Effect of moisture on maintenance-free bearing life

The harm of moisture is reflected in two aspects: direct damage to metal surfaces, and damage to lubricating oil/grease, which indirectly leads to bearing damage.

Moisture will cause corrosion on metal surfaces. For lubricating oils and greases, moisture will cause the base oil in the oil to oxidize and deteriorate. When the oxidation products come into contact with water, they will generate acidic substances that corrode the metal. In addition, water causes the oil to oxidize and deteriorate, forming sludge, which affects the viscosity and normal fluidity of the oil, further causing lubrication problems. Therefore, the whole problem starts with a small amount of water, causing a chain effect, and finally accumulates into a big harm.

1. Hydrogen-induced cracking:

Also known as hydrogen embrittlement or hydrogen damage, it can cause metal damage and is not widely considered in bearing manufacturing and maintenance. For such cases, water can be a partial source of hydrogen, which can also be produced by electrolysis and corrosion. Water can promote electrolysis and corrosion, and high-strength steels are particularly susceptible to this problem. In addition, additives added to lubricating oil and grease contain sulfur, and mineral oil itself also contains certain sulfur impurities, which will promote corrosion and cracking of metals. Both humid atmosphere and free moisture may cause hydrogen embrittlement problems in metals.

2. Corrosion:

Water will cause metal to rust and corrode. After corrosion damage is formed on the surface of the bearing raceway, it will destroy the smoothness of the lubricating oil film, leading to poor lubrication and further aggravating the damage.

3. Oxidative deterioration of lubricating oil:

Water will cause the base oil in the oil to oxidize and deteriorate. If high temperature and impurities are added, the oxidation rate will increase significantly. In addition, water will also cause the loss and consumption of antioxidants in the lubricating oil, leading to oxidation and deterioration of the lubricating oil. Oxidation of lubricating oil will form acidic substances, paint films on metal surfaces, and increase the viscosity of the oil, leading to metal corrosion, affecting metal cooling and the normal function of certain components.

4. Consume additives in oil:

The main components of lubricating oil and grease are base oils 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 hydrolysis, agglomeration, and loss of additives. 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. Affect the normal flow of lubricating oil:

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

6. Bubble increase:

Moisture will affect the surface tension of the oil, causing the bubbles in the oil and the foam on the oil surface to increase. For ordinary oil, only 1000ppm of moisture in the oil will cause the foam problem to be serious. The consequence is that the metal surface cannot form a complete Lubricant film, a series of problems will occur: increased oil temperature, increased oxidation, metal cavitation, poor oil flow, all of which will cause damage to the bearings. The bubble problem sometimes also affects the normal operation of the oil slinger or oiler.

7. Affects oil film strength:

Bearing lubrication relies on lubricating oil to form an oil film between two metal contact surfaces. The oil film separates the direct friction between metals and protects the metal. Moisture entering the metal contact stress area of the bearing will destroy the integrity of the oil film and reduce the strength of the oil film. For bearings with heavy loads and low speeds, this hazard is especially obvious and can cause metal fatigue damage, metal scratches, and chipping.

8. Breeding bacteria:

Water will 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 and form corrosive substances, causing the lubricating oil and grease to become rancid and deteriorated. They will indirectly harm the bearings by affecting lubrication.