What are the causes of gearbox damage? Hubei Kaihang intelligent equipment has the following analysis:
First, first understand the manufacturing process of the reducer gear, and then gradually analyze.
Gear manufacturing process:
Preparation → forging blank → normalizing treatment (low temperature annealing) → roughing → semi-finishing → hobbing → tooth end chamfering → high frequency quenching → finishing (grinding end face B → grinding end face C → insert key groove → grinding inner hole → Grinding → deburring → inspection
Second, gear selection and heat treatment
According to the design requirements, the two types of gear transmissions have their own advantages and disadvantages. However, due to the large load on the hard tooth surface and long service life, it is widely used.
Usually, gear transmissions are divided into two categories, namely hard-toothed gear transmission and soft-toothed gear transmission.
Usually, the tooth surface hardness of a pair of meshing gears is greater than 350HBS, which is called a hard tooth surface gear, otherwise it is called a soft tooth surface gear.
There are many materials and heat treatment methods for hardened gears, such as several commonly used ones:
(1) 40Cr. 45#.45Mn2 steel, which can be treated by high-frequency tempering or nitriding in the final heat treatment.
(2) 20Cr.20CrMnTi.20CrMnVB.20CrNiH, etc. can be carburized and quenched,
(3) 38CrMnAl can be used to achieve higher hardness by nitriding process, and some special materials should be treated with special heat treatment methods.
The manufacturing materials and heat treatment process of the gear have a great influence on the bearing capacity and dimensional weight of the gear. Before the 1950s, gears used carbon steel, and in the 1960s, alloy steel was used. In the 1970s, case hardened steel was used. According to the hardness, the tooth surface can be divided into two types: soft tooth surface and hard tooth surface.
(b) The gear surface of the soft tooth surface is lower, but the manufacturing is easier and the running is better.
It is used in general machinery where the size and weight of the transmission are not strictly limited, and in small quantities. Because the paired gears have a heavier burden on the small wheels, the hardness of the small gear teeth is generally higher than that of the large wheels in order to make the working life of the large and small gears substantially equal.
Third, gear damage form, broken teeth analysis
Gear damage form
The gear of the reducer is damaged, such as broken teeth and gear wear. According to the experience of Weigao transmission engineers for many years: the gear damage form is in addition to the abnormal wear of the broken teeth and gears (this is called abnormal wear, because the normal wear of the gear can not be considered as a fault. Abnormal wear refers to the premature wear of the gear In addition to the wear life that the gear should have, there are also damaged forms such as pitting and peeling of the tooth surface. Pitting and spalling of the tooth surface occur mostly in the middle of the upper part of the tooth height.
2. Analysis of the cause of broken teeth
(1) The reason why the gear of the reducer is broken is caused by manufacturing quality defects.
(B1) The reasons for the gear breakage caused by the manufacturing quality are: no suitable steel, poor casting quality, low quenching hardness, insufficient gear hardness, easy bending teeth, insufficient spheroidization, fatigue due to alternating stress during use. Damage, etc...
(B2) The gear meshing accuracy has little effect on the broken teeth. Although the meshing accuracy of the gear has a certain degree of influence on the broken tooth, the degree of influence on the broken tooth is not large. Because the meshing precision of the gear is insufficient, the contact surface of the gear is insufficient, and the contact stress is increased and the load is uneven. This is not the main cause of the broken tooth.
(B3) Another reason for the broken teeth is that the load is too large and the root is defective, and the bending strength of the teeth is insufficient. (The main factors affecting the bending strength are the magnitude of the load force acting on the gear teeth and the degree of the defect of the tooth root. The gear meshing accuracy is poor, and does not change the magnitude of the load force on the gear teeth and the degree of defect of the tooth root, but only increases The contact stress of the teeth).
(B4) Causes of gear wear In addition to the poor manufacturing quality of the reducer, there are some problems that occur during use, such as the lack of oil in the reducer and the use of semi-fluid lubricating fluid.
