XI
XI
DuringJanuary, 1905, a comparative test of the working efficiency of four belt dressings and preservatives was made by T. Farmer, Jr., and the writer. The test was made on the regular belt-testing machine of Sibley College, Cornell University, a full description of which appeared on pages 705-707 of Vol. 12,Trans. A. S. M. E.This machine tests the belt under actual running conditions, though our belts were in somewhat better than average condition. The four belts were new 4-inch Alexander No. 1 oak-tanned single-ply, and were 30 feet long. Particular care was taken to keep them free from oil and dirt. The belts were first tested as received from the manufacturer, after which each belt was treated with one of the dressings and again tested.
[8]Contributed to Power by William Evans.
[8]Contributed to Power by William Evans.
The dressings were two semi-solids, designated No. 1 and No. 2; a bar, No. 3, and neatsfoot oil, No. 4. As the first three are proprietary articles, it was not thought best to give their names, though any one familiar with the actions of belt dressings will readily recognize No. 1 from its peculiar curve. In applyingthe dressings, we followed directions carefully, and in the case of Nos. 2 and 3 exceeded them. The belt was given a five-hour run, during which two or three applications of the dressing were given, and then it was set aside in a warm place to allow it to absorb the applied dressing. After thus "soaking" for at least forty-eight hours, the belt was again run, this time for three hours, with one more application of the dressing. As No. 3 was a bar of sticky dressing, it will readily be seen that this precaution was not really necessary. No. 4, the neatsfoot oil, was not applied during the last run, as we were afraid of getting too much oil in the belt. As this oil is so extensively used by engineers for dressing belts, special care was taken to get the best possible results with it.
Fig. 82.
Fig. 82.
In Fig. 82, the result of the test with the neatsfoot oil is shown graphically. This curve is platted to show the relation between initial tension per inch of width and horse-power per inch of width. One reason for the drop in horse-power in the treated belt is that the slipwas materially increased; in the lowest tension at which any power at all was transmitted, about 15 pounds per inch of width, the slip ran up as high as 25 per cent.
Fig. 83.
Fig. 83.
In Fig. 83, which shows the comparative value of the four dressings, the highest horse-power delivered to the belt was taken as the standard. The horse-power delivered by the belt was divided by this standard, and the result, expressed in percentage, was used as the percentage of available horse-power transmitted. This comparison shows the great superiority of dressing No. 1 at all times, and especially at low tensions. In looking at this chart, it is well to remember that No. 3 is a sticky dressing.
As the time of the test was so short, we were unable to determine the ultimate effect of the dressings on the leather of the belts. We could only approximate this by a chemical test and a close examination of the belts at the end of each test. The chemical analysis showedno ammonia or rosin in any of the dressings; No. 2 had a trace of mineral acid, and all had oleic acid as follows: No. 1, 0.27 per cent; No. 2, 29.85 per cent; No. 3, 3.5 per cent; No. 4, 0.7 per cent.
The practical test showed no ill effects except from No. 3, the sticky dressing, which ripped and tore the surface of the belt. The high initial tensions caused overheating of the journals, even though we kept them flooded with oil. On the low initial tensions there was no tendency to heat, even when the maximum horse-power was being transmitted by dressing No. 1. In the latter case we oiled the bearings once in every two or three runs (a "run" comprised all the readings for one initial tension), while in the former we oiled the bearings after each reading and sometimes between them; even then we were afraid that the babbitt would get hot enough to run. The readings for each run varied in number from two to a dozen, but only the one giving the maximum horse-power was used in drawing the curves. The belt speeds during the tests varied between 2000 and 2500 feet per minute, most of the tests being made at about 2200 feet per minute.