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CHAIN DRIVES II Lecture #18 Course Name : DESIGN OF MACHINE ELEMENTS Course Number: MET 214. Chains are designed for 3 basic applications: 1) Transmitting power 2) Conveying or moving parts and materials by utilizing the linear motion inherent in chain drives
Course Name : DESIGN OF MACHINE ELEMENTS
Course Number: MET 214
1) Transmitting power
2) Conveying or moving parts and materials by utilizing the linear motion inherent in
3) Timing or synchronizing motion including synchronizing the movement of values in engines
Due to the diversity of the applications, several different types of chains are available. A few examples of the different types of chains in use are shown in the figures on the subsequent slides.
Major types of chains have been illustrated on the previous slides. Only roller chains will be discussed in detail.
The components of a roller chain are shown in the figure below.
A precision steel roller chain is a series of journal bearings held in precise relationship to each other by the connecting link plates.
Chains are not endless. One link is always detachable, so the chain can be mounted and dismounted at will. Each roller link requires a pin link for assembly. A chain normally has an even number of links. If an odd number of links is required, an offset link can be used. An offset link is a pin link and a roller link combined. Offset links wear faster than straight links and should be avoided when possible.
All chains are classified according to pitch, roller diameter, and width between roller links. Collectively, these dimensions are known as the gearing dimensions since they determine the form and width of sprocket teeth. The key dimensions are shown in the figure below. On a chain, the width is an internal dimension because it corresponds to the width of a sprocket tooth.
The table on the next slide shows major proportions for medium to large roller chains
(designated as RC) . The right hand figure in the chain number stands for size. The number 0 stands for medium to large chains. The numbers to the left of the zeros in the table below denote the number of 1/8 inches in the pitch. The pitch is based upon multiples of 1/8 inch. For example; as shown in the table:
Double pitch chains, which mesh with every other tooth, are intended for slower speeds and lighter loads that the equivalent single pitch chain. A double pitch chain is shown in the figure below.
Double pitch chains will not fit sprockets made for standard chains because of the difference in chordal pitch of the sprockets. Double pitch chains are useful on low speed equipment at long center distances, where cost and weight must be minimized.
The compactness of rollers chains is further enhanced by the use of double, triple and four strand chains. The rollers in different strands are aligned by means of a common pin. The figure below shows a chain with double strands.
Due to the torsional flexibility plus low weight in belt drives, flat belt drives can be used in almost any shaft position. Due to the effects of gravity, the shafts of chains drives should be horizontal but not necessarily on the same level. To avoid interference, the slack slide should be the lower strand. The figures below show good and bad design practices.
Provisions to take up excess slack should always be included in the design. Two methods are available.
1) Change of center distance between shafts
2) application o f chain tighteners
Adjusting center distance is often a simple matter of moving an electric motor or adjusting the bearings. Chain tighteners become necessary when two or more sprockets rotate on fixed centers. Proper location of chain tighteners is illustrated in the figure provided below.