There are a lot of things that effect tooth wear...carbide composition (cobalt content), material abrasiveness, material average particle size, drum design (perhaps the biggest influence), water distribution, load in the drum (depth and speed).
Unknown to many users, most carbide used in milling teeth comes from a waste process while making a different carbide product. If it didn't these teeth would cost significatly more. The problem becomes the content of additives in the carbide..additives like cobalt..which affects both the strength and wear resisatance of the carbide materials...too little and the tips become too hard and break easily, too much and the tips wear too fast because the material is softer. Due to the demands in the different primary products which generates the waste carbide, this content may vary over time...greatly affecting the characteristics of the milling teeth.
As most have you have seen, teeth typically wear out in the body before the carbide is gone...known as "body wash". Variations in the amount of wear are in part material dependant (silica content, cutting depth, and particle size), but in great part due to drum design as well. The ultimate design parameter that controls tooth wear is how efficiently a given cutter drum gets the millings up on the primary conveyor belt. The drum which takes the fewest rotations to get the cuttings rap onto the belt will invariably have the best tooth wear. You can guage your drum evacuation efficiency by observing the surge pile remaining at the rear of the drum when lifting out of the cut...a small pile is good. Drum flight configuration, and drum kicker plate angles and locations are key..as well as the elevating angle of the discharge conveyor.
Water jhas a great effect on the wear as well. Not only does water cool the teeth, but it adds lubricant to the cutting action, and tooth rotation in the holders as well. Sufficient water is very important, but equally so is the uniform distribution of water across the drum. Water spray should always be to the front of the tooth, never to the rear of the holder. Spraying water under pressure to the rear of the holder on conventional holders, will drive the milling fines into the rear of the holder bore, which fines will then cause the teeth to bind and wear out very prematurely (flatted carbides most common sign)
Several mentions have been made in other posts on this forum about the importance of cleaning asphalt build up on the sides of the drum. The only time this occurs (with the possible exception of milling sand mixes which by their nature mill "hot") is either when the outside cutters are not correctly positioned and the milling drum is generating drag heat at it's edges, or no water spray is reaching the outer cutters causing overheating. A correctly designed/repaired outside edge pattern in combination with adequate water spray will no longer generate build up at the drum edges.
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Originally Posted by bean
