Usually, sprockets with 12 teeth are used in low-speed bucket elevators (chain speed less than 45 m/min.). High-speed bucket elevators normally require 24-tooth sprockets. It is important to choose a sprocket with suitable pitch-line clearance. Excess conveyed material may accumulate in the bottom of the casing, which can cause accelerated wear. Worn chain and sprockets will not engage correctly; the sprockets may have to be replaced. Sometimes, welding material onto the tooth at the point of excessive wear will restore the sprocket, but it is not recommended. Additionally, this procedure is extremely difficult with the sprocket that is located at the top of the bucket elevator. Even sprockets with hardened teeth are subject to excessive wear in bucket elevators, due to the abrasive nature of conveyed materials. For example, in cement conveyors, there is a point of sprocket hardness at which wear is virtually eliminated. However, it is impractical and expensive to make such hard teeth in standard sprockets. In the 1980s, detachable-tooth sprockets were developed, which permit the replacement of the tooth part only. The body of the sprocket remains on the shaft, which reduces repair time and costs. By using special materials in the tooth insert, high tooth hardness is achievable, and therefore, wear life is increased. Use of detachable-tooth sprockets is increasing, especially in the cement industry.
