Prevent Crusher Downtime from
Oversized Rocks & Boulders
Crusher downtime is one of the most expensive and disruptive problems in mining, quarrying, and mineral processing. While wear, maintenance, and planned shutdowns are unavoidable, a large share of unplanned stoppages comes from one repeatable cause: oversized rocks entering the crusher feed.
A single boulder that cannot pass through the crusher opening can bring production to a halt in seconds. In many operations this happens week after week, quietly consuming throughput, wear-part life, and operating margin.
To estimate what this means for your own plant, download the Crusher Downtime Loss Calculator (Excel) and enter your crusher capacity, typical stoppage time, and frequency.
How oversized rocks stop productions
Crushers are designed for a defined maximum feed size. When material exceeds that limit, it can:
- Bridge across the crusher opening
- Jam or choke the feed
- Damage teeth, liners, and wear plates
- Trigger overload trips and motor overcurrent
- Force rock breaker or manual intervention
Any of these events stops material flow and pushes the plant into emergency response mode.
The cost is more than lost tonnes
Lost production is usually the most visible cost, but it is rarely the only one. Each boulder-related stoppage creates a stack of secondary costs that accumulate over time:
- Lost production
Tonnes that were scheduled to be crushed simply do not get produced. - Wear-part damage and accelerated wear
Liners, teeth, side plates, and chute liners are subjected to shock loads and oversized contact, shortening their service life even when nothing visibly breaks. - Rock breaker operating cost
Clearing boulders jammed in crushers or chutes consumes hammer time, operator hours, and hydraulic or electrical power, often under difficult access conditions. - Idle haulage and queuing
Trucks, loaders, and conveyors continue burning fuel and labour while waiting for the crusher to restart. - Energy spikes during stop and restart
Shock loading through conveyors, drives, and motors increases electrical demand and mechanical stress. - Maintenance disruption and safety exposure
Unplanned call-outs, interrupted planned work, and personnel exposure during clearing all add cost and risk.
If you are only counting lost tonnes, you are usually underestimating the real financial impact of recurring oversize events.
Safety and H&S exposure during clearing
Clearing a jammed crusher or chute is one of the higher-risk tasks in most plants. When a boulder blocks flow, operators may need to:
- Work in confined or restricted areas
- Work under unstable or suspended rock
- Use heavy tools or rock breakers
- Perform awkward lifting, pulling, and pushing
Every prevented blockage is one less time people are exposed to these conditions.
Example: Limestone quarry (production loss only)
Based on operating experience from limestone quarries, a single boulder incident typically results in 15–30 minutes of lost crusher time, including stopping feed, clearing the obstruction, and restarting the plant.
The example below uses 20 minutes as a realistic mid-range value.
Typical limestone quarry
- Crusher capacity: 800 tonnes per hour
- Boulder-related stoppage: 20 minutes
- Frequency: 1 event per week
Lost production per event
800 t/h × (20 ÷ 60) = 267 tonnes
Annual lost production
267 t × 1 × 52 ≈ 13,900 tonnes per year
If limestone contribution margin is €8 per tonne:
≈ €110,000 per year in lost production
This is production loss only. It does not include wear parts, rock breaker time, labour, fuel, energy spikes, maintenance disruption, or safety-related costs that occur every time a boulder blocks the crusher.
What this means for higher-value mining operations
In many mining operations, crusher throughput is much higher (often 2,000–6,000 t/h), and the economic value per tonne is also significantly higher. Under those conditions, even the same number of boulder-related stoppages can translate into hundreds of thousands or millions of euros per year in lost value.
Calculate your own site impact
Because capacity, stoppage duration, and product value vary widely from site to site, the most accurate way to estimate the cost of oversized rock events is to use your own numbers. Typical primary crushers experience 0.5–3 oversize events per week
Use the Crusher Downtime Loss Calculator (Excel) to enter:
- Crusher capacity (t/h)
- Typical stoppage duration (minutes)
- Frequency (events per week)
- Contribution margin or product value (€/t)
The spreadsheet calculates annual lost tonnes and annual production loss for your operation.
If you want a more complete picture, you can request the extended calculator, which includes:
- Rock breaker hours and tool wear
- Wear-part life and replacement cost
- Idle fleet fuel and labour
- Maintenance call-outs
- H&S exposure assumptions
Why this loss is preventable
These stoppages happen because oversized rocks reach the crusher without warning. Real-time boulder detection identifies problem rocks before they enter the crushing zone, allowing operators to stop or isolate feed in a controlled way and deal with the boulder in open space rather than inside the crusher.
This reduces:
- Emergency shutdowns
- Equipment damage
- Rock breaker time
- Safety exposure
How and where detection is installed is covered in Installation & Sensing Technology.
A practical layer of protection
Boulder detection adds a real-time protection layer to the existing material handling system. It ensures that only material within safe size limits reaches the crusher, protecting equipment, production, and people at the same time.
Preventing even a small number of boulder-related stoppages per year can recover more value than the cost of the system.
FAQ — Crusher Downtime and Oversized Rocks
What is the most common cause of unplanned crusher downtime?
Oversized rocks entering the crusher are one of the most frequent causes. A single boulder can bridge the opening, trip drives, or force rock breaker intervention.
Why are boulder-related stoppages so expensive?
Because the crusher is usually the highest-throughput part of the plant. When it stops, haulage, conveyors, and downstream processing are also affected.
How long does a typical boulder-related stoppage last?
In most operations it ranges from 10 to 30 minutes, depending on access, material condition, and clearing method.
Why can’t blasting alone eliminate oversized rocks?
Geology, joints, and face conditions mean oversize will always be produced, even with good blast design.
How does boulder detection reduce downtime?
By identifying oversized rocks before they reach the crusher so they can be handled in a controlled way instead of becoming a blockage.
Is rock breaker use a reliable solution?
Rock breakers clear blockages after they occur, but they do not prevent downtime, wear, or safety exposure.
Can boulder detection be added to an existing plant?
Yes. Systems are installed on conveyors, feeders, or dump pockets and integrated with existing PLC and interlock logic.
Does preventing a few stoppages really make a difference?
Yes. Even one or two avoided events per week can recover large amounts of lost production and reduce wear and safety risk.