An overheat protection device for a salt bath electric furnace

Abstract

This utility model discloses an overheat protection device for a salt bath electric furnace, comprising a control cabinet, a salt bath electric furnace, and a circulating water pump. The control cabinet is equipped with a thermostat, an electric furnace control circuit, and a water pump control circuit, and also includes a protection circuit. The protection circuit includes an electrical contact pressure gauge, a temperature control switch, and a relay. The electrical contact pressure gauge is installed on the circulating water pump pipe and electrically connected to the thermostat. The upper limit of the electrical contact pressure gauge is connected to the salt bath electric furnace control circuit formed by the electric furnace control circuit. The temperature control switch and relay are both installed in the control cabinet, connected in parallel across the thermostat, and connected in series with the salt bath electric furnace control circuit via wires. The overheat protection device described in this utility model effectively solves the problem of overheating at the contact point of the copper busbar and electrode handle caused by insufficient circulating cooling water. It has the advantages of simple operation and convenient use, and can be widely used in cooling circuit protection.

Description

Technical Field

[0001] This utility model relates to the field of overheat protection technology for salt bath electric furnaces, specifically an overheat protection device for salt bath electric furnaces. Background Technology

[0002] Three-phase high-temperature salt bath furnaces are used to heat machined metal parts in molten salt solution or mixed salt baths for various heat treatments, such as quenching, annealing, tempering, normalizing, cyaniding, and carburizing. The furnace uses salt as a heating agent. The melting of the salt is achieved by adjusting the transformer output voltage from 5.5 to 17.6 volts, which is transmitted to the heating electrodes through copper busbars. The electrodes heat up and melt the crystalline salt. The maximum operating temperatures reach 600℃, 850℃, and 1300℃ respectively. To prevent overheating at the contact points between the copper busbars and electrode handles, circulating cooling water must be introduced into the electrode handles during operation.

[0003] Since the salt bath electric furnace heating system and the circulating cooling water system are two independent control systems, the operating procedure is to first start the circulating water pump, and then start the salt bath electric furnace heating. The existing control schematic diagrams for the salt bath electric furnace heating and the circulating water pump are as follows: Figure 1 and Figure 2 As shown, the specific working principle and process are as follows: like Figure 2 As shown, the working process of the circulating water pump is as follows: the three-pole circuit breaker QF3 is energized → the start button SB4 is pressed → the AC contactor coil KM2 is energized and engaged → the AC contactor main contacts KM2 are closed → the water pump motor is energized and starts pumping water → the stop button SB3 is pressed → the AC contactor coil KM2 is de-energized and disengaged → the AC contactor main contacts KM2 are opened → the water pump motor is de-energized and stops pumping water.

[0004] like Figure 1 As shown, the working process of the salt bath electric furnace is as follows: the three-pole plastic-cased circuit breaker QF1 and the single-pole circuit breaker QF2 are powered on → the start button SB2 is pressed → the AC contactor coil KM1 is energized and closes → the AC contactor main contacts KM1 close → the transformer TC operates → the heating electrode is energized and starts heating → when the set temperature is reached, the temperature controller alarm contact opens → the AC contactor coil KM1 is de-energized and opens → the AC contactor main contacts KM1 open → the heating electrode is de-energized and stops heating.

[0005] The existing control system for the salt bath furnace, which consists of two independent systems for heating and circulating cooling water, presents several risks and problems. Operators frequently make operational errors, such as starting the furnace without turning on the water pump. This often leads to overheating at the contact points between the copper busbars and electrode handles due to the lack of circulating cooling water, potentially damaging electrical components and causing a fire. Therefore, to prevent overheating at the contact points due to insufficient circulating cooling water, it is necessary to modify the existing control circuit of the salt bath furnace to provide an overheat protection device. This would prevent operator errors, extend the service life of the copper busbars, reduce the workload of maintenance electricians, and, to a certain extent, prevent dangerous accidents such as fires. This is therefore essential. Utility Model Content

