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 still 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.
The HSI primary design, which delivers a higher percentage passing spec the first pass, crushes more efficiently than its jaw counterpart, some experts say, on a wider range of materials, including concrete and asphalt recycle, all soft and medium aggregates and many hard and abrasive aggregates. New thoughts and experiments focusing on the HSI primary, secondary circuit are producing positive real-world results.
Savings In C&D
Greystone Large Crusher
Fresno, Calif.-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 its customers. For most jobs in California and the surrounding states, the UltraMax 1400-45 with its on-board UM 45 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, in Monterey, Calif., at the Fort Ord military base, Kroeker encountered an unusually challenging application for its crushing and screening circuit. The materials being crushed from 352 demolished military homes contained an extremely high amount of reinforcing materials in the 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. The wider settings delivered about 60 percent passing spec the first pass, increasing the amount of returns. Running only 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 UM 04 impactor, the smallest impactor the company manufactures, 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 UM 04 for further reduction. Materials crushed by the UM 04 were discharged to the screen-feed conveyor for final sizing.
Immediately Kroeker experienced a substantial increase in production. According to Strickland, "After installing the UM 04, our 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. Cost savings were reported with impactor blow bars as wear life increased substantially on the UltraMax 1400-45, since the overs were sent to the UM 04 secondary impactor.
After inserting the UM 04 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 UM 04 impactor's aprons were set at 2.5 in. and 1 in. respectively for final reduction. The end result was more than 90 percent passing a Class II A, B 1-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 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.
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.
This results in 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 1211201183802ber of flat and elongated pieces from the compression crusher circuit, which 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. While not an entirely new idea, 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.
The jaw crusher: Suitable for crushing, recycling, demolition, quarry and many other applications
Fintec 1107 is mounted directly onto chassis on 4 pins. This has the added benefit of eliminating stress on the chassis. The crusher is welded in low stress areas, thus giving longer life.
Hydraulic wedge adjustment system on CSS, Minimum CSS of 40mm on recycling applications. The Hydrostatic drive thus enabling reverse movement on crusher to clear any blockages. Maximum clearances under both crushing chamber and also along discharge conveyor for serviceability.
The feed material is directly loaded by an excavator into the feed hopper, which has a nominal volume of 7 m3 (9.2yds3). The feeder is equipped with a grizzly section located at the discharge end for removal of fines. This feature allows the passage of fine material direct to the discharge conveyors, so that it does not pass through the Jaw Crusher feed opening.
This design makes possible a high production capacity by avoiding the accumulation of fine material (sometimes mud or clay) at the bottom end of the crushing chamber. The layer of fine material separated by the grizzly feeder is fed on to the main conveyor belt before the drop point from the jaw crusher and reduces the impact from the larger stones on the belt, beneath the Jaw Crusher. The fine material and the crushed product are transported on the main conveyor.
Set to deliver
By design, impactors deliver a much higher percentage of material passing spec the first pass than that of a jaw crusher. 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. Or, 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, the more oversized material returning to the primary crusher reduces the load potential of primary feed material, limiting hourly production.
At the point in which wear costs increase and productivity decreases, incorporating a smaller secondary HSI crusher in the circuit pays off big. By adding a secondary impactor--like Eagle Crusher's UM 04 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, improving production. Since the percentage passing spec the first time through the crusher is dramatically higher with an impactor primary versus a jaw primary, the secondary impact crusher can be much smaller than a cone secondary. This means not only the initial purchase price but also long term horsepower and fuel requirements are significantly reduced.