Chains 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... 

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

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. 

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... 

The tooth form for flat-top chain sprockets is covered by ASME B29.17 and will be discussed later in the design section of this chapter. This section considers sprockets only for standard flat-top chains described in this book. The only flat-top chains covered in this book are unit link chains with IVi-in. pitch. Thus the number of styles of sprockets discussed here is very limited. 

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. 

Chain-sprocket interaction is very complex in theory. It can be even more so when the effects of wear and elastic deformation of the chain and sprocket under load are considered. A discussion of these effects is beyond the scope of this book. This book must limit the scope to the tooth forms and dimensions as specified by ASME B29 standards and accepted practice. The following sections discuss basic tooth designs for roller chain, silent chain, engineering steel chain, and flat-top chain. 

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... 

Standard dimensions for silent chain sprocket profiles... 

Engineering Steel Drive Chain Sprocket Tooth Form General... 

The sprocket tooth form for engineering steel drive chains is specified in the ASME B29.10 standard. A drawing of the tooth form and the equations for computing the main dimensions are shown in Figure 4-36. It differs from the tooth form for roller chain in that the pitch line clearance and bottom diameter are slightly smaller than the theoretical root diameter. These differences permit the use of a less precisely made tooth form for engineering steel drive chains than the machine-cut tooth form for roller chains. Engineering steel chain drives are often operated in locations where mud, dirt, ore, rock dust, etc. get into the chain. These drives are often exposed to the weather. Pitch line clearance and the undercut bottom diameter both help provide proper chain-sprocket action under such adverse conditions. 

Figure 4-36 also shows the important diameters of engineering steel drive chain sprockets and the equations for computing them. It is important that the bottom diameter not be larger than the root diameter. The difference is called undersize compensation. It is provided mainly to accept the possible buildup of material in the tooth pockets. It also allows for some production variation. The... 

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