What Causes Gearbox Failure

What causes gearbox failure

Many industrial applications rely on gearboxes (or gear drives) to keep their applications running smoothly. Gearboxes play an important role in 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.  

Like any piece of mechanical equipment, gearboxes can fail. Failure can take down a whole system, resulting in costly downtime and the need for component replacement. It is possible for some equipment to fail on its own. However, there are some causes of gearbox failure that are easily preventable.

Designing Gearboxes Against Failure 

Engineers calculate the mechanical rating of a drive with consideration for classic fatigue failures. This includes damage such as 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 to account for the nature of the driven equipment and its operation. When a designer has the complete details of an application, they will be able to design a gear drive that the end user can depend on.  

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 failure of any one component could shut a whole system down.  

Improper application or maintenance issues are the main causes of preventable gearbox failure. These failure factors include: 
  • Lubrication: Users must follow the owners’ manual when selecting the lubrication type and quantity. Using the wrong lubricant or putting too little in the gearbox will cause damage to the gearing and bearings. On the contrary, adding too much lubrication may cause the gearbox to overheat.  
  • 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. If this exceeds the overhung load limit of the gearbox, shafts and bearings will be damaged. 
  • Contamination: The gearbox should be protected from the ingress of water and other contaminants. Foreign substances can reduce the effectiveness of the lubricant to prevent metal-to-metal contact in the gears and bearings. Excessive water in the gearbox will also lead to rust inside the drive. 
  • Improper Alignment: The motor, gear drive, and driven equipment shafts should run true to each other. Good alignment will reduce unexpected load on the shaft extensions, bearings, and prevent looseness in the application that leads to impact damage. Misalignment will put excess pressure on components and contribute to wear and tear damage.  
  • Excess Load: Running a gearbox over its nameplate load limit will cause damage. Keep in mind that the torque limit of the gearbox is defined by the motor power and speed, so a change to either can affect its performance.  
Both the designer of a gearing system and the end user are responsible for performance. There are many variables that affect performance and service. Designers and users must understand a system's role and capacity.  

The End User's Role in Keeping Gearboxes Running 

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 the equipment in the system. Following this will help end users to maintain a fully-operating system. 

How to Prevent Gearbox Failure 

An end user can take steps that will not only prevent failure, but enhance the life and efficiency of a gearbox.  

Lubrication Maintenance Plan 

If a manufacturer recommends a maintenance plan, the user should adhere to it. Lubrication is key to keeping a system running smoothly; pay careful attention to the recommended lubrication, and do not over or under-lubricate. Make a plan (based off manufacturer’s recommendations) and execute it. 

Resources to Monitor Performance 

Monitoring gearing performance is essential to system life. While health and performance can greatly inform an operator about the state of the system, it is not practical for an operator to constantly watch a gearbox in operation.  

Operators can use remote monitoring to keep track of performance and stay ahead of issues. Regal Rexnord's Perceptiv platform offers a range of flexible and customizable monitoring and diagnostic solutions. Perceptiv helps operators maintain optimal performance and improve reliability. Additionally, Perceptiv offers features like lubrication monitoring, which provides insight on when an actual oil change is needed rather than an operator depending on a prescribed interval plan. 

Smart Breathers & Desiccant Breathers 

Making sure a gearbox interior is free of moisture and particulates will extend its life. As a gear drive warms up, the air inside it expands. Breathers allow the expansion to escape the box without damaging the shaft seals. When the gearbox stops moving, the internal air cools down, contracts, and pulls external air into the box. A breather can filter moisture and particles to prevent contamination from entering.  

The AirMax® line of breathers is effective at protecting against moisture and particulate intrusion. Learn how AirMax helps keep your gearbox running longer. 

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. 

Autogard torque limiters lead the industry in overload protection. Learn more about Autogard and how torque limiters can protect your gearing system. 

Robin Olson

Robin is the Director of Applications Engineering at Rexnord Industries, Gear Group. In 1995, Robin joined Falk, which was acquired by Rexnord in 2005, and has previously worked in the Engineering Technical Services, Warranty, Product Engineering, and Marine Product groups during her career.  She is active in the American Gear Manufacturers Association (AGMA), acting as a contributing member of the Helical Gear Rating Committee, Chairperson of the AGMA 925 (Gear Surface Distress) subcommittee, and is honored to act as US delegate to ISO Working Groups 6 (Gear calculations) and 15 (Micropitting).  Robin holds a Bachelor of Science in Physics from the University of Wisconsin - LaCrosse and a Master of Science in Physics from the University of Wisconsin - Madison.