Editor’s note: This is the second in a series of articles by Fred Fairchild on ways to upgrade feed mills. The first article appeared in the December 2014 issue of World Grain and more articles on this topic will appear in future issues of the magazine.
Almost 15 years ago, Kansas State University released information, through trade journals, regarding validation of testing and identifying the moisture content in mixed feeds and its effect on pellet quality. A flat surface capacitance plate was installed in the end of ribbon mixer and when the product was fully mixed, by time standards recommended for the type of mixer used, the plate and the control system with it was able to accurately determine the moisture content of the mixture.
Using this moisture, tests were run adding various amounts of additional water to the mix to determine the affect the moisture would have on the quality of the pellets made. It was found that consistent PDI’s could be maintained for similar mixes of ingredient to be pelleted. This testing was done using a patented flat plate sensor and control system invented by AgriChem, Inc. of Ham Lake, Minnesota, U.S.
Possible New Approach to Mix Uniformity
The accepted standard for testing the uniformity of mixed feed ingredients has been determining the coefficient of variation between samples taken from a feed at a specific time of mixing. This required using a marker of some type in the mix, stopping the mixer after mixing for a specified time, and taking samples from various locations in the mixer and comparing the strength of the marker from each location and determining the variation of the marker strength for the locations.
If the coefficient of variation Cv was a value of 10 or less, the mix was considered adequately mixed. This testing method required shutting down the mixer and extracting 10 samples from different locations in the mixer. The most commonly used marker was the amount of the salt, and a Quan-Tab test was run on each sample to determine the concentration of salt in each sample and its variance with the other samples taken at that time. This method takes time and is highly subject to human error. The Cv value is basically an index of mixer efficiency versus mixing time.
An outcome of the mixture moisture testing developed for the previous pellet quality study has also shown that the uniformity of a mixture of a feed formula occurs when the moisture in the mix becomes uniform. All of the different ingredients in a mix initially have their own moisture content, and the blending and mixing of these ingredients then becomes a uniform moisture as the mix is blended. An on-line mixing sensor mounted in the end wall of a mixer allows mixing time to be monitored and the mixer to be controlled in real time, according to David Greer, president of AgriChem Inc.
The theory behind this test suggests a possible new approach to determining mixing thoroughness. The dielectric signal sent from the plate sensor has three components that can be calibrated and accurately measured: moisture, density and temperature.
According to experiments recently conducted by AgriChem, Inc., for which a patent is pending, moisture has the greatest affect. When ingredients are added to a mixer, each has its own moisture content. At the beginning of the mixing cycle, each ingredient flows over the sensor plate and the sensor senses their individual
This causes an erratic signal to be sent to the control system readout. Further mixing causes the individual ingredient responses to disappear and generates a new signal characteristic of the mixture. When this value reaches a steady state, it is possible to determine that the ingredients are fully mixed or blended.
AgriChem conducted an experiment to determine if this approach would work for measuring completeness of mixing a batch of ingredients. Results of that experiment are shown in Figure 1. The experiment began by placing corn meal in a small (1,000-pound) research mixer. The addition of the corn meal took 60 seconds, and another 60 seconds of mixing time was required for the sensor to reach a steady state, as seen by the “flat-lining” of the signal from the sensor at about 2 minutes time.
At this point, the meal was fully mixed. To further test the system’s response, two 1% moisture additions were added sequentially to the mix and the signal was measured constantly during the addition and mixing cycle. The signal again flat-lined, indicating mixing was complete with the moisture additions at about 6 minutes.
Thus, the Agrichem sensor and control system may give a precise time when a mixture is complete without stopping to take samples and determining the Cv of mixture. This would allow operators to know when a mix was completely mixed and the mixer is ready to discharge. AgriChem, Inc. plans to do a third-party verification of this method. If verified, this system will allow operators to only mix for the time needed with each mixture. This could be a revelation in the feed industry. AgriChem also may use the sensor signals to possibly determine the density of a mix.
Gear Reducer Improvements
Most conveying and mixing equipment used in the feed industry is powered from fixed speed motors that seldom match the required speed needed for the equipment. A shaft mounted gear reducer was used in most applications. These reducers had a fixed speed ratio between their input and output speeds generally of 5:1, 9:1, 15:1 or 25:1. This resulted in the use of v-belt and pulley speed reduction or speedup between the motor shaft and the gear reducer input shaft. The v-belt drive required regular maintenance to keep the belts tight and the pulleys aligned. These types of pulley drives required awkward removable guards and were highly subject to weather conditions.
In building the new O. H. Kruse Feed Technology Innovation Center at Kansas State University, a newer type of gear reducer drive was used on the conveying equipment. For shaft-mounted situations, Baldor Dodge Motorized Torque-Arm II (MTA) gear reducers were used.
A standard speed motor is directly connected to the reducer and eliminates the need for a v-belt reduction drive. This is possible because this new torque-arm reducer can be obtained with many different internal gearing combinations that allow it to furnish the required output speed for the equipment or speeds close the equipment needs.
This is a completely enclosed and easily mounted motor and gear reducer drive.
Drives for screw conveyors and feeders used Dodge Baldor Quantis Right-Angle Helical Bevel (RHB) reducers with direct coupled motors. This also eliminated the need for v-belt drives for speed reductions.
Using these types of drives greatly reduced maintenance requirements and eliminated v-belt drives. Not having v-belt drives also minimized sources for creating potential fire sources due to slipping belts.