Gear shaft processing technology analysis – arrangement of heat treatment process

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In the entire process of shaft processing, sufficient heat treatment processes should be arranged to ensure the mechanical properties and processing accuracy requirements of the gear shaft and improve the processing performance of the workpiece.
Generally, normalizing treatment is arranged first after the shaft blank is forged to eliminate forging internal stress, refine the grains, and improve the cutting performance during machining.
Tempering and tempering treatment is arranged after rough machining. In the rough machining stage, most of the machining allowance of the gear shaft is removed after rough turning, drilling and other processes. The cutting force and heat generation during rough machining are very large. Under the action of force and heat, the shaft produces a lot of internal stress. The internal stress can be eliminated through tempering treatment, replacing aging treatment, and the required toughness can be obtained at the same time.


After semi-machining, except for important surfaces, other surfaces have reached the design size. Only finishing allowance is left for important surfaces. At this time, local quenching treatment is arranged on the teeth to meet the designed hardness requirements and ensure the wear resistance of these surfaces. The subsequent finishing process can eliminate quenching deformation.

Gear shaft processing technology analysis – processing sequence arrangement

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The machining sequence is arranged according to the principle of base surface first, rough first then fine, main first then secondary. For general parts of gear shaft, after the center hole is prepared, the outer circle is processed first, and then other parts are processed, and it is important to separate rough and fine processing. In the gear shaft processing technology, heat treatment is used as a sign, rough processing before quenching and tempering treatment, semi-finishing before quenching treatment, and fine processing after quenching. After separating the stages in this way, the fine processing of the main surface is guaranteed, and the stress during processing of other surfaces will not affect the accuracy of the main surface.
When arranging the order of gear shaft processes, the following points should also be noted.


(1) The rough machining of the tooth profile of the shaft should be arranged after the semi-finishing of the outer circles of the gear shaft. Because the gear shaft has a relatively large workload and is difficult to process, the processing position should be appropriately placed a little later to increase the positioning height of the positioning reference. The tooth profile finishing should be arranged after all the outer circles of the part are processed, so as to eliminate the heat treatment deformation caused by the local quenching of the tooth profile.
(2) The processing sequence of the outer circle surface should be to process the large diameter outer circle first, and then the small diameter outer circle, so as not to reduce the rigidity of the workpiece at the beginning.
(3) The processing of secondary surfaces such as keyways on gear shafts should generally be arranged after the outer circle finishing or rough grinding and before the outer circle finishing. If the keyway is milled before finishing, on the one hand, before finishing, the vibration caused by intermittent cutting will affect the processing quality and easily damage the tool; on the other hand, the size requirements of the keyway are also difficult to guarantee. These surface processing should not be arranged after the main surface finishing, so as not to damage the main surface accuracy.

Thickness determines the size of the gear

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The main function of the gear is transmission. Why are some gears large and some gears small? Some people may say it is because of the size of the mold, but not all gear moduli are the ratio of pitch to circumference. The larger the modulus, the stronger and thicker the teeth, and the larger the size of the gear. The tooth height of a standard gear is equal to 2.25 times the modulus, and the tooth thickness is equal to 0.5*3.14*modulus, that is, the larger the modulus, the larger the teeth. The modulus is also large, the higher the number of teeth, the thicker the gear teeth, and if the number of teeth is determined, the larger the radial size of the wheel. Gears with larger moduli also have larger numbers of teeth. The modulus determines the size of a single tooth profile, not the size of the gear, and has nothing to do with the pressure angle. The modulus is the largest parameter that affects the gear. This does not mean that the gear is large. This should also be determined according to the use environment. If a small gear should be used in a place, it is definitely not suitable for a large gear. So it is not the bigger the better, the right one is the best.
The diameter of the involute gear is d=zm, which is the modulus multiplied by the number of teeth. The modulus is related to the load-bearing capacity of the gear. When the gear is made of the same material and heat treated, the larger the modulus, the stronger the load-bearing capacity; the number of teeth is related to the transmission ratio. The speed of the gear is related to this number as n1*z1=n2*z2.


Therefore, there are two factors that determine the size of the gear, the load-bearing capacity and the transmission speed ratio.
Module m
(1) This module is equivalent to the model of the gear, which can determine the size of the gear. Other parameters are the same. The larger the module, the larger the size of the gear.
Number of teeth z
(2) Needless to say, the number of teeth is the number of teeth in the gear. This is related to the gear ratio. The two meshing gears are in the best possible state.
Pressure angle α
(3) The pressure angle usually refers to the pressure angle on the pitch circle. There are other pressure angles: the pressure angle on the base circle, etc. It is generally believed that the pressure angle is on the pitch circle, and the standard gear is 20 degrees.
Helix angle β
For cylindrical spur gears, there is no helix angle, or the helix angle is 0, but cylindrical helical gears have a helix angle. This helix angle also has a certain range of values. See the Mechanical Design Manual for details. Here it is mentioned that if it is a bevel gear, then the pressure angle we refer to is the positive pressure angle on the bevel gear partition ring.

Casting of gear rings and gears and how to repair damaged gear rings?

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Large gear rings are important and indispensable parts of equipment, just like gears. Although the two are similar, their main function is to transmit and change the direction of force. However, in addition to this, the protection of the main body of the machine system by the drive of the gear ring cannot be ignored.
The outer teeth of the large gear ring are divided into two types of tooth shapes: drum teeth and straight teeth. It can change the contact conditions of the teeth and improve the ability to transmit torque, thereby meeting the requirements of cost protection and extending the service life. The large gear ring is a thin-walled ring forging. It is easy to have problems such as uneven wall thickness, folding, and ellipse during the forging process. Therefore, the quality of the casting can be improved by controlling the details of the casting process.
Therefore, it can be said that the large gear ring is a very important component for protecting the service life of the machine. So when the large gear is damaged, how should we repair it?

First, the steel castings should be processed. Different processing methods should be used for large gears with different degrees of damage, and the damaged parts of the large gear ring should be processed;

Then, welding should be carried out. Before welding, it should be noted that there should be no impurities such as dirty oil, rust, slag, etc. near the welding part, otherwise it will affect the welding effect;

After the welding treatment, there may still be relatively small pores or sand holes on the surface of the steel casting. After removing these defects, the area should be repaired.

After the welding treatment, the damaged large gear ring can be used normally again, which not only saves the production cost of the enterprise, but also helps to reduce the loss of resources, which can be said to kill two birds with one stone.