[0006] The technical problem to be solved by this utility model is to address the problems existing in the background art, thereby providing an overheat protection device. This overheat protection device prevents the salt bath electric furnace from being turned on without turning on the water pump. It not only solves the problem of overheating at the contact point of the copper busbar and electrode handle caused by insufficient circulating cooling water, but also avoids operator misoperation, thereby extending the service life of the copper busbar. Specifically, it is an overheat protection device for salt bath electric furnaces.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows: an overheat protection device for a salt bath electric furnace, comprising a control cabinet, a salt bath electric furnace, and a circulating water pump. The salt bath electric furnace is equipped with heating electrodes and thermocouples, as well as a circulating water inlet and a circulating water outlet. The circulating water pump includes a pump motor and pipes. The outlet of the circulating water pump is connected to the circulating water inlet of the salt bath electric furnace through a pipe, and its inlet is connected to the circulating water outlet of the salt bath electric furnace through a pipe. The control cabinet is equipped with a thermostat, an electric furnace control circuit, and a water pump control circuit. The control cabinet detects the temperature of the salt bath electric furnace through the thermostat and supplies power to the salt bath electric furnace and the circulating water pump through the electric furnace control circuit and the water pump control circuit, respectively, to control the operation of the heating electrodes and the water pump motor. It also includes a protection circuit electrically connected to the electric furnace control circuit, the protection circuit including an electrical contact pressure gauge, a temperature control switch, and a relay. The electric contact pressure gauge is installed on the pipeline of the circulating water pump. The electric contact pressure gauge is electrically connected to the temperature controller. The upper limit of the electric contact pressure gauge is connected to the salt bath electric furnace control circuit formed by the electric furnace control circuit. The temperature control switch and relay are both installed in the control cabinet. The temperature control switch and relay are connected in parallel across the two ends of the temperature controller and connected in series with the salt bath electric furnace control circuit through wires.

[0008] Furthermore, in the overheat protection device for a salt bath electric furnace described in this utility model, the control protection circuit further includes a second relay and a buzzer. The second relay and the buzzer are both installed in the control cabinet. The second relay and the buzzer are connected in parallel across the two ends of the temperature controller and connected in series with the control circuit of the salt bath electric furnace through wires.

[0009] Furthermore, the overheat protection device for a salt bath electric furnace described in this utility model includes a furnace control circuit comprising a circuit breaker, an AC contactor, a transformer, a connecting copper busbar, a single-pole circuit breaker, a furnace stop button, a furnace start button, an AC contactor auxiliary contact, a small relay normally closed contact, an AC contactor coil, and a furnace indicator light. The input terminal of the transformer is electrically connected to the output terminal of the circuit breaker via AC contactor one, and the output terminal of the transformer is connected to the heating electrodes inside the salt bath furnace via connecting copper busbars. The single-pole circuit breaker, electric furnace stop button, electric furnace start button, AC contactor auxiliary contact one, miniature relay normally closed contact, AC contactor coil one, and electric furnace indicator light are respectively installed in the control cabinet, and the temperature controller alarm contact is configured in the temperature controller; The input terminal of the temperature controller is electrically connected to the output terminal of circuit breaker one through a single-pole circuit breaker, while the output terminal of the temperature controller is connected to the control circuit of the salt bath electric furnace through a wire. The thermocouple in the salt bath electric furnace is electrically connected to the temperature controller through a wire to form a temperature measuring circuit. The input terminal of the electric furnace stop button is electrically connected to the output terminal of the single-pole circuit breaker, and the output terminal of the electric furnace stop button is connected to one of the contacts of the temperature controller alarm contact in the temperature controller through the electric furnace start button; the auxiliary contact of the AC contactor is connected in parallel to both ends of the electric furnace start button. Another contact of the temperature controller alarm contact is electrically connected to the pressure gauge via a normally closed contact of a small relay. The upper limit of the electric contact pressure gauge is connected to the control circuit of the salt bath electric furnace through the coil of the AC contactor. The electric furnace indicator light is connected in parallel to both ends of the AC contactor coil.

