Comprehensive Conveyor Design Guide

Basic Theory

Conveyor Classification & Structure

Conveyors are classified based on their operational principles, structural features, and applications. The most common types include:

Belt Conveyors

Consist of a continuous belt supported by idlers and driven by pulleys. Used for transporting bulk materials over long distances.

Chain Conveyors

Use chains to move materials. Suitable for heavy loads and high-temperature environments.

Screw Conveyors

Utilize rotating helical screws to move materials. Ideal for granular or powdered materials.

Roller Conveyors

Consist of rollers mounted on a frame. Used for transporting unit loads such as packages and pallets.

Common Conveyor Types Comparison

Conveyor Type	Advantages	Limitations	Best Applications
Belt	High capacity, low friction	Limited incline angle	Bulk materials, long distances
Chain	High strength, high temps	Higher maintenance	Heavy loads, harsh environments
Screw	Enclosed, dust-tight	Limited distance, higher power	Powders, granules, short distances
Roller	Low cost, simple maintenance	Limited to unit loads	Packages, pallets, assembly lines

Selection Criteria

Material characteristics (size, weight, abrasiveness, moisture content)
Throughput requirements (tons per hour)
Distance and layout constraints
Environmental conditions (temperature, humidity, dust)
Maintenance accessibility and costs
Energy efficiency considerations

Calculations

Conveyor Power Calculation

The power required to drive a conveyor belt is calculated based on the following factors:

P = (Q × L × g) / (3.6 × η)

Where:

P = Power required (kW)
Q = Mass flow rate (kg/h)
L = Conveyor length (m)
g = Acceleration due to gravity (9.81 m/s²)
η = Efficiency of the drive system

Mass Flow Rate Calculation:

Q = W × S × ρ

Where W = belt width (m), S = belt speed (m/s), ρ = material density (kg/m³)

Engineering Tip

Always include a safety factor of 1.2-1.5 when selecting a motor to account for starting loads and unexpected conditions.

Pulley Diameter Calculation

Pulley diameter is critical for belt life and proper tracking. It must be sufficient to prevent excessive bending stresses in the belt.

D = (n × t) / (π × sin(180°/n))

Where:

D = Pulley diameter (mm)
n = Number of plies in the belt
t = Thickness of one ply (mm)

Minimum Pulley Diameter Guidelines:

Belt Type	Minimum Diameter (mm)
Light duty fabric	100-200
Medium duty fabric	200-400
Heavy duty fabric	400-600
Steel cord	600-1200

Belt Tension Calculation

Proper belt tension is essential for efficient conveyor operation and preventing slippage.

T = (Q × L × g) / (2 × S)

Where:

T = Belt tension (N)
Q = Mass flow rate (kg/h)
L = Conveyor length (m)
g = Acceleration due to gravity (9.81 m/s²)
S = Belt speed (m/s)

Factors Affecting Tension:

Conveyor inclination angle
Material characteristics
Belt length and weight
Idler friction
Starting and stopping conditions

Warning

Insufficient tension can cause belt slippage, while excessive tension reduces belt life and increases power consumption.

Starting Torque Calculation

Starting torque is the torque required to accelerate the conveyor from rest to operating speed.

T_start = T_running × (1 + α × t)

Where:

T_start = Starting torque (N·m)
T_running = Running torque (N·m)
α = Acceleration rate (m/s²)
t = Acceleration time (s)

Typical Acceleration Rates:

Light duty conveyors: 0.1-0.2 m/s²
Medium duty conveyors: 0.2-0.3 m/s²
Heavy duty conveyors: 0.3-0.5 m/s²

Best Practice

Use soft start devices to gradually increase torque and reduce mechanical shock to the system.

Motor Selection Steps

Proper motor selection is critical for efficient conveyor operation.

Step 1: Calculate Required Power

Determine the power needed based on the conveyor load and operating conditions.

Step 2: Consider Environmental Factors

Ambient temperature
Altitude
Dust and moisture levels
Explosion hazards

Step 3: Select Motor Type

AC induction motors (most common)
DC motors (for variable speed)
Servo motors (for precise control)

Step 4: Determine Motor Size

Select a motor with sufficient power and torque, considering the safety factor.