(B5) Manufacturing quality factors for abnormal wear are:
1 gear material does not meet the requirements, resulting in abnormal wear;
2 gears have defects such as blisters, pores and looseness, and insufficient spheroidization;
3 heat treatment hardness is not enough or no heat treatment;
4 gear meshing accuracy, motion accuracy can not meet the requirements;
5 Arc gears are sensitive to the error of the center distance, especially the positive error of the center distance, which not only reduces the bending strength of the teeth, but also increases the sliding wear.
(2) The lack of oil in the reducer has a great influence on abnormal wear. If the lubricating oil of the reducer leaks, the manager fails to find out in time, the reducer continues to run, and the reducer continues to work in the absence of oil until the top of the tooth is sharpened and found. Open the cover of the reducer. At first glance, a layer of metal powder was piled up on the bottom of the tank, which indicates that oil shortage has a great influence on abnormal wear.
(3) Metal particles aggravate the wear of the gears. Magnetic particles should be used to adsorb metal particles. The reducer adopts a semi-fluid lubricating fluid, and the worn metal particles of the gear are mixed in the lubricating fluid to further wear the gear. It is recommended to add several magnetic bodies to the fuel tank to absorb the metal particles in the lubricating fluid by magnetic action, which can reduce the metal particle content of the lubricating fluid.
Fourth, how to improve the strength of the gear
Increasing the strength of the gear mainly refers to the bending strength and the contact strength of the tooth surface. There are several methods:
1. Select the appropriate displacement coefficient. Designing the gear (positive displacement) can increase the tooth thickness of the gear teeth and improve the bending strength of the gear teeth, but it is not recommended.
2, in the manufacturing process, increase the root radius, improve the surface quality, can also improve the strength of the gear.
3. It is recommended to select materials (such as 40Cr, 45#, 45Mn2 steel; 0Cr.20CrMnTi.20CrMnVB.20CrNiH) and heat treatment methods (surface quenching, carburizing, high-frequency quenching) to improve the surface hardness of the teeth and improve the tooth surface. Contact fatigue strength.
Fifth, the method to improve the contact strength of the gear transmission:
The contact strength is independent of the modulus. The modulus is related to the bending strength. The contact strength is mainly related to the hardness of the tooth surface. You can:
1. Tooth surface modification (a particularly important part now, it can also improve the meshing performance and avoid impact)
2.
3. Heat treatment (generally medium carbon steel, high-frequency quenching of surface after quenching and tempering, improve hardness; low-speed heavy-duty gear low carbon alloy steel carburizing and quenching, hardness improvement, contact strength)
4. Lubrication center distance and number of teeth have nothing to do with this contact strength. Besides, the gear ratio you need has been determined. How can the number of teeth and center distance be changed?
Gear machining accuracy (high precision will improve the meshing performance and thus improve the contact strength)
6. Reasons and prevention of tooth wear of gears:
1. Metallographic anomalies, such as coarse tissue, require fine needle-shaped martensite and a small amount of pearlitic ferrite - metallographic analysis;
2, quenching hardness is low, 40Cr recommended HRC48-55 / motor shaft, large gears need to be lower (if the hardness of the large gear and shaft teeth are not matched, it will also produce excessive wear);
3. If the requirements of the appliance are very high, try intermediate temperature cyanidation or carburizing and quenching.
4, the depth of hardening is not enough, at least to ensure that the root of the tooth is 1mm hardened; if the structure allows, you can choose a larger modulus, but not as a recommended solution.
(a) The hard-toothed gear has high load-bearing capacity. After the gear is cut, it is quenched, surface hardened or carburized and quenched to increase the hardness. However, in the heat treatment, the gear is inevitably deformed, so it is necessary to grind, grind or finish after the heat treatment to eliminate the error caused by the deformation and improve the accuracy of the gear.
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