DE29900018U1 - Temperature alarm device for electric crucible furnaces for melting aluminum, brass, copper and bronze alloys up to a total output of 120 KW - Google Patents

Description

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Title:

Temperature alarm device for electric crucible furnaces for melting aluminum, brass, copper and bronze alloys up to a total output of 120 KW.

The temperature alarm device belongs to the field of foundry engineering.

According to the state of the art that I know of, there is currently no alarm device for melting crucible furnaces with a thermocouple!

During my 10-year professional experience, I noticed that every year several furnaces were damaged, causing a not insignificant financial loss, here two

Examples. Example 1:

If the metal solidifies in the crucible, it will cause the crucible to burst when it is melted again. If the crucible bursts in the presence of the technical supervisor, emptying it will prevent the metal from solidifying. In this case, only a small loss occurs.

If the crucible bursts unnoticed, the damage is much greater, as not only the crucible but also the furnace is destroyed.

Example 2:

The metal flowing out of the burst crucible escapes from the furnace chamber. It is led out through the furnace outlet opening, where it immediately solidifies and blocks the outlet opening. This causes the metal level in the furnace chamber to rise and reach the furnace's heating elements, causing a short circuit. The furnace is cut off from the power supply. The metal level in the crucible and in the furnace chamber equalizes and solidifies. In special cases, this can lead to the furnace being completely destroyed.

Example 3:

If the temperature sensor in the oven is damaged, it will no longer be supplied with energy

This leads to the solidification of the metal in the crucible. When trying to open the crucible

If you try to save it, about 90% of the crucible will be broken.

I have set myself the task of developing an alarm device for crucible furnaces, which works with a thermocouple, whereby the possible damage to the
thermocouple is also monitored. This problem is solved here with a
Temperature sensor and solved with a self-made sensor.

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It is an alarm device that prevents damage or destruction to the furnace and the crucible.

The benefit of such an alarm device is that it prevents the oven from being completely destroyed, thus preventing considerable financial loss.

It works in the following cases :

• In case of power supply faults in the oven’s electrical system,

• If the metal crucible is destroyed (metal escapes from the furnace outlet opening),

• In case of oven overheating (defect in the device that regulates the oven temperature),

• If the systems that supply the heating elements in the oven are not switched on or off,

• If the heating elements in the oven (coils etc.) are damaged to such an extent that the temperature in the oven can no longer be maintained.

This alarm device monitors the conventional temperature sensor and temperature controller. If one or both of the above elements are destroyed or defective, an ALARM is triggered!

The control of the correct functioning of the furnace only reacts to defects that can destroy the system.

The alarm device is equipped with a voltage-free output directly on the relay contacts. A telephone dialer, a radio alarm device or a telephone exchange equipped with an alarm output can be connected to these relay contacts.

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Principle of operation of the alarm device:

The temperature alarm device is switched on using the rocker switch S1

At the same time, an LED diode from the tens LED display (D4 to D13) lights up

This LED display lights up dot by dot.

Which LED lights up when switched on depends on the temperature in the oven chamber, which is measured with the thermocouple Q (Fig.2).

Three LEDs in this display light up in different colors and have the following meaning:

• LED D6 (red) means that the temperature falls below the lowest temperature measured by this device.

• LED-D8 (yellow) shows the temperature center = monitoring temperature.

• LED -D11 (red) indicates that the maximum temperature has been exceeded.

The temperature fluctuations are visible on the LED display. The monitoring temperature (LED D8) may be approximately 25°C lower (LED D6) or 50 ^° C higher (LED D11), otherwise the ALARM goes off.

The center point (LED-D8 on) can be set when the device is put into operation using adjustable resistors P2 and P3 (Fig.3). With this setting, the temperature of the oven chamber must be equal to the mean temperature to be monitored (= monitoring temperature)!

The rocker switch S2 (Fig.4) switches the device to the monitoring mode.

In every foundry, the temperature of the electric furnaces is reduced at the end of the shift using a controller. When the device is switched on at the same time as S1, no LED lights up, as the temperature is still too high at this point and is not yet detected by the temperature alarm device. Over time, however, the temperature drops and the LED diodes light up one after the other, starting with D13, then D12, D11, etc.

