What is included in the heat treatment of the slewing bearing?

The function of heat treatment of slewing bearing is to improve the material mechanical properties, eliminate residual stress and improve the metal machining properties, different heat treatments are adopted at different stages in the processing of slewing bearings. Commonly used are annealing, normalizing, aging, tempering, quenching, nitriding, etc. Let’s briefly introduce each heat treatment process separately.

1.Anneal

Anneal is the process of heating the slewing bearing forging to a certain temperature, keeping it for a long time, then slowly cooling it. The main purpose is to release the residual stress during forging, increase the forging toughness, reduce the forging hardness to facilitate subsequent processing, improve the forgings internal structure, refine the grains and enhance the forgings mechanical properties.

2.Normalizing

Heat the slewing bearing forgings to a temperature of 30~50℃ higher than AC3, keep warm for a period of time before cooling out of the oven, it needs to be cooled quickly after being out of the oven, generally water spray, mist spray or air cooling is carried out. Because it does not need to be cooled with the furnace and the measures of accelerated cooling are adopted, heat treatment efficiency is higher, after normalizing, the forgings grains are more refined and the distribution is more uniform, which can improve the forgings comprehensive mechanical properties, improve forgings machinability, make forgings easier to process.

3.Aging

Aging is the process of placing the machined slewing bearing at a higher temperature or room temperature for a period of time, so that the rings can release the internal stress and fully deform. Aging at a certain higher temperature is called artificial aging, aging in a natural state is called natural aging. Artificial aging generally heats the slewing bearing ring to about 150°C and keeps it for about 12 hours, which can eliminate the internal stress of the slewing bearing ring and make the slewing bearing ring more stable. Generally, aging treatment is carried out after rough machining and heat treatment of the slewing bearing, for precision slewing bearings, an aging treatment will be carried out for almost every process, on the one hand, it can ensure high machining accuracy and prevent processing deformation, on the other hand, it can fully eliminate the slewing bearing internal stress to ensure that the slewing bearing will not be deformed after delivery, which will affect the accuracy.

4.Tempering

Tempering is a heat treatment process in which the rough-machined slewing bearing forging is first quenched and then tempered at high temperature. The quenching temperature and tempering temperature are determined according to the slewing bearing ring size, specific hardness and mechanical properties. Generally, the slewing bearing ring is heated to 850℃ for a period of time, then quenched, the quenching medium is generally oil or water medium, high temperature tempering is carried out after quenching, the slewing bearing ring is heated to 630℃ for a period of time and then air-cooled. After tempered, the slewing bearing ring has excellent comprehensive mechanical properties, the strength and toughness are well matched and it has high strength, excellent toughness, plasticity and cutting performance, etc.

5.Quenching

Quenching is to quickly heat the tooth surface and slewing bearing raceway to the quenching temperature, then immediately use the quenching liquid to cool the heated part. After cooling, the surface of the raceway and tooth is hard, the core is soft, it has the advantages of surface wear resistance, fatigue resistance, high overall toughness and good impact resistance. Quenching not only makes the slewing bearing raceway and teeth strong and wear-resistant, but also increases the raceway and teeth load and improves the slewing bearin comprehensive performance.

6.Nitriding

Nitriding is a treatment method that allows nitrogen atoms to penetrate into the metal surface to obtain a layer of nitrogen-containing compounds. The nitriding layer can improve the hardness, wear resistance, fatigue strength and corrosion resistance of the part surface. Due to the nitriding treatment temperature is low, the deformation is small and the nitriding layer is thin (generally no more than 0.6~0.7mm), the nitriding process should be arranged as far back as possible. In order to reduce the deformation during nitriding, it is generally necessary to perform stress-relieving high-temperature tempering after cutting.

Understand the slewing bearing heat treatment process and function. When we choose to use the slewing ring or gear, we need to reasonably request the slewing bearing to do the corresponding heat treatment according to the use further to meet our use needs. For example, the geared slewing bearing frequently used with high torque generally requires tooth quenching; Another example is the slewing bearing that is often used with large tilting moments, which generally require tempering. Correct and reasonable heat treatment can make the slewing bearing have excellent performance in use.