MF1172 Testing Mixer Performance - KSRE Bookstore

MF-1172 1

Feed Manufacturing

Testing Mixer
Performance

The objective of dispersion in the mixing

the mixing process is to process. Mixers may have

produce feed in which Tim Herrman dead spots, where small
nutrients and medication Extension State Leader amounts of ingredients
are uniformly distributed. Grain Science and Industry may not be readily incor-
Well-mixed feed en- porated into the feed. This

hances animal perfor- Keith Behnke situation is aggravated
mance and is an essential Feed Manufacturing Specialist when mixing ribbons,

step in complying with augers, or paddles become

Food and Drug Adminis- Department of Grain Science and Industry worn. Ground grain or

tration (FDA) Current soybean meal should be

Good Manufacturing Practices density and static charge, sequence the first ingredient added into a

regulations (Title 21 C.F.R. of ingredient addition, amount of horizontal mixer. Vertical mixers

225.30,130). ingredients mixed, mixer design, generally provide an optimal mix

A satisfactory mixing process mixing time, cleanliness of the when micro-ingredients are added

produces a uniform feed in a mixer, and wear or maintenance of early in the matching process (e.g.,

minimum time with a minimum the mixer. Feed manufacturers can during or after soybean meal, but

cost of overhead, power, and labor. control most of these variables prior to grain).

Some variation between samples through equipment maintenance Buildup of material on ribbons,

should be expected, but an ideal and operation described below. paddles, or augers can reduce

mixture would be one with minimal Particle size of grain ingredients mixer performance. The FDA

variation in composition (Lindley). is controlled through the grinding Current Good Manufacturing

Measuring the variation in finished operation. Coarsely ground grain (a Practices (GMPs), which pertain to

feed is the crux of mixer testing. large particle size) can have a production of medicated feed,

A number of factors that deter- detrimental effect on a batch of require that equipment be main-

mine mixer performance are feed’s mixing properties. For tained and cleaned (Title 21 C.F.R.

considered below. Understanding example, ground grain with a 225.65, 165). Residual material on

how these factors affect the mixing particle size of 1,200-1,500 mi- mixing parts can also lead to feed

process is essential when interpret- crons reduces the likelihood of contamination (cross-contamination).

ing the results of a mixer test. uniform incorporation of micro- Overfilling or under-filling a

ingredients compared to grain mixer can lead to inadequate

Factors that Determine ground to an average particle size mixing. Overfilling a mixer can

Mixer Performance of 700 microns. A large particle inhibit the mixing action of ingre-
size variation between grain and dients in horizontal mixers at the
Several factors determine the micro-ingredients also can result in top of the mixer. Filling a mixer
dispersion of ingredients in a feed. increased segregation after mixing. below 50 percent of its rated
These factors include ingredient capacity may reduce mixing action
particle size and shape, ingredient The sequence of ingredient and is not recommended.
addition also determines ingredient

Kansas State University Agricultural Experiment Station and Cooperative Extension Service

2

The mixing time necessary to Ten samples are advised; this Sample Evaluation
produce a homogenous distribution recommendation is based on the Sample evaluation involves 1)
of feed ingredients should be statistical analysis procedures
measured for each mixer. Mixing described in step 3 of Sample selecting the micro-ingredient or
time is a function of mixer design Evaluation. Mixer test results are tracer to test for feed uniformity; 2)
and the rotational speed of the less accurate when fewer samples assaying the samples for the
ribbon, paddle, or auger. The best (data points) are used. specified ingredient level; 3)
way to establish the appropriate analyzing the data collected during
mix time is to conduct a mixer If you are evaluating mixer samples analysis; and 4) interpret-
performance test. performance using a micro-ingredi- ing the data.
ent that requires an expensive
Mixer Performance Testing laboratory assay, (e.g. drug), it may Step 1: Selecting
Mixer performance testing become necessary to make a trade a Micro-ingredient
off between the cost and accuracy
consists of two parts: sampling and of the test. A micro-ingredient is defined as
sample analysis. Procedures for an ingredient that comprises 0.5
sampling mixers, analyzing To select the optimum mixing percent or less of the final feed.
samples, and interpreting results time, feed samples must be col- Testing mixer performance using a
are described below. lected at intervals over an extended micro-ingredient will provide a
period. For example, a horizontal better indication of feed unifor-
Sample Collection mixer can be evaluated for optimal mity, since micro-ingredients are
The first step in mixer testing mixing time as follows: run the typically more difficult to incorpo-
mixer for two minutes, stop the rate into a large batch of feed.
involves collecting representative mixer and collect 10 representative
feed samples. This process depends samples from predetermined Salt is a commonly recom-
on the type (horizontal versus locations, run the mixer two more mended micro-ingredient to test
vertical) and design of the mixer. minutes, stop the mixer and collect mixer performance. Salt is common
ten samples from the same loca- in most feeds, it comes from only
For example, it is difficult to tions as the previous sampling. one source, and it is both inexpen-
collect a representative sample Repeat this process for ten minutes sive and easy to perform a salt
directly from a vertical mixer using (five sampling times). assay. Physical characteristics that
a grain probe, hence, collecting make salt an attractive ingredient
samples at evenly spaced intervals As mentioned above, it is for testing include the following: it
during mixer discharge is recom- difficult to collect samples directly is more dense than most feed
mended. from vertical mixers. In this ingredients, its shape is generally
instance, a sampling scheme will cubic rather than spherical, and it is
Samples can be taken from the involve separate batches of feed smaller than most other particles. If
spout end of portable grinders/ that have different mixing times. It the mixer will uniformly incorpo-
mixers or near the discharge point is important to perform this test rate salt, those ingredients with
for a stationary vertical mixer. using the same feed ration and more typical physical properties
same sequence of ingredient (shape and density) should pose no
Horizontal mixers are usually addition to the mixer. problem during mixing.
accessible from the top which
permits sample collection directly Safety precautions must be Step 2: Assaying Procedures
from the mixer using a grain probe. followed when sampling a mixer. Assaying samples for salt
In every instance, use proper
Samples should be drawn from lockout, tag-out procedures (disen- content may be performed using
10 predesignated locations or at gage power) before reaching into a several techniques. The sodium
even intervals during mixer dis- mixer to collect a sample. Do not (Na+) or chloride (Cl-) ions from
charge. Identify the location, or place your hands near moving salt (NaCl) may be analyzed after
time sequence, by numbering the augers when collecting samples mixing the feed sample in a water
sampling bags; this step will help during mixer discharge. solution. “Quantab” (Environmen-
one interpret the data (see Figure 1). tal Test Systems, Elkart, Indiana)