[0010] Furthermore, the overheat protection device for a salt bath electric furnace described in this utility model includes a water pump control circuit comprising a circuit breaker II, an AC contactor II, a thermal relay I, a thermal relay II, a water pump stop button, a water pump start button, AC contactor auxiliary contacts II, AC contactor coil II, and a water pump indicator light. The circuit breaker II, AC contactor II, thermal relay I, thermal relay II, water pump stop button, water pump start button, AC contactor auxiliary contact II, AC contactor coil II and water pump indicator light (30) are respectively installed in the control cabinet; The water pump motor is electrically connected to the output terminal of circuit breaker 2 via thermal relay 1 and AC contactor 2 in sequence. The input terminal of the thermal relay 2 is electrically connected to the output terminal of the circuit breaker 2, and the output terminal of the thermal relay 2 is connected to the control circuit of the salt bath furnace in sequence through the water pump stop button, the water pump start button and the AC contactor coil 2. The auxiliary contact of the AC contactor is connected in parallel to both ends of the water pump start button; The water pump indicator light is connected in parallel to both ends of the AC contactor coil.

[0011] Furthermore, in the overheat protection device for a salt bath electric furnace described in this utility model, the input terminals of both circuit breaker one and circuit breaker two are connected to a three-phase AC power supply, which is a three-phase four-wire power supply; and the input terminal of the single-pole circuit breaker and the output terminal of circuit breaker one, as well as the input terminal of the thermal relay two and the output terminal of circuit breaker two, are all connected to the same phase of the three-phase AC power supply.

[0012] The overheat protection device for a salt bath electric furnace described in this utility model has the following advantages compared with the prior art: By adding four components to the existing control circuit to form a protection circuit, the protection circuit consists of an electric contact pressure gauge, a temperature control switch, a small relay, and a buzzer. Firstly, the electric contact pressure gauge is installed on the circulating cooling water pipeline. The upper limit switch of the electric contact pressure gauge is connected to the control circuit of the salt bath electric furnace. Only when the circulating cooling water pressure reaches the set pressure and the upper limit switch of the electric contact pressure gauge closes, can the heating system of the salt bath electric furnace start working by pressing the start button installed on the control cabinet. Otherwise, it will not start. This avoids the problem of overheating at the contact points of the copper busbar and electrode handles caused by the heating system operating without circulating cooling water. Secondly, a temperature control switch is installed at the contact point between the copper busbar and the electrode handle. The temperature control switch is connected in series with the coil of the small relay KA1. When the temperature at this point reaches the predetermined value, the temperature control switch closes, the coil of the small relay KA1 is energized, and the normally closed contact of KA1 opens, thereby stopping the heating system of the salt bath furnace. At the same time, the normally open contact of KA1 closes, causing the buzzer to flash and sound, reminding the operator to check the site, thus enhancing its safety performance.

[0013] Therefore, the overheat protection device described in this utility model effectively solves the problem of overheating at the contact point of the copper busbar and electrode handle caused by insufficient circulating cooling water by improving the control circuit of the existing salt bath electric furnace. It avoids operator error, extends the service life of the copper busbar, greatly reduces the workload of maintenance electricians, and to a certain extent avoids dangerous accidents such as fires. It has the advantages of simple operation and convenient use, and can be widely used in cooling circuit protection. Attached Figure Description

[0014] The present invention will now be described in further detail with reference to the accompanying drawings.

[0015] Figure 1 This is a schematic diagram of the heating control principle of an existing salt bath electric furnace. Figure 2 The control schematic diagram of an existing circulating water pump; Figure 3 This is a block diagram illustrating the control principle of the overheat protection device described in this utility model. Figure 4 This is a schematic diagram of the heating control principle of the salt bath electric furnace described in this utility model; Figure 5 This is a schematic diagram of the control principle of the circulating water pump described in this utility model.

[0016] The diagram shows: 1-Circuit breaker I, 2-AC contactor I, 3-Transformer, 4-Connecting copper busbar, 5-Heating electrode, 6-Thermocouple, 7-Single-pole circuit breaker, 8-Thermostat, 9-Electric furnace stop button, 10-Electric furnace start button, 11-AC contactor auxiliary contact I, 12-Thermostat alarm contact, 13-Miniature relay normally closed contact, 14-Electric contact pressure gauge, 15-AC contactor coil I, 16-Electric furnace indicator light, 17-Thermostat switch, 18-Relay I, 19-Relay II, 20-Buzzer, 21-Circuit breaker II, 22-AC contactor II, 23-Thermal relay I, 24-Water pump motor, 25-Thermal relay II, 26-Water pump stop button, 27-Water pump start button, 28-AC contactor auxiliary contact II, 29-AC contactor coil II, 30-Water pump indicator light. Detailed Implementation

[0017] The following specific embodiments illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification.

