Appication of Medium Frequency Hardening in Slewing Bearing
As the component parts of construction machinery,slewing bearing is mainly used in tower crane,crane,excavator and port machinery. Because of the specificity in composition,the quality impact the usage efficiency of host directly.
Slewing bearing ¡®s ife time depends on the quality of medium frequency hardening,and the inner quality depends on the depth of hardening zone, shape distribution,hardness,crack condition, hardening organization and other aspects,so we control the hardening quality by sensor, sprinkler,heat temperature and hardening liquid.
1. processing and technical requirements
Slewing bearing processing:
Rough lathing - Finish lathing -Hardening-Drilling-Grinding- Assembly
Technical requirements:
Depth of hardening zone:3-5mm, hardness:55-62HRC,no crack.
The chemical composition of the material
|
No
|
The chemical composition % |
|
C |
Si |
Mn |
Mo |
Cr |
Ni |
S |
P |
Cu |
|
42CrMo |
0.38~0.45 |
0.17~0.37 |
0.50~0.80 |
0.15~0.25 |
0.90~1.2 |
¡Ü0.30 |
¡Ü0.035 |
¡Ü0.035 |
¡Ü0.30 |
|
50Mn |
0.48~0.56 |
0.17~0.37 |
0.70~1.00 |
--- |
¡Ü0.25 |
¡Ü0.25 |
¡Ü0.035 |
¡Ü0.035 |
¡Ü0.25 |
|
Note: The chemical composition of the other material must obey the standard set by the country, the allowed dispersion of the chemical composition must accord to the provision of GB222 |
2. Establish of induction hardening
1) Characteristic of induction heating
The induction heating uses the principle of electromagnetic induction, create the induced current in the working surface,means forming the turbulent flow.
2) Confirmation of induction hardening technical data
Medium Frequency Hardening process include: confirming hardening temperature,pre-cold time,density of hardening liquid and so on.
l Hardening heat time
Induction heat means quick heat, the temperature is more higher than normal hardening heat.
l Heating temperature is closely related to the steel''s original organization . The more thin , the more easier phase transition occurs in heating. . Therefore, the heating temperature can be appropriately reduced .
l the majority of rough materials used in factory is in pre-modulated modulation and normalizing state ,quenching temperature can be lower .As to the 50Mn and 42CrMo material , quenching temperature should be 900-950 degrees .
the purpose of pre-cooling is to reduce quenching deformation, stop quenching cracks .
l Cooling
The way of cooling shoud be linked to the workpiece material, heating method and depth of hardened layer.
l Tempering
Slewing bearing hardening will do rapid heating and cooling to partial surface of the workpiece, leading to large thermal stress and organizational stress . After the completion of organizational changes, form into higher residual stress. So, must be done low temperature tempering in order to eliminate part of the stress.
Technology application above is also used in different size rolling or different material but basically same carbon content, hardenability slewing bearing . Detection after quenching , the test results can basically meet the technical requirements.
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