In-Pit Crushing and Conveying System

Overview

An in-pit crushing and conveying system, often shortened to IPCC, moves ore and waste out of an open pit on a belt instead of in trucks. Haul trucks are the largest cost in most open pits, burning diesel to grind up a long ramp loaded and roll back down empty. An IPCC plant cuts that haul short: trucks tip into a crusher placed near the digging face, the crusher reduces the rock to a size a belt can carry, and a conveyor lifts it straight up the pit wall to the surface. The crushing plant is built on skids so it can be relocated as the pit deepens and the face moves, which is why it is called semi-mobile rather than fixed or fully mobile.

The system runs as a chain. A Dump Pocket takes the truck tip, an Apron Feeder meters the rock into the Primary Crusher, a Discharge Feeder draws the crushed product onto the Out-of-Pit Conveyor, and the whole plant sits on a Support Structure, powered by the Electrical System system and run from the Control Room.

How the flow works

Trucks back up to the Dump Pocket and tip run-of-mine rock onto a Rock Ladder that slows the fall so it does not damage the plant. The rock collects in the pocket, and the Apron Feeder drags it forward at a steady rate into the crusher. Metering matters because the crusher works best fed evenly, and a feeder that can speed up and slow down keeps the chamber full without choking it. The Primary Crusher reduces the rock, the Surge Bin under it buffers the surges, the Belt Feeder meters product onto the main belt past a Belt Scale that counts tonnes, and the conveyor carries it up to the surface. Each stage feeds the next, so the plant runs as one continuous machine.

The apron feeder

The Apron Feeder is the rugged conveyor that handles raw, sharp, oversize rock straight from the trucks. Instead of a rubber belt it uses overlapping Apron Pan steel pans bolted to heavy Apron Chain crawler-type chains, carried on Support Roller rollers and driven by a Feeder Drive through Feeder Sprocket sprockets. The steel pans take the impact and abrasion that would destroy a belt, and the variable-speed drive lets the operator match feed rate to crusher load. The apron feeder is the buffer between the violent truck dump and the steady appetite of the crusher.

The primary crusher

The Primary Crusher is usually a gyratory crusher: a tall conical Mantle on a gyrating Main Shaft swings inside a ring of fixed Concave Liner liners, nipping and breaking rock as the gap opens and closes around the chamber. The shaft is made to gyrate by an Eccentric Assembly driven through a Bevel Gear Set from the Crusher Drive, and its top is located by a Spider Bearing. The mantle and concaves are manganese steel wear parts that work-harden in service and are replaced when worn, and the cast Crusher Frame takes the heavy crushing reactions. A gyratory crusher accepts large feed and crushes continuously, which suits the high throughput an IPCC plant needs.

Conveying out of the pit

The Out-of-Pit Conveyor carries the crushed product up the pit wall. A single Conveyor Belt of steel-cord rubber runs over hundreds of Carrying Idler trough idlers and Return Idler return idlers, driven by one or more Drive Station stations. Because the belt climbs a steep grade fully loaded, each drive carries a Backstop to stop it running back if power is lost, and a Belt Take-Up keeps it tensioned against the climb. A conveyor moving ore up the wall replaces a stream of trucks grinding up the ramp, which is the whole economic point of the system.

Relocation and structure

The plant is semi-mobile so it can keep up with a deepening pit. The Support Structure mounts everything on a heavy Skid Base with a Support Frame and Access Platform walkways. When the face has moved far enough, Relocation Jack jacks lift the plant, it is dragged or carried to a new prepared pad closer to the digging, and the conveyor is extended. This relocation happens a few times over the life of a pit, far less often than a truck haul changes, which is the trade-off: a fixed plant would be cheaper but would soon be too far from the face, while a fully mobile plant would cost much more.

Power, control, and economics

The plant draws from the mine grid through a skid Substation, with a Motor Control Center for the smaller motors and Variable-Frequency Drive drives that soft-start the large ones and set feeder and belt speed. A Control System runs the sequence, reads the belt scale, and trips the plant on overload or blockage, while a Control Room with LCD Panel screens lets one operator oversee the whole flow. The case for IPCC is energy and cost: a conveyor on grid power moves material far more cheaply per tonne than a diesel truck fleet, with fewer operators and less maintenance, and it cuts the diesel exhaust and dust of a long haul, which is why deep, long-life pits increasingly build crushing and conveying into the pit rather than trucking everything to surface.