Sprockets

Most P/M parts weigh <2.27 kg (5 lbs), although parts weighing as much as 15.89 kg can be fabricated in conventional P/M equipment. Many early P/M parts such as bushings and bearings were very simple shapes, in contrast to the complex contours and multiple levels often produced economically in the 1990s. The P/M process is not shape-sensitive and normally does not requke draft. Parts such as cams, gears, sprockets, and levers are economically produced. 

A more permanent installation is provided by a chain-driven sampler, widely used in paper (qv) and steel (qv) mills, manufactured as the E Sampler by QCEC (20). A cup, which is attached to a chain positioned perpendicular to flow, travels down through the Hquid flow and returns to the upper sprocket, where the sample is drained into a container. Flow-proportional timers can be installed to change the rate of sampling with flow rate (see Flow l asurel nt). 

The traveling-grate furnace requires less labor, increases the output per unit of grate area, and produces more uniform product than the WetheriU. furnaces. The traveling grate is an endless chain of cast-iron bars, driven by sprockets, which traverses a firebrick chamber. Anthracite briquettes are fed to a depth of ca 15 cm. After ignition by the previous charge, the coal briquettes are covered by 15—16.5 cm of ore/coal briquettes. The latter are dried with waste heat from the furnace. Zinc vapor evolves and bums in a combustion chamber and the spent clinker faUs into containers for removal (24,25). 

Bucket Elevators. In a bucket elevator, a series of buckets attached to an endless belt or chain are filled with material and lifted vertically to a head pulley or sprocket, where the material is dumped. The buckets are then returned back down to a tail pulley or sprocket at the bottom. Bucket elevators are not self-feeding. They must be fed at a controlled rate to avoid overfilling the buckets and damagiag the machinery. In the usual arrangement of a bucket elevator, the chain or belt path is vertical or steeply inclined ia a single plane. Special chain supported bucket systems that can travel ia two and three planes have been developed. 

The gravity take-up must be used when handling hot materials in order to maintain chain and sprocket tooth engagement, as the chain length changes with thermal expansion. 

Since it is good practice to maintain a selected inventory of spare parts for drives, economy can be achieved by standardizing conveyor drives throughout the plant. For example, intermediate speed reduction by means of V belts, sheaves or chains, and sprockets can frequently permit using the same speed-reducer size for several drives. Thus, it may be necessary to keep only one repair-stock speed reducer for a number of conveyors. 

The silicon-controlled rectifier with a dc motor has become predominant in adjustable-speed drives for almost all commonly used conveyors when speed adjustment to process conditions is necessary. The low cost of this control device has influenced its use when speed synchronization among conveyors is required. This can also be done, of course, by changing sheave or sprocket ratios. 

Spaced-Bucket Positive-Discharge Elevators Elevators of this type (Fig. 21-5b) are essentially the same as centrifugal-discharge units except that the buckets are mounted on two strands of chain and are snubbed back under the head sprocket to invert them for positive discharge. These units are designed especially for materials which are... 

Amongst the many other applications for acetal resins should be mentioned links in conveyor belts, moulded sprockets and chains, blower wheels, cams, fan blades, check valves, pump impellers, carburettor bodies, blow-moulded aerosol containers and plumbing components such as valve stems and shower heads. 

Belt Driers A belt drier consists of a set of hinged shelves between two endless chains. As the belt so formed travels on large sprocket wheels, its path lies within... 

The twisting rubber hoses or o ringed elbows which connect the rotating pan necks with pipe and the wear plate to the face of the stationary valve The condition of the high impact nozzles mounted on the cloth wash manifold and, for wet cake discharge, the sluicing manifold The support rollers which take the vertical load of the entire machine and the horizontal thrust rolls that maintain the rotating frame concentric The toothed rim and sprocket which drives the pan filter... 

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

Where a vertical lift is required, the most widely used equipment is the bucket elevator, consisting of buckets fitted to a chain or belt which passes over a driven roller or sprocket at the top end. Bucket elevators can handle a wide range of solids from heavy lumps to fine powders and are suitable for use with wet solids and slurries. 

Ketten-glied. n. link (or member) of a chain, -isomerie, /. chain isomerism, -kokken, m.pl. streptococci, -linie,/. catenary (curve), -moldktil, n. chain molecule, linear molecule, -polymer, n. chain polymer, linear polymer, -rad, n. sprocket wheel, -reaktion, /. chain reaction, -trieb, m. chain drive. 

A fresh start and the true beginning of bicycles becoming a popular means of transportation can be traced to around 1886 and the efforts of John Kemp Starley and William Sutton. With equal-sized wheels, tubular steel diamond-shaped frame geometry, and a chain-and-sprocket chain drive to the rear wheel, the safety bike looked much like the modern version. 

An 1869 patent by France s Barberon and Meunier foresaw today s deraillcurs. It described a mechanism that would shift a belt or chain sideways among three sprockets or discs. That same year, Barberon and Meunier also patented a primitive gear hub. 

There is no basis for the theory that only when pushing the whole stroke vertically do the muscles work efficiently, and that the backward-and-foiward foot movement over the top and bottom wastes energy. Certainly, there is some efficiency loss, but it is minimal. Toe clips and better variable gear systems have further minimized top-dead-center problems associated with the standard circular sprocket design. 

A force is required to rotate an object. The response to the force depends not only the size of the force, but also on the manlier in which the force is applied. A bicyclist must push down on a pedal to cause the sprocket to rotate. But if the shaft to which the pedal is attached is vertical, no rotation results. The greatest response occurs when the bicyclist pushes down on the pedal when the shaft is horizontal. The concept of torque is used to describe rotational motion. The bicyclist pushing down on the pedal when the shaft is vertical produces zero torque. The maxiniuiii torque is produced when the shaft is horizontal. In this case the torque is the product of the force and the length of the shaft. For any other position between vertical and horizontal, the torque is the product of the force, shaft length, and sine of the angle made by the shaft and direction of the force. A force develops power when linear motion is involved and a torque develops power when rotational motion is involved. The power developed by a force is the product of force and linear velocity (P = Fv) and the power developed by a torque is the product of torque and angular velocity (P = Tw). 

The term chain drive denotes a combination of chain and sprockets, with the sprockets mounted on rotating shafts. 

Drive sprocket is usually the sprocket that is provided with the shaft import power (usually the smaller diameter sprocket). 

Driven sprocket is the sprocket and shaft that the chain is transferring power to (usually the larger diameter sprocket). 

Center distance is the length between the centers of the drive and drive sprocket shafts. 

Pitch diameter (of either the drive sprocket or driven sprocket) is generally on a theoretical circle described by the centerline of the chain as it passes over the sprocket. 

Angle of itirap or angle of contact is the angular section of a sprocket that is in contact with the chain. 

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. 

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. 

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. 

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

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