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High carbon chromium bearing steel annealing

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1 High carbon chromium bearing steel annealing on Tue May 13, 2014 2:26 am


  High carbon chromium bearing steel spheroidizing annealing is to obtain ferrite matrix uniformly distributed on the fine carbide particles, small, uniform, round, for cold working and final quenching tempering after tissue preparation. Traditional spheroidizing annealing process is slightly higher than the temperature of the Ac1 (e.g., GCr15 is 780-810 ℃) heat preservation with the furnace after slow cooling (25 ℃ / h) to under 650 ℃ from air cooling. The process of heat treatment time is long (more than 20 h), and the carbide particles are not uniform, after annealing effect after cold working and the microstructure and mechanical properties of the final quenching tempering.

  Hydrostatic bearing with its high rotary precision, good rigidity, high bearing capacity, no wear, high durability and is widely used in M210, M131W, 3160 a grinding machine, and 2 a710, FYT10 kong boring head. With the development of numerical control technology, hydrostatic bearing is widely used in machining center CNC machine tool spindle. Below is in the repair process to explore and try to get some experience, is only for your reference.
  1. The hole choke:
  (1). Change the internal throttling to external throttling, and equipped with pressure gauge pressure inferior vena instantly. Make maintenance convenient, especially can easily be regular cleaning, this is an internal choke.

  (2). The throttling ratio. Throttle than the theoretical value is between 1.2 ~ 1.5 beta, and according to many years of experience in 1.25 is preferred. In maintenance, so need to before and after the geometrical precision of the spindle, the geometry precision of bearing bush, alignment, roundness and taper of strict control, in order to ensure the beta. Determined according to bearing capacity of the machine tool e (eccentricity) to the center of the main shaft and bearing shell geometry, the beta value is the best.
  (3). The oil cavity when don't put the spindle, the oil outlet of oil column must agree (observation), if inconsistent, should be taken to change the choke aperture method, to change its flow. 4 cavity, for example, generally, left, right cavity under the oil column, between 20 to 25 mm hole diameter is 0.25 ~ 0.4 mm.

  2. The film feedback choke:
  Film feedback throttle bearing stiffness is very big, but our machine also often appear in running watts, the phenomenon such as hair, off pressure. Thin-film feedback is the most critical, practice that bearing lock, hair, the main reason is: (1) thin film caused by plastic deformation; (2) feedback slowly. External load mutation, film also have no reaction, shaft and tile has been friction; (3) thin film fatigue. Film with long time, fatigue deformation, equivalent to change the feedback parameters.
  Film thickness and use some fatigue resistant material, all can get good result. Usually adopt rigid film, preload lotus, reserved aperture method. Specific practice is: will be 1.4 mm thick film instead of 4 mm thick membrane rigidity, in inferior vena pad is 0.05 mm thick foil paper, make the main shaft to adjust to than the ideal place to the location of the 0.05 mm high. Purpose is when the main shaft bearing (after grinding wheel weight, cutting force), just returned to the ideal center.

  Later, according to characteristics of supercooled austenite transformation, development of isothermal spheroidizing annealing process: in the cold heat, quick to Ar1 below a certain temperature range (690-720 ℃) isothermal, completed in the process of isothermal austenite to ferrite and carbide, shift can be directly released after the completion of air cooling. This process has the advantage of saving heat treatment time (about 12 to 18 h) the whole process, after processing of carbide tiny evenly in the organizations.
Another time saving process is repeated spheroidizing annealing: cooling after it was first heated to 810 ℃ to 810 ℃, cooling after heated to 790 ℃ to 790 ℃ from air cooling. Although the process can save some time, but more complex operation.

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