750

THE COLLIERY GUARDIAN.

April 20, 1916.

Conveyor Belts.—Capacities of Various Widths of Conveyors operating at 100 ft. per minute and handling
material of various weights.

'Table I.—Flat Conveyor Belts. (Jeffrey Conveyor Co.). (See fig. No. 2).

Formulae : Cubic feet per hour at 100 ft. per m nute — 1'5 w2, where w — width of belt in inches.

Regarding the tensile strength of rubber conveyor
belts, when you have obtained the actual horse-power
required for driving the belt, it is easy to find the actual
working tension the belt has to stand. To obtain the

Width of belt in inches.	Cross section of load in sq_. feet.	Cubic feet per hour at 100 ft. per min.	Cubic yards per hour at 100 ft. per min.	Bushels per hour at 100 ft. per min.	Tons per hour at 100 ft. per minute.				
					Weight of material in lb. per cubic foot.				
					2.5	50	75	100	125
10	0’025	150	5'5	121	1'9	3'8	5'7	7'6	9'5
12	0'036	216	8'0	174	2 7	5'4	8'1	10'8	13'5
14	0'049	294	10 9	236	3'7	7'4	11'1	14'8	18’5
16	0'064	384	14'2	309	4'8	9'6	14'4	19'2	24'0
18	0'081	486	18'0	391	6T	12'2	18'3	24'4	30'5
20	0'100	600	22 2	482	7'5	15'0	22'5	30'0	37'5
22	0'121	726	26’9	584	9T	18'2	27'3	36'4	45'5
24	0'144	864	32'0	694	10'8	21'6	32'4	43'2	54'0
26	0'169	1,014	37'5	815	12'7	25'4	38T	50'8	63'5
28	0T96	1,176	43'5	945	14'7	29'4	44T	58'8	73'5
30	0'226	1,350	50'0	1,085	16'9	33'8	50'7	67'6	84'5
32	0'256	1,536	56'9	1,235	19'2	38'4	57'6	76'8	96'0
34	0'289	?	1,734	64'3	1,293	21'7	43'4	65'1	86'8	108'5
36	0'324	1	1,944	72'0 •	1,562	24'3	48'6	72 9	97'2	121'5
38	0'361	j 2,166	80'2	1,741	27'1	54'2	81'3	108'4	138'5
40	0'400	I 2,400	89 0	1,928	30'0	’ 60'0	90'0	120'0	'	150'0
42	0'441	:	2,646	98'0	2,126	33'3	66'2	99'3	132'4	165'5
44	0'484	2,904	107'5	2,334	36'3	72'6	108'9	145'2	181'5
46	0'529	3,174	117'5	2.551	39'7	79'4	119'1	158'8	198'5
48	0'576	3,456	, 128 0	2,777	43'2	86'4	129'6	172'8	216 0

The above figures are for perfect loading arrangements ; 25 per cent, should be deducted for ordinary practice.

Fig 12.

Conveyor Belts.

Ta.ble II.—Troughing Belts with Three Idlers (Jeffrey Conveyor Co.,. (See fig. No. 3).

Formulae : Area of cross section in square feet — 0’000583 w2, cubic feet per hour at 100ft. per minute = 3'5w2,
where w = width of belt in inches.

Width of belt in inches.	Cross section of load in sq. feet.	Cubic feet per hour at 100 ft. per min.	Cubic yards per hour at 100 ft. per min.	Bushels per hour at 100 ft. per min.	Tons per hour at 100 ft. per minute.  !	Weight of material in lb. per cubic foot.				
					25	50	75	100	125
10	0'058	350	12'9	!	281	4'4	8'8	13'2	17'6	22'0
12	0'081	504	18'7	405	6'3	12'6	18 9	25'2	31'5
14	0T14	686	23'4	551	8'6	17'2	25'8	34'4	43 0
16	0'149	896	33'2	720	11'2	22'4	33 6	44'8	56'0
18	0'189	1,134	42'0	911	14 2	28'4	42'6	56'8	71'0
20	0'233	1,400	51'9	1,125	17'5	35’0	52'5	70'0	87’5
22	0'282	1,694	62'7	. 1,361	21'2	42'4	63’6	84'8	106’0
24	0'336	2,016	74'7	1,620	25'2	50'4	75'6	100'8	126’0
26	0'394	2,366	87'7	1,901	29'6	59'2	88'8	|	118'4	148’0
28	0'457	2,744	101'6	2,205	34'3	08'6	102'9	|	137’2	171'5
30	0'525	3,150	116'7	2,531	39'4	78'8	118'2	157’6	197’0
32	0'597	3,584	132'7	2,880	44'8	89'6	134'4	179'2	224'0
34	0'674	4,046	150'0	3,251	50'6	101'2	151'8	202'4	253'0
36	0'756	4,536	168'0	3,645	56'7	113'4	170’1	226 8	283'5
38	•	0'842	5,054	187'0	4,061	63'2	126 4	189'6	252'8	316'0
40	0'903	5,600	208'0	4,500	70 0	140'0	210'0	280'0	350’0
42	1’029	6,174	229'0	4,961	77'2	154'4	' 231'6	308'8	386’0
44	1'129	6,776	251'0	5,445	84'7	169'4	254'1	338'8	423’5
46	1'231	7,406	274'0	5,951	92'6	185'2	277'8	370'4	463'0
48	1'344	8,064	299'0	6,480	100'8	201'6	3u2‘4	403 2	504'0

The above figures are for perfect loading arrangements ; 25 per cent, should be deducted for ordinary practice.

