Blast Hole Stemming Loader

Overview

After a blast hole is drilled and charged with explosive, the top portion of the hole is filled with inert material called stemming. Stemming is what makes the explosive do useful work. Without it, the expanding gases from detonation take the path of least resistance and blow straight up out of the collar, producing a loud, dangerous, and largely wasted blast. A well-placed column of crushed aggregate confines those gases long enough for the shock to fracture and heave the rock. The blast hole stemming loader is the machine that places this material quickly, consistently, and without sending people to walk a charged pattern with shovels.

The machine is a self-propelled aggregate handler. A Truck Chassis and Cab carries a Stemming Hopper of crushed rock across the bench. A Vibrating Feeder draws material out, a Discharge Conveyor lifts it, a Metering Gate gate controls the flow, and a Discharge Boom boom drops a measured volume neatly into each hole. The whole sequence is run by one operator from the cab, which keeps personnel out of the charged area.

Why stemming matters

The quality of stemming directly affects blast performance and safety. The material should be angular crushed rock rather than rounded gravel or drill cuttings, because angular particles interlock and resist being ejected. The right size is roughly one tenth of the hole diameter, large enough to wedge but small enough to flow. Too little stemming, or stemming that is too fine, leads to stemming ejection: the column shoots out, gas escapes early, and the blast produces flyrock, excessive noise, and poor fragmentation. A loader that meters a consistent column length to every hole removes a large source of variability in the blast, which is why mines increasingly weigh and record what each hole receives.

Chassis and mobility

The Truck Chassis and Cab is an off-highway truck sized to carry the laden hopper across rough bench surfaces. A diesel Diesel Engine drives the wheels through a Powershift Transmission and powers the plant through a Power Take-Off. The drive Drive Axle units use planetary final drives and large Off-Highway Tire units to handle the loose, broken ground of a recently drilled pattern. The Operator Cab gives the operator a clear view of the hole collars and an in-cab display of the metering system.

Hopper and feeder

Crushed aggregate is held in the Stemming Hopper, lined throughout with abrasion-resistant plate because the material is hard and constantly moving against the walls. A Grizzly Screen bar screen across the top rejects any oversize rock that would jam the spout. At the bottom, a Vibrating Feeder of the vibrating-pan type draws material out at a controlled rate; the eccentric Vibrator Motor keeps the aggregate flowing and prevents it from bridging over the outlet. The hopper sits on Load Cell units so the machine knows by weight exactly how much it has dispensed.

Conveying and metering

A Discharge Conveyor lifts the aggregate from the feeder up to discharge height. It is a reinforced belt running on Idler Roller rollers between a drive and tail Conveyor Pulley, turned by a hydraulic Conveyor Motor. The flow per hole is set by the Metering Gate gate, a hardened Slide Gate driven by a Gate Cylinder. Combining the gate opening with the weighed hopper reading lets the control system deliver a target mass or volume to each hole and stop cleanly when it is reached.

Positioning over the hole

The Discharge Boom is what makes the machine accurate. An articulated Boom Arm, moved by Boom Cylinder units, swings a telescoping Discharge Spout out over the pattern. A Hole Locator cone centers the spout on the collar so the aggregate drops cleanly into the hole rather than spilling onto the bench. Because the operator can reach several holes from one machine position, the loader can stem a row at a time without repositioning for every hole, which is where most of its productivity advantage over hand stemming comes from.

Hydraulics, control, and variants

The Hydraulic System system, driven from the PTO, powers the feeder, conveyor, gate, and boom. The Control System system, built around a Plant Controller, reads the load cells and gate position, meters each charge, and logs the volume placed in every hole for the blast record. Variants scale with the operation. Large surface mines use machines with big hoppers and long booms matched to large-diameter holes and wide patterns. Quarries and construction blasting use smaller, more maneuverable units. Some designs combine stemming with the placement of stemming plugs or gas bags that further improve confinement, and others integrate with the drill rig's hole-position data so the boom can find each collar with less operator input.