Contemplating Conveyor Safety

Many conveyors still look as they did in the 1800s—they consist of little more than a chain pulling paddles through a metal box.
By Holger Streetz | July 27, 2019

In this month’s column, I’m going to focus on drag technologies, and improvements available for the hundreds-of-years-old principle. Many conveyors still look as they did in the 1800s—they consist of little more than a chain pulling paddles through a metal box. Energy that should move material is instead used to overcome friction of the chains and steel paddles as they run over the bottom panels. Furthermore, the steel-on-steel contact wears on the components and bottom panels as they move through the conveyor. More importantly, they increase the risk of sparks, especially in tight places. When the distance between the cover and the outer wall is very narrow, woodchips and sawdust can agglomerate there. Also, when a conveyor belt slides sideways and up against the drive roller’s cover, the heat from the increased friction can ignite woody material.

Prevention measurements include fire-resistant rubber conveyor belts, cleaning routines, fire alarms and sprinklers, or dual chains, one example being  SMART conveyors by BE&E. The dual chains run in ultra-high, molecular-weight- (UHMW) lined channels outside the material path. This type of polyethylene has very long chains for more effective load transfer. Running the chains on UHMW decreases internal friction of the conveyor; the only metal-on-metal contact is at the sprockets. Using two chains instead of one increases the chain life, as it reduces the load on each chain. It also decreases the chains’ exposure to mechanical and acidic wear. Using one chain, that one component endures all the stress of the load. Chains in the one-chain set up are thus the most maintenance-heavy part of these machines.

Safety First
Although many features have been added to improve conveyor safety, there are still lethal accidents. One such accident occured in Europe during a maintenance shutdown, when a contractor was working on a conveyor when someone turned on the equipment. An easy way to prevent someone from starting equipment while another person is working on it is the lockout procedure. This best practice is part of the safety indoctrination at Pinnacle Renewable Energy and many other Northern American pellet plants.

To improve maintenance and prevent fires from happening, it is crucial to have enough space between the belt and the wall so that maintenance teams can easily clean the gaps. Post-maintenance checks improve the safety further, as well as the two-man rule (actions require the presence of two individuals at all times). Further improving reliability are sensors that detect conveyor belt sliding, and automatically set off an alarm to stop the conveyor. Using high-performance lubricants with long-life and emergency operating features help increase the lubrication intervals; alternatively, automated lubrication systems decrease manual work to a minimum. Using a paddle design that allows wood to wedge between “fingers” in the paddles rather than beneath them not only prevent the material from wedging in the gap beneath the paddles, but also provides an initial fail point in the event an obstruction occurs in the conveyor. Therefore, instead of the obstruction damaging the chain or sprocket, a smaller (and less costly) component breaks first.

Author: Holger Streetz
International Operations Manager, Bathan AG