You selected the right AGMA Class gearbox . You calculated the belt tension perfectly. But the moment you hit "Start," the belt snaps or the gearbox makes a terrifying clunk. The culprit is likely your Starting Method . In conveyor systems, the starting torque profile matters more than steady-state power. Note: We previously discussed VFDs as Energy Savers for pumps and fans. For conveyors, however, the goal is not lowering your electric bill—it is preventing your gearbox from exploding. Table of Contents 1. The Physics of Shock Loads 2. Why Soft Starters Stall Conveyors 3. The VFD Torque Advantage 4. Comparison: Cost vs. Protection 5. Final Verdict Advertisement 1. The Physics of Shock Loads When an AC induction motor starts Direct-On-Line (DOL), it draws 600% to 800% of its rated current (Inrush Current). More importantly, it produces a sudden spike known as Locked-Rotor Torqu...
Starting a belt conveyor is not only about steady-state motor power. In many industrial applications, acceleration time is a critical design parameter that directly affects:
- Motor starting torque
- Gearbox stress
- Belt tension and slip
- VFD sizing and ramp settings
This article explains how to calculate belt conveyor acceleration time step-by-step using practical engineering methods and a realistic worked example.
Figure 1: The "Soft Start" ramp. Controlling Acceleration Time (tacc) reduces mechanical shock and prevents the belt from lifting off the idlers .
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1. Why Acceleration Time Matters
If a conveyor accelerates:
- Too fast → high shock loads, belt slip, gearbox damage
- Too slow → unnecessary cycle time and reduced productivity
Correct acceleration time ensures smooth startup, controlled belt tension, and acceptable motor torque.
2. Basic Parameters Required
Conveyor data
- Belt speed, v (m/s)
- Total moving mass, mtotal (kg)
- Drive pulley diameter, D (m)
Drive system
- Gearbox ratio, i
- Gearbox efficiency, ηg
- Motor torque capability
Assumptions
- Uniform acceleration (linear ramp)
- No belt slip
- Motor torque is approximately constant during acceleration
3. Step 1 – Determine Target Belt Speed
The final belt speed is specified by the process:
v = required belt speed (m/s)
Typical industrial belt conveyors operate between 0.5 m/s and 2.5 m/s.
4. Step 2 – Calculate Required Linear Acceleration
Acceleration is defined as:
a = v / t
- a = linear acceleration (m/s2)
- t = acceleration time (s)
At this stage, t is unknown and will be verified against motor torque capability.
5. Step 3 – Calculate Acceleration Force
Newton’s second law applies to conveyor acceleration. However, a belt conveyor includes rotating components such as pulleys, rollers, shafts, and couplings, which resist acceleration due to their rotational inertia.
To account for this effect in a practical engineering calculation, an Equivalent Mass (meq) is used:
meq ≈ 1.1 × mtotal
The 1.1 factor is an empirical approximation; for critical applications, reflect individual component inertias to the motor shaft.
The acceleration force is then calculated as:
Facc = meq × a
This force represents the additional effort required to accelerate the belt, the conveyed load, and the rotating components.
Engineering Note:
For high-inertia systems (large pulleys, long conveyors, or low-speed drives), a detailed inertia calculation should be performed. For applications requiring precise motor acceleration analysis, full inertia reflection to the motor shaft should be performed.
For high-inertia systems (large pulleys, long conveyors, or low-speed drives), a detailed inertia calculation should be performed. For applications requiring precise motor acceleration analysis, full inertia reflection to the motor shaft should be performed.
6. Step 4 – Total Conveyor Force During Acceleration
Total force during acceleration is:
Ftotal = Frunning + Facc
- Frunning = steady-state running force (friction + gravity)
- Facc = acceleration force
Running force can be calculated using standard motor power and torque methods, as explained here:
How to Calculate Motor Power and Torque for a Belt Conveyor »
7. Step 5 – Convert Linear Force to Pulley Torque
Torque at the drive pulley is:
Tpulley = Ftotal × (D / 2)
This is the torque required at the pulley shaft during acceleration.
8. Step 6 – Check Motor Torque Capability
Motor torque during acceleration must satisfy:
Tmotor ≥ Tpulley / (i × Î·g)
If this condition is not met, the acceleration time must be increased (reducing a and Facc) or a larger motor selected.
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9. Worked Example – Industrial Belt Conveyor
Given:
- Belt speed, v = 1.0 m/s
- Total moving mass, mtotal = 580 kg
- Running force, Frunning = 370 N
- Drive pulley diameter, D = 0.25 m
- Gearbox ratio, i = 20
- Gearbox efficiency, ηg = 0.95
Assume acceleration time: t = 5 s
1. Acceleration:
a = 1.0 / 5 = 0.20 m/s2
2. Equivalent mass:
meq = 1.1 × 580 = 638 kg
3. Acceleration force:
Facc = 638 × 0.20 = 127.6 N
4. Total force:
Ftotal = 370 + 127.6 = 497.6 N
5. Pulley torque:
Tpulley = 497.6 × (0.25 / 2) = 62.2 N·m
6. Motor torque:
Tmotor = 62.2 / (20 × 0.95) = 3.27 N·m
This torque is within the capability of a standard 0.75 kW motor.
A 5 s acceleration time is safe and acceptable.
10. Practical Engineering Guidelines
- Typical conveyor acceleration time: 3–10 s
- Heavy or long conveyors: 8–15 s
- Ensure motor or VFD can deliver 150–200% rated torque during startup
- Longer acceleration reduces belt tension and mechanical shock
11. Conclusion
Belt conveyor acceleration time is a balance between mechanical safety and operational efficiency.
By accounting for acceleration forces (including inertia) and verifying motor torque capability, engineers can select ramp times that protect belts, gearboxes, and motors while maintaining productivity.
This step-by-step method is suitable for most industrial belt conveyor systems and complements steady-state motor power calculations.
To continue the conveyor design process, also check startup belt tension calculations here: How to Calculate Belt Tension During Startup (Take-up & Safety Check) »
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