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The working conditions of a cement plant do not foster long service life for machinery, due to dust, heat, moisture and vibration. Therefore it is essential that every opportunity is taken to improve the efficiency and reliability of the plant. Bearings are common to most pieces of equipment, so by concentrating on improving the service life of this critical component, significant savings can be made in maintenance and production costs. NSK Europe has developed several materials and technologies to improve bearing performance.
Poor lubrication and high contamination levels are responsible for 80% of premature bearing failure and therefore make up the two key factors in determining bearing life. The cement industry uses both wet and dry processes to manufacture the finished product, resulting in both dust and moisture causing problems for the bearings. Cement dust is hygroscopic, meaning that it absorbs the lubricating oil from the bearing grease, resulting in a grinding paste inside the bearing.
In such environments, general maintenance and re-lubrication is essential to ensure continued reliable performance, however, fresh lubricant can quickly become contaminated and cause failure itself. Where this is the case, pure maintenance will not resolve the issue; there is a requirement for materials technology, which can take the form of NSK's Hi-TF and Super-TF bearing materials.
NSK has developed these special bearing steels specifically for harsh operating conditions and they have proven very effective already in both the steel and mining industries. Following on from this success, they have been made available for products used in the cement industry in the latest ranges of spherical roller bearings, high capacity EM and EW series cylindrical roller bearings, as well as tapered roller and ball bearings. NSK has examined the main issue of contamination of lubricant, literally under a microscope. The debris particles become indented on the bearing raceway, causing stress concentrations at the edges of these indentations. Secondly, if the viscosity of the lubricant is not high enough, then the metal surfaces come into direct contact, leading to stress concentrations around the contact areas. In both cases cracks form on the surface of the material at the stress concentration points which leads to an accelerated rate of fatigue damage and, ultimately, shorter bearing life.
Tough steel microstructure
The solution to this issue lay in the microstructure of the steel used to make the bearings and the heat treatment process. NSK has developed Hi-TF and Super-TF with a unique microstructure which is able to relax the stress concentrations on the edges of the indentations. These materials have a high volume of retained austenite and improved hardness when compared to conventional bearing materials. All of this innovation has resulted in greatly increased bearing life when operating in contaminated conditions. Based on customer requirements, NSK will suggest which material is right for the application.
When compared to bearings made of ordinary carburised steel, Hi-TF offers up to 7 times the expected life with contaminated lubricant, while Super-TF even improves on that by offering up to 10 times the expected bearing life with contaminated lubricant. Where the service life is reduced by insufficient lubrication, Super-TF can still provide around 5.5 times (4.7 times for Hi-TF) the life expected from a similar bearing made of carburised steel. However, results from a laboratory need to be proven in the field and NSK has been providing solutions to many industries including mining, steel production as well as cement production, all of which offer extremely harsh operating environments. Two recent solutions for the cement industry demonstrated the effectiveness of Hi-TF to resolve persistent bearing failures: the first, a screw pump conveying system and the second, a high temperature fan.
Screw pump conveyor reduces bearing consumption by 50%
In the case of the screw pump conveying system, a large angular contact bearing was suffering from contamination with cement dust. This resulted in wear to the bearing raceways and increased clearances to such an extent that the bearings had to be changed to avoid a catastrophic failure. NSK carried out a detailed site survey resulting in a recommendation to install Hi-TF bearings, which would provide increased resistance to the contamination as well as running quieter and smoother, while also offering increased shock load protection.
Since the installation of the Hi-TF bearings, the plant has reduced bearing consumption by more than 50% and saved on production losses and maintenance time as a result. In light of these improvements, the plant has since installed Hi-TF bearings in other locations, with similar results.
Replacement fan bearing saves over #8364;9.130 per year
In the second case, a cement plant was experiencing regular bearing failures on a fan that was operating at 150
| Product Model | Inside Diameter | Outside Diameter | Thickness |
| 6001-2NSE NACHI | 12 | 28 | 8 |
| 6901-2NSE NACHI | 12 | 24 | 6 |