Roller chain sprockets

The shape (see Figure 3-31) of the standard form of tooth used on the roller-chain sprockets permits the rollers to ride farther out on the teeth as the chain is stretched... 

The ASME B29.1 standard defines the dimensions, tolerances, and tooth form for standard roller chain sprockets. These will be discussed in the design section later in this chapter. 

For large roller chain sprockets, cast iron is commonly used. Cast roller chain sprockets have cut teeth, and the rim, hub, face, and bore are machined. Cast iron is often used in the large sprockets of drives with large speed ratios. Cast iron is acceptable in this case because the teeth of the larger sprocket are subjected to fewer chain engagements in a given period. For severe service, cast steel or steel plate is preferred. 

A cast iron shear pin hub sprocket is shown on the left side of Figure 4-21. It operates exactly like the similar roller chain sprocket shown in Figure 4-8. These are often used in conveyor drive... 

On roller chain sprockets, elongation is absorbed by the rollers riding farther out on the working face of the sprocket tooth as the links pass around the sprockets. A trace of the path would be vaguely parabolic. The link would move in, seat briefly on the sprocket bottom diameter, and then move out again. 

Figure 4-24 shows the important diameters of roller chain sprockets and the equations for computing them. The hrst three terms are given dimensions. The first and third terms, P and are standard dimensions and can be obtained from Table 2-6. The second term, N, must be supplied by the sprocket designer. Tolerances on critical limiting dimensions are given in ASME B29.1 or can be... 

FIGURE 4-28 Forces on roller chain sprocket teeth. 

Web thickness of single-strand cast roller chain sprocket wheels as a function of chain pitch... 

Maximum bore and hub diameters of roller chain sprockets (with standard keyway)... 

Inspect the sprockets for signs of worn teeth. As roller chain sprocket teeth wear in a drive, the teeth begin to take on a hooked shape. A badly worn roller chain drive sprocket is shown in Figure 15-1. Engineering steel drive sprockets wear in a similar way. 

Where a vertical lift is required, the most widely used equipment is the bucket elevator, consisting of buckets fitted to a chain or belt which passes over a driven roller or sprocket at the top end. Bucket elevators can handle a wide range of solids from heavy lumps to fine powders and are suitable for use with wet solids and slurries. 

Sprockets. To secure full advantage of the modern roller chain, it should be operated on sprockets having accurately machined teeth, the profile of which has been specified or approved by the ANSI [14]. This profile, which is made up of circular arcs, is designed to compensate for the increase in pitch due to natural wear and thereby provides maximum efficiency throughout the life of the sprocket. 

In general, four types of sprockets are available for roller chains. They are steel plate without hubs, cast iron or steel with hubs on one or both sides, split type, double-duty type. 

Shaft Centers. It can be readily seen that on any chain drive the minimum center distances must be more than one-half the sum of the diameters of the two sprocket wheels. Experience has shown that best results are usually obtained when the center distance between shafts is 30 to 50 times the chain pitch. Forty times the chain pitch is about normal, and 80 times the pitch is maximum. In highly pulsating loads, 20 to 30 times the pitch is more nearly the correct center distance. Center distances of 10-12 ft are permissible with finished steel roller chains operated at moderate speeds without the use of idlers. On distances greater than this, an idler should be used to eliminate the possibility of swaying or flopping, which may cause the chain to jump the sprocket. When idlers are used, they should be placed on the slack strand of the chain. The number of teeth in the idler should be the largest possible and preferably not less than the number in the smaller sprocket of the drive. 

Sprockets. Since the silent chain has not had the same wide usage as roller chains and because of the different types of construction that have been employed, there has been but little standardization of specializations. Each manufacturer has more or less carried out its own design and ratings, with the result that the sprockets to be used with this type of chain very accordingly. 

Shaft Centers. As in roller chains, the minimum distance between shaft centers for silent chains must, in order to provide tooth clearance, be greater than half the sum of the two sprocket diameters. On large-speed reductions, experience has shown that the center distance should not be less than eight-tenths the difference in diameters of the two sprockets. 

The power is provided to the drawworks by the prime movers at the master clutch (see Figure 4-9) and is transmitted to the master clutch shaft via sprockets and roller chain drives. The speed and the torque from the prime movers are controlled through the compound. The compound is a series of sprockets, roller chain drives, and clutches that allow the driller to control the power to the... 

The roller chain uses a steel roller to engage the sprocket. The rolling action between the roller and the profile of the sprocket teeth causes the roller to rotate on a bushing, creating less friction than the traditional belt drives. There is some axial sliding action between the roller and bushing. 

Chain drives and sprockets 58/1059 Table 58.7 Roller chain numbers by chain pitch... 

Chains, sprockets, conveyor chains or rollers Dispersions in oils or greases (polyglycol for high temperatures)... 

A thirty-foot deep slope-shaft was sunk at the west end of the loading platform to communicate with the underground sorting yard. Trucks were controlled on the slope by a Head-Wrightson tram creeper-retarder, the mechanism of which consisted of two heavy-duty roller-chains driven by venical motorized sprockets. Each link carried a steel dog which projected upwards and engaged an axle of any truck pushed over it, and thus either propelled it to the surface or lowered it slowly underground. 

Most machines use power transmission components to transfer power from a motor, engine or other prime mover to an element of a machine where a useful function occurs. Some common power transmission components are belts, pulleys, ropes, sheaves, chains, sprockets, gears, and friction rollers. Many of these components create pinch, nip, or shear points. 

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