Offshore engineering and large herringbone gear manufacturing

1. Advantages of large herringbone gear in aviation and ocean engineering

The diameter of large gears used in aviation and ocean engineering generally needs to be more than 2.5m. The commonly used large gears are spur gears. This spur gear has certain characteristics and advantages, such as convenient processing, no axial load and simple application. However, this spur gear also has some shortcomings, such as the overall size of the gear is very large, the weight is relatively heavy, there are many materials required for production, and the corresponding production cost is relatively high. The large herringbone gear is mainly formed by its left and right helical gears with opposite rotating directions and equal helical angles, so it has all the advantages and characteristics of spur gear, such as no axial load; In addition, it also has the advantages of helical gear, such as great bearing capacity, very high coincidence coefficient and strong transmission stability.

In addition, because the helical gear widens the tooth width of the gear, the width of the helical gear can be designed to be narrower. At the same time, because the and the drive drum are connected by bolts, the diameter of the gear can be smaller than the width of the spur gear. The advantages of herringbone gear make up for the disadvantages of spur gear. For example, it occupies a small space, its own weight is very light, the required materials are relatively few, and the production cost is relatively low. In addition, it does not need to control the welding quality of medium carbon steel. Therefore, herringbone gear is more in line with the needs of marine engineering equipment for high quality and light self weight. In recent years, it has been widely used in marine engineering.

2. Manufacturing technology of large herringbone gear

Herringbone gear is a kind of cylinder. It is a right-handed tooth in a certain part of the tooth width, and the other end is a left-handed tooth in the tooth width. Herringbone gear has stronger bearing capacity, relatively high transmission balance and smaller axial load. It has a very wide application and importance in the transmission system of heavy machinery in marine engineering. Herringbone gear shaft can be manufactured separately on both sides according to needs, and only then reassembled; Or make both sides into a whole, but this will leave an over pass groove at the bite position of both sides; Or it can be manufactured by gear shaping, but it also needs to disconnect the tooth surfaces on both sides. The manufacturing and processing technology of herringbone gear is relatively complex, and the processing difficulty coefficient is relatively high. Generally, the method with high frequency is the finger gear milling cutter processing method.

In the process of herringbone gear processing, it should be noted that the herringbone gear shaft must be positioned in the process of assembly, and the position error of the herringbone center plane needs to be controlled within the standard of assembly adjustment, so that the herringbone gear can achieve better effect in gear transmission.

Generally speaking, the large herringbone gear used frequently in offshore engineering projects is made of 34crni1mo material. The following points should be paid attention to in the manufacturing process;

(1) The modulus m of large herringbone gear shall be between 28-36mm;

(2) The helix angle of herringbone gear shall be controlled between 20-28 °;

(3) The tooth surface hardness of large herringbone gear should be controlled between 240-280hb;

(4) The error between the common normal lines of the left and right herringbone gears should also be controlled. Generally, the error of the common normal line should be less than 0.1mm.

In the aspect of single-chip gear in herringbone gear, the gear wall is relatively thin, the tooth width is small, but the outer diameter is relatively large. In the processing process of herringbone gear, the key and difficult point is the processing control of herringbone gear deformation, which will occur at any time in the process of heat treatment and machining. Therefore, controlling the deformation of herringbone gear in the process of heat treatment and machining can ensure the internal and external quality of herringbone gear products. This is also an aspect that needs to be paid attention to in the process of gear processing. To solve this problem, we should strictly follow the established process. First of all, forging blank; Secondly, normalize; In addition, lathe roughing shall be carried out; In addition, flaw detection shall be carried out; Thirdly, roughing (milling) teeth should be processed and manufactured; After that, carry out quenching and tempering treatment; The subsequent construction process requires lathe semi finishing, flaw detection, marking (check of tooth shape and hole phase position), drilling by drilling machine, lathe finishing, combination (same rotation direction), fine rolling (milling) tooth processing, split, combination (different rotation direction), drilling and reaming. Finally, magnetic particle flaw detection of tooth surface shall be carried out.

In the manufacturing process, normalizing technology is required after the forging blank is finished, mainly because the grain size of herringbone gear material needs to be refined, which can reduce the deformation of herringbone gear in the subsequent quenching and tempering process. Before the quenching and tempering treatment, it is also necessary to add a rough hobbing process, so that the herringbone gear can ensure that the root position of the herringbone gear can achieve good comprehensive mechanical performance after the heat treatment process, and the surface hardness can meet the requirements of the project. In addition, after the quenching and tempering process, the lathe processing process (finish turning and semi finish turning) needs to be added. This process is mainly to control the heat generated in the drilling process, so as to control the positioning internal roundness in the large thin-walled herringbone gear. After the drilling process, the finish turning process needs to be added, Only in this way can we solve some unnecessary problems.

In the production process of large herringbone gear, the forging blank process, quenching and tempering process, gear processing process and the combination of left and right gears need to be paid attention to. These four processes are directly related to the production quality of large herringbone gear and will also have an impact on the manufacturing cost of herringbone gear.

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