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Safe and sound: Crusher safety

By |  July 14, 2015

PQ1507_crusher-safety1RA rock the size of a dining room table is plugged in the jaw crusher. After assessing the situation, a few people decide to wrap a chain around the rock and lift it out with a wheel loader.

After securing the chain around the rock in the crushing chamber, a man still in the chamber tells the loader operator to lift the rock. The operator lifts it about three feet into the air when, suddenly, the chain snaps. The rock plunges back into the crusher, missing the man’s leg by a matter of inches.

Stories like these involving crusher blockages unfortunately still happen in the industry. Fortunately, this particular event unfolded without an injury. Still, an inch or two one way or another can often make the difference between a safe trip home from work and no trip home at all.

“I’ve heard and read stories about guys getting killed,” says Paul Smith, international marketing manager for Astec’s Aggregate and Mining Group. “These machines can be deadly. After 20 years of climbing into quarries, I still keep my head on a swivel.”

New equipment and technologies have emerged to minimize some of the dangers associated with clearing a blocked crusher. These have surely eliminated some accidents and enhanced worker safety.

Still, a crusher accident can happen in a moment’s notice. When a worker makes a poor decision. When someone is in a rush. When someone is simply inexperienced.

Aggregate producers can’t control all of the factors that lead to accidents related to crusher blockages. They can, however, create a work environment and culture that best positions people to return home from work every day.

Best use of your workforce

To Smith, one of the key factors that should be addressed related to crusher safety is a company’s workforce. A number of people operating and working around crushing equipment don’t have the adequate experience, he says. Producers and recyclers sometimes turn to a transient workforce, and that can present problems.

“Our industry is so much about tribal knowledge,” Smith says. “We’re still relying on grandpa to educate a grandson to operate a plant. Or, we’re adding crews to do short-time jobs and leaning on temporary labor.”

Transient workers might know how to operate loaders, Smith says, but do they know how to run a crushing plant? Are they shoving oversized material into the crusher? Are they packing the crusher full?

“Ultimately, it still comes back to the person feeding the plant,” Smith says. “They need to be properly equipped and understand what we are doing.”

Effective operators and contractors tend to put one of their best teams on crusher duty because they realize production starts and stops with these workers. But teams often consist of just two people – a loader operator and a plant operator. A third person can make a difference in a number of areas, Smith says.

“Any good producer I’ve talked to will have a loader operator, a plant operator and a ground guy,” he says. “Their sole job is to keep an eye on the plant and make sure it doesn’t have any problems.”

The third person is the one who can prevent unnecessary maintenance. For example, if a chute is about to plug up, this worker can help to prevent major issues.

“What would have been a 10-minute cleanup could be a $30,000 repair bill otherwise,” Smith says.

A contribution of that magnitude from a third person on a crushing team single-handedly justifies that person’s employment.

“It’s a luxury to have a third guy, but I would argue that having a guy at $15 an hour on the ground pays for itself,” Smith says. “Maybe this is the new guy who’s being trained, or it’s the boss’ son. I do know that if that guy prevents a cone crusher from going down and losing a thrust bearing once or twice a year, he’s going to pay for himself.”

Operating a crusher at 90 percent efficiency versus 80 percent or less will boost a company’s bottom line, as well. A third person focused on the crushing operation should improve efficiency, Smith adds.

A good loader operator offers advantages, as well.

“We’re always trying to react on the design side to keep a crusher from plugging up, but we still hear from customers that their loader operator is their most important asset,” Smith says.

Barry Proctor, a salesman with Elrus Aggregate Systems, offers loader operators a simple rule to follow as they’re delivering material to a jaw crusher.

“Use a 30-[in.] x 54-[in.] jaw for example,” he says. “Take 80 percent of the first number – that’s 24 in. That’s the lump size you want to put into that crusher. Size the crusher to the size of the material. If you want to have max production, you’ll pay attention to those rules.”

Other helpful tools

The workforce isn’t the only area producers can focus on to avoid crusher blockages and enhance safety related to crushers. The most economical form of crushing is blasting, Smith says, so tighten shot patterns to reduce the amount of oversized material.

