![<?echo $_SERVER['SERVER_NAME'];?>](/template/twentyseventeen/skin/images/header.jpg)
1Proposal of the problem In 2007, Ziyang Locomotive Co., Ltd. provided two 1840kW narrow-gauge freight diesel locomotives for the Brazilian railway. The locomotive model is SDD8. This type of locomotive uses 310 series sliding bearing traction motor. The center distance of the motor is 39317mm, and the maximum speed is 3100r/min, the user strongly demands that the traction gear ratio is 93/18, and the driving gear is mounted on the motor shaft with a taper of 1:1912. In order to meet the locomotive traction and user requirements, the modulus and pressure angle of the gear pair are finally determined, and the gear pair is an angular displacement spur gear. The gear pair of the gear pair and the traction drive gear of the heavy-duty locomotive (Model SDD1) provided by the company to the Sudan Railway are similar in terms of tooth profile, and the gear structure (, 2) and the locomotive operating environment are similar. Therefore, drawing on the design experience and rectification measures of the traction gear of SDD1 locomotive, it is effective for the design of the traction gear of SDD8 locomotive.
Our company provided two batches of SDD1 locomotives to the Sudan Railway before and after 2006. During the one-year period of operation, there were several problem of gear root fractures. The shortest gear operation period was less than one month. In this regard, our company set up a research team, the research team carried out thematic analysis and related experiments from design to process, and analyzed the material defects, metallographic structure, heat treatment state, crack initiation and expansion of the fractured gear. The gear belongs to the conclusion of high stress and low cycle fatigue damage. At the same time, our company also carried out technical exchanges on gear selection and heat treatment with experts from Zhengzhou Machinery Research Institute to discuss materials and heat treatment from a deeper level. Through finite element analysis, it is found that the assembly stress of the thin-walled gear reaches twice the root stress generated by the gear during the meshing process. Under the strict technical measures, the appropriate reduction of the assembly interference can effectively reduce the tensile stress of the root portion. The large residual stress generated by the surface strengthening of the root portion can effectively balance the tensile stress generated by the assembly. Through the discussion and research of the above various links, our company has rectified the SGD1 locomotive driving gear, and the rectified active gear loading has not broken again.
In this paper, through the research on the traction gear of the SDD1 locomotive, the idea of ​​solving the problem is clarified, and the traction drive gear of the SDD8 locomotive is optimized. It is expected that through the implementation of these measures, the thin wall traction with small safety factor will be achieved. The service life of the gear has been greatly improved. By adopting a continuous improvement process, it is possible to believe that the life of the drive gear to reach one overhaul cycle is possible.
2 Comparison of two types of locomotive traction drive gears The structural gears of the SDD1 and SDD8 locomotive traction drive gears are all thin-walled gears (the rim gear ratio is less than 1). Refer to the calculation method of GB/T3480-1997, when the gear wheel When the edge thickness is relatively smaller than the full tooth height of the tooth, the root bending stress of the tooth will increase significantly. In addition, the railway conditions in Brazil and Sudan are very poor, and the impact of the locomotive during operation is very large, and the impact on the gear is also very large. It is calculated that the safety margin of the gear is low and it is easy to break the teeth. Therefore, the gear must be optimized.
Analysis of 3SDD1 locomotive traction drive gear breaking teeth 3.1 Physical and chemical inspection 3.1.1 Macro analysis The gear has been broken into 3 parts, and two adjacent teeth have fallen off the gear. The inner bore of the gear has severe dry friction marks. One of the broken teeth is that the entire tooth falls off the gear (hereinafter referred to as the first broken tooth), and there is a significant fatigue bead line on one side of the fracture. From the shape of the fatigued bead line, fatigue originates from the tooth. On the root surface, the fatigue source is the line fatigue source; the other side has a slight fatigue bead line, the fatigue source has been damaged, and the tooth surface also has obvious impact marks. The other tooth of the broken tooth falls off (hereinafter referred to as the second broken tooth), the entire tooth top of the tooth has been sharpened, and the fatigue fracture line also has a fatigue bead line. The fatigue source also originates from the tooth root; the other side fracture is brittle. Fracture. A black covering is attached to the gear section. From the topography of the covering, the lubricating oil is attached to the section after being blackened by a higher temperature.
3.1.2 Component detection The driving gear material is 20CrMnMoA. Samples are taken at the heart of the gear for chemical composition detection. The driving gear chemical composition meets the standard requirements.
