How to prevent bearing corrosion and wear
1. Water corrosion
If a large amount of water or corrosive substances enter the interior of the bearing, the lubricant cannot provide sufficient protection for the raceway surface, and corrosion will occur. This process will soon lead to deep rust. A thin protective oxide film is formed on the clean steel surface exposed to the air.
However, this film is not impenetrable. If water or corrosive elements contact the steel surface, corrosion spots will be formed, which will soon lead to deep rust. This makes the appearance of gray and black stripes across the raceway, which is mainly consistent with the spacing of the rolling elements. The following figure:
Corrosion cases:
1.1 corrosion may be the most common reason for the short service life of paper machine bearings.
The bearings of these machines are exposed to water, especially in wet parts. Whether it is the papermaking process itself or washing with water during machine cleaning, the existence of water is very dangerous for bearings.
1.2 the corrosion risk of non rotating bearings is the highest, such as in roll magazine.
If the lubricating oil of non rotating bearings contains free water, this water will accumulate at the bottom of the bearing. At a certain distance from the rolling contact point, the concentration of water is the highest, as shown in the following figure:
The reason is that the free water in the oil is heavier than the oil and will sink until there is a proper clearance between the roller and the raceway.
1.3 the bearings of the dryer are corroded by another type.
High temperature and corrosive chemicals may cause corrosion, which is called etching. For example, some EP additives have been shown to be corrosive at high temperatures. (the lubricant may cause corrosion to the bearing after decomposition).
Deep corrosion usually leads to premature and long-term spalling of materials, because the materials will be affected by structural changes, and the area of the bearing surface will be reduced to the extent of overload.
resolvent:
The best way to avoid corrosion is to keep the lubricating oil away from water (or corrosive media).
The picture on the right shows the corrosion stripe across the runway, which is consistent with the distance of the rolling element. Several steps of stop / forward action. Ineffective sealing will allow pollutants (water / corrosive liquid) to enter the bearing, causing corrosion damage. This bearing is difficult to operate.
2. Friction corrosion - contact corrosion
Fretting corrosion occurs in the relative movement between the bearing ring and the shaft or bearing seat, which is caused by too loose fit or error. Relative motion may cause small particles of matter to leave the surface.
When exposed to oxygen in the atmosphere (or the air between surfaces), these particles will oxidize rapidly. Due to fretting corrosion, the support of the bearing ring may be uneven, which has an adverse impact on the load distribution of the bearing. The corrosion area also plays the role of crack notch.
Appearance: areas with rust on the outer surface of the outer ring or the inner diameter of the inner ring. At the corresponding position, the raceway trajectory can be clearly marked.
As shown in the figure above, the fit of the bearing inner race on the shaft is too loose. Either adjust the tolerance or use a special anti micromotion paste to slow down the fretting wear speed. (it is better to increase cooperation)
As shown in the above figure, the fretting corrosion of the inner ring is caused by the taper or roundness (machining) or bending of the shaft surface. In the above two figures, OEM customers sometimes repair the shaft by knurling. Knurling is not recommended for after-sales use and maintenance.
Over time, improper contact will lead to early fretting corrosion and cracking! (outer ring of spherical roller bearing)
Outer ring cracking due to fretting corrosion. The fretting corrosion trace at the crack is still clearly visible! (the clearance of bearing chamber is too large)
