The analysis of the causes of KOYO bearing heating

Rough on the bearing parts can observe the microstructure after quenching overheat. But exactly judge the degree of superheat must observe the microstructure. If appear in GCr15 steel quenching organization coarse acicular martensite, organization for quenching overheating. Reasons may be the high quenching heating temperature or heat insulation time is too long cause comprehensive overheating; Also may be due to the original organization banded carbide, low carbon zone between two belts forming local martensite acicular bulky, cause local overheating. Overheating in the organization retained austenite increase, dimension stability. Overheating due to quenching organization, steel crystal bulky, to cause a decline in parts of toughness, impact resistant performance, lower KOYO bearing's life also. Serious overheating will cause the quenching crack quenching temperature on the low side or even bad cooling will generate more than standard stipulated in the microstructure of austenite organization, called owe hot organization, it decreased the hardness, wear resistance sharply reduced, affecting the service life of bearing bearing parts in the process of hardening cooling by internal stress formation of quenching cracks crack said. Of the cause of the crack are: due to quenching heating temperature is too high or cooling, the thermal stress and quality of metal volume change of the organization stress is greater than the fracture strength of steel; The original defects on the surface of the work ( Such as surface microcrack or scratches) Or steel internal defects ( The non-metallic inclusions such as slag, serious, white spots, shrinkage residual, etc. ) When quenching form stress concentration; Serious surface decarbonization and carbide segregation; Parts hardening after tempering lack or not timely temper; The previous process caused by salt stress, cold forging folding, deep turning tool and the oil groove sharp edges, etc. In conclusion, the causes of quenching crack could be one or more of the above factors, the existence of internal stress is the main reason for the formation of quenching cracks. Quenching crack deep and long, fracture surface is flat, the broken section without oxidation color. It is often a longitudinal straight on bearing ring crack or annular crack; On the bearing steel ball shape with s-shaped, T or ring. The characteristics of the quenching crack is crack on both sides without decarburization phenomenon, with obvious difference between crack forging cracks and materials. KOYO bearing parts in heat treatment, there is the thermal stress and organization stress, the internal stress can overlay or partially offset each other, is complex and changeable, because it can as the heating temperature, heating rate, cooling, cooling speed, parts of the change of the shape and size changes, so the heat treatment deformation is inevitable. Know and grasp its change law can make the deformation of the bearing parts, Such as ring elliptic, large size up, etc. ) In the scope of the controllable, be helpful for production. , of course, in the process of heat treatment, mechanical collision also can make parts deformation, but the deformation is can be used to improve operation to reduce or avoid. Bearing parts in the process of heat treatment, if they are in oxidizing medium heat, surface oxidation happens to make the surface of carbon mass fraction decreases, causing surface decarburization. The depth of the surface decarburization layer over the last machining allowance can make the parts scrap. The determination of surface decarburization layer depth is available in the metallographic examination metallography and microhardness method. The surface microhardness distribution curve measurement shall prevail, to do the arbitration criterion. Caused by a lack of heating, cooling, quenching causes such as improper operation of KOYO bearing parts surface phenomenon known as quenching soft point of local hardness is not enough. It can cause surface to surface decarburization abrasion resistance and fatigue strength of serious decline. The temperature of the bearings with bearing operation began to slowly rise, 1 - After 2 hours to reach steady state. The normal temperature of bearing for machine heat capacity, heat dissipating capacity, rotational speed and load. If you don't appropriate lubrication, installation, bearing temperature will rise sharply, appear unusually high temperature, must stop at this moment, take the necessary precautions. Using thermal device can monitor the bearing temperature at any time, and realize e. automatic alarm when the temperature exceeds or stop to prevent the shaft accidents. High temperature is bad for the bearing lubricant. Sometimes KOYO bearing overheating can be classified to the bearing lubricant. If the bearing temperature for a long time even the transfer of more than 125 ℃ lower bearing life. The causes of high temperature bearing include: insufficient lubrication or excessive lubrication, lubricants contains impurities, heavy load, bearing ring, clearance, high friction and oil seal and so on. So the continuity of bearing temperature monitoring is necessary, whether measured bearing itself or other important parts. If it is on the basis of the operating conditions, the temperature change of any fault has occurred. Regular bearing temperature measurement by using a thermometer, digital thermometer, for example, can accurate bearing temperature measurement and display by ℃ or Fahrenheit units. The importance of bearing, means that when the damage cause of equipment downtime, so this type of bearings shall be equipped with best temperature probe. In just under normal circumstances, bearing lubrication or lubrication after there will be a natural temperature rise and the last one to two days. Usually, working temperature over 150 ° use KOYO bearing called high temperature bearing, due to chromium bearing steel in the use of temperature over 150 °, the hardness will fell sharply, size is not stable, the bearing can't work normally. So for the working temperature at 150 ° to 350 ° work under the condition of bearing, if rings and rolling body still choose ordinary high carbon chromium bearing steel manufacturing, it must be special tempering treatment was carried out on the bearing parts, shall generally be higher than working temperature tempering under 50 °. After tempering treatment according to the requirements of the bearing steel, can be used in normal working temperature. But after tempering hardness decreased, bearing life. When KOYO bearing operating temperature higher than 350 °, must use high temperature resistant bearing steel manufacturing.