Mobile Screening Plant

Overview

A mobile screening plant is an inclined vibrating screen, a feed hopper, a power unit and a set of stockpiling conveyors built onto one tracked chassis so aggregate can be sized at the pit, the recycling yard or the construction site rather than at a fixed plant. A loader tips crushed rock into the hopper, or an upstream crusher feeds it directly, and the plant splits that single feed into several sized products that build separate stockpiles around the machine. Because the plant moves on its own crawlers, it follows the work as stockpiles grow and the feed point changes.

The plant is built from a handful of modules on a common frame. The Feed Hopper and Feeder holds a buffer of rock and meters it onto the deck, the Vibrating Screen does the sizing, the Product Conveyors carry each fraction to its own pile, the Diesel-Hydraulic Power Unit drives every motor, and the Tracked Undercarriage move the plant, all coordinated by the Control System and carried on the Main Chassis.

The vibrating screen

The working heart of the plant is the Vibrating Screen, an inclined three-deck vibrating box. Feed lands on the Top Deck, the coarsest of the three. Material too large to pass its apertures travels down the slope and off the end as oversize. What passes through drops to the Middle Deck, which makes the next cut, and the throughs from that fall to the Bottom Deck for the final split between the smallest product and the fines. With three decks the plant makes four products in one pass: the overs off each deck plus the fines that fall through the bottom.

What sorts the material is motion. The whole Screen Box is thrown several thousand times a minute by the Exciter Drive. The exciter carries a pair of Exciter Shaft units with bolt-on Counterweight masses; when the Exciter Motor spins them, the rotating unbalance throws the box. A single shaft gives a circular stroke, while two shafts geared together through the Exciter Housing give a linear stroke that suits fine and wet duty. The throw, usually 6 to 12 mm, is set by how much counterweight is fitted, and the screen runs at 800 to 1000 rpm. The shaking lifts each particle clear of the media so it gets repeated chances to find a hole. The live box rides on heavy Screen Support Spring units that let it shake freely while keeping the vibration out of the chassis.

Screening media

Each deck carries replaceable Coarse Screen Media, Mid Screen Media and Fine Screen Media panels held in a Deck Frame. Woven spring-steel wire is the usual choice because its open area is high, but fine cuts on damp or clay-bound feed tend to blind, where the holes plug with packed fines, so those decks often use self-cleaning wire or modular polyurethane panels that flex and shed the buildup. Woven media is drawn tight by the Media Tension Rail rails so it does not flap and tear, and it rests on Deck Support Rubber strips that cushion it and cut the noise. When the feed carries clay, Wash Spray Bar nozzles wash water through the decks to scrub the aggregate clean, which turns the plant into a wet screen and sends the dirty water and fines to a separate wash line.

Feeding

Steady, even feed is what makes a screen accurate, so the plant does not dump rock straight onto the deck. The Feed Hopper holds a buffer with Hopper Wall panels that fold out for a wide loader target and fold in for transport. A Static Grizzly bar grid at the back holds tramp oversize out of the machine. Below the hopper a Feed Belt, run by the Feeder Drive Head head, draws material out and spreads it across the full screen width, with Feed Skirting skirting keeping it on the belt. The feed speed is trimmed against screen load so the decks stay covered without flooding, since an overloaded deck buries the media and lets oversize carry through to the wrong pile.

Power and hydraulics

The Diesel-Hydraulic Power Unit unit is a turbocharged Diesel Engine with SCR aftertreatment driving a Hydraulic Pump Pack. A variable Piston Pump feeds the main circuit and Gear Pump units run the auxiliaries, all drawing from the Hydraulic Reservoir. Every function is hydraulic: the exciter, the Track Drive Motor drives, the feeder and every conveyor run on their own hydraulic motors, so each can be started, stopped and speed-trimmed on its own with no mechanical driveline between modules. The Oil Cooler keeps the oil in range, which matters because the exciter draws steady power all shift.

Tracks, chassis and conveyors

The Tracked Undercarriage are excavator-style crawlers for short repositioning moves; the plant is floated on a low loader between sites. Everything bolts to the Main Frame, with the live screen carried on the sprung Screen Cradle cradle and Walkways platforms for deck access. Under the box the Collector Chute chutes gather each fraction and drop it onto the Oversize Conveyor, the Mid Product Conveyor and the Fines Conveyor, folding belts that stockpile each product clear of the others. The whole sequence runs under the PLC Controller, which uses a Level Sensor and pressure sensors to hold the feed rate, and the operator works from a Radio Remote.

Variants and use

Screening plants sit downstream of a crusher in an aggregate train, sizing its product into saleable fractions. Two-deck versions making three products serve simpler sand-and-gravel work, while five-deck versions split many narrow sizes at once. Wet-screen versions with spray bars clean clay-bound feed for concrete sand. The same format scaled down screens topsoil, compost and demolition rubble, where the plant separates reusable hardcore from soil. The tracked, self-powered build trades the lower running cost of a fixed screen house for the ability to size material wherever it is produced.