MEC 240 Conveyors

Conveyors, Pulleys & Belts

Overview of Conveyance Systems

Almost all goods interact with conveyors at some point in their manufacturing or distribution process. Conveyors consist of large pulley and belt drive systems used for efficient material movement through a production process, minimizing human labor and enhancing automation in material handling.

Types of Conveyors

There are several varieties of conveyors designed for different load types and applications:

  • Gravity Fed: Rely on gravity to move goods along a slope, ideal for lighter items and accumulation.

  • Powered: Utilizes electric motors and drive components to move items, suitable for heavier loads and long distances.

  • Unpowered: Operated manually or by gravity, often used for lighter loads and in workstations. Most conveyors use powered motors for operation, selecting motor size based on load requirements and operational speed.

Conveyor Features and Control

High starting torque requirements are common in powered conveyor systems. Capable speed control is crucial to regulate conveyor speed, typically measured in linear feet per minute (LFPM). This regulation is essential for maintaining consistent speed under variable loads, which can range from small items to multi-ton equipment. Various sensors and control systems, such as variable frequency drives (VFD), ensure optimal performance and safety.

Torque and Gear Systems

Industrial conveyors often utilize gearboxes to increase torque and ensure efficient transfer of mechanical power. Gearboxes help drive the main rollers and the conveyor belt, allowing these systems to handle significant weight and stress during operation.

Mechanical Transmission in Conveyor Systems

To effectively transmit mechanical output from the motor to the gearbox and then to the conveyor, a systematic approach is utilized. This transmission relies on:

  • Shafts: Metallic rods that transmit torque and rotation in mechanical systems. Key features of shafts may include keyways, threads, and splines.

    • Alignment between shafts is critical for power transmission; misalignment can lead to unwanted vibrations and potential component failures, such as bearing melting or coupling breakage.

  • Couplings: Devices that connect two shafts to transmit mechanical power between components effectively. There are two main types:

    • Rigid Couplings: Provide no flexibility to accommodate misalignment, maintaining precise alignment. Examples include sleeve, flange, and gear couplings.

    • Flexible Couplings: Allow for some misalignment, essential in applications experiencing vibrations or shifts. Examples include Oldham, universal, jaw, and bellows couplings.

Flexible Couplings

Designed to accommodate a degree of misalignment in machinery, flexible couplings allow for thermal expansion and other movement due to mechanical operations. Two types of flexibility exist:

  • Mechanical Flexibility: Achieved through design clearances allowing relative movement.

  • Material Flexibility: Uses materials resistant to flexing, providing durability in high-stress environments.

Conveyor System Applications

Flexible couplings are advisable for conveyor systems with shafts that are prone to misalignment due to external forces or uneven load distribution.

Mechanical Advantage

The Golden Rule of mechanics asserts that power gained is lost in distance, and vice versa. This principle underscores the efficiency and effectiveness of mechanical systems, which can be analyzed through input (F1) and output force (F2) ratios in various distances.

Mechanical Systems: Levers

  • Class 1: Fulcrum is in the middle (e.g., seesaw).

  • Class 2: Load in the middle (e.g., wheelbarrow).

  • Class 3: Effort in the middle (e.g., tweezers).

Mechanical Advantage of Levers

  • Class 1: Advantage varies (greater, lesser, or equal to 1) based on the positions of load and effort.

  • Class 2: Always greater than 1, providing a force multiplier effect.

  • Class 3: Always less than 1, acting as a speed multiplier for rapid movements.

Relationships between Speed and Torque

  • Speed: Measured as Distance traveled over time.

  • Torque: Represents the rotational power and is measured in Newton-meters (Nm) or foot-pounds (ft-lbs). Speed is typically conveyed in revolutions per minute (RPM).

Ratios in Mechanical Systems

A ratio indicates how many times the first number contains the second, vital in determining performance in mechanical systems. For belt drives, the driver (A) and driven (B) are specified in the standard ratio A:B, influencing operational efficiency and load transport capabilities.

Sheaves and Belt Drives

  • Sheave: A pulley with a grooved wheel specifically designed to hold a belt, crucial in the power transmission process.

  • Belt Drives: Common methods for transmitting power through mechanical systems rely on friction between the belt and pulley.

  • Types of Belt Drives:

    • Open Belt Drive: Shafts arranged parallel, rotating in the same direction.

    • Crossed Belt Drive: Shafts rotate in opposite directions.

    • Quarter Turn/Twist Belt Drive: Shafts positioned at right angles, rotating together in one direction.

    • Compound Belt Drive: Multiple pulleys transmitting power to various shafts simultaneously.

Belt Drive Advantages

  • Economical system design that is simple to install and maintain.

  • Operates with minimal noise and vibration, enhancing worker comfort and product integrity.

  • High lifespan due to less wear and tear, lubrication-free operation with less maintenance required.

Belt Drive Disadvantages

  • Angular velocity ratios may vary, complicating performance measurement and load equity.

  • Sensitivity to heat and moisture can impact materials, leading to potential failure or reduced efficiency.

  • Limited load capacity compared to alternatives like chains, which may be more suited for heavier applications.

Calculating Belt Speed

Belt speed is measured in Surface Feet per Minute (SFM). A basic calculation example is:

  • SFM = (Diameter in inches × RPM) / 12. Operating at specific SFM may depend more on the product needs and application requirements rather than solely on calculated values.

Conclusion

Understanding the intricacies of mechanical systems, particularly levers, torque transmission, and belt drives, is essential for effective conveyance operations. Knowledge of these systems enhances operational efficiency, product safety, and overall manufacturing effectiveness.