What is product bridging and rat-holing? And how can it be prevented?

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Common dry product feeding issuesOver the last 26 years VeloDyne has handled all types of chemicals, powders, pellets, flakes and chips. Through handling various materials, a lot of testing and lessons learned have come about. VeloDyne offers free material testing to our customers because we know how crucial it is to have minimal flow issues when metering or conveying a product. The two most common product flow issues are bridging or rat-holing. These issues can be detrimental to your process but with properly designed equipment they can be avoided.

Product Bridging or “arching” and rat-holing are both issues that result in a no-flow condition. Bridging, is a case where material that is being discharged or fed forms a bridge or arch over the feed auger or discharge point in a silo cone/hopper. Rat-holing is a condition where the material forms a hole or narrow channel above the feed auger or outlet in a hopper while the remaining material is stationary against the hopper wall. Both of these conditions result in the product not flowing as desired.

There are various ways to combat these product flow issues; hopper design, vibration, conditioning screws, and fluidizing nozzles. This is where knowing the material flow characteristics pays off in the design and use of the equipment. Conical and angled hoppers both create a distinct flow path for the material, it is up to the design engineer to calculate the correct pitch of the hopper walls that best fits the products flow characteristics. Proper hopper design is key but not always the solution. Vibration is commonly used when handling chemicals and other bulk solids materials. When a screw feeder is designed into your process often times a second conditioning screw is utilized to help keep a consistent material flow source to the auger. On the discharge cone of a silo system for example; vibration, air fluidizing nozzles, and bin activators are all ways to help condition product flow and prevent bridging and rat-holing issues.

VeloDyne is dedicated to providing each customer with the right solution for their application. We take pride in offering material testing and use our many years of experience to avoid these common feed issues when handling powders, pellets, flakes and chips.

If you are experiencing one of these issues VeloDyne would be happy to find a way to provide a solution for you. Contact us today.