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When the midpoint is reached (LED-D8 lights up), LED-D6 and LED-D11 are switched on. If LED-D6 or LED-D11 lights up, this simultaneously means ALARM, as a result of which LED-D15 (red) lights up (Fig.4).

When the average temperature (= monitoring temperature) is reached, which is measured with the thermocouple Q, the following happens in the alarm device:

The transistor T-3 opens and the LED D8 lights up. At the same time, the transistor T1 is opened by D2 after about 10 seconds and the relay Re. 1 switches on (closes the contacts). The base of the transistor T1 is supplied with a negative potential through the contacts of Re. 1 and the resistor R21, so that Re. 1 maintains its state (contacts closed). The contacts are opened again when we switch off the device with the switch S1 (see Fig. 4).

By second closed contacts of Re-1, the LED diodes D6 and D11 are switched on via the transistors T4 and T5 (point B Fig.4 and Fig.3).

The positive voltage generated at the thermocouple Q (Fig.2) reaches the input of the operational amplifier IC-3-A (PIN 2). As a result of the cascade amplification (IC-3-A, IC-3-B and IC-3-C) we achieve a voltage of 0 to +4.5 V at the output of the IC-3-C (PIN 8) that can be regulated with P1. The LED display is supplied with this voltage.

3 Examples of alarms:

1. When the temperature falls below the lowest point, LED D6 lights up. PIN 17 of IC-4 opens T4 and R15 passes the negative voltage through the contacts of Re-1 (Re-1 switched on, contacts closed!) and then through R23 to the base of transistor T2. Transistor T2 goes into the blocking state, which causes relay Re-2 to switch off (Fig.4). This means ALARM!, LED D15 lights up red!

2. If the temperature is exceeded, LED D11 lights up. The ALARM is triggered by a negative voltage on PIN 12 of IC-4 and then via T5 and R18, just as if the temperature were to fall below the set limit (negative voltage at the base of transistor T2).

3. If the thermocouple Q breaks, the voltage at PIN 5 of IC-4 will change and as a result an alarm will also be triggered!

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The sensor S3 is connected to terminal K1 (connections 7 and 8) (Fig.4). The sensor is installed under the outlet hole of the furnace. When the hot metal flows out of the furnace chamber, connections 7 and 8 are interrupted. As a result, the relay Re-2 is de-energized (open contacts) and the ALARM is triggered, D15 lights up red.

The S3 sensor works in every operating state of the alarm device. It is independent of the rest of the monitoring electronics. This means that the crucible will always be protected against bursting!

A telephone dialer, a radio alarm device or a telephone exchange equipped with an alarm output can be connected to connections 5 and 6 of terminal K1 (Fig. 4).

The auxiliary contacts of the electrical oven contactor, through which the heating coils of the oven are supplied with energy, are connected to connections 9 and 10 of terminal K1. This monitors the oven to see if the heating coils are supplied with energy before the average temperature is reached. In such a case, contacts 9 and 10 are closed, a negative voltage comes through the closed contacts of the de-energized Re-1 on the basis of transistor T2. As a result, T2 goes into the blocking state and LED D15 lights up red (ALARM!). This monitors the oven to see if the heating elements are supplied with energy before the average temperature is reached. After the monitoring temperature is reached, these auxiliary contacts of the oven contactor are out of operation.

Structure and function of sensor S3 at terminal K1 (Fig. 5)

It is a small aluminum tube. A limit switch with an M 14x1 thread is screwed into one side. A copper wire is soldered to the other end.

A cylinder is placed on the copper wire inside the tube. The copper wire is soldered in such a way that the spring is in the tensioned state as shown in Fig.5.

When a crucible bursts, the hot metal flows directly onto the sensor. The tin solder is released, the spring relaxes and pushes the copper wire with the attached cylinder directly onto the limit switch, which opens its contacts. This de-energizes the relay Re.2 due to the loss of the negative pole. This means ALARM!

Claims (1)

-1-CLAIMS OF PROTECTION: 1. Temperature alarm device for electric crucible furnaces for melting aluminum, brass, copper and bronze alloys up to a total output of 120 KW, marked by an electronic method that uses a thermocouple to monitor the electric melting furnace Temperature alarm device with protection claim 1, marked by an automatic sensor with a spring and a limit switch that is installed under the outlet hole of the furnace and changes the state of the limit switch when the crucible bursts.