Method of reducing silicon burning in intermediate frequency electric furnace
It is normal to occasionally damage a few SCRs during the use of the intermediate frequency electric furnace. If you burn the silicon frequently, you will be alert. The working current of the thyristor is several thousand amps, and the voltage is usually one or two thousand volts. Good protection of the main control board and good water cooling conditions are necessary.
Overload characteristics of thyristor: The damage of thyristor is called breakdown. Under normal water-cooling conditions, the current overload capacity can reach more than 110%; no voltage overload capacity, that is, silicon is definitely damaged under overvoltage conditions. Considering the surge voltage, manufacturers often choose silicon components based on 3-4 times the operating voltage when manufacturing equipment. For example, when the rated working voltage of the intermediate frequency cabinet is 1750V, two silicon components with a withstand voltage of 2500V are selected to work in series, which is equivalent to a withstand voltage of 5000V.
The correct installation pressure of SCR: 150-200KG/cm2. When the equipment leaves the factory, it is generally press-fitted with a hydraulic press. The maximum strength of an ordinary wrench can not reach this value, so there is no need to worry about the silicon being crushed when the pressure is manually installed; if the pressure is loose, it will burn the silicon due to poor heat dissipation.
SCR radiator structure: water-cooled cavity + multi-copper pillar support. If the circulating water is too hard, it will scale in the water cavity and cause poor heat dissipation; if leaves and other debris enter the water cavity, it will also cause poor water flow.
The factory test temperature of the SCR is 100°C (junction temperature). Under normal circumstances, keeping the circulating water temperature of the electric cabinet below 45°C can ensure its normal operation. The hand-held infrared thermometer is very useful. The 350℃ thermometer is only a few hundred yuan, which is not too expensive. Use it to measure the temperature of the thyristor and the temperature of the radiator of the working power supply, and it can find abnormal points in time and deal with faults.
The mesa of the heat sink must match the size of the component mesa to prevent voltage bias and distortion, which may damage the device. The radiator countertop must have a high level of flatness and smoothness. It is recommended that the surface roughness of the radiator is less than or equal to 1.6mm, and the flatness is less than or equal to 30mm. During installation, the countertop of the component and the countertop of the radiator should be kept clean, clean and free of dirt such as oil and dirt.
When installing, keep the tabletop of the silicon component and the tabletop of the heat sink completely parallel and concentric. During the installation process, it is required to apply pressure through the center line of the component so that the pressure is evenly distributed throughout the contact area. When the user manually installs, it is recommended to use a torque wrench to alternately and uniformly apply force to all the tightening nuts, and the pressure must meet the specified requirements.
When reusing the water-cooled radiator, pay special attention to checking whether the countertop is smooth and level, and whether there is scale and blockage in the water cavity, and pay particular attention to whether the countertop is sinking. If the above situation occurs, it should be replaced.