Silent Chain Power Ratings

The fatigue limit is more than just a theoretical number. It is the basis for the low-speed part of the American Chain Association (ACA) power ratings for roller, engineering steel, and silent chains. Those ratings are given in chapters 5-7 of this book. Published values for maximiun allowable working load are usually equal to the fatigue limit. 

Silent chain power capaeity is rated in units of power per unit of chain width. For any given pitch, increased chain width results in greater chain strength, increased power capacity, and increased cost. When several chain widths satisfy the specified requirements, narrower chain widths are generally more readily obtained and less costly. Wider chains will provide a more robust, shock-resistant drive. 

The fatigue limit is a most important consideration in designing silent chains. The lower-speed part of the power ratings for silent chains is based on a minimum fatigue limit. 

Lubrication and environmental considerations are not discussed here. Silent chain drives generally run at higher speeds than other types of chain drives. Oil bath or oil stream lubrication is usually specified in the power ratings. These types of lubrication require a casing, which shields the drive from most contaminants. 

The authorship of the first combined manual in 1982 was a combined effort of the technical committee and other representatives of the member organizations of the ACA over a period of 25 years. The second edition is the fruit of an additional 20 years of research, testing, and analysis by the member companies of the ACA. New power ratings were developed for roller and silent chains. A new chapter on flat-top conveyor chains was developed and written. And new expanded information on installation, lubrication, and maintenance was included. 

Chapter 5 has new increased power ratings for roller chains. It also has new information on selecting drives with a life of other than 15,000 hours. Chapter 7 has new increased power ratings for silent chains. All of the chapters on selecting chain drives were reorganized to make the selection steps similar. 

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