PROCESS EQUIPMENT UPDATE
conveyance system and more. Tight seals between these processes will help to keep dust from escaping. However, dust collectors should be used at any point where the material may escape, and regularly assessed to ensure proper airflow. Besides creating dust, aeratable materials are also prone to flooding. Tey will flush out of a feed screw and overfill the system if the feeder is not designed properly. A centre rod works better than an open flight in this case. It may also be beneficial to use smaller, more frequent refills to prevent aeration. Vibrators can also help to
densify the material and make it easier to work with.
FEEDERS FOR ABRASIVE MATERIALS Abrasive materials can quickly damage the feeder. However, the wrong feeder lining can also damage the material. Selecting the right feeder for abrasive materials means finding a liner suitable for the particle size and hardness of the material. An abrasion-resistant bolt-in liner made from steel, carbide, or polyethylene can help to protect the feeder. However, this may not be suitable for large particles dropped
from a distance. As the hardness and abrasion resistance of the liner increases, it also becomes more brittle, so it will be more susceptible to damage from heavy impacts. Tis also makes it harder to form and handle, so fabrication will be more challenging. To find the right balance of hardness and abrasion resistance, it’s helpful to have a good material sample and assessment of the overall process.
To select the right feeder for
your materials, you need a clear understanding of how the material flows
FEEDERS FOR COHESIVE MATERIALS Cohesive materials tend to stick to each other and clump together. Te first line of defence against this problem is the hopper design. An asymmetrical mass-flow hopper will help to discourage rat-holing. Te hopper should also have a completely smooth surface, with no ledges or protruding welds for the material to stick to. You might use external paddles and a flexible hopper to de-clump the material as it moves into the feeder. Or, a slow-spinning, vertical or horizontal agitator will break up the material before it enters the feeder. Air pads or vibration might also help. However, agitation devices should cycle, not work continuously, or they can cause the material to become airborne or compacted. A properly designed screw feeder will be best for cohesive materials. Te opening from the hopper to the feeder should be as large as possible. A screw with a larger centre shaft, smaller flights and progressive pitch will also help the material fill the screw flights evenly and feed consistently. Different materials flow in different ways. A feeder that works for one material might not work for another. To select the right feeder for your materials, the best defence is a clear understanding of how the material flows. Giving your equipment manufacturer a sample of your materials and testing the process beforehand will help to ensure your equipment works properly when it’s installed.
Wade Almy is engineering manager at APEC.
www.apecusa.com
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