Several Induction Hardening and Quenching Process

There are several heating methods for quenching and hardening process.

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One-time heating method

One-time heating method or simultaneous heating method is the most common method of induction hardening. When this method uses two rectangular tubes to surround the surface of the workpiece for rotating heating, it is customarily called a single shot method (Single Shot).

The advantage of the one-time heating method is to complete the entire surface area of the workpiece that needs to be heated at one time. Therefore, its operation is simple and the productivity is high. It is suitable for workpieces with a small heating area. For workpieces with a particularly large heating area, the one-time heating method is required. Considerable power, high investment cost.

The most common examples of the one-time heating method are small and medium modulus gears, CVJ bell-shaped shell rods, inner raceways, supporting pulleys, supporting wheels, leaf spring pins, dials, valve ends, valve rocker arcs.

(1) One-time quenching of half shaft

Some data have compared the area of equipment with the same output of half-shaft induction hardening.

The half-shaft quenching process has now been changed from scanning quenching to transverse magnetic field heating and quenching. The production cycle has been reduced from a few minutes to 40s. While the production efficiency has been greatly improved, the bending and torsion fatigue strength of the half-shaft has also been increased by more than 10 times.

(2) Gear quenching once

Another improvement in the application of the one-time heating method to the gear heating process is the use of an oblique wrap-shaped induction coil instead of the entire surrounding-shaped induction coil. As we all know, different gear modules should be heated by different current frequencies. If the current frequency is too high or too low, the temperature of the tooth tip will be higher or lower than the cogging when heating with the induction coil surrounding the gear.

When using an oblique package induction coil for rotary heating, since each mass point on the tooth surface is heated only when it turns to the area covered by the induction coil, the actual heating conditions are heating, stopping, heating, stopping… each The mass point is only heated once per revolution to the effective circle coverage area, and the rest of the time is the uniform temperature time. Therefore, it helps prevent the tooth tip temperature from being too high or too low. This kind of oblique package type sensor is obtained in a domestic machine tool factory Value and application.

Scanning quenching method

This method is often used when the workpiece heating area is large and the power supply power is small. At this time, the calculated heating area S refers to the area contained by the induction coil. Therefore, the same power density requires a small power supply and low equipment investment costs. , Suitable for small batch production, typical examples are large diameter piston rods, corrugated rolls, rolls, oil pipes, sucker rods, steel rails, machine tool guides, etc.

(1) Shaft scanning quenching with steps

The stepped shaft was once stipulated by the old process that the hardened layer near the step can be interrupted, and even examples are given in some mechanical design manuals. The difficulty of this process is solved by the application of the rectangular tube transverse magnetic field heating method, which allows the longitudinal current to flow through the steps. Similarly, when using the scanning method, when an oblique bag-shaped sensor is used (the top is regarded as a circle, the arrow direction is regarded as an ellipse), because the eddy current induced on the workpiece is also an oblique bag, which passes through the small diameter of the step, At the same time through the large diameter of the steps, therefore, the hardened layer at the steps can be connected when the steps are not much different.

(2) Quenching method combining scanning and heating once

For camshafts, when the cam width and the journal width are very different, the double station is generally used, and the two kinds of sensors each heat the cam and the journal, but there is also a method, which is to use the sensor with the width and the cam width. In addition to heating the cam by the primary heating method, the journal can be quenched by the scanning method. The induction coil has two quenching liquid inlet pipe heads.

Subsection heating and quenching method

A typical example is the multiple cams of a camshaft. Each time one or more cams are heated. After quenching, another part of the cam is heated. The gears can be quenched tooth by tooth.

Segmented scanning quenching

Typical examples are valve rocker shafts or variable-speed prosthetic shafts. Multiple parts on a shaft are scanned and quenched, and the quenching width can be different. Scanning quenching per tooth can also be included in this category.

Heating and quenching in liquid

Heating and quenching in liquid, that is, the heating surface of the induction coil and the workpiece are immersed in the quenching liquid for heating. Since the power density obtained by heating the surface is greater than the cooling rate of the surrounding quenching liquid, the surface heats up quickly. After electricity, the surface of the workpiece is quenched due to heat absorption in the core of the workpiece and cooling of the quenching liquid.

This method is generally suitable for steel workpieces that require a small critical cooling rate. For self-cooling and quenching of the workpiece, the workpiece is placed in the air. After the induction coil is powered off, the core of the workpiece absorbs the surface heat. When the cooling rate of the heating surface is greater than the critical cooling rate, it will be hardened.

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