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29.10.2021  |  3067x
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Gravimetric feeding preferable because of variation in flow properties

Testing of pet food and salmon feed was done to argue why a gravimetric feeding system is preferable when working with mixed meal types.

Investigation density and flow properties

Variations in both density and flow property often occur in mixed meal types used for the animal, aqua and pet food productions, density variations above 15 % are not unusual – these variations possibly occur due to variations in the recipe and since meal can compact in bins. This article focuses on the differences in meal mixes for pet food and aqua feed production and what type of knowledge testing the product will generate. Testing of two material types: pet food – dog and aqua feed – salmon was done to argue why a gravimetric feeding system is preferable when working with mixed meal types

Testing and Results

Four types of tests were performed in the Jesma test laboratory: bulk density, angle of repose, particle size, and moisture content. Bulk density can interfere with powder flow, large variations between loose and tapped bulk density may signify a poorer flowing material. Using the compressibility index for measuring the bulk density it shows for pet food – dog 20,47 % indicating a passable flow character and for aqua feed Salmon 22,89% also indicating a passable flow character placing both materials (food and feed) around the middle of the scale for flow properties testing.
Further analysis of the material using Angle of Repose testing indicates a fair flow property for the dog food but indicates possible hang-ups for salmon feed, these possible hang-ups are considered when recommendations for best-suited equipment are given.

Gravimetric feeding system

Testing the materials indicates the behavior and flow properties of the given products. These tests are used to ensure the best possible accuracy when choosing the type of equipment. In this case, Jesma recommends a gravimetric feeding system because of the large variations between the loose and tapped bulk density.
A gravimetric system, which will be able to operate with dosing and flow accuracy of +/- 0,5 % independent of variations in recipe and bulk density as opposed to a volumetric system, which will operate with flow variation above 15%.

Recommendations
To ensure continuous production, the following recommendations are given based on the testing done on the Pet food and the Aquafeed:
  • The pre-bin feeding the extruder/ pellet mill should be able to hold at least 1½ of the mixer batch size.
  • The pre-bin feeding of the extruder/ pellet mill should be sized to correspond to 5 – 10 min production.
  • Should be equipped with an efficient agitator to prevent hang-ups (this is most critical in the case of Aqua Feed)

Why test your product?

Testing enables product knowledge, knowing about flow properties, changes in density, and the like, allows design adaptions according to the physical properties of the product. For example, choosing the type of bin or silo best suited for the given type of product. Testing your raw material and ingredients will ensure the equipment is designed to achieve the highest possible productivity and performance of your weighing and dosing system and eliminate quality losses and production stops.
Lord Kelvin said many years ago: “To measure is to know. If you cannot measure it, you cannot improve it.” That is our motto assisting our clients in any phase of a project involving dosing and weighing of ingredients for animal, aqua, and pet food production.

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