Silent Chain

Some of these are shown in Figure 3-26. Because most modern power transmissions use roller chains, silent chains or the offset link (Ewart) chains, these will be the only chain types discussed since they are quite important in oil field applications. 

In what follows, the pertinent design data are given for the roller chain, silent chain, and the offset link chain (API chain). 

In ehapter 1, the evolution of the chain industry was ouflined from the first cast chains to flat-top chains. This book outlines four major kinds of chain from an industry standpoint roller chains, silent chains, engineering steel chains, and flat-top chains. 

Silent chains are less affected by chordal action and joint friction than other chains silent chains engage sprockets with reduced vibration, noise, and frictional losses. 

There are many similarities between the teeth of sprockets for roller chain, silent chain, the various engineering steel chains, and flat-top chains, and yet there are important design and conceptual differences. There are also basic differences in the terminology of design factors and even in the way the teeth are expected to interface with their chains. 

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. 

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]. 

There are six types of chains used for power transmission. These are roller, silent (inverted tooth), offset link (Ewart with bushing), detachable (open Ewart), pintle (closed Ewart), and bead,... 

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

To guide silent chains on their sprockets, a number of arrangements are used. They can, however, all be grouped under one of two heads flanged links as part of the chain, or flanged jaws of the sprockets. 

Silent chains are furnished in pitches varying from to 3 in. and in weights capable of transmitting from a fraction of a horsepower up to several thousand. They can be operated at speeds up to 3,500 ft/min, but, where long life and low maintenance are desired, should be held between 1,200 and 1,500 ft/min. Although they can be... 

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. 

Practically all sprockets used with silent chain are made with cut teeth. Those with up to 25 teeth are usually cut from a steel forging and are furnished with a solid hub. For sprockets with more than 25 teeth, a semisteel is used, and the sprockets are available in either solid or split form. 

As a protection for equipment against overload, sprockets are sometimes provided for silent chains with a shearing pin or a break-pin hub. A pin of a known strength is used, and an overload of sufficient magnitude shears the pin and leaves the plate free to turn on the hub. After the overload condition is remedied, a new pin may be easily inserted and the drive again made ready to operate. 

Shaft Centers. As in roller chains, the minimum distance between shaft centers for silent chains must, in order to provide tooth clearance, be greater than half the sum of the two sprocket diameters. On large-speed reductions, experience has shown that the center distance should not be less than eight-tenths the difference in diameters of the two sprockets. 

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. 

Small roller-chain wheels should be hardened when used on moderate and highspeed drives, very low-speed heavily loaded drives, and when operating under abrasive conditions or when the drive ratio is greater than 4 1. Steel silent chain pinions should be hardened. 

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. 

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].

Service Factors for Width-Silent Chain Driver [5]... 

Types of chains that will be discussed in this section are roller, leaf, and silent chains. 

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. 

Silent chains are similar to roller chains in that each has a master or connecting link to facilitate ease of installation and removal from a machine. They are usually made of high-carbon steel or heat-treated steel alloys. As a result, this type of chain provides trouble-free service for extended periods. 

The design consists of two hubs with sprocket teeth connected by a chain of the single-roller, double-roller, or silent type. 

Results of a chemical activation induced by ultrasound have been reported by Nakamura et al. in the initiation of radical chain reactions with tin radicals [59]. When an aerated solution of R3SnH and an olefin is sonicated at low temperatures (0 to 10 °C), hydroxystannation of the double bond occurs and not the conventional hydrostannation achieved under silent conditions (Scheme 3.10). This point evidences the differences between radical sonochemistry and the classical free radical chemistry. The result was interpreted on the basis of the generation of tin and peroxy radicals in the region of hot cavities, which then undergo synthetic reactions in the bulk liquid phase. These findings also enable the sonochemical synthesis of alkyl hydroperoxides by aerobic reductive oxygenation of alkyl halides [60], and the aerobic catalytic conversion of alkyl halides into alcohols by trialkyltin halides [61]. 

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