Crumbling/ sifting/coating

The aim of crumbling is to breaking up pellets into smaller particles agglomerated for small animals (chicks, quails, etc) from the pellets manufactured.

Usually the crumbler consists of two corrugated rolls situated below the cooler/drier exit. The pellets can then be diverted into the crumbler, if crumbles or granules are desired, or they can by-pass it. .The distance between the two rollers can be adjusted for getting the desired size for the crumbles produced.

One of the rollers rotate at a higher speed in order to perform a “slicing” of pellets rather than a crushing.

The crumbles production is expensive because, for obtaining crumbles of good quality, it is needed:

  • To grind fine meal in order to increase pellets consistency.
  • to produce pellets of very good quality (good pelletizing and good drying/cooling)
  • recycle products too thin at the sifting and to pellet it again, which reduces the overall production rate.

The main issue is setting up the end of the batch cycle by stopping the recycling of fine particles. The operations manager can choose to incorporate the final fine particles to the batch or to eliminate them.

The separation of fine particles is typically performed by a sifting. The excessive presence of fine particles in the feed may be badly tolerated by some animals. For this reason, livestock farmers require their feed suppliers to avoid this excessive presence of fine particles.

Two sieves can be used for generating three particle size distribution classes :

  • A coarse sieve retaining agglomerates or any foreign matter with large sizes. The majority of the pellets pass through the sieve and the large particles are eliminated.
  • A fine sieve retaining the pellets and allowing the selection of fine particles to be recycled on the pellet mill.

For avoiding their soiling, some sieves can be equipped with rubber balls in motion in their lower part.

After sifting, liquids (often fat and/or enzymes but also vitamins or organic acids) can be incorporated into the feed at a step called spray coating outside the pellets.

This is the last step of dosing and the formula is definitely considered complete at this step.

Most of the time, this incorporation is performed on a very simple device consisted of :

  • a hopper with two levels
  • a dosing system allowing flow rate management
  • a spraying zone
  • a mixtures screw
  • a retention screen

The liquids to be sprayed are brought from their tanks to the incorporation place (with or without buffer tank) through piping systems and pumps.