Types of Sprockets

For this reason, sprockets normally should be obtained from the manufacturer of the chain unless chains and sprockets are manufactured to a tight and accepted standard such as ASME B29.1. Wear causes the chain to elongate and alters the form of the sprocket teeth. Thus, worn sprockets should always be replaced when a new chain is installed (or vice versa). 

Sprockets are made in various ways and from many materials. Manufacturing methods and materials are chosen to produce a tooth form with the precision and surface finish that is needed. Added processing, such as heat treatment, is done to give the load-carrying capacity, rotating speed capability, and service life that the sprockets must have. 

The two basic types of sprockets— precision and semiprecision—are mainly classified by the way they contact and operate with the chain. The two types may be subdivided by materials and manufacturing methods. Other factors include economics and the degree of accuracy required by the chains with which the sprockets are paired. 

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 

Sprockets with machine-cut teeth are smoother and quieter in operation. They are commonly used in moderate- to high-speed drives. Sprockets with cast or flame-cut teeth are less costly, and they give adequate life when used on slow-speed drives and conveyors. The various kinds of sprockets that are furnished by manufacturers are reviewed in the following sections. 

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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. 

The type of sprocket to be used depends entirely upon local or load conditions. The steel plate without hubs is the cheapest and is furnished for bolting to suitable hubs or flanges. The cast-iron or steel type fitted with hubs is made for direct mounting upon shaft and is fastened in place by either keys or setscrews or a combination of both. The split type is almost a necessity when the hub is mounted on a shaft with other pulleys or sheaves. Its construction facilitates installation and removal, but because of its extra cost it is usually not recommended except when solid hubs cannot be installed. The double-duty sprockets are made with steel rims or plates that may be removed or replaced without disturbing the hub, shaft, bearing, etc. Plates and hubs can be obtained either solid or split. They are particularly adapted for jobs requiring changing of drive ratios or where replacements must be made quickly. 

Split sprockets (Figure 4-18) are sometimes used when the sprocket must be mounted between bearings. This type of sprocket can be installed and removed without disturbing the shaft and other parts of the machine. 

The major differences probably arise from the intended function of each type of sprocket tooth. For example, the sprockets for roller chain absorb pitch elongation from wear in one way, but the sprockets for engineering steel conveyor chain absorb that same pitch elongation in a very different way. 

Two different types of sprocket and gear wheel (a) includes assembly this is made of steel and produced by machining. The individual teeth are cut. It is necessary to divide it in to two elements due to production technique reasons, (b) does not include assembly this is produced from sintered metal, the teeth being sintered in accordance with the required tolerance and surface quality the advantages being no waste material, short processing time and no assembly. 

The wire-flange sprockets (Figure 3-35c) are assembled by simply inserting a preformed, crimped wire of the proper number of teeth and pitch along the edges of the teeth of the sprocket. This type of guide is recommended particularly in the case of independently mounted electric motors that are not likely to stay in accurate alignment. 

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. 

The Ewart links are usually cast in one piece with no separate bushings or pins. The material used is generally malleable iron, although steel is also extensively employed. As a general rule the maximum speed at which this type of chain is operated is about 400 ft/min, and even at that speed it is apt to be quite noisy. Because the links used in this chain are not machined and the pitch is not very uniform, the teeth of the sprockets used with them are, in turn, generally not machined. 

There is a wide variety of commercially available sprockets. While they may vary in design, methods of manufacture, and materials of constmction, they all have some common features. They will all have hardened teeth designed to mate with a specific type of chain, sufficient web strength to effectively transmit their rated horsepower or torsional forces, and a boss or hub that can be bored to the mating shaft s diameter. 

A variety of mounting configurations are used to attach sprockets to their mating shafts. The most common has a tapered keyway that acts as a wedge when the key is driven in. No setscrews are provided with this type of key installation. 

The "planar loop" extractor provides for shallow to intermediate bed depths and is offered by one American and several European companies. In this type the extractor compartments move along a path in a vertical plane. Chains driven by sprockets are used to move the compartments along the path (around the loop). Vertical tower types of these extractors have also been built and operated successfully however, building and maintenance requirements appear to have prevented their continued use. The horizontally elongated type of loop or belt extractor is offered by two European and one American supplier. The vertically elongated configuration appears to have been abandoned. 

Tail section A term used in both belt and chain conveyor work to designate that portion of the conveyor at the extrane opposite end from the delivery point. In either type of conveyor it consists of a frame and either a sprocket or a drum on which the chain or belt travels, plus such other devices as may be required for adjusting belt or chain tension. 

