Proper Mounting Helps Prevent Gearbox Failure

Essential to providing speed and torque control to the motors of almost all industrial machinery, gearboxes can be found in applications ranging from machine tools to conveyor belts to industrial robots to heavy-duty mining equipment. Because they are durable mechanical devices designed to withstand the high temperatures, pressures and extreme conditions found in industrial environments, gearboxes tend to be installed and then neglected; however, failure of these workhorses can have catastrophic results, bringing production to an unplanned halt. Improper motor mounting and/or incorrect specification of the mounting position may be the root cause of gearbox failures that are often attributed to other culprits, such as misalignment, thermal instability and bearing issues. Fortunately, today’s gearbox designs make proper mounting easier than ever before, helping to eliminate costly failures, downtime and production losses.

First, let’s explore the gearbox types most often employed in manufacturing and industrial settings, including:

• Worm gearboxes: Preferred in low-duty applications, the worm-style gearbox is found where higher speed and torque levels, as well as noise reduction, swift stops and shock absorption, are necessary. They feature worm gears, which boast a shaft with a spiral section that, when engaged, runs a toothed wheel.
• Helical-Bevel gearboxes: Commonly employed in automation and power transmission service, bevel gearboxes contain bevel gears, which interlock the beveled edges of the two gears, transferring rotation between them. The design enables an increase or decrease in the gear ratio between the drive and wheels to increase or decrease force.
• Inline gearboxes: This design utilizes helical gears with angled teeth. They have a higher contact level with each other and allow more than one gear tooth to be in contact during operation, resulting in less vibration, longer lifespan and quieter operation in this type of gearbox.
• Planetary gearboxes: With aligned input and output shafts, planetary gearboxes offer higher torque-to-weight ratios and reduced noise. They are also compact in nature, making them suitable for robotics applications.

Common Causes of Gearbox Failure

While gearbox failure can be attributed to many factors, including misalignment, lubrication issues, thermal instability, vibration and bearing problems, many of these malfunctions may, in fact, be the consequence of improper installation and/or specification of the gearbox.

For example, while misalignment itself can result in gear damage, causing bending, overloading and eventual failure of the gearbox, incorrect alignment is often the result of improper installation, such as mounting a vertically constructed gearbox in a horizontal position.

Similarly, oil levels can be affected by improper selection and installation of the gearbox. Knowing the correct mounting position of the gearbox is vital to achieving the right oil quantity for the gearbox, which, in turn, is essential to ensuring that gears and bearings are properly lubricated. Too little oil will leave critical components such as gears and bearings dry, creating friction that leads to breakdown of these components and, ultimately, the gearbox itself. Conversely, too much oil will result in thermal instability as too much oil has the potential to limit space for thermal expansion during operation, which will eventually put too much pressure on the seals, causing them to fail.

Gearbox failure triggered by excessive vibration, a consistent and excessive twisting and side-to-side movement of the gears and other components that sooner or later brings about shaft failure, noise, fatigue and cracks in critical components, may also be attributed to incorrect mounting of the gearbox, as improper mounting and support structures can contribute to vibration.

And, any of these issues – misalignment, too little oil, thermal instability and vibration – can also lead to premature bearing failure, which is responsible for about half of all gearbox malfunctions.

Minimizing Gearbox Mounting Failures

Since improper gearbox installation may be the root cause of some of the most common gearbox breakdowns, it is essential that mounting is done right. The first step is ensuring that gearbox motor installation is performed correctly. To do so, make sure the coupling is the specified distance from the motor face. Neglecting this step may cause axial thrust loads, resulting in premature failure of motor or adapter bearings. A torque wrench should also be used to the specified torque. Skipping this essential step may create too much stress on the bearings, resulting in failure down the road.

Further, gearbox manufacturers, including STOBER, are working on initiatives to help manufacturers avoid mounting errors, such as offering simplified mounting options and designing gearboxes so they can be mounted in all four horizontal output positions without any additional modification to the unit.

Gearboxes are the industrial workhorses that keep manufacturing plants moving. Improper motor mounting and specification of the mounting position are often the root cause of premature gearbox failure, so it is essential to get the job done right from the start. For more information on proper mounting techniques or to learn more about simplified mounting options, please contact a JHFOSTER engineer.