The working mode of high-power electromagnetic induction heater is completely different from that of household induction cooker

Modification of multiple sets of coils in one electromagnetic induction heater

The working mode of high-power electromagnetic heaters is completely different from that of household induction cookers. It adopts a full-bridge quasi-resonant soft switching working mode. The thermal efficiency is as high as over 95%. There is no voltage breakdown of the power tube, and the voltage and current are abundant. It is very large, has all kinds of protection circuits, and has high reliability. Except for hidden faults caused by man-made process reasons, almost no faults caused by other factors have been found. Due to the high cost of high-power electromagnetic heaters, their promotion and application are subject to certain restrictions. If they want to compete with civilian induction cookers, the only way is to have multiple induction heating coils in one machine (one machine can be used in multiple temperature zones) to reduce the Cost per temperature zone. In addition to its advantages in reliability and thermal efficiency, the outstanding feature of electromagnetic heaters is that the electromagnetic heater elements and electrical appliances form an electrical box that is completely separated from heat dissipation, and there is a pulse power output transformer and resonance between the circuit and the induction heating coil. The capacitors are double electrically insulated and isolated. In the event that the electromagnetic heating coil is accidentally damaged, no electric shock will occur due to the isolation and insulation of the resonant capacitor and pulse power output transformer. These are the first issues to consider in business. It is also the use of pulse power output transformers that makes it possible and relatively easy to implement one movement with multiple induction heating coils.

The following issues should be noted when restructuring:

1. The electromagnetic heating control board should be designed and debugged according to the total power of several load units connected in parallel.

2. The resonant capacitor and heating coil should always be combined together to ensure that the increase or decrease in the unit coil does not affect the resonant frequency of the entire combination.

3. The increase or decrease in the unit coil causes the power change to be different from the normal adjustment. The IGBT, zero-voltage capacitance, IGBT absorption capacitance, etc. of the original 5kw electromagnetic heater must be adjusted accordingly.

4. After multiple units are connected in parallel, the power can only be adjusted centrally according to the original control method. If you want to adjust the power of a single unit, you can increase the resonant capacitance by switching capacitors in each unit to detune the circuit and reduce the power. . In addition, considering that the moment when several units switch capacitances at the same time, the total load may open circuit instantly, so the control circuit in the original electrical box must also add a load open circuit protection function to prevent the power tube from appearing in a hard switching state when the load opens.

Material selection for cold work molds and heat treatment of cold mold steel Material selection for cold work molds and heat treatment of cold mold steel

During the cold stamping process, due to the relatively large deformation resistance of the punched material, the working part of the mold, especially the cutting edge, is subject to strong friction and extrusion, so the mold should have high hardness, strength and wear resistance. In addition, the punching die is subject to impact force during the working process, which requires the die to have a certain degree of toughness, especially when punching thick steel plates or punching smaller apertures on thick steel plates. From the perspective of manufacturing technology, mold materials are also required to have good cold working properties (such as easy cutting, high processing smoothness, etc.) and hot working properties (good forging performance, good hardenability, small deformation during heat treatment, etc.). During the cold heading and cold extrusion process, the deformation resistance can reach 200-250Kg/mm2: during continuous operation, the mold temperature can reach about 300°C. Therefore, cold heading and cold extrusion dies require higher strength, toughness and certain red hardness than cold stamping dies. There are conflicts with each other in terms of performance requirements. In order to meet the requirements of the mold in terms of hardness and wear resistance, the alloy composition is often increased to form a large amount of carbides in the structure. However, this will affect the toughness of the matrix and worsen the cutting performance. Therefore, these contradictions must be correctly handled when selecting mold materials and determining the thermal energy treatment process. The working life and wear of the mold are also related to the design of the mold and the operating methods during use. If you ignore this, even if you choose advanced mold materials, the material properties will not be fully utilized.

Part fatigue load limits

Data show that most early failures of parts are caused by fatigue. Material selection is important when fatigue is known to be a major factor. Parts subjected to static loads will not break until the stress exceeds the yield point. In properly quenched and tempered steel, this is 75-90% of the strength limit. However, parts under dynamic loading or cyclic loading will fracture with stresses as low as 70% of the strength limit in low-cycle fatigue (1-100,000 times), and as low as 70% of the strength limit in high-cycle fatigue (more than 100,000 times). 4096 will break at the extreme strength level. Design data such as stress levels, cycle requirements and stress concentration factors are all useful in steel selection. The strength, toughness and fatigue limits of the material must also be known. A better approach is to test the part under simulated or real operating conditions. Complex parts such as crankshafts, welded assemblies and frames require highly accurate stress analysis to determine fatigue parameters. Once the applied stress, load cycles and stress concentration area are determined, it is easy to select materials and heat treatment methods. If unusually high stresses are encountered, it is usually more appropriate for designers to rely on structural shape changes to create suitable parts than for materials engineers to rely on material selection and heat treatment. For example, a larger shoulder or a thicker section will reduce stress much more effectively than changing the tissue. When volume, weight or shape is constrained, materials engineers have five tools that can be used individually or together to improve fatigue characteristics:

1) Use strong and tough steel to resist low cycle fatigue.

2) Formulate the material, heat treatment or surface treatment such as shot peening or rolling. Figure 4 The influence of hardness and strain percentage of quenched and tempered 1045 steel on the low cycle fatigue life in the area with greater stress. Produces high surface compressive stress. This will improve high cycle fatigue resistance (generally only when the number of cycles approaches 100,000 does compressive stress become effective in improving low cycle fatigue properties). Materials engineers must also ensure that post-heat treatment processing (such as grinding) can be precisely controlled to prevent damage to the workpiece surface. On and near the surface of the part, the service strength of the material plus the compressive stress will exceed the working stress by at least twice.

3) Use steel that is particularly clean or has particularly good surface quality.

4) Improve the surface finish of the maximum stress area by fine grinding or polishing.

5) Apply plating or abrasion-resistant coverings to resist damage caused by certain types of abrasion and corrosion fatigue.