[0018] It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding. They are not intended to limit the scope of this invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, provided they do not affect the effectiveness or purpose of this invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," and "right" used in this specification are merely for clarity and not intended to limit the scope of this invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of this invention.

[0019] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "connection" and "provided with" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0020] It should be noted that the term "comprising" or any other variation is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Example 1

[0021] like Figures 3 to 5 As shown, this embodiment provides an overheat protection device for a salt bath electric furnace, including a control cabinet, a salt bath electric furnace, and a circulating water pump. The salt bath electric furnace is equipped with heating electrodes 5 and thermocouples 6, as well as a circulating water inlet and a circulating water outlet. The circulating water pump includes a water pump motor 24 and pipes. The outlet of the circulating water pump is connected to the circulating water inlet of the salt bath electric furnace through a pipe, and its inlet is connected to the circulating water outlet of the salt bath electric furnace through a pipe. The control cabinet is equipped with a thermostat 8, an electric furnace control circuit, and a water pump control circuit. The control cabinet detects the temperature of the salt bath electric furnace through the thermostat 8 and supplies power to the salt bath electric furnace and the circulating water pump through the electric furnace control circuit and the water pump control circuit, respectively, to control the operation of the heating electrodes 5 and the water pump motor 24. It also includes a protection circuit electrically connected to the electric furnace control circuit, which includes an electrical contact pressure gauge 14, a temperature control switch 17, and a relay 18. The electric contact pressure gauge 14 is installed on the pipeline of the circulating water pump. The electric contact pressure gauge 14 is electrically connected to the temperature controller 8. The upper limit of the electric contact pressure gauge 14 is connected to the salt bath electric furnace control circuit formed by the electric furnace control circuit. The temperature control switch 17 and the relay 18 are both installed in the control cabinet. The temperature control switch 17 and the relay 18 are connected in parallel across the two ends of the temperature controller 8 and connected in series with the salt bath electric furnace control circuit through wires.

[0022] Furthermore, using the overheat protection device for a salt bath electric furnace provided in this embodiment, the furnace control circuit includes a circuit breaker 1, an AC contactor 2, a transformer 3, a connecting copper busbar 4, a single-pole circuit breaker 7, an electric furnace stop button 9, an electric furnace start button 10, an AC contactor auxiliary contact 11, a small relay normally closed contact 13, an AC contactor coil 15, and an electric furnace indicator light 16; the input terminal of the transformer 3 is electrically connected to the output terminal of the circuit breaker 1 via the AC contactor 2, and the output terminal of the transformer 3 is connected to the heating electrode 5 inside the salt bath electric furnace via the connecting copper busbar 4; the single-pole circuit breaker 7, the electric furnace stop button 9, the electric furnace start button 10, the AC contactor auxiliary contact 11, the small relay normally closed contact 13, the AC contactor coil 15, and the electric furnace indicator light 16 are respectively installed in the control cabinet, and a temperature controller alarm contact 12 is configured in the temperature controller 8; the temperature controller... The input terminal of the thermostat 8 is electrically connected to the output terminal of the circuit breaker 1 via the single-pole circuit breaker 7. The output terminal of the thermostat 8 is connected to the control circuit of the salt bath furnace via a wire. The thermocouple 6 inside the salt bath furnace is electrically connected to the thermostat 8 via a wire to form a temperature measuring circuit. The input terminal of the furnace stop button 9 is electrically connected to the output terminal of the single-pole circuit breaker 7. The output terminal of the furnace stop button 9 is connected to one of the contacts of the thermostat alarm contact 12 inside the thermostat 8 via the furnace start button 10. The auxiliary contact 11 of the AC contactor is connected in parallel across the two ends of the furnace start button 10. The other contact of the thermostat alarm contact 12 is electrically connected to the pressure gauge 14 via the normally closed contact 13 of the miniature relay. The upper limit of the pressure gauge 14 is connected to the control circuit of the salt bath furnace via the coil 15 of the AC contactor. The furnace indicator light 16 is connected in parallel across the two ends of the coil 15 of the AC contactor.

