Page images

certainly fastened rails, it seemed very rational to trust a leather belt to travel with the same speed. Thus reassured, the doubter might smile at the suggestion of danger of risking a light belt to journey at the same rate. But there had been no light pulleys made suitable for this use. Those previously in use, made of two iron rims, covered with wooden lags bolted thereto, were rejected as unfit.

Although the superior convenience of belts over wheel-work and shafting for transmitting power, had induced many attempts to use them thirty years ago, yet the experimenters had commonly failed of successfully operating them with the low rate of speed then used. Pulleys had not been made sufficiently light and well balanced for any one to adventure to use them with the high speed required for leather belts to operate advantageously. With the slow speed, it was necessary to strain the belts so tightly on the pulleys, to produce sufficient adhesion, without slipping around on the smooth surfaces, that the lacings and texture of the leather yielded; and so frequent repairs were required, that the superintendents of mills nearly all abandoned the use of them for transmitting the power from the motors to the mill shafting. They fell back on the old system of slowly revolving heavy shafting and wheels.

To carry out the proposed system, new patterns of pulleys were therefore made. The first pulley, 10 feet diameter, proved to be imperfect, and when tested with a velocity of about 8,500 feet per minute, the rim soon made its exit through the roof of the wheel-house, and continued its course in a parabolic curve through the air several hundred yards, until it finally transmitted its motive power to plough a furrow in a meadow. A re-modeled pulley, made to take the place of the wandering one, stood the test; and has continued faithful, without deserting its post, to perform the duty assigned to it ever since, during a period of sixteen years. The same belt has also remained in use, in good order, after travelling about a quarter of a million of miles every year in its daily circuits, with a velocity of 6,000 feet per minute.

As a test of the efficacy of this small three-inch shaft to transmit the power from three water-wheels, it may be stated that not a single shaft or coupling has required renewal or repairs, and they appear still capable of a much longer service. This

same three-inch shaft has also served to transmit all the power of the steam engine used in times of drought.

The contrast between the two systems of high and low rates of speed of shafts and belts, for transmitting power from motors to manufactories, is instructively exhibited in these two narrated instances of the practical application of each of them, with conclusive results of the failure of the latter.

To avoid the use of the brittle teeth of wheels, quite recently the adhesion by friction of the surfaces of wheels has been employed for the transmission of power. To intensify the friction, the adhesion has been increased by turning grooves and ridges on the faces of the wheels brought together by pressure.

This arrangement has been found advantageous for engaging and disengaging heavy washing machines and other apparatus in dye-houses and bleacheries, where leather and india rubber belts fail.

It may be questioned whether there is not a great loss of power by transmission through a length of three hundred feet of a three-inch shafting?

Undoubtedly some power is lost by friction in this case; but not so much as by the massy shafts described, or by a similar line of main shaftings in mills, where the friction is much augmented by loading the shafts with numerous pulleys, and by the tension of numerous belts.

If kept in line and properly attended, the friction of a naked shaft of the length of three hundred feet is so small as to be easily turned by the hand of a man. The friction being caused by the weight of the shaft only, is not affected by any extent of power transmitted by it while revolving, whether it vary from one to an hundred horse power.

Where high velocities of mill gearing are used, it is desirable to limit any accidental extreme acceleration, that might prove injurious.

This was readily accomplished by the simple arrangement of a latch to be lifted by a touch of the whirling arm of the ball regulator, whenever the accelerated speed causes it to rise to a certain prescribed limit. The lifting of this latch disengages the connection of the regulator with the gate of the water-wheel, and simultaneously engages another adjacent revolving wheel, that instantaneously shuts the gate more quickly than can be

done by hand. By this automatic action, the water-wheel itself is made a self-regulating machine.

A wire extended from the distant mill, like a bell-wire, serves to communicate with the same latch by a slight pull of the hand, and to shut the gate of the water-wheel by the same automatic arrangement. This was devised for use only in case of accident, requiring the immediate stoppage of the machinery. This same system should be applied to automatically shutting off steam from an engine, whenever the velocity may accidentally become accelerated beyond a prescribed limit, to endanger the machinery..

The very important advantage of combining together the action of the several motors of a manufactory to coöperate in concert for equalizing the regulation of the speed of the looms, self-actors, and other machines, requiring great uniformity of movements, is readily available, where the velocity of a mile per minute of a connecting belt is adopted. While the strongest shafting and cog-wheels fail to accomplish this work, even with the most massive materials, as has been described, all four of the water-wheels of the Georgia Mill have been very satisfactorily and successfully made to act in unison by a single belt of only 8 inches in width. This belt serves to transmit back and forth between the motors any excess of power that either may receive, and to return any surplus, to an extent of sixty horse power. A range of variation of 120 horse power is thereby available for maintaining an equable movement of all the machines of a large manufactory, with admirable regularity. The elasticity and slight slipping of the belts relieves the shocks of more than one hundred tons of water-wheels, which break the teeth and shafting made of rigid, unyielding iron.

