6. Large Pitch Conveyor Chains
Selection and Handling (1) The chain speed of a scraper application is slow, 0.3 to 0.6 m/min., and 3 m/min. in the bucket application. The chain tension is the highest dur- ing the test period, before water is poured into the tank. Before water is poured into a 40-m tank, one chain is exposed to tension of 10 kN. (2) 403 stainless steel chain has sufficient corrosion resistance for most sewage facilities. If there is a high concentration of chlorine (as found in sea water, for example), if there are high levels of sulfur from hot springs, or if the tanks are contaminated, 304 stainless steel should be used, at least for side plates. Chains for Special Applications Chains used in water treatment applications are operated at low speeds and not subjected to any heavy shock loads. It is not necessary in this application to consider chains with tensile strength greater than 19 tonf. For that reason the following chains were developed: (1) ACR 810 Chain is a small chain made of 403 stainless steel. It has a ten- sile strength of 10 tonf. This was the first chain to be used in scraper applications to be equipped with rollers. The rollers reduce wear on the sprocket and the chain. Insert-tooth sprockets have been developed for this chain as well. (See Figure 6.30.) (2) Engineered plastic chain (ACP Chain, Figure 6.31), developed in the United States, is a light-weight chain with high corrosion resistance. It does not have rollers (similar to cast iron chain). Due to its light weight (one-half to one-fourth the weight of stainless steel chain), installation is relatively simple. One of the problems with this chain is that engineered plastic expands and contracts as the water temperature changes. Therefore, it is difficult to keep the chain under constant tension. Tensile strength (25 to 40 kN) is much lower than either cast iron or stainless steel chain.
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