[0023] Furthermore, using the overheat protection device for a salt bath electric furnace provided in this embodiment, the water pump control circuit includes a circuit breaker 21, an AC contactor 22, a thermal relay 23, a thermal relay 25, a water pump stop button 26, a water pump start button 27, an AC contactor auxiliary contact 28, an AC contactor coil 29, and a water pump indicator light 30. The circuit breaker 21, AC contactor 22, thermal relay 23, thermal relay 25, water pump stop button 26, water pump start button 27, AC contactor auxiliary contact 28, AC contactor coil 29, and... The water pump indicator lights 30 are respectively installed in the control cabinet; the water pump motor 24 is electrically connected to the output terminal of the circuit breaker 21 through the thermal relay 23 and the AC contactor 22 in sequence; the input terminal of the thermal relay 25 is electrically connected to the output terminal of the circuit breaker 21 in sequence, and the output terminal of the thermal relay 25 is connected to the control circuit of the salt bath furnace through the water pump stop button 26, the water pump start button 27 and the AC contactor coil 29 in sequence; the AC contactor auxiliary contact 28 is connected in parallel to the two ends of the water pump start button 27; and the water pump indicator lights 30 are connected in parallel to the two ends of the AC contactor coil 29.

[0024] In practical applications, the overheat protection device for a salt bath electric furnace provided in this embodiment is used. The input terminals of circuit breaker 1 and circuit breaker 21 are both connected to a three-phase AC power supply. This three-phase AC power supply is a three-phase four-wire power supply, with the three phases being U-phase, V-phase, and W-phase. The input terminal of the single-pole circuit breaker 7 is electrically connected to the output terminal of circuit breaker 1, and the input terminal of the thermal relay 25 is electrically connected to the output terminal of circuit breaker 21. These terminals are all connected to the same phase of the three-phase AC power supply, specifically the W-phase. The salt bath electric furnace is an RXD-75 type, and the transformer is a ZUSG-753 type. Example 2

[0025] This embodiment, based on Embodiment 1, enhances safety by employing an overheat protection device for a salt bath electric furnace to promptly alert operators. The protection circuit includes a second relay 19 and a buzzer 20, both installed in the control cabinet. These relays are connected in parallel across the temperature controller and in series with the salt bath electric furnace control circuit via wires. The buzzer 20 causes it to flash and emit an audible sound, promptly alerting operators to check the site and thus enhancing safety.

[0026] The working principle of the overheat protection device for a salt bath electric furnace described in this utility model is as follows: like Figure 5The diagram shown is a control schematic of a circulating water pump. The working process of the circulating water pump remains unchanged from the existing process: the three-pole circuit breaker QF3 is powered on → the start button SB4 is pressed → the AC contactor coil KM2 is energized and closes → the main contact of the AC contactor KM2 closes → the water pump motor is energized and starts pumping water → the stop button SB3 is pressed → the AC contactor coil KM2 is de-energized and disconnects → the main contact of the AC contactor KM2 opens → the water pump motor is de-energized and stops pumping water.

[0027] like Figure 4 The diagram shown is a schematic of the improved heating control principle of the salt bath electric furnace. The working process of the salt bath electric furnace is slightly different from the existing process: The three-pole plastic-cased circuit breaker QF1 (circuit breaker 1) and the single-pole circuit breaker QF2 (single-pole circuit breaker 7) are powered on → the water pressure reaches the set value, and the upper limit point of the pressure gauge P (pressure gauge 14) closes → the start button SB2 (furnace start button 10) is pressed → the AC contactor coil KM1 is energized and engages → the main contact of the AC contactor KM1 closes → the transformer TC (transformer 3) operates → the heating electrode 5 is energized and begins heating → when the set temperature is reached, the temperature controller alarm contact 12 opens → the AC contactor coil KM1 (AC contactor auxiliary contact 11) is de-energized and disconnects → the AC... When the main contactor KM1 of the current contactor opens, the heating electrode 5 loses power and stops heating. If the temperature at the electrode handle exceeds the operating value of the temperature control switch TS (temperature control switch 17) during heating, the contact of the temperature control switch TS (temperature control switch 17) closes. The coil KA1 (relay 18) of the miniature relay is energized. The normally closed contact KA1 (relay 29) of the miniature relay opens. The coil KM1 (coil 15) of the AC contactor loses power and opens. The main contact of the AC contactor KM1 (normally closed contact 13 of the miniature relay) opens. The heating electrode 5 loses power and stops heating. At the same time, the normally open contact KA1 (relay 29) of the miniature relay closes. The buzzer HA (buzzer 20) flashes and emits a sound.

