design calculations of jaw crusher

Design Calculations of Jaw Crusher

Jaw crushers are widely used in mining, construction, and recycling industries to break down large rocks into smaller, manageable pieces. The design of a jaw crusher involves several critical calculations to ensure efficiency, durability, and optimal performance. Below are the key design considerations and calculations involved in the engineering of a jaw crusher.

1. Determination of Crushing Force
The crushing force is a fundamental parameter in jaw crusher design. It depends on the hardness of the material being crushed and the size of the feed opening. The maximum crushing force (F) can be estimated using the following formula:

\[ F = \sigma \times A \]

Where:
- σ = Compressive strength of the material (MPa)
- A = Cross-sectional area of the feed opening (mm²)

For example, if crushing granite with a compressive strength of 150 MPa and a feed opening area of 0.1 m², the crushing force would be approximately 15 MN (Mega Newtons).

2. Toggle Plate Design
The toggle plate acts as a safety mechanism to protect the crusher from overload conditions. Its thickness must be calculated based on the maximum crushing force and material properties. The required thickness (t) can be determined using:

\[ t = \sqrt{\frac{F \times L}{S \times W}} \]

Where:
- F = Maximum crushing force (N)
- L = Length of toggle plate (mm)
- S = Allowable stress of toggle material (MPa)
- W = Width of toggle plate (mm)

3. Power Requirement Calculation
The power required to operate a jaw crusher depends on its capacity and efficiency. The motor power (P) can be estimated using Bond’s Law or empirical formulas such as:

\[ P = K \times Q \times W_i \left( \frac{1}{\sqrt{d_{80}}} - \frac{1}{\sqrt{D_{80}}} \right) \]

Where:
- K = Empirical constant (~10 for most applications)
- Q = Throughput capacity (tonnes/hour)
- W_i = Bond Work Index (kWh/tonne)
- d₈₀ & D₈₀ = Product and feed particle sizes at which 80%