Is my leaf chain rusty or fretting?
I was recently called for chain lubrication advice by a customer who had noticed his leaf chain going rusty very quickly. When he sent over some pictures, I saw that the chain was not in fact rusty but suffering from fretting.
What is the red dust in between leaf chain link plates?
Fretting on leaf chain can be identified by a red dust appearing from in between the chain link plates. It is redder in colour than surface rust, which is normally found on the outer surfaces of the link plates, – and bears a strong resemblance to chilli powder.
Many people confuse fretting with rusting, but it is a completely different process. Rusting is caused by iron reacting with water and oxygen to form hydrated iron oxide, which has an orange-brown colour.
In the early stages, leaf chain can be saved from rusting by cleaning and wire brushing it before relubrication with oil. In applications where the chain is regularly being washed or working in damp environments, specialist lubrication or a corrosion resistant chain, such as our SuperShield coated leaf chain, will maximise protection against rust.
What causes leaf chain fretting?
Vibrations caused by repeated surface movement, coupled with the leaf chain being under load, can cause fretting. This movement can be so small that you may not even see it. Over time, the rubbing action removes the protective film of the lubricant from the chain pins and links and forms pits in the surfaces. The debris created is much harder than the steel surfaces of the chain and increases the leaf chain wear rate.
Why is chain fretting a problem?
Because of fretting, leaf chain fatigue strength, or its capacity to withstand loads over time, may diminish. Fatigue cracks appear in the fretting area, usually the bores of the link plate holes, while micro cracks occur in the chain plates. Because they are so small, these micro cracks are hard to find during an inspection. Usually, the first you will know of them is when a chain suffers a catastrophic failure. This is why it is so important to recognise this ‘red rust’ as an indicator of chain fatigue in a thorough inspection.
In what types of applications does leaf chain fretting typically occur?
Leaf chain fretting typically occurs where the chain is permanently under a load. This could be where an attachment is fitted to a forklift truck or in an elevator where the chain always has the lift car to support. We have also seen fretting occur where forklifts are transporting loads over long distances, even when working with within their load carrying capacity.
How can I reduce the risk of leaf chain fretting?
Effective lubrication is key to reducing the risk of fretting. If the lubricant adheres only to the exterior of the leaf chain and doesn’t penetrate the leaf joints, the chain has not been adequately lubricated. If the lubricant does not reach the internal surfaces of the chain when it is under load, you will have issues with rapid wear and fretting if vibration is also present.
If fretting continues to be a problem, you could consider fitting a hydraulic accumulator. This is a shock-absorbing device that connects to the lifting mechanism and stores energy to smooth out pulsations.
So if your leaf chain appears to have a chilli power red rust, you need to take immediate action to prevent a serious problem.
For further information on identifying and preventing leaf chain fretting, feel free to get in touch
By Peter Church