In the early 1900s, crushed stone producers began using portable crushing plants that, according to Rock Products at the time, were "a machine, or rather a combination machine, mounted upon wheels and made in several sizes, varying in capacity from 8 to 20 tph."

But, Cedarapids' 1925 debut of its One-Piece Outfit marked the beginning of truly portable and productive crushing and screening systems. The unit combined a jaw crusher, bucket elevator and revolving screen on a single frame.

In the early 1940s, Cedarapids developed its Commander Series portable crushing and screening plants to assist the U.S. military, particularly the Corp. of Engineers, during World War II. The single-chassis plants combined a 30-in. reciprocating feeder, 4- Yen 10-ft horizontal vibrating screen, 10- Yen 36-in. jaw crusher and 30- Yen 22-in. roll crusher. An elevating wheel returned crushed stone to the screen to close the circuit.

Following the war, many new portable plant configurations appeared on the market. Companies such as Pioneer Engineering Works, Universal Engineering, Lippmann Engineering, Diamond Iron Works, Iowa Manufacturing and New Holland Manufacturing supplied plants as highway work increased in remote areas.

Four portable plants were credited with producing 600,000 tons of asphalt and concrete aggregate for largest highway job in 1947: the Maine Turnpike.

In the late 1950s, portable crushing plants became a critical component of supplying aggregates, particularly in rural areas, as construction geared up on the U.S. interstate highway system. One highway agency director warned that to meet the highway program's estimated demand for 9.7 billion tons of aggregate over the next 13 years, producers needed to get into the "roving rock business."

Aggregate producers' slowness getting into the roving rock business encouraged contractors to do so. Rock Products reported that during the 1958-to-1960 period, about half of the aggregates used in highway construction were produced by highway contractors rather than purchased from established aggregate producers. It is not surprising, therefore, that many current aggregate companies grew out of highway construction firms.

Today, portable crushing/screening plants remain in the mainstream of established aggregate production:

* developing greenfield quarries;

* processing and stockpiling rock at multiple, small- to medium-sized operations; and

* moving about a single large quarry, following the retreat of working faces.

Contractors continue to use portable plants for processing rock on construction sites and for recycling concrete, brick and asphalt. In response to aggregate producers and contractors, manufacturers have developed plant sizes, options and production capabilities to support a wide range of applications. Operators benefit from designs that are more portable, systems that set up and tear down quicker and easier, and production rates that formerly were only possible with large permanent plants.

Buyer beware Making money with a portable crushing plant, however-as more than a few contractors and concrete recyclers have discovered too late-is not as simple as lowering the legs, unfolding the conveyors and pushing a button. Realizing the benefits of a portable system requires correctly matching the plant to the application (see Making a Match, page 32).

A single-chassis or closed-circuit plant, with hopper/feeder, crusher and screen on one frame, can make set up and tear down quicker and mobility easier. But weight and size restrictions limit the size of crusher and screen that can be mounted on one chassis. This, in turn, limits the production rate achievable, depending on the type of crusher and feed material.

Using a hopper/feeder and crusher on one chassis and one or two screens on a second chassis (open-circuit plant) increases transportation costs and set up and tear down time. But, an open-circuit system can accommodate larger, generally higher production-rate units. Lower production costs might offset higher mobilization costs, depending on the amount of material to be crushed at a site.

In tight locations, particularly on construction sites or recycling jobs, a two-chassis plant could make set up, operation and stockpiling difficult. Some producers would argue, however, that two shorter plants provide greater flexibility in arrangement than one long plant.

An open-circuit system also provides more flexibility for incorporating secondary cone crushers or horizontal- or vertical-shaft impactors. For jaw plants, opening the closed-side setting (css) and adding a secondary crusher can dramatically increase throughput. Depending on the material, it also might improve product shape (more cubical) by decreasing the reduction ratio at each crushing stage.

Typical production capabilities for large portable jaw crushers are as great as 600 tph or more at an 8-in. css; typically 200 tph or less at a 2-in. css, according to some manufacturers' data. Rated capacities usually are based on continuous feed of dry material.

Continuous feed is often difficult to achieve in the field. It is partly dependent on a balance between the capability of the loading tool and operator; the recirculating load, if any; and the size of the hopper/feeder.

