The pulley plays a vital role in the transmission system of a crusher. Its design and application directly affect the machine’s performance, stability, and safety. Below is a detailed introduction to the use of pulleys in crushers.
1. Core Functions of Pulleys in Crushers
(1) Power Transmission
This is the most fundamental function. The motor transmits torque to the main shaft pulley of the crusher via V-belts (or trapezoidal belts), driving the movable jaw or rotor to perform crushing operations.
(2) Speed Reduction and Adjustment
The motor typically operates at high speeds (e.g., 1480 rpm or 980 rpm), while the crusher requires a relatively lower working speed (e.g., 200–300 rpm for the eccentric shaft of a jaw crusher). By matching a small pulley (drive pulley) on the motor with a large pulley (driven pulley) on the crusher, effective speed reduction is achieved, precisely adjusting the speed to the crusher’s optimal operating level.
The transmission ratio (i) = diameter of the driven pulley (D) / diameter of the drive pulley (d) = speed of the drive pulley (n1) / speed of the driven pulley (n2).
(3) Cushioning and Protection
This is the most prominent advantage of belt drives over rigid couplings. Crushers often experience drastic load fluctuations, such as when processing extremely hard materials or uncrushable objects (e.g., tramp iron).
V-belts possess a degree of elasticity and flexibility, allowing them to absorb sudden impacts and vibrations, creating a “soft connection.” This effectively protects critical components such as the motor and the crusher’s bearings and shaft from damage caused by overload shocks.
(4) Overload Protection
In extreme overload scenarios (e.g., chamber jamming), the belts will slip on the pulley, cutting off power transmission. This acts as a mechanical safety clutch, preventing motor burnout or more severe mechanical damage.
(5) Cost Reduction and Ease of Maintenance
Belt drives have a simple structure, making them less expensive to manufacture and maintain than gearboxes and other reduction devices.
Installation and center distance adjustment are relatively straightforward, and alignment requirements between the motor and crusher shafts are less stringent compared to couplings.
Replacing belts is far more cost-effective and time-efficient than replacing a set of gears or repairing a broken shaft.
2. Common Types and Features of Pulleys
The following types of pulleys are commonly used in crushers:
(1) V-Belt Pulley
The most common type. The pulley groove has a trapezoidal cross-section that matches the V-belt.
Based on belt specifications, they are categorized into classical V-belts (e.g., Type B, C, D) and narrow V-belts. Narrow V-belts offer higher power transmission capacity and longer service life, making them the preferred choice for modern large crushers.
They often feature a multi-groove design, with multiple parallel grooves on a single pulley to accommodate several belts, meeting the high power demands of crushers.
(2) Webbed Plate Structure
Crusher pulleys are typically large castings (cast iron or cast steel) or welded structures.
Due to their large size (diameters can reach 1–2 meters or more), reinforcing ribs are often designed between the spokes to reduce weight while ensuring structural strength, enhancing rigidity and preventing deformation.
(3) Materials and Manufacturing Processes
Materials: Usually made of high-strength cast iron such as HT250 or cast steel like ZG270-500. Cast iron offers low cost and good damping properties, while cast steel provides higher strength for heavy-duty applications.
Process: Large pulleys are mostly cast and must undergo rigorous dynamic balancing tests. Smaller pulleys may be welded from steel plates and machined.
3. Usage, Maintenance, and Common Issues
(1) Belt Selection and Matching
Belts must be selected based on the crusher’s designed power, speed, and transmission ratio, ensuring the correct type, specification, and quantity.
Belts must be replaced as a set! Replacing only one worn belt is not allowed. Uneven lengths between new and old belts will cause uneven force distribution, leading to rapid failure of the new belt.
(2) Belt Tension Adjustment
Proper tension is critical. Insufficient tension causes belt slippage, reducing transmission efficiency and causing abnormal heat generation and wear. Excessive tension increases bearing load, leading to overheating and premature bearing failure.
Tension is typically adjusted by moving the motor along its base rails to change the center distance. Professionally, a tension gauge is used for measurement. Empirically, pressing the midpoint of the belt should yield a deflection within the specified range.
(3) Alignment Issues
The end faces of the motor pulley and the crusher pulley must lie in the same plane, ensuring parallel alignment. Misalignment causes the belt to run off-track, accelerating wear and leading to premature failure.
(4) Common Failures and Causes
Belt Slippage: Insufficient tension, excessive belt wear, or overload.
Abnormal Belt Wear/Breakage: Improper tension, defective pulley grooves (burrs, corrosion), misalignment, incorrect belt type, or oil contamination.
Pulley Vibration: Failed dynamic balancing of the pulley, bent shaft, excessive bearing clearance, or bearing damage.
Conclusion
For crushers, the pulley is far more than a simple transmission component. It is a critical assembly that integrates power transmission, speed reduction, cushioning protection, and overload protection. Its reliability and stability directly determine the continuous operational capability of the entire crushing production line. Therefore, strict adherence to specifications in selecting, installing, and maintaining pulleys and belts is essential to ensure efficient, stable, and long-lasting crusher operation.
