Check list for feed mill visits
Important aspects that can be reviewed during regular walkthroughs of the feed mill
By Wilmer Pacheco, Adam Fahrenholz, and Charles Stark
Ensuring that a feed mill is functioning correctly and complying with federal and state regulations is essential when producing feeds that fulfill the nutritional needs of animals. We have had the opportunity to visit several feed mills in different countries in North America, South America, Europe, the Middle East and North Africa, and of course several states within the United States in particular. During these visits, there are several key points we typically review depending on facility layouts and the type of animal feeds being produced. This month, we’d like to share some thoughts regarding some important aspects that can be reviewed during regular walkthroughs of the feed mill.
Receiving Operations
Ingredient definitions: It is very important to have specification sheets for all ingredients being used at any feed mill. Ingredient specification sheets should contain critical information such as expected nutrient values (e.g., minimum protein and fat, maximum fiber and moisture, etc.), expected physical properties (e.g., color, odor, particle size, etc.), basis for rejection, and statements that address regulatory compliance. A feed mill should share ingredient specification sheets with suppliers, and include these sheets as part of the purchasing agreement.
Ingredient receiving: Receiving pits should have a grid large enough to allow adequate ingredient flowability, but small enough to prevent foreign material (e.g., plastic, wood, etc.) from entering the feed mill. A temporary additional grid is sometimes used for certain problematic ingredients with the highest likelihood of containing smaller and/or particularly concerning foreign material.
Warehousing: Ingredients should be placed at least one foot away from any wall. Ensuring ingredients have an adequate distance from walls can increase cleanliness, discourage pests (especially mice), and prevent ingredient contamination if condensation occurs on the walls. Other important considerations are to use the first in, first out (FIFO) principle and to store medications away from micro ingredients (e.g., vitamins, minerals, amino acids, etc.). Some feed mills may store micro ingredients in moisture- and temperature-controlled rooms if available. Additionally, shatter-resistant light bulbs and adequate lighting should be used to prevent contamination and allow for proper inspection of ingredients during storage.
Grinding Operations
Feeder: It is important to ensure feeders are in good working condition without excessive wear. Leaking feeders will lead to inconsistent hammer wear which can increase variations in motor load and poor grinding operations. In addition, a change in the size of the ingredient being ground (e.g., wheat instead of corn) may lead to inconsistent feeding of the grinding chamber due to higher leakage of small grains through the feeder if it is improperly adjusted or maintained. Leakage throughout the feeders can also create issues even before the equipment starts operating. When the aspiration system starts, material can potentially be pulled through the feeder into the grinding chamber. This could create a higher energy demand or plug the system before the grinding operation begins.
Magnets: Cleaning and monitoring the magnets on a daily basis helps protect the grinding equipment. Regularly checking magnets directly ahead of grinding will also provide an indication as to whether magnets upstream (e.g., in the transitions of the elevators that transfer the material from the storage silos to the surge over the grinding system) are being cleaned correctly. Magnets should be cleaned more frequently after preventive or corrective maintenance (e.g., changing elevator buckets) as there is a higher likelihood of foreign material entering the transferring and grinding systems.
Hammers: Hammers should have a uniform wear regardless of the position in the grinding chamber. Uneven wear could indicate poor feeding of the material or lack of hammer rotation. Using hammers with a hard facing (e.g., tungsten carbide coated hammers) can increase their life span and grinding efficiency. These results occur due to the hammers having a higher number of sharp edges compared to normal hammers that hit the material with a dull and flat surface.
Screens: Screens should not be damaged nor contain holes that could allow unground material to pass through. Holes in hammermill screens could create problems with particle size distribution (e.g., a higher percentage of large particles) and lead to problems in other feed mill operations, particularly during pelleting. If the feed cleaners between the mixer and the mash or finished feed bins (if mash diets are being produced) are removing whole grains, this could be an indicator of problems with holes in the hammer screens. It is also important to monitor the amount of material being ground with each screen as overuse of screens can cause heavy wear. As a result of this wear, material can be deflected and prevented from passing through the screens, which can reduce grinding capacity and efficiency. Feed mill managers and maintenance personnel should record amps and production rates of new hammers and screens and then monitor the decrease in production rate as those hammers and screens wear to determine the point at which the increased energy cost exceeds the replacement cost of new equipment.
Batching and Mixing
Scale accuracy: The precision (e.g., the minimum unit of weighing) and accuracy of scales should allow for weighing all desired ingredients within a range of tolerance established by regulation and quality specifications.
Flexible connectors: Flexible connectors on scales should be in good condition to avoid scale variations due to vibration when the scales are not being loaded or discharging ingredients. During a walkthrough, it is critical to spend time in the control room and monitor the scales for any undesirable variation.
Scale discharges: Ingredients should enter the mixer following this order: majors (e.g., ground corn, SBM, DDGS), minors (e.g., phosphates, carbonates, salt), micros (vitamin and mineral premixes, amino acids, enzymes), and then any ingredients added by hand. Discharging major and minor scales at the same time can create uniformity issues for the minor ingredients, which are typically denser. If these ingredients enter the mixer too quickly, they can accumulate at the bottom of the mixer and mix poorly. Depending on the facility, a 3 to 5 second delay in discharging the minor scale could improve mixer uniformity.
