The following extracts from " Cassier's Industrial Management & Mechanical Handling " deals with malleable iron chains for conveyors, but as the chains can be used for other purposes also, the details below are of interest.

Although there are a considerable number of conveyor chains on the market, there are six types which are pre-eminently useful and successful, representing the survival of the fittest. They are all well-tried chains, having been on the market for at least a quarter of a century, quite long enough to prove their worth. These surviving types are the Ewart detachable or pinless chain, the Gray pin chain, the Ley bushed chain, the Ewart roller chain, the De Brouwer hot coke conveyor chain, and, finally, the steel bushed roller chain. The latter is much used for gravity-bucket conveyors handling coal in power houses ; it has been made up to three feet in pitch for exceptional duty.

The first three types are often employed single strand, whilst the last three are always used double strand. Some of these types of conveyor chains are also successfully utilized as driving chains ; but, generally speaking, for the latter purpose the chains are of shorter pitch and run at much higher speeds. The running speed of a conveyor chain ranges from less than one foot per minute up to a maximum rarely exceeding 200 feet per minute.

As a rule, the chains enumerated are made of malleable cast iron, preferably cast from a reverberatory or air furnace, and not from a cupola ; because in the latter case the molten metal can absorb sulphur, silicon and other impurities from the coke. Malleable iron chains are not materially affected by a moderate degree of heat; so that they can be used successfully in connection with continuous drying oven and furnace work. Other materials sometimes utilized for making such chains are wrought iron drop forgings, manganese steel castings, gunmetal, phosphor bronze, brass and aluminium. All these alternative materials are much more expensive than malleable iron. The tensile strength of Ley's blackheart malleable iron is 50,000 pounds per sq. inch, and the elongation as much as 15 per cent. Cast steel can only be used for heavy links and the skin is very rough. Occasionally malleable iron links are galvanized to avoid corrosion.

Sprocket wheels for light duty are usually made of cast iron and cast from metal patterns ; but on severe duty chilled metal wheels give far better service and are more economical in the end, in spite of the higher first cost. Cast steel wheels are also used to a limited extent. Machine cut chain wheels are much more expensive than cast wheels and have to be made of soft metal; but small chain wheels in forged steel can be hardened after cutting and make a very good job. Cut wheels are only feasible when required in quantities, the cost being otherwise prohibitive.

For wheels subjected to exceptionally severe duty, working in grit and dust, cast manganese steel can be sometimes used to advantage, being exceptionally hard and durable. But it must be borne in mind that manganese steel sprocket wheels are not only high in first cost, but take a long time to make, the long delay in delivery being sometimes fatal to their adoption. The difficulty of machining manganese steel can be got over by casting a soft iron or steel bush in the boss, and this bush can then be easily bored and keywayed.

Most of these chains in various sizes are manufactured in quantities as standardized products by reputable and well-established firms, and are obtainable at short notice with the same facility as standard bolts and standard steel sections, such as angles and joists ; so that there is no anxiety as to the possibility of obtaining renewals at short notice. This is of very great practical advantage, both to the engineer and the user. Slow delivery of special chains is often a fatal objection to their adoption. It is also important that a chain should be selected for which a good many sprocket wheel patterns are available, the chains alone being useless without the wheels.

Ewart Chain.

Fig. 33.