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The **Induction Molding Quenching-Tempering Process** has become increasingly important as the complexity of steam turbine manufacturing continues to grow. As part requirements become more demanding, especially regarding hardened layer distribution, deformation control, and batch production, traditional quenching methods face significant challenges. Parts are typically heated to 900–950°C before quenching, but this process often leads to deformation due to thermal expansion, uneven hardening, phase transformation, and asymmetrical geometry. Additionally, residual stresses from machining can further contribute to distortion during quenching, particularly in thin-walled components.
To address these issues, EMA has introduced a series of press-hardening machines that combine induction heating with conventional compression-type quenching, specifically designed for circular and disc-shaped parts. For example, in the case of a sliding sleeve mold quenching (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 uniformly. A correcting mandrel is positioned, and quenching is performed. The mandrel helps prevent deformation by limiting expansion during heating. After cooling, the part maintains high dimensional accuracy.
Key process parameters for the sliding sleeve include 100 kW power at 20 kHz, with a quenching and tempering cycle of 60 seconds. Surface hardness reaches 650–720 HV1, with a quenching depth of 0.3–0.6 mm. Core hardness is between 320–420 HV1. Deformation is tightly controlled, with roundness <0.05 mm, flatness <0.06 mm, and taper <0.05 mm. The Cpk value exceeds 1.67, ensuring consistent quality.
For bevel gears, as illustrated in Figure 2, an upper and lower pressing mold is used to clamp the workpiece during quenching. Parameters include 250 kW power at 10 kHz, with a 4-minute cycle. Surface hardness ranges from 680–780 HV30, and the quenching depth is 0.8–1.2 mm. The core hardness is 350–480 HV30. Deformation is minimized, with tooth roundness <0.03 mm, flange roundness <0.03 mm, and flange flatness <0.05 mm.
The advantages of induction molding and quenching include minimal deformation due to immediate quenching after heating, efficient and uniform cooling through four independently controlled channels, long-lasting molds with little wear, low energy consumption, and precise workpiece dimensions. Compared to traditional systems, EMA’s setup integrates seamlessly into production lines, eliminating the need for separate tempering furnaces or cleaning equipment. It also supports protective atmosphere quenching, reducing oxide layers and improving surface finish.
EMA also specializes in large gear and rack induction hardening. Using a single-tooth "tooth profile" method, they have successfully quenched wind turbine gears, mining machinery components, and large racks with a module of 63. The system ensures even hardened layer distribution by controlling temperature, cooling, and sensor gaps. High-precision inductive probes automatically position the tooth profile, minimizing manual adjustments and deformation risks.
A follower system adapts to gear deformation, maintaining optimal inductor gaps. In continuous quenching, edge effects can cause overheating or underheating, leading to cracks. EMA’s temperature control system divides the tooth length into sections, measuring energy distribution in less than 0.01 seconds. If deviations occur, the system alerts operators and adjusts power levels accordingly.
EMA’s single-head quenching machine can handle parts up to 4 meters in diameter, and with a protective atmosphere cover, it prevents oxidation, eliminating the need for shot blasting or grinding. This is especially beneficial for heavy-duty gears, where post-quenching inspection is time-consuming. By quenching under a protective atmosphere, such steps are avoided.
For larger gears with many teeth, EMA developed a double-heating head quenching machine, significantly increasing efficiency and reducing crack risk. This technology was applied in the induction hardening of a super-large modulus rack for the Three Gorges Dam ship lift, which includes 4 large gears and 4 vertical racks totaling 113 meters in length, supporting a 34,000-ton load.