Free Engineering Tool
Hammer Centrifugal Force Calculator
Calculate centrifugal force on crusher and mill hammers. Enter hammer mass, CG radius, and rotor speed to get force on retention pins and bolts.
Results
Centrifugal Force Formula
The centrifugal force acting on a rotating hammer at its center of gravity:
- m — hammer mass (kg)
- R — distance from rotation center to hammer CG (m)
- ω — angular velocity (rad/s) = 2πn/60
- n — rotational speed (RPM)
Force-to-Weight Ratio
This tells you how many times the hammer’s own weight the centrifugal force equals. Values of 500–2000× g are common in industrial hammer mills.
Pin Sizing (Double Shear)
For a hammer retained by a pin in double shear:
Where τallow is the allowable shear stress (typically 60–80 MPa for medium carbon steel with safety factor 3–5).
Practical Example
Given: Hammer mass = 5 kg, R = 400 mm, Speed = 1500 RPM
ω = 2π × 1500 / 60 = 157.08 rad/s
F = 5 × 0.400 × 157.08² = 49,348 N (49.3 kN)
F / (m×g) = 49,348 / (5 × 9.81) = 1,006 × g
Tip speed at R: v = ω × R = 157.08 × 0.4 = 62.8 m/s
⚠️ Important: This is the centrifugal force only. Impact forces during crushing add significant dynamic loads. Always use adequate safety factors (3–5) for pin, bolt, and disc sizing.
Centrifugal force determines the load on hammer retention pins, bolts, and pivot points. It is essential for:
- Sizing fasteners (pins, bolts) for adequate shear and fatigue strength
- Designing rotor discs to withstand distributed loads
- Predicting hammer behavior (swing-out angle for swing hammers)
- Ensuring safe operation — a thrown hammer is a lethal projectile
A 5 kg hammer at 1500 RPM on R=400mm experiences ~49 kN — equivalent to hanging 5 tonnes from the pin.
Higher centrifugal force:
- Keeps swing hammers extended — hammers stay in radial position, maximizing effective diameter and impact energy
- Increases impact force — impact energy is proportional to mv² (tip speed squared)
- Higher pin loads — requires stronger retention hardware
- More disc stress — disc holes experience bearing stress from pins under centrifugal load
For a pin in double shear:
- Required pin area = F / (2 × τallow)
- Pin diameter = √(2F / (π × τallow))
- Use τallow = 60–80 MPa for medium carbon steel
- Apply safety factor 3–5 for dynamic/fatigue loads
Example: F = 49 kN, SF = 4, τallow = 70 MPa → d = √(2 × 49000 × 4 / (π × 70)) = 42 mm pin required.
Unequal hammer masses create unbalance forces that cause:
- Vibration — grows with RPM², leading to bearing failure
- Bearing damage — reduced bearing life by factor of (F/F₀)³
- Structural fatigue — cracking of frame, foundation bolts, and welds
- Poor product quality — uneven grinding, inconsistent particle size
Always weigh and arrange hammers for minimum unbalance.
Common causes of uneven wear:
- Non-uniform feed — material entering one side of the rotor more than the other
- Material variation — different hardness zones in feed material
- Screen condition — worn or damaged screen sections cause uneven discharge
- Breaker plate alignment — misaligned plates deflect material unevenly
- Initial mass differences — even small manufacturing tolerances compound over time
Implement a regular hammer rotation schedule: flip (180°), swap positions, and weigh before reinstalling.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional rotor balancing for crushers and hammer mills. Reduce vibration and extend bearing life. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