3.1.3 Metallographic detection Take two teeth near the second broken tooth fracture on the gear to perform metallographic detection. In the polished state, the non-metallic inclusions were 110 grade plastic and 110 grade brittle. Meet the requirements of advanced quality steel standards. The carburized layer of the gear is relatively uniform from a macroscopic perspective. The carburized layer is almost completely worn off by one tooth of the tip end (the portion where the second broken tooth remains on the gear). In the middle of the tooth root, there is a crack extending perpendicularly to the inner hole. It can be confirmed by observation under a microscope that the crack is a stress crack. There is a layer of light near the inner hole which is obviously lighter than the base. The hardness test proves that the hardness of the area is lower than the hardness of the base and is the secondary tempering zone. The carburized layer is organized into fine needle-like tempered martensite with a small amount of granular carbide. The matrix structure is low carbon tempered martensite with a small amount of ferrite. The carburized layer and the matrix structure are normal.
3.1.4 Hardness and depth of hardened layer detection Since the first broken tooth falls off the gear before the second broken tooth, the heat affected is smaller than the second broken tooth, and its hardness and hardened layer depth can represent the gear itself. The heat treatment level, therefore, the first broken tooth is detected, and the test result is seen. It can be seen that the depth of the hardened layer is 1192mm, which meets the technical requirements of 1170~2150mm. The hardness of 707HV1 from the surface of 012mm is converted into 60HRC, which meets the requirements of HRC of gear surface hardness (58-62). The tooth hardness is uneven and the gear heat is The depth of the affected area is inconsistent. The hardness and the depth of the hardened layer show that the heat treatment process of the gear is normal, and the decrease of the surface hardness of the gear is caused by the thermal influence of the dry friction between the inner bore of the gear and the motor shaft.
3.1.5 Scanning electron microscopy analysis Sampling in the fatigue source area was performed by scanning electron microscopy. There are no non-metallic inclusions and other metallurgical defects in the fatigue source zone. The fatigue strips are widely spaced, the fatigue source is linear, and the radial ridges in the source region are many and the height difference is large. It has the typical characteristics of high stress and low cycle fatigue.
3.2 Finite element analysis of the gear under stress state The driving gear is designed to be mounted on the shaft of the traction motor of the locomotive through the 1:1912 taper interference fit. It is assumed that only one tooth is in working condition, according to the gear. The working condition establishes a single tooth model of the gear. The model was built using the finite element analysis software ANSYS. The finite element model was generated by the facet tetrahedral element, the contact between the shaft and the gear was established, and the tangential force of the gear was applied to obtain the calculation model, as shown. The material used in the calculation model is 20CrMnMoA.
Modulus of elasticity / N? Mm-22.06×105 density/kg? M-37850 tensile strength / MPa1175 assembly interference / mm0.221 Poisson ratio 0.3 round circumferential tangential force / N56500 yield strength / MPa885 root diameter / mm115.64 After calculation, the finite element calculation results of the gear, From the calculation results, the following conclusions can be drawn: (1) The maximum equivalent stress of the root portion of the gear is 1100 MPa, which has exceeded the yield limit of the material.
(2) The stress of the gear root is composed of two parts, that is, the expansion stress generated by the interference assembly at the root of the tooth and the bending stress generated by the load of the gear at the root of the tooth, the former being the main influence.
(3) The gear does not meet the design requirements whether it is static strength or fatigue strength.
The most effective solution is: (1) increase the diameter of the gear tooth root circle, that is, increase the ring gear thickness.
Since the gear ratio and the motor center distance have been determined by the user, it is impossible to significantly increase the root circle diameter.
(2) Replace the material and replace 20CrMnMoA with a material with better mechanical comprehensive performance.
(3) Appropriately reduce the interference of the gear and the shaft, and reduce the maximum equivalent stress at the root.
(4) Improve the heat treatment quality of the gear and strengthen the tooth surface.
4SDD8 locomotive traction drive gear optimization design 4.1 Selection of gear material Locomotive traction gear (especially the drive gear) requires high strength, hardness, impact toughness and dimensional accuracy due to its special work. From the material point of view, the important factors affecting the bending fatigue strength of the gear are the yield strength of the material itself, non-metallic inclusions, surface decarburization, metallographic structure and residual stress. At the same time, the hardenability and hardenability of the material should also be considered. , superheat sensitivity, tempering stability, deformation cracking and dimensional stability; in addition, metallurgical factors of materials are also important issues that cannot be ignored, such as composition, purity, high-magnification, low-magnification, oxygen content, residual Austenite and carbide grades, etc.
