Transmission chain drives

The dynamics of power transmission chain drives are not conducive to high-speed operation. Since proper installation requires some looseness in the chain, they tend to separate from the sprockets at higher speeds. In general, transmission chains are limited to a maximum sprocket speed of 3,600 revolutions per minute (rpm). 

Why do we use the word driver We tend to think that pumps are powered by r-r motors. However, some pumps are powered by internal combustion engines, or with turbines or hydraulic motors. Not always are pumps and drivers connected h a direct coupling. Some pumps are coupled through pulleys, chain drives, gearboxes or even transmissions. 

Power transmission chains provide a positive drive even when operated under very adverse temperatures (-60 to 600°F) and other environmental conditions. These pow er transmission systems are very flexible with regards to their field applications. In general, chain drives are primarily selected for low-speed and medium-speed service. Some silent chain designs may be used in high-speed serv ice [8,13]. 

Chain-drives normally are used to provide positive power transmission between a driver and driven unit where direct coupling cannot be accomplished. Chain-drives generally have two distinct running speeds driver or input speed and driven or output speed. Each of the shaft speeds is clearly visible in the vibration profile and a discrete narrowband window should be established to monitor each of the running speeds. 

There are two types of flexible intermediate drives used to transmit torsional power belt drives and chain drives. Flexible belts are used in industrial power transmission applications primarily when the speeds of the driver and driven shafts must be different or when the shafts must be widely separated. The trend toward higher speed primary drivers and the need to achieve a slower, useful driven speed are additional factors favoring the use of belts. In addition to V-belts, there are round belts and flat belts. Chain drives are typically used in applications where space is limited or obstructions prevent direct coupling of machine-train components. 

Unlike V-belts, chain drives do not rely on friction to deliver power. As a result, transmission of power is positive (i.e., no slippage) and in many ways resembles the action of gears. A chain is constmcted in such a way that it provides a connection between the teeth of the drive pinion and driven sprockets. 

Since chain drives are designed to provide positive transmission of power from the pinion to the driven sprocket, there is little loss of efficiency. When properly installed, chain drives can approach 98 per cent efficiency. However, they are somewhat limited in speed and span. 

Properly designed chain drives can transmit almost unlimited power. As a result, this type of drive is suitable for low- to moderate-speed applications where the transmission of high force is needed. 

Chain drives and transmission gears are enclosed or properly covered. 

Chain drives do not require pre-tension between shafts for power transmission, thereby reducing bearing loads. 

Roller chain drives are used in a wide range of power transmission applications for all basic industries such as food processing, materials handling, oil field equipment, construction, agricultural equipment, and machine tools. 

Before writing the revision for Chains for Power Transmission and Material Handling, John wrote several magazine articles and contributed a chapter on chain drives to a mechanical engineering handbook. 

Link-Suspended Basket Centrifuges In centrifuges with diameters larger than 762 mm (30 in), the basket, curb, curb cover, and drive form a rigid assembly flexibly suspended from three fixed posts (also known as a three-column centrifuge). The three suspension members may be either chain hnks or stiff rods in ball-and-socket joints and are spring-loaded. The suspended assembly has restrained freedom to oscillate to compensate for a normal out-of-balance condition. The drive is vertical with more efficient power transmission compared to the base-bearing type. 

Drive Types. Variable-speed drives may be selected on a chain-strength basis when operating with infrequent high chain loads such as from a torque convener, variable-speed motor, or multispeed transmission. 

This section is an overview of flexible drive chains and sprockets. It provides the basic knowledge required to install, operate, and service this means of power transmission. 

Drives such as pumps, fans, blowers, and many other types of machinery commonly employ silent chains as their prime source of power transmission. Because of their unique design, silent chains provide the most positive means of traction. Because of this, they often are used in important applications such as timing drives on critical equipment. 

The drive sprocket is injection-moulded in rubber-toughened PA6.6, which is resistant to repeated impact over a wide range of temperatures, and which shows excellent abrasion resistance. The plastic sprocket absorbs the shock of gear changes better than metal, causes less wear on the chain, and provides a quieter ride. The polymer is resistant to lubricants and other liquids. Reduced firiction improves power transmission and, coupled with a lower weight, results in better performance. 

In order to measure a Mossbauer spectrum one has to detect recoilless absorption or emission of a selected y radiation as a function of the Doppler velocity of the sample and a reference material relative to each other. In the most common case of transmission geometry, absorption of the y rays is measured, and the reference material is a standard source, which is moved. Thus, the most important components of a Mossbauer spectrometer are a Doppler velocity drive system and an energy selective y detection chain with appropriate recording system. 

The drive chain wheel at the head of the elevator is of three-piece segmental construction and has no teeth, force transmission being effected solely through friction, The great weight of the chain and buckets ensures that high frictional... 

Simple apparatus may be connected directly to the shaft of a motor or a turbine. More often, there will be some form of transmission device between the driver and the load. This device may be a coupling, a gear train, a belt, or a chain. The following discussion will not cover variable-speed drives. Most of the safety considerations for the fixed-ratio devices treated below apply to all moving and rotary equipment. 

The major uses of the four types of chain fisted above are in drives (power transmission), conveyors, bucket elevators, and tension hnkages. Each of these applications is discussed in detail in subsequent chapters. Some standard chains are designed for use in only one of these application. However, some chains are designed so that they can be adapted to more than one use. 

In the power transmission field, standard roller chain applications range from fractional horsepower drives to those requiring in excess of 1000 hp. The V4-in. pitch chains, weighing less than 2 oz./ft., have been applied to such intricate machines as microfilm projectors. On the other hand, large-pitch multiple-strand chains, weighing over 50 Ib./ft., meet the requirements of such heavy-duty service as oil field equipment (Figure 2-9). 

Double-pitch power transmission roller chains are particularly applicable to power drives where speeds are slow, loads are moderate, or center distances are long. For such applications, the longer pitch results in a lighter and less expensive chain. 

Now let us consider the advantages of chains from the standpoint of drives. Chains have certain advantages, in addition to those just named, over other types of power transmission equipment. 

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