Gearboxes play an important role in many industrial applications, connecting the prime mover to the driven equipment. Gearing ensures that a system has the correct rotational speed, torque, and direction to effectively move product. Gearbox failure can be devastating to the success of an operation.
Designing Gearboxes Against Failure
Engineers calculate the mechanical rating of a drive considering classic fatigue failures. This includes damage like gear tooth durability (pitting), gear tooth strength (bending), bearing spalling (L10), shaft bending, and shaft torsion. Gear designers also understand how a gearbox will be used. They can apply application and service factors to modify the mechanical ratings according to the nature of the driven equipment and its operation. When a designer has
the complete details of an application, they can design a dependable gearbox.
Gearbox Failure Causes
There are many reasons a gearbox can fail. Gearboxes contain gearing, shafts, bearings, bolts, lubrication piping, cooling devices, and other components. A single component failing could shut a whole system down, resulting in costly downtime and necessary replacement. There are some preventable causes of gearbox failure, including:
Lubrication: Follow the owners’ manual for proper lubrication type and quantity - using the wrong type or amount will damage the gearing and bearing or can cause overheating.
Overhung Loads: Belts and chains put a load on the end of the gearbox input shaft. This can also occur when flywheels, rigid couplings, and other devices are mounted on shafts. Exceeding the overhung load limit of the gearbox damages the shafts and bearings.
Contamination: Contaminants reduce the effectiveness of the lubricant to prevent metal-to-metal contact and excessive water in the gearbox will cause rusting.
Improper Alignment: Good alignment reduces unexpected load on the shaft extensions, bearings, and prevents looseness leading to impact damage.
Excess Load: Running a gearbox over its nameplate load limit causes damage. The
torque limit of the gearbox is defined by the motor power and speed, so changes to either can affect performance.
Preventing Gearbox Failure
Once the gearing system is in place, the user is responsible for the drive's operation. End users must understand the needs, capabilities and limitations of their gear systems. They should make sure to read and follow an operation manual for their equipment to help maintain a fully- operating system.
End users can not only prevent failure, but also enhance the life and efficiency of a gearbox.
Lubrication Maintenance Plan
If a manufacturer recommends a maintenance plan, it should be followed. Lubrication is key to keeping a system running smoothly; pay careful attention to the recommended lubrication, and do not over or under-lubricate. Make an informed plan and execute it.
Performance Monitoring
Monitoring gearing performance is essential to system life. While health and performance can inform an operator about the state of the system, it is impractical for an operator to constantly watch a gearbox in operation.
Operators can use remote monitoring to keep track of performance and anticipate issues. Data from sensors can help operators maintain optimal performance and improve reliability. Lubrication, thermal and vibration monitoring can inform an operator of needed service and help pinpoint inefficiently running components.
Smart Desiccant Breathers
Making sure a gearbox interior is free of moisture and particulates extends its life. As a gear drive warms up, the air inside expands. Breathers allow the expansion to escape without damaging the shaft seals. When the gearbox stops moving, the internal air cools down, contracts, and pulls in external air. A smart breather can filter moisture and particles to prevent contamination from entering, and report when it needs replacing.
Torque Limiters
A torque limiter can extend the life of a gearbox in certain applications. Torque limiting couplings are added to the high or low-speed shafts of a gearbox. When a torque overload happens, the limiter will lock and stop the system. It acts like a circuit breaker, stopping the system before costly damage can occur.
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