Roller chain

The number of speed reduetions is another way to classify conveyor drives. Most common of the speed-reduction methods is the two-step system, in which the motor is coupled to a speed reducer and the slow-speed shaft of the reducer is connected to the conveyor-drive shaft by a V belt or a roller chain. The second reduction not only permits the use of a simpler speed reducer but also allows a more flexible layout of the motor and reducer mounting plate. On many installations this eliminates the need for a specially designed drive mount. 

Chain Conveyors These devices for handling containers are available in either roller-chain designs or less costly types. There is a variety of slat conveyors that use both single and double strands of roller chain, as well as a slider type using cheaper chain. In general, slat chain conveyors are used only on loads which are too heavy for economical handling by belt, roller, or wheel units or which have odd shapes not suitable for roller or wheel units. They are particularly adaptable to pallet handhng, as are simple open strands of chain with flat-surfaced attachments. 

Some of these are shown in Figure 3-26. Because most modern power transmissions use roller chains, silent chains or the offset link (Ewart) chains, these will be the only chain types discussed since they are quite important in oil field applications. 

Where accurate and higher-speed chain drives are required, roller chains are used. Roller chains are fundamentally a development of the block chain in which rollers have been inserted. The addition of the rollers increases the overall efficiency of the chain and permits it, in its ordinary form, to be operated at high speeds a rate of 600-800 ft/min is usually recommended. The links can be furnished in a multitude of shapes, one common form being the offset shown in Fig. 3-28. This type of chain is furnished in pitches, i.e., center distance between rollers, from up to 2 in. and in breaking strengths, dependent upon the materials and the construction used, from about 10,000 to 200,00 lb [8,11]. 

Precision tools are used in the manufacture of roller chains, and a high degree of accuracy is maintained. The chain is made up of links, pins, and bushings, all fabricated from a high grade of steel, with the pins and the bushings ground to ensure accuracy of pitch. 

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. 

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... 

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. 

Roller Chains. These chains are primarily selected for low and medium-speed service and for conveyor work, although roller chains are sometimes used for higher speeds because they operate more smoothly and quietly. 

Number of Teeth in Wheei. For roller chains, pinions should have 17 teeth or more for moderate-speed drives and 21 teeth or more for high-speed drives. Fewer teeth may be used for low-speed drives, with 12 teeth a recommended minimum. 

Small roller-chain wheels should be hardened when used on moderate and highspeed drives, very low-speed heavily loaded drives, and when operating under abrasive conditions or when the drive ratio is greater than 4 1. Steel silent chain pinions should be hardened. 

Prime Ratio. Ratios in excess of 7 1 are generally not recommended for roller chains. If greater speed reduction is required, it is desirable and usually more economical to compound two or more drives. 

Figure 3-39. Chordal action of roller chain (courtesy of Link-Belt Co.).

Figure 3-40. Typical roller chain tensioning methods [8].

In what follows, the pertinent design data are given for the roller chain, silent chain, and the offset link chain (API chain). 

Roller Chain. Table 3-18 gives the typical service factor for roller chain drives [5], Table 3-19 gives the basic roller chain design dimensions for ANSI standard roller chains by ANSI chain number [14]. 

Horsepower Ratings for Single-Strand Roller Chain Driver... 

Heavy Duty Offset Sdebar Power Transmission Roller Chain andSprocket Teeth, A N.SIStaftdiard B g9.1. 29.10M-I981. ... 

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... 

Roller chains Probably the most common of all chains is the roller chain, which is found in applications such as ... 

Because of the versatility of roller chain drives, certain standards have been established. With these standards, interchangeability of chains is possible between one manufacturer and another. As long as chains are identifiable, they can be cross-referenced easily without any serious operational problems arising. Table 58.7 shows the standard roller chain American Standards Association (ASA) number by pitch length for single, double, and triple strand chains. 

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... 

As with high-horsepower belt drive applications, chain drive designers often employ multiple chains. As illustrated in Figure 58.26, the chains in a multiple chain drive are all of the same size as a single roller chain (i.e., the pitch and roller sizes are all the same). 

Roller chains are constructed by connecting two side plates together with pins that have bushings and rollers attached. The side plates are classified as either the pin link or roller link. The pin links are located outside the roller links and connect the roller links together. This provides an alternate pin and roller link combination. 

Silent chains are similar to roller chains in that each has a master or connecting link to facilitate ease of installation and removal from a machine. They are usually made of high-carbon steel or heat-treated steel alloys. As a result, this type of chain provides trouble-free service for extended periods. 

The length obtained by this formula should be rounded upward to the nearest whole number. For a roller chain, the resultant number must be raised to the nearest even whole number of pitches or an offset link must be used to obtain the proper installed length. The proper chain length in inches is found by multiplying L by the pitch for the ASA type from Table 58.7. 

With the increased speed and horsepower capabilities of modem chain drives, the role of lubrication has increased in importance. The precision roller chain is actually a series of connected journal bearings and it is essential that lubrication minimizes the metal-to-metal contact of the pin/bushing joints of the chain. Many factors affect lubrication performance and chain life including heat, improper lubrication, windage, contamination, and oil viscosity. 

Visually inspect coupling mechanical components (roller chains and gear teeth, and grid members) for wear and/or fatigue. 

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