3.1.5 Mixing operation-Dry

3.1.5  Mixing operation-Dry

The mixing process determines, to a high degree, the capacity of the whole manufacturing process and the quality of the final product. Lack of proper mixing can lead to reduced diet uniformity, affecting not only animal performance but regulatory compliance as well. Mixing of batch in batch mixer (Fig. 3.6) is done generally for 3 to 4 minutes for proper mixing. The mixing accuracy/ homogeneity  of a mixer indicates how efficiently a single ingredient is distributed among the totality of other ingredients. The homogeneity (Fig. 3.7) is expressed by the coefficient of variation CV (per  cent).  A  good  mixer  should have   a  CV ≤ 5  per   cent   in  less mixing time. Interlocks are provided to ensure that only one batch at a time is mixed in the mixer. Quality control officer should also check for proper mixing of batch ingredients in mixed feed.

 

Fig. 3.6 Batch mixer

 

The influencing factors on the mixing accuracy are:

•         Properties of  components:  Best mixing  results are achieved, if  the particles in  a mixture have only small differences in regard to granulation and specific weight

Rule of thumb:

•         Granulation: Differences between components max. 3 mm

•         Bulk density: Differences between the components smaller 0.5 t/m3

•         Accuracy of proportioning:  Proportioning has to fulfil the requirements

•         Type of mixer (conical, U-shaped)

•         Mixing time: Specific for each mixer type. The mixing time of conical shaped mixer: 5-20 min, circular horizontal single ribbon / peddle type mixer – 3 to 4 minutes and horizontal twin shaft paddles -1 to 2 minutes.

•         Liquid addition: Liquids have to be added after the mixing process.

While going around the plant, the animal nutrition officer should ensure that the operators are cautious about the effects of using less or more raw materials. He should ensure that weighing of raw material is in accordance with the feed formula. Periodically, he should also check accuracy of the scale.