The wood and paper industries have some of the most arduous applications for industrial chain. And a particular challenge is the gripper chain on log stackers.
FB chain has found a solution that is helping its customers to achieve increased chain life and reduce machine downtime.
Chain is often thought of as a standard component. A series of identical links, pins and plates assembled in set configurations to meet a number of requirements. Different types of chain are defined by International standards allowing designers to develop machinery using chain with known properties and strengths. Those same standards also make it easier to replace and repair a chain with compatible parts.
But sometimes you need a chain that’s a little different, a little tougher, a little more specialised – that’s been designed for a particular piece of specialist equipment – that’s when you need a custom developed chain.
One application we’ve identified for a custom developed chain is the gripper chain on log stackers. Log stackers are vehicles, primarily used in the wood and paper industries that have a huge hydraulic claw fitted to them. This claw, or grapple, lifts up huge bundles of logs and then the vehicle moves the load around the yard to wherever it is needed next.
These log stackers are key to the efficient running of any operation handling timber and the effectiveness of the grapple is essential in maximising their load-carrying capability.
Impressive pieces of machinery, some log stackers can pick up a 7-ton bundle of logs which may be up to six metres long; that’s 16 m3 of wood in just one lift.
Although the grapple is powerful, an equally important component is the chain that helps to grip the logs tightly during the lift. If the chain is not doing its job or worse, if it should fail, then the heavy, unpredictable logs could spill out, potentially causing injury to any nearby personnel. As well as the safety issues, a failure of the chain would result in lost production with all the associated, unexpected costs.
Issues with the standard chains
The manufacturers of the grapples usually supply them with fairly standard leaf chains, which are secured on both sides by rivet bolts with washers. Using this construction of gripper chains has the disadvantage that the rivet bolts very often struggle with the lateral loads. Due to the dynamic loads, elongated holes form in the washers. The rivet bolts slip through the washers, the bolts loosen, and then the chains can break.
The bolts are then often welded by maintenance staff along with the washers. But this is only a temporary solution which costs unnecessary time and money. The welding often doesn’t last very long, because the hardened chain pins are not that suitable for welding due to their high carbon content.
Much more expensive than the quick fix, however, is the unnecessary downtime of these expensive machines. In the worst case, production cannot be maintained as planned due to missing or interrupting a log delivery.
FB Chain develops a custom solution
During a visit by FB Chain to a paper manufacturer in Austria to look at a conveyor chain application, the customer mentioned that the original chain being used in their log stacker was not performing as it should, and they were losing load capacity and suffering regular breakdowns. Having inspected the chain and consulted with the customer, we knew we could develop a better solution.
As the major issue was the chain breaking, we supplied an upgraded chain, ensuring that it was strong enough to take the loads. However, it was heavy, and there were still some issues with the chain loosening and not gripping the logs. We identified that the chain was quickly becoming inflexible, and the shape of the links was not ideal, which meant that it was not locking into the surface of the logs.
FB then supplied a second chain which was an improvement, but the chain continued to seize up due to a combination of high lateral loads and dynamic loads. “Each time we were making improvements to the chain’s operating life, but we still felt the chain could be improved to optimise their operations further,” explained FB Sales technician Peter Vorwalder, “We therefore decided to make a chain specifically for this log grapple application.”
The custom chain was built with pins which fully rotate in the outer links, a top hat-pin on one side and a welded collar on the other end which allowed the chain to remain flexible and take the high lateral load. The radius on the link plates was increased and the plates made harder.
The key point of the custom log gripper chain:
- Leaf chains with wear-resistant and dynamically loadable chain pins, very strong against lateral loads
- Fine-punched, heat-treated and wear-resistant chain links with full radius, shot-peened
- Optimized joint play tuned for use in wood grapples
- High fatigue strength, high breaking strength, long service life
- Functional dimensions matching the original, as fitted chain
The custom chain proves its worth
The necessary flexibility and stability was successfully achieved, along with long-lasting strength and durability – and all with a precise fit. The customer has reported that after over 5,000 operational hours the chain is operating exactly as it did on the first day with no problems and no sign of notable wear. They are delighted as their investment has quickly paid for itself thanks to the chain’s reliability and long service life.