In today’s episode of the Dust Safety Science podcast, we feature the first half of an ‘Ask Me Anything’ session with Brian Knapp, Vice President, Electronics Division for 4B Components in Illinois.
Brian has 15 years of experience in the grain and feed industries, with a special focus on hazard monitoring systems and components. He spoke about hazard monitoring on bucket elevators and drag/belt conveyors at the Digital Dust Safety Conference in 2020 and continues to share his expertise on this important topic.
What are Common Ignition Sources in Elevators and Conveying Equipment?
Belt Slippage
Brian identified belt slip as one of the primary ignition sources in bucket elevators in particular.
“When the belt starts to slip, you have friction that’s generated between the motor or pulley that’s turning at a different speed than the belt, and that’s going to generate heat,” he says. “You experience the same thing that people probably experience with vacuum cleaners – the belt burns off with a real bad smell. There is also a lot of heat generated when you have that ignition source in there [and it] can cause a fire and explosion with the dust that’s in the air.”
Belt or Pulley Misalignment
Misaligned belts and pulleys are another frequent ignition source.
Belts can shift in one direction or another. Occasionally, just as the material feeds in, they can shift over a little and then come back to the center. In other cases, the belt is a bit loose and hangs over to one side. As it rubs against the machine casing, it can generate a lot of heat, damaging the equipment as well.
There is a common assumption that if a pulley is misaligned, the belt would also be misaligned. However, the pulleys are wider than the belt and the belt may not track over with the pulleys. This makes monitoring pulleys particularly crucial in the head section of these elevators, since a misaligned pulley could cause many problems.
Overheated Bearings
Issues can also be caused by bearings. According to Brian, ultimately every bearing is going to fail. This generates heat, which could ignite grain dust. Although it may be outside the leg casing, dust can accumulate on those bearings, causing dust layering on top of the bearings, which differs from gas hazards in that it reduces the temperature required to ignite the dust as opposed to when it is airborne.
An Overview of Belt and Drag Conveyor Issues
Belt conveyors are generally horizontal, with maybe a slight incline, but otherwise they are similar to bucket elevators. One is vertical and the other is horizontal, but they experience the same ignition challenges.
Drag conveyors are slightly different because they do not have belts that experience slippage or misalign chains on sprockets. However, there are still bearings to monitor on drag conveyors because each one has four bearings. Even with regular maintenance, there will eventually be a time when these bearings overheat.
What Equipment is Used to Monitor These Hazards?
Brian explained that belt slippage is typically monitored by speed sensors mounted on the top and bottom of the bucket elevator.
“We want to monitor when the belt is slowing down,” he says. “The belt is driving the bottom pulley. We know what the normal running speed of that pulley is and we monitor that continuous speed. If it drops, you need to be able to determine whether the belt is slowing down because the motor is running at a slower speed or because it is slipping. If the top monitor stays the same and the bottom slows down by 20%,there’s a slippage, so you shut the motor off to prevent damage to the belt and the ignition risk as well.”
For belt alignment issues, a commonly used technology is a Rub Block, which is a brass block with a temperature probe in it. When the bottom rubs, it’s generating heat, so you’re monitoring the heat generated by the belt in that brass block.
“The other technology is using a force-activated misalignment sensor,” Brian says. “If a belt comes over and makes contact, immediately you get an alarm.”
What Maintenance Measures are Recommended?
Brian recommended that when protection systems are initially installed, they should be thoroughly inspected and tested, followed by annual testing. Recommended maintenance steps include:
- Regular greasing of bearings (as recommended by the manufacturer)
- Monitoring vibration on bearings, which can be carried out by specialist companies
Conclusion
Brian emphasized the importance of making sure that any hazard-monitoring equipment is located in the right place.
“One of the things we find regularly is that the sensors are mounted in a position where they may not detect the misalignment at all or in the case of a bucket elevator with a boot pulley, it may have fallen into the travel or may have 20 inches of travel. The position of the sensors and installation in general with these systems is really one key aspect of it – because if it’s not positioned right, then nothing else matters.”
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Brian Knapp directly:
Email: [email protected]
Website: https://www.go4b.com/
If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.
Resources mentioned
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Dust Safety Professionals
Companies
4B Components
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