Heat treatment for the spherical roller bearings
Dec 06, 2022
Spherical roller bearings have two rows of rollers and can accept radial loads as well as axial loads in either direction. High radial load capacity, especially suitable for heavy or oscillating load operation. But can not simply bear the axial load. This kind of bearing outer ring raceway is spherical, so its alignment performance is good, can compensate for coaxiality error. But have in the bearing industry ten years of experience in the old workers told us, if the spherical roller bearing heat treatment is not proper is will occur certain impact. But what will happens if the heat treatment of spherical roller bearings is improper? In consultation with professional technical staff, summarized the following points.
1. Spherical roller bearing heat treatment deformation
Bearing parts in the heat treatment, there are thermal stress and arrangement stress, this internal stress can be superimposed or partially offset with each other, is complex and changeable, because it can change with the heating temperature, heating speed, cooling method, cooling rate, part shape and size changes, so heat treatment deformation is inevitable. Recognize and grasp its changing rules can make the deformation of bearing parts (such as the ellipse of the ring, size up, etc.) placed in a controlled range, which is conducive to production. Of course, in the heat treatment process of mechanical shock will also make the parts deformation, but this deformation is able to use to improve the operation to reduce and prevent.
2. Spherical roller bearing overheating
From the rough mouth of the bearing part, the overheating of the microstructure after quenching can be observed. However, to determine exactly how overheated it is, the microstructure must be observed. If a coarse needle-like martensite appears in the quenched tissue of GCr15 steel, it is a quenched superheated structure. The cause may be excessive surface heating caused by excessive quenching heating temperature or heating and holding time being too long; It may also be due to the severe banded carbide of the original tissue, forming a local martensite needle-like coarse in the low-carbon zone between the two belts, resulting in local overheating. The retained austenite in the superheated structure increases and the dimensional stability decreases. Due to the overheating of the quenching structure, the crystals of the steel are coarse, which will lead to a decrease in the toughness of the parts, a decrease in impact resistance, and a decrease in the life of the bearing.
3. The spherical roller bearing is underheated
If the quenching temperature is low or the cooling is poor, a tostenite structure that exceeds the standard rule will occur in the microstructure, called the underheated structure, which reduces the hardness and wear resistance sharply, affecting the bearing life.
4.Spherical roller bearing quenching soft spot
Due to insufficient heating, poor cooling, improper quenching operation and other reasons, the phenomenon that the local hardness of the bearing parts is not enough is called quenching soft spot. Like surface decarburization, it can cause a serious decrease in surface wear resistance and fatigue strength.
5. Surface decarburization of spherical roller bearings
During the heat treatment process of the bearing parts, if they are heated in an oxidizing medium, the surface will be oxidized to reduce the mass fraction of carbon on the surface of the part, resulting in surface decarburization. If the depth of the surface decarburization layer exceeds the processing allowance, the part will be scrapped. The determination of the depth of the surface decarburization layer can be carried out in metallographic examination by metallographic method and microhardness method.
6. Quenching cracks in spherical roller bearings
The cracks formed by the internal stress of the bearing parts during the quenching and cooling process are called quenching cracks. The reasons for the formation of such cracks are: due to the high quenching heating temperature or too rapid cooling, the thermal stress and the design stress of the metal mass volume change are greater than the fracture resistance of the steel; the original defects of the working surface (such as surface fine cracks or scratches) marks) or internal defects of steel (such as slag inclusions, serious non-metallic inclusions, white spots, shrinkage cavity residues, etc.) cause stress concentration during quenching; severe surface decarburization and carbide segregation; insufficient tempering of parts after quenching Or not tempered in time; the cold shock stress caused by the previous process is too large, casting folds, deep turning tool marks, sharp edges and corners of oil grooves, etc.
In summary, the causes of quenching cracks may be the above factors or a variety of factors, the existence of internal stress is the primary cause of quenching cracks. And Luoyang Huigong bearing has brought in heat treatment line of the world-class Aichelin technology, pusher furnace carburizing quenching and roller hearth secondary quenching, and can visually display its entire production, monitor and record automatically its processing parameters and quality data, to provide assurance for product quality.
1. Spherical roller bearing heat treatment deformation
Bearing parts in the heat treatment, there are thermal stress and arrangement stress, this internal stress can be superimposed or partially offset with each other, is complex and changeable, because it can change with the heating temperature, heating speed, cooling method, cooling rate, part shape and size changes, so heat treatment deformation is inevitable. Recognize and grasp its changing rules can make the deformation of bearing parts (such as the ellipse of the ring, size up, etc.) placed in a controlled range, which is conducive to production. Of course, in the heat treatment process of mechanical shock will also make the parts deformation, but this deformation is able to use to improve the operation to reduce and prevent.
2. Spherical roller bearing overheating
From the rough mouth of the bearing part, the overheating of the microstructure after quenching can be observed. However, to determine exactly how overheated it is, the microstructure must be observed. If a coarse needle-like martensite appears in the quenched tissue of GCr15 steel, it is a quenched superheated structure. The cause may be excessive surface heating caused by excessive quenching heating temperature or heating and holding time being too long; It may also be due to the severe banded carbide of the original tissue, forming a local martensite needle-like coarse in the low-carbon zone between the two belts, resulting in local overheating. The retained austenite in the superheated structure increases and the dimensional stability decreases. Due to the overheating of the quenching structure, the crystals of the steel are coarse, which will lead to a decrease in the toughness of the parts, a decrease in impact resistance, and a decrease in the life of the bearing.
3. The spherical roller bearing is underheated
If the quenching temperature is low or the cooling is poor, a tostenite structure that exceeds the standard rule will occur in the microstructure, called the underheated structure, which reduces the hardness and wear resistance sharply, affecting the bearing life.
4.Spherical roller bearing quenching soft spot
Due to insufficient heating, poor cooling, improper quenching operation and other reasons, the phenomenon that the local hardness of the bearing parts is not enough is called quenching soft spot. Like surface decarburization, it can cause a serious decrease in surface wear resistance and fatigue strength.
5. Surface decarburization of spherical roller bearings
During the heat treatment process of the bearing parts, if they are heated in an oxidizing medium, the surface will be oxidized to reduce the mass fraction of carbon on the surface of the part, resulting in surface decarburization. If the depth of the surface decarburization layer exceeds the processing allowance, the part will be scrapped. The determination of the depth of the surface decarburization layer can be carried out in metallographic examination by metallographic method and microhardness method.
6. Quenching cracks in spherical roller bearings
The cracks formed by the internal stress of the bearing parts during the quenching and cooling process are called quenching cracks. The reasons for the formation of such cracks are: due to the high quenching heating temperature or too rapid cooling, the thermal stress and the design stress of the metal mass volume change are greater than the fracture resistance of the steel; the original defects of the working surface (such as surface fine cracks or scratches) marks) or internal defects of steel (such as slag inclusions, serious non-metallic inclusions, white spots, shrinkage cavity residues, etc.) cause stress concentration during quenching; severe surface decarburization and carbide segregation; insufficient tempering of parts after quenching Or not tempered in time; the cold shock stress caused by the previous process is too large, casting folds, deep turning tool marks, sharp edges and corners of oil grooves, etc.
In summary, the causes of quenching cracks may be the above factors or a variety of factors, the existence of internal stress is the primary cause of quenching cracks. And Luoyang Huigong bearing has brought in heat treatment line of the world-class Aichelin technology, pusher furnace carburizing quenching and roller hearth secondary quenching, and can visually display its entire production, monitor and record automatically its processing parameters and quality data, to provide assurance for product quality.
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