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Gear Low Cost, Less Power Consumption
Jun 22, 2017

In the case of gear processing, the conventional process is to place the workpiece in an atmosphere furnace and to heat it in a carburizing atmosphere to achieve higher hardness and abrasion resistance. But this method will often cause the small area of the gear as a result of rapid heating, will be earlier than the root to reach the austenitizing temperature, and thus faster carbon absorption, and ultimately lead to uneven distribution of the entire gear carburization, hardness is not uniform And the result of the deformation.

Since the 1990s, there has been a low-pressure carburizing technology in a vacuum environment, which can effectively improve the surface stress of the gear, reduce the gear deformation, improve the fatigue life of the parts, and also in terms of cost control. Has a certain advantage

In the low-pressure carburizing process, the first part in a vacuum environment heated to the austenitizing temperature, and then injected into the carburizing gas, so that the entire surface of the gear can be evenly distributed, the depth is also easier to control. Multiple alternating carburizing and pulsed carburization can achieve higher levels of carbon in the deep layer. Since the heating is done in a vacuum environment and does not come into contact with water and air, there is no intergranular oxidation phenomenon in the atmosphere furnace, and the bending fatigue of the gear is improved.

The gears produced by low pressure vacuum carburizing process have the characteristics of no internal oxidation, good surface quality, small deformation, stable process, long service life, low cost, less power consumption and no pollution, and the degree of automation is higher than that of traditional process. Therefore, this technology is widely used in automotive engines, transmissions, aero engines and other parts of the heat treatment.

In the traditional atmosphere of the furnace carburizing process, because the tooth top part of the more carbon absorption, deeper penetration layer, may be excessive expansion, destruction of the entire parts of the shape accuracy. Therefore, the gear produced by this process must undergo a large number of grinding operations at a later stage to compensate for the deformation. The use of low-pressure carburizing process, because the carburizing uniform, will not appear excessive expansion, the latter part of the grinding work has also been reduced accordingly, the overall processing efficiency can be improved. According to statistics, the use of air furnace carburizing method, 16 hours can process 10 parts, each part time consuming 1.6 hours; and the use of low pressure carburizing method, processing 10 parts only 2.5 hours, an average of 0.25 hours per part, Work efficiency is more than 6 times the former.

Quenching is the means of heating the workpiece to reach the austenitic temperature, but also the prerequisite for carburizing. The traditional atmosphere furnace carburizing process and vacuum low pressure carburizing process are used oil quenching method. In the case of heating, the liquid medium at the surface of the part is vaporized to form a gas film due to heat. This film separates the part from the medium, resulting in a reduction in the quenching speed. The benefits of oil quenching method is to use oil mixing, remove the film, improve the efficiency of quenching.

However, the effect of the furnace carburizing process and the vacuum low pressure carburizing process using the oil quenching method is different, the former will be in some dead ends, such as tooth tooth removal, leaving difficult to remove the film. The whole parts due to the uneven degree of quenching will produce different compressive stress, more likely to cause deformation of parts. While the latter although the oil quenching method, but in a vacuum environment for oil quenching process can effectively remove all the film, and will not leave any dead ends. This allows you to better keep the geometry of the part.

In addition to oil quenching method, the vacuum carburizing process is often quenched by gas quenching method. Gas quenching is a gas as a quenching medium, its biggest advantage lies in the workpiece shape and material according to the special requirements to adjust the quenching process, and gas quenching method of thermal conductivity can be increased by gas flow and pressure to adjust the means to make it Reach or near the level of oil or water-based media.

Compared with the two methods, the oil quenching method lacks flexibility, and the cooling rate of some kind of quenching oil is not necessarily applicable to different models and different specifications. The quenching method can be adjusted due to quenching pressure, quenching gas and its flow rate can be selected, the cooling rate can be controlled. The use of gas quenching for the parts quenching, can significantly reduce the deformation, and the root of the effective hardening layer thickness is greater, almost equivalent to the tip of the hole at the effective hardening layer. Moreover, this way more environmentally friendly quenching, processing of the gear is very clean when baked.

Vacuum heat treatment furnace in accordance with the nature of the operation can be divided into periodic, semi-continuous and continuous three types. According to the furnace structure can be divided into single-chamber, double-chamber, three-chamber and multi-chamber several types.

Single chamber low pressure vacuum carburizing furnace on the parts of the heating carburizing and high pressure gas quenching two processes are carried out in the same room, cooling rate and production efficiency is relatively low. The double chamber low pressure vacuum carburizing furnace consists of a heated carburizing chamber and a gas quenching chamber. Parts in two rooms were heated and cooled separately, which significantly improved cooling rate and production efficiency. Three chamber low pressure vacuum carburizing furnace in addition to heating room, but also equipped with oil chamber and gas quenching chamber, respectively, oil quenching and gas quenching operation. And multi-chamber low-pressure carburizing high-pressure gas quenching furnace is a number of carburizing chamber, diffusion room, gas quenching chamber, oil chamber and other components.

Compared with the periodic vacuum carburizing furnace, semi-continuous and continuous vacuum carburizing furnace production efficiency is higher, respectively, higher than the former 25% and 40%. The semi-continuous and continuous low pressure carburizing high pressure gas quenching automatic production line composed of these two kinds of equipment will become one of the future development trend of carburizing heat treatment equipment for high quality gears and other parts.