The normal operation of the bearing is inseparable from effective lubrication, but not everyone may pay attention to the harm of moisture to the bearing. In fact, moisture has a great impact on the service life of the bearing, With only a small amount of water (close to 500ppm), the service life of rolling bearing will be greatly reduced. The harm of water is reflected in two aspects: direct damage to metal surface 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 then accumulating into great harm. This paper discusses the harm of moisture to bearings and its consequences and phenomena from nine aspects.
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 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 the corrosion and cracking of metal. Humid atmosphere and free water may cause the hydrogen embrittlement of metal.
Water will cause metal rust and corrosion. After corrosion damage is formed on the surface of bearing raceway, it will destroy the flatness and smoothness of lubricating oil film, resulting in poor lubrication and further aggravate the damage.
Water will promote the oxidation and deterioration of the base oil in the oil, if coupled with high temperature The oxidation rate of impurities (such as fine metal wear debris) 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 the lubricating oil will form acidic substances, paint film on the metal surface, increase the viscosity of the oil, lead to metal corrosion, affect metal cooling and the normal function of some parts.
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, extreme pressure agent, antirust agent, detergent dispersant, anti emulsifier, etc. Water will cause hydrolysis, agglomeration and loss of additives. Some sulfur and phosphorus extreme pressure agents will denature in the presence of water NTN bearings to generate sulfuric acid or phosphoric acid, increase the acid value of oil and form a corrosive acidic environment.
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 leads to poor oil flow and lack of oil in the machine.
Moisture will affect the surface tension of oil, resulting in the increase of bubbles in NSK bearing oil and foam on the oil surface. For general oil, only 1000ppm of water in the oil is needed, 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 aggravating, 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.
Bearing lubrication relies on lubricating oil to form an oil film of INA Bearing between two metal contact surfaces. 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.
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.
9. Loss of lubricating oil and grease