目前，牽引電機主要通過牽引電機側的主動齒輪與齒輪箱側的從動齒輪嚙合來傳遞扭矩。 牽引電機軸多為外錐結構，齒輪為內錐結構。 形成過盈配合。

運轉中，轉軸與齒輪之間存在微振動、扭力、擠壓等作用，易形成應力集中。 因此，在高級維修時，采用磁粉探傷重點檢查轉軸，尤其是轉軸錐面和齒輪的根部。 檢測。 檢查時發現，上述部位多次出現磁痕。

結合轉軸運行環境對顯示磁痕進行分析，并判定其性質，即是非相關顯示、偽顯示還是相關顯示(疲勞裂紋)，以為轉軸是否繼續使用及牽引電機在線運行評估提供重要支撐。

1、顯示磁痕

在機車牽引電機先進維修過程中，采用便攜式磁粉探傷儀和80-250目混合黑色磁粉對轉子軸進行磁粉干檢測，在圓周方向發現磁痕 軸錐面和齒輪的根部。

  有兩種類型的磁跡線，其特點是：

  ①第一類磁跡：以磁跡中間的一點為起點向兩側發展的小曲線，中間粗，兩端尖，對稱延伸，磁跡密集， 清除;

②第二類磁跡：磁跡松散，分布較寬，在特定位置，沿圓周方向斷續。 磁跡很長（甚至長達一整圈），但不是很清晰。

2  磁痕分析、驗證與判定

在長期使用過程中，牽引電機軸反復承受交變應力。 根據應力分析可知，與齒輪結合的軸錐面根部圓周方向是應力集中最大的部位。

如果這部分原有的小缺陷、表面劃痕、缺口和內部氣孔結構可能形成疲勞源，交變應力的反復作用就會產生疲勞裂紋。

與磁跡對應的疲勞裂紋的特點是：發生在應力集中部位，從磁跡中間的某一點向兩側發展。 可以看出，第一類磁跡符合疲勞裂紋的特征。

根據此類磁跡的特點，可以初步判斷為疲勞裂紋。 此類磁標記的識別可采用以下三種方法：

(1)根據磁跡特征直接判斷為疲勞裂紋。

(2)由于轉軸表面交變應力最大，疲勞裂紋從表面開始出現，故可采用著色探傷的方法進行復檢。 如果在著色探傷過程中仍出現磁痕，則判斷為疲勞裂紋。

（3）由于轉軸疲勞裂紋尺寸較小，使用便攜式磁粉探傷儀和320-400目磁懸浮進行磁粉濕法復檢（濕法靈敏度 磁粉法的靈敏度高于干磁粉法）。 如下圖所示，磁性標記是可見的。 仍表現出疲勞裂紋的特征，判定為疲勞裂紋。

在使用中，牽引電機軸錐面根部與齒輪結合的圓周方向反復受到交變扭矩、彎曲、振動、擠壓、軋制等作用。 這部分容易發生局部硬化，使磁導率發生變化，產生漏磁場。  ，從而在軋制和開卷的界面上形成磁痕。 滾動作用線往往沿軸向有較小的位移，因此磁痕多圈平行地顯示在轉子的滾動部分上。

  局部硬化造成的磁跡的特點是：磁跡松散，分布較寬，位置特異，沿圓周方向呈斷續的磁跡。 磁跡很長（甚至長達一整圈），但不是很清晰。 可以看出，第二種磁標記符合局部硬化磁壓痕的特點。

  根據這種磁痕的特點，可以初步判斷為局部硬化引起的無關顯示，不屬于缺陷的范疇，不會對轉軸造成傷害。 此類磁標記的識別方法如下：

  (1)根據磁跡的特點或用放大鏡觀察轉軸表面有無擠壓、滾壓等痕跡，可直接判斷為局部硬化引起的無關顯示。

  (2)局部硬化造成的不相關顯示磁痕是由磁導率差異引起的漏磁場形成的，因此可以采用色透檢測的方法進行復檢。 如下圖所示，經檢查無缺陷顯示。 顯示不相關，確定為局部硬化所致。

(3) 旋轉軸退火后再次進行磁粉檢查。 如果磁跡消失，則確定為局部硬化引起的無關顯示。

綜上所述

  (1)確定轉軸磁粉探傷所顯示的磁痕，可采用多種檢測方法進行識別和復檢。

  (2)疲勞裂紋對轉軸的危害很大。 必須準確判斷識別，提前排除損壞，確保牽引電機安全運行。

  (3) 局部硬化引起的不相關跡象不是裂紋缺陷，不會對軸造成危害。

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At present, the traction motor transmits torque mainly by meshing the driving gear on the side of the traction motor with the driven gear on the side of the gearbox. Traction motor shaft for the outer cone structure, gear for the inner cone structure. An interference fit is formed.

