How much does moisture affect bearing life?

The normal operation of bearings is inseparable from effective lubrication, but the harm of water to bearings may not be taken seriously by everyone. In fact, water has a great impact on the life of bearings. Only a small amount of water (close to 500ppm) can greatly reduce the life of rolling bearings. The harm of water is reflected in two aspects: direct damage to the metal surface and damage to lubricating oil/grease, the latter indirectly causing bearing damage.

Water can cause rust on the metal surface. For lubricating oil and grease, water can cause the base oil in the oil to oxidize and deteriorate. The oxidation products will come into contact with water again, and acidic substances will be generated to corrode the metal. In addition, water causes oil oxidation and deterioration, generating sludge, affecting the viscosity and normal fluidity of the oil, and further causing lubrication problems. Therefore, the beginning of the whole problem is just a small amount of water, which causes a chain reaction and accumulates into a big harm. This article discusses the harm of water to bearings and the consequences and phenomena caused by it through 9 aspects.

1. Hydrogen-induced cracking: Also known as hydrogen embrittlement or hydrogen damage, it can cause metal damage, but it has not received widespread attention in bearing manufacturing and maintenance. For this type of situation, water may be a part of the source of hydrogen. Electrolysis and corrosion can also produce hydrogen. Water will promote electrolysis and corrosion. High-strength steel is particularly susceptible to this problem. In addition, the additives added to lubricating oils and greases contain sulfur (additives, anti-wear agents, etc.), and mineral oils themselves also contain certain sulfur impurities, which will promote metal corrosion and cracking. Humid atmosphere and free water may cause metal hydrogen embrittlement. 2. Corrosion: Water can cause metal rust and corrosion. After the corrosion damage on the surface of the bearing raceway, it will destroy the smoothness of the lubricating oil film, resulting in poor lubrication and further aggravation of damage. 3. Lubricating oil oxidation and deterioration: Water will cause the base oil in the oil to oxidize and deteriorate. If high temperature and impurities (such as fine metal grinding chips) are added, the oxidation rate will increase significantly. In addition, water will cause the loss and consumption of antioxidants in the lubricating oil, resulting in oxidation and deterioration of the lubricating oil. Lubricating oil oxidation will form acidic substances, paint film on the metal surface, increase the viscosity of the oil, lead to metal corrosion, affect metal cooling and the normal function of some parts.

4. Consume additives in the oil:

The main components of lubricating oil and grease are base oil and some additives. In addition to antioxidants, there are other additives such as anti-wear agents, rust inhibitors, detergents and dispersants, anti-emulsifiers, etc. Water will cause additives to hydrolyze, agglomerate, and lose. Some sulfur-phosphorus extreme pressure agents will denature in the presence of water, generate sulfuric acid or phosphoric acid, increase the acid value of the oil, and form a corrosive acidic environment.

5. Affect the normal flow of lubricating oil:

Water will cause sludge and oil emulsification. These agglomerated impurities are suspended in the oil and affect the normal flow of the oil. In addition, these impurities will accumulate in the oil supply hole of the bearing. Other hazards include filter element clogging. In severe cold weather, the water in the oil may also freeze, which also causes poor oil flow and lack of oil in the machine.

6. Increased foam:

Water will affect the surface tension of the oil, resulting in increased bubbles in the oil and foam on the oil surface. For general oil, only 1000ppm of water in the oil will cause serious foam problems. The consequence is that the metal surface cannot form a complete lubricating oil film, and a series of problems will follow: increased oil temperature, increased oxidation, metal cavitation, and poor oil flow, which will damage the bearing. The bubble problem sometimes affects the normal operation of the oil slinger or oiler.

7. Impact on the strength of the oil film:

Bearing lubrication relies on a layer of oil film formed between the two metal contact surfaces by the lubricating oil. The oil film separates the direct friction between the metals and protects the metals. If water enters the metal contact stress area of the bearing, it will destroy the integrity of the oil film and reduce the strength of the oil film. For heavy-load, low-speed bearings, this hazard is particularly obvious, causing metal fatigue damage, metal scratches, and fragmentation.

8. Breeding of bacteria: Water can breed bacteria, microorganisms and fungi. The main harm of these substances is that they affect the normal flow of oil. In addition, they can clog the filter element, form corrosive substances, cause the lubricating oil and fat to become rancid and deteriorate, and indirectly harm the bearing by affecting lubrication.