scheme of jaw crusher

Scheme of Jaw Crusher: An Overview of Design, Operation, and Application

The scheme of a jaw crusher refers to its fundamental design blueprint, operational principles, and the systematic arrangement of its core components to achieve the primary crushing of hard, abrasive materials. This article delves into the working mechanism based on the typical double-toggle design, compares key design types, examines critical components and their functions, and outlines practical considerations for selection and operation. Understanding this scheme is crucial for optimizing performance, maintenance, and application in industries such as mining, quarrying, and recycling.

1. Working Principle and Kinematic Scheme
The core operational scheme of a double-toggle jaw crusher is based on an eccentric shaft that drives a pitman (connecting rod), creating an elliptical motion at the bottom of the moving jaw. This motion results in a cyclical process:

• Opening Stroke: As the pitman moves upward and away from the fixed jaw, the moving jaw retreats. The crushed material descends by gravity through the crushing chamber.
• Closing & Crushing Stroke: The pitman moves downward and towards the fixed jaw. The moving jaw advances, compressing the material against the fixed jaw until it fractures due to exceeding its compressive strength.

This reciprocating action reduces large feed (top size can exceed 1 meter) to a smaller product size determined by the crusher's closed-side setting (CSS).

2. Comparison of Primary Design Schemes
While the double-toggle design is common for heavy-duty service, two main schemes dominate the market. Their key differences are summarized below:

Feature	Double-Toggle (Blake Type) Jaw Crusher	Single-Toggle (Overhead Eccentric) Jaw Crusher
Kinematics	Complex: Eccentric shaft drives pitman & two toggle plates. Moving jaw has elliptical motion.	Simpler: Eccentric shaft is directly located above the crushing chamber. Moving jaw has elliptical/rocking motion.
Wear on Jaw Plates	Lower relative wear due to less rubbing/abrasion during crushing cycle.	Higher wear potential due to both compression and significant sliding/rubbing action.
Weight & Cost	Generally heavier, more massive frame; higher initial cost due to more parts (e.g., two toggles).	Lighter construction for same feed size capacity; lower initial cost.
Efficiency & Output	Traditionally considered slightly less efficient but extremely robust for very hard, abrasive materials.	Higher throughput per unit weight; more aggressive crushing stroke often leads to higher capacity in many applications.
Typical Application	Primary crushing of very hard, abrasive rock (e.g., granite, trap rock) in stationary plants.	Versatile; widely used in both stationary and mobile plants for hard to moderately abrasive materials.

3. Key Components in the Crusher Scheme
The functionality relies on an integrated system of components:

• Frame: Heavy-duty rigid structure supporting all other parts.
• Fixed & Movable Jaw Dies: Replaceable manganese steel wear liners that form the crushing surfaces.
• Eccentric Shaft: Forged or cast high-strength steel component that converts rotary drive motion into reciprocating crushing action.
• Toggle Plate(s): A safety mechanism designed to fracture under uncrushable overload (like tramp iron), protecting other components from catastrophic damage.
• Tension Rod & Spring: Maintains toggle plate(s) in position and provides compensation for wear on jaw dies.

4.Application Case Study: Primary Crushing in a Granite Quarry
A large granite quarry in Scandinavia was experiencing premature failure of jaw plates and excessive downtime in its primary crushing stage using older single-toggle crushers on highly abrasive granite.

• Problem: Low operational availability (<75%), high cost per ton due to frequent liner changes and component stress.
• Solution: Implementation of a modern heavy-duty double-toggle jaw crusher scheme was selected after analysis.
• Implementation: The new crusher's kinematics generated less sliding friction against the abrasive granite compared to the previous model. Its robust frame handled peak loads from large feed blocks.
• Result: Operational availability increased to over 92%. Wear life of manganese jaw plates improved by approximately 40%, significantly reducing cost per ton of crushed material and maintenance labor hours.

5.FAQ Section

Q1: What is meant by "closed-side setting" (CSS) in a jaw crusher scheme?
A: The CSS is the minimum gap between the fixed and moving jaw dies at their closest point during the crushing cycle (the bottom of the stroke). It is a critical parameter that determines the maximum product size output from the crusher.

Q2: Why are toggle plates often made from cast iron?
A: Toggle plates are engineered as a sacrificial component with a calculated breaking point—a mechanical fuse or shear pin for protection against uncrushable material entering chamber like tramp metal or bucket teeth which could cause severe damage if not stopped.

Q3: How does feed material characteristics influence choice between single- vs double-toggle schemes?
A: For extremely hard (high compressive strength >250 MPa) and highly abrasive materials like quartzite or basalt where minimizing liner wear is paramount—double toggle designs may be preferred despite higher capital cost because their kinematics reduce abrasion—whereas single toggle designs offer advantages where versatility or higher capacity-to-weight ratio matters most such as limestone processing plants where abrasiveness isn't extreme but production demands are high.

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References
1.Swedish Institute for Standards SIS-CEN/TC 151/WG 4 - Test methods for size reduction equipment
2."Mineral Processing Design" by B.A.Wills & J.P.Finch – Chapter on Crushing
3.Case study data adapted from aggregate producer reports published within European Aggregates Association (UEPG) technical bulletins