Analysis on the Cause of Shafting of Herringbone Gear Reducer

Summary:From the analysis of the reducer structure, it can be seen that the axial positioning of the driving...

From the analysis of the reducer structure, it can be seen that the axial positioning of the driving shaft (I axis) and the intermediate shaft (II axis) are guaranteed by the herringbone gear of the output shaft (III axis). In other words, the neutral plane of the three-axis herringbone gear determines the neutral plane of the two-axis herringbone gear. The neutral surface of the two-shaft passive gear determines the neutral surface of the one-shaft (input shaft) herringbone gear. That is to say, the neutral plane of one-axis herringbone gear is determined by the neutral planes of two and three axes, and its errors are accumulated. The analysis is as follows:
    The drive shaft of the reducer generally occurs early in the operation of the reducer. Because the negative torque of the reducer inevitably occurs during the entire operation cycle of the pumping unit, it causes the two tooth surfaces of the same tooth of the reducer to alternately carry. When the clearances of the gear pairs on both sides are different, the gears will move axially at the moment of exchanging the bearing surface to adjust the position of the center surface of the herringbone gear. As the axial movement between the meshing tooth surfaces is sliding friction, as the number of exchanges increases, the gap between the two sides of the tooth will gradually increase, and the amount of axial movement also increases. At the same time, if the tooth shape error is large or the tooth surface hardness is reduced, the tooth surface wear will also be accelerated. When the amount of pulsation exceeds 1mm, the change in tooth shape will increase sharply, so that the meshing of the gear pair changes from rolling friction to sliding friction. The tooth surface will wear rapidly in a short time. The amount of pulsation also increased rapidly with the increase of noise, which forced the reducer to stop running.
    It can be seen from the above analysis that one axis moves: one is that the hardness difference between the tooth surfaces of the same gear shaft is large, resulting in inconsistent wear rates of different tooth surfaces of the same tooth; second, the two tooth surfaces of the same tooth caused by tooth shape errors are opposite to their The center plane itself is asymmetric. The gap between the two sides of the herringbone teeth on the same shaft is different; the third is due to the insufficient hardness of the tooth surface to accelerate the wear of the tooth surface; the fourth is the insufficient interference between the two-axis disk gear and the shaft assembly, making it the shaft under the action of positive and negative torque 3. The hole assembly property changes and becomes unstable. Fifth, the machining accuracy is insufficient. It is well known that the current domestic reducer gear processing is mostly carried out according to the helical gear processing technology. That is, the same rotation direction is completed in the same process, and the gear tooth of the other rotation direction is to be completed in another process or another equipment. How can we ensure that the backlash of the two helical gears with different rotation directions on the same shaft is controlled during the forward and reverse rotation? Is the tooth profile accuracy controlled? At present, the method of line marking and tool setting is generally adopted in China. For this reason, two issues are drawn: line accuracy and tool setting accuracy. The tooth shape error is mostly determined by the cutter and equipment and equipment adjustment. For this reason, companies with a sound quality assurance system keep the tool sharpening and tool inspection in a controlled state. The equipment is also regularly adjusted, that is, the process is fixed. Sixth, the steering and commutation impacts of the reducer also have a certain effect on the shaft shift. In summary, the neutral surface of the one-axis herringbone gear of the reducer is sought during the load-bearing operation. In operation, due to the inevitable negative torque of the reducer, the tooth surfaces on both sides of the same tooth become alternate bearing surfaces. Therefore, the neutral plane is constantly searching in the cycle, which also produces a one-axis movement. So one-axis movement is inevitable, but control is also necessary.

Control measures
    a. Improve the manufacturing accuracy, increase the accuracy of the marking, tool setting and the angle of the hob machine tool holder. Strictly control the precision of gear tooth profile;

    b. Strictly control the tooth side clearance, which can be selected during assembly to achieve an optimal combination;

    c. Strictly control the hardness difference between the left and right gear teeth on the same shaft, so that the wear speed of the gear teeth on both sides of the gear in the same stage is close to, generally does not exceed HB10;

    d. Strictly carry out uniform loading test and forward and reverse loading test before leaving the factory (a loading test device is recommended to everyone afterwards). Make sure that the contact trace reaches 90% in the length direction and 75% in the height direction;

    e. Ensure the minimum interference between the hole of the gear on the second shaft and the shaft, which can ensure that the hole shaft will not be unstable when the maximum negative torque occurs regardless of the rotation direction of the output shaft of the reducer.


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