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Wear and Tear

Features - Operations Focus

Manufacturers of shredding and grinding equipment know the signs it is time to change wear parts.

Kelley Stoklosa May 17, 2012

Running multiple types of materials through a grinder or shredder can take a lot out of the machine’s wear parts. Once wear parts start to break down, a product’s quality will diminish. An operator could begin to notice greater fuel consumption and possibly an increase of black smoke as the engine struggles to process material.

Knowing when to replace wear parts and addressing replacement in a timely manner can help extend the life of a machine and maintain product quality.


Dirty Jobs
The general consensus among equipment manufacturers is that abrasive materials such as sand and dirt as well wet materials like leaves and grass are tough on a machine’s wear parts. Asphalt shingles can cause the most wear, according to manufacturers. Like dirt, shingles will break down the wear parts quickly by gripping onto the parts.

“It is hard to imagine a more abrasive feed stock than shingles, says Shane Donnelly, of DoppstadtUS, a grinder and shredder manufacturer located in Avon, Ohio.

Manufacturers say lower speed machines like shredders will experience wear to their parts at a slower pace than faster speed machines like grinders.

Debris will have a dramatic effect of the life of a wear part, says David Daymon, dealer parts sales lead for Morbark Inc., a manufacturer of equipment for the forestry, recycling, and biomass markets located in Winn, Mich. Operators need to understand what they are grinding or shredding.

He says, “If it is a dirty application like a landfill and you have a lot of sand or gravel or dirty material like stumps, it will affect your wear parts by almost 60-70 percent less wear life than if you were running clean material through a machine.”
 

Speed Control
Tim Griffing of Continental Biomass Inc. (CBI), a Newton, N.H.-based company that specializes in stationary and portable biomass recovery systems, says grinders will show greater wear more quickly than a shredder, mainly due to the speed of a grinder.

“Being slow speed, there is very little wear,” Griffing says, adding, “Speed is crucial to wear. The higher the speed, the more wear. The finer the product, the more wear. If you want to make a small product you are going to have more wear.”

Grass, leaves and dirt cause the most wear in a grinder, says Griffing. “If you put grass, leaves and dirt in a shredder, it won’t matter—it will fall through before it does anything,” he adds.

Because a shredder operates at a low speed, the wear will typically take place at a slower rate compared to a higher-speed grinder. However, shredders with larger teeth designed to handle material with a larger diameter will be more sensitive to heavily contaminated material.

“For example,” Donnelly says, “a more aggressive tooth may work in logs, stumps and green waste but may not be suited to contaminated material in C&D [settings]. The more fines or dirt that is in the in feed material will determine how much wear there is due to abrasion.”

While harder surfaced wear parts will likely resist breaking down due to abrasion, they also are more apt to crack or break when they come in contact with a contaminant, Donnelly adds. Similarly, heterogeneous feed stocks will make it more difficult to predict what the deterioration characteristics will be on a machine’s wear parts.

Griffing says anyone using a grinder should look out for steel contamination, as the higher-speed machines will not take well to this type of material.

“We use different speed rotors for different applications. If we are going to do a small product, we are going to use a high-speed grinder. If we are doing a product that is contaminated with steel we use a medium speed grinder,” Griffing explains.
 

Slow Motion
Wear and tear will happen at a slower rate on a shredder, typically, than on a grinder, but wear parts should still be inspected on a regular basis. General maintenance will go a long way on a shredder, just as it will with a grinder. Low-speed, high-torque shredders also have parts on them that will need to be maintained and eventually replaced. Namely, center cutting edges and the replaceable tips will break down over time, according to David Whitelaw of Grinder Guy, Tampa, Fla. Some shredders do not have replaceable parts, but work can be performed on them to keep product quality high.

“This is usually about 10-20 percent compared to high speed grinders,” says Whitelaw. “Some low-speed shredders do not have replaceable tips or replaceable cutting edges. This means welding must be done on a consistent basis to keep material in spec and to keep the machine from needing replaced. All this heat from welding stresses the metals of the shredders. Product size increasing and reduced production is the first sign of wear on the shredding shafts.”


Time for Change

The most telling sign it is time to switch out wear parts will be the quality of the finished product. New wear parts will produce a uniform product size, with less production effort. As the parts begin to succumb to time and wear, production efforts will have to intensify to maintain a consistent, quality product. After some time, even increased production efforts cannot accommodate for the worn out wear parts and the end product will come out of the shredder or grinder off spec.

Donnelly says experienced operators would be able to tell when their engine is starting to use more RPMs (revolutions per minute). He warns that this can cause overheating and a higher volume of black smoke being emitted from the exhaust as the engine tries to keep up with the feedstock. An operator also likely will notice the machine is going through fuel faster than usual.

Consistency is not only preferred when it comes to feedstock, says Whitelaw, it is also better to keep the same operator with the same machine.

“When multiple operators are involved, operational cost is sure to increase because accountability goes out the window,” he says. “An experienced operator or at least the same operator on the same grinder or shredder can save thousands in wear and operational cost.”

Replacements are easy to schedule if the material is consistent. Whitelaw gives the example that grinding a homogeneous material like pallets might be in spec for 100 hours per tip life, making it simple to plan when the machine needs to be serviced. He adds that if each product is produced individually, it should still be possible to estimate a wear life for machines that are processing multiple materials. Keeping a log of tonnage and the number of hours between each wear parts service will help an operator be prepared by being able to see in black and white how processing various material sources will affect parts.

“We recommend checking [wear parts] twice a day, but most people only check them maybe once a day,” says Griffing about wear part maintenance.

It also is important to remember that equipment comes with an operator’s manual for a reason. Many equipment manufacturers like Donnelly stress the importance of not getting too lax on general maintenance like greasing and regular oil changes and taking samples to determine if there is any contamination in the machine.

 

The author is assistant editor and can be contacted at kstoklosa@gie.net.

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