Rope Transmission of Large Power
In Mills and Factories
This text is a re-edited and quite compressed version of a lecture given at the Institution of Mechanical Engineers, Manchester, in October 1876, by Mr. James Durie. He was a consulting engineer to the Dundee (Scotland) Lilybank Foundry, owned by Messrs Pearce Bros. Mr. Durie became a member of the Institution in 1875 and this lecture was, so to say, his "maiden speech" there. Pearce Bros, according to a contemporary brochure, were "Makers of Rope Gearing for .... Mills and Factories, Etc".
Both Durie and Pearce Bros had been engaged in rope power transmission since the early 1860s and their cooperation in this field resulted in a joint Patent Application and Grant in 1879:
Mr. Durie started his lecture in this way:
The best means of transmitting power from the prime mover - steam engine - to the various machines in a mill or factory has long been a matter of great importance to the engineer and to the manufacturer.
Until lately toothed gearing (spur and/or bevel wheels) and vertical and horizontal (line)shafts were almost universally employed for primary power distribution in (multi-storey) mill buildings. Individual machines were driven from the lineshafts on the various floors by leather belts on flat pulleys.
The ease of operating leather belts, plus the absence of noise and vibration, led engineers in the United States and in Germany to also apply (very wide) leather belts for primary power transmission, i.e., directly from the prime mover to the lineshafts in the mill; thus doing without gear wheels and vertical shafts. This proved quite efficient and successful, but the system has some serious limitations in maximum belt length. Wide belts also require a lot of space.
I now want to put before our Institution the plan of using round ropes working on grooved wheels instead of broad leather belts working on flat pulleys as a substitute for toothed gearing in primary mill drives. The firm I'm connected with has over 13 years of experience in this mode of transmitting power, and wherever it has been applied to replace toothed gearing, in old mills and new, it has always given complete satisfaction.
Rope transmission instead of toothed gearing
A. in new-built mills
In rope transmission, the flywheel of the prime mover is made wider than with geared transmission. It takes the shape of a drum with the appropriate number of parallel grooves for the ropes. The ropes usually are 5¼ in. or 6½ in. circumference; another size of rope, 4½ in. circumference, is employed for smaller powers. Heavier ropes could be used, but only where large pulleys can be fitted.
Because the right proportion between the diameter of the ropes and that of the pulleys is important! If the pulleys are too small, the rope strands are bent and strained too much and the rope core will be ground into dust. The life of the ropes depends on the size of the pulleys. Normally, the circumference of a pulley π . D should not be less than thirty times that of the rope.
The distance to be bridged between any pair of shafts can problemlessly range from circa 20 to over 60 ft.
The number of ropes and their size are determined by the power to be transmitted. The power each rope can handle depends linearly on both its size and its speed. The rope speed (equal to the circumferential velocity of the grooved wheel, if no slip occurs) is generally set from 3,000 to 6,000 ft./min. With this, and the power of the steam engine known, the number of ropes required can be calculated from the experience that has been gained in previous cases.
Take as an example the mill shown in Figures 1 and 2. This factory for spinning and weaving of jute is operated by Messrs. A. and J. Nicoll at Dundee. It was fitted up by Messrs. Pearce Brothers, Lilybank Foundry. The complete rope system shown here has now been in operation for nearly six years.
A little aside
The brothers Alexander and James Nicholl came from one of Dundee's oldest textile families. In the early 1870s they became deeply (and very successfully) involved in the then emerging India jute industry, which centered around Calcutta. At the time of Mr. Durie's lecture at the Institution, the Nicoll brothers were well established and wealthy manufacturers, owning or participating in various flax and jute mills.
- engine flywheel: 22 ft. diameter, 4 ft. 10 in. overall width, 18 grooves
- ground floor lineshaft, pulley 7 ft. 6 in. diameter, with 5 ropes transmitting 115 ihp
- first floor lineshaft, pulley 5 ft. 6 in. diameter, with 4 ropes transmitting 92 ihp
- attic lineshaft No. 1, pulley 5 ft. 6 in. diameter, with 4 ropes transmitting 92 ihp
- attic lineshaft No. 2, pulley 5 ft. 6 in. diameter, with 2 horizontal ropes transmitting 46 ihp
- weaving shed lineshaft, pulley 7 ft. 6 in. diameter, with 5 ropes transmitting 115 ihp
The engine makes 43 r.p.m. so the circumferential velocity of the flywheel is 2972 ft./min. The power of the engine varies from 400 to 425 ihp. The power transmitted by each of the ropes is circa 23 ihp. The ropes are 6½ in. circumference. The tension in the rope is power / speed, which calculates to 256 lbs., far below the breaking strength of the rope.
