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Author Topic: Plastic bearing load caused by temperature factor
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  Hong Kong
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Plastic bearing load caused by temperature factor    (Posted Wed, Jun 25 '14 at 03:15 UTC)

In the mechanical press, the crankshaft to pass a big torque, the support to bear the load of large, therefore, used in most of crank shaft support and connecting rod bearing. NTN bearing has the stable work, the advantages of low noise from general plastic SKF 6206 Deep Groove Ball Bearings, if you can guarantee the liquid friction lubrication, sliding surface is lubricating oil without direct contact, you can greatly reduce the friction loss and wear of surface formed by the oil film also has a certain vibration absorbing ability. However, with the continuous development of the press to high speed, high precision, sliding bearing in use process is easy to heat, causing the "burn" phenomenon and crankshaft.
Bearing heating, mainly NTN bearing cooling speed is lower than the speed of the bearing to generate heat, broke the heat balance and make the bearing temperature bearing. The causes are:
(1) the traditional design method of sliding bearing is suitable for the mixed lubrication and solid lubrication bearing, is based on the unit area of the sliding bearing pressure P (pv) or less or pv (pv) or less to design:
P = Pg/DaLa
Type: Pg - nominal pressure;
Da - bearing inside diameter;
La - bearing length.
But actually bearing [p] due to the material composition, manufacture process and use occasion difference, is not as random variables, for the constant effect on NTN bearing pressure p also due to process different, the influence of processing error of a variable. According to the traditional method, even the plastic bearings, "qualified" under a certain environment temperature and speed, with the passage of time, the temperature may be increased, until the break through the allowable temperature, affect the normal use of the machine tool.
1) bearing design parameters: including the number of rolling element bearings, ring throwing, wall thickness and clearance, etc.
2) bearing parts manufacturing error: including NTN bearing raceway and rolling body surface roughness, grain degree and the roundness error. A large number of experimental study show that the waviness of plastic bearing vibration influence of dominant, and the influence of surface roughness and the roundness is relatively small.
3) bearing working conditions: bearing in the process of operation, load, speed, lubrication condition the influence of the three aspects of bearing vibration is the largest.
4) bearing installation parameters, bearing and shaft and bearing seat, and the bias of installation and other factors also affect the vibration of the bearing.
The waviness in NTN bearing ring of the self-contained parts or under the condition of close cooperation between the shaft, ring up with adjacent components are likely to match the shape and deformation. If there is a deformation, can produce vibration in the operation. As a result, the bridge and the shaft are machined to the required tolerance is very important. Local damage due to the operation or installation errors, a small number of bearing raceway and rolling element may be damaged. In the running, rolled plastic bearing damaged parts will produce a certain vibration frequency. Vibration frequency analysis can identify the damaged NTN bearing parts. The vibration behavior of applications in many applications, the stiffness with the surrounding the stiffness of the same structure. Due to this characteristic, can choose correctly bearing (including preload and clearance) and its application in the configuration, it is possible to reduce the vibration in the application.

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