Wear
The effect of wear on a roller chain is to increase the pitch (spacing of the links), causing the chain to grow longer. Note that this is due to wear at the pivoting pins and bushes, not from actual stretching of the metal (as does happen to some flexible steel components such as the hand-brake cable of a motor vehicle).
With modern chains it is unusual for a chain (other than that of a bicycle) to wear until it breaks, since a worn chain leads to the rapid onset of wear on the teeth of the sprockets, with ultimate failure being the loss of all the teeth on the sprocket. The sprockets (in particular the larger of the two) suffer a grinding motion that puts a characteristic hook shape into the driven face of the teeth. (This effect is made worse by a chain improperly tensioned, but is unavoidable no matter what care is taken). The worn teeth (and chain) no longer provides smooth transmission of power and this may become evident from the noise, the vibration or (in car engines using a timing chain) the variation in ignition timing seen with a timing light. Both sprockets and chain should be replaced in these cases, since a new chain on worn sprockets will not last long. However, in less severe cases it may be possible to save the smaller of the two sprockets, since it is always the larger one that suffers the most wear. Only in very light-weight applications such as a bicycle, or in extreme cases of improper tension, will the chain normally jump off the sprockets.
The lengthening due to wear of a chain is calculated by the following formula:
M = the length of a number of links measured
S = the number of links measured
P = Pitch
In industry, it is usual to monitor the movement of the chain tensioner (whether manual or automatic) or the exact length of a drive chain (one rule of thumb is to replace a roller chain which has elongated 3% on an adjustable drive or 1.5% on a fixed-center drive). A simpler method, particularly suitable for the cycle or motorcycle user, is to attempt to pull the chain away from the larger of the two sprockets. Any significant movement (e.g. making it possible to see through a gap) probably indicates a chain worn up to and beyond the limit. Sprocket damage will result if the problem is ignored.
Read more about this topic: Roller Chain
Famous quotes containing the word wear:
“For something is amiss or out of place
When mice with wings can wear a human face.”
—Theodore Roethke (1908–1963)
“The hat is not for the street: it will never be democratized. But there are certain houses that one cannot enter without a hat. And one must always wear a hat when lunching with people whom one does not know well. One appears to one’s best advantage.”
—Coco Chanel (1883–1971)
“We never really are the adults we pretend to be. We wear the mask and perhaps the clothes and posture of grown-ups, but inside our skin we are never as wise or as sure or as strong as we want to convince ourselves and others we are. We may fool all the rest of the people all of the time, but we never fool our parents. They can see behind the mask of adulthood. To her mommy and daddy, the empress never has on any clothes—and knows it.”
—Frank Pittman (20th century)