The normal operation of bearings can not be separated from effective lubrication, but the harm of moisture to bearings may not be everyone's attention, in fact, moisture has a great impact on the life of bearings, only a small amount of water (close to 500 ppm), the life of rolling bearings will be greatly reduced. Moisture is harmful in two ways: direct damage to metal surfaces, and damage to the lubricant/grease, which indirectly leads to bearing damage.
Moisture on the metal surface will cause corrosion, on the lubricating oil, grease, moisture will cause oxidative deterioration of the base oil in the oil, the oxidation products and water and then contact, and generate acid corrosion of the metal. In addition, water causes oxidative deterioration of the oil, generating sludge, affecting the viscosity and normal fluidity of the oil, further causing lubrication problems. So the whole problem starts with just a small amount of water, causing a chain effect, accumulating into a big harm. This paper discusses the harm of water on bearings through 9 aspects and the consequences caused by the phenomenon.
1. Hydrogen cracking:
Also known as hydrogen embrittlement or hydrogen damage, can cause metal damage, but in bearing manufacturing and maintenance has not been widely emphasized, for this type of situation, water may be part of the source of hydrogen, electrolysis and corrosion will also produce hydrogen, water will promote electrolysis and corrosion, high-strength steels are particularly susceptible to suffer from this problem. In addition, the additives added to lubricants and greases contain sulfur (additives, antiwear agents, etc.), and mineral oils themselves contain some sulfur impurities that can promote corrosion and cracking of metals. Humid atmosphere and free moisture can cause hydrogen embrittlement problems in metals.
2. Corrosion:
Water can cause metal rust, corrosion, bearing raceway surface formation after corrosion damage, damage to the lubricant film leveling smoothness, resulting in poor lubrication, further aggravate the damage.
3. Lubricant oxidation deterioration:
Water will promote oxidative deterioration of the base oil in the oil, if coupled with high temperature, impurities (such as fine metal abrasive debris), the oxidation rate will increase significantly. In addition, water can also cause the loss of antioxidants in the lubricant, consumption, resulting in oxidative deterioration of the lubricant. Lubricating oil oxidation will form acidic substances, metal surface varnish, the viscosity of the oil increases, resulting in metal corrosion, affecting the metal cooling and the normal role of certain components.
4. Consumption of additives in the oil:
Lubricating oil, grease is the main component of the base oil, there are some additives, in addition to antioxidants, there are other additives such as anti-wear agents, rust inhibitors, cleaning and dispersing agents, anti-emulsifiers and so on. Water will cause additives hydrolysis, agglomeration, loss, some sulfur and phosphorus extreme pressure agent in the presence of water will be denatured, generating sulfuric acid or phosphoric acid, increase the acid value of the oil, the formation of corrosive acidic environment.
5. Affect the normal flow of lubricants:
Water will lead to sludge, oil emulsification, these impurities into a mass suspended in the oil to affect the normal flow of oil, in addition to these impurities will be blocked in the bearing oil supply holes. Other hazards there are cartridge blockage, in cold weather, the water in the oil may also freeze, also causing poor oil flow, the machine lack of oil.
6. Foam increase:
Moisture will affect the surface tension of the oil, resulting in oil bubbles and oil surface foam increase, for the general oil, oil only 1000 ppm of water, foam problems will be very serious, the consequences are metal surfaces can not form a complete lubricant film, a series of problems occur: oil temperature, oxidation increases, metal cavitation, oil flow is not smooth, and bearings will cause damage. Bubbles sometimes also affect the oil ring or the normal operation of the oil filler.
7. Affect the strength of the oil film:
Bearing lubrication is to rely on lubricating oil in the two metal contact surfaces between the formation of a layer of oil film, the oil film separates the direct friction between the metal, to protect the metal, if the moisture into the bearing of the metal contact force area, will destroy the integrity of the oil film, reduce the strength of the oil film, for the heavy load, low-speed bearings, this harm is particularly obvious, will cause metal fatigue damage, the formation of metal scraping, cracking.
8. Breeding bacteria:
Water will breed bacteria and microorganisms, fungi, the main harm of these substances is to affect the normal flow of oil, in addition to clogging the filter element, the formation of corrosive substances, resulting in lubricating oil, grease putrefaction, deterioration, through the impact of the lubrication of the bearing indirectly jeopardize.