This is a 3D model of a flaking mill (flaker) used in the oil seed industry.
Once the cracks have been discharged from a conditioner, they are sent to the flaker. A magnetic separator is usually mounted on the main flaker feed line to remove any entrained ferrous metals, and the feed hoppers themselves should be fitted with level switches to prevent over feeding.
The flaker itself consists of a single pair of smooth rolls with a small operational clearance between the two. The cracks enter the flaker from a feed hopper; they then pass between the flaker mill rolls where they are pressed flat. This process is known as flaking. For soybeans, this is the final preparation stage prior to solvent extraction. It should be noted that the rolls have an operational clearance, but are mounted with no clearance at all.
After flaking, the flakes pass through a discharge chute to a hopper or conveyor. Air is passed through the flakes to remove the moisture that has accumulated on the flake surface due to flaking. If the moisture was allowed to remain it would hinder the solvent’s access to the flake, and this would slow the oil extraction process.
Design and Function
The primary purpose of flaking is to increase the contact cross sectional area of the flake. This increase in area allows more solvent -which is used to extract the oil in the next process stage- to come into contact with the oil in the cells. The path of the oil escaping the cells is also shorter due to flaking. Both of these factors lead to a much more efficient solvent extraction process. Ideally, the flakes should have a thickness of between 0.25mm and 0.40mm, but the exact thickness depends upon the type of extractor used.
One of the most important aspects of flaking is ensuring that the feed is fed evenly across the entire length of the flaker mill rolls. A feeder is used to spread the feed uniformly across the rolls, this ensures the flaker is operating at maximum capacity and also promotes even wear across the rolls.
To ensure flake uniform thickness, the rolls are set using hydraulic cylinders or mechanical spindles. The standard 0.5m diameter roll is no longer standard due to the recent trend of building higher capacity flakers. Roll diameters of up to 80cm, and roll lengths of over 200cm, are now becoming more common.
Flakes should be sampled regularly to ensure correct thickness uniformity. It's typical that flaker rolls wear more in the middle than at the edges, this unfortunately leads to thicker flakes passing through the center of the mill where the clearance between the rolls is greatest. Some adjustments can be made to correct this, but this can also cause stress on the rolls which leads to pitting or chipping of the roll. If the roll is deformed, it should be replaced or ground as soon as possible. Grinding can usually be done in-situ without the need for removing the rolls.