Chain & Sprocket Systems and Maintenance

Chain and sprocket drives of one form or another have been driving machines and conveying materials for over a thousand years. The chain manufacturing industry has developed numerous types and sizes of drive chains. Although it is a mature form of power transmission, there are still many industrial applications for which drive chain is suited. It is economical, resistant to shock loads, easy to install, has the ability to transmit high torque, operates in hostile environments, and is efficient. Chain and sprocket drives are highly engineered and manufactured within close tolerances.

Chain Function Chain can be grouped into two functions: material handling and power transmission. Some chains are used for both purposes. If the chain is transferring or conveying raw material or finished products, it is considered a material handling chain. If the chain’s primary purpose is transferring power from one shaft to another, it is for power transmission. In some applications, special attachments—for moving materials—are part of a power transmitting chain’s construction. The chain drive system consists of a driving sprocket, one or more driven sprockets, and a loop of chain. A sprocket is a wheel that on the outside diameter has evenly spaced, uniformly shaped teeth, which provide positive engagement with the chain. Because the chain is hinged at every link, it is able to wrap around the sprockets’ teeth, connecting the driver and driven units. Power and torque are transmitted from the drive sprocket mounted on the shaft of the prime mover, and then connected to one or more driven sprockets by the chain. As the chain drive system operates, every link in the chain undergoes “cycle loading.”

The working or tight side of the chain is under full tension, while the slack side is under minimum tension. The sprockets, turning on their respective shafts and connected by a chain, deliver the power or transfer the load to accomplish work. During operation, a phenomenon known as “chordal action” occurs in a chain drive system resulting from the fact that chain link is a straight-line segment trying to follow the circular path of the sprocket pitch diameter. Because the line of approach of the chain is not tangent to the pitch circle, it is lifted to the top of the circle and then dropped down. There is a surge of force in the chain caused by the change in speed as it makes this rise and fall. An increase in chain velocity can aggravate this event, resulting in vibration and pulse loading in the system. Excessively worn parts may amplify this effect. Standard roller chain is the most common type of drive chain used in industry. ANSI & ISO maintain standards for design, dimensions, and interchangeability. Pitch, distance from center of pin-to-pin, roller diameters, width, and load ratings are defined. Standard roller chain is made up of alternating roller links and pin links. Each link is constructed by placing rollers onto bushings and pressing roller link plates onto the bushings. The side plates into which two pins are pressed, hold the rollers and bushings in place. The assembly is secured by the press fit between the pins and the plates (often accompanied with a rivet on the end of the pins), spring clips, or cotter pins through holes in the end of the pins. Chain & Sprocket Alignment Proper alignment within the recommended tolerances prevents premature component wear. It also reduces the loads that are applied to the supporting shafts and bearings. A simple straight edge, wire, or laser system can be used to align the sprockets. Sprocket shafts should be parallel. The offset of sprocket faces should be <.0625"/foot of shaft centerline distance. Angularity should be

Conclusion The sum of parts is equal to the whole when it comes to a roller chain drive system. Worn parts that are not replaced correctly in a timely manner will cause a ‘chain-reaction’ resulting in ancillary damage to connected components, increased labor, higher maintenance costs, more unscheduled downtime, and potentially an inferior manufactured product. Check your chain & sprocket drives often.