California Crushing
New Thinking About Primary and Secondary Crushing Saves West Coast Crushing Contractor Big Money
A new way of applying the primary/secondary crusher circuit — combining a larger horizontal-shaft impact (HSI) crusher with a smaller secondary HSI crusher — is proving to be profitable for some aggregates producers, increasing production and decreasing wear costs in an array of applications.

Although some applications call for the primary-jaw/secondary-cone circuit to reduce wear costs and maintain productivity, some producers say it's overkill for crushing many recycle and aggregate materials.

Some experts say the HSI primary design, which delivers a higher percentage passing spec on the first pass, crushes a wider range of materials more efficiently than its jaw counterpart. New thoughts and experiments focusing on the HSI primary/secondary circuit are producing positive results.

Savings in C&D
Fresno, California-based demolition contractor Kroeker Inc. typically uses a portable Eagle Crusher UltraMax 1400-45 open-circuit crushing plant and separate 6-ft. x 20-ft. triple-deck screening plant to tackle a variety of custom crushing applications. For most jobs in California and the surrounding states, the UltraMax 1400-45 — with its on-board UM45 impactor featuring a 50-in. solid-steel rotor — easily handles both primary and secondary crushing while averaging production capacities in excess of 250 TPH.

Recently, at the Fort Ord military base in Monterey, California, Kroeker encountered an unusually challenging application for its crushing and screening circuit. Three hundred fifty-two demolished military homes that needed to be crushed contained an extremely high amount of reinforcing material in their lightweight concrete walls. “On typical jobs, we will fill one 40-yard bin with rebar each week. With this material, we are filling two 40-yard bins every day,” says Jason Strickland, superintendent for Kroeker Inc.

This forced Strickland to open the apron settings on the 1400-45, and production suffered as a result. The wider settings delivered about 60 percent passing spec the first pass, increasing the amount of returns. Running only at about 30 percent of feeder speed capacity, Kroeker averaged 1,500 tons of spec product per day.

Halfway through the more than 100,000-ton application, Kroeker worked with Eagle Crusher to add a skid-mounted UM04 impactor, Eagle's smallest impactor, into the crushing circuit. Instead of oversized materials from the upper and middle screen decks being sent back to the primary impactor, a conveyor carried the overs to the UM04 for further reduction. Materials crushed by the UM04 were discharged to the screen-feed conveyor for final sizing.

Immediately, Kroeker experienced a substantial increase in production. According to Strickland, the company's average production increased to 2,200 tons per day even though much of the feed was a 70 lb./cu. ft. lightweight concrete. Strickland estimates that when crushing normal California concrete recycle, production will increase to 3,000 tons per day.

The cost of the nearly 47 percent increase in productivity at the Fort Ord application was a relatively low $118,000 for the base skid-mounted impactor with diesel power and an additional 4 gallons of fuel per hour. Since the overs were sent to the UM04 secondary impactor, wear life increased substantially on the UltraMax 1400-45 blow bars. Cost savings were reported as a result.

After inserting the UM04 into the circuit, Strickland opened the settings on the UltraMax 1400-45 plant impactor to 4 in. for the primary and 2 in. for the secondary apron. The UM04 impactor's aprons were set at 2.5 in. and 1 in., respectively, for final reduction. The end result, therefore, was more than 90 percent passing a Class II A, B1-in. minus spec the first time through the circuit — from feed material ranging up to 36 in. wide.

Crush, then Re-crush
Kroeker's primary impact crushing plant, producing 60 percent in-spec product on the first pass, limited the amount of concrete needing further reduction. This allowed the company to use a small secondary crusher, an option that cannot be duplicated with a jaw/cone circuit. A potential drawback to the jaw primary/cone secondary circuit is that a high percentage of the materials are crushed twice.

“The optimum product size from a jaw primary crusher is plus 4-in.,” explains Jay Giltz, applications manager for Eagle Crusher Company. “If the settings are closed tighter than this, production declines and jaw dies wear out quickly, increasing wear costs.” This results in an overwhelming majority of the material being sent from the jaw over the screen and into the secondary cone crusher.

