How to size a crusher unblocking boom

Unblocking booms are rarely chosen well from a catalogue. The supplier offers three models, purchasing picks the middle one, and six months later the operator finds that the hammer cannot reach the bottom of the chamber — or that it hits too hard for the structure carrying it. The boom works; it just does not solve the problem it was bought for.

Sizing goes the other way around: start from the crusher, the rock and the structure, and work back to the configuration. Five decisions, in the order they come up.

1. Reach: get to everything that can block

Reach is not "the length of the boom." It is the distance from the boom's pivot to the farthest point in the chamber where a rock can wedge — measured in plan and in depth, with the hammer tilted to its working angle.

There are three zones to cover, and they are not in the same place for every crusher type:

• Gyratory crusher: the feed ring above the top shell, where oversize bridges, and the annular zone between the mantle and the concaves. The boom sits above the top shell; it must reach down into the chamber, not just sweep over it.
• Jaw crusher: the feed opening, usually rectangular and elongated. A rock can wedge in any corner, so lateral reach matters as much as frontal reach.
• Horizontal shaft impactor (HSI): the feed chute, right next to the rotor. The boom geometry has to work close to the rotor without requiring its removal.

The practical rule: on the plant layout, trace the envelope of every possible blockage point, then check that the hammer — not the tip of the boom — reaches all of them with at least the attack angle it needs. A boom that covers 90% of the chamber leaves 10% of blockages to be cleared by hand, which is exactly what you were trying to eliminate.

This is also where you decide between a short, heavy reach and a long, slender one. A longer reach means a lighter hammer for the same moment; if the rock calls for a heavy hammer, either the mounting point moves closer or the base gets more massive.

2. Hammer energy: enough to break, not so much it hurts the structure

A hydraulic hammer is characterized by its impact energy, expressed in foot-pounds (ft·lb) or joules. The right level depends on three things: the rock's strength, the size of the pieces to break, and how often blockages occur.

The classic mistake is oversizing "to be safe." A hammer that is too heavy:

• requires a heavier boom, therefore a heavier base and foundation;
• transmits more load into the crusher structure if the boom is bolted to it;
• costs more to buy and maintain, without clearing a rock any faster than the correctly sized hammer would have broken it in two blows.

Conversely, a hammer that is too light on hard, abrasive ore just "scratches" the rock, overheats, and eventually fatigues the tool with nothing to show for it.

That is why IC Boom System configurations are not sold off a catalogue page: the hammer class is paired with the chosen reach, then checked against the real rock — hardness, abrasiveness, the size of the pieces you actually see blocking. A secondary jaw crusher and a high-tonnage primary gyratory do not call for the same energy class, and the reach/hammer pair is set together, never separately.

One detail that matters: the hammer tool (moil point, chisel, blunt) is a choice too. On very hard rock, a conical point concentrates the energy; on fractured rock, a flat chisel splits better.

3. Mounting interface: where does the load go?

This is the most neglected decision, and the most expensive one to fix afterwards.

An unblocking boom works in bending and torsion, and every hammer blow sends an impulse into its base. Three options:

On an existing plant, this gets settled with the structural drawings in hand, not with a quick site walk. The loads that count are those of the hammer in operation, not the static weight of the boom. This is why an interface review before the order is part of our installation method: delivery day is not the moment to discover that the base plate does not match the bolt pattern on the structure.

4. Control: where does the operator stand?

The boom exists so that nobody goes near the chamber. If the operator has to stand over the crusher to run it, the risk has been moved, not removed.

Two choices:

• A fixed operator station with a direct view of the chamber, shielded from flying rock — usually the most reliable option on primary crushers where the boom is used several times per shift.
• A portable radio remote, which lets the operator pick the best vantage point — practical where the view from a fixed station is poor.

In both cases, plan the interlocks: the boom must not be able to enter the chamber while the crusher is running unless the site's risk assessment explicitly allows it, and the hammer must be inhibited outside its working envelope. A chamber camera is often an inexpensive addition that transforms day-to-day use.

5. Environment: cold, dust, access

In Canada, the cold question is not optional. A boom installed in Abitibi, Northern Ontario or Northern British Columbia works at temperatures where standard hydraulic oil thickens and elastomers harden. To specify at order time: the service temperature range, heating of the hydraulic power unit, the fluid choice, and whether the operator station is enclosed.

Abrasive crusher dust wears pins, rods and seals; rod guards and greasing intervals belong in the specification, not in the after-sales conversation.

Finally, maintenance access: can the hammer tool, a hose or a pin be changed without dismantling the boom? A boom that has to come out of service for a day for routine maintenance ends up not being maintained.

What to send to get a sized proposal

A serious proposal cannot be made without these:

1. Crusher type and model, with the plant layout or, failing that, photos and dimensions of the feed opening.
2. The rock: type, compressive strength if known, feed size distribution, typical size of the pieces that block.
3. Current blockage frequency and the clearing method used today.
4. The structure available for mounting, with its drawings if they exist.
5. The site temperature range and the preferred control mode.

With those five items, the configuration — reach, hammer, base, control — is sized in a matter of days, and the proposal states its assumptions in writing. See the IC Boom System product page for the available configurations, or request a proposal directly.

Frequently asked questions

Can an unblocking boom be installed on a crusher that is already in service? Yes — that is the most common case. The constraint is the interface: the existing structure has to be checked for the hammer's dynamic loads, or an independent pedestal has to be planned. Installation is then scheduled inside a shutdown window.

Does the boom replace an operator? No, it replaces a method. An operator still controls the boom, but from a protected station, out of the fall zone and without entering the chamber.

How long does it take to clear a blockage with a boom? It depends on the rock and the hammer, but the order of magnitude is minutes, versus hours for manual or explosive clearing once shutdown and restart are counted.