Calculation Example

Let's calculate the power required for a belt conveyor with the following parameters:

Given Parameters:

Belt width (W) = 1.2 m
Belt speed (S) = 2.5 m/s
Material density (ρ) = 1000 kg/m³
Conveyor length (L) = 50 m
Drive efficiency (η) = 0.85

Step 1: Calculate Mass Flow Rate

Q = W × S × ρ = 1.2 × 2.5 × 1000 = 3000 kg/s = 10,800,000 kg/h

Step 2: Calculate Power Required

P = (Q × L × g) / (3.6 × η) = (10,800,000 × 50 × 9.81) / (3.6 × 1000 × 0.85) = 176.5 kW

Result

Required motor power: 176.5 kW

With safety factor (1.2): 211.8 kW

Select a 220 kW motor

Structure Design

Pulley Structure Design

Pulley design involves selecting the appropriate diameter, width, and construction based on the application requirements.

Pulley Components

Shell (drum)
End disks
Hub
Shaft
Bearing housings

Pulley Types

Drive Pulley

Power transmission to the belt

Return Pulley

Changes belt direction

Snub Pulley

Increases wrap angle around drive pulley

Take-up Pulley

Maintains belt tension

Design Tip

Pulley diameter should be at least 100 times the belt thickness to prevent excessive bending stress.

Bearing Selection

Bearings are critical components that support the rotating parts of the conveyor system.

Types of Bearings Used

Roller Bearings

High radial load capacity

Ball Bearings

High speed, moderate load capacity

Spherical Roller Bearings

Self-aligning, high load capacity

Plain Bearings

Simple, low speed applications

Bearing Selection Factors

Load magnitude and direction
Operating speed
Environmental conditions
Maintenance requirements
Expected service life

L₁₀ = (C/P)^p × 10⁶ revolutions

Where L₁₀ = rated life, C = dynamic load capacity, P = equivalent dynamic load, p = exponent (3 for ball bearings, 10/3 for roller bearings)

Maintenance Tip

Proper lubrication is essential for bearing life. Select the appropriate lubricant based on speed, temperature, and environmental conditions.

Tensioning Device Design

Tensioning devices maintain proper belt tension, ensuring efficient power transmission and preventing belt slippage.

Types of Tensioning Devices

Gravity Take-up

Uses weights to maintain constant tension

Screw Take-up

Manual adjustment with screws

Hydraulic Take-up

Automatic tension control using hydraulic cylinders

Pneumatic Take-up

Uses compressed air for tension control

Tensioning Device Selection

Conveyor length and application
Belt type and thickness
Load characteristics
Environmental conditions
Maintenance accessibility

Best Practice

For long conveyors, use gravity or automatic tensioning systems. For short conveyors, screw take-ups may be sufficient.

Troubleshooting

Misalignment Causes

Belt misalignment is a common problem that can cause premature wear and damage to the conveyor system.

Common Causes

Improper installation of pulleys and idlers
Uneven settling of the conveyor structure
Worn or damaged pulleys and idlers
Incorrect belt tracking
Material build-up on pulleys
Uneven loading of material

Detection Methods

Visual inspection of belt tracking
Measurement of belt position relative to centerline
Observation of wear patterns on belt edges
Monitoring of idler and pulley alignment

Correction Methods

Adjust pulley alignment
Install self-aligning idlers
Clean pulleys regularly
Ensure even material loading
Replace worn components

Warning

Ignoring misalignment can lead to belt damage, increased power consumption, and potential system failure.

Slippage Causes

Belt slippage occurs when the drive pulley rotates without moving the belt, resulting in reduced efficiency and potential damage.

Common Causes

Insufficient belt tension
Worn or damaged drive pulley lagging
Material build-up on drive pulley
Excessive load on the conveyor
Wet or oily belt conditions
Improper drive pulley diameter

Detection Methods

Visual observation of pulley rotation vs. belt movement
Measurement of belt speed vs. pulley speed
Monitoring of motor current draw
Observation of material flow rate

Correction Methods

Increase belt tension
Replace worn pulley lagging
Clean drive pulley regularly
Reduce material feed rate
Install belt scrapers and cleaners
Use proper belt dressing if needed

Tip

Install a slip monitoring system to detect and alert operators to slippage conditions before damage occurs.

Belt Tear Analysis

Belt tears can be catastrophic, leading to costly downtime and repairs. Understanding the causes is essential for prevention.

Common Causes

Foreign objects in the material stream
Damaged or misaligned chute work
Worn or damaged conveyor components
Improper belt splicing
Excessive tension
Abrasive materials

Prevention Methods

Install magnetic separators and metal detectors
Regular inspection of chute work
Proper maintenance of conveyor components
Quality belt splicing procedures
Correct belt tensioning
Use of impact beds at loading points

Emergency Response

Stop the conveyor immediately
Isolate the damaged area
Assess the extent of the damage
Implement temporary repairs if possible
Plan for permanent repairs or replacement

Information

Modern conveyor belts may include rip detection systems that can quickly identify and respond to belt damage.