How long a set of knives last in a TMR mixer is a function of the material they are made from (e.g. steel vs. carbide-tipped vs. carbide-coated), the number of loads mixed per day, the types and amounts of ingredients processed (e.g. chopped silage vs. round bales) and degree of ingredient contamination with soil, sand and especially small stones and rocks.
Feedstuffs, and forages in particular, are very abrasive and wear normal steel at an amazing rate. Yet, the greatest cause of wear will be from stones and other hard material that cause chipping and premature dulling of the knives. Thus steel blades generally last the least amount of time and require regular sharpening, while carbide blades last much longer and are well worth the higher price, especially when processing forage.
Carbide-tipped blades are very resistant to abrasion and can stay sharp for a long time, however they are very susceptible to chipping and cannot be sharpened. Carbide-coated knives are self-sharpening and generally less susceptible to chipping than carbide-tipped knives, and overall seem to be the best choice, though there can still be a wide range in quality and resistance to wear.
With vertical auger mixers, effectiveness of processing and quality of cut can be improved by replacing a portion of the blades every 6 months or so. Since the majority of the actual cutting takes place towards the bottom third of the mixer where the auger diameter and edge speed is greatest, this is where the knives wear the fastest. Consequently, the bottom blades can be replaced with new ones, and then the replaced bladed moved upwards, to keep the lower blades as sharp as possible, while still maintaining effectiveness in breaking up whole bales with the upper blades.
Dr. Alan S. Vaage Ph.D.
Ruminant Nutritionist