Chain block and
26 July 2004
lever hoist ï„¶inspection
The more portable these manually-operated rigging tools get, the more attention they require whilst in service, saysDerrick Bailes
Hand chain blocks were once used in their thousands as permanently installed facilities for routine manufacturing and maintenance work. They were generally very heavy, very robust and relatively expensive but would last a lifetime. Today they are usually regarded as portable tools, and price and light weight are considered more important than durability. Consequently they are more likely to be dropped, badly stored and generally abused than their permanently installed predecessors. These changes need to be reflected in the in-service inspection regime, which aligns closely with that recommended for lever hoists, which have always been regarded as portable tools.
As with any equipment about to be inspected, the object must be reasonably clean. However, caution must be the watchword as regards the methods used. Both hand chain blocks and lever hoists have a friction brake and there is lubricant on adjacent bearings, gears etc. Using a pressure washer can remove essential lubricant and cause it to migrate into the brake. Also, as many components will corrode and seize if left wet, careless cleaning can create more problems than it solves. For example, the brake has a ratchet and pawl mechanism. If the pawl seizes it can be forced up by the ratchet wheel but will not drop back and, on release of the hand chain or lever, the load will drop.
If the equipment has already got wet, allow it dry without the application of direct heat. Never immerse the equipment in lubricant, diesel or similar substances in an attempt to displace water. Inspect it after it has dried in case any corrosion occurs which might cause it to malfunction.
When inspecting the equipment, try to be methodical. It’s always a good idea to work from the top down. Look at:
(1) The shape of the top hook and the fit of the safety catch. If the hook has been on too large a connection or point loaded it can cause distortion even within its SWL.
(2) The condition of the block or hoist body. In particular, look for distortion of the frame and missing or damaged gear covers which might cause the mechanism to jam. Many modern blocks and hoists have frames comprising two plates and spacer studs. If the spacer studs have become loose it will allow the frame to rack.
On a hand chain block, check the hand chain wheel for damage and also the guide or casing which prevents the hand chain from being displaced. Remember that if the chain is displaced in service it can fall and cause serious injury. Check the condition of the chain and in particular the link which joins the ends. This is often not welded and the join may be not be smooth. Bear in mind the possibility of injury to the operative’s hands. Excessive wear is unlikely but bent and stretched links are possible and generally arise if the chain has become snagged on the load.
On lever hoists, check the condition of the lever, the reversing ratchet and the free wheel mechanism. Whilst it is certainly a bad practice, it is not unknown for operatives to extend the lever with a scaffolding tube, which almost inevitably results in damage.
(3) The security of the slack end anchor for the load chain. Usually on a hand chain block the chain is anchored back to the frame and on a lever hoist it has a stop on the chain. Whatever method is used, it is absolutely essential that it is effective. Many people do not realise just how much force can be applied to the anchor or stop in the event that the chain is fully run out.
It can easily be as much as twice the SWL, and here’s why. Usually when the chain is fully run out it is because the operative didn’t realise and kept lowering off, thus opening the brake. However, as the load doesn’t descend, the brake stays open. At this point the load on the anchor is the same as that on the hook. If the operative then tries to lower the load further it adds torque to the loadwheel and thereby more load on the anchor or stop. Depending on the design and state of maintenance, some blocks and hoists can require almost as much effort to start lowering as to lift, so the operative will pull quite hard before eventually realising what has happened. If the anchor or stop is not adequate, the chain will run through with potentially disastrous consequences. This is why the British Standard for hand chain blocks specifies an anchor strength of 2.5 times the SWL of the chain. Unfortunately, amongst those devices that do not adhere to this requirement, we often see slack end stops which are little more than a glorified key ring or a piece of bent mild steel bar tack welded at the ends, or a mild steel bolt substituted for the anchor on a block.
(4) The condition of the load chain. Essentially check for wear between the bearing surfaces of the links, bent links, stretched links and corrosion. Wear generally occurs gradually and is usually revealed by an operational test before the loss of strength becomes a problem. However, bent or stretched links and corrosion can occur at any time. Bent links are usually the result of abusing the chain by loading it across an edge or, worse still, using it as a sling by wrapping it around the load and back hooking.
The chain used in a block or hoist has a finer tolerance on the pitch than sling chain, ensuring it can accurately mate with the pockets in the load wheel. Bent or stretched chain will therefore not mate properly and can lack articulation. Also the bottom hook always has a swivel so that if the load rotates, it will not twist the chain. Wrapping and back hooking renders the swivel ineffective. When the block or hoist is hung up with the chain run out, the links should appear to line up without twist. A simple articulation test is to lower the chain to the floor and look for locking between links.
(5) The condition of the bottom hook and safety catch. As for the top hook, check for distortion and that the safety catch is present and functional. Check also that the swivel is free. This is one component where the inspector can easily do some basic maintenance, removing any debris such as cement and adding a drop of oil.
Having completed the above it is always worth doing an operational test, preferably with a light load of about 5% of the SWL. Check that it operates smoothly in both directions. When lowering, blocks and hoists rely on the load to pull the brake in. Generally 5% of the SWL is the minimum they can be guaranteed to sustain but this can increase due to corrosion and lack of maintenance. If slippage occurs at this load, the equipment should be withdrawn from service for maintenance.
If the load chain jumps or makes a cracking noise during lifting or lowering, this is an indication that the chain is not mating accurately with the loadwheel. There are several possible reasons, including the wrong load chain, worn load chain, worn load wheel or a build up of debris in the bottom of the load wheel pockets. The latter can be cured by removing the debris but, whatever the reason, if this indication occurs the equipment should be withdrawn from service.
With a hand chain block, check that the hand chain runs smoothly over the wheel without jumping. As for the load chain, if jumping does occur, the equipment should be withdrawn from service.
Finally, check that the SWL is clearly displayed and the ID mark is legible.