"We find that the knives of the shear or cutting area of the concrete pulverizer attachment are most subject to wear and damage. Pins and bushings are also subject to ancillary wear and damage," says Kozul. "When the attachments become worn and damaged, production is noticeably affected. The shears do not cut as well, and the scrap metal we are cutting can get bound in the shears. On concrete pulverizer attachments, materials can also get jammed or bound in the teeth."
Most crushing attachments are designed so that cutting edges can be removed, replaced and taken back to the shop to be "rebuilt" via hardfacing. This can significantly extend their working life.
Rob Murray, product line manager, Stanley Hydraulic Tools, cites a contractor in Minnesota that alternates two sets of cutting edges between three concrete pulverizers. "They don't let the [edges] wear down so far that they have to apply a lot of heat on them to build them back up. And they're able to get four or five years out of two sets," he states.
"The problem comes when... you let them get worn down so far that you have to apply too much heat to them," he explains. "Pretty soon they become brittle and they will break."
A replacement cutting edge kit for a concrete pulverizer may run anywhere from $2,000 to $4,500, depending on the size of the attachment, he notes. Compare that to the cost of a four-hour rebuild plus materials, and the cost difference is substantial.
To eliminate any guesswork, Stanley LaBounty provides a template for its Swift-Lock cutting edges. "A customer can hold the template against the tooth and verify if it is worn down to the point where it needs to be maintained or not," says Murray. The template makes rebuilds easier, as well. "[The welder] is able to use that template to build it back up to original specifications."
Shear blades, on the other hand, aren't designed for rebuilding. "They're made of a special hardened alloy material that is not conducive to being welded on," says Murray. Instead, they are indexable -- in other words, they can be rotated to extend wear life. "If the wear has created a radius on the cutting edge of the blade to a certain specified dimension, it needs to be rotated. When all four sides or segments are used, it's disposed of."
"We watch for the shape of the blades, and look for clearances," notes Kozul. "For a shear to cut correctly, there are specified tolerances between the knives. Once production slows or steel materials start to bind, we try to repair or replace the blades as necessary."
ADDED COSTS OF NEGLECT
It's not uncommon for operators to cut thinner materials when shear blades are sharp, then move into heavier steel or concrete processing as they start to dull. However, there is a risk in letting the blades wear too far.
"If you neglect maintenance and let it wear to an extreme, you could be putting on additional loads that are detrimental to the structure," Rafn points out. "What happens is a tooth will get worn so thin that it will break off and you won't notice it's missing. Then you start wearing into the receiver, and you're in trouble."
On concrete crushing attachments, the factory-machined cast receiver is weld-in replaceable, but at a price roughly equivalent to the cutting edge kit. "It requires a little more effort, but it's not catastrophic," says Rafn. "In the shears, it's a little more problematic because now you're down into some structural material. Yes, it can be remanufactured, but at quite a cost."
The costs of neglect can quickly mount up over time, eating away at your ROI. "You could build a case around doing maintenance [based on] 'this is what it's going to cost' and 'this is what it's going to save.' But if you don't do it" Murray states, "you are going to end up compromising your return on investment schedule."