[0028] Therefore, the overheat protection device for a salt bath electric furnace described in this utility model forms a protection circuit by adding four components to the existing control circuit. The protection circuit consists of four parts: an electric contact pressure gauge, a temperature control switch, a small relay, and a buzzer.

[0029] First, the electric contact pressure gauge 14 is installed on the circulating cooling water pipeline. The upper limit switch of the electric contact pressure gauge 14 is connected to the control circuit of the salt bath electric furnace. The heating system of the salt bath electric furnace can only start working when the upper limit switch of the electric contact pressure gauge is closed when the circulating cooling water pressure reaches the set pressure (set to 0.02MPa). Otherwise, it will not start. This avoids the problem of the heating system of the salt bath electric furnace working without circulating cooling water, which would cause overheating at the contact point of the copper busbar and electrode handle.

[0030] Secondly, a temperature control switch TS is installed at the contact point between the copper busbar and the electrode handle. The temperature control switch TS is connected in series with the coil of the small relay KA1. When the temperature at this point reaches the predetermined value (set to 70℃), the temperature control switch TS closes, the coil of the small relay KA1 is energized, and the normally closed contact of KA1 opens, thereby stopping the heating system of the salt bath furnace. At the same time, the normally open contact of KA1 closes, causing the buzzer to flash and sound, reminding the operator to check the site, thus enhancing its safety performance.

[0031] In summary, the overheat protection device described in this utility model, by improving the control circuit of the existing salt bath electric furnace, effectively solves the problem of overheating at the contact point of the copper busbar and electrode handle caused by insufficient circulating cooling water. It avoids operator errors, extends the service life of the copper busbar, greatly reduces the workload of maintenance electricians, and to a certain extent prevents dangerous accidents such as fires. It has the advantages of simple operation and convenient use, and can be widely used in cooling circuit protection.

[0032] Other aspects of this utility model that are not detailed herein are all conventional techniques known to those skilled in the art.

[0033] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Various modifications and variations can be made by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. made using the present utility model should be included within the protection scope of the present utility model.

Claims

1. An overheat protection device for a salt bath electric furnace, comprising a control cabinet, a salt bath electric furnace, and a circulating water pump. The salt bath electric furnace is equipped with heating electrodes (5) and thermocouples (6), as well as a circulating water inlet and a circulating water outlet. The circulating water pump includes a water pump motor (24) and a pipe. The outlet of the circulating water pump is connected to the circulating water inlet of the salt bath electric furnace through a pipe, and its inlet is connected to the circulating water outlet of the salt bath electric furnace through a pipe. The control cabinet is equipped with a thermostat (8), an electric furnace control circuit, and a water pump control circuit. The control cabinet detects the temperature of the salt bath electric furnace through the thermostat (8) and supplies power to the salt bath electric furnace and the circulating water pump through the electric furnace control circuit and the water pump control circuit, respectively, to control the operation of the heating electrodes (5) and the water pump motor (24). Its features are: It also includes a protection circuit electrically connected to the electric furnace control circuit, the protection circuit including an electric contact pressure gauge (14), a temperature control switch (17) and a relay (18); The electric contact pressure gauge (14) is installed on the pipeline of the circulating water pump. The electric contact pressure gauge (14) is electrically connected to the temperature controller (8). The upper limit of the electric contact pressure gauge (14) is connected to the salt bath electric furnace control circuit formed by the electric furnace control circuit. The temperature control switch (17) and relay one (18) are both installed in the control cabinet. The temperature control switch (17) and relay one (18) are connected in parallel across the two ends of the temperature controller (8) and connected in series with the salt bath electric furnace control circuit through wires.

