How Blasting Affects Crushing & Screening
Recognising that upstream activities have a direct impact on productionCrushing and screening performance is often measured by what happens at the plant: tonnes produced, product sizes achieved, equipment utilisation and the consistency of the final material. But the performance of a crushing and screening train can be influenced well before material reaches the primary crusher.
On projects where rock is drilled and blasted, blast fragmentation can have a direct effect on the material presented to the crushing circuit. The size and consistency of the blasted material can influence feed requirements, handling, crusher performance and overall production.
The crushing process starts before the crusher
A primary crusher is designed to receive and reduce rock within a particular range of feed sizes. When blasted material is presented to the crusher, the characteristics of that feed can vary considerably depending on the geology and the blast outcome.
A blast that produces a relatively consistent and manageable fragmentation profile can make it easier to maintain a steady feed to the crushing circuit. By contrast, a blast that produces a high proportion of very large oversize material may create additional challenges before and during crushing.
This is why Eco-Match ensures we understand the relationship between blast fragmentation and crusher feed; it is a vital factor when planning a project.
What is blast fragmentation?
Blast fragmentation refers to the size distribution of rock produced after drilling and blasting. The objective of blasting is generally to break in-situ rock into a size and distribution that can be handled and processed effectively. The resulting material is rarely uniform. A blast may produce a combination of fines, smaller rock and larger pieces of oversize. The proportions can vary depending on factors including the geology, rock characteristics, blast design and site conditions. For a crushing operation, this resulting size distribution becomes the starting point for the next stage of the process.
Oversize material can create additional challenges
One of the most obvious effects of blasting on crushing is the amount of oversize material produced. Large rocks may exceed the acceptable feed size of the primary crusher or make feeding the crusher less efficient. Depending on the project and equipment, oversize material may need to be managed through additional breaking or handling before it can enter the crushing circuit. This can introduce an additional step between blasting and crushing.
Oversize may require:
- Hydraulic breaking
- Secondary breaking
- Additional loading and handling
- Temporary stockpiling
- Additional equipment or labour
These activities can affect the overall production chain and may reduce the consistency of material being presented to the crusher.
Consistent feed supports consistent production
A crushing circuit generally performs best when it receives a reasonably consistent feed. This does not mean that every rock needs to be identical in size. Rather, significant variations in feed size and material characteristics can make it more difficult to maintain stable operating conditions. Consistent feed can help the crusher operate closer to its intended operating range and can make downstream screening and material handling more predictable.
Where a blast produces a highly variable feed, the crushing operation may experience periods of high oversize, changes in feed characteristics or interruptions while unsuitable material is managed. This can have an impact on production rates even when the crushing equipment itself is operating correctly.
Blasting can influence downstream screening
The effects of fragmentation don’t necessarily stop at the crusher. The particle-size distribution entering the crushing circuit can influence the distribution of material produced by the crushing stages and ultimately affect screening. If the feed contains significant variation, the amount of material reporting to different size fractions may also vary. This becomes particularly important when a project requires specific final products or grading envelopes. For example, producing a material below a particular top size is not necessarily enough to meet a required aggregate specification. The overall particle-size distribution also matters, and the crushing and screening circuit therefore needs to be considered as a complete system, with the characteristics of the feed material forming part of that equation.
While Eco-Match does not undertake drilling or blasting, where we are appointed as the crushing and screening subcontractor on a project, we recognise the value of engaging with the contractor responsible for blasting. Understanding the planned fragmentation, expected feed characteristics and potential oversize can help both contractors better understand how their respective activities interact.
Planning the interface between blasting and crushing
Good communication between the teams responsible for upstream rock breaking and downstream processing can help identify potential issues before they affect production.
Before a crushing operation begins, it can be useful to establish:
- Expected maximum feed size
- Expected fragmentation profile
- Available feed volumes
- Material characteristics
- Required production rates
- Required final products
- Stockpile arrangements
- Any requirements for managing oversize
This provides a clearer understanding of what the crushing and screening circuit will be expected to process. It also helps ensure that the plant configuration is based on realistic project conditions rather than theoretical feed assumptions.
Frequently asked questions
What happens if blasted rock is too large for the crusher?
Material that exceeds the crusher’s acceptable feed size may need to be reduced through secondary breaking or hydraulic breaking before it can be processed. This adds an additional step to the material-handling process and can affect overall production efficiency.
Can blasting affect the final aggregate product?
Yes. The fragmentation and characteristics of the feed material can influence how the rock behaves through the crushing circuit and the resulting particle-size distribution. Where specific aggregate grading requirements apply, the complete crushing and screening circuit needs to be considered.
How does blasting affect crusher performance?
Blasting determines the size and distribution of material presented to the crushing circuit. A well-fragmented and relatively consistent feed can support more predictable crushing, while excessive oversize or significant variation in feed size can create additional handling and processing requirements.
What information should a crushing contractor receive about blasting and the feed material?
Useful information includes the expected maximum feed size, anticipated fragmentation profile, rock type and characteristics, available volumes, required production rate and final products. This helps the crushing contractor assess whether the proposed crushing and screening configuration is suitable for the material expected on site.