How to reduce the risk of turned pins in high bearing pressure applications
Some applications like drilling rigs, piling rigs and port equipment experience very high temporary loads. These high loads are generated by the harsh environment, dirt and debris. When drilling and piling, an additional factor is the inconsistency of the ground structure that’s being worked through.
Basic physics can help calculate the force required to start moving a load and the force required to keep the load moving. What is much harder for the designer to calculate in boom and mast working applications are the peak loads that components might experience. These peak loads are often linked to maintenance or the functioning of other parts.
For example, the performance of wear pads in a boom directly impact inertia which has to be overcome and therefore the load that the leaf chain experiences.
Excessive internal friction caused by temporary extreme loading, made worse by inadequate lubrication, results in turned pins. It is important to note that extreme loads on a brand-new leaf chain can result in turned pins even on its very first movement.
The likelihood of turned pins occurring increases when the internal leaf chain bearing pressure exceeds 0.18 kN/mm² – this would be 14% to 15% of a leaf chain’s tensile strength (UTS). With some machinery stands allowing operating loads up to 20% UTS it is clear that the chance of turned pins is high even without working in demanding environments.
Effective lubrication is a key factor in reducing the risk of turned pins on a leaf chain. It is common for users to wrongly assume that their leaf chain has been adequately lubricated. If the applied lubricant adheres only to the exterior of the leaf chain and doesn’t penetrate the leaf chain joints, this can easily lead to problems caused by inadequate lubrication.
Selecting the correct lubricant for these extreme pressure applications makes a huge difference. We would suggest using a leaf chain lubricant with extreme pressure additives. We do not recommend a specific lubricant for extreme pressure but would suggest that you speak with a lubrication specialist.
Xtreme Pressure Leaf Chains
We have developed a range of leaf chains which are designed for high bearing pressure applications. These Xtreme Pressure Leaf Chains are designed to allow the pin to rotate freely and all the links are slip fit which allows for greater penetration of lubrication. These leaf chains are interchangeable with ISO standard leaf chain but care must be taken when specifying as the pin lengths are different.