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The **Induction Molding Quenching-Tempering Process** has become increasingly essential as steam turbine manufacturing technology advances, leading to more stringent requirements for part precision and hardened layer distribution. As production volumes grow, the need for consistent and controlled quenching becomes even more critical. Typically, parts are heated to temperatures between 900°C and 950°C before quenching, but this process often leads to deformation due to thermal expansion, uneven hardening, and structural asymmetry. Additionally, internal stresses from machining can further contribute to distortion during quenching, especially in thin-walled components.
To address these challenges, EMA has developed a series of press-hardening machines that combine induction heating with conventional compression quenching. This approach is particularly effective for circular and disc-shaped parts. For example, in the molding and quenching of a sliding sleeve (as shown in Figure 1), the deformed elliptical part is first centered and clamped using a non-magnetic device. The part is then heated to 900°C, ensuring uniform temperature distribution. A correcting mandrel is positioned, followed by quenching. The mandrel helps prevent deformation by controlling expansion during heating. After cooling, the part maintains high dimensional accuracy.
Key process parameters for the sliding sleeve include a power of 100kW at 20kHz, with a quenching and tempering cycle lasting 60 seconds. Surface hardness reaches 650–720HV1, with a quenching depth of 0.3–0.6mm and core hardness of 320–420HV1. Deformation measurements show roundness <0.05mm, flatness <0.06mm, and taper <0.05mm, with a Cpk value exceeding 1.67.
Similarly, the bevel gear induction quenching process (Figure 2) uses 250kW at 10kHz, with a 4-minute cycle. Surface hardness ranges from 680–780HV30, and the quenching depth is 0.8–1.2mm. The results show excellent control over tooth roundness (<0.03mm), flange roundness (<0.03mm), and flange flatness (<0.05mm).
The advantages of induction molding and quenching include minimal deformation, efficient and uniform cooling, low wear on molds, and precise workpiece dimensions. Compared to traditional systems, EMA’s equipment integrates seamlessly into production lines, eliminating the need for separate tempering furnaces or cleaning machines. It also allows for quenching under a protective atmosphere, reducing oxide formation and improving overall efficiency.
For large gears and racks, EMA employs a single-tooth "tooth profile" quenching method. This technique is used for wind power gears, mining machinery, and large toothed racks with a modulus of 63. The system ensures an even hardened layer along the full length of the tooth. High-precision inductive probes and follower systems help maintain proper sensor gaps, preventing deformation and ensuring uniform energy distribution. To manage the end effect during continuous quenching, EMA developed a temperature control system that divides the tooth length into segments and measures energy levels automatically. If deviations occur, the system alerts operators and adjusts power accordingly.
EMA’s single-head quenching machine, equipped with a rotary indexing table, can handle parts up to 4 meters in diameter. Adding a protective atmosphere cover prevents oxidation, eliminating the need for shot blasting and grinding. For heavy-duty gears, quenching under a protective atmosphere reduces the risk of cracks and improves quality. However, for larger gears with more teeth, the process can be time-consuming. To address this, EMA introduced a double-heating head quenching machine, significantly boosting efficiency and reducing cracking tendencies. This technology is also applied to rack induction hardening, such as in the Three Gorges Dam’s ship lift mechanism, which includes massive gears and vertical racks spanning 113 meters.