Hey Grinder Guy, how does a star screen work?

ask-the-grinder-guyStar screens are getting more and more popular since most of the issues of the star screens of the past, have been resolved. Star screens are pretty simple and similar to a disc screens.  So how do they work?
1. Rubber stars have a hole in the center and are slid over a shaft.
2. The ends of the shafts have bearings and one end has a sprocket.
3. Shafts are aligned so the stars on one shaft go in between stars on the next shaft.
4. A chain ties the sprockets of each shaft together with an electric or hydraulic motor for power.
5. These shafts rotate at basically the same speed in the same direction.
6. The rotating stars actually move and carry material along the top of the stars, from one shaft to the next,  until there are no more shafts left
7. The amount of shafts and the size of the stars vary.
So, where does the screen come in?
• The space between the stars actually determines the range of particle size;
• The speed of the stars rotating on the shaft creates the actual particle size;
• The slower the rotating shafts, the more time and opportunity material has a chance to fall through the gap between the stars;
• The faster the stars rotate, the faster the material moves across the top of the stars, the finer the particles that actually make it through between the stars; and
• So, a single star deck can produce multiple product sizes and all dependent on the space between each star on a single shaft and the speed of rotation of the stars.
For example, a 1-inch space between stars, with 1/2-inch wide stars, could produce 1/4-inch, 1-3/4-inch material or any size in between. This is because the star rotation speed is moving the materials across the top and the other shafts have a star splitting the 1-inch gap with another 1/2-inch star.
So why are they becoming more popular?
• Because the stars are flexible, they are able to limit the amount of buildup from wet materials, giving the ability to produce much more than a traditional screen in wet moist applications;
• With many mulch operations removing the fines from their product, the range of product sizes available from the star screen is advantageous, and the production is much greater than a trommel screen. You can just remove fines, or scalp overs with the same deck; and
• Heavier materials work well, like soil blends, but no aggregates, as they will wear away the rubber stars.
So, what do you do?
• Try one in your applications;
• Stationary electric decks are relatively cheap compared to a portable machine;
• Electric drives are better than hydraulic drives because the ability to adjust speeds is much greater in an electric motor because of the much higher rpm;
• Find a machine with some kind of cleaning system. You will get buildup but with a cleaning system, you will not;
• If you have a contaminants problem, paper, plastic, stone, find a unit with an inert material removal system or stone separator; and
• There are many three product machines on the market that can remove dirt and scalp overs at the same time. What can that do for your business?
Operational cost is always a concern. While there are a lot more moving parts, the production difference in most materials more than makes up for the additional maintenance costs.
How do you know? Try it, there’s no better way.
Dave Whitelaw grinderguy@askthegrinderguy.com

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