Heating control device capable of prolonging service life of heating element, control method and sintering furnace

Abstract

The invention provides a heating control device capable of prolonging the service life of a heating element, a control method and a sintering furnace. The heating control device comprises the heating element, an alternating current power supply, a transformer and a power adjusting module. The AC power supply is used for providing power; the alternating current power supply transmits current to the heating element through the transformer; the input end of the power adjusting module is electrically connected with the transformer, and the output end of the power adjusting module is electrically connected with a heating element; the power adjusting module is used for adjusting the conduction angle of the waveform in the input voltage of the heating element, and / or adjusting the cycle number of the waveform in the input voltage of the heating element; and the heating element is used for heating. Taking a silicon carbide rod as an example, the sintering service life of the heating element can be prolonged from 200 heats to 800 heats, and then the service life of the sintering furnace is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of heating devices, and in particular to a heating control device, a control method and a sintering furnace for extending the service life of a heating element. Background Art

[0002] Take silicon carbide heating elements, for example. Conventional heating elements are made through a recrystallization process, with no increase in density during combustion. Heating elements made using a reaction sintering process, however, are a tough, oxidation-resistant material with controlled resistance and uniform heating characteristics.

[0003] The porosity of silicon carbon rods produced by the reaction sintering process is less than half of that of traditional recrystallized silicon carbide heating elements. Whether it is oxidation or reduction reaction, their reaction speed with the process atmosphere is slower than that with the process atmosphere, which is equivalent to extending the life of the heating element.

[0004] In order to increase the service life of the heating element sintering furnace, the rated voltage and current parameters of the heating element can be formulated, a specific electrical control structure or a specific control method can be adopted to further improve the service life of the heating element. The commonly used circuit forms and connection methods of the heating element are as follows: Figure 1 , Figure 1 SSR stands for solid-state relay module, which receives the control output of the instrument and uses the solid-state relay module to cut off or connect the current in the circuit to control heating. This control method has no interference from high-order harmonics in the power grid environment and is low-cost. However, since the current cut-off or connection of the solid-state relay module causes a very large current impact in the circuit, it has a great impact on the normal operation of other equipment in the power grid. In addition, when the heating element ages, power adjustment cannot be performed, which can easily lead to unqualified sintering effects.

[0005] In the actual application process, the service life of the silicon carbon rod can also be extended by increasing the power initially supplied by the power supply, because the resistance of the heating element decreases as the furnace temperature rises, reaching a minimum value at around 600℃~800℃, and then the resistance slowly increases as the temperature rises. Figure 2 As shown, since W = U 2 / R, that is, W is inversely proportional to R. The gradual increase in resistance at high temperature leads to a gradual decrease in heating power, so it will be impossible to continue to heat up to the required sintering temperature. At this time, we believe that the life of the heating element no longer meets the actual needs and needs to be replaced with a heating element with a smaller resistance, or the voltage is adjusted by the electronic control module to continuously increase the output current to achieve the expected sintering state, which is equivalent to extending the service life of the silicon carbon rod sintering furnace.

[0006] This method of increasing the power supply to extend the service life of the heating element has certain limitations, because the resistance of the heating element slowly increases as the number of times the furnace is used increases. When the resistance of the heating element increases to the point where the power supply cannot meet the power required for sintering, unqualified sintering will still result, affecting customer shipments, delaying production cycles, and causing time and economic losses to customers.

[0007] Therefore, it is necessary to develop new methods and devices for extending the service life of heating elements. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a heating control device, a control method and a sintering furnace for extending the life of the heating element. Taking the silicon carbide heating element as an example, the life of the heating element can be increased from 200 furnace times to more than 800 furnace times while the sintering furnace is running continuously without stopping. This significantly increases the service life of the sintering furnace and has broad application prospects.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a heating control device for extending the life of a heating element.

[0011] The heating control device includes a heating element, an AC power supply, a transformer and a power adjustment module;

[0012] The AC power source is used to provide electric power; and the AC power source transmits electric current to the heating element through a transformer;

[0013] The input end of the power regulating module is electrically connected to the transformer, and the output end of the power regulating module is electrically connected to the heating element; the power regulating module is used to adjust the conduction angle of the waveform in the input voltage of the heating element, and / or to adjust the frequency of the waveform in the input voltage of the heating element;

[0014] The heating element is used for heating and raising the temperature.

