A Grizzly Screen, also known as a Grizzly Feeder or Scalping Grizzly, is a robust screening device used in various industries to separate larger-sized materials from finer particles before they enter a processing system or equipment.
A grizzly is a grid of parallel metal bars set in an inclined stationary frame, with a slope of 30° - 45°. The slope and the path of the material are usually parallel to the length of the bars. The length of the bar may be up to 3 meters and the spacing between the bars is 50 - 200 mm.
The material of construction of the bars is manganese steel to reduce wear. Usually, the bar is shaped in such a way that its top is wider than the bottom, and hence the bars can be made fairly deep for strength without being choked by lumps passing partway through them.
A stationary grizzly is usually adopted for dry material and is not satisfactory for moist and sticky material.
If the grizzly is used for wet screening, a very much smaller angle is employed.
Grizzly Screen Working
A coarse feed is fed at the upper end of the grizzly. Large chunks roll and side to the lower end while small lumps having a size less than the opening in the bars fall through the grid into a separate collector.
If the angle of inclination to the horizontal is greater, the greater the output but the lower the screening efficiency. Stationary inclined woven-metal screens operate in the same way that separate particles 12 - 100 mm in size.
A grizzly finds its greatest application in the separation of the undersize from the feed to a primary crusher. Stationary grizzly is the simplest of all separating devices. It requires no power and is the least expensive to install and maintain. As the openings in the grizzly have a tendency to get blocked by wedge-shaped particles, the labor requirement for operating the grizzly is high. Also, it is difficult to change the opening in the bars.
The Grizzly Screen's primary function is to remove oversized material, such as rocks or debris, before it reaches downstream equipment like crushers or screens. This helps protect the downstream machinery from damage and ensures the efficient processing of finer materials. Grizzly Screens are commonly used in industries such as mining, quarrying, construction, and recycling.
Advantages and Disadvantages
These are stationary inclined screens.
Usually, screens are a grid of metal bar.
The opening of the screen is large.
The handle is large-size feed.
Capacity is large.
Labour requirement is large.
Cheap construction.
Also Read: Vibrating Screen Machine Working Principle and Operations
Screening in Separation Process | Screening in Engineering
Separation of Solids Based on Particles Size
Screen Analysis in Chemical Engineering | Fractional Distribution Curve (graph)
Take these Notes is, Orginal Sources: Unit Operations-II, KA Gavhane