Magnetic Ore Milling Work - 4

Magnetic Ore Milling Work - 4

 No such departure was as radical as that of the method of crushing the ore. Existing

machinery for this purpose had been designed on the basis of mining methods then in

vogue, by which the rock was thoroughly shattered by means of high explosives and

reduced to pieces of one hundred pounds or less. These pieces were then crushed by

power directly applied. If a concentrating mill, planned to treat five or six thousand tons

per day, were to be operated on this basis the investment in crushers and the supply of

power would be enormous, to say nothing of the risk of frequent breakdowns by reason

of multiplicity of machinery and parts. From a consideration of these facts, and with his

usual tendency to upset traditional observances, Edison conceived the bold idea of

constructing gigantic rolls which, by the force of momentum, would be capable of

crushing individual rocks of vastly greater size than ever before attempted. He reasoned

that the advantages thus obtained would be fourfold: a minimum of machinery and parts;

greater compactness; a saving of power; and greater economy in mining. As this lastnamed

operation precedes the crushing, let us first consider it as it was projected and

carried on by him.

Perhaps quarrying would be a better term than mining in this case, as Edison's plan was

to approach the rock and tear it down bodily. The faith that "moves mountains" had a

new opportunity. In work of this nature it had been customary, as above stated, to depend

upon a high explosive, such as dynamite, to shatter and break the ore to lumps of one

hundred pounds or less. This, however, he deemed to be a most uneconomical process,

for energy stored as heat units in dynamite at $260 per ton was much more expensive

than that of calories in a ton of coal at $3 per ton. Hence, he believed that only the

minimum of work should be done with the costly explosive; and, therefore, planned to

use dynamite merely to dislodge great masses of rock, and depended upon the steamshovel,

operated by coal under the boiler, to displace, handle, and remove the rock in

detail. This was the plan that was subsequently put into practice in the great works at

Edison, New Jersey. A series of three-inch holes twenty feet deep were drilled eight feet

apart, about twelve feet back of the ore-bank, and into these were inserted dynamite

cartridges. The blast would dislodge thirty to thirty- five thousand tons of rock, which

was scooped up by great steam-shovels and loaded on to skips carried by a line of cars on

a narrow-gauge railroad running to and from the crushing mill. Here the material was

automatically delivered to the giant rolls. The problem included handling and crushing

the "run of the mine," without selection. The steam-shovel did not discriminate, but

picked up handily single pieces weighing five or six tons and loaded them on the skips

with quantities of smaller lumps. When the skips arrived at the giant rolls, their contents

were dumped automatically into a superimposed hopper. The rolls were well named, for

with ear- splitting noise they broke up in a few seconds the great pieces of rock tossed in

from the skips.

It is not easy to appreciate to the full the daring exemplified in these great crushing rolls,

or rather "rock-crackers," without having watched them in operation delivering their

"solar-plexus" blows. It was only as one might stand in their vicinity and hear the

thunderous roar accompanying the smashing and rending of the massive rocks as they

disappeared from view that the mind was overwhelmed with a sense of the magnificent

proportions of this operation. The enormous force exerted during this process may be

illustrated from the fact that during its development, in running one of the early forms of

rolls, pieces of rock weighing more than half a ton would be shot up in the air to a height

of twenty or twenty- five feet.