Chain is a critical component in any design of drag conveyor and much like any other component, affects the conveyor performance. This poses the question as to what is the best drag conveyor chain? To answer this, we first need to have an understanding of chain corrosion and wear.
What are the effects of corrosion on drag conveyor chains?
Conveyor chains carrying raw wood and wood pulp have been found to wear mainly due to corrosion caused by the acidity in the wood. Nowadays, steel chains are used in drag conveyors because of the additives that can be added to adjust strength and longevity. Unfortunately though, the acid eats away at the steel and as the chain surface erodes, the wear problem increases as the worn surfaces become abrasive.
This process of corrosion particularly affects the pins and bushings. In most chains, other adjacent parts should fail before the pins, but erosion often causes the pins to fail before the rest of the chain. By calculation, the sidebars of this chain should break before the pin, but it’s often not the case.
Recognizing the corrosive effect of wood-created biomass acids on the chain, we designed our corrosion-resistant chain with the very large pins. The pins of our chain can withstand harsh environments and vibration and are stronger than the sidebars themselves.
To combat corrosion, most drag conveyor chains run outside the material path minimising exposure to acid resulting in a longer chain life.
What does mechanical wear do to drag conveyor chains?
Mechanical wear along with corrosion also has a significant impact on the performance of drag conveyor chains. Whilst corrosion is in effect cleaned out from the outer chain parts, it remains around the pins and being abrasive it therefore mechanically wears them away.
It’s important to keep the number of times the chain flexes and bends to a minimum because of the level of mechanical wear. Conveyors run the chain along wear strips outside the material path, minimizing chain movement. So, the chain only curves around sprockets or when turning corners.
But in single chain conveyors, the chain is bent sideways by the paddles as the loading on single chain is not even so the chain wobbles constantly causing the chain to wear at a faster rate.
What about friction?
Low friction is the aim of a good conveyor chain design. The lower the friction load the longer the conveyor lasts. Friction causes reduced efficiency in a conveyor as it is using energy to move the material on it and to overcome the friction holding it back which adds to the running costs.
How strong does a conveyor need to be?
Drag conveyor chains need to be able to cope with the force applied to them and will need to have a large working load in comparison to their weight.
Businesses use various factors to determine chain working loads, but they often use different calculation methods. It differs from calculating ultimate strength, which involves engineers determining which part of the chain will break first and with how much force. Instead, they calculate the working load as a percentage of the ultimate strength by combining several internal factors. This percentage varies greatly.
FB Chain prefer to work with conservative factors that we apply to all chains when determining how to calculate the working load. This prevents us from overestimating the strength of our chains. This is significant because we use working load to determine which chain and conveyor will work best for the customer’s application.
A chain with a high strength-to-weight ratio that hasn’t been overestimated is ideal. A chain that can withstand high working loads but weighs too much (a low strength-to-weight ratio) is not good as a conveyor system must move not only material, but also the conveyor components.
Getting the right drag chain giving the performance required for the application is crucial. Not doing so costs more money, time and energy.
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