Induction hardening of gears and stars

Contour quenching and quenching when rotating are not the same thing

Contour hardening of teeth means that the inductor and the mode form a heating close to the profile of the tooth: it is important to warm up the working surfaces and the root in a given proportion. This approach is used when the bearing capacity of the tooth is critical. Tempering when rotating the crown is easier by kinematics: the gear or asterisk rotates in a ring or profiled inductor, and the heating is distributed around the circle due to the rotation of the part.

For a small asterisk, sometimes a uniform hardening in a circle is enough, and for a responsible gear with a task on the root of the tooth, a different inductor, a different frequency and a soul setting are needed. UralInduktor forms the concept of the solution, and the Chinese plant performs detailed design and manufacture of equipment.

What data is especially important

For gears and stars, it is not enough to tell the outer diameter. The parameters of the tooth crown are needed, because they determine the electromagnetic concentration of heat, the risk of overheating of the edges and the ability to get the desired structure in the tooth root.

part type: cylindrical gear, asterisk, crown, sector, external or internal engagement;

module, number of teeth, crown width, outer and root diameters, size of the hub;

brand of steel, cementation or volume heat treatment before induction operation, if it is already provided;

the required hardness and effective depth of the layer: on the side surface, on the top and on the root of the tooth;

whether it is necessary to harden the entire crown, only the working profile or separate zones;

Permissible cutting, post-hardening grinding requirements and control method;

productivity, the number of sizes and the need for replacement inducers.

Metallurgy of the tooth and hardening cooling

On toothed parts, overheating is especially dangerous: an excessively hot top of the tooth can give unwanted fragility, and an unheated root is insufficient endurance. Therefore, the depth of the layer cannot be replaced by the reference depth of the current penetration. The real hardened layer is formed by the combined action of frequency, time, field distribution, thermal conductivity of steel and cooling intensity.

For asterisks take into account the shock mode of the chain and wear roller, and for gears - contact fatigue and the work of the tooth root on the bend. Tempering medium, shower shape and cooling delay are determined by the task. Without a technological test, it is impossible to promise the same result for different steels and modules.

Which series are usually recommended

For small teeth, compact parts, and relatively shallow contour hardening, ABC and ABB are often considered. For a significant part of typical gears and stars of medium size, AVZ becomes a convenient starting point. For more massive crowns, greater depth of the layer or parts with a developed hub, AVN is often checked. LN can be useful for repair local operation or experimental work, but with serial hardening of toothed parts, it usually loses to specialized equipment in repeatability.

If the nomenclature is wide, it is worth immediately discussing not one universal inductor, but a set of replaceable ones. A simple inductor is usually included in the delivery, and complex profiled and interchangeable kits are calculated separately. The final series and frequency are always specified after the analysis of gear geometry and trial processing.

Correct approximate calculation for a toothed crown

The following approximate calculation is only intended to estimate the power range. Assume a gear rim with an outside diameter of 160 mm, root diameter of 120 mm and width of 20 mm must be heated for hardening. The active volume can be estimated as an annulus: π × 20 × (80² − 60²) mm³, approximately 176 cm³. At a steel density of 7,85 g/cm³, the heated rim mass is approximately 1,38 kg.

If you take the average heat capacity of 0,60 kJ/(kg·C) and heat from 20 to 850 °C, the useful heat will be 1,38 × 0,60 × 830 ~ ≈ 687 kJ, or about 0,19 kWh. With a imputed total CDI of the 50 process, the electrical energy will be approximately 0,38 kWh. If the active heating time of one part is about 40 seconds, the average calculated load will be 34 kW. In fact, the limit of the heated volume does not exactly match the root diameter, so it's just a reference: the result changes because of the tooth profile, the concentration of the field on the edges, the rotation, and the pattern of the rocking soul.

Delivery, verification and confirmation of the result

The equipment comes with Russian-language control and documentation. After assembly, the plant checks the installation with the inductor ordered. Then a second check is performed in Miass with full connection without load. Commissioning takes place at the customer on his details with the registration of acts.

Price on request. Warranty - 18 months under contract, with reference to shipment or commission act. The depth of the layer, hardness, zone pattern and deformation are confirmed by checking on a real part or an agreed sample.

What to send for selection

Send the drawing of the gear or asterisk, module, steel grade, the required hardness and depth of the layer to the tooth. We will offer the technological scheme, ABC series, ABB, AVZ, AVN or LN, as well as the inductor design and test procedure. Price on request.