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New Techniques for Scan Hardening with No Soft Zone
With its residual soft zone, traditional scan hardening is inadequate for mission-critical components with stringent requirements for smoothness and heavy loads such as:
- Ultra-low vibration systems (e.g., magnetic-resonance imaging, MRI, technology)
- High mechanical-stress systems (e.g., tunnel-drilling machines)
- Systems where continuous rotation is required or where challenging environmental conditions mandate maintenance-free systems with high lifetime (e.g., wind turbines, tidal plants and oil platforms)
Carburizing is limited as a process alternative by furnace size and long process times. Single-shot induction hardening is impractical due to its high power requirement. A better hardening method is needed to efficiently and reliably harden very large, high-value rings. In response to this need, a process to scan harden arbitrarily large rings with no remaining soft zone has been developed and patented.[1] This process differs from conventional scan hardening primarily at the start and end location of the scan, where steps are taken to avoid unwanted tempering and changes in the hardened-zone microstructure.
Comparing this process to single-shot induction hardening, a 6-meter-diameter ring can be processed with a 200-kW scanning system, which is 1/8th the power the single-shot process would require. In contrast to carburizing, which would require several hundred hours in the furnace, the time required for the induction scan-hardening process (less than two hours) is negligible. Moreover, the cost-intensive and time-consuming straightening operation to clean up the distortion caused by carburizing can be avoided altogether.
Scan hardening and tooth hardening on both the inside and outside diameters of the workpiece can be done on the same induction machine with minimal setup times. Manufacturers of large ring bearings with small production runs appreciate this flexibility and the freedom to process diverse workpieces while holding equipment costs at a minimum.
Enlarged Image
| | Fig. 6. Inductor movement and spray setup during the end sequence of induction hardening |
Characteristics of Induction Scan Hardening with no Soft ZoneScan hardening with no soft zone requires two inductor assembles, each comprised of an inductor and a spray head. The inductors are narrow to create a compact hardening zone. Flux concentrators focus the magnetic field for one-sided hardening.
Start Sequence
The inductor assemblies are brought together in a back-to-back orientation and are then energized with independent power supplies. Both assemblies travel side-by-side in the same direction for a short distance. One of the assemblies reverses directions, so the inductor assemblies travel in opposite direction. This technique avoids the formation of a soft zone at the start location (Fig. 4).
Figure 5 depicts the hardening result with the etched case and with two hardening passes along the workpiece axis at 0.5 mm and 5 mm depths after tempering. The start location is still recognizable, and one can see that the entire area has been hardened with a relatively constant case depth.
End Sequence
Like the start sequence, the end sequence relies on precise control of the quenching sprays and the tight motion control of the inductors and sprays to achieve a uniform case depth with no soft zone at the end location (Figs. 6 and 7). The resulting bearing surface meets stringent requirements
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发表于 2013-4-10 20:20:15
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( 湘ICP备16021836号-4 )，中华人民共和国工业和信息化部备案号：湘ICP备16021836号-1，
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发表于 2013-4-10 20:22:33
发表于 2013-6-14 11:34:27
