What a gyratory crusher blockage really costs

Ask a shift supervisor what a gyratory blockage costs and the answer comes in hours: "two, three hours, depends on the rock." Ask the controller and there is no line item for it. A blockage is the most visible cost on the floor and the most invisible one in the accounts — which is why the fix often waits for years.

This article does not give you a number. It gives you a method to calculate your own, with six items that most sites never add up together. The figures that appear below are example values chosen to illustrate the arithmetic, not site data: replace them with yours.

What actually happens during a blockage

An oversize rock bridges in the feed ring, or several pieces wedge between the mantle and the concaves. The gyratory loads up, the amps climb, the PLC sheds load or the operator stops it. From there the sequence is almost always the same:

1. Crusher stops, then the feed (trucks or upstream grizzly) has to be diverted or held.
2. Lockout, visual inspection, decision on the clearing method.
3. Clearing: crane hook, manual bar, excavator, or a blast if the rock is massive — each with its own mobilization time.
4. Lockout removal, empty restart, gradual return to load.
5. Catching up on the downstream circuit, if there is capacity to do so.

The "official" downtime covers step 3. The cost covers all five.

The six items to add up

1. Lost production — in margin, not in price

This is the main item, and the one most often calculated wrong. The basic formula:

Lost tonnes = nominal throughput (t/h) × total stoppage time (h)

Two corrections apply. First, the duration to use is the total duration — from feed stop to return to nominal throughput — not the clearing time. Second, the value of a lost tonne is not its sale price: it is the contribution margin it would have earned or, if the crusher is the site bottleneck, the value of the metal or finished product that tonne would have produced downstream.

If the crusher is not the bottleneck — because there is enough surge capacity between crushing and grinding — the real loss is smaller, as long as the stockpile holds. That is why "how many hours of stock do we have between the crusher and the mill?" is the first question to ask.

2. The restart

A gyratory does not go back to full load the second the rock breaks. There is the lockout removal, the empty restart, the gradual ramp-up of feed, and often a slug of accumulated fines that forces a second period of reduced throughput. On the sites we visit this item is rarely measured: time it once with a stopwatch over three or four events and take the average.

3. Labour and equipment mobilized

Operator, mechanics, sometimes a crane operator and a mobile crane, sometimes a blaster: the loaded hourly cost of each, multiplied by the mobilization time, which is longer than the clearing time. If the crane comes from a contractor, add the waiting time and the minimum billable call-out.

4. Wear and induced damage

Every blockage ends in an impact: the rock gives way, drops into the chamber, and the mantle and concaves absorb it. Clearing with bars or hooks damages liners, and with repetition wear parts get replaced ahead of schedule. This item is calculated over the year: number of blockages × attributable share of premature wear × cost of a liner set and its changeout.

5. The starved downstream circuit

If the grinding circuit stops for lack of feed, its own restart has a cost: energy, circuit instability, recovery loss while it settles back into regime. On a processing plant this item can exceed the crusher's direct cost. It only kicks in once the surge stockpile is exhausted — hence the value of knowing how long that stockpile lasts.

6. Risk and penalties

Two items you do not put in a formula but cannot ignore. Manual clearing exposes people to falling rock and confined-space hazards: the cost of an incident does not average out. And if the site has delivery commitments — a tonnage contract, a ship waiting, a just-in-time customer — the contractual penalties for a shortfall are read in the contract, not in an estimate.

The worked example — fictional values

To illustrate the mechanics, take arbitrary round numbers. These are not site data.

Per event: 1,000 t/h × 3 h × $10/t = $30,000 of production, plus $600 of labour, plus $200 of wear — about $30,800. Over the year: 40 × $30,800 ≈ $1.2 million, before the starved mill, before penalties, before risk.

Change a single variable and the conclusion changes: at 200 t/h with a six-hour stockpile, item 1 collapses and labour and risk dominate instead. That is exactly why the calculation has to be done with your own data rather than a benchmark read somewhere else.

Three ways to cut the bill

Reduce the frequency. Blast fragmentation, an upstream scalping grizzly, control of the size of rocks loaded into trucks: everything that keeps the oversize from reaching the gyratory. Effective, but rarely sufficient — some oversize always gets through.

Reduce the duration. This is where an unblocking boom changes the arithmetic: clearing drops from hours (mobilization, lockout, improvised method) to minutes, from a protected station, with no crane and no blaster. In the example above, cutting the total duration from 3 h to 30 min brings item 1 from $30,000 to $5,000 per event. What remains is to compare that annual gap with the cost of the boom — see how to size an unblocking boom and the IC Boom System product page.

Reduce the consequences. A properly sized surge stockpile between crushing and grinding, and a written clearing procedure instead of an improvised one, shrink items 5 and 6 even if the frequency does not move.

What this calculation lets you decide

Once the annual cost is on paper, the investment decision takes a form management knows how to read: a known recurring cost against a known one-time investment, and a payback period. If you would rather have that costing done with your data and documented — assumptions, sources, sensitivities — that is the kind of work our feasibility studies service covers, and it can also start with a simple request for proposal.

Frequently asked questions

Should I count the clearing time or the total stoppage time? The total time, from feed stop to return to nominal throughput. Clearing time alone understates the cost, often by half.

How do I find the margin per tonne if the site does not publish it? Ask management accounting for the contribution margin per crushed tonne or, on a mine site, the recoverable value per tonne of mill feed. Failing that, run the calculation with two assumptions (low and high) and present the range.

Is a jaw crusher blockage costed the same way? Yes, with the same items. Durations and clearing methods differ, and so does the downstream buffer — see our comparison of crusher types.