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Different Mixer Testing Methods


By Samira Hassanpour, Amir Attar, Alireza Abbasipour, New Millennium Feed Processing Co. (www.nmfeed.com), Mashhad, Iran


Introduction


One of the most essential and critical operations in the process of feed manufacturing is mixing, where the individual ingredients are combined into their proper ratios and uniformly distributed throughout the entire mass, yet it is frequently given little consideration. Creating a completely homogeneous blend is the objective in mixing; if the ingredients are not properly mixed, then nutritional quality cannot be assured. Insufficient mixing time and filling the mixer over the rated capacity are often implicated as common sources of variation in finish feed. Mixer performance can also be affected by other factors such as particle size and shape of the ingredients, ingredient density, static charge, sequence of ingredient addition, worn, altered, or broken equipment, improper mixer adjustment, poor mixer designed, and cleanliness. Measuring of mixing time necessary to produce a homogenous repartition of feed ingredients should be done for each mixer. Mixing time is a function of mixer design and the rotational speed of the ribbon, paddle, or auger.


Routine inspection of the mixer, proper mixer “tuning”, maintenance of all liquid systems and close attention to ingredient inventories will go a long way to ensure that the nutrient specifications prescribed by the nutritionist, actually reach the target animal.


Mixing Process


The mixing process consists of several vital process components. These include: mix cycle, mix time, tip speed, and mixing element design. Mix cycle – the mix cycle consists of a dry mix time and wet mix time. This differentiation is very important. As a general rule of thumb, the mixing process requires that the dry ingredients be added to the mixer and mixed for a predetermined amount of time. This is due to the fact that liquids can reduce the dispersiblity of dry ingredients within each other by coating the dry particles with liquid. On the other hand, the wet mix time is required to efficiently disperse the liquid throughout the mix. This dispersion is necessary as some liquids (i.e. molasses, fat) have the tendency to clump. Therefore, the uniform distribution of the liquids throughout the mix cannot be assured. Mixing time -The actual time required to prepare different products can vary greatly depending on the type of mixer that is being used. Most people knowledgeable in the field of mixing stress the importance of running mixing tests to best determine the ability of any mixer to properly prepare your product. Through test work (under controlled conditions) it is possible to determine the optimum mix time of your product to assure good product development in a reasonable period of time and with efficient use of energy. This mixing time data can then be collected with the material specifications to assist in the sizing and selection of the right wetted solids mixer.


PAGE 32 JANUARY/FEBRUARY 2020 FEED COMPOUNDER


Mix uniformity guide C.V., % Rating Corrective Action < 10 Excellent None 10-15 Good Increase mixing time by 25-30% 15-20 Fair


> 20 Poor


Increase mixing time 50%; look for worn equipment, overfilling, or ingredient sequencing


Possible combination of all the above. Consult extension personnel or feed equipment manufacturer


Best uniformity of ingredients is achieved by optimal mixing time. Increasing the mixing time causes the uniformity of ingredients to increase or variation in ingredients to decrease. But beyond a certain time, segregation of ingredients starts or variation increases. Optimum mixing time is the point at which the variation is at its best minimum value.


There is usually an optimal mix time, which must be determined experimentally. Because efficiency of mixing is determined by measuring the standard deviation of some critical component, the experiment is tedious. This requires taking multiple samples, at least ten, from various parts of the mixer at a succession of times. Often, mixing times are determined by using an easy-to-analyze component, such as salt, but care must be taken that the results apply to the material of most interest, since it may have different particle size and density than salt does. Tip speed – if a mixer has a poor uniformity result and changing the mix times is not an option, the speed of the mixing elements at their tips can be increased. However, most mixer manufacturers can assist regarding the proper balance between tip speed and mix uniformity. Mixer/mixing element design – occasionally, a change in the mixing element or mixer design may be necessary to achieve a good, uniform mix. This decision is not one to be made lightly; many times, this modification requires a substantial capital investment. However, occasionally, this decision must be made.


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