Drive Chains

Co.). In direct contact with the scraped surface is the process fluid which may deposit ciystals upon chilling or be extremely fouhng or of very high viscosity. Motors, chain drives, appropriate guards, and so on are required for the rotating element. For chilling service with a refrigerant in the outer shell, an accumulator drum is mounted on top of the unit. 

Roller conveyors are quite frequently powered, the simplest method being use of a pressure belt in contact with the lower surface of the rolls. A special ripple belt with raised pads is capable of starting up the load but does not build up excessive blocked pressure if the line fills up. Other similar drives are available, with varying degrees of control over the applied power. Most expensive of the powered roller units are those in which each roll is equipped with V-belt or chain drives. Pusher bars suspended from overhead chain conveyors may also be used to move containers along a roller hne. 

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. 

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. 

Between the development of the chain-drive bicycle in the 1880s, and before Henry Ford popularized... 

For a situation where large torques are involved, such as a bicycle drive, a chain linkage is superior to a belt. A person putting all his or her weight on a pedal probably would make most belt systems slip. Another advantage of a chain over a belt is that a chain is more efficient, mainly because it does not require any ambient tension. The return side of a chain drive has only enongh tension to snpport itself. Furthermore, the chain links are equipped with rollers, which can rotate as they contact the teeth, reducing the frictional forces and wear. 

For designation of rotation and discharge, For motor position, belt or chain drive,... 

Figure 12-119C. AMCA standard motor positions for belt or chain drive centrifugal fans. Reprinted from AMCA Publication 99-86 Standards Handbook, 1986, Standard AMCA No. 99-2407-66, with written permission from Air Movement and Control Association International, Inc., 1986. All rights reserved.)...

Variations in required speed or speed increase or decrease from the driver may be handled by gear boxes, belt or chain drive, magnetic drive, magnetic or fluid couplings, or variable-speed motors. 

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]. 

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

Where accurate and higher-speed chain drives are required, roller chains are used. Roller chains are fundamentally a development of the block chain in which rollers have been inserted. The addition of the rollers increases the overall efficiency of the chain and permits it, in its ordinary form, to be operated at high speeds a rate of 600-800 ft/min is usually recommended. The links can be furnished in a multitude of shapes, one common form being the offset shown in Fig. 3-28. This type of chain is furnished in pitches, i.e., center distance between rollers, from up to 2 in. and in breaking strengths, dependent upon the materials and the construction used, from about 10,000 to 200,00 lb [8,11]. 

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. 

For silent chain drives, pinions with 21 teeth or more are recommended for general applications and at least 25 teeth are recommended for high-speed applications. The recommended minimum is 17 teeth. 

Properly engineered silent chain drives having ratios as great as 12 1 will perform satisfactorily. However, it might be more economical to consider a compound drive where the ratio is 8 1 or larger. 

Chain Tension. All chain drives should have some means of controlling the chain sag caused by normal joint wear. This is of utmost importance when the drive is subject to shock or pulsating loads or to reversals in direction of rotation. The most common methods taking up chain slack are (1) drive units mounted on adjustable base plat, slide rails, or similar units these are used extensively in motor-driven applications and (2) the use of adjustable idlers (Figure 3-40) and chain tensioners. 

With large ratios, the angle of contact becomes smaller and the number of teeth engaged with the chain decreases. For angles less than 120°, 0 increasingly becomes a critical factor in the design of chain drives. 

Roller Chain. Table 3-18 gives the typical service factor for roller chain drives [5], Table 3-19 gives the basic roller chain design dimensions for ANSI standard roller chains by ANSI chain number [14]. 

Silent Chain. Table 3-21 gives the typical service factors for silent chain drives [5]. 

Tables 3-22 and 3-23 give the horsepower ratings per inch width for silent chain drives [5,15].

Drilling Applications. Drilling equipment utilizes chain drives in various applications on the drilling rig itself and its auxiliary equipment. The drives for this type of equipment are called compound drives. Such drive equipment are subject to vary severe operational loads. Table 3-24 gives the typical service factors for these chain drives [16]. 

Auxiliary brake chain drives have been omitted because of the Indefinite nature of the load. Each manufacturer has established successful drives, but these are suited to specific conditions which cannot be reduced to simple terms. Most such drives violate the rules of chain speeds and loads and are successful only because of the short duration of use and deviation from calculated loads. It is recommended that the drawworks manufacturer be consulted. 

The power is provided to the drawworks by the prime movers at the master clutch (see Figure 4-9) and is transmitted to the master clutch shaft via sprockets and roller chain drives. The speed and the torque from the prime movers are controlled through the compound. The compound is a series of sprockets, roller chain drives, and clutches that allow the driller to control the power to the... 

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. 

Unlike gear sets, there can be two distinctive tooth-mesh frequencies for a chain-drive system. Since the drive and driven sprockets do not directly mesh, the meshing frequency generated by each sprocket is visible in the vibration profile. 

Chains drive function in essentially the same basic manner as belt drives. However, instead of tension, chains depend on the mechanical meshing of sprocket teeth with the chain links. 

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. 

Like V-belts, chain drives are used to transmit power from a driver, such as an electric motor, to a driven unit. 

Typically, chain drives are used in applications where space is limited or obstmctions prevent direct coupling of machine-train components (e.g., timing chain in an engine). 

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. 

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). 

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. 

Like V-belts, chains tend to stretch during prolonged operation. When this occurs, excessive looseness permits the chain to separate from the sprockets. Therefore, periodic inspection of chain tension is essential for proper operation of chain drives. Excessive looseness can be corrected by removing one or more links from the chain. 

---