Drilling Jumbo

Overview

A drilling jumbo is the machine that drills the blast holes for underground development: tunnels, mine declines, drifts and caverns. It carries one to three hydraulic rock drills on articulated Drill Booms mounted to a self-propelled Carrier Chassis. The operator positions each Feed Beam against the face, and the rig drills a pattern of 60–120 parallel holes, 43–64 mm in diameter and typically 3.5–5.3 m deep, which are then charged with explosives and fired. A two-boom jumbo can complete a full face pattern in an 18 m² tunnel in roughly one to two hours.

Modern jumbos drill electrically. The diesel engine is used only for tramming between headings; at the face the rig is plugged into the mine's 400–1,000 V supply and the Hydraulic Powerpack motors drive the hydraulics. This keeps diesel exhaust out of the heading during the longest part of the work cycle and provides the steady 55–75 kW per boom that percussion drilling consumes.

How it works

Each boom carries a top-hammer drifter, the Hydraulic Rock Drill. Inside it, a Percussion Piston is cycled hydraulically at 50–70 Hz. Each stroke sends a compressive stress wave through the Shank Adapter and down the Drill Rod and Bit to the tungsten-carbide button bit, which crushes the rock at the hole bottom. A separate Rotation Motor indexes the bit between blows so each impact hits fresh rock, and the Feed Cylinder keeps the bit pressed against the bottom with up to 25 kN of thrust. Nitrogen-charged Pressure Accumulators absorb the hydraulic pulsation that the percussion circuit generates.

Flushing is continuous. Water from the mine main, boosted by the Water Booster Pump to 12–20 bar, enters the drill string through the Flushing Head, passes down the hollow rod, exits at the bit and carries the cuttings back up the annulus. The Flushing Flow Guard cuts percussion automatically if flow is lost, drilling dry for even a few seconds overheats the bit and packs the hole with cuttings. Where water would damage the ground, an Air-Mist System substitutes an air-water mist.

Booms and hole accuracy

Blast results depend on holes that are straight, parallel and collared in the right place. The Boom Arm is a telescoping box section moved by Boom Lift Cylinders and Boom Swing Cylinders; a Feed Rollover Actuator rolls the feed through 360° so the same boom can drill face holes, contour holes and bolt holes in the walls and roof. Encoders and Feed Inclinometers on every joint feed the Rig Control Computer, which holds the feed automatically parallel as the boom moves, the operator steers the collar position and the geometry stays fixed.

On computerized rigs the drill plan is loaded as a file. The rig is navigated to the tunnel line, and the control system displays each planned hole on the cab's LCD Panel; in fully automatic mode it positions the boom, collars, drills to depth with anti-jamming logic and moves to the next hole. Measurement-while-drilling data (penetration rate, feed and percussion pressures per hole) is logged for ground characterization.

Drilling starts with collaring: the Stinger anchors the feed against the face, the Rod Centralizer clamps the rod on axis, and the drill begins at reduced percussion and feed until the bit is seated, then ramps to full power. The Drill Cradle carries the drifter along the Feed Rail on replaceable wear pads, with hoses managed by the Hose Trolley.

Carrier and power

The Carrier Frame is articulated at a central Articulation Joint giving ±40° steering, with planetary Drive-Steer Axles and four Wheel Assembly units on smooth-tread underground tyres. The Tramming Diesel Engine trams the rig at up to 15 km/h. At the face, four Levelling Jack outriggers lift the carrier and hold the rig rigid against drilling reactions.

Electrical supply arrives through the Trailing Cable Reel, which pays the trailing cable out and in under power, into the Main Switchgear with earth-fault monitoring, mandatory in most jurisdictions for trailing-cable machines. Each boom has its own Powerpack Electric Motor and Main Hydraulic Pump, so the booms drill independently. Hydraulic heat is rejected through the Hydraulic Oil Cooler into the same water circuit used for flushing, and the Filter Bank keeps the oil clean enough for the drifter's tight valve clearances.

Operator environment

The operator works from a FOPS-certified Operator Cab rated to ISO 3449, with noise inside held below 80 dB(A) against roughly 115 dB(A) at the drill. Proportional Boom Joysticks and the Drilling Control Panel run boom positioning and the drilling cycle; on automated rigs one operator routinely supervises both booms drilling simultaneously.

Maintenance

The drifter is the consumable heart of the machine. Shank adapters last on the order of 1,500–3,000 drill-metres, bits 200–400 m between regrinds, and the drifter itself is rebuilt with new Oil Seals, piston and bushings every 400–800 percussion hours. Feed wear strips, centralizer bushings, hoses and O-Ring Set seal kits are routine changeouts; hydraulic cleanliness and flushing-water filtration dominate drifter life between rebuilds.