The dryer is a necessary equipment in the injection molding industry. It is necessary for maintenance personnel to understand its working principle and wiring method. The main circuit of the dryer is connected to the fan and the heating rod. It is very simple and will not be described. This article mainly explains the control circuit.
First introduce the most important component in the dryer: the thermostat.Detailed explanation of plastic dryer control circuit
Its function is to adjust the heating state according to the temperature of the hot air. The input is 220V AC voltage and temperature signal; 220V voltage is output to the heating relay coil, and the heating status is detected to output an alarm signal. Terminal numbers and functions are marked on the side of the thermostat.
For example, a certain type of thermostat: 1, 3 is the power input of the thermostat, 3 is the neutral terminal; 5, 6 (main, no) control the on and off of the heating relay coil circuit; 9, 10 thermocouple signal input.
The model dryer control circuit is described in detail.
Fan control：
It can be seen that there is a transformer under the relay, which changes the voltage of 380V to 220V and provides it to the control circuit (different from this in other dryers, the power of the control circuit is provided by the phase line and the neutral line), and take one end of the transformer output and each phase The ports with the line voltage of 380V are used as the neutral terminal.
The two leads of the output end of the transformer are connected to the lower end of the fan switch, the fan switch-the neutral terminal of the thermostat-the fan relay coil-the fan switch, and the fan control circuit. Press the fan switch, the coil is energized, the relay is closed by electric shock, and the fan is energized to work.
Heating control：
The power input of the thermostat, the upper left outlet of the fan switch is connected to the lower right inlet of the electric heating switch, the upper right of the electric heating switch is connected to the main terminal of the thermostat, and the main terminal is connected to the 220V phase terminal through a wire, and the thermostat is zero. The wire end is connected to the outlet end of the neutral wire of the fan switch. When both switches are closed, the thermostat can get 220V voltage input to control heating. This is also a reason why the fan cannot turn on and the electric heater cannot be turned on. We also noticed that there is a connection between the two switches. This wire is used to make the electric heating indicator provide a neutral wire, which can give a light when the electric heating switch is pressed.
Heating control circuit. The neutral terminal of the fan switch-N terminal-fan relay terminal-heating coil-fan relay auxiliary contact-no terminal-main terminal-electric heating switch-fan switch is an electric heating control circuit. The thermostat controls the on-off between main and no through the internal circuit to change the energized state of the heating relay coil. The function of the heating relay coil and the auxiliary contact of the fan relay in series: when the fan relay is not closed, the circuit that controls the heating relay coil is in an open state and does not heat. This is another reason why the fan does not turn on and the electric heater cannot be turned on.
Alarm control：
Alarm and No terminal are connected in series with power supply and alarm device. The alarm device is an air switch trip unit or a dryer alarm indicator. Alarm and No are normally open states. When the heating is abnormal, it will be turned on. After turning on, the indicator light will sound an alarm, or the trip unit will be triggered and the air switch will trip.
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