Smelting management automatic control system

The resistance furnace is an industrial furnace that uses current to heat the electric heating elements or heating medium inside the furnace, so as to heat the workpiece or material. It is a heating furnace where heat energy is generated when current passes through the resistance material.

Vacuum furnace means that, in the specific space of the furnace cavity, the vacuum system (composed of vacuum pump, vacuum measuring device, vacuum valve and other components that are assembled elaborately) is used to discharge some substances out of the furnace cavity to make the pressure in the furnace cavity less than one standard atmospheric pressure (101.325 kPa), so as to realize the vacuum state in the furnace cavity.

Intermediate-frequency quenching means metal parts are placed inside an induction coil which is energized with alternating current to generate alternating electromagnetic fields and then induce alternating current inside the metal parts. Due to the skin effect, current mainly appears on the surface of metal parts, so the surface temperature is the highest. Spray cooling or other forms of cooling is applied below the induction coil soon. Since heating and cooling mainly occur to the surface of metal parts, the surface modification is very obvious, while the internal modification is basically unchanged. So, it can achieve special heat treatment effects.

The medium-frequency smelting furnace often adopts the following four configuration methods. Each of them has its own advantages and disadvantages. Usually, the specific configuration method needs to be selected based on the casting process requirements, on-site power conditions, production objectives and development scale of the equipment demander in order to meet users’ requirements for the efficiency, safety and stability of the equipment, and facilitate flexible adjustment of processes or scale expansion.

Intermediate-frequency power supply is a static frequency conversion device that converts three-phase power supply into single-phase power supply. It is widely applied to various kinds of load.

Intermediate-frequency power supply is mainly applied to smelting, insulation, sintering, welding, quenching, tempering, heat transfer, liquid metal purification, heat treatment, bending and crystal growth of types of metal. The standard output power series: 30 kW-4,000 kW. The standard configuration of the smelting furnace series: 5kg (30 kW)-5,000 kg (4,000 kW). The standard oscillation frequency series: 400 Hz-10 kHz. The medium-frequency induction heating technology applies the electromagnetic induction principle and eddy current to heat workpieces. Induction heating has achieved rapid development in recent years due to a series of advantages such as fast heating speed, high internal heating efficiency of materials, uniform heating, good selectivity, high product quality, almost no environmental pollution, excellent controllability and easy production automation. At present, induction heating has been widely applied in industries such as casting and smelting, forging billet heating, metal surface heat treatment and aluminum electrolysis. Among such industries, the traditional heating is mainly realized by using coal, oil, and gas as energy sources or using box-type electric furnaces. Such traditional heating methods have some defects such as high energy consumption, poor labor conditions, serious environmental pollution and difficulty in controlling the process quality, which seriously restricts the development of China’s equipment manufacturing industry. Therefore, it is inevitable that the induction heating technology is publicized in all aspects to transform China’s traditional industries. The development of this technology is closely related to the development level of the induction heating power supply.

The SCR device of medium-frequency power supply can generate a large amount of higher harmonic current, so it can be considered as a harmonic source. In order to reduce the harmonic harm, harmonic is mainly inhibited by increasing the number of rectifier pulses when designing the SCR device. In normal cases, 6-pulse rectification is applied to intermediate-frequency power supply devices below 1,000 kW, and the harmonic generated is mainly (6k ± 1)^th(k is a positive integer) characteristic harmonic current; 12-pulse or 24-pulse rectification can be applied to intermediate-frequency power supply devices above 1,000 kW, which depends on the capacity. The 12-pulse rectification circuit consists of two groups of 6-pulse three-phase bridges connected in parallel. The AC side of two groups of bridges respectively connects to two secondary windings of the three-winding transformer. One winding applies the Y connection method, and the other applies the delta connection method. The voltage phase difference of two windings is 30°. When two groups of bridges are controlled synchronously, the triggering angle of two groups of rectifier bridges will be the same. Analysis shows that the 5^thharmonic current and the 7^th harmonic current from two groups of rectifier bridges will offset each other on the primary side of the transformer. Similarly, the 17^thharmonic current will offset the 19^thharmonic current. In such a case, the minimum order of characteristic harmonic will be the n^thharmonic and the 13^thharmonic, followed by the 23^rdharmonic and the 25^thharmonic. The current wave of the primary line of the transformer is three-step wave, which approaches the sine wave.