The harm of moisture to maintenance-free bearings

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 of which indirectly causes 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 finally accumulates into a big harm.

1. Hydrogen-induced cracking:

Also known as hydrogen embrittlement or hydrogen damage, it can cause metal damage, but it has not been widely valued in bearing manufacturing and maintenance. For this kind of situation, water may be 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 oil and grease contain sulfur (extreme pressure additives, anti-wear agents, etc.), and mineral oil itself also contains certain sulfur impurities, which will promote metal corrosion and cracking. Humid atmosphere and free water may cause hydrogen embrittlement of metals.

2. Corrosion:

Water will cause metal rust and corrosion. After the corrosion damage on the bearing raceway surface, 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, and increase the viscosity of the oil, leading to metal corrosion, affecting metal cooling and the normal function of certain components.

4. Consuming additives in 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, extreme pressure agents, rust inhibitors, detergent dispersants, anti-emulsifiers, etc. Water will cause additives to hydrolyze, agglomerate, and flow. Some sulfur and phosphorus extreme pressure agents will denature in the presence of water, generating sulfuric acid or phosphoric acid, increasing the acid value of the oil and forming a corrosive acidic environment.

5. Affecting the normal flow of lubricating oil:

Water can cause sludge and oil emulsification. These impurities are suspended in the oil and affect the normal flow of oil. In addition, these impurities will accumulate in the oil supply hole of the bearing. Other hazards include filter blockage. 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 an increase in bubbles in the oil and foam on the surface of the oil. 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, poor oil flow, and damage to the bearing. The bubble problem sometimes affects the normal operation of the oil slinger or oiler.

7. Impact on oil film strength:

Bearing lubrication relies on a layer of oil film formed between two metal contact surfaces by lubricating oil. The oil film separates the direct friction between 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 oil film strength. For heavy-load, low-speed bearings, this hazard is particularly obvious, causing metal fatigue damage, metal scratches, and fragmentation.

8. Breeding bacteria:

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