Mixer Testing


An integral part of the quality assurance program should be routine mixer testing. Procedures for mixer testing are relatively simple and involve taking samples at specific time intervals. The test used and statistical treatment are relatively straightforward.


Sampling


Accurate sampling is essential for a mixability study to be valuable. An analysis is only as good as the sample. The purpose of good sampling is to obtain a small part of a feed that is representative of the whole. One cannot take only the fines or only large particles and expect to obtain an accurate analysis. The factors listed here are important in order to obtain good samples. These apply to all samples and not just to those taken for mixability studies.


Important factors to obtaining good samples:


1. Planning 2. Location 3. Quantity 4. Timing


5. Tools used for sampling 6. Containers 7. Proper labeling 8. Sampling preservative


Choosing a Test Substance


Multiple assay methods have been used for mixer evaluation. The following criteria should be considered when choosing the test substance:


The method to determine the level of the substance should be highly reproducible and have a low variation (e.g., for lab methods, the analytical variability should be less than the target CV for the mixer). Only one ingredient should significantly contribute to the concentration of the test substance in the mix to avoid masking non-uniformity. The assay principles should be based upon a common ingredient, nutrient, or chemical that comes from a single source. Salt, therefore, is a good selection while protein or nitrogen would be a poor selection. With respect to selection of the test substance, one or all of the following nutrients would appear to be suitable in most instances: sodium chloride zinc


• • • • •


manganese copper


Other test substances can be acceptable provided that they are indicative of product homogeneity and can be tested at an approved laboratory.


The assay procedure should be relatively simple, fast, accurate, and precise and should be able to perform in the mill or laboratory, and not require expensive equipment or highly qualified personnel. Should the initial mixer test not meet the accepted standards,


At least five issues must be considered in validating the mixing process: 1. Selection of the tracer.


2. Addition of the tracer to the test feed. 3. Sampling the feed. 4. Analyzing the samples. 5. Interpreting results.


FEED COMPOUNDER JANUARY/FEBRUARY 2020 PAGE 33


the results should be re-evaluated and original samples re-assayed if necessary. If the original samples are reanalyzed and show that the mixing is adequate, these results will be taken as true. If the results of the original test are confirmed and the CV is above the critical limit, a second test must be performed following the identical procedures. Should the second mixer test indicate that the mixing is adequate, these results will be taken as correct.


When the second mixer test verifies that mixing is not adequate, an immediate investigation must be made as to the cause. Continue corrective action and mixer efficiency testing until adequate mixing uniformity is achieved.


Microtracer method


Inclusion and subsequent analysis for tracer particles (e.g. Micro Tracers, Inc) is another method for mixer testing. The ideal tracer would be added at a micro level, similar to the addition level of critical microingredients (i.e. vitamins, minerals or medications). It is reasonable to make the inference that if microingredients are completely mixed then macroingredients will also be mixed. Microtracers are generally premixed with ground corn, salt or with vitamin, mineral or medicated premixes prior to their use in testing mixing.


After mixing, samples were taken directly from mixer. Microtracer particles were separated from the feed sample with rotary magnet where iron particles were fixed on the magnetic surface of rotary detector. The iron particles are demagnetized and then sprinkled onto a large filter paper. The filter paper is then moistened with 50 % ethanol. When spots begin to develop, the paper is transferred to a preheated hot plate and dried. All particles are counted. Number of spots presents concentration of added tracer in sample. Variation from the expected number is calculated to determine mixer performance.


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