Word Finder - pulleys

definition

One of the simple machines; a sheave, a wheel with a grooved rim, in which a pulled rope or chain lifts an object (more useful when two or more pulleys are used together, as in a block and tackle arrangement, such that a small force moving through a greater distance can exert a larger force through a smaller distance).

definition

To raise or lift by means of a pulley.

Pulleys and drums for communi cating a constant velocity ratio are circular.

Wrapping ConnectorsBelts, Cords and Chains Flat belts of leather or of gutta percha, round cords of catgut, hemp or other material, and metal chains are used as wrapping connectors to transmit rotatory motion between pairs of pulleys and drums.

One train of mechanism may diverge into two or moreas when a single shaft, driven by a prime mover, carries several pulleys, each of which drives a different machine.

F = T1 Ti = T1 (I ef9) Ta(ef 1)j When a belt connecting a pair of pulleys has the tensions of its two sides originally equal, the pulleys being at rest, and when the pulleys are next set in motion, so that one of them drives the other by means of the belt, it is found that the advancing side of the belt is exactly as much tightened as the returning side is slackened, so that the mean tension remains unchanged.

The position of the reversing link is altered by means of a cord, passing over two pulleys, fixed respectively in the engine-house and on the derrick.

The substitution of machinery for hand labour in cutting coal has long been a favourite problem with inventors, the earliest plan being that of Michael Meinzies, in 1761, who proposed to work a heavy pick underground by power transmitted from an engine at the surface, through the agencies of spear-rods and chains passing over pulleys; but none of the methods suggested proved to be practically successful until the general introduction of compressed air into mines furnished a convenient motive power, susceptible of being carried to considerable distances without any great loss of pressure.

The pulleys, which are made as large as possible up to zo ft.

But a floor, however heavy, suspended by three wire ropes and properly balanced over large, well-mounted pulleys, requires an amount of energy to work it which does not exceed that required to operate a platform of moderate dimensions, and there is a freedom, a safety and a facility of working with a complete floor which no partial platform can give.

The Torque Was Measured By Weights 0 And P Suspended By Silk Ribbons Passing Over The Pulleys N And Round The Disk Kl.

Cords require either cylindrical drums with ledges or grooved pulleys.

The angular velocities of a pair of connected circular pulleys or drums are inversely as the effective radii.

The length L of an endless belt connecting a pair of pulleys whose effective radii are r,, r,, with parallel axes whose distance apart is c, is given by the following formulae, in each of which the first term, containing the radical, expresses the length of the straight parts of the belt, and the remainder of the formula the length of the curved parts.

When the a,ces of a pair of pulleys are not parallel, the pulleys should be so placed that the part of the belt which is approaching each pulley shall be in the plane of the pulley.

This form is extended to include the cases of several pulleys on the same sifaft.

Such persons may sometimes get a good deal of exercise in a short time by the use of dumb-bells, of elastic cords, or of cords running over pulleys and weighted at one end.

These wheels receive motions from bands and pulleys from a steam or other engine contained in the car.

Benjamin (American Machinist, 1898) on castiron pulleys loaded by a belt to imitate the conditions in practice led him to the conclusion that the rim is usually not sufficiently rigid to load the arms equally, and that the ends of the arms are subjected to bending movements of opposite sign, that at the nave being almost invariably the greater.

Pulleys are also built up of wrought iron and steel, and can then be constructed entirely free from internal stress; they are thus much lighter and stronger, and are not liable to fly to pieces like cast iron if they break.

Pulleys are also made of paper, wood and other materials.

Wooden pulleys are preferably made of maple, the rim being formed of small sections morticed, pinned and glued together, with the grain set in such directions that any warping of the material will leave the cylindrical form practically unaltered.

Wooden pulleys are generally made in two halves, bolted together at the rim and nave, and are provided with wooden spokes dovetailed into the rim and secured by keys.

The rims of pulleys, round which flat bands are wrapped, may be truly cylindrical, in which case the belt will run indifferently at any part of the pulley, or the rim may be swelled towards the centre, when the central line of the band will tend to run in the diametral plane of the pulley.

Parallel shafts may be driven by flexible bands or connectors passing over pulleys, the central planes of which coincide, without any guiding arrangements for the belting.