Type of drive can be an internal rotating shaft with three blades attached. The shaft extends outside and can have a driven pulley. It generally has a sprocket and chain drive, a gear box or a VFD motor. External girth gear drive can also be provided to the rotary screen if there are more than one concentric screens for separation of two-or three-sized particles. This will depend on length and diameter of each screen and may not always be possible. 

Another type of simultaneous stretching may be accomplished with a pantograph type stretching process (32). This expandable frame rides on the tenter rails (Fig. 12). The clips are initially packed close together by a drive sprocket at the entrance to the tenter oven. After transporting the web through the preheat zone, the pantograph is expanded in the machine direction at... 

Crawler crane means equipment that has a type of base mounting which incorporates a continuous belt of sprocket driven track. 

The most common type of chain tightener is an idler sprocket mounted on an adjustable bracket, either manually adjusted or spring loaded. Rollers, shoes, and vibration dampeners are also used for regulating chain excess tension. The idler design and installation should be capable of providing enough adjustment to remove two full pitches of chain. This avoids the need for a less desirable offset link. 

Type A sprockets are flat and have no hub at all. They are usually mounted on flanges or hubs of the device that they are driving. This is accomplished through a series of holes that are either plain or tapered. 

Type B sprocket hubs are flush on one side and extend slightly on the other side. The hub is extended to one side to allow the sprocket to be fitted close to the machinery that it is being mounted on. This eliminates a large overhung load on the bearings of the equipment. 

Type C sprockets are extended on both sides of the plate surface. They are usually used on the driven sprocket where the pitch diameter is larger and... 

Type D sprockets use anA sprocket mounted on a solid or split hub. The type A sprocket is split and bolted to the hub. This is done for ease of removal and not practicality. It allows the speed ratio to be changed easily by simply unbolting the sprocket and changing it without having the remove bearings or other equipment. 

This chapter is intended to give the reader an overview of the various standardized types of chain and their uses. Chains may be classified in many different ways. From a theoretical viewpoint, ehain is a eontinuous flexible rack engaging the teeth on a pair of gears. Certainly, a sprocket, being a toothed wheel whose teeth are shaped to mesh with a chain, is a form of gear. From a viewpoint based on its history and development, chain is a mechanical belt running over sprockets that ean be used to transmit power or convey materials. Neither of these aspects relate to the praetieal standpoints of either the producer or the user of the product. 

Standard roller chains are defined as pitch proportional, which makes them different from othCT types of chains with rollers. The ASME standards nominal dimensions for these chains are approximately proportional to the chain pitch. The pitch of a roller chain is the distance betweai the centers of adjacent joint members. The three most important roller chain dimensions are pitch, roller diameter, and inside chain width, as indicated in Figure 2-5. These dimensions detramine the fit between the chain and the sprockets. 

The American National Standard, ASME B29.2, Inverted Tooth (Silent) Chain and Sprockets covers one type of silent chain for drives. The standard hsts nine sizes of silent chain with pitches from 0.1875 in. to 2.0 in., and widths from 0.25 in. to 20 in. This standard mainly standardizes the sprocket... 

Bar-link chains are sometimes called block and bar or steel block chains. Figure 2-24 shows a typical example of a bar-link chain. This type of chain usually consists of two outer sidebars, one center bar, and two pins making np a two-link section. Bar-hnk chain usually does not have bushings, with the center bar flexing directly on the pin. Sprocket contact is with the ends of the center bars. No ASME standard cnrrently exists for bar-link chains. 

Wear is a most important consideration in designing silent chains, just as it is in other types of chain. The two major concerns in designing silent chain are joint wear, and link plate and sprocket wear. 

Offset sidebar drive ehain is a series of identical offset links. The pins are free to articulate in the bushings and the rollers are free to turn on the bushings. The rollers are uniformly spaced so they can engage the teeth on a sprocket and transmit motion and force. The components of such a chain are shown in Figure 3-36. The diameter of the rollers in this type of chain is less than the sidebar height. 

Some type D sprockets consist of a solid hub and a split plate (Figure 4-2). Other type D sprockets are made with both the hub and the plate split (Figure 4-7). In the manufacture of any split sprocket, care must be taken to prevent any variation of the pitch at the split line. Figure 4-7 shows special dowels on the split for this purpose. 

FIGURE 4-21 Types of cast iron sprockets for engineering steel chains. 

Another type of special-purpose sprocket is shown in Figure 9-34. This is a compensating sprocket. It is used to drive the head shaft in conveyors that use long-pitch engineering steel chains. 

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