A: Doug Kitch, CPM Roskamp Champion, says:
Keeping your hammermill maintenance expenses low starts before the hammermill is installed at your plant. By carefully selecting the hammermill’s wear parts and determining the best way to operate the mill for your application, you can minimize required maintenance while ensuring that the mill provides top grinding performance. To expedite and simplify maintenance, you also should select wear parts designed for easy replacement.
Selecting the screen area. The hammermill should have at least 14 square inches of screen area per horsepower for most applications. Too little screen area will make the mill inefficient and cause your material to heat up during grinding. When using a very fine screen (with holes less then 1/16 inch), you may need to use more screen area per horsepower because the screen has less open area.
Selecting the hammer pattern. The number of hammers in your mill is called the hammer pattern. For a large-diameter hammermill (with a diameter of 38 inches or more) that uses hammers over 10 inches long, the number of hammers you’ll need for a screen with large (at least 1/8-inch) holes is typically one hammer per every 2.5 to 3.5 horsepower. For a large-diameter hammermill with the same hammer size but smaller screen holes, you may need more hammers to prevent them from “rocking” back and forth on their pins and quickly wearing and enlarging the hammer holes. To produce a finer grind, you should also use more hammers.
Setting the tip-to-screen clearance. In most applications, the clearance between the hammer tip and the screen has only minor influence on grinding performance. Generally, a larger tip-to-screen clearance provides the greatest grinding capacity and efficiency. For a fibrous or other tough-to-grind material, however, setting the hammer tip near the screen can achieve a finer grind, but this can also increase screen and hammer wear.
Setting the tip speed. To achieve a finer final size when using a screen with holes smaller than 1/8 inch, you should use a high tip speed (greater than 18,000 fpm). This speed is more efficient in producing finer grinds and permits the hammer to do more of the grinding work, minimizing screen wear. Use a lower tip speed and a screen with larger holes to produce a coarser, more uniform grind.
CPM Roskamp Champion, Waterloo, IA, supplies grinding, pelleting, and cooling process technology equipment for the animal feed, food processing, and biofuel industries.