DesignWithAjay’s Guide to Calculating Shear Force in Shredder Blades for Different Materials
At Ajay Industries, we engineer shredder blades not just for cutting—but for precision shearing. Whether you’re processing HDPE, rubber, aluminum, or e-waste, understanding how to calculate shear force is essential for optimizing blade geometry, motor torque, and overall machine performance.
This guide walks you through the core principles and formulas used to calculate shear force across different materials, ensuring your shredder designs are both powerful and efficient.
What Is Shear Force?
Shear force is the force required to slice through a material by applying opposing forces parallel to its surface. In shredders, this force is delivered by rotating blades that shear the material at contact points.
Shear Force (F)=Shear Stress×Cross-sectional Area
Where:
- Shear Stress ≈ 80% of the material’s yield strength (rule of thumb)
- Area = Contact surface between blade and material
Material-Specific Shear Stress Values
| Material | Yield Strength (PSI) | Shear Stress (80%) | Notes |
|---|---|---|---|
| HDPE | ~4350 | ~3480 | Soft plastic, low resistance |
| Rubber | ~2500 | ~2000 | Elastic, high friction |
| Aluminum | ~18,000 | ~14,400 | Ductile, low density |
| Mild Steel | ~36,000 | ~28,800 | High strength, blade wear risk |
| E-Waste Mix | Variable | ~10,000 (avg) | Composite, unpredictable loads |
Step-by-Step Calculation Example (HDPE)
Let’s say your blade contacts a cross-sectional area of 0.5 in² while shredding HDPE:
- Shear Stress = 80% of 4350 PSI = 3480 PSI
- Force = 3480 × 0.5 = 1740 lbs
To convert this into torque:
Torque=Force×Blade Radius
Assuming a blade radius of 1.75″:
1740×1.75=3045 in-lbs
To calculate motor horsepower:
HP=(Torque×RPM)/5252
At 5 RPM:
(3045×5)/5252≈2.9 HP
Apply a safety factor (e.g., 2×):
2.9×2=5.8 HP
DesignWithAjay’s Blade Optimization Tips
- Blade Geometry: Use hooked or serrated profiles for high-friction materials like rubber.
- Spacing & Overlap: Adjust blade spacing to match material thickness and shear zone.
- Material Selection: Use D2 tool steel or EN31 for high-wear applications.
- Simulation: Validate shear force using SolidWorks Simulation or FEA tools.
What You Get with Every Shredder Design
- Parametric CAD models with blade geometry
- Material-specific torque and shear calculations
- BOM with blade specs and material ratings
- Exploded views for assembly and maintenance
- Revision history and customization notes
Real-World Example: Multi-Material Shredder
Design Goal: Shred HDPE, rubber, and aluminum Blade Spec: 36-blade twin-shaft with 1.75″ radius Calculated Shear Force:
- HDPE: 1740 lbs
- Rubber: 1000–1200 lbs (variable)
- Aluminum: 7200 lbs Motor Spec: 7.5 HP with torque limiter Outcome: Smooth operation across materials, reduced blade wear, and optimized energy use