Ferrography analysis method: online monitoring technology for rolling bearings

Online monitoring technology for rolling bearings: Ferrography analysis (bearing monitoring):

Analytical iron spectrometer, direct reading iron spectrometer and online iron spectrometer. Ferrographs are usually divided into these three categories.

The high-gradient magnetic field is used to deposit the solid foreign matter contained in the oil sample flowing through the magnetic field on the glass piece to observe the shape and size of the foreign matter particles. The iron spectrum analysis technique is particularly suitable for identifying and predicting rolling fatigue. a way. A part of the lubricating oil of the rolling bearing is taken as an oil sample. Color and material, so that the type of wear can be clearly identified, the operating state of the machine is predicted, and hidden dangers are discovered in time.

However, it also has excellent identification ability for non-ferrous metals such as copper, sand, organic matter and sealing debris. In principle, the ferrography technology is aimed at identifying strong magnets such as steel.

It is certain that the bearing has begun to appear fatigue microcracks. When the length-to-thickness ratio of the oil sample is 10 1 fatigue-peeling particles, when the steel-like spherical particles having a diameter of 15 μm appear in the oil sample. When the length is greater than 10 μm, abnormal fatigue wear in the bearing has begun, and when the length is greater than 100 μm, the bearing has failed.

The length is between 20 50 μm and the third type of fatigue debris is a length to thickness ratio of 30 1 fatigue sheets. Sheets often have holes. When fatigue begins to appear, the number of such flakes increases significantly, which can be used together with spherical particles as a sign of fatigue.

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Prescribed conditions for normal inspection of bearings

Routine inspection of rolling bearing goods must be carried out in accordance with the conditions specified in the national standards.

    (1) Temperature conditions at the time of measurement

    The ambient temperature during measurement is specified to be 20 ° C. The temperature of bearings, gauge blocks, standard parts and measuring instruments must be the same. The above method of placing them on the same metal plate can achieve the necessary temperature balance as quickly as possible. Otherwise, It takes hours or even days to reach this balance.

    In order to get the correct measurement results, foreign countries rely on mechanization of measurement to avoid touching the objects by hand or wearing insulated gloves.

    (2) Measurement area regulations

    For the measurement of the inner or outer diameter of the bearing, the domestic regulations are measured within the area from the south end of the ferrule to each of the maximum chamfer coordinates, while the foreign regulations are specified to be within the area of ​​the two sides of the ferrule that are twice the chamfering coordinates. measuring.

    (3) Specification of the size standard

    In the measurement of bearing dimensional tolerance by comparative measurement method, the specified mass or standard part is used as the dimensional reference for comparative measurement. The measuring block must meet the requirements of the standard JB/T1078 “Quantity Block”, and the standard parts must conform to the competent authority of the manufacturer. Provisions.

    (4) Regulations of measuring instruments

    The meter used for the measurement must be calibrated and have the accuracy and magnification ratio appropriate for the bearing being tested.

    (5) Allowable measurement error

    In principle, the measurement error can be tolerated below 10% of the tolerance.

    (6) Probe radius and gauge pressure

    In order to reduce the measurement error, it is necessary to reduce the pressure-measurement force of the gauge and increase the radius of curvature of the probe to the extent possible.

    When measuring the inner and outer diameters of the bearing, the measured force and the radius of curvature of the probe can be selected.

    (7) The mandrel used for the measurement

    In the case of measuring bearings such as Kia, Kea and Sd, the taper of the taper mandrel used for cylindrical bore bearings is in principle specified as 1/5000 to l/10000. For tapered bore uranium, the basic taper of the taper mandrel is specified. It is 1/12.

    (8) Provisions for measuring load

    When measuring Kia, Kea and Sia, Sea and other items, it is necessary to apply the necessary measurement load so that the rolling element and the ferrule are in normal contact position to obtain stable measurement values.

    (9) Rules for measuring reference planes

   For general rolling bearings, the non-printing end face of the ferrule is taken as the reference surface during the measurement. For the angular contact ball bearing and the tapered roller bearing, the end face subjected to the thrust load is taken as the reference surface.

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Principles and methods for determining the repair of bearings

First, determine the best time for bearing repair

    It is better to change the state of the rolling bearing to the repair, which is judged from the damage law and characteristics of the bearing. The damage of the most used small and medium-sized bearings is usually based on fatigue and excessive wear of the ferrule or rolling element. When the rolling surface of the bearing enters the third stage of wear, or pitting and spalling have occurred, the bearing will quickly become ineffective, and the damage of the raceway surface is already severe, the repair is difficult, or the repair value has been lost.

    However, before the above-mentioned stage of the bearing, the wear is relatively slight, and the fatigue may occur only in the depth of several micrometers to several tens of micrometers below the surface layer of the rolling surface, so that the bearing can be repaired at this time, and the better can be obtained at a small cost. Repair effect. In summary, the repair period of the rolling bearing has been fully utilized for a period of time when the bearing has been working for a long period of time, and it is most appropriate to enter the repair before the damage occurs.

