A: Paul Matarazzo, Acrison, says:
The most critical items when choosing a feeder to handle your cohesive material are the hopper’s design, the metering auger, and/or the cylinder configuration.
A cohesive material can (and will) build up on hopper walls to the point where it either ratholes or bridges, resulting in a decrease in output or no output at all. A properly designed hopper will ensure material flow. Avoid shallow hopper angles. Vertical-walled, negative-sloped, and cylindrical hoppers work best and, when combined with a wide throat area at the hopper bottom, will help minimize material bridging across the feed chamber. Hopper coatings with a low coefficient of friction can also be used. Other options include hopper agitators and vibrators. Use caution when considering these devices, since they can cause some materials to pack and will create problems with performance, cleaning, and even possible drive overload.
A cohesive material can build up on a metering auger or form a plug, resulting in a decrease in output and the possibility of blocking off of the entire material flow. Metering augers with less surface area or self-wiping options are available. Exercise caution when using self-wiping augers if the material contains large particles or doesn’t react well with shear. Release coatings are also available for metering augers. In conjunction with a properly configured auger, give some consideration to the coatings and clearances of the discharge cylinder.
Acrison, Moonachie, NJ, manufactures volumetric and gravimetric feeding equipment for the dry bulk solids industry.