Air vents: Do not forget that mixers are never completely empty as they are full of air. This air must be displaced through a venting system as ingredients enter the mixer. If the system is being plugged by excessive accumulation of fine particles or if the air displacement gates do not open correctly, the mixer will be constantly under pressure. Increased pressure can create issues when micro ingredients are entering the mixer by gravity as the air under pressure will try to move them in the opposite direction (upwards) and create mixing problems.
Mixer filling rate: It is important to remember that mixers are designed in terms of volume rather than weight. Therefore, stating that a mixer has 8- or 10-ton capacity could be inaccurate as the capacity of the mixer will be influenced by the density of the ingredients in a batch. Feed mills producing corn-soybean meal-based diets could potentially mix the same number of tons in a batch. However, commercial feed mills producing a wide range of finished feeds for various species must pay attention to the density of their formulas and adjust the weight of the batch to avoid overfilling the mixer.
Liquid addition (mixer): Liquid ingredients (e.g., amino acids, choline, fat) should be added into the mixer after completion of the dry cycle. Adding liquid as dry ingredients enter the mixer can lead to clumping of ingredients and poor mixing overall. Of course, this will depend on the amount of liquid ingredients added into the mixer. If multiple liquids are added, the ingredient with the lowest inclusion or the one that has the greatest water solubility should be added first.
Pelleting Process
Feed conditioning: During feed conditioning, it is important to monitor conditioner filling and feed distribution. A conditioner filling of 60% is recommended. Both factors can be altered by adjusting the angle of the picks/paddles or using a variable frequency drive (VFD) on the drive motor. If one section of the conditioner is not completely full, steam could escape through the top of the feed and condense on the opposite side. This unwanted condensation can create differences in the meal’s moisture content entering the pelleting chamber, which can lead to higher variation in motor load or roll slips.
Pellet mill motor: It is important to pay attention to the pellet mill motor load as variations could be caused by feed surges from upstream equipment (e.g., conditioner, hygieniser), poor mash feeding into the pellet mill, moisture differences in the conditioned mash, poor distribution of feed in the pelleting chamber, and/or poor adjustments of rolls in relation to the pellet die.
Rolls and die: Both components should wear evenly and the die should be free of foreign material. Use food grade grease when lubricating the rolls and monitor grease usage so as not to use an excessive amount that will leak into the feed nor an insufficient amount for bearing protection.
Cooling: The bed depth in the cooler/dryer should be uniform regardless of the cooling system style (e.g., horizontal or counterflow cooler). Differences in bed depth could be caused by inconsistent filling or discharging of the cooler. Differences in bed depth can lead to moisture and temperature differences in the pellets exiting the cooler. Up to a 0.8% moisture difference has been previously observed due to poor feed distribution. Moisture differences can lead to finished feeds with different nutrient density and physical quality. In addition to measuring the temperature of the pellets leaving the cooler, it is important to monitor moisture content (using an in-line moisture analyzer or laboratory methods) and correct potential issues by either changing pellet bed depth or airflow.
Crumbling: To produce uniform crumbles, rolls have to be aligned with the same clearance across the width of the rolls. Pellets must be uniformly fed across the entire width to promote a consistent wear and crumble size. Inconsistent or uneven feed distribution leads to uneven wear of the rolls, which can negatively influence crumble uniformity and create more fines due to attrition of pellets. An easy way to verify proper alignment of the rolls is to collect samples from the sides and the center of the crumbler and compare them visually. In general, around 75% of the crumbles should be between 1- and 3-mm. Crumble quality could be evaluated using a box that separates the crumbles by size; less than 1-mm, 1- to 2-mm, 2-to 3-mm, and more than 3-mm. It can also be measured using U.S. Sieve numbers: #18 (1,000 µm), #10 (2,000 µm), and #7 or 6 (2,830 or 3,360 µm).
Post pellet liquid application systems: It is important to make sure that these systems are calibrated (both dry flow and liquid flow) and can accurately add the proper amount of liquid ingredients. If using nozzles, it must be ensured they are atomizing the liquid ingredient and adding it in a fan pattern.
Load-Out/Packaging
Bulk load-out processes should be inspected for accurate weighing, minimal damage to pelleted feeds, and general cleanliness. Weighing can be audited by verifying tare weights on specific trucks on a regular basis, while physical quality can be verified by sampling. Both of these actions are often already parts of a regular quality assurance program verifying that feeds are not cross contaminated in a non-empty truck and that they meet nutritional specifications. If the loadout area is not clean, a walkthrough should identify where messes are being created.
For packaged feeds, bagging scales should be regularly checked, and bag weights should also be verified as part of a quality program. A regular walkthrough should verify these checks are being completed and should also observe tag/label placement and clarity, pallet uniformity, and proper warehousing procedures.
Lastly, some general items that should be noted during a full facility walkthrough might include: making sure all containers are labeled, that utensils (e.g., shovels, brooms) are properly maintained and separated by area and/or use type if necessary (possibly by use of color codes to prevent cross contamination from a dirty to a clean area), that trip/slip/fall hazards are not present, that employees are using PPE as appropriate, and that general sanitation is meeting the goals set forth by facility management. Each of these important key points can easily be reviewed during the daily and weekly walks around the feed mill, and doing so regularly will help to make sure each individual operation is working correctly and that the facility as a whole is efficient, safe, and producing a good quality feed.