Now two coal seams are mined at Sakito colliery, Nagasaki, upper one 2.18 m lower one 1.60 m thick, inserting middle shale of 0.36 m thick.
Since may 1932, the working method is radically organized using the retreating longwall system, whose working face is parallel to dip and 156 m long. Both seams are worked at the same time but the lower is always abvancing than the upper. As face machines we use pick hammer type and at faces we introduced shaking conveyors and at levels belt conveyors.
By the new method of working, the output of coal per head per day increased to 3.11 tons against 1.85 tons for the former working, notwithstanding the number of faces decreased from 40 to only 4. And total output of coal per day is recently 1, 761 tons.
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