The normal operation of bearings is inseparable from effective lubrication, but the harm of water to bearings may not be valued by everyone. In fact, water has a great impact on the service life of bearings. With only a small amount of water (close to 500ppm), the service life of rolling bearings will be greatly reduced. 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.
Water will cause corrosion on the metal surface. For lubricating oil and grease, water will cause the oxidation and deterioration of the base oil in the oil, and the oxidation products will contact with water again to form acidic substances to corrode the metal. In addition, water causes the oxidation and deterioration of oil, generates oil sludge, affects the viscosity and normal fluidity of oil, and further causes lubrication problems. Therefore, the beginning of the whole problem is only a small amount of water, causing a chain effect and accumulating into great harm. This paper discusses the harm of moisture to bearings and its consequences and phenomena from nine aspects.
1. Hydrogen induced cracking:
Also known as hydrogen embrittlement or hydrogen damage, it can cause metal damage, but it has not received extensive attention in bearing manufacturing and maintenance. For this kind of situation, water may be a part of the source of hydrogen, electrolysis and corrosion will also produce hydrogen, water will promote electrolysis and corrosion, and high-strength steel is particularly vulnerable to this problem. In addition, the additives added in lubricating oil and grease contain sulfur (additives, anti-wear agents, etc.), and the mineral oil itself also contains certain sulfur impurities, which will promote the corrosion and cracking of metals. Humid atmosphere and free water may cause hydrogen embrittlement of metals.
2. Corrosion:
Water will cause metal rust and corrosion. After corrosion damage is formed on the surface of the bearing raceway, it will destroy the flatness and smoothness of the lubricating oil film, resulting in poor lubrication and further aggravate the damage.
3. Oxidation 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 the oxidation and deterioration of the lubricating oil. The oxidation of lubricating oil will form acidic substances, paint film on metal surface and increase the viscosity of oil, resulting in metal corrosion, affecting metal cooling and the normal function of some parts.
4. Additives in consumed 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 agent, antirust agent, detergent dispersant, anti emulsifier and so on. Water will cause hydrolysis, agglomeration and loss of additives. Some sulfur and phosphorus extreme pressure agents will denature in the presence of water to produce 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 oil sludge and oil emulsification. These agglomerated impurities are suspended in the oil, affecting the normal flow of oil. In addition, these impurities will accumulate in the bearing oil supply hole. Other hazards include clogged filter element. In severe cold weather, the water in the oil may freeze, which also causes poor oil flow and lack of oil in the machine.
6. the bubble increased:
Moisture will affect the surface tension of oil, resulting in the increase of oil bubbles and oil surface foam. For ordinary oil, only 1000ppm of water is needed in the oil. The problem of foam will be very serious. The consequence is that the metal surface can not form a complete lubricant film. A series of problems will follow: oil temperature rising, oxidation increasing, metal cavitation, and oil flow are not smooth. It will cause damage to the bearing. Bubble problems sometimes affect the normal operation of the oil slinger or oiler.
7. Influence on oil film strength:
Bearing lubrication is 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 metal. If moisture 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. This harm is particularly obvious for bearings with heavy load and low speed, It will cause metal fatigue damage, metal scraping and fragmentation.
8. Breeding bacteria:
Water will breed bacteria, microorganisms and fungi. The main harm of these substances is to affect the normal flow of oil. In addition, they will block the filter element and form corrosive substances, resulting in the putrefaction and deterioration of lubricating oil and grease, and indirectly endanger the bearing by affecting the lubrication.
Water will cause corrosion on the metal surface. For lubricating oil and grease, water will cause the oxidation and deterioration of the base oil in the oil, and the oxidation products will contact with water again to form acidic substances to corrode the metal. In addition, water causes the oxidation and deterioration of oil, generates oil sludge, affects the viscosity and normal fluidity of oil, and further causes lubrication problems. Therefore, the beginning of the whole problem is only a small amount of water, causing a chain effect and accumulating into great harm. This paper discusses the harm of moisture to bearings and its consequences and phenomena from nine aspects.
1. Hydrogen induced cracking:
Also known as hydrogen embrittlement or hydrogen damage, it can cause metal damage, but it has not received extensive attention in bearing manufacturing and maintenance. For this kind of situation, water may be a part of the source of hydrogen, electrolysis and corrosion will also produce hydrogen, water will promote electrolysis and corrosion, and high-strength steel is particularly vulnerable to this problem. In addition, the additives added in lubricating oil and grease contain sulfur (additives, anti-wear agents, etc.), and the mineral oil itself also contains certain sulfur impurities, which will promote the corrosion and cracking of metals. Humid atmosphere and free water may cause hydrogen embrittlement of metals.
2. Corrosion:
Water will cause metal rust and corrosion. After corrosion damage is formed on the surface of the bearing raceway, it will destroy the flatness and smoothness of the lubricating oil film, resulting in poor lubrication and further aggravate the damage.
3. Oxidation 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 the oxidation and deterioration of the lubricating oil. The oxidation of lubricating oil will form acidic substances, paint film on metal surface and increase the viscosity of oil, resulting in metal corrosion, affecting metal cooling and the normal function of some parts.
4. Additives in consumed 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 agent, antirust agent, detergent dispersant, anti emulsifier and so on. Water will cause hydrolysis, agglomeration and loss of additives. Some sulfur and phosphorus extreme pressure agents will denature in the presence of water to produce 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 oil sludge and oil emulsification. These agglomerated impurities are suspended in the oil, affecting the normal flow of oil. In addition, these impurities will accumulate in the bearing oil supply hole. Other hazards include clogged filter element. In severe cold weather, the water in the oil may freeze, which also causes poor oil flow and lack of oil in the machine.
6. the bubble increased:
Moisture will affect the surface tension of oil, resulting in the increase of oil bubbles and oil surface foam. For ordinary oil, only 1000ppm of water is needed in the oil. The problem of foam will be very serious. The consequence is that the metal surface can not form a complete lubricant film. A series of problems will follow: oil temperature rising, oxidation increasing, metal cavitation, and oil flow are not smooth. It will cause damage to the bearing. Bubble problems sometimes affect the normal operation of the oil slinger or oiler.
7. Influence on oil film strength:
Bearing lubrication is 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 metal. If moisture 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. This harm is particularly obvious for bearings with heavy load and low speed, It will cause metal fatigue damage, metal scraping and fragmentation.
8. Breeding bacteria:
Water will breed bacteria, microorganisms and fungi. The main harm of these substances is to affect the normal flow of oil. In addition, they will block the filter element and form corrosive substances, resulting in the putrefaction and deterioration of lubricating oil and grease, and indirectly endanger the bearing by affecting the lubrication.
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