Engineering Steel Chain Sprocket Teeth

Engineering Steel Drive Chain Sprocket Tooth Form General 

H = BARREL HEIGHT OR ROLLER DIAMETER Dr = ROOT DIAMETER 

FIGURE 4-36 Standard tooth form for engineering steel offset sidebar drive chain. 

The first five terms are given dimensions. All except N, are obtained from the ASME B29.10 standard. The remaining dimensions that define the tooth form will be discussed in the following paragraphs. 

The main purpose of the pocket radius is to reduce the stress concentration between the working face and the bottom diameter. The pocket radius should intersect the working face below the point where the loaded roller makes contact with the tooth. The maximum pocket radius can be equal to the roller radius, but it is better to have a pocket radius smaller than the roller radius. 

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In an engineering steel chain with rollers, the load from transmitting power or conveying materials is first transferred from the working faces of the sproeket to the outside of the chain rollers, or vice versa. In drives, there also may be an impaet foree when the sprocket teeth pick up rollers from the tight span of the chain. 

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. 

If the speed is slow (in the drip or manual lubrication range), the small sprocket may have as few as nine teeth. Even then, the chain and sprockets may have more power capacity than cold rolled shafting when the small sprocket has only nine teeth. The small sprocket in a typical engineering steel chain drive should have about 12 teeth. If speeds are high (in the oil stream lubrication range), the small sprocket should have at least 15 teeth. 

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. 

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. 

Idler sprockets for roller and engineering steel chain drives wear in a different way. There is not much pressure on the working faces of the teeth on an idler sprocket. So idler sprockets usually wear at the bottom of the tooth space. A badly worn idler sprocket for roller chain is shown in Figure 15-2. When the tooth space is worn deeply enough, the chain rollers may bind against the tooth tips as they enter and leave the idler sprocket. 

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