In erection and maintenance, chain pulley blocks are the most commonly used lifting devices. Information about specifications, operation and inspection of chain pulley blocks is given in this article.
ANSI/ASME B30.16-2007 Overhead Hoists (Underhung)
ASME B30.16 applies to the construction, installation, operation, inspection, testing, and maintenance of hand chain-operated chain hoists and electric and air-powered chain and wire ropes hoists used for, but not limited to, vertical lifting and lowering of freely suspended, unguided, loads which consist of equipment and materials.
In India, chain pulley blocks are made as per IS 3832: 2005 (Hand-Operated Chain Pulley Blocks – Specification). This standard lays down the general requirements and testing of the hand-operated chain pulley blocks, worm or spur gear type. They are tested at 50% overload as specified in the standard.
They are generally provided with alloy steel load chain as per IS 6216: 1982. This standard prescribes the requirements for lifting chains, Grade T (8), accurately calibrated for use as load chains in pulley blocks and other lifting appliances. These are electrically welded round steel short link chains, fully heat-treated and tested and comply with the general conditions of acceptance of IS 5616: 1982.
Design safety factor shall be 4.0 or more.
Specifications for a chain pulley block include following items.
- Lifting Capacity (Safe Working Load).
- Number of falls of load chain.
- Effort on hand chain to raise safe working load.
- Weight of Chain pulley block assembly for 3.0 meter lift.
- Extra weight for each additional meter lift.
Effort on hand chain to raise safe working load by one reputed Indian manufacturer for various capacity of chain pulley blocks is as under.
|Lifting Capacity in Kg.||500||1000||2000||3000||5000||8000||10000|
|Effort on Hand Chain in Kg.||20||36||38||36||45||52||48|
Light chain pulley blocks and chain blocks requiring less pull on hand chain may be selected for easy of operation.
Operation and Inspection
Check and verify that structure or other equipment (e.g. travelling trolley) that will support the chain pulley block has a rated load capacity equal to or greater than the rated load capacity of the chain pulley block to be used.
- Check that chain is properly seated in sheaves and that chain is not twisted, kinked, or damaged.
- Don’t wrap chain around load or use chain as a sling.
- Don’t leave load suspended when chain block is unattended unless specific precautions have been instituted and are in place.
Inspect break mechanism, load chain and hook as under.
Break is of self actuated screw and disc type. Brakes require more than audible-visual inspection. Check frequently by stopping chain block with / without load at various positions to test holding power and amount of drift. If drift is noticed, adjust break.
Periodically check evidence of worn, glazed, or oil-contaminated friction discs; worn pawls, cams or ratchet; corroded, stretched, or broken pawl springs.
Inspect contact points for excessive wear.
One manufacturer has suggested to measure inside length of 5 links under light tension using a caliper-type gauge. They have recommended replacing the chain if measurement exceeds maximum allowable gauge length as given below.
|Chain Wire Diameter in mm||Normal Length of 5 Links in mm||Maximum Length of 5 Links in mm|
Hook requires replacement because of excessive bends, twists, or throat opening indicating abuse or overloading.
Check for cracks (dye penetrant, magnetic particle, or other suitable detection method). Remove the crack if superficial by grinding. Replace the hook if it is deep.
Hook must be replaced when throat opening measurement has increased 5% over the original throat opening dimension of a new hook.
A bend or twist of the hook exceeding 10 degrees from the plane of the unbent hook requires replacement.
Measure hooks depth at load bearing point (base, bowl or saddle). Hook must be replaced when wear at load bearing point is 10% of the original depth of the hook load bearing point.
Never repair hooks by welding or reshaping. Heat applied to the hook will alter the original heat treatment of the hook material and reduce the strength of the hook.
Manufacturers / Suppliers
Some of the Indian manufacturers / suppliers and their website address are as under.