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In my report, rendered 1870, for the year 1869, will be found (pages 579 to 581) some remarks on wire ropes, to which I take pleasure in adding the following notes upon steel cables, kindly furnished me by Mr. A. S. Hallidie, of San Francisco.
Steel-wire flat ropes are in general use throughout California and Nevada, more particularly at Gold Hill and Virginia City. The durability of steel rope, as compared to iron ropes, is as 6 to 5. The weight (for equal strength) of steel rope, as compared with iron rope, is as 6 to 10. The life of a steel rope working in the Virginia City mines, hoist ing at the rate of 1,000 feet per minute, 6 to 8 hoists per hour, for a vertical height of 1,000 feet, is, on the average, about two years. The steel wire of which the rope is composed is especially manufactured for this purpose, ordinary steel wire being unsuitable. The best wire does not become brittle after two years' wear, but possesses still the admirable quality of being tough as lead and hard as steel.
The great tensile strength of steel wire recommends it strongly for the purpose of hoisting from great depths. A 13-gauge steel wire sustains a breaking-strain of 1,400 pounds; whereas the same size best charcoal bright wire sustains a breaking-strain of but 770 pounds; and the steel wire will bear, without breaking, two turns over its own part.
The importance of using ropes of high tensile strength, such as steel alone affords, may be illustrated by the case of a rope manufactured by Mr. Hallidie about the first of January. This rope was 2,000 feet long, 5 inches wide, inch thick, 9,360 pounds in weight, and made of iron wire. The breaking-strain of this rope was estimated at 72,000 pounds, and the working load should be one-sixth of this, or 12,000 pounds. Subtracting from the latter amount the weight of the rope itself, we have 2,840 pounds as the weight of cage and ore that could be safely hoisted; that is, 22 per cent. of working load.
Now, a steel rope of the same capacity would weigh only 4,800 pounds, and the weight of cage and ore that could be safely hoisted would be 7,200 pounds, or 60 per cent. of the working load; and there would be a saving in dead work equal to the difference in weight of the ropes, or 4,560,000 foot-pounds at each hoist. For rough work, moreover, the steel rope has an advantage, inasmuch as it stands abrasion much better than iron.
In round wire ropes steel again shows its superiority over iron, both in its life and useful effects. The life of a round steel wire rope varies according to the character of the hoisting-machinery. In many cases such ropes have lasted three and four years. As a rule, the drum and pulleys should be 100 times the size of the rope.
Endless wire rope tramways.-The use of endless wire ropes for aboveground transportation, which was alluded to in my report of 1870, (page 568,) has been perfected on a somewhat different principle, already mentioned in Chapter I of this report, and now to be more fully described and illustrated.
In the rough mountainous portions of the gold and silver mining regions of the Pacific coast, there is an immense amount of ore which
would be of great value if it were not for the cost of hauling or transporting it to the mill or furnaces to be worked; in many cases this is done by packing on mules' backs, hauling by teams, or sliding down chutes, as the case, may require, and the cost is from 50 cents to $10 per ton per mile, according to circumstances.
During the winter months, when the snow falls to great depths in the Sierra Nevadas, it is not practicable to transport ores, except at intervals, on sleds, and consequently work has to be suspended.
The importance of a cheap and regular mode of transporting the ores from the mine to its reducing-works has called forth many ingenious arrangements by those interested in mining.
In Europe, where the Hodgson wire tramway is in use, which was
referred to in the chapter on Mining Appliances, report for 1870, some success seems to have attended these experiments. So far, the only patents
granted to American citizens in the United States have been issued to Mr. A. S. Hallidie, of San Francisco, California, for various improvements and inventions
in endless-rope ways
and difficult roads.
The grip-pulley has already been referred to in the last report, (page 564,) its office being to receive the rope in its groove, and by the pressure of the rope on the clips in the circumference of
the pulley, to grip the rope and prevent it from slipping in the groove of the pulley. By referring to Figs. 1 and 2, it will be seen how this is accomplished: h, rope; i i, clips working in recesses cast in the circumference of wheel 11, and on fulcrums XX. The part K is cast separately and bolted on to the wheel after the clips are fitted.
On the line of the route, at distances of about 250 feet, but regulated by the configuration of the country, are erected strong posts with horizontal,
cross-arms, sufficiently high above the ground to clear obstructions, &c. On each end of the horizontal arm is a bearing-pulley, the groove of which is semicircular, and of sufficient size to allow the rope to run in it, and covering half its circumference. Immediately over each of the bearingFig. 3.
pulleys is another pulley, smaller in diameter, the groove of which is a quarter circle, covering onefourth of the circumference of the rope. Fig. 3 shows the pulleys in position; a the upper pulley, b the lower pulley, h the
A steel-wire rope of three-fourths inch diameter is stretched along the route around the end or grippulleys, and in the grooves of the bearing-pulleys which are attached to the horizontal arms of the posts. The upper pulley, a, is placed over the bearing
pulley and rope, as shown in Fig. 3, the circumference of the two pulleys running in close contact, but having an open space sufficiently large to allow the carrier f to pass between the pulleys on their outer sides.
The ends of the steel-wire rope (made from spring-steel wire) are spliced together, forming an endless rope; and motion being imparted to it through the grip-pulley, it will travel in the direction actuated, supported at intervals by the bearing-pulleys, and retained in position between the pulleys on the horizontal arms of the posts, as shown in Fig. 3.
About 50 feet apart there are attached to the rope, by means of thin steel clasps, projecting arms also of steel, about four inches long, and of a form as shown in Fig. 4, the outer end of which is fitted with a journal and collars so as to take a suspension-bar, which hangs vertically and being at right angles to the arm, keeps it in horizontal position. c and f, Fig. 3, show this arrangement complete. It is designated as the "carrier."
For conveying an ore-sack or box holding about 150 pounds, one of these carriers is used, having a hook at the lower end of a curved suspension-rod; but when it is necessary to convey a car or self-dumping buckets, or a load greater than 200 pounds, the number of these carriers