Below the hook devices are many and varied. They range from the simple to the sophisticated, from the lightweight to the heaviest capacities. Ingenious methods to attach to a load are sometimes needed, and here engineers can display great imagination.
But there is more to below-the-hook devices than simply finding ways to grip an awkward load. Chains and shackles sometimes require specialised materials for ATEX, clean-room and other applications. Wireless communication of data can be another requirement. Digital devices for weighing loads – to warn against overload, for example – and measuring tensions add to safety, but their data-logging contributes to efficiency and can be integrated into Industry 4.0 automation and productivity gains.
Manufacturers of below-the-hook devices are equally varied. Some specialise in one or other of the applications we have described; some are more broad-ranging. Wisconsin-based Caldwell, for example, have just celebrated their 70th year in business and would fit into the latter category. In that time they have accumulated, by acquisition or growth, expertise in vacuum units, coil hooks, heavy mill duty processing equipment, turner units that rotate big weldments and chassis for cars and trucks.
“We make anything that goes below the hook,“ says Jeff Ferchen, their director of business development, “and we have a lot of standard products, but 60% of everything that we do is custom made.”
To that end, Caldwell have created SmartSpec. An online computer programme that lets customers modify standard products to fit their own individual needs. Customers log on where it shows Caldwell’s standard products, and then asks ‘do you want it bigger, smaller, or padded to protect your load, or with shackles in different places?’ It will do the calculations and do the drawings to get it the way you want it. “Previously you had to go through our engineering group, which would take three to five days to get to an engineering proposal design to review,” says Ferchen. “Now it takes three to five minutes.” So that’s an example of how we have worked on the customisation of lifting devices over the years.
An exact marriage between load and lifting devices – and the client’s philosophy – pays dividends, he says. He gives an example of a large agricultural machinery manufacturer. (John Deere is one of their clients.) They might be redoing their manufacturing line for their tractors and wanting to lift a cab door panel onto its unit. It could be done by hand, he says, “but workforces are changing, people of different sizes and both genders are picking up these parts, and John Deere has a policy that if anything weighs over 35lbs (16kg) they will offer the operator a below-the-hook lifting device rather than insisting it be lifted by hand. That is just John Deere’s requirement, it is not general.
So we are trying to create something, just a small device, that will plug onto that panel.” But it is about more than finding a way to attach to the load to grip it for lifting. A person has to fit that device, and you have to make it easy and comfortable for that person. “This is exactly the kind of situation where you get into ergonomics and how people install things. On small loads like that details become all-important.”
Caldwell also do high-capacity BTH devices, for loads like steel and aluminium coils for example, with capacities of 25t and more. “For large loads and small ones, either way we try to collaborate with end users’ engineers to figure out what the best design is; again you try to get the details right.”
Getting it right Of course there are many different ways that a lifting device can attach to a load. A lip or a hole may be present to give a fixing; it may be possible to lift from underneath. “Sometimes there is no suitable lifting point. Then vacuum lifting can be very useful – but not for finished painted parts. When it is unfinished though, when you want to move steel sheet from a stack onto a table, then you could well use it.”
Lifting clamps are another option for flat sheets. Magnets are possible – but only, he says, if the surface is clean and dry. “We use those in our own facilities to move heavier plates into a machining centre. So there are lots of options below the hook, and despite what I said about customising you don’t necessarily have to make a special lifting device for everything. It depends on what it is, where you are picking it up from, and where you are moving it to.“
You can change the plane or the orientation – rotate a sheet from horizontal to vertical for instance. “We have vacuum units that can do that, and they are useful for glass installation, or for granite slabs for countertops.”
Weight is not really an issue for vacuum lifting, as long as you can put in enough suction pads. “You put in lots of calculations from an engineering perspective. Depending on how big and how wide it is, you may have to use more pads to cover the surface area.
The thickness of the material matters as well, because you can get deflection where the sheet starts bending down and peeling away from the suction caps. The design of your flexible, rubber suction seals can be crucial there.”
The vacuum for Caldwell lifters comes from a power pack unit that is built on to each device; calculations give the pump capacities that are needed to lift safely within the standards.
The Caldwell catalogue shows a huge variety of ways in which an object can be picked up. It is the odd-shaped loads that are, predictably, the most challenging, where the centre of gravity sits off to one side. “One side of a spreader beam carries more the load if it is an odd shape, so making sure that you can lift it level and stable is one of the main requirements that we look at. We get accused of asking a lot of questions of our customers, but the reason we ask a lot of questions is because if we don’t get all the information it is really expensive to fix it after the fact. So it is really about communication and consultation.
Is the device designed for the load, or the load for the device? It can work both ways he says. “Sometimes the client has already created the product and we have to work around them to figure out how to lift it. If they get us onside earlier in the conversation we can say, ‘Hey, have you thought about how you’re going to lift this transformer from your facility onto the truck and then from on the truck to the job site?’ So they can modify the design by adding lifting rings or lugs to it. Some of these guys just think about how they get it out of their facility, not thinking of where it’s going to go after that. Lifting points that you could put on to safely manoeuvre it after it has left the factory can make all the difference.”
Hazardous environments can be coped with. Heat becomes an issue in steel mills, aluminium mills, titanium mills. Heat shields on the lifters can protect the motors and the gears above the load; specialised lubrication may be needed. “Automation and digitalisation are becoming big as well, and that perspective is bringing in many more safety features. Clients want electronic indicators that turn green to show that the load is properly and safely engaged. A lot of robotics are happening these days in manufacturing facilities, so we are starting to work with that.”
