Operations Focus: Expert Advice

Whether running a jaw crusher, a cone crusher or an impact crusher there are several signs it is time to replace a wear part, with the most obvious being diminishing production. The makeup of the material being fed into a crusher will make a difference in the amount of wear and the metallurgy of the wear part should best suit the job being performed.

While some operators choose the "school of hard knocks" approach to making these determinations, Construction & Demolition Recycling has gathered advice from equipment manufacturers to help make the process of replacing wear parts easier. Sometimes experience is what will help crusher operators know when it is time to replace a part and what the crusher needs, but Gary Smith, president of Construction Equipment Co. (CEC), Tualatin, Ore., advises maintaining a relationship with the equipment manufacturer or dealer.

"Nobody knows the crusher you are running better than the vendor," Smith says. "As design updates and improvements come in, they are going to come from the manufacturer. It is important to maintain that relationship with them to keep current with them on what is available to you to reduce your wear costs."

The following five tips from veterans of the crusher manufacturing business can help make the process of replacing wear parts less of a guessing game.
 

1. Perform a daily visual inspection. Ryan Newman, part sales manager for Astec company KPI-JCI, Yankton, S.D., says when using a horizontal impact crusher, there are many indicators that blow bars will need to be replaced.

"As blow bars wear, you move the apron closer to the rotor to maintain your desired output size. So, you'll have some idea of the wear incurred based on how far you have moved the apron in order to maintain output size."

"A visual inspection no less than one time per day while the machine is not operating is another way to check for wear," he adds.

Other signs that blow bars need to be replaced, according to Newman, are an increase in recirculating load or oversize material coming out of the crusher. "Operators should also note how the wear is occurring; uneven wear can be caused by the feed method or feed rate," Newman says. He also recommends that blow bars extend at least three-quarters of an inch above the rotor to help avoid rotor damage.

When it comes to other impactor liners, Newman says, "You are best served doing a visual inspection no less than one time per day while the crusher is not running. More abrasive applications may require a visual inspection more than one time per day."

Signs that wear parts need to be replaced in a jaw crusher are "purely visual," according to Smith. "You can look down the chamber and see the corrugations are wearing off." He adds that most crushing occurs in the bottom half of the chamber and recommends flipping the jaw dies to get similar surfaces on each one.

In a cone crusher, indicators that wear parts need to be replaced will be a drop in production and an increase in re-circulating material, Smith says.
 

2. Follow the lockout/tagout procedure. Safety should always be of utmost importance in the inspection and replacement of wear parts. Both Smith and Newman emphasize the lockout/tagout procedure, which turns off the power source and ensures that only the person with the key can turn it back on.

"It is the number one thing that can prevent injuries in that situation," Smith says. "It is just too simple not to."

Newman says once the lockout/ tagout is done, the largest safety concerns then become strains, pinch point and crushing type injuries. "Wear parts can weigh anywhere from a few pounds to thousands of pounds," says Newman. "Therefore, one should always ensure the proper lifting devices and techniques are used."
 

3. Consider hardness and abrasiveness when estimating wear life. "The higher the strength or abrasiveness [of material], the shorter the life of the wear part," explains Newman. He adds that the size of the material going through the crusher also should be considered.

"Increased levels of fines that don't need to be crushed will increase the wear rate," Newman says. He emphasizes that all unnecessary fines should bypass the crusher if at all possible.

Asphalt tends to be more abrasive than concrete. Beyond that, Smith says operators should consider the virgin material that the concrete was made from. Some concrete with low silica levels will cause incredibly little wear while higher ranges of silica in concrete makeup will cause more wear.
 

4. Avoid putting contaminants into the crusher. The amount of contaminants introduced, such as re-bar and mesh, can accelerate wear and/or cause failures by puncturing belts and plugging discharge openings. Typically, concrete and construction and demolition debris will possess more contaminants as compared to milled asphalt pavement, Newman warns.

While most crushers have systems built into them to minimize damage caused by tramp iron, those systems do not always prevent damage. In fact, catastrophic damage is still possible. "Steel is not your friend in a crusher," Smith warns.

Oversize material is another common problem that will decrease the life of a wear part. Inadequate preparation of the feed material increases wear and can result in premature failure of the wear parts.
 

5. Use wear parts with a low chrome content if steel is present, otherwise use high chrome. According to Newman, to determine how much chrome a wear part should have in an impactor consider feed size and the amount of steel being sent through the crusher. "I say this because, although a higher chrome content can extend life, it also increases the brittleness of the part."

Newman adds, "The rule of thumb is if steel is present or there is a lot of oversized material, one should use low chrome. If steel is not present and the majority of the material is the correct size for the crusher one can use high chrome. Medium chrome has a niche application somewhere in the middle."

"A higher percentage of magnesium content may be necessary in applications with higher end hardness and abrasiveness," says Newman. Regarding magnesium, he adds, "One does have to be careful, though. If the material is abrasive but not hard, going to a higher percentage of magnesium may not necessarily provide longer life for the wear parts."

The author is associate editor of Construction & Demolition Recycling and can be reached at ksmith@gie.net.