Cause analysis of KOYO bearing failure inspection method

According to the formation mechanism of the grinding bearing metamorphic layer on the working surface of the imported bearing, the main factors affecting the grinding of the metamorphic layer are the effects of grinding heat and grinding force. Below we will analyze the reasons for bearing failure.
1. KOYO bearing grinding heat
    In the grinding process of KOYO bearings, the grinding wheel and the workpiece contact area consume a large amount of energy, generating a large amount of grinding heat, resulting in local instantaneous high temperature in the grinding zone. Using the linear heat transfer heat transfer theoretical formula to derive, calculate or apply the infrared temperature and thermocouple method to measure the instantaneous temperature under experimental conditions, it can be found that the instantaneous temperature in the grinding zone can be as high as 1000-1500 °C in 0.1-0.001 ms. Such instantaneous high temperature is sufficient to cause high temperature oxidation, amorphous structure, high temperature tempering, secondary quenching, and even burn cracking of the surface layer at a certain depth on the working surface.
    (1) Surface oxide layer
    The surface of the steel under transient high temperature acts on the oxygen in the air and rises into a very thin (20-30 nm) thin layer of iron oxide. It is worth noting that the thickness of the oxide layer is corresponding to the test results of the total thickness of the surface-grinding metamorphic layer. This shows that the thickness of the oxide layer is directly related to the grinding process and is an important indicator of the quality of the grinding.
    (2) amorphous layer
    When the instantaneous high temperature of the grinding zone causes the surface of the workpiece to reach a molten state, the molten metal molecular flow is uniformly applied to the working surface, and is cooled by the base metal at a very fast speed to form a very thin layer of amorphous state. Organizational layer. It has high hardness and toughness, but it is only about 10 nm and is easily removed in precision grinding.
    (3) high temperature tempering layer
    The instantaneous high temperature in the grinding zone allows the surface to be heated to a temperature above the tempering heating of the workpiece at a certain depth (10 to 100 nm). In the case where the austenitizing temperature is not reached, as the temperature to be heated is increased, the surface layer will be re-tempered or high-temperature tempered in accordance with the heating temperature, and the hardness will also decrease. The higher the heating temperature, the more the hardness decreases.
    (4) Two-layer quenching layer
    When the instantaneous high temperature of the grinding zone heats the surface layer of the workpiece above the austenitizing temperature (Ac1), the austenitized structure of the layer is re-quenched into martensite structure during the subsequent cooling process. For workpieces with secondary quenching burns, the secondary quenching layer must be a high-temperature tempering layer with extremely low hardness.

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Matters needing attention during the use of NTN bearings

In addition to excellent quality, NTN bearings are also very precise parts. They are high-performance bearings. If they are used improperly during operation, they will not achieve the expected functional effects, and they will easily damage the bearings. I have definitely paid attention to it.
Generally speaking, the quality of bearings in NTN bearings is very strong. It is not comparable to ordinary bearing products, but even if the bearings are good or bad, for example, the bearings produced in authentic Japan are much better than the bearings produced in the domestic joint venture. So how do we detect the quality of NTN bearings?
One-piece cage is better than two bodies
Although the new process uses an integral cage, it only saves material, and the performance of the rotation is worse than the two. In general, the service life of the bearing is related to three factors, one is the quality of the bearing itself. The second is to use the environment. The third is the installation method.
Is the chamfer bright?
The chamfer of the bearing does not determine the quality of the bearing, but it reflects the machining method of the bearing. The chamfer is black, indicating that heat treatment such as quenching increases the hardness of the bearing, and some people think that the chamfer is black and it is not processed completely. This is a misunderstanding.
Surface feel bearing quality
According to sales experience, many customers say that as long as the bearing surface is bright, the quality is good, which is wrong. The brightness of the bearing surface should be bright, and the reason for this blackness is that the steel used in the bearing is up to standard and its grinding process and cutting fluid used, etc., the former two are the main ones.
Even if the smiling dust that is invisible to the naked eye enters the bearing, it will add wear, vibration and noise to the bearing.
When taking the NTN bearing directly by hand, wash the sweat on your hands and apply high-quality mineral oil before stopping the operation. Pay special attention to rust prevention during the rainy season and summer.
Under certain premise operations, NTN bearings are able to achieve longer lifespans that are better at traditional contests, especially under light load conditions. These extraordinary operating preconditions are when the rolling surfaces (tracks and rolling elements) are effectively separated by a lubricant film and the surface damage that may be caused by contaminants is limited. In fact, under the premise of fantasy, the so-called Eternal bearing life is possible.

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The importance of NSK bearing grease stability

In general, the amount of grease in the NSK bearing always exceeds the actual amount required to directly participate in the lubrication, in the cavity of the holder and the bearing cover, and forms a contour on the periphery of the rolling element. During this process, the bearing temperature rises rapidly due to the resistance of the excess grease. Although most of the excess grease is squeezed out at the beginning of the run, the grease that is squeezed into the raceway attachment may still be carried by the rolling element into the raceway. In the early stages of the bearing, most of the grease is squeezed out of the raceway very quickly (less than a minute), and the build-up grease is discharged a small amount while circulating along with the bearing rotor. At this time, the bearing temperature continues to rise until the excess bearing grease is completely discharged, which can be called the walking phase of the grease. According to the grease quality and filling amount in the bearing structure, this time may last for more than ten. Minutes, even hours.
After the remaining bearing grease is completely discharged, the remaining small amount of grease forms a thin layer of grease film on the mutual contact surface of the rolling element, the raceway and the cage, thereby entering the normal stage of the bearing. . At this time, the temperature gradually drops and reaches equilibrium. In other words, long-term lubrication is mainly borne by this layer of grease film. In addition, during the long-term operation of the bearing, the contour of the rolling element and the raceway and the grease on the cage are shrunk to separate a part of the base oil, and after flowing into the raceway, the lubrication is also supplemented. .
Different bearing greases are not the same in the contours of the bearings. It is necessary to form a contour that is relatively straightforward. The running time is short. In the long-term operation, the bearing temperature is low and stable. This is an ideal one. Grease is especially important for grease channeling.
Some so-called eddy-flow greases are not easy to form contours, and even if they are contoured, they are easy to collapse. At this time, the excess grease repeatedly returned to the raceway is in a state of being strongly stirred for a long time, and the bearing torque is large and the temperature is high. Unbalanced, noise may also be generated, and grease is also prone to deterioration and loss.
NSK bearing temperature rise treatment
When the bearing temperature rises, first judge whether it is malfunctioning. If it does rise, it should be treated as follows:
(1). Check the cooling water pressure, water flow and piping system is normal. If the water pressure is low, the filter may be clogged and cannot be disposed of in time. It can be shut down and put into use when it is confirmed that it can work.
(2). Check the oil pressure of the governor. If the oil pressure is low, the cooling water hydraulic valve may be closed.
(3). Check if the bearing has abnormal sound, NSK bearing and check if the bearing swing is abnormal.
(4). Take oil samples to see if there is any change in oil color.

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