It will be seen from Figure 3, a section of two grooves plus ropes, that the ropes do NOT rest on the bottom of the groove, but on its V-shaped sides; these sides are generally made at an angle of about 40° to each other. If the angle is more obtuse, the rope might slip; if more acute, the rope might be wedged fast into the groove.
The ropes used for rope gearing are made of hemp carefully selected, the qualification of a good rope being that the fibres should be as long as possible, and that the rope should be well twisted and laid, and yet be soft and elastic. It is also very important that the ends of the rope should be united by a uniform splice, which should not be of a greater diameter than the other part of the rope. To effect this object, the splice is made about nine or ten feet long for a rope of 6½ in. circumference.
At this point, Mr. Durie exhibited a specimen of a rope 7 in. circumference, which showed very little wear after working 4½ years under a load of 205 lbs. at a speed of 2900 ft./min., transmitting 18 ihp. Also a specimen of a new rope showing the mode of splicing.
Under the influence of the load on the rope, the returning side of the rope is as much slackened as the pulling (working) side is tightened. It is therefore advisable, when possible, to have the pulling side of the rope at the bottom of the wheel, so that the top side is slackening and sagging into the grooves. When the opposite is the case, the ropes tend to fall sooner out of the grooves. It is however not always practicable or even possible to arrange this, e.g. when ropes have to be led to both sides of a driving pulley. In Figure 1, compare the pulleys B-C-D with the pulleys E-F.
It will further be noticed from Figure 1 that none of the primary lineshafts (B-C-D-F) have less than four ropes. These run at only 256 lbs. It is permissable to (temporarily) increase the load by taking one rope off its wheels. In case a rope needs tightening (which is rather often), that rope is simply taken off at the first occurring meal hour. The mill can then run on as usual but with one rope less; and the missing rope is replaced after tightening (shortening by resplicing) at the next meal break.
In the Figures 4, 5 and 6 is shown the arrangement of rope transmission in the extensive Samnuggur Jute Factory, Calcutta, which is a one-storey building, all the machinery, both spinning and weaving, being on the ground floor.
A little aside
Samnuggur Jute Factory Co Ltd was floated in Calcutta, in 1873, by Thomas Duff in conjunction with the brothers Alexander and James Nicoll and Joseph Johnston Barrie, all from Dundee. It was a very modern design and particularly successful at a time when other Calcutta mills languished or failed. Samnuggur proved the ability of the Calcutta mills to compete with Dundee for the American and Australian markets.
The engines are placed near the middle of the building. They are about 1000 ihp, and make 43 r.p.m. The flywheel is 28 ft. diameter and 6 ft. 7 in. wide. The rope speed here is 3782 ft./min. The ropes are 6½ in. circumference; 18 ropes transmit the power to the right-hand or spinning side, and 7 ropes to the left-hand or weaving side, making a total of 25 ropes. Each rope transmits 40 ihp. The load on each rope is 349 lbs., rather more than in the other example. Nearly all the shafts are driven by more than one rope, with the exception of some of the lineshafts in the weaving shed. Rope gearing was only adopted here after extensive enquiry into its suitability in the warm and humid climate of Calcutta; and the results are very satisfactory.
We here do interrupt Mr. Durie's lecture for a moment. During the discussion following the completed lecture, some additional examples of recently completed installations were described by another Member attending the lecture. We include that information here for easy comparison.
Mr. John Musgrave showed and explained drawings of a mill his firm had recently erected in India, the Howrah Jute Spinning and Weaving Mill, Calcutta, shown in the Figures 7 and 8. This mill is driven by a pair of horizontal tandem compound engines, running at 40 r.p.m., capable of about 800 ihp at 80 lbs./sq.in. boiler pressure. The engine has a fly pulley or drum of 57 tons weight, 28 ft. diameter and 5 ft. 9 in. wide, with 22 ropes of 6½ in. circumference. Rope speed is 3520 ft./min. He remarked upon the great weight of the drum, which he held favourable for smooth running of the mill.
Another example Mr. Musgrave did show was the Budge Budge Jute Weaving Mill, also in Calcutta, shown in the Figures 9, 10, 11 and 12. This smaller plant is driven by a pair of 250 ihp horizontal tandem compound engines, running at 50 r.p.m. with 70 lbs./sq.in. boiler pressure. The fly pulley here is 18 ft. diameter and 3 ft. 4 in. wide, with 15 ropes of 5 in. circumference. Rope speed is 2850 ft./min. Al power is conveyed to an 8 ft. pulley on the first lineshaft in the weaving shed and further distributed from there to the other lineshafts by the number of ropes necessary for the power required to drive the machinery.