2. The overheat protection device for a salt bath electric furnace according to claim 1, characterized in that: The control and protection circuit also includes a second relay (19) and a buzzer (20). The second relay (19) and the buzzer (20) are both installed in the control cabinet. The second relay (19) and the buzzer (20) are connected in parallel across the two ends of the temperature controller and connected in series with the control circuit of the salt bath electric furnace through wires.

3. The overheat protection device for a salt bath electric furnace according to claim 2, characterized in that: The electric furnace control circuit includes a circuit breaker (1), an AC contactor (2), a transformer (3), a connecting copper busbar (4), a single-pole circuit breaker (7), an electric furnace stop button (9), an electric furnace start button (10), an AC contactor auxiliary contact (11), a small relay normally closed contact (13), an AC contactor coil (15), and an electric furnace indicator light (16). The input terminal of the transformer (3) is electrically connected to the output terminal of the circuit breaker (1) via AC contactor (2), and the output terminal of the transformer (3) is connected to the heating electrode (5) in the salt bath furnace via connecting copper busbar (4). The single-pole circuit breaker (7), the electric furnace stop button (9), the electric furnace start button (10), the AC contactor auxiliary contact one (11), the small relay normally closed contact (13), the AC contactor coil one (15), and the electric furnace indicator light (16) are respectively installed in the control cabinet, and the temperature controller alarm contact (12) is configured in the temperature controller (8); The input terminal of the temperature controller (8) is electrically connected to the output terminal of the circuit breaker (1) through the single-pole circuit breaker (7), and the output terminal of the temperature controller (8) is connected to the control circuit of the salt bath furnace through the wire. The thermocouple (6) in the salt bath furnace is electrically connected to the temperature controller (8) through the wire to form a temperature measuring circuit. The input terminal of the electric furnace stop button (9) is electrically connected to the output terminal of the single-pole circuit breaker (7), and the output terminal of the electric furnace stop button (9) is connected to one of the contacts of the temperature controller alarm contact (12) in the temperature controller (8) through the electric furnace start button (10); the auxiliary contact one (11) of the AC contactor is connected in parallel to both ends of the electric furnace start button (10); Another contact of the alarm contact (12) of the thermostat is electrically connected to the pressure gauge (14) via a normally closed contact (13) of a small relay. The upper limit point of the electric contact pressure gauge (14) is connected to the control circuit of the salt bath electric furnace through the AC contactor coil (15); The electric furnace signal lamp (16) is connected in parallel to both ends of the AC contactor coil (15).

4. An overheat protection device for a salt bath electric furnace according to claim 3, characterized in that: The water pump control circuit includes circuit breaker two (21), AC contactor two (22), thermal relay one (23), thermal relay two (25), water pump stop button (26), water pump start button (27), AC contactor auxiliary contact two (28), AC contactor coil two (29), and water pump indicator light (30). The circuit breaker 2 (21), AC contactor 2 (22), thermal relay 1 (23), thermal relay 2 (25), water pump stop button (26), water pump start button (27), AC contactor auxiliary contact 2 (28), AC contactor coil 2 (29) and water pump indicator light (30) are respectively installed in the control cabinet; The water pump motor (24) is electrically connected to the output terminal of the circuit breaker (21) in sequence through thermal relay one (23) and AC contactor two (22); The input terminal of the second thermal relay (25) is electrically connected to the output terminal of the second circuit breaker (21). The output terminal of the second thermal relay (25) is connected to the control circuit of the salt bath furnace in sequence through the water pump stop button (26), the water pump start button (27) and the second AC contactor coil (29). The auxiliary contact 2 (28) of the AC contactor is connected in parallel to both ends of the water pump start button (27); The water pump indicator light (30) is connected in parallel to both ends of the AC contactor coil two (29).

5. An overheat protection device for a salt bath electric furnace according to claim 4, characterized in that: The input terminals of both circuit breaker one (1) and circuit breaker two (21) are connected to a three-phase AC power supply, which is a three-phase four-wire power supply. The input terminal of the single-pole circuit breaker (7) is electrically connected to the output terminal of circuit breaker one (1), and the input terminal of the thermal relay two (25) is electrically connected to the output terminal of circuit breaker two (21), which are all the same phase of the three-phase AC power supply.

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