The hardened steel heated to the following a Ac1 temperature, heat preservation time cooling to room temperature heat treatment process called tempering.
(1) the tempering of the objective: to relieve quenching stress, prevent cracking; Stable organization, and stable size; Improve toughness.
(2) the tempering process: after quenching rings into back to the stove (common fan air furnace, with the oven, oil furnace and XiaoYan furnace), heated to temper temperature, heat preservation 2 ~ 3 h, in the air in the free cooling. Table 2-51 is generally tempering norms.
Table 2-51 general tempering norms
Name precision grade tempering equipment tempering temperature / ℃ tempering time/h
Small and medium rings general product oil furnace or electric stove 150 ~ 1702.5 ~ 3
Class C, B level oil furnace 150 ~ 1703.5 ~ 4
General electric product large contractor 150 ~ 1606-12
By oil XiaoYan furnace and furnace, due to temperature, the temperature is even born fast, holding time can be short some, 1.5 ~ 2.5 h, contractor shall be released after oil removal and in addition to salt; The industrial frequency (frequency for frequency 50 Hz) induction calefaction temper, born soon because of the temperature, can use higher heating temperature and heat preservation of time that a short process, continuous heating to 180 ~ 190 ℃, about 5 min with temperature, temperature to come after cooling.
(3) high temperature tempering:
Some bearing with organization, performance and dimension stability specific requirements, the need of high temperature tempering treatment.
(4) additional tempering
The heat treatment of bearing in grinding process rings, can produce grinding stress. Grinding stress make after heat treatment residue in the internal stress metal collar to distribution, will lead to the precision of the collar is changed, even produce surface cracking. Grinding again immediately after the tempering temperature with less than 20 ~ 30 ℃ temperature again tempering (but need to take measures to avoid oxidation and affect surface roughness), can in time to eliminate grinding stress, further stabilize organization, and improve the precision of collar stability. This kind of tempering that additional tempering.
Additional tempering heat preservation time and tempering number should be based on the bearing precision grade and parts size to choose: general product is 3 ~ 6 h a, grade B and C level 15 ~ 24 h, 2 ~ 3 times, additional tempering standards and technology can reference 2-52 and 2-53
Table 2-52 general contractor tempering norms
Contractor size/mm effective thickness ~ 66 ~ 1212 ~ 2020 ~
Design outer diameter of 100100 ~ 200200 ~ ~ 300300 ~
Temperature / ℃ 130 ~ 150130 ~ 150130 ~ 150130 ~ 150
Holding time/h oil furnace 3 ~ 4567
Air furnace 3.5 ~ 4.55.56.57.5
Note: air furnace additional tempering such as found oxidation color person, can shorten appropriately holding time.
Table 2-53 additional backfiring technology
Name precision grade the temperature of the medium / ℃ time/h
in
small
type
set
Circle P2 level after the coarse grinding oil: 120 ~ 15015
After fine grind: 120 ~ 15015
P4 oil 120 ~ 15024 level
P5 level, level at the oil or air 130 ~ 1403 ~ 7.5
Short at the cylindrical roller bearing, P0 level 130 ~ 1403 ~ 7 oil
Air 130 ~ 1403.5 ~ 7.5
P5, moves, P0 level 130 ~ 1403.5 ~ 7.5 air
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