What are Lifting tackles?
- According to the Factories Rules-no lifting machines chains, ropes and lifting tackles should taken into use unless it has tested and all parts have been thoroughly examined by a competent person and a certificate of such examination specifying the safe working load obtained.
- Also no lifting machine, chain, rope or lifting tackle should, except for the purpose of testing, loaded beyond the safe working load. The safe working load shall plainly marked on each such gear together with an identification mark and corresponding entries made in a register.
- Whenever these cannot be marked, a table showing the safe working loads of every kind and Size of lifting machine, chain rope or lifting tackle in use should be displayed in prominent positions.
- Lifting tackles mean; fiber rope slings wire rope slings, chain slings, hooks, rings, shackles and similar gear. Generally, manila; and sisal ropes are used in handling or hoisting and lowering operations.
- There are various grades of ropes and therefore while purchasing, their guaranteed breaking strengths should obtained from the manufacturer in order to assess the safe working loads of the ropes.
Features of Lifting tackles:
- Fibre ropes are very susceptible to mechanical damage and they should therefore be frequently inspected for their strength. Particular care is necessary when it is suspected that the rope may have been contaminated by chemical action.
- Periodical inspection of the whole length of rope is necessary to detect broken wire, amount of wear, corrosion, rust, etc. Broken wires, in a rope must always regarded as a warning sign Wire ropes must not knotted. They should joined solacing.
- For the same working load, the chain sling is 5 to 8 times as heavy as wire rope but it has a longer life, stand up better rough use and is almost 100% flexible. The chain is obtainable in many grades viz., wrought iron, mild steel, high tensile steel and alloy steel.
Testing of Lifting Tackles:
- Wrought chains require to periodically heat treated to-remove brittleness. The standard hook is either of a circular section or trapezoidal. The former meant for light loads upto 5 tons.
- Shackles according to difference in shapes known respectively as D and Bow shackles. The pins are usually of circular section. The methods of securing shackle pin in position vary according to the nature of the use of the shackles.
- When there a risk of the pin working out, pins secured by means of a nut and a cotter pin. A cotter pin affords more rigidly than a plain pin. All slings, rings, hooks, shackles, swivels, couplings, sockets etc. should be as per Indian Standards. Permissible working load of one leg should calculated from the ready table of sing diameter; varying angles between two legs.
- Faber rope of less than 12mm dia should not used for a sling or a lifting device. For ropes, safe working load can calculated by dividing the minimum breaking load quoted by the manufacturer; by factor of safety depending on the use.
|Rope Dia (mm)||12||14-17||18-23||24-39||40 and above|
|Factor of Safety||12||10||8||7||6|