exceeds 60 t, any unexpected dynamic behavior can be an issue for a safe and reliable operation. Research is conducted on a small industrial scale smooth DRC at the Institute of Mineral Processing Machines. Results of the crushing force dynamics under extreme conditions, as well as the related product particle size distribution and the influence of the mineral structure of a variety of rocks on the nipping behavior are presented. (C) 2016 Elsevier Ltd. All rights reserved.