Tracking chain wear is a vital element of any chain inspection or service of materials handling equipment.
In most cases, leaf chain failure is a gradual process in which the chain elongates as it wears. And the accumulative effect of chain wear is a marked increase in the actual pitch of the chain.
Once your leaf chain has reached, or exceeded, the recommended limit of extension then it's time to take action.
While there are plenty of devices on the market that will tell you whether your leaf chain is worn or not, the bigger priority is to be able to accurately determine the extent of the wear.
A measurement of 2% elongation, for example, is a sign that you should be making plans to replace your chain. While a measurement of 3% elongation means that your chain is dangerous and should be immediately taken out of service.
So what is the key to be able to simply and accurately assess the chain wear of your safety-critical lifting equipment?
In this blog post we explore three crucial elements to consider when you're assessing the effectiveness, and trustworthiness, of your chain wear tool.
When it comes to safety and compliance of your leaf chain, it's vital to ensure the highest level of accuracy of your chain wear measurements.
If a chain is measured over too great a length, then there is the risk of underestimating the true extent of the wear. And if the length of chain that's being measured isn't long enough, then a far greater level of precision is going to be required than might be typically available out in the field.
Another priority is to take the guesswork out of aligning the measurement device with the pin centre line. Being able to accurately find the centre line using solely ‘visual’ methods can be a major challenge.
The measuring tool that you choose needs to be perfectly aligned with the centre of the relevant pin. The FB chain wear gauge, for example, incorporates "V" jaws that always locate on the centre of the relevant pin for accurate measurement.
In contrast, if you're using a measuring tape or steel rule you'll be relying on a high degree of visual accuity - and the need for an extremely steady hand.
2. No human error
Even assuming that you're able to hold the tape or rule steady, there's always the risk that your reading will be subject to what's known as ‘parallax error’ which is dependent on the position of the individual technician’s eyes.
It's hardly surprising that visual errors occur using the tape or steel rule method when you take into account the fact that 0.25% wear could amount to just 0.75mm over 300mm (12 inches).
As a result, many people claim that only someone who is ambidextrous, possesses three hands and two sets of eyes would be able to use a tape or steel rule accurately!
3. No need for calculation
The ideal chain elongation measuring device should be as ‘foolproof’ as possible and should remove the need for the user to have to perform any complex arithmetical calculations.
If you're using a tape or steel rule, you will have to first take an accurate measurement before you can calculate the percentage of elongation. And this can inevitably lead to error and confusion when out in the field.
Let's consider for example the manual calculation that was required to assess the percentage of wear in the following scenario where the chain was 5/8” pitch chain (15.875mm) and was measured over a length of 18 pitches.
The actual length measured was judged to be 286.7mm. The following percentage-of-wear formula was then applied:
X= ((L- (P x N)) x 100) / L
(Where P = pitch of chain; N = pitches measured; L = measured length and X = percentage wear.)
And the final calculation was as follows:
X = ((286.7-(15.875 x 18)) x 100) / 286.7 = 0.33%
The reality is that only a skilled service engineer is going to be able to use a tape or steel rule with any reasonable degree of accuracy. And even without the need to perform calculations, a tape/steel rule requires certain expertise.
A professional chain wear gauge on the other hand will provide a simple, precise, repeatable and foolproof means of determining the nominal pitch of a chain - whether the device is in the hands of a skilled practitioner or a complete novice.