Water hazards to maintenance-free bearings

The normal operation of bearings is inseparable from effective lubrication, but the harm of moisture to maintenance-free bearings may not be taken seriously by everyone. In fact, moisture has a great influence on the life of the bearing. Only a small amount of water (close to 500ppm) can shorten the life of rolling bearings. Will be greatly discounted.

Moisture is harmful in two ways: direct damage to metal surfaces, and damage to lubricating oil/grease, which indirectly leads to bearing damage.

Moisture will cause corrosion to the metal surface. For lubricating oil and grease, water will cause the base oil in the oil to oxidize and deteriorate, and the oxidation product will contact with water again to generate acidic substances to 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, and further causes lubrication problems. So the whole problem starts with a small amount of water, causes 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, but it has not received widespread attention in bearing manufacturing and maintenance. For this type of situation, water may be part of the source of hydrogen. Electrolysis and corrosion will also produce hydrogen, and water will Promotes electrolysis and corrosion, and high-strength steels are especially 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 corrosion and cracking of metals. Both a humid atmosphere and free moisture can cause hydrogen embrittlement problems in metals.

2. Corrosion:

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

3. Oxidative deterioration of lubricating oil:

Water will promote the oxidation and deterioration of the base oil in the oil. If high temperature and impurities (such as fine metal wear debris) are added, the oxidation rate will increase significantly. In addition, water will also cause the loss and consumption of antioxidants in the lubricating oil, resulting in oxidative deterioration of the lubricating oil. Oxidation of lubricating oil will form acidic substances, paint film on the metal surface, increase the viscosity of the oil, cause metal corrosion, affect metal cooling and the normal function of certain components.

4. Consumable additives in oil:

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

5. Affect the normal flow of lubricating oil:

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

6. Foam increase:

Moisture will affect the surface tension of the oil, resulting in the increase of air 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 surface. Lubricating oil film, a series of problems will follow: rising oil temperature, intensified oxidation, metal cavitation, poor oil flow, all of which will cause damage to the bearing. Air bubbles sometimes affect the normal operation of the oil flinger or oiler.

7. Affect the oil film strength:

Bearing lubrication is to rely on lubricating oil to form a layer of oil film between two metal contact surfaces. The oil film separates the direct friction between the metals and protects the metal. If water enters the metal contact stress area of the bearing, it will Destroying the integrity of the oil film and reducing the strength of the oil film, especially for heavy-load, low-speed bearings, will cause metal fatigue damage, metal scratches, and cracks.

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 also block the filter element and form corrosive substances, causing lubricating oil and grease to become rancid and deteriorated, and indirectly damage the bearing by affecting lubrication.