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Heat Treatment Quality Control of Tapered Roller Bearing Ring

wallpapers Tech 2020-06-10
High carbon chromium steel tapered roller bearing rings are shown in Figure 1 and Figure 2. Due to its own structural characteristics, there is the problem of uneven thickness. For example, the outer diameter of the 31315 is 19.33mm, and the thinnest point is 4.89mm; the inner width of the 31315 is 18.2mm, and the weakest point is 9.1mm; it is tough to prepare the heat treatment process.
In the heat treatment process, due to the structure of the ferrule itself, the heat treatment process, processing equipment and human factors, it has caused defects such as overheating, underheating, cracking, excessive deformation, knocking, etc. of the ferrule structure. These defects directly cause product scrappings such as overheating, cracking, severe decarburization and severe knocking injuries. Although some mistakes will not cause the product to be scrapped, it will have an impact on service life. For example, the underheated Tornite exceeds the standard, which will affect the service life of the bearing and cause the bearing to break early. Some defects cause economic losses (such as excessive heat treatment deformation, which requires plastic and labour-intensive). Therefore, it is necessary to strengthen the quality control of heat treatment.
1. Prevent overheating (coarse needle martensite)
The structure of high carbon chromium steel bearing ring after quenching should be cryptocrystalline, beautiful crystal or small needle martensite. Due to the limitation of the structure of the tapered bearing ring, when the structure of the thick-walled end meets the requirements, the thick needle-shaped martensite shown in Fig. Three may appear as a superheated structure. This microstructure exceeds the "JB/T1255-2014 rolling bearing high carbon chromium bearing steel parts heat treatment technical conditions" standard requirements. This microstructure will reduce the toughness of the bearing, reduce the impact resistance, and reduce the life of the bearing. Severe overheating may even cause quenching cracks. The reason is that the quenching heating temperature is too high or the heating and holding time is too long. It may also be that the raw material carbide is severely banded or the size distribution of the annealed carbide is uneven. The measures taken are selected according to the material standards (such as the wall thickness sufficient thickness exceeds 15mm, GCr15SiMn steel can be used), and the heating temperature and heating time are reasonably selected. Strictly control the carbide banding. Improve the annealing quality, and take effective measures in time if there is a power outage or equipment failure.
Second, prevent the generation of underheated (block or needle-shaped tortoise) tissue.
The structure of high carbon chromium bearing steel bearing rings is more evident after quenching. The needle-shaped austenite is shown in Fig. 4, the larger agglomerate austenite is shown to be shown in Fig. 5. The masses of block-shaped trinite are mixed together, as shown in Fig. 6, and the band-shaped torticite is shown in Fig. 7, which exceeds the requirements of "JB/T1255-2014 Rolling Bearing High-carbon Chromium Bearing Steel Parts Heat Treatment Technical Conditions" and is called underheated structure.
3. Prevent quenching cracks
Most of the cracks generated during the quenching of the part are caused by the cooling stress in the martensite transformation temperature range. The tensile weight generated near the surface of the region due to the quenching stress exceeds the fracture strength of the steel at this temperature. After pickling, the quenching crack ring is shown in Figure 8; the main difference between the quenching crack, the material crack and the forging break is that there is no decarburization on both sides of the quenching crack;
4. Control the carbon potential to prevent decarburization of the surface
If the bearing parts are heated in an oxidizing medium during the heat treatment process, the surface will undergo oxidation to reduce the mass fraction of carbon on the surface of the parts, resulting in decarburization of the surface. The depth of the surface decarburization layer exceeds the final processing allowance will make the parts scrapped. The determination of the bottom of the surface decarburization layer can be used in the metallographic examination of the metallographic method and microhardness method. The arbitration criterion can be made based on the measurement method of the surface layer microhardness distribution curve.
5. Analyze the reasons and take measures to prevent knock bumps
After quenching and tempering of the ferrule, it was found that there were visible knock bumps, as shown in Figure 12 and Figured 13, which caused the bushing to be scrapped. The reason is that in the heat treatment process, the workpiece falls in the production line during the oil tank, at the interface (such as between the hot and cold cleaning agent, between the cold cleaning machine and the tempering furnace), the tempering furnace blanking port, and the ferrule during the polishing process. Colliding with each other produces knocking injuries.
6. Control quenching deformation to prevent scrapping due to abnormal size
In the process of quenching heating and cooling and the transformation of the structure of the bearing ring, thermal stress and tissue stress is inevitably generated. The change of this stress causes the deformation of the ring and the size of the ring.
The deformation caused by the quenching of the bearing ring includes the expansion and contraction of the size and the change of the geometric shape. For the expansion and contraction of the scale, if the amount of expansion and contraction is too large, and the grinding allowance is too small, it will result in black leather or turning pattern after grinding. Cause scrap. If the deformation is too large, such as warpage deformation of the plane, after the grinding of the flight is completed, the surface of the aircraft is left with black skin or turning patterns, resulting in scrapping.

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