Mixer and the Mixing Process.
Theory and Practice.The mixer is used to produce product in which nutrients and medication are uniformly distributed. A w ell blended product enhances performance and is an essential step in complying with Food and Drug Administration (FDA) Current Good Manufacturing Practices regulations. A satisfactory process produces a uniform blend in a minimum time with a minimum cost of overheads, power, and labour. Some variation between samples should be expected, but an ideal mixture would be one with minimal variation in composition. Measuring the variation in finished product is the crux of blender testing. A number of factors that determine blender performance are considered below. Understanding how these factors affect the mixing process is essential when interpreting the results of a blender test. Factors that Determine Blender Performance Several factors determine the dispersion of ingredients in the product. These factors include ingredient particle size and shape, ingredient dispersion in the Blending process. Blenders may have dead spots, where small amounts of ingredients may not be readily incorporated into the product. This situation is aggravated when Blending ribbons, augers, or paddles become worn. Ground grain or soybean meal should be the first ingredient added into a horizontal blender. Vertical blenders generally provide an optimal mix when micro-ingredients are added early in the matching process (e.g., during or after soybean meal, but prior to grain). Buildup of material on ribbons, paddles, or augers can reduce blender performance. The FDA Current Good Manufacturing Practices (GMPs), which pertain to production of medicated product, require that equipment be maintained and cleaned. Residual material on Blending parts can also lead to product contamination (cross-contamination). Overfilling or under-filling a blender can lead to inadequate Blending. Overfilling a blender can inhibit the Blending action of ingredients in horizontal blenders at the top of the blender. Filling a blender below 50 percent of its rated capacity may reduce Blending action and is not recommended. Density and static charge, sequence of ingredient addition, amount of ingredients mixed, blender design, Blending time, cleanliness of the blender, and wear or maintenance of the blender. Product manufacturers can control most of these variables through equipment maintenance and operation described below. Particle size of grain ingredients is controlled through the grinding operation. Coarsely ground grain (a large particle size) can have a detrimental effect on a batch of product’s Blending properties. For example, ground grain with a particle size of 1,200-1,500 microns reduces the likelihood of uniform incorporation of micro-ingredients compared to grain ground to an average particle size of 700 microns. A large particle size variation between grain and micro-ingredients also can result in increased segregation after Blending. The Blending time necessary to produce a homogenous distribution of product ingredients should be measured for each blender. blending time is a function of blender design and the rotational speed of the ribbon, paddle, or auger. The best way to establish the appropriate mix time is to conduct a blender performance test. blender Performance Testing performance testing consists of two parts: sampling and sample analysis. Procedures for sampling blenders, analyzing samples, and interpreting results are described below. Sample Collection The first step in testing involves collecting representative product samples. This process depends on the type (horizontal versus vertical) and design of the blender. For example, it is difficult to collect a representative sample directly from a vertical blender using a grain probe, hence, collecting samples at evenly spaced intervals during blender discharge is recommended. Samples can be taken from the spout end of portable grinders/blenders or near the discharge point for a stationary vertical blender. Horizontal blenders are usually accessible from the top which permits sample collection directly from the blender using a grain probe. Samples should be drawn from 10 pre-designated locations or at even intervals during blender discharge. Identify the location, or time sequence, by numbering the sampling bags; this step will help one interpret the data (see Figure 1). blender test results are less accurate when fewer samples (data points) are used. If you are evaluating blender performance using a micro-ingredient that requires an expensive laboratory assay, (e.g. drug), it may become necessary to make a trade off between the cost and accuracy of the test. To select the optimum blending time, product samples must be collected at intervals over an extended period. For example, a horizontal blender can be evaluated for optimal blending time as follows: run the blender for two minutes, stop the blender and collect 10 representative samples from predetermined locations, run the blender two more minutes, stop the blender and collect ten samples from the same locations as the previous sampling. Repeat this process for ten minutes (five sampling times). As mentioned above, it is difficult to collect samples directly from vertical blenders. In this instance, a sampling scheme will involve separate batches of product that have different blending times. It is important to perform this test using the same product rationale and same sequence of ingredient addition to the blender. Safety precautions must be followed when sampling a blender. In every instance, use proper lockout, tag-out procedures (disengage power) before reaching into a blender to collect a sample. Do not place your hands near moving augers when collecting samples during blender discharge. Sample Evaluation Sample evaluation involves 1) selecting the micro-ingredient or tracer to test for product uniformity; 2) assaying the samples for the specified ingredient level; 3) analyzing the data collected during samples analysis; and 4) interpreting the data. Step 1: Selecting a Micro-ingredient A micro-ingredient is defined as an ingredient that comprises 0.5 percent or less of the final product. Testing blender performance using a micro-ingredient will provide a better indication of product uniformity, since micro-ingredients are typically more difficult to incorporate into a large batch of product. Salt is a commonly recommended micro-ingredient to test blender performance. Salt is both inexpensive and easy to assay. Physical characteristics that make salt an attractive ingredient for testing include the following: it is denser than most product ingredients, its shape is generally cubic rather than spherical, and it is smaller than most other particles. If the blender will uniformly incorporate salt, those ingredients with more typical physical properties (shape and density) should pose no problem during blending. Step 2: Assaying Procedures Assaying samples for salt content may be performed using several techniques. The sodium (Na+) or chloride (Cl-) ions from salt (NaCl) may be analyzed after blending the product sample in a water solution.
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