3

Interpretation of Mixer Tests

Percent Coefficient of Variation Rating Corrective Action
<10% Excellent None
10-15% Good Increase mixing time by 25–30%
15-20%
Fair Increase mixing time 50%, look for worn
>20% equipment, overfilling, or sequence of
ingredient addition

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

chloride titrators measure the 9 10
dissolved Cl-, while the Omnion 78
Sodium Analysis involves a meter
with a specific sodium electrode 56
that measures the Na+ (Omnion, 34
Inc., Rockland, Massachusetts). 12

Step 3: Data Analysis Figure 1. Sampling scheme used to evaluate mixing performance in a horizontal
The average salt concentration paddle mixer.

(mean) and variation between
samples (standard deviation) are
calculated to arrive at a single
value described as the coefficient
of variation (CV). A desirable CV
for a well mixed feed, using the salt
assay method, should be at or
below 10 percent. Calculating the
coefficient is performed using the
following equation:

%CV = S x 100
y
∑ = sum Step 4: Interpreting the Results
y = ∑ yi yi = individual sample A CV below 10 percent is
n
analysis results considered a good mix. Variation
s = s2 n = total number of in the assay procedure may be as
high as 5 to 6 percent, indicating
s =2 ∑(yi 2)-ny 2 samples that the actual variation due to
n-1 mixing is about 5 percent. If the
Inexpensive calculators are CV is over 10 percent, increase the
where: available that are programmed with mix time and/or inspect the system
%CV = percent coeffi- a statistical function that automati- for factors that caused the poor
cient of variation cally calculates the coefficient of ingredient distribution (e.g.,
s = standard variation or the standard deviation sequence of ingredient addition or
deviation and mean. particle size).
s2 = variance
y = mean

4

Example 1. The sampling scheme that was Literature Cited
To illustrate the variation in salt followed is illustrated in Figure 1.
The lowest salt concentration was Lindley, J. A. 1991. Mixing
concentration for a feed sample, at location 1 (53 percent less than processes for agricultural and food
consider the following example. the mean concentration) and the materials: 1. fundamental of
Samples were taken from a hori- highest salt concentration was at mixing. Agric. Engng Res.
zontal paddle mixer with a 2-ton location 9 (23 percent greater than 48.153-170
capacity using a 4-foot grain probe. the mean concentration). Salt was
Quantab titrators were used to added to the mixer as a premix Title 21, Code of Federal
measure the salt ion content with after ground grain and soybean Regulations, Part 225.30 and 130.
the following results: meal. The auger used to convey the Equipment. 1993 ed.
premix discharged near the center
Location Salt (%) of the mixer. Complete feed was Title 21, Code of Federal
1 0.24 discharged from the mixer end Regulations, Part 225.65, 165.
2 0.51 where samples 9 and 10 were Equipment Cleanout Procedures.
3 0.55 drawn. 1993 ed.
4 0.42
5 0.59 Results suggest that insufficient
6 0.55 mixing action (or time) resulted in
7 0.59 a low micro-ingredient distribution
8 0.59 at one end of the mixer. Possible
9 0.64 corrective action could include
10 0.55 positioning the premix auger closer
to sampling locations 1 and 2 (end
Mean 0.523 opposite to the mixer discharge
port) or increasing mixing time
Standard Deviation 0.1156 from 3 to 5 minutes.

Coefficient of Variation 22.10% A particle size evaluation
revealed that ground milo was
1,150 microns. Adjusting the roller
mill to reduce particle size below
800 microns should improve mixer
performance and feed efficiency in
this example.

Brand names appearing in this publication are for product identification purposes only. No endorsement is intended,
nor is criticism implied of similar products not mentioned.

Publications from Kansas State University are available on the World Wide Web at: http://www.oznet.ksu.edu

Contents of this publication may be freely reproduced for educational purposes. All other rights reserved. In each case, credit Tim Herrman
and Keith Behnke, Testing Mixer Performance, Kansas State University, October 1994.

Kansas State University Agricultural Experiment Station and Cooperative Extension Service

MF-1172 October 1994

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