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The best fine grinding-machines that it was then possible to obtain were so inefficient as to involve a loss of 82 per cent. of the power applied. The thought of such an enormous loss was unbearable, and he did not rest until he had invented and put into use an entirely new grinding-machine, which was called the "three-high" rolls.
It was a most noteworthy invention, for it brought into the art not only a greater efficiency of grinding than had ever been dreamed of before, but also a tremendous economy by the saving of power; for whereas the previous efficiency had been 18 per cent. and the loss 82 per cent., Edison reversed these figures, and in his three-high rolls produced a working efficiency of 84 per cent., thus reducing the loss of power by friction to 16 per cent.
Not only did he develop thoroughly the refining of the crushed ore, so that after it had passed the four hundred and eighty magnets in the mill, the concentrates came out finally containing 91 to 93 per cent. of iron oxide, but he also devised collateral machinery, methods and processes all fundamental in their nature. Intermediate rolls. Three-high rolls. Vertical dryer. Belt conveyors.
Thus, he was obliged to begin again at the foundation, and he devised a crushing-machine which was subsequently named the "Three-High Rolls," and which practically reversed the above figures, as it developed 84 per cent. of work done with only 16 per cent. loss in friction. A brief description of this remarkable machine will probably interest the reader.
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