design of eccentric shaft for jaw crusher

Designing an eccentric shaft for a jaw crusher is a critical task as it directly influences the crusher’s performance, durability, and efficiency. The eccentric shaft converts rotary motion into the reciprocating motion of the moving jaw, enabling crushing action. Below is a structured approach to designing an eccentric shaft for a jaw crusher:

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1. Design Considerations

Before starting calculations, consider:

• Material Selection: Typically forged alloy steel (e.g., EN24, AISI 4340) for high strength and fatigue resistance.
• Crushing Force: Determined by the hardness of the material being crushed.
• Stroke Length: Dictated by crusher specifications (typically 20–30 mm).
• Speed of Rotation: Usually ranges from 200–300 RPM.
• Bearing Selection: Must handle radial and axial loads (e.g., spherical roller bearings).
• Safety Factor: Typically ≥3–5 for dynamic loads.

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2. Key Design Parameters

(A) Input Data Required

1. Maximum feed size & crushing capacity (tons/hour).
2. Jaw plate dimensions & stroke length (e = eccentricity).
3. Motor power (P) and speed (N).
4. Material properties (σ_y, σ_u, τ_max).

(B) Calculations

(i) Torque Transmission
The torque (T) transmitted by the shaft depends on motor power (P) and speed (N):
\[
T = \frac{60 \times P}{2 \pi N}
\]

(ii) Crushing Force Estimation
The crushing force (F_c) can be approximated using empirical relations or based on material compressive strength:
\[
F_c = \frac{P}{\mu \cdot v}
\]
where:

• μ = mechanical efficiency (~0.7–0.9),
• v = linear speed of jaw (~0.05–0.15 m/s).

Alternatively:
\[
F_c = \sigma_c \cdot A
\]
where:

• σ_c = compressive strength of rock (~150–350 MPa),
• A = effective crushing area.



(iii) Shaft Diameter Calculation
The shaft experiences combined bending (M) and torsional (T) stresses due to eccentricity (e):
\[
M = F_c \times e
\]

Using ASME Code for solid shafts:
\[
d^3 = \frac{16}{\pi \tau_{max}} \sqrt{(K_m M)^2 + (K_t T)^2}
\]
where:

• K_m, K_t = shock/fatigue factors (~1.5–3),
• τ_max = allowable shear stress (~55–75 MPa).

(iv) Eccentricity Determination
Eccentricity (e) governs stroke length:
\[
e ≈ Stroke / 2
\]
(For example, if stroke is 25 mm → e ≈ 12.5 mm.)

(v) Bearing Load Calculation
Radial load on bearings due to crushing force:
\[
F_r ≈ F_c / 2
\]
Axial load may be negligible unless misalignment occurs.

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3. Finite Element Analysis (FEA) Validation

After initial sizing, perform FEA to check:

• Stress concentration near keyways/fillets.
• Fatigue life under cyclic loading.
• Deflection limits (<0.1 mm/m).

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4. Manufacturing Considerations