Roller chain

ANSI chain (ASME B29.1) is numbered by pitch: the first digit times 1/8 inch, so 40 chain has a 1/2 inch pitch and 50 chain a 5/8 inch pitch. ISO 606 uses codes like 08A and 10A for ANSI equivalents and 08B and 10B for the European (BS) series. 08A and 08B share a 12.7 mm pitch but differ in roller diameter and inner width, so they are not interchangeable.

Measure the pitch between adjacent pin centres, the roller diameter and the inner width between the inner plates. These three dimensions separate the A and B series. Also note the number of strands (simplex, duplex, triplex) and the total number of links or length required.

Chain is usually replaced at about 3 % elongation over nominal length, and earlier on drives with large sprockets or where precise timing matters. Check by measuring a span of many links under tension and comparing with nominal pitch. Elongated chain rides up the teeth and wears sprockets quickly.

A clip connecting link is used with an even number of links, fits quickly and holds well; the clip's closed end must face the direction of travel. An offset link allows an odd number of links but is weaker and should be avoided on heavily loaded drives. Design the centre distance to allow an even link count.

Stainless chain resists corrosion from water, food processing or mild chemicals, but its breaking load is usually lower than carbon steel chain of the same size. Zinc or nickel plated chain gives moderate corrosion protection while keeping strength close to standard chain. Recalculate the load when switching to stainless.

Oil should be applied into the gap between inner and outer link plates on the slack strand, where it can reach the pins and bushings. Depending on speed, use manual or drip lubrication at low speed, oil bath at medium speed and forced spray at high speed. Thick grease only coats the outside and does not reach the pin joint, so it works poorly.

On a horizontal drive, the slack strand sag is typically about 2 to 4 percent of the centre distance. An overtight chain increases joint wear and bearing load, while too much slack causes whipping and tooth jumping. Vertical drives or shock loaded drives benefit from an automatic tensioner.

Use a proper chain breaker instead of a chisel and hammer so the link plates are not bent. A spring clip connecting link must be fitted with its open end facing away from the direction of chain travel. Always wear eye protection, as pins and clips can fly off when pressed.