LPM 221: Commercial Poultry Production and Hatchery Management (1+1)

GRINDING MILL

• In the feed processing process there may be a number of ingredients that require some form of processing.
• These feed ingredients include coarse cereal grains like maize, which require particle size reduction to improve the performance of the ingredient and to increase the nutritive value.
• There are many ways to achieve this particle size reduction.
• Generally, two types of mills are commonly used in the poultry feed mill for grinding the feed ingredients.
  • Hammer mill
  • Roller mill

Hammer mill Hammer mills use impact grinding principle to reduce the particle size of feeds. The major components of the hammer mill include, A delivery device to introduce the material to be ground into the path of the hammers.  A rotor comprised of a series of machined disks mounted on the horizontal shaft performs this task. Free-swinging hammers that are suspended from rods running parallel to the shaft and through the rotor disks. The hammers carry out the function of smashing the ingredients in order to reduce their particle size. A perforated screen. The holes in this screen may be as small as 3 mm to 8 mm diameter. Advantages Able to produce a wide range of particle sizes Work with any friable material and fibre Ease of use Lower initial investment when compared with a roller mill Need minimal maintenance Particles produced using a hammer mill will generally be spherical, with a surface that appears polished. The ground product is removed by either gravity- or by air-assistance.

 Disadvantages

• Less energy efficient when compared to a roller mill
• May generate heat (source of energy loss)
• Produce greater particle size variability (less uniform)
• Hammer mills are noisy and can generate dust pollution

Roller mill

• Roller mills accomplish size reduction through a combination of forces and design features.
• If the rolls rotate at the same speed, compression is the primary force used.
• If the rolls rotate at different speeds, shearing and compression are the primary forces used.
• If the rolls are grooved, a tearing or grinding component is introduced.
• Their slower operating speeds do not generate heat, and there is very little moisture loss.
• Particles produced tend to be uniform in size; that is, very little fine material is generated.
• The shape of the particles tends to be irregular, more cubic or rectangular than spherical.
• The irregular shape of the particles means they do not pack as well.
• For similar-sized particles, bulk density of material ground on a roller mill will be about 5 to 15 percent less than material ground by a hammer mill.

Advantages energy efficient uniform particle-size distribution little noise and dust generation Disadvantages little or no effect on fiber particles tend to be irregular in shape and dimension may have high initial cost (depends on system design) when required, maintenance can be expensive