This system was necessarily introduced to prevent the waste of water that ensues when two mill regulators are used to control the flow of water successively from one pair of wheels above another lower pair. The two regulators cannot be made to act harmoniously; for each one is governed by the varying load of machinery imposed on each motor. The annoying waste of the surplus water in times of drought, shut off by the regulators, and flowing past without useful effect, can be prevented entirely by using only one regulator on the upper wheels for controlling the whole of the machinery.

Thus a small leather belt, of only eight inches width, has been successfully employed for many years, and is still employed, with the velocity of a mile a minute, to control the speed of four water-wheels, like leather reins to bridle four steeds.

In a manufactory operated by two independent motors, with distinct lines of shafting, the two systems may be connected even by an inch belt moving with high velocity, to modify, wonderfully, the sudden extremes of speed, so disadvantageous where machines are operated, requiring nice adjustments of power.

Statement of Facts and Rules that may serve for calculating safely the Velocities of Belts and Pulleys.

In the present experimental state of the introduction of pulleys and belts, moving with high velocities for the transmission of power to a distance from motors, a few facts may be briefly stated to inspire confidence in the operators of mills to adopt new arrangements, by learning what has been found practically successful.

A good leather belt, one inch wide, or a bridle rein, has sufficient strength to lift 1,000 lbs.

The speed of a mile per minute for main driving found both safe and advantageous for practical use. ponderous locomotive engines are caused to move.

leather belts, has been This is no faster than

The capability of belts to transmit power is determined by the extent of its adhesion to the surface of pulleys.

The extent of adhesion of belts varies greatly under varying circumstances of the use of them; and is very limited in comparison with the absolute strength of the leather.

The adhesion and friction, causing the belt to cling to the surface of a pulley without slipping, is mainly governed by the weight of the leather,—if used horizontally.

If belts are strained tightly on the pulleys, then the adhesion is increased in proportion to the increased tension produced.

The weight of leather in vertical belts tends to produce a sag beneath the under side of the under pulley; and, if loosely put on, might not touch it at all, to transmit power by adhesion. For this reason it is necessary to strain on more tightly all vertical belts, with a dependence on the elastic stretch of the leather for producing adhesion.

A vertical belt of single leather of the width of six inches, and with a velocity of 5200 feet per minute, has practically been used very satisfactorily at the Georgia mill, during several years, to operate 10,400 self-acting mule spindles, and the spoolers and warpers for the same; and another belt of similar width and velocity, 110 feet in length, has served to transmit the power from a 24 feet water-wheel, 18 feet long, under a fall of 20 feet, with the same velocity of 5,200 feet.

A 24-inch belt of single leather with the velocity of 4,850 feet per minute, has transmitted all the power of a steam-engine of six feet stroke, thirty inch cylinder, making forty revolutions per minute; and with so slack a tension on the returning side as to flap and wave with an undulating movement.

These statements are specified simply to show what has been done by belts running with certain vetocities,-not for the purpose of holding them up as models for imitation.

No fixed rule can be given for calculating the actual adhesion of belts; for this adhesion depends on so many contingent facts of their relative positions and weights, as affected by greater or less lengths and breadths, and lightness. As the result of experimental observations, it may safely be calculated, that with a properly slack belt, the effective adhesion of a horizontal belt may be taken at 30 lbs. to each inch of width of short belts, and double of this on long belts, with three-fold or more, if tightly strained on the pulleys; which never should be done; for this increases the friction of the bearings and waste of power, in addition to injuring the durability of the leather for service.

Clamps with powerful screws are often used to put on belts with extreme tightness upon the pulleys, and with most injurious strain upon the leather. They should be very judiciously used for horizontal belts, which should be allowed sufficient slackness to move with a loose undulating vibration on the returning side, as a test that they have no more strain imposed than what is necessary simply to transmit the power.

Rather than to continue to use horizontal belts with overstrained tightness to obtain the necessary adhesion, it is often better to use larger pulleys, which require less adhesion to transmit an equal extent of power.

On the scientific principle that the adhesion, and consequently the capability of leather belts to transmit power from motors to machines, is in proportion to the pressure of the actual weight of the leather on the surface of the pulley, it is manifest, that as longer belts have more weight than shorter ones, and that broader belts of the same length have more weight than narrower ones, it may be adopted as a rule, that the adhesion and capability of belts to transmit power, is in the ratio of their relative lengths and breadths. A belt of double the length or breadth of another, under the same circumstances, will be found capable of transmitting double the power. For this reason it is desirable to use long belts. By doubling the velocity of the same belt, its effectual capability for transmitting power is also doubled.


The standard of "a horse power," generally adopted, is the measure of force that is sufficient to raise 33,000 lbs. 1 foot high, in a minute, or 1 lb. 33,000 feet high in a minute.

It is only necessary to divide this standard measure of 33,000 lbs, by the number of feet velocity per minute, of the belt, and the quotient will indicate the actual tension (in lbs.) required to be imposed on the belt to transmit one

horse power.

« PreviousContinue »