• Product/dust gets blown out of the throat
• Product/dust leaks out of the shaft openings
• Product/dust gets under the shaft seal and burns due to friction
• Product builds up on the outside of the screen, essentially blinding the screen
• Product is held up in the grinding section causing excessive fines

This situation occurs when you connect an impermeable bag to the discharge or use a solid connection between the discharge and the container. Another possibility is that a venting port with filter in the transition piece might be too small or the filter might be blinded. The solution is to allow the process gas to vent at the discharge using a dust bag, filter, or the Fitzpatrick Product Containment System (PCS).

Q: Thermal protection stops the mill after a short period of operation. What can I do?
A: Motor overloading can be caused when you try to process too much material through the mill too quickly. Slow down the feed to the mill.

A second problem may be that the mill is not fed in a continuous way. Sudden charges of product to the chamber might cause the motor to surge and overheat. A typical example is a pneumatic conveyor receiver that discharges directly into a FitzMill chamber. The solution here is to provide a more continuous, uniform feed rate such as a properly designed rotary valve or a feed screw and hopper.

Q: How can I obtain fewer fines in the finished product?
A: If you are using impact (flat) blades, it is possible that changing to knife edged blades will help.

When you use screens with round openings, a change to mesh screens or screens with square openings which have a greater total open area which can reduce the amount of impact between the product and the screen and therefore generate less fines. A note of caution: Mesh or square screens are not as strong as round hole screens and could be subject to failure.

It may be that another rotor speed/screen size combination exists that produces fewer fines. It might be possible to reduce the rotor speed and use a screen with smaller screen openings to produce less fines. Alternatively, a faster rotor speed with larger screen openings may produce fewer fines.

Conversion to a bar rotor in combination with rasping screens might be another solution.

Q: How do I obtain a tighter particle size distribution?
A: A uniform feed rate is required in order to produce a more uniform end product. More consistent hand-feeding (keeping the amps as constant as possible) or using a metered feed system may be required.

Q: How do I prevent screen blinding (material building up on the inside of the screen?
A: Over feeding can cause screen binding and over heating.

If the product contains fat or oil, cooling the mill might improve the process.

Q: Can I reduce the noise generated from the FitzMill?
A: The sound level produced by a FitzMill largely depends on the material to be ground, speed of the mill, the design/size construction of the process facility, along with the mill configuration. A closed in-line mill generates significant less noise than a hand-fed unit with dust ring discharge.

On the DASO6 up to the HASO30 models, we offer optional noise attenuation shrouds around the chamber and motor. This shroud consists of a frame with removable panels attached with quick-release clamps for easy removal and cleaning. The panels have a SS304 outer shell with a 2.5 cm thick pad, shrink-wrapped with a cleanable material.

The use of these panels can reduce noise levels of 95 dBa down to 80- 85dBa.

Additional information is available in the machine manual.