A Perspective On Mixing And Mix Uniformity: Part 3 - Mixing Equipment, Horizontal Batch Mixer, Short

Mixing Equipment

There are three basic types of mixers used in the feed blending operation: horizontal batch, vertical batch, and continuous. The horizontal batch mixer is by far the most common piece of blending equipment used. The vertical screw mixer is sometimes found in smaller feed mills and is quite frequently used on farms. They are generally slower than a comparably sized horizontal blender.

The continuous blenders vary widely in design and capacity. They are often used to blend liquids into a base mix as well as in the steam conditioning of a pellet mash. Additionally, the continuous mixers are found in plants where continuous rather than batch proportioning is used to arrive at a final homogeneous blend of ingredients.

Horizontal Batch Mixer

This blender is generally equipped with right and left hand ribbon flights which convey material from one end to the other while it is tumbling in the mixer. Other designs include batch paddle mixers in which plows or paddles replace the ribbons. By using paddles, an even higher percentage of liquids may be added at the mixer. The plows are adjustable so that pitch can be set to obtain the desired blending operation.

Horizontal mixers are frequently equipped with multiple discharge openings or with a bottom, which opens along the entire length to facilitate rapid and complete cleanout. They may also be equipped with a surge bin beneath the mixer to reduce emptying and cycle time.

The major advantages of the horizontal mixer over the vertical mixer are the shorter mixing time and the fact that higher percentages of liquid may be added to the blend.

Short-Cycle Mixer

The current generation of mixers are often referred to as Ashort-cycle@ mixers because they are so effective at mixing that a 1.0 minute mixing cycle or less can be obtained. These mixers generally have twin mixing rotors or twin shafts with paddles. Studies conducted at Kansas State on such a mixer (Forberg) found that a simple ration had a CV of less than 5% after only 15 seconds of mix time. A more complex formula with up to 5% liquid addition will mix in less than one minute.

If a short cycle mixer is to be retrofitted into an existing feed mill, caution should be taken to ensure that the batching system is capable of a cycle time less than the anticipated mixing cycle.

These mixers are more expensive than the more typical ribbon mixers but have attributes that are attractive in many situations.