Digman and Shiebout: Chopper Adjustments and Particle Size

Posted on December 4, 2012 in Forage Foundations
Dr. Matthew Digman with the U.S. Dairy Forage Research Center and Jason Schiebout with Scherer Corrugating & Machine, Inc. led an open discussion on chopper adjustments and particle size in harvesting corn silage.
“There is a lot of debate about proper length of cut and roll gap and how the two interact,” Digman said.
The goal of kernel processing is to achieve starch degradability. Corn is energy to the cow and energy translates to milk. By breaking up the outer, indigestible portion of the corn kernel, the more surface area of digestible material is exposed and the faster digestion can occur.
Length of cut is governed by the cutter head, where the roll speed can be varied. The more material pushed through between cuts can cut down on the machine’s energy use; however, a longer length of cut is generally not good for the cows or managing the porosity in packing a bunker.
When it comes to theoretical lengths of cut (TLC), some parts of the country want to go 1.5-inch TLC. In the Midwest, it is generally 5/8- to 1-inch and California likes it even shorter, Schiebout said.
He discussed various machines and what is being offered today by a number of manufacturers. A trend is bigger processing rolls and all different tooth sizes.
According to Digman, Kevin Shinners, University of Wisconsin biological systems engineering professor, began research in kernel processing in 2000. He found that of all the machine variables, the clearance between processing rolls had the greatest impact.
Schiebout offered the following maintenance tips for processing rolls:
  • Go through the bearings and make sure there is no moisture in there.
  • Even if you don’t replace rolls every year, you should replace the bearings.
  • Look at belt wear.
  • Make sure rolls are parallel.
Determining when to replace rolls has more to do with how many tons run through the machine and if or how often it gets plugged, than it does the amount of hours its been used, Schiebout said. Figuring out how much down time that plugging has cost your operation can help you realize when the cost of a new set of rolls may be advantageous. Another indication of a time to replace the rolls is when the points or tips become evened out.
Kernel processing is an added benefit, and many harvesters were curious how to get an added payback for it. A lot of harvesters are charging by the acre, by the hour or by the ton. Schiebout suggested setting a base target, say 60 percent, with your customer. Then perform a quick processing score by collecting samples in the field a few times a day and send it to a lab. If you process better than 60 percent, you earn a premium.
Digman did caution about setting too high of a premium, as one key factor in your dairy/harvester relationship is to maintain dairy profitability. If you don’t ensure the dairy remains profitable, you may end up not being paid all together.
As to the recommendation for processor settings, Digman said the old recommendation is in flux. For now, consider a start point of 5/8-inch TLC and a roll gap of 3 mm.
“Ultimately it depends on what your customer wants,” Digman concluded.

Category: Equipment
Forage Foundations
Forage harvesting