A common arrangement for driving a lathe spindle, in either direction at several definite speeds, is to provide a countershaft on which are mounted two fixed pulleys and two loose pulleys to accommodate two driving belts from the main shaft, one of which is open and the other crossed.

The belts are moved laterally by the forks of a striking gear pressing on the advancing sides of the belts, and the pulleys are arranged so that the belts either wrap round the loose pulleys, or can be shifted so that one wraps round a fixed pulley, while the other still remains on its loose pulley.

The dimensions of the pulleys are generally so arranged that the return motion of the lathe spindle is faster than the forward motion.

An alternative arrangement consists in providing two loose pulleys on the counter-shaft, driven by open and crossed belts respectively, and arranging two clutches on the shaft, so that by the movement of a sliding block, controlled by hand, one or other of the clutches can be put in gear.

The proportions of cone pulleys for open or crossed belts may be determined by considering the expression for the half length (1) of a belt wrapping round pulleys of radius r 1 and r 2 respectively, and with centres distant c apart.

When pulleys are mounted on shafts which are parallel to one another, the band will retain its position, provided that its central line advances towards each pulley in the diametral plane of this latter.

Guide pulleys are set with their diametral planes in the planes containing corresponding pairs of tangents, and a continuous belt wrapped round these pulleys in due order can then be run in either direction.

Frames or blocks containing pulleys or sheaves are used in combination for lifting heavy weights.

Soon afterward the company added wheels, gears, and pulleys which allowed children to create vehicles of all kinds as well as items with gears.

The piercer uses hooks to pierce through specific parts of the body; these hooks are attached to pulleys or another mechanism and used to lift the piercee off of the ground for a period of time.

The Greeks used an intricate design of pulleys and wheels so that a float would rise and fall with the water, automating the "machinery," and through a gear system maintain time on a disk on the front of the clock.

Each machine guides the user through a specific movement while controlling the motion with a series of pulleys.

Some of the best options have dual adjustable pulleys that allow you to manipulate the angle of resistance for a wide variety of exercise options.

Belts (the most frequently used of all wrapping connectors) require nearly cylindrical pulleys.

Pulleys are usually cast in one piece, and the proportions of the various parts are designed to resist the unknown stresses due to contraction of the casting in cooling, in addition to the stresses to which pulleys are subjected in use.

In determining the dimensions of corresponding drums of cone pulleys it is evident that for a crossed belt the sum of the radii of each pair remains a constant, since the angle a is constant, while for an open belt a is variable and the values of the radii are then obtained by solving the equations r 1 = l/ir - c(a sin a + cos a) + 2c sin a, r 2 = l/7r - c(a sin a +cos_a) - lc sin a.

If the motion is reversed the condition is no longer satisfied and the belt will leave the pulleys.

In the most general case two points may be chosen on the line of intersection of the diametral planes, and tangents drawn to the pitch circles of the pulleys.

A usual value of for hemp ropes on cast-iron pulleys is 0.3, and the exponential log ratio is therefore 0 3ur cosec 20 when 9 =7r.

An endless chain B, passing through guides C and D, encircles these pulleys and the single loose pulley E of the lower block, as indicated.

Having attached the pulleys, the cables were threaded through from the rails on the prompt side wall.

Activities from Inventor's Workshop link directly to the teaching of wheels and axles, gears, pulleys and cams.

The main drive pulley was 4.25 " in diameter and the rear idler pulleys, running on ball bearings, 3.5 " .

This wire is passed over any number of small idler pulleys to the surface being cut.

This system presents the greatest advantages in point of economy of driving power, especially where the gradients are variable, but is expensive in first cost, and is not well suited for curves, and branch roads cannot be worked continuously, as a fresh set of pulleys worked by bevel gearing is required for each branch.

The surface arrangements of a modern deep colliery are of considerable extent and complexity, the central feature being the head gear or pit frame carrying the guide pulleys Surface which lead the winding roes from the axis of the it arrange= g P P to the drum.

To prevent accidents from the breaking of the rope while the cage is travelling in the shaft, or from over-winding when in consequence of the engine not being stopped in time the cage may be drawn up to the head-gear pulleys (both of which are unhappily not uncommon), various forms of safety catches and disconnecting hooks have been adopted.