Below the hook devices pay back their investment very quickly, he says. “It is about efficiency and productivity gains at the end of the day. The customised device may cost you a little bit more, but in the long term it is going to be safer and more effective and more productive.”
And there are some solutions that he is quite proud of. “We are working with a titanium mill right now that is manufacturing ingots, and on the top of each ingot there is a knob like the doorknob to your front or back door. We have created a lifting device that comes down and grabs this knob and picks it up and moves it, and all this is happening 30 feet up in the air. Our engineers have come up with a pretty unique design for that, with automation and indexing mechanisms and so on.
“We have done stuff for SpaceX. And we have been involved with a dinosaur fossil, a large one, that is still embedded in its rock. We have created a lifting device that allows the scientists to turn it and flip it so they can chisel away at this fossil over time.”
Horses for courses
A dinosaur fossil is hardly an everyday lifting application; but some below-the-hook requirements can be specialised in ways that are far from obvious. German manufacturers Cromox are specialists in below-the-hook devices from stainless steel and other alloys.
“In certain environments, you have to be very careful about the materials you use for lifting,” says their spokeman, Alexander Schönberger. “Explosion-prone situations are one; environments where you have chemicals in the air are another. Chlorides for instance are common; so is hydrogen fluoride. That is a very aggressive chemical that is used in manufacturing stainless steel items which have been welded. They are dipped in it to eliminate the oxides on the surface of the weld for corrosion resistance.”
Clean rooms, say for chip production or pharmaceuticals or batteries for electric vehicles, have to be particle free. “But normal lifting chains or painted chain slings produce emissions through particles rubbing off where the links grid against each other,” he says.
“Again, you might manufacture something that has a very smooth surface, say a bearing; and you do not want to rub against that with something hard like a hook. So we design special below-the-hook devices for these.” Often a load has no obvious lifting point.
Cromox makes a series of different lifting points – swivels, hoist screws and the like which are attached to the load and give a proper lifting option. These too can be designed for clean rooms so that they do not emit particles.
“We also supply the defence industry. They of course have loads that are so hugely valuable that one dropped load would be catastrophic; so lifting attachments that are tailor-made for each load are required. That of course is much more reliable than having riggers attach slings around your valuable asset.”
Defence applications have specific requirements regarding particle emissions, but in many cases magnetism is also an issue for them. “We have one very urgent inquiry just today, for some hoisting links used on minesweepers, and we have to provide them at a very quick pace. They are made out of 318 LM, which is an austenitic ferritic duplex mixture steel; the ferritic element makes it magnetic, which is a requirement for that application.
“Some applications require even more specialised steels and alloys. I cannot share details, but I can say that there is very special stuff for submarines and suchlike.”
Generally, he says, Cromox can provide anything that is required by the client if the material is weldable and available on the market. In some cases there may be minimum order quantities because the material is not stocked by steel mills and are created specially. This is getting into very specialised areas indeed.
Cromox cater for more general lifting as well, offering stainless steel chain slings – for example 316 L for ATEX-proof , electro-polished against corrosion, round sling connectors for connecting round slings to a chain, and so on. “We have just completed a project in the US where we designed a lifting system for a furnace that is for heat treatment of aluminium cones for spacecraft.”
More than a one-trick pony
Below-the-hook devices are not just for lifting. Load monitors are widely-used and, being mounted between hook and load, fit the definition. Load links replace part of the lifting rope: they work in tension. Strain gauges within them flex in line with the load, so sense it directly; and they send that information electronically to a monitoring device.
Load pins are used in standard or specially made bow shackles to replace the normal pin. They too contain strain gauges; but in this case the deflection of the pin and the strain are transverse across the load. The pin, therefore, deforms not on tension but in shear. Again, strain gauges measure the deformation; but more complex calibration is needed to convert this data into a load reading.
Southampton-based DLM are specialists in the design and manufacture of below-the-hook load monitoring and cable working equipment for the lifting and rigging industries. The load cells within pins and shackles have a transmitter board which sends a 2.4Ghz signal to a handheld device, say a smartphone or a tablet, or it can send it directly to a PC through a dongle device. “The dongle is a product that was only released to market last year,” says their technical manager Ryan Phillips. It is Microsoft Windows based and can be used to generate certificates, log data, or to show live readings. “Some clients wanted to feed the output from our load cells directly into their computer. You can still use a handheld as well if desired – the dongle just makes it easier getting the data into the PC.”
The telemetry load pins are battery powered – these are also the pins used in DLM’s Telemetry Shackles, which combine a load pin with a marine grade shackle. “We custom design and manufacture the pin to fit the shackle; it is the entire pairing that is considered a unit. But we also do cable-powered versions of load cells; these are intended to be used in permanent power solutions.”
For telemetry load cells, the battery is rechargeable via a USB. Users are not able to access the batteries for safety reasons, as they are lithium; they are built into the load cell end cap and can only be accessed by DLM. They give up to 700 hours of continuous use – noncontinuous use is two years. The device would be paired with a handheld display that gives a warning of low charge.
“500t capacity is the highest available in our standard product range,” he says, “but we strive to meet even the most demanding of customer requirements, meaning we essentially don’t have a limit for custom-made load cells, which we offer in a variety of formats. For subsea applications once again we aim to meet the specific needs of our customers, but our standard products can withstand pressures down to 2,000 metres.”
We have done no more than scratch the surface of the almost infinite variety of below-the- hook devices; but it is a flavour of what is available. So if you are lifting a load, think beyond hooks and rigging slings. There may well be something much more convenient, much more efficient and a little bit more ingenious out there, that might just be exactly what your load requires.
