The farm shows are done and I've had an opportunity to see a lot of different mixers. It reinforces my belief that manufacturers are more concerned about marketing than mixing. If you have watched enough rations being mixed and know the basic principles of mixing, it's fairly easy to sort out what works. Without getting into mixer design flaws, here are the basic concepts of how mixing works.
Principle number one: Is it easier to mix one egg with one elephant or a room full of eggs with one elephant? Of course, it's easier to mix equal quantities of dissimilar ingredients. Some sources suggest that the limit is about 40 to 1, or 250 lbs. in a 10,000 lb. ration. Another source says the limit is 3%, or 300 lbs. in a 10,000-lb. ration.
Principle number two: How do you mix a room full of eggs with an elephant? First, let's assume that a room full of eggs is a lot of eggs and we know how big an elephant is. This is actually fairly close to many of our feed rations with big round bales. We have one large item that has to be mixed with many smaller items. It's important to process the ingredients to similar sizes. This is why vertical mixers are so popular. They are able to process big tough ingredients into smaller pieces, so they can be mixed.
Principle number three: Moisture matters. It's been a long time, but the last time I mixed a bag of Quick Crete to set a post, the amount of water I used made a huge difference. A small amount of water in a very dry product will not mix. You must have a minimum amount of liquid to blend in with a dry product. A feed ration acts the same way. The water is absorbed immediately and the rest of the feed is still dry. You may have to distribute your liquids differently, or add it with other ingredients before it goes in the ration.
Principle number four: Tumble, don't shake. The basic mixing principle is tumbling products that fall into a cavity. The mixer has to move material and create holes for this material to fall into. If you watch tumble and reel mixers, this action is very easy to see. As you fill the mixer, the material tumbles and flows until the reel or tub gets so full, the material no longer tumbles. At this point, the material rolls with the movement of the mixer and mixing stops. Auger mixers tumble feed from the top to the bottom as the material is moved to the back. Once the void in the back of the mixer is filled, mixing stops. Vertical mixers are great at processing material because they don’t have any high-pressure pinch points that can destroy the reel and auger mixers. However, vertical mixers have to create their own cavity for the feed to flow into. They do this by making a cavity on the bottom of the feed column, so that feed from the top of the mixer can flow to the bottom. This is not easy to do and many vertical mixers fail to do this. Front to back motion is even more difficult with twin screw mixers. The principle is the same, pull feed from the bottom into the screw and let feed from the top fall into the cavity. In addition, the front screw has to pull in feed from the back screw and the back screw pulls in feed from the front.
If tumbling mixes feed, what's wrong with shaking feed? The next time you buy a can of mixed nuts, finish off half the can and try this. Rotate the can and watch how the peanut hulls, crumbs and nuts blend together. The small and large and the heavy and light pieces all mix together. Of course, now you can't pick out the good pieces. Next, shake the can and the pieces start to separate out. Think about the Penn State Shaker Box Test. As you shake the box, you are separating the big particles from the small ones. Mixers must move and tumble feed into a cavity. If they shake the feed they not only don't mix, but separate the ingredients.