    Second, the method of determining the timing of bearing repair

    The specific judgment method of whether the bearing should be repaired, that is, the specific judgment method that the bearing has been fully utilized and the adjacent damage occurs is as follows:

    1) Using the bearing working condition monitoring instrument

    It is the most convenient and reliable method to judge the working condition of the bearing and determine when the bearing should be repaired by using the instrument such as iron spectrometer or SPM or I-ID-1 bearing working condition monitoring instrument.

    For example, when using the HD-1 type instrument, when the pointer approaches the danger zone from the warning zone, and the pointer does not return after taking measures such as improving lubrication, it can be found that the bearing itself is a problem. When the bearing is repaired. How far from the danger zone begins to repair, can be adjusted by experience.

    With such an instrument, it is safe and economical to make full use of the bearing working potential, to repair the bearing in time, and to avoid malfunctions.

    2) Monitor with simple tools

    In the case where the above instruments are not available, the operator can hold a tool such as a round bar or a wrench against the outer casing of the machine that is closest to the bearing, and shame the ear on the tool to monitor the sound of the bearing transmitted by the tool. Of course, it can be modified with a medical stethoscope. .

    The normal bearing operation sound should be uniform, smooth and not harsh. The abnormal bearing operation sound has various intermittent, impact or harsh sounds. First of all, you should get used to the normal bearing operation sound, then It is possible to grasp the abnormal operation of the bearing, and then through the accumulation of practical experience, it is possible to further analyze what kind of abnormal sound corresponds to what kind of bearing abnormality. There are many types of abnormal sounds in bearings, which are difficult to tell, and mainly rely on experience accumulation.

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Causes of defects in bearing surface grinding

During the grinding process, the working surface of the bearing is ground by a grinding wheel that rotates at a high speed. Therefore, if the equipment is not operated and adjusted according to the operation instructions during grinding, various defects will occur on the working surface of the bearing, thus affecting The overall quality of the bearing. When the bearing is in precision grinding, the roughening requirements are very high, and the grinding marks appearing on the working surface can be observed by the naked eye.

    Performance showing cross spiral traces

    The reason for this kind of trace is mainly due to the poor straightness of the busbar of the grinding wheel and the unevenness. When grinding, the grinding wheel and the workpiece are only partially in contact. When the workpiece or the grinding wheel reciprocates several times, the performance of the workpiece will reappear. The spiral is visible to the naked eye. The pitch of these spirals is related to the workpiece table speed and the workpiece rotation speed, and is also related to the grinding wheel axis and the table rail.

    (1) The main reason for the formation of spirals
   
    1. The grinding wheel is poorly trimmed, the corners are not chamfered, and the coolant is not used for trimming;

    2. The guide rail guides too much lubricating oil, causing the workbench to float;

    3. The machine tool accuracy is not good;

    4. Grinding pressure is too large.

    (2) The cause of the formation of the spiral

    1. The V-shaped guide rail is not rigid, and the grinding wheel is offset when grinding, but the edge of the grinding wheel is in contact with the working surface;

    2. When the quarrel is repaired, the commutation speed of the worktable is unstable, and the precision is not high, so that the edge of the grinding wheel is slightly trimmed;

    3. The workpiece itself is poorly rigid;

    4. There are crushed and spalled sand on the grinding wheel and iron scraps from the workpiece grinding on the surface of the grinding wheel. For this purpose, the finished grinding wheel should be rinsed or brushed with cooling water;

    5. The grinding wheel is not well trimmed, and there are partial bulges.

    Fish scales appear on the surface

    The main reason for the surface scale of the fish scale is that the cutting edge of the grinding wheel is not sharp enough, and the phenomenon of "clamping" occurs during grinding, and the vibration is large at this time. The specific reasons for the appearance of scales on the surface of the workpiece are:

    1. There are garbage and oil on the surface of the grinding wheel;

    2. The grinding wheel is not trimmed;

    3. The grinding wheel becomes dull. The trimming is not sharp enough;

    4. The diamond fastening frame is not strong, the diamond is rocking or the diamond quality is not good and not sharp;

    5. The hardness of the grinding wheel is not uniform.

    Working face

    The main reason for the surface reappearing of the fluff marks is that the abrasive grains are sandwiched between the workpiece and the grinding wheel after the coarse-grained abrasive grains are detached.

    The specific reasons for the surface of the workpiece being roughened during grinding are:

    1. Traces left over from rough grinding, not worn away during fine grinding;

    2. The coarse abrasive grains and the fine abrasive grains in the coolant are not cleaned;

    3. When the coarse-grained grinding wheel is just finished, the abrasive particles are easy to fall off;

    4. The material toughness is valid or the grinding wheel is too soft;

    5. Improper matching of abrasive grain toughness and workpiece material toughness.
 
    Straight wave marks on the surface of the workpiece

    We cut the cross-section of the ground axis of the milled workpiece and enlarge it to see that its periphery is similar to a sine wave. The center of the sine wave is not rotated, and the trajectory around the sine wave is the waveform cylinder, which is also called a polygon.

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