The same plan, according to Mr. Musgrave, is being applied to the Attleborough Doubling Mill his firm is now erecting at Nuneaton. This mill will be driven by a compound engine of 500 ihp, running at 45 r.p.m., the fly pulley being 22 ft. diameter, 3 ft. 8 in. wide, grooved for 14 ropes of 7 in. circumference. Rope speed here will be 3150 ft./min. The mill is four storeys high, and the power will be transmitted directly to 7 pulleys of 6 ft. diameter, each having two ropes over it.
We now return to Mr. Durie, to attend the second part of his lecture.
Rope transmission to replace toothed gearing
B. in existing (older) mills
The first (and most simple) plan is to put in a new grooved flywheel, or to place grooved segments upon the existing flywheel. The normal running r.p.m. of the steam engine should however be high enough to obtain acceptably fast rope speeds. Remember: half the rope speed means twice as many ropes to transmit a given power. Another requirement is sufficient width of the wheel pit to house the wider fly pulley (as it is so aptly named by Mr. Musgrave).
If this plan cannot be followed, we use (or modify) the original toothed second motion shaft and put the required grooved pulleys on that. Ropes are led directly from these "second-motion pulleys" to the (existing) lineshafts on the different storeys of the mill. All vertical shafts and bevel gears are discarded. In some instances, with very slow-running beam engines, it proves necessary to put in an intermediate shaft, to get sufficient speed.
Is it worthwhile to replace the old geared system with a rope system?
In a geared system, the first driver is the spur-wheel fitted directly on the crankshaft of the steam engine. This engages the (smaller) pinion on the second-motion shaft. This runs faster than the engine. In order to ensure these two wheels working together well, their teeth must be accurately of the same pitch and size. Furthermore it is essential that the centres of the engine shaft and the second-motion shaft are rigidly fixed at the correct distance from each other.
This object is attained (in a horizontal engine) by extending the engine bed casting to directly support the pillow blocks of the second-motion shaft; or (in a beam engine) via the original heavy foundations. Then the wheels ought to work smoothly and without much noise. Often this desirable state of things is NOT attained. A short walk through the streets of any manufacturing town suffices to attest to this fact - the rumbling and clunking noise of badly fitting gears can sometimes be heard from several hundred yards off.
If the mill has more than one storey, the power will be taken upwards from the second motion shaft on the ground floor, by means of an upright shaft and bevel wheels, requiring heavy and strongly fixed wall-boxes to support these securely.
As an example of the old type of gear-drive, we add this Plate from Rees's Cyclopædia, Lemma Mill, 1813. The mill is driven by an giant waterwheel, and to get sufficient speed for the lineshafts and machinery, an intermediate upgearing is unavoidable.
Ropes for power transmission are - as compared to gears - much more elastic and forgiving. For that reason, the supports of rope-driven shafts and pulleys can be lighter than is possible with geared drives. The latter also need more accuracy in aligning, and heavier walls to keep that alignment under varying load conditions. Cast iron brackets on the cast iron columns of the mill building, as bearing supports for the lineschats, will do well with rope drives; as they will NOT do with the cumbersome gear drives.
The greatest advantage of rope transmission as compared to toothed-gearing transmission systems is the entire freedom from any risk of a total breakdown; when a rope shows symptoms of giving way - and ropes always DO give symptoms of weakness long before they break - the weak rope can quickly be removed and work proceed. A new or respliced rope can be put in at any meal hour or evening.
The estimated cost of rope maintenance is £ 5.-- per annum per 100 iph. This is made up of the cost of renewal of the ropes, and occasional wages for tightening them. Some ropes have been found to run 10 years; but as a general rule the life of a rope is from 3 to 5 years.
The friction loss of rope gearing (when run at high speed, as is very advisable anyway), is considerably less than that of toothed gearing. In consequence, the consumption of lubricants is much reduced. Mr. Durie cannot give definite information on this point, since - in all cases where rope gearing has been substituted for the old toothed-gearing - extensive other alterations were made at the same time; or the engines were after the alteration run at 10-15 r.p.m. higher speed (so improving throughput).
But everyone who has substituted rope gearing for toothed gearing testifies to the great improvement and steadiness of driving obtained after the alteration, and that the machinery turns off a greater weight of yarns in the same time. In these times of shorter labour working hours and increasing foreign competition, refurbishment can offer fresh chances to those who own old mills, that, with their heavy gears, when not modernized, cannot safely be run any faster.