During operation, there are micro-vibration, torsion, extrusion and other effects between the rotating shaft and the gear, which are easy to form stress concentration. Therefore, in advanced maintenance, magnetic particle inspection is used to focus on checking the rotating shaft, especially the cone surface of the rotating shaft and the root of the gear. Detection. Examination found that the above parts of the magnetic mark many times.

Combined with the operating environment of the rotating shaft, the display magnetic trace is analyzed, and its properties are determined, namely, non-correlated display, pseudo display or correlated display (fatigue crack), which provides important support for whether the rotating shaft continues to be used and the online operation evaluation of the traction motor.

1, display magnetic trace

In the advanced maintenance process of locomotive traction motor, the portable magnetic particle flaw detector and 80-250 mesh mixed black magnetic powder were used to detect the magnetic particle dry of the rotor shaft, and the conical surface of the magnetic trace shaft and the root of the gear were found in the circumferential direction.

There are two types of magnetic track, characterized by:

(1) The first type of track: a small curve developed from a point in the middle of the track to both sides, thick in the middle, sharp at both ends, symmetrical extension, dense magnetic track, clear;

(2) The second type of magnetic track: loose magnetic track, wide distribution, in a specific position, discontinuous along the circumferential direction. The track is long (even a full circle), but not very clear.

Magnetic trace analysis, verification and determination

In the process of long-term use, the traction motor shaft is repeatedly subjected to alternating stress. According to the stress analysis, the circumferential direction of the shaft cone root combined with the gear is the part where the stress concentration is the largest.

If this part of the original small defects, surface scratches, notches and internal pore structure may form a fatigue source, the repeated action of alternating stress will produce fatigue cracks.

The fatigue crack corresponding to the track is characterized by that it occurs at the stress concentration and develops from a certain point in the middle of the track to both sides. It can be seen that the first kind of magnetic trace conforms to the characteristics of fatigue cracks.

According to the characteristics of this kind of magnetic trace, it can be preliminarily judged as fatigue crack. The following three methods can be used to identify such magnetic markers:

(1) Fatigue cracks can be directly judged according to the magnetic track characteristics.

(2) Due to the maximum alternating stress on the surface of the rotating shaft, fatigue cracks begin to appear from the surface, so the method of color inspection can be used for reinspection. If the magnetic marks still appear in the process of color inspection, it is judged as fatigue crack.

(3) Because the fatigue crack size of the rotating shaft is small, portable magnetic particle flaw detector and 320-400 mesh magnetic suspension are used for wet magnetic particle reinspection (the sensitivity of wet magnetic particle method is higher than that of dry magnetic particle method). As shown below, the magnetic marker is visible. It still shows the characteristics of fatigue crack and is judged as fatigue crack.

In use, the circular direction of the cone root of the traction motor shaft and the gear is repeatedly subjected to alternating torque, bending, vibration, extrusion, rolling and other effects. This part is prone to local hardening, so that the permeability changes, resulting in magnetic leakage. , thus forming magnetic marks on the interface between rolling and uncoiling. The rolling action line often has a small displacement along the axial direction, so the magnetic trace is displayed in parallel on the rolling part of the rotor.

The magnetic trace caused by local hardening is characterized by loose magnetic trace, wide distribution, specific position, and discontinuous magnetic trace along the circumference. The track is long (even a full circle), but not very clear. It can be seen that the second magnetic marker conforms to the characteristics of locally hardened magnetic indentation.

According to the characteristics of this magnetic trace, it can be preliminarily judged as irrelevant display caused by local hardening, which does not belong to the category of defect and will not cause damage to the rotating shaft. The identification method of such magnetic markers is as follows:

(1) According to the characteristics of magnetic track or using a magnifying glass to observe whether there is extrusion, rolling and other traces on the surface of the rotating shaft, it can be directly judged as the irrelevant display caused by local hardening.

(2) The unrelated display magnetic marks caused by local hardening are formed by the leakage magnetic field caused by the permeability difference, so the color penetration detection method can be used for reinspection. As shown in the picture below, no defect is shown after inspection. Showed no correlation, determined to be due to local hardening.

(3) Magnetic particle inspection shall be carried out again after annealing of the rotating axis. If the trace disappears, it is determined to be an irrelevant display caused by local hardening.

From what has been discussed above

(1) To determine the magnetic trace shown by magnetic particle inspection of the rotating shaft, a variety of detection methods can be used for identification and reinspection.

(2) Fatigue cracks do great harm to the rotating shaft. It is necessary to accurately identify and eliminate damage in advance to ensure the safe operation of traction motor.

(3) Unrelated signs caused by local hardening are not crack defects and will not cause harm to the shaft.