FEATURE SEALS & BEARINGS
BEARING FAILURE: THE CAUSES AND CURE
When used correctly, bearings will survive their predicted fatigue life. Many premature failures are down to avoidable mistakes. Brammer and NSK Bearings look at common types of bearing damage and how they can be prevented
W
hen damage is initially suspected, further investigation will be
required to determine the exact nature, and importantly the cause, of deterioration. As most types of damage can be prevented by correct mounting, lubrication and sealing, it is vital that a damaged bearing is not simply replaced without uncovering the underlying reasons. If these are not rectified, the cycle of damage is likely to continue. Bearing damage is often attributed
simply to ‘wear’. Wear is surface deterioration caused by sliding friction between raceway and rolling element surfaces. In most cases there is an adequate oil film between these surfaces which will prevent damage, however this can change dramatically in the presence of contaminating materials. These typically enter a bearing through a faulty seal or contaminated lubricant, and can cause misalignment in the bearing, especially in tapered bearings where some surfaces will be subject to greater abrasion than others. A full clean before installation and
effective lubrication management or filtration can prevent this. Slightly harder foreign particles such as metal debris, dirt or grit tend to cause pitting. These contaminants are usually caused by wear elsewhere in the machinery and, when carried through the machine in lubricating fluid, result in damage throughout the system.
CORROSION There are several types of corrosion which can damage a bearing. Etching is caused by moisture entering a bearing through damaged seals, or as steam or condensate. Care must be taken when washing down equipment, particularly in food or pharmaceutical factories where wash-downs are frequent, and effective re-lubrication must take place immediately after thorough drying. Rust corrosion is most common on ring surfaces rolling elements, and can be caused by high tempratures and humidity when stationary, as well as the presence of water droplets.
20 JUNE 2018 | FACTORY EQUIPMENT Corrosion can also be caused by
improper handling and it is advised to keep bearings in their protective packaging until just before use and, where possible, to use protective lint- free gloves when handling bearings. Electrical corrosion, meanwhile, is caused by electric currents passing through the thin film of lubricating fluid found at the race and rolling elements of a bearings. The resulting burning can cause fluting or groove-like corrugations in the bearing surface, and can be prevented by fully insulating the bearing from surrounding instruments to protect against any electrical difference between the inner and outer rings, or electrical potential difference of frequency.
DETERIORATION There are several other types of damage which can be caused by insufficient lubrication, and these tend to manifest themselves through various stages of deterioration, meaning early identification could prevent a complete failure. The first stage is often discolouration or staining due to a reaction of the lubricant at high temperatures. This is followed by peeling or flaking as lubrication levels drop further and temperatures rise, causing small fragments of the raceway surface to become detached. If left untreated, cracks can develop, leading to irregular operating. These types of damage can also be caused by debris contamination or by incorrect mounting so these factors as well as lubrication management
Left: The effects of electrical corrosion on a bearing surface
Right: A bearing damaged by flaking
should be assessed to prevent recurrence. Cleanliness at the point of bearing
installation is also crucial in preventing damage. Dirt, grit or metallic particles in the housing can cause denting of the bearing raceway or rolling element surface. If denting is identified, the housing should be thoroughly washed, while the filtration system for lubrication should be checked and repaired if necessary. Most types of bearing damage are
easily avoidable if installed carefully and maintained as part of a wider programme taking into account other system components. To simply replace a bearing without knowing the cause of failure can prove very costly in terms of time and equipment. It is always best to examine the system as a whole and identify the root cause of the failure as this method will provide a greater payback in the long run. If in doubt, speak with your supplier to seek expert help. When selecting a supplier, look to authorised distributors of the leading brands who have strong supplier relationships, allowing you to benefit from the breadth of their knowledge and expertise. Above all, selecting the right partner and tapping into their knowledge and experience will help to identify issues before they arise, reducing unplanned downtime and increasing business efficiencies.
Brammer
www.brammeruk.com T: 08447 363665
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