Our company has used 15CrNi6, 20CrMnMoA, 20Cr2Ni4 and 17CrNiMo6 materials in the selection of traction drive gears. For gears with high safety margin, these materials can meet the requirements of use. The SDD8 locomotive traction drive gear is a thin-walled gear with a small safety margin. How to select materials is especially important. The material 17CrNiMo6 is a refined vacuum deoxidizing steel. It has a perfect process guarantee method after more than 10 years of domestic exploration, and the material meets the requirements of German DIN50602 standard. Its characteristics are: one is to greatly reduce the internal defects of the material and improve the fatigue resistance of the workpiece; the second is complete deoxidation, the maximum oxygen content is less than 20ppm, the relevant test data prove that the same B-type test piece has better impact toughness than ordinary smelting The steel is 57. In addition, the alloying element Ni can greatly improve the toughness of the gear. Mo can improve the hardenability of the gear during heat treatment, and can effectively reduce the temper brittleness of the gear.
Moreover, experts from ZF Germany also pointed out that 17CrNiMo6 material is especially recommended for gears with small safety factor. The DJ4 locomotive traction gear imported from Germany's Siemens company also uses this material.
Based on various factors, it is finally determined that the SSD8 locomotive drive gear is made of 17CrNiMo6 material, which can meet the requirements of GB-T8359-2000 "General requirements of gear materials and heat treatment quality".
4.2 Determination of gear parameters Considering the characteristics of diesel engine and locomotive, the dynamic load factor is 1125. At this time, the diesel engine runs evenly and smoothly, and the locomotive is slightly impacted. Considering the gear manufacturing precision, running speed, running-in effect and lubricating oil characteristics, the gear pair The impact of the calculated dynamic load factor is 11025.
The driving gear adopts a large positive displacement, which can improve the crown coincidence, thereby improving the contact strength and bending strength of the tooth surface; but at the same time, because the gear modulus is small and the number of teeth is small, the thickness of the tooth tip is limited. The maximum displacement of the gear. The displacement coefficient of the traction drive gear of SDD8 locomotive is determined to be 0141mm, and the design thickness of the tooth top is 3148mm. Through the selection of the displacement coefficient and the trimming of the tooth top, the actual meshing position of the gear pair can be changed, and the position of the gear pair can be changed. The length and position of the biting section are adjusted so that the sliding coefficient of the gear tooth flanks is converted to favor gear gluing and wear resistance.
Compared with the traction drive gear of SDD1 locomotive, the pressure angle of the SDD8 locomotive drive gear is smaller, the gear pair drive is smoother and the impact is smaller; at the same time, the thickness of the tooth top is increased, and the wear period of the gear is increased, but it is also suitable. The bending strength of the root is weakened.
4.3 The modification of the gear is to improve the transmission quality and reliability of the traction gear of the SDD8 locomotive. When designing the gear, it must fully consider improving its anti-adhesive strength and wear resistance, reducing the dynamic load during initial meshing, reducing the eccentric load and reducing Noise, etc. Therefore, the meshing modification scheme is implemented at the time of design.
The meshing modification is performed to offset the gear machining error, the installation error, and the disadvantages caused by the deformation of the gear teeth, thereby improving the gear load carrying capacity and reducing the noise, reducing the impact and sliding speed at the start of the meshing, thereby facilitating the formation of the lubricating oil film, thereby Improve the anti-adhesive and wear resistance of gear teeth. We calculate the tooth deformation by finite element analysis, and comprehensively obtain the tooth profile modification of the main and driven gears.
The tooth orientation of the teeth makes the gears evenly contact in the tooth direction under working conditions, which is an effective way to reduce the load concentration (eccentric load). According to the relevant information such as the gear manual, in this low-speed condition, it is recommended to use a spiral asymmetrical drum shape on the unilaterally supported main gear with large load. The principle of shape correction is the middle of the gear teeth. The load is mainly based on continuous working conditions, and both ends of the gear teeth are mainly loaded under starting conditions.