With such a high percentage being re-crushed by the cone, producers have no choice but to employ a large secondary crusher to match the capacity of the primary crusher. The results are a higher initial purchase price, higher horsepower requirements, increased fuel consumption, and potentially higher wear costs. Additionally, the final product off the belt may contain a number of flat and elongated pieces from the compression crusher circuit — pieces that will not meet the cubical requirements of asphalt producers.

Producers and contractors like Kroeker are now taking another look at a unique combination of primary and secondary crushing. Many material processors are experiencing significant cost advantages by matching the large primary HSI crusher with a smaller secondary impactor to increase production and maximize component wear life. They are also reaping the benefits of a cleaner cubical spec product that can be sold to all customers.

Set to Deliver
By design, impactors deliver a much higher percentage of material passing spec the first pass than jaw crushers do. The primary and secondary apron settings of an HSI crusher can be set to deliver the desired amount of passing product to optimize circuit efficiency.

In hard rock and heavily reinforced concrete recycle applications, the settings can be opened so that as little as 60 percent passes spec upon initial reduction. In medium rock and normal asphalt and concrete recycle applications, apron settings can be tightened to where more than 80 percent of the initial reduction will pass spec.

After primary reduction and screening, contractors and producers in many applications can successfully re-circulate oversized materials back to the primary impactor for final reduction.

Portable crushing contractors, like many Eagle Crusher customers operating UltraMax crushing and screening plants, make a living off primary and secondary crushing with only one impactor.

However, as the percentage of re-circulating load increases (as in the case of Kroeker's Fort Ord application), contractors should consider adding a secondary impactor to the circuit. Re-circulated material increases wear on impactor blow bars and apron liners, raising the cost per ton produced.

Additionally, oversized material returning to the primary crusher reduces the load potential of primary feed material and limits hourly production.

When wear costs start to increase and productivity to decrease, incorporating a smaller secondary HSI crusher in the circuit pays off big. By adding a secondary impactor — like Eagle Crusher's UM04 impactor with a 27-in. x 32-in. feed opening and production capacities reaching 100 TPH — apron settings in the primary impactor can be increased.

By opening these apron settings and diverting oversized material from the primary circuit, significantly more feed material can be loaded into the primary impactor — thus improving production. Since the percentage passing spec the first time through is dramatically higher with an impactor primary versus a jaw primary, the secondary impact crusher can be much smaller than a cone secondary. This significantly reduces not only the initial purchase price, but also the long-term horsepower and fuel requirements.

“A customer can purchase the UM04 impactor for about one-third the cost of a cone secondary,” says Giltz. Since the apron settings are opened wider, producers and contractors can run higher chrome or titanium bars in the primary crusher without the fear of breaking or chipping a bar.

With the relatively small size of the oversized feed material (averaging no larger than 3 to 4 in.) entering the secondary crusher, super-high chrome blow bars can be used in the secondary crusher. This significantly reduces wear costs and, in turn, the cost per ton of product.

Field Tests Prove Two is Better than One in Aggregate, Too!
Eagle Crusher has a more cost-effective way to crush aggregate — by coupling a horizontal-shaft impact primary with a smaller HSI secondary.

After completing field tests in New York , the company found that placing a UM04 behind an UltraMax® 1400-45 helps alleviate the re-circulating load and produces a more salable #8, 1/2-in.-minus asphalt spec product.

“The UM04 is making an extremely cubical product, which the asphalt producer needs,” comments Bob Mrozinski, field salesman for Capitol Equipment, an Eagle Crusher dealer.

This new way of applying the primary/secondary crusher circuit is proving to be profitable for some aggregates producers. “One of my customers was able to pay off the cost of his 04 skid in just three months,” said Jay Giltz, applications manager for Eagle Crusher Company.

Eagle Crusher also found that when a smaller secondary HSI crusher is coupled with the primary impactor, the wear life of wear parts increases and the overall cost per ton is reduced.