secondary crushing with jaw crushers

Secondary Crushing with Jaw Crushers: An Overview

While jaw crushers are most commonly associated with the primary crushing stage, where large feed material is initially reduced, their application in secondary crushing is a well-established and often advantageous solution. Secondary crushing follows primary crushing and further reduces the material size to prepare it for final grinding or specific product sizing. This article explores the use of jaw crushers in this role, examining their operational principles, comparative advantages, and practical applications in modern aggregate and mining operations.

The Role of Jaw Crushers in Secondary Crushing

In a traditional setup, cone crushers or impact crushers typically handle secondary crushing duties. However, jaw crushers configured for finer output can effectively serve as secondary crushers. This is achieved by setting a smaller closed-side setting (CSS), which is the narrowest gap between the jaw plates at the bottom of the chamber. A jaw crusher used secondarily often has a different geometry—such as a steeper nip angle and optimized kinematics—to enhance efficiency at smaller settings and improve particle shape.

The key advantage lies in simplicity and robustness. Jaw crushers have a straightforward linear compression action, making them less sensitive to variations in feed moisture and clay content compared to some cone crushers. They generally offer lower capital cost, easier maintenance, and reduced operational complexity.

Comparative Analysis: Jaw vs. Cone Crusher for Secondary Duty

The choice between a jaw crusher and a cone crusher for secondary crushing depends on specific operational parameters. The table below outlines key considerations:

Feature	Jaw Crusher (Secondary Duty)	Cone Crusher (Secondary Duty)
Crushing Action	Linear compression (squeezing).	Gyratory compression within a lined chamber.
Particle Shape	Can produce more slabby or elongated particles depending on jaw profile. Typically generates more fines at tight settings.	Generally produces more cubical product shapes due to multi-zone crushing action.
Wear & Maintenance	Simpler structure; wear parts (jaw plates) are easier and faster to replace.	More complex mechanical design; mantle and concave replacement is more labor-intensive.
Sensitivity to Feed	Tolerates damp, sticky material better; less prone to packing/choking.	More efficient with dry to moderately moist feed; sticky feed can cause packing issues.
Capital Cost	Typically lower for equivalent capacity.	Typically higher.
Operational Efficiency	Lower energy efficiency per ton of final product at smaller sizes due to single crushing zone.	Higher energy efficiency in reducing hard, abrasive materials to intermediate sizes due to inter-particle crushing in a packed bed.
Best Suited For	Less abrasive rock, softer materials, mixed demolition concrete, applications prioritizing simplicity and low OPEX over perfect shape.	Highly abrasive hard rock (e.g., granite, basalt), applications where strict product shape and size distribution are critical.

Real-World Application: Case Study

A prominent example comes from a granite quarry operation in Scandinavia facing challenges with high wear costs on their secondary cone crusher processing very abrasive rock.

• Challenge: The existing secondary cone crusher required frequent mantle and concave replacements, leading to high downtime and parts costs.
• Solution: The quarry trialed a heavy-duty jaw crusher specifically designed for secondary/tertiary duties as a replacement.
• Implementation: A jaw crusher with specially hardened manganese steel jaws and an optimized stroke was installed.
• Result: While the product shape was slightly less cubical than the cone crusher's output, it was fully acceptable for their downstream asphalt and concrete plants. Crucially:
  • Wear part life increased by approximately 40%.
  • Maintenance downtime was reduced by over 30% due to simpler更换 procedures.
  • Overall cost per ton of produced aggregate decreased significantly.

This case demonstrates that where ultimate particle shape is not the paramount concern, a robust secondary jaw crusher can offer superior total operating economics.

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Frequently Asked Questions (FAQs)

1. Can any jaw crusher be used for secondary crushing?
Not optimally。 While technically possible by adjusting the CSS， primary jaw crushers are designed for high capacity on large feed。 Secondary-duty jaw crushers often feature different designs， such as deeper chambers or specific kinematics，to improve performance at smaller settings，control product shape，and manage increased wear from finer abrasion。

2。 What are the main drawbacks of using a jaw crusher for secondary crushing?
The primary limitations are particle shape and size distribution。 Jaw crushers typically produce a less uniform product with more elongated grains compared to cone crushers。 They also tend to generate more fines when operated at very tight closed-side settings， which may be undesirable for certain products。

3。 How does wear compare between primary and secondary jaw crushing applications?
Wear patterns differ significantly。 In primary crushing， wear is concentrated on the lower section of the jaws where large rocks are initially gripped。 In secondary crushing，with consistently smaller feed，wear is more evenly distributed across the entire jaw plate surface but can be more severe per ton of output due to increased abrasion from already-crushed material。

4。 Is feed size critical for a secondary jaw crusher?
Yes， it is paramount。 The feed must be pre-sized by the primary crusher to match the receiving opening of the secondary jaw。 Ideally，the maximum feed size should be no more than 80% of the crusher's gape width to ensure proper feeding without bridging or choking。

5。 When is a secondary jaw crusher clearly not suitable?
It is generally not suitable when producing high-value aggregates requiring excellent cubicity (e.g.,for exposed architectural concrete)，when processing extremely hard/abrasive ores where energy efficiency is critical，or when very precise closed-circuit sizing with high recirculating loads is needed—cone or impact crushers are typically superior in these scenarios