Invented by Aucklander Bryan Bartley and Wellingtonian Jim Macdonald (hence the name Barmac), this rock crusher was revolutionary. It uses two simple concepts: the rocks crush themselves as they hit each other, and some rocks also form layers on the crusher’s metal surfaces, protecting these from wear and tear. A stream of broken rocks about 50 millimetres in diameter is fed into the top. Some rocks fall down the middle into a spinning drum which flings them out. Other rocks fall down each side of the drum and are smashed by rocks which are being flung out of the drum. Shattered rocks fall out as gravel and sand.
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Source: Metso Minerals