Gyratory Crusher

Overview

The primary gyratory crusher is the first size-reduction machine in most large open-pit mines, accepting run-of-mine rock directly from 200–400 t haul trucks and reducing boulders up to 1.5 m across to a product passing roughly 200 mm. Machines are designated by feed opening and mantle diameter, a "60-110" has a 60-inch (1,524 mm) opening, and the largest pass more than 10,000 t/h. Unlike a jaw crusher, which crushes on alternate strokes, a gyratory crushes continuously around its full circumference, which is why it dominates duties above about 2,000 t/h.

The working principle dates to Charles Brown's 1877 patent and has changed remarkably little: a conical head gyrates inside a fixed conical bowl, and rock falling into the annular cavity between them is nipped, broken, and dropped further down on each gyration until it exits at the discharge setting.

How it works

The Main Shaft Assembly hangs from the top of the machine in the Spider Assembly, a two-armed casting spanning the feed opening whose bronze Spider Bushing acts as a spherical pivot. At the shaft's lower end, the Eccentric Assembly does the work: the Eccentric Sleeve sleeve, its bore offset 25–50 mm from its rotation axis, turns at 85–150 rpm around the shaft. The shaft top is fixed at the spider pivot, so the rotating offset swings the shaft bottom in a circle and the head sweeps a conical path, the gyration. Importantly the head does not spin with the eccentric; it rolls slowly against the rock load, distributing wear around the Mantle.

Torque enters through the Drive Train: a 400–1,200 kW Main Drive Motor turns the horizontal Countershaft, whose spiral Bevel Pinion meshes with the Bevel Ring Gear shrunk onto the eccentric. The crushing chamber is formed between the manganese-steel mantle on the head and the tiers of Concave Ring segments lining the Top Shell. Both surfaces are Hadfield manganese steel, which work-hardens from ~200 HB to over 500 HB under impact, and both are seated on poured Liner Backing Compound so crushing loads spread into the shells without point contact.

Hydraulic setting adjustment

The discharge setting is controlled by the Hydraulic Adjustment (Hydroset) system, an arrangement introduced by Allis-Chalmers in the 1940s and now universal. The entire main shaft, several hundred tonnes including the head, rests on the Step Bearing atop the Hydroset Piston in a vertical cylinder in the bottom shell hub. Pumping oil under the piston raises the shaft, closing the gap between mantle and concaves; bleeding oil lowers it. Operators use this daily to compensate liner wear and hold a constant product size, reading shaft height from the Shaft Position Transducer.

The same circuit is the overload protection. When tramp metal, a tooth from a shovel bucket, a drill rod, enters the chamber, crushing force spikes and the Hydroset Power Unit relief valving lets the shaft drop rapidly, opening the setting to pass the object before structural damage occurs. The system then repressurises and restores the setting automatically.

Lubrication and sealing

Every sliding interface, eccentric bushings, step bearing, gear mesh, countershaft, is flooded by the Lubrication System, a separate skid circulating 200–400 L/min of ISO VG 150–320 oil through duplex Duplex Oil Filter elements and a Lube Oil Cooler. Loss of lube flow trips the main drive within seconds; bushing temperature trends from the embedded Temperature Sensor (RTD) RTDs are the primary health indicator for the eccentric. Rock dust is the enemy of all of this, so the Dust Seal Assembly, a spherical collar between head and bottom shell, usually pressurised with filtered air, excludes fines from the eccentric chamber.

Operation and wear life

Gyratories run choke-fed: the Control & Monitoring System regulates the upstream apron feeder to keep the chamber full, which improves rock-on-rock breakage and evens liner wear. Mantles last 6–12 months and concaves somewhat longer, with relines being the dominant maintenance event, a full concave change takes 3–7 days of crane work inside the Top Shell. Spider arm shields, discharge liners and the spider bushing are the other recurring consumables. A well-maintained machine runs 15,000–20,000 hours between major overhauls and the shells themselves last the life of the mine.