Mismatched equipment can significantly drive up production costs. A crusher consistently running empty between loader bucketfuls or a loader always waiting for a hopper to empty before dumping its bucket are observed often at portable operations.

A smaller hopper has the advantage of meeting highway weight and height limits without being removed from the crushing plant and transported separately. If a single loading tool, such as a wheel loader, is being moved with the plant, then its size is likely limited to what fits on a lowboy trailer. In this case, a smaller hopper may be sufficient.

On the other hand, if the system can handle it and a larger loader or two smaller loaders are available, a larger, separately transported, skid-mounted or leg -supported hopper may be necessary to maximize production.

What's new? Review of the entire range of portable crushing plants on the market would fill a book. Although standard models satisfy most needs, many manufacturers and fabricators custom-build plants. Following, therefore, is a review of some of the portable plants introduced or promoted by manufacturers during the past year (also see More Information on page 33).

Eagle Crusher Co.'s Stealth3 closed-circuit portable plants use the company's UltraMax 05 impactors with a 33- Yen 32-in. feed opening. The tri-axle Stealth3 is rated at more than 100 tph. A 4- Yen 12-ft double-deck screen separates two products and returns oversize to the integral hopper/feeder.

Grasan's KR1010 portable crushing plant has a Hazemag APSE 1010/Q primary impactor with a 25- Yen 40-in. feed opening. The tandem-axle plant is 45 ft long and weighs 74,500 lb. Six independent hydraulic legs provide complete operational support. Standard auxiliary hydraulic couplings power separate radial stackers or return conveyor. A matching 5- Yen 10-ft screening plant is available.

Kolberg-Pioneer's 3350 portable jaw is rated at 275 to 475 tph at a 4-in. and 8-in. css, respectively. It has a hydraulic, dual-wedge adjustment system to change the css and replaceable lower wear lips. The crusher requires a 200-hp electric motor or 250-hp diesel engine.

Lippmann Milwaukee's 30- Yen 62-in. jaw plant is designed to accept large slabs of concrete. It has a 62-in. Yen 18-ft vibrating grizzly feeder, hydraulic leveling and transfer points with extra clearance to pass rebar and uncrushables. The company also introduced a portable 4248 horizontal-shaft impactor plant with an 8-cu-yd hopper, 15-ft-long vibrating grizzly feeder, under-crusher pan feeder and 60-in. Yen 40 11/42-ft rear discharge conveyor.

Nordberg recently introduced several portable crushing plants, including the quad-axle NW105. It is available in two models: VF, with a front-discharge conveyor; and VFR, which is designed for side discharge but has no on-board conveyor. The C105 jaw crusher has a low profile and a one-side, wedge-type setting adjustment. Options include a variable-speed feeder drive, a fines-reject conveyor, power hydraulic jacking and diesel power. A larger NW125-VF20 jaw plant also is available.

Svedala Industries' DU 1108 and DU 1208 portable jaw crusher plants are rated at 556 tph (8-in. css) and 794 tph (10-in. css), respectively. They both have three axles, 10 11/42-cu-yd hoppers, heavy-duty vibrating grizzly feeders and 42-in. front-discharge conveyors. Maximum travel height is 13 ft 6 in. A crane is not needed to prepare the plant for transport or to set up for crushing. Electric power is standard; diesel power is available.

Telsmith's 3055 jaw crusher, available on a portable chassis, is rated at 195 to 600 tph at a css of 3 11/42 to 8 in. It requires 150 hp.

Like any rock-processing operation, to get the most rock and profit out of a portable crushing plant, the equipment must fit the application. Here are a few factors to consider:

* feed material characteristics-size; compressive strength; abrasiveness; gradation; and, in the case of concrete, steel reinforcement;

* crusher product requirements-number and proportion of aggregate products; gradation; and particle shape;

* mobilization requirements-set up and tear down time constraints, need for a crane; distance transported; number of loads; and highway weight limits; and

* operating requirements-space available for plant set up; power source (electric or diesel); number of operators for the crusher, loading tool and ground maintenance; type of loading tool (excavator, wheel loader or haul truck); need for ramps; dust control; on-site mobility; and production rate.