Now that you own a crop processor,
what should you be looking for?

Mike Rankin
Crops and Soils Agent - Fond du Lac County
University of Wisconsin - Extension

     Obviously, the first step in setting up your forage harvester equipped with a crop processor will be choosing the theoretical length of cut (TLC) and processor roll clearance. Currently, we are recommending that you start with a 3/4 in. TLC and 0.12 in. roll clearance. If processing level is not sufficient for your needs, roll clearance can be reduced, but this will reduce harvesting rate and increase required power. Crop conditions and machine set-up can change throughout the harvesting day, so you should check the level of processing on every load and adjust the roll clearance to deliver the level of processing you need.

     Although processing rolls are hardened, they will wear with time. The rate of wear will vary considerably, and will be affected by such factors as TLC, roll clearance, cutting height, soil type and quality of roll construction. There is no set parameter that is used to quantify roll wear. You will probably first notice roll wear by loss of capacity and insufficient level of processing despite proper roll clearance. The teeth on new rolls will be sharp to the touch. Worn rolls will have a rounded, less aggressive tooth profile. Rolls sometime will wear more on one side than the other because the cutterhead knife helix forces crop toward the direction of the helix. Greater crop flow from the outside rows of large row-crop heads can cause greater processor wear at the edges of the rolls on large capacity self-propelled harvesters.

    If rolls are worn or slightly damaged by a foreign object, they can be re-grooved or replaced. Replacement rolls cost about $1,500 at retail. Rolls can be sent back to the manufacturer for re-grooving for about 1/2 the cost of new rolls. Re-grooved rolls are first annealed to remove the surface hardening, then the grooves are re-machined by bobbing and are flame hardened back to specifications. Tolerance specifications may be difficult to maintain on re-grooved rolls, so the same level of clearance may not be possible as when the rolls were new. Typically, re-grooved rolls will not have the same life as new rolls. Generally, rolls can only be re-grooved once. Also, re-grooved rolls will be slightly smaller in diameter, so shims or bearing adjustments may be required to maintain proper roll clearance.

     About the only other item that causes major concern with crop processors are the roll bearings and bearing mounts. Bearing life is directly related to loading and speed. The roll tip speed should be equal to or slightly greater than cutterhead tip speed so as not to restrict material flow. Small diameter rolls must turn faster than large diameter rolls, so small diameter rolls need to have better quality bearings. What affects bearing life more is loading. Loading is directly related to throughput and TLC. There have been field reports of pre-mature roll bearing failures when operators have gone to TLC greater than 1 inch. This could be due to two factors: bearing load and feeding uniformity.

     Let's discuss bearing loading first. Consider the differences between the cutterhead and the processing rolls. The cutterhead is a massive machine component. It is typically large in diameter so it acts as a flywheel. It is supported by large bearings to withstand the large cutting forces and the drive is typically very robust. On the other hand, the crop processing rolls are usually much smaller in diameter than the cutterhead, with lower capacity bearings and simple belt drives. We need to be careful that we don't transfer too much of the size reduction chore of the forage harvester from the high capacity, robust cutterhead to the processing rolls. The crop processor was not designed to replace the function of the cutterhead, but rather to merely process the kernel and cob fractions.

     Now let's consider feeding uniformity. With most crop processors, one roll is fixed and the other spring loaded to allow for some relative displacement. On most forage harvesters, every other knife must be removed from the cutterhead in order to achieve TLC of 3/4 inch or greater. Fewer knives in the cutterhead can result in less uniform feeding of the crop processor. At very high feed-rates, this non-uniform feeding can cause the rolls to separate slightly as each "slug" passes through the processing rolls. If a cutterhead operates at 1000 rpm and has 6 knives, in less than 3 hours more then 1 million "slugs" have passed through the processing rolls. This type of cycling displacement of the rolls can lead to fatigue failure of the bearings and the slide bearing housings of the spring loaded roll. The longer the TLC, the greater the roll displacement and the faster you can expect bearing or bearing mount failure.

For more information contact Mike Rankin