Modern Machine-Shop Practice, Volumes I and II - Joshua Rose

The coefficients given in [Table III.] are remarkably high, and show a great superiority for the rawhide over tanned leather in point of adhesion. The belt in question was very soft and pliable, but a little twisted from use on a cone pulley where it had rubbed against one side. It is not desirable, on account of its soft and adhesive nature, to use this kind of belt where frequent shifting is required, and when used on cone pulleys it is liable to climb and stretch against the side of the cone; but for a plain straight connection, there seems to be little room for improvement. [Table IV.] contains the results of similar experiments upon an oak-tanned leather belt made by Chas. A. Shieren & Co. Here the coefficients are much smaller than those given in [Table III.], and there is quite a marked difference between the coefficients for 10 in. and 20 in. pulleys.

As before noticed, the outside temperature has its effect, and it is probable that much lower results would have been obtained had the experiments been made in the heat of midsummer. The high coefficients obtained, together with the rapid increase of tension, show that the pulling power of a long horizontal belt must, in many cases, be limited by its strength rather than by its adhesion.

[Table V.] gives the results of experiments upon a light planer belt at very slow and very high speeds. As would naturally be expected, much higher coefficients were found at the high speed on account of the greater velocity of sliding.

TABLE V.

OAK-TANNED LEATHER BELT 2′′ WIDE BY ³⁄₁₆′′ THICK AND 30′ 4′′ LONG, WEIGHING 4 LBS., ON 20′′ CAST-IRON PULLEYS. DRY AND SMOOTH, TAKEN FROM SERVICE ON PLANER.

No. of Exper- i’nt.	Sum of Tensions T + t			T - t Work- ing.	T		t		T ⁄ t		Per- cent- age of Slip.		Velocity of Slip in ft. per min.		Arc of con- tact.		Coef- ficient of Friction.	Dura- tion of run at time of experi- ment.	Remarks.
No. of Exper- i’nt.	Initial.	Work- ing.	Final.	T - t Work- ing.	T		t		T ⁄ t		Per- cent- age of Slip.		Velocity of Slip in ft. per min.		Arc of con- tact.		Coef- ficient of Friction.	Dura- tion of run at time of experi- ment.	Remarks.
429	100	110		40	75		35		2	.14	1	.2		.54	179	°	.243		18 r.p.m.
430		115		60	87	.5	27	.5	3	.18	6	.1	2	.75	178		.372
431		118		70	94		24		3	.92	16	.5	7	.42	178		.440
432		105		20	62	.5	42	.5	1	.47		.3		.14	179		.123
433		112		50	81		31		2	.61	3	.5	1	.57	178		.309
435	200	204		40	132		82		1	.61		.2		.09	180		.152
436		206		60	133		73		1	.82		.7		.32	180		.191
437		208		80	144		64		2	.25	1	.8		.81	179		.260
438		210		100	155		55		2	.82	3	.7	1	.66	179		.332
439		212		120	166		40		3	.61	7	.7	3	.47	179		.411
440		215		140	177	.5	37	.5	4	.73	18	.4	8	.28	179		.497
442	100	110		60	85		25		3	.40		.3	7	.12	178		.394		950 r.p.m.
443		120		80	100		20		5			.7	16	.62	178		.518
445		125		90	107	.5	17	.5	6	.14		3	71	.25	177		.587	Start.
446		125		90	107	.5	17	.5	6	.14		25	593	.7	177		.587	min.
448	200	200		80	140		60		2	.33		.4	9	.5	179		.271
449		200		100	150		50		3			.5	11	.87	179		.352
450		195	175	120	157	.5	37	.5	4	.20		.8	19		179		.459
451	150	175		120	147	.5	27	.5	5	.36		.9	21	.38	178		.540
452	135	160		120	140		20		7			20	475		178		.626

It may here be mentioned that the sum of the tensions was the horizontal pressure of the belt against the pulleys, and that no allowance was necessary for the effect of the centrifugal force. At the speed here used, the tension indicated in the belt at rest was about 50 lbs. greater than when in motion.

TABLE VI.

SHOWING THE AVERAGE COEFFICIENT OF FRICTION AND VELOCITY OF SLIP FOR A NUMBER OF EXPERIMENTS IN WHICH THE SLIP APPROXIMATED 2 PER CENT.

No. ex- per’ts in av’ge.	Per- cent age of Slip.		Veloc. of Sl. in ft. per m.		Coeffi- cient of Fric- tion.		Belt.			Pulleys.	Remarks.
3	1	.4	5	.6		.661	5¹⁄₂′′ old belt.	Table	[I]	20′′ diam. pap. cov’d	Belt in	nor. w’k’g	con.
2	1	.7	6	.8		.44	5¹⁄₂′′ old belt.	„	[I]	20′′ di. cast-iron sur.	„	„	„
2	1	.55	6	.2		.575	5¹⁄₂′′ old belt.	„	[I]	20′′ di. cast-iron sur.	Belt dressed with “Beltiline.”
5	1	.7	6	.8		.452	2¹⁄₄′′ dbl. belt.	„	[II]	20′′ di. cast-iron sur.	B’t dry as us. on plan’r.
2	1	.5	6			.818	2¹⁄₄′′ dbl. belt.	„	[II]	20′′ di. cast-iron sur.	Belt dressed with “Sankey’s Life of Leather.”
2	1	.7	6	.8	1	.38	4′′ r’hide b.	„	[III]	20′′ di. cast-iron sur.	Belt in	nor. w’k’g	con.
11	1	.8	3	.6		.861	4′′ r’hide b.	„	[III]	10′′ diameter.	„	„	„
1	2			.45		.432	4′′ r’hide b.	„	[III]	10′′ diameter.	„	„	„
1	1	.9		.86		.691	4′′ r’hide b.	„	[III]	20′′ diameter.	„	„	„
7	1	.94	3	.88		.617	4′′ o.tan’d b.	„	[IV]	10′′ diameter.	„	„	„
4	1	.85	7	.40		.906	4′′ o.tan’d b.	„	[IV]	20′′ diameter.	„	„	„
2	1	.5		.67		.251	2′′ o.tan’d b.	„	[V]	20′′ diameter.	B’t dry	as us. on	plan’r.
2		.8	38			.529	2′′ o.tan’d b.	„	[V]	20′′ diameter.	„	„	„

TABLE V.

OAK-TANNED LEATHER BELT 2′′ WIDE BY 3⁄16′′ THICK AND 30′ 4′′ LONG, WEIGHING 4 LBS., ON 20′′ CAST-IRON PULLEYS. DRY AND SMOOTH, TAKEN FROM SERVICE ON PLANER.

TABLE VI.

SHOWING THE AVERAGE COEFFICIENT OF FRICTION AND VELOCITY OF SLIP FOR A NUMBER OF EXPERIMENTS IN WHICH THE SLIP APPROXIMATED 2 PER CENT.

OAK-TANNED LEATHER BELT 2′′ WIDE BY ³⁄₁₆′′ THICK AND 30′ 4′′ LONG, WEIGHING 4 LBS., ON 20′′ CAST-IRON PULLEYS. DRY AND SMOOTH, TAKEN FROM SERVICE ON PLANER.