Fig 17

KI

Much thought and attention has been given to the
design and manufacture of conveyor idlers, and many
types have been evolved. Figs. 6 to 17 inclusive show
various forms of idlers. Fig. 6 is essentially wrong in
principle. The various peripheral velocities due to the
increasing diameters cause an abrasive action, which
quickly rubs the covering off any belt. Fig. 7 shows a
four-pulley idler, and denotes the attempt to arrive at
a better belt curvature; one disadvantage is the many
roller edges which come into contact with the belt, and
another is the additional number of bearings. Fig. 8 is
the dish-pan idler; this form soon cuts the belt, as is

shown in the diagram giving loaded position. Fig. 9
shows the usual type of idler, in which the cutting edges
of the rollers are a disadvantage and the poor curvature
of the belt. Fig 10 shows a method of getting away
from the cutting edges of the rollers by placing the
centre roller behind the inclined rollers. Fig. 11 shows
the liability of the belt being cut if this type is used.
Fig. 12 is a four-roller idler to obtain good curvature of
belt; idlers are also constructed with five rollers to attain
this object. The number of position of bearings are a
■disadvantage. In fig. 13, in the endeavour to obtain
good belt curvature, an idler constructed of a spiral
spring 5 in. diameter, with 2 coils per inch of .width,
has been proposed. The springs under the weight of
the belt and its load stretch and sag to a smooth curve
of approximately circular shape, and the belt bends to a
troughed form *in contact with and supported by the
spring across its entire width. A pure rolling contact

at all points is expected. Fig. 14 shows a type of idler
with good features. We have good curvature, no
cutting edges, and few bearings. Fig. 15 shows a strong
and easily-get-at-able type of ball bearing. Idlers fitted
with ball bearings have come into use, and are likely
to supplant the older types of plain idlers. Some forms
of ball-bearing idlers seem much too lightly constructed,
considering the material to be handled and the rough
usuage consequent on gold mining operations. Types
of ball bearing idlers so constructed that the pulley has
to be cut to pieces in order to get at the ball race would
seem to be a wrong method to be adopted. The use
of side-guide idlers or boards for the purpose of keeping
a belt straight is quite wrong in principle, and a method
very destructive to belt. Fig. 16 shows Reddaway’s
patented arrangement to obtain good alignment of belt.
Fig. 17 shows the Johnstone. idler, consisting of a
number of pulleys of different diameters running free
on the shaft.

Conveyor Belts.—Idler Spacing, Speed and Load Factors. (Robins Conveyor Co.)

	Size of Conveyor.	12 in.	14 in.	16 in.	18 in.	20 in.	22 in.	24 in.	26 in.	28 in.	30 in.	32 in.	34 in.	36 in.	42 in.	48 in.
veigh ?5 lb. foot.	Troughing Idlers Spaced	51ft.	51 ft.	51 ft.	5 ft.	5 ft.	5 ft.	41 ft.	41 ft.	ft.	4| ft.	4 ft.	4 ft.	4 ft.		
■ial y 5 to 1 ubic	Speed Factor	0'023	0'026	0'029	0 046	0’050	0’056	0’069	0 069	0'072	0'082	0'096	0'106	0'117		
Mater ing 2. per c	Load Factor	0'068	0 068	0'068	0’175	0’075	0'075	0 075	0'075	0'069	0'069	0'065	0'065	0’065		
4 -’+='  % O	Troughing Idlers Spaced	5 ft.	5 ft.	5 ft.	41 ft.	4| ft.	4| ft.	4 ft.	4 ft.	4 ft.	4 ft.	31 ft.	31ft.	31ft.		
Material v ing 75 to 1 per cubic	Speed Factor	0'020	0'026	0'030	0 048	0 052	0 058	0'071	0'071	0'075	0'084	0'098	0'108	0’119		
	Load Factor	0'068	0’068	0'068	0'075	0'075	0’075	0'075	0'075	0'069	0 069	0 065	0'065	0’065		

Return idlers spaced 10 ft. apart. Top guide idlers usually spaced 45 ft. apart.

In preceding table, under proper spacing of idlers, find
the speed and load factor. Formulae :—

Speed factor x conveyor speed in feet per minute
= Result I.

Load factor X load in tons per hour = Result II.

The sum = Result III.

Result III. X length of conveyor in feet =
Result IV.

Result IV. -e 1,000 = horse-power at given speed
and load.

If conveyor is inclined : Tons per hour x height lifted
in feet added to Result IV., and then 4- 1,000 = horse-
power required.

If conveyor has trippers, either fixed or travelling :
add for each tripper the horse-pownr, and add 15 per
cent, for contingencies.

J.

U k •
“■ &

Plan
Fig 16

actial pull as compared with the useful pull, the follow-
ing figures may be used :—

Bare single pulley................ 1'6

Lagged single pulley.............. 1'5

Tandem bare pulley................ 1'3

Tandem lagged pulley.............. 1'2

These figures may be safely worked to.

Maximum allowable tension per ply :—

4 ply = 23 lb. per inch per ply.

-	„	=	22

6	„	=	21

7 and	8	,,	—	201	,,	,,	,,

Over	8	„	=20	„	„	,,

Head and tail pulleys should be of the largest diameter
admissible. A pulley of 5 in. in diameter for each ply of
the belt is the minimum, and 8 in. should be adopted
if possible. Large pulleys increase the life of the belts
very considerably by eliminating the heavy strain that is
imposed when made to bend round the small diameter.
In this connection an interesting point has been advanced
by some makers of belts, namely—that belts should be
constructed with an uneven number of plies, and instead
of the usual 4, 6, or 8 ply, it should be 5, 7, or 9 ply,
especially in the steeper drives.