The meshing modification of the traction gear of the SDD8 locomotive includes the profile modification of the driving gear and the tooth profile modification, and the tooth profile modification of the driven gear.
Refer to the drive gear and driven gear drawings for specific modifications.
4.4 Heat Treatment of Gears and Surface Strengthening Gear Materials After the selection is completed, the heat treatment and surface strengthening process of the gears are crucial. There are three main types of stresses on the gears, namely friction, contact stress and bending stress. For thin-walled gears, the influence of the interference stress is also considered. In order to make the tooth surface have good wear resistance, the new gear is still carburized and quenched, the hardness of the tooth surface should reach (58-62) HRC, the core hardness is most sensitive to the bending stress, and the hardness of the core is determined according to domestic and foreign experience. For the (38 ~ 45) HRC. The heat treatment quality of the gear is guaranteed by a strict heat treatment control system.
The main problem of SDD1 locomotive traction drive gear breaking is that the high stress and low cycle fatigue damage caused by the yield strength of the material after the superposition of the basic assembly stress, low cycle pulse root bending stress and subsurface heat treatment residual tensile stress, Any reduction in any one can improve its fatigue strength. The SDD8 locomotive drive gear is a thin-walled gear. After assembly, there is a large assembly tensile stress on the root surface. The residual compressive stress generated by the powerful peening of the tooth surface can effectively balance the tensile stress. It has been shown that the effect of cracks can be eliminated when the residual compressive stress layer is about 5 times deeper than the crack depth. Assuming that the fatigue life ratio of shot peening is 1, the general shot peening can reach 3128, and the enhanced shot peening can reach 4132.
4.5 Determination of the interference of the gear press fitting 4.5.1 Calculation of the interference of the conical surface 4.5.2 Determination of the interference of the press fit According to the calculated value, the interference is determined to be 01135~01150mm.
After adopting this value, the finite element analysis calculates that the assembly stress of the gear is lower than the calculated value of the SDD1 locomotive gear. 32. At the same time, the displacement calculation of the gear pump: q=kdmnB(1) where: q is the row of the pump Quantity, mL / r; k is the correction factor; d is the pitch diameter of the gear, mm; mn is the gear modulus, mm; B is the tooth width, mm.
The gear pump we use has a rated displacement of 462mL/r and a rated speed of 2000r/min. At the initial stage of design, the rated speed of the motor is 1450r/min. We match the speed of the gear pump to 1769r/min. Type change, its rated speed is increased to 1480r / min. The speed of the gear pump is increased to 1806r / min, the theoretical flow is 710L / min.
4.2 Further reasonable and perfect performance The non-standard gear pump designed by us avoids many unfavorable factors of the cycloidal pump in the structure. After more than two months of on-site industrial assessment, the gear pump has no abnormal temperature rise after the start or stop phase. The phenomenon, and no failures, indicates that the improvement of the design is successful. However, some new problems have also been exposed. Workers report that although the gear pump works very reliably, the noise reaches more than 110 decibels, and the noise pollution is serious, requiring improved performance.
Due to the high speed matching of the original design gear pump, the flow rate reaches about 750L/min, while the speed control coupling only needs about 500L/min, and nearly 30 streams need to be bypassed and drained. Therefore, it is very reasonable to reduce the gear pump speed to reduce noise and flow, and to make the transmission box performance better. Through design calculation, when the speed of the YOT750D coupling gear pump is reduced to 1506r/min, the flow rate is tested to meet the requirements, reaching 550L/min, and the noise is reduced to below 100dB. The user is basically satisfied in the field test.
5 Conclusion After this design and improvement, we have a consensus: Gear pump is a kind of pump suitable for oilfield drilling rigs, with high reliability, strong anti-pollution ability, medium noise, medium efficiency and low failure rate. However, after reducing the speed of the gear pump, the noise still cannot meet the noise requirements of the power rig for the power unit, and further improvement of related components is needed to reduce noise. At present, the spur gear pump can be changed to a herringbone or helical gear pump, and the noise can be reduced by about 10 dB. If the noise is reduced to about 80 dB required by the user, the fuel pump needs to use a centrifugal pump or other low noise pump or sound absorption. Guards, which will require further testing to verify and improve.
Wheel Weights,Adhesive Wheel Balance Weights,FE Wheel Balance Weights
Lug Nuts,Bolts,Screws,Nuts Co., Ltd. , http://www.nswheelnuts.com