Silent Chain Sprocket Teeth

The pitch diameter probably is the most important diameter of the sprocket. Unfortunately, one cannot measure it directly, so manufacturers usually closely control the diameter in production. 

N NUMBER OF TEETH B - DIAMETER TO BASE OF WORKING FACE 

NOTE 1. TEETH MAY BE EITHER ROUNDED ITOPPEDI OR SQUARE ITURNEDI. 

SHAPE OF ROOT LINE BELOW WORKING FACE MAY VARY WITH TYPE OF CUHER. 

FIGURE 4-34 Layout of standard sprocket tooth form for silent ehain. 

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Sprockets should have at least 21 teeth for long drive life and smooth operation. Drives using sprockets with fewer teeth are likely to have increased vibration and noise because of chordal action (see Figure 5-2 and Figure 5-3, and the explanation used for roller chain). Each sprocket must be large enough to accommodate the bore and keyway specified for the shaft on which it will be mounted. Table 7-2 fists the maximum recommended bore and minimum hub diameter for standard silent chain sprockets with up to 33 teeth. 

An ANS silent chain sprocket cannot have fewer than 12 teeth. The number of teeth on the large sprocket should generally be no more than 120. 

Figure 3-33. Silent chain and differential type sprocket teeth [8],...

Practically all sprockets used with silent chain are made with cut teeth. Those with up to 25 teeth are usually cut from a steel forging and are furnished with a solid hub. For sprockets with more than 25 teeth, a semisteel is used, and the sprockets are available in either solid or split form. 

The design consists of two hubs with sprocket teeth connected by a chain of the single-roller, double-roller, or silent type. 

Other nonstandard silent chains are duplex, conveyor, and specialty chains. Duplex silent chains (Figure 2-18) have teeth extending on both sides of the pitch Une to permit the chain to run on serpentine drives where sprockets engage both sides of the chain. 

Link plate and sprocket wear is a consideration in designing silent chains. The link plates engage the sprockets instead of rollers, bushings, or full links. Excessive wear of the mating surfaces of silent chain link plates and sprocket teeth can cause erratic action and increase noise and vibration. 

Joint wear is a major consideration in desigrung silent chains. As the chain mns over the sprockets, the joints flex. Material is worn off the joint components and the chain gets longer. The chain then rides farther out on the sprocket teeth. This can increase noise and rednce efficiency. 

Tensile forces are transferred from the sprocket teeth to the joints through the driving hnk plates (Figure 3-32). The holes and the crotch in the hnk plates are significant stress risers. The driving link plates are primarily tensile members in silent chain. They are not subjected to much bending. 

Sprockets for roller chain and silent chain are normally made from steel or cast iron with machine-cut teeth. The woiking surfaces of the teeth are usually highly finished. Sprockets for engineering steel chains are generally made from steel or cast iron and the teeth are often flame-cut or cast. Sprockets for flat-top chain may be made from steel, cast iron, or plastic. The teeth are usually machine-cut on steel and cast iron sprockets and molded on plastic sprockets. These are generalities, and exceptions are not hard to find. That is especially true with engineering steel... 

There are many similarities between the teeth of sprockets for roller chain, silent chain, the various engineering steel chains, and flat-top chains, and yet there are important design and conceptual differences. There are also basic differences in the terminology of design factors and even in the way the teeth are expected to interface with their chains. 

As silent chain wears, the effective pitch increases and the chain wraps a larger pitch diameter farther out on sprocket teeth. Whrai elongation becomes excessive, the chain may begin to skip or jump sprocket teeth, damaging the chain or sprockets. The estimated maximum permissible chain elongation, in percent, is 200IN, where N is the nnmba- of teeth on the larger sprocket. 

Many roller and silent chains can be easily placed on the sprockets of a drive by hand. Pull the ends of the chain together around one sprocket with the rollers seated in the sprocket teeth. Hold the ends in place on the sprocket and connect the chain endless as described earlier. Figure 14-25 shows the final connection on a roller chain drive. 

Inspect the sprockets of roller and engineering steel chains for unusual wear on one side of the teeth. Inspect the sprockets of silent chains for uneven wear across the face of the teeth. Refer to Table 15-1 for more information. 

Inspect the drive for dirt packed between the sprocket teeth and the rollers of roller or engineering steel chains. Inspect for dirt packed between the sprocket teeth and the link plates of silent chain. Dirt in these spaces can stretch the chain or damage rollers. Refer to Table 15-1 for more information. 

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