Rock breakers are a useful tool to keep oversized rocks from reaching the crusher, too.

“It’s very practical to have a rock breaker right next to the primary crusher,” says Ilkka Somero, Metso’s product manager for jaw crushers. “Often, you don’t even need to break the rocks. It’s enough to pull or push the rocks a little bit. Then the materials flow again.”

Breakers and hydraulic hammers attached to excavators are also useful to reduce oversized material that can be loaded into a crusher, Somero adds. Smith suggests prepping material with a grizzly feeder if possible, as well.

Still, there’s an additional cost associated with a grizzly, he says, as there is with a breaker. A sensor is yet another option for operators to alert themselves when oversized material is present in the feeder. Sensors obviously won’t pull a large rock from the crusher for you, though.

“They still cause the operator to react,” Smith says. “The oversized piece of material still has to be extracted. You have to shut down the plant. It’s not a perfect solution, but it does help you from plugging the crusher.”

Crusher design is another area some manufacturers have focused on to help producers and recyclers avoid blockages and create safer work environments. Sandvik, for example, addresses the blockage issue with its Prisec horizontal shaft impact (HSI) crusher.

According to Rowan Dallimore, an impact crusher manager at Sandvik, the Prisec model can be cleared while the crusher is running. To clear blockages, Dallimore says users stop the feeder and activate the hydraulic system. This lifts either the first or second curtain, allowing a blockage to pass through the crusher.

“Once the blockage has been cleared the curtain can be lowered, and they will reset automatically into the previously set position with the hydraulic system switched off and the feed re-started by the crusher,” says Dallimore, who estimates that the Prisec clears about 90 percent of blockages without having to stop the crusher. “All of this is done with the crusher still running and no operator intervention inside the crusher.”

Such a system saves users considerable time, too. Clearing a blocked crusher can take an hour or more, Dallimore says. He estimates that a typical blockage occurs in a stationary plant between five and six times a year, with mobile crushers experiencing even more blockages.

Recycling’s unique issues

A mobile C&D recycling application, which presents contaminants to a crusher, has its own challenges.

“With the recycling business we never know what we’re going to crush within reason,” Dallimore says. “When it’s on a tracked mobile unit, they can be on one site one week and on a completely different site crushing completely different material the next week.”

Concrete crushing typically involves handling plastics, PVC and rebar, and these present hazards to equipment.

“These don’t necessarily behave well in a crusher,” Smith says. “You have the potential to rip belts; for stuff to get hung up at the bottom of the crusher. Or, it might block the discharge part of the crusher and you get buildup in that area.”

Asphalt presents unique problems in a recycling application, as well. It can stick like chewing gum to discharge chutes and other components, plugging up the machine over time.

Even a few days or a week of use can block up a crusher, Smith says.

“Every producer is encouraged when they start up a new plant to baby the plant for a period of time,” he says. “See how the equipment handles that material. If they move it to a second location, things like moisture index change.”

The introduction of new material on a new site might require more frequent cleaning than before. But even cleaning a crusher presents safety issues.

“I’ve read a story about a guy inside an impact crusher on a recycle job,” Smith says. “The door of the impactor was open, and he was inside it cleaning off some of the asphalt buildup. While in there, he motioned the guy to turn the impactor a little bit. When the guy did that the impactor came up to full speed, and the guy got chewed up in a matter of seconds.”

All the more reason to treat every task related to clearing a blocked crusher with extreme caution.

“Some of these machines behave like Swiss watches: They require a certain amount of oil,” Smith says. “We do a lot of things to safeguard and keep bad things from happening, but you still need to find, hire and train the right people. We really need to do that.”


Take note

Concrete crushing typically involves handling plastics, PVC and rebar, and these present hazards to equipment.

Kevin Yanik

About the Author:

Kevin Yanik is the editor-in-chief of Pit & Quarry magazine. Yanik can be reached at 216-706-3724 or kyanik@northcoastmedia.net.

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