The first reaction of most farmers who get their combine or tractor stuck in the mud is to reach for that old chain in the back of the half-ton.
But how do they know if it is up to the job?
“That’s a million dollar question,” said Don Sayenga, executive director of the North American Chain Manufacturer’s Association.
“It’s tough to eyeball. The best rule of thumb is if it’s an old chain and you’re really going to put a load on it, then don’t depend on it.”
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He said one way to evaluate the chain’s potential strength is to look for markings on the links.
Many manufacturers label intermittent links along the chain with a code that signifies its strength.
Chains are rated based on the working load limit, but Sayenga said that figure doesn’t represent the total strength of the chain.
“The working load limit is a fraction of the actual tested strength of the chain,” he said.
“The fraction varies, sometimes it’s one-fourth.”
The working load limit builds in a safety factor because chains lose strength over time.
Friction wears away metal at the contact point on the links every time the chain is used, reducing metal thickness and therefore the strength of the chain. Corrosion has a similar effect, eating away the links.
Metal fatigue is another issue, which Saynega said wears away the strength of the metal every time it is bent or strained.
An old chain isn’t the only way to pull a combine out of the muck.
Towing straps and cables are also widely used, said Glen Blahey, a health and safety specialist with the Canadian Agricultural Safety Association in Winnipeg.
“They all work fine provided they are appropriately rated for the work that they’re going to be doing.”
One of the keys to a successful tow is choosing a device that is stronger than the towing tractor, Blahey said.
“Producers know what the pulling capacity of their tractor is,” he said.
“ You want to make sure that your cable (strap or chain) exceeds the capacity of that tractor.”
Most towing straps, which look like a large and lengthy seat belt, have a label that rates their capacity.
However, straps stretch during a tow, which can be dangerous if they are not properly attached to the towing tractor.
Blahey heard of a case this year where a producer used a clevis and locking pin that wasn’t strong enough for the tow.
“Because the clevis wasn’t rated high enough for the towing capacity, (it) opened up on the tractor that was towing. Because it (the strap) had been stretched, it became like a slingshot…. It ended up shooting back at the stuck piece of equipment. It went through the windshield of the piece of stuck equipment, narrowly missing the operator.”
He said it is a good example of why connecting devices are a crucial piece of towing equipment.
“Does the clevis have some sort of locking device, so the pin can’t work out? Are the clevises rated for that load?”
Blahey said it is also important to connect cables, straps and chains in the correct place.
“On the piece of equipment doing the towing, you always hook at the drawbar level, below the centre of the rear axle,” he said.
Otherwise, the towing tractor could potentially flip over backward.
