Apron Feeder Product

Overview

An apron feeder is the standard machine for extracting coarse run-of-mine ore from beneath a dump hopper and metering it into a primary crusher or onto a conveyor. Haul trucks dump 200–400 t loads — including boulders past a metre across — into a hopper directly above the feeder, and the feeder converts that violently intermittent input into a steady, controllable output of anywhere from 500 to over 14,000 t/h. No other feeder type tolerates this combination of impact, lump size and abrasion, which is why apron feeders sit under virtually every gyratory crusher station.

The design borrows directly from crawler-tractor undercarriage. The pans ride on the same sealed-and-lubricated track chain, rollers and tail wheels used on Caterpillar D9/D11-class dozers, components proven over decades against shock and dirt. Manufacturers literally specify chain by dozer class.

How it works

The working element is the Pan Chain Assembly: an endless loop of overlapping Apron Pan plates bolted across two strands of Track Chain Strand. The overlap, like roof shingles reversed against the direction of travel, prevents fines from sifting between pans on the loaded run. Material sits as a deep bed — up to 1.5 m under the hopper — and the feeder works by dragging the bed's bottom layer forward, with the Shear Gate at the hopper exit shearing the column to a set depth.

The Drive Unit turns the Head Shaft Assembly at only a few rpm: a 90–500 kW Drive Motor feeds a shaft-mounted Planetary Gearbox with a ratio in the hundreds to one, restrained by a Torque Arm. Segmented Drive Sprocket rims engage the chain bushings and haul the loaded strand toward discharge. Because torque demand at breakaway — starting under a full hopper of wet, compacted ore — can be 150–200 % of running load, drives are sized for stall and fed by an Variable Frequency Drive that also gives the stepless 0.02–0.40 m/s speed range used for feed-rate control.

At the loading end, the Tail Shaft & Take-Up runs in sliding Take-Up Frame carriages pushed by hydraulic Take-Up Cylinder units. These hold chain tension as pins and bushings wear and elongate the chain by up to several hundred millimetres over its life, and their relief valving cushions the shock when a boulder lands directly over the tail.

Impact and support

Under the dump zone the chain does not ride on rollers at all: continuous Impact Rail beams support the links as a line contact, spreading boulder impact that would destroy individual rollers. Along the rest of the carry run, sealed Carrying Roller units — standard crawler track rollers — take the bed weight, while Return Roller sets guide the empty strand back. All of this hangs off two deep plate-girder Frame Stringer beams in the Feeder Frame, which also reacts the hopper interface loads through the Skirtboard System system and its replaceable Skirt Wear Liner plates.

Some leakage of fines through the pan line is unavoidable, so a Dribble Conveyor — a small drag-chain unit in a trough beneath the feeder — runs continuously, scraping spillage back into the discharge stream instead of letting it bury the undercarriage.

Control and protection

Feed rate is usually closed-loop on the downstream machine: a radar Cavity Level Sensor over the crusher cavity, or the crusher motor power signal, sets the VFD speed so the crusher stays choke-fed without flooding. Protection instrumentation includes a tail-shaft Zero-Speed Sensor that trips the drive on chain stall, take-up pressure monitoring for tension loss or chain breakage, and full-length Pull-Cord Switch emergency stops.

Wear and maintenance

The chain joints dominate the maintenance budget. Sealed Sealed Chain Pin cartridges last 25,000–50,000 hours depending on ore abrasiveness, after which the chain is replaced or re-pinned in sections. Pans themselves, in manganese or chromium-carbide grades, wear mostly at the Pan Wear Bar lip; sprocket tooth wear is handled by swapping bolt-on Sprocket Tooth Segment pieces without removing the head shaft. The Pan Bolt fasteners — over 700 on a large feeder — are torque-audited on schedule, since one loose pan quickly destroys its neighbours. Properly maintained, the frame and shafts outlast several chain generations across a 20-year station life.