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Problems Worthy Attention On Control Gear Quenching Distortion

Posted: 2014-01-25 04:58:56  Hits: 2136
The quenching is the main link of the gear distortion. The basic method of control of quenching distortion is making each part of the gear cooling uniformity as much as possible. In addition, there are also some problems worthy of attention:
1. The influence of the distortion is the steel’s hardenability. If the steel’s hardenability get higher, the volume of the change for participate in the organization get bigger also. When the workpiece hardening completely and the whole are in martensite, the volume difference reaches the maximum before and after quenching, the change of the volume of the steel with 1% carbon content is about 1%. If only half hardening, and half of the volume quenching into martensite, the volume difference before and after quenching will be one time smaller than the former. So the smaller hardenability, the smaller quenching distortion, otherwise the quenching distortion get bigger.      
In a lot of quenching gears, in order to solve the problem of distortion, we often use the way to reduce the core hardness, but from the gear strength consideration, the core hardness can’t be low, because a lot of gear’s fatigue failure are an important reason why the core hardness is low, so this becomes a big contradiction in gear production. In order to solve the contradiction of the gear strength and the center of hardness requirement cause heat treatment distortion, we must be reasonable limits the hardenability of steel.
Experiments show that, if steel hardenability (or the core hardness) is close, Its distortion is close, it provides favorable conditions for control of distortion. For the gear quenching distortion, the height of steel hardenability is important, but the bandwidth of steel hardenability is more important, it is the volatility of harden ability. Just because the hardenability of steel has an important significance in gear quenching distortion, all countries bring the hardenability into steel standard. In recent years, the bandwidth of steel harden ability narrows down, such as the German "carburizing and quenching steel delivery technical conditions" in the new rules for narrow hardenability of steel, its bandwidth from ordinary hardenability steel 8HRC reduce to 5 HRC.
2. Pressure forced quenching. Many domestic gear producers advocate free quenching in abstracto, in order to simplify the process, convenient operation, lower the cost, therefore, the pressure forced quenching process and the equipment development affected by a lot. It is a pity that, such as bevel gears with special structure use free quenching is difficult to control distortion. For decades, the gear industry has been plagued by bevel gears distortion in our country. In fact, like the bend distortion of the small twist bit and the long and thin bar etc in heat treatment production, everyone used the pressure straightening to realize the stable volume production. For gear manufacturing of the bevel gear with thin walled and big disk and the parts such as automobile synchronizer gear sets, using press quenching can also eliminate or reduce the effect of the various potential distortion factors that existing in the production process and heat treatment process, it is much lower than the free quenching in price. So press quenching should be an important and indispensable technique.
Recently, Foreign developed a moulded type induction quenching technology for special gear, especially the quenching for bevel gear and synchronizer gear, it has been achieved a obvious results. This new process combines the advantage of induction hardening and moulded quenching can make less distortion, and it can reduce or cancel the subsequent working procedure. And because the induction hardening adopts water-based coolant quenching, so the gear doesn’t need to clean after heat treatment. Meanwhile, the built-in sensors can not only heating quenching, can also be used to heat the tempering parts without additional equipment, so the production cost is reduced greatly.   

Miss Lavendie Lee 
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