When you are trying to get a job done, the last thing you want to encounter is a problem with a mechanical power transmission product. Fortunately, when it comes to gearbox repairs, simple observations can tell you a lot about what is wrong with your power transmission equipment. This guide will help you troubleshoot gearbox problems, understand their causes and learn how to prevent future gearbox issues.
Gear Drive Basics
The purpose of power transmission equipment is to provide torque and a rotary motion between the primary mover and the equipment driven. Gearbox repairs can follow a problem in the loading, installation, support, alignment or maintenance of a mechanical power transmission product. Additionally, missing components such as shafts and gears can cause distress to a piece of power transmission equipment, causing it to run less efficiently, increasing the expense of using the machinery, and shortening its lifespan.
In order to work well, a gearbox needs proper lubrication, preventative maintenance and regular visual inspections. You also need to ensure that the temperature, vibration and noise parameters all meet the guidelines of the mechanical power transmission product.
When Loads are not Uniform
Gear tooth surface distress or a fracture is often a result of the misalignment of gears under operating loads. The supporting structure of power transmission equipment, which includes shafts, gears and bearings, should not have any abnormal elastic deflections so the machinery can maintain proper, uniform loads. Use the AGMA ratings as a guide.
Failure Mode Classifications of Gear Distress
In regards to gearbox repairs, there are four main failure classifications: surface fatigue or pitting, wear, plastic flow and breakage. You can often see the physical distress differences when looking at through-hardened and surface-hardened gear teeth in the mechanical power transmission product.
Surface fatigue and pitting. Surface fatigue in power transmission equipment relates to repeated sub-surface or surface stresses that go beyond the limit a particular material can endure. Pitting is the result of placing a high amount of stress on the uneven surface of a gear tooth. Pitting in a mechanical power transmission product can happen in a short amount of time and occurs mainly in through-hardened gearing. When there is pitting, the pit is steep at the end and looks like an arrowhead whose tip faces the direction of the point of contact. While some pitting is normal on through-hardened gears, you can reduce it by using a quality lubricant and minimizing load weights and speeds when breaking in gears.
Spalling. Spalling is a gearbox repair term that refers to a large area of surface material that breaks away from a tooth and looks like interconnected or overlapping pits in one location. High-contact stress, improper heat treatment, insufficient core hardness/case depth and too high of a load usually cause spalling, which can also look like longitudinal cracks on a tooth’s surface.
Power transmission equipment wear. Moderate to heavy wear of a mechanical power transmission product impairs the performance of a gear drive. Inadequate lubrication, surface contact within the machinery, improper loads and contaminants can remove the metal from the surface of a gear tooth and dedendum areas; change the shape of a tooth; cause cracks; or result in breakages. To prevent wear, you should use a quality lubricant, conduct lube changes regularly and filter present contaminates.
Plastic flow wear. Plastic flow wear is a deformation caused by the softness of a surface and sub-surface of a material in power transmission equipment. It generally occurs with soft gear materials and gives the ends of a gear tooth a fin-like appearance or creates a rounded depression on the contact area of the tooth. You can prevent plastic flow wear by using harder surface and sub-surface materials, decreasing contact stress and increasing the accuracy of spacing between the gear teeth.
Breakage
The ultimate failure in regards to gearbox repairs is breakage, which occurs when the tensile stresses exceed the endurance of a gear’s tooth within power transmission equipment. Breakages can occur at the tooth root fillet, the more tensile side of a tooth, or areas of distress on a shaft. You can prevent breakage within a mechanical power transmission product by reducing the amount of bending stress and transient loads, controlling torque, using lubricants and installing resilient couplings.
Posted under Articles, Tips and Tricks on Tuesday, June 28th, 2011