Bearing speed and friction coefficient

     The speed of the bearing is mainly limited by the temperature rise caused by the frictional heat inside the bearing. When the speed exceeds a certain limit, the bearing cannot continue to rotate due to burns. The limit rotation speed of the bearing refers to a limit value that does not cause frictional heating that causes burns and can continuously rotate.
       Therefore, the ultimate speed of the bearing depends on the type, size and precision of the bearing as well as the lubrication method, the quality and quantity of the lubricant, the material and type of the cage, and the load conditions. The limit speeds of various types of bearings using grease lubrication and oil lubrication (oil bath lubrication) are respectively included in the bearing size table. The values ​​indicate the standard design of the bearing under normal load conditions (C/P>=13, Fa/Fr<= 0.25 or so) The limit value of the rotation speed when rotating downward. In addition, depending on the type and grade of the lubricant, the lubricant may be superior to other properties but not suitable for high-speed rotation.
       The corrected load condition of the limit speed C/P<13 (that is, the equivalent dynamic load P exceeds 8% of the basic dynamic load C), or the axial load in the combined combined load exceeds 25% of the radial load. The following formula corrects the limit speed. Na=f1*f2*n where na: corrected limit speed, rpm f1: correction factor f2 related to load conditions: correction factor n related to combined load: limit speed under normal load conditions, rpm (refer to bearing size Table) C: Basic dynamic load rating, N{kgf} P : Equivalent dynamic load, N{kgf} Fr: Radial load, N{kgf} Fa: Axial load, N{kgf} Limit of ball bearing with seal ring Speed ​​limit with contact seal (RS type) Ball bearings are limited by the line speed of the seal contact surface, allowing the line speed to depend on the rubber material of the seal.
       Precautions for high-speed rotation When the bearing rotates at a high speed, especially when the speed is close to or exceeds the limit speed stated in the dimension table, the following should be noted:
     (1) Using precision bearings
     (2) Analyze the internal clearance of the bearing (considering the reduction of the internal clearance of the bearing due to the temperature rise)
     (3) Analyze the type of material of the cage (for high-speed rotation, it is suitable to use a copper alloy or phenolic resin cutting cage. There is also a synthetic resin molding cage suitable for high-speed rotation)
    (4) Analyze the lubrication method (using the lubrication method suitable for high-speed rotation, such as circulating lubrication, jet lubrication, oil mist lubrication and oil-air lubrication). The friction coefficient of the bearing (reference). In order to facilitate comparison with the sliding bearing, the friction torque of the rolling bearing can be used as the bearing. The inner diameter is calculated by the following formula: M=uPd/2 where M: friction torque, mN.m{kgf.mm} u: friction coefficient, bearing load, N{kgf} d: bearing nominal inner diameter, mm friction coefficient u by bearing type The bearing load, speed, and lubrication method have a great influence.

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Characteristics and application of spindle bearing oil

Spindle bearing oil is a special lubricant for spindle bearings of precision machine tools and similar equipment. It plays an important role in ensuring the working accuracy and performance of the spindle and prolonging its service life. It is also called bearing oil.

    Its main performance:

    1, suitable viscosity and good viscosity temperature characteristics

    In order to make the machine tool spindle temperature not too high, the machine tool will be thermally deformed, affecting the machining accuracy or making the bearing poorly lubricated. The lubricating oil of the appropriate temperature should be selected according to the spindle bearing structure, the rotating speed and the bearing clearance, and it is required to have good viscosity-temperature characteristics. To prevent the change in viscosity due to excessive changes in the operating temperature of the spindle and the ambient temperature, which affects the lubrication performance.

    2, good lubricity

    In order to maintain a uniform oil film between the main shaft and the bearing contact surface, and the impact film is not damaged when the spindle starts or stops moving, maintaining good lubrication performance reduces friction and friction heat, reduces spindle temperature rise, and ensures The effect of processing accuracy requires good lubrication performance.

    3, good oxidation resistance

    When the machine tool spindle adopts the circulating lubrication method, the spindle bearing oil is required to be used for a long time without deterioration, so it is required to have good oxidation resistance.

    4, good rust resistance

    Since the oil is inevitably mixed into the condensed water in the air or the machine coolant during the operation of the spindle lubrication system, the oil is required to have good rust resistance.

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