If you run a milling machine then you know that wear is going to occur. But there are some areas of the machine that naturally wear more than others. Below are the major wear parts for half-lane and smaller milling units.
The teeth, or tooling, on the drum are probably the biggest wear part of a milling machine because they are in constant contact with the asphalt. These teeth are constantly spinning when grinding the asphalt, but if buildup of material causes a tooth to stop spinning it will cause uneven wear on the tooth, says Tom Chastain, product manager for paving and milling with Dynapac. A worn tooth will affect how well the drum mills. And if the tooth isn't replaced it can wear into the holder and cause more damage to the machine and be costly to repair.
A worn tooth can be visibly seen in two ways. First, a contractor can look at the tooling on the drum and see which teeth are worn or uneven, Chastain says. Round tips indicate even wear, says Jan Schmidt, vice president of product support for Wirtgen America. If a tip is flat on one side it has worn unevenly.
A contractor can also look behind the machine at what he is milling to indicate wear. A worn tooth will produce a solid streak in the milling pattern, according to Chastain.
The lifespan of the teeth varies depending on many different factors. These include the type of material being cut, the depth of the cut, and how fast the milling unit itself is moving, says Schmidt.
How often teeth need replacing also depends on the job and the above factors, says John Hood, sales manager for paving and milling products with Bomag Americas. "Depending on the job and the scope of the work, I've seen tool changes in very abrasive, heavy cut situations done in as short a period of time as every 30 minutes," Hood says. "It's a variable that's all over the place."
Whether you're replacing teeth daily or weekly, the tooling is one wear part a contractor cannot ignore.
Moldboard wear strips
The moldboard helps clean out the trench and keeps cuts clean. These strips are often made of hardened steel or carbide, and like the teeth are in constant contact with the asphalt. That constant contact wears the strips down and can even cause the strips to bend. If they wear too far the containment door will start to wear, Chastain says. Repairs to the containment door can be costly.
Wear on the moldboard results in more material being left in the trench and a less smooth surface. As a result, the finishing crew has more cleanup work to do, Hood says.
Chastain says that on average moldboard wear strips will need to be changed once or twice a season depending on the type of material being milled.
"It's going to be a contractor's decision as far as when they want to do it. Most milling contractors have a set maintenance as far as when they do certain things. But, if the wear strips have worn themselves down to paper thin then you do need to replace them," Chastain says. "If everything looks pretty normal, then they might let it go." Contractors should also keep an eye out to make sure the strips wear evenly, he adds.
Depending on what size milling unit a contractor has, the undercarriage may be tires or tracks, Schmidt says. Most half-lane units will have tracks while smaller utility units can have tracks or tires.
Tires are usually not profiled, Schmidt says, so it's easy to judge where there is wear on the tires. If you see exposed rims, the tires need to be replaced.
On tracked units, track pads cover the undercarriage to protect it from wear and damage. A worn or damaged track pad can cause inconsistent cut patterns, Hood says. "As that pad comes around, instead of making a smooth transition from the top to the ground, it's like you're walking along with a limp," he says. "And when you do that it's tough to maintain a consistent cut because sometimes your grade controls can't keep up and you don't get a good, smooth finish."