Cracking Mill Performance and Developments

摘要

Using the coarsest roll corrugations that will obtain an acceptable particle size is the best way to minimize fines production and maximize roll corrugation life. For most hot dehulling systems this means 3-1/2 corrugations per inch for the top pair of rolls, and typically 5 corrugations per inch for the bottom pair of rolls. For cold processes, the top corrugations may be either 3-1/2 or 5 corrugations per inch depending on the type and size of soybeans processed. The bottom rolls will typically be 5 or 6 corrugations per inch. Using a 5-5 combination in both the top and bottom rolls may reduce the inventory of spare rolls, and greatly decreases the chances of rolls being installed in the wrong position. For hot dehulling systems, higher roll speed differentials will be required for the cracking rolls, Typically the ratio will be 2:1 to insure a clean cut of the soybean. Even so, the cracked beans from a hot dehulling system will be more elongated and sliver like than the particles produced in cold operations. When a single pair of rolls are used simply to split the bean into 1/2's, a lower ratio of 1.5:1 will generally be acceptable. In cold processed, roll speed differential ratios on the order of 1.5:1 will provide the best results in terms of minimizing fines while providing good hull separation. The 1.5:1 ratio will also promote good roll corrugation life if the cracking mill is properly maintained and operated. The fast roll speed of the cracking mill is important for both machine capacity, and to reduce any tendency for problems with the belt drives (higher speeds =lower tension in the belts). Depending on the diameter of the rolls, fast roll speeds from 750 to nearly 1000 RPM yielding peripheral speeds from 2,500 Ft/Min (10″ diameter) to 3,100 Ft/Min (12″ and 16″ diameter) will be most productive. Lower roll speeds may improve roll corrugation life by reducing slip, but can lead to increased fines production due to higher loading in the nip of the rolls.