[0015] At present, ordinary sintering furnaces often use a connection method of four heating elements in series or two series and two parallel. By increasing the number of heating elements in the furnace, the temperature uniformity and heating rate of the furnace are guaranteed. However, as time goes by, the aging degree of the four heating elements is different, resulting in different resistance values ​​of each resistor. If the resistance of the first heating element at the power supply end ages seriously, the current cannot pass through other heating elements normally, causing the furnace to fail to heat up.

[0016] In order to overcome the problem of different aging degrees of the above-mentioned four heating elements, the present invention only adopts one heating element, but only adopts one heating element (such as a single threaded silicon carbide rod). As the heating furnace is used, the heating element is continuously oxidized, resulting in a gradual increase in the resistance of the heating element. Subsequently, it is easy to find that the heating power is difficult to increase, and the sintering effect of the sintering furnace cannot be guaranteed.

[0017] In order to further overcome the above-mentioned difficulties, the present invention adopts an AC power supply, a transformer and a power regulation module, wherein the transformer can regulate the power input by the AC current so that the voltage output by the transformer can change without changing the structure of the sintering furnace, thereby not delaying the production; the power regulation module is further adopted to regulate the waveform conduction angle and / or frequency of the input voltage of the heating element, so that when the heating element ages, the voltage limit value can be changed and the power supply power can be adjusted to extend the service life of the heating element in the sintering furnace.

[0018] In summary, the present invention replaces multiple heating elements with one heating element, sets an AC power supply and a transformer to perform gear shifting adjustment on the transformer output voltage, and sets a power adjustment module to adjust the conduction angle and / or frequency of the input voltage of the heating element, thereby achieving effective voltage regulation during the sintering process of the sintering furnace without affecting customer shipments or delaying production frequency.

[0019] Preferably, the transformer comprises a primary coil and a secondary coil coupled to each other, the primary coil is connected to the AC power source, and the secondary coil is connected to the heating element.

[0020] Preferably, the number of the heating element is single.

[0021] Preferably, the heating element comprises any one of silicon carbon rods, silicon molybdenum rods or resistance wires, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of silicon carbon rods and silicon molybdenum rods, a combination of resistance wires and silicon molybdenum rods, and a combination of silicon carbon rods and resistance wires.

[0022] Preferably, the outer diameter of the silicon carbide rod is 70-80 mm, for example, it can be 70 mm, 72 mm, 73 mm, 74 mm, 75 mm, 76 mm, 77 mm, 78 mm, 79 mm or 80 mm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] Preferably, the silicon carbide rod has a hollow hole therein.

[0024] Preferably, the diameter of the hollow hole is 50-55 mm, for example, it can be 50 mm, 50.6 mm, 51.2 mm, 51.7 mm, 52.3 mm, 52.8 mm, 53.4 mm, 53.9 mm, 54.5 mm or 55 mm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0025] Preferably, the silicon carbide rod is a double-threaded silicon carbide rod or a single-threaded silicon carbide rod.

[0026] Preferably, the spacing between the spiral grooves in the double-threaded silicon carbide rod or the single-threaded silicon carbide rod is 2 to 6 mm, for example, it can be 2 mm, 2.5 mm, 2.9 mm, 3.4 mm, 3.8 mm, 4.3 mm, 4.7 mm, 5.2 mm, 5.6 mm or 6 mm, but is not limited to the listed values, and other values ​​not listed in the range are also applicable.

[0027] Preferably, the double-threaded silicon carbide rod or the single-threaded silicon carbide rod comprises a threaded hot end and a tubular cold end located at one end of the threaded hot end.

[0028] Preferably, the silicon-molybdenum rod is a U-shaped silicon-molybdenum rod.

[0029] Preferably, the silicon-molybdenum rod is a solid silicon-molybdenum rod.

[0030] Preferably, the power regulation module includes a solid-state relay and / or a thyristor module.

[0031] Specifically, a solid-state relay (SSR) is a switching device that replaces traditional electromagnetic relays with semiconductor devices. It isolates the input signal from the output load through a photocoupler, and has the advantages of fast response, high durability, and no mechanical wear. Its regulation principle is mainly based on the control of load current, that is, through technologies such as pulse width modulation (PWM) or phase cutting, the relay can accurately adjust the conduction time, thereby achieving the regulation of load power.

[0032] The present invention has no special limitation on the specific structure or model of the solid-state relay. The model or structure of the solid-state relay familiar to those skilled in the art may be adopted, and may also be adjusted accordingly according to actual conditions, which will not be described in detail here.

[0033] More specifically, solid-state relays use DC to control AC, and have only two states: closed and open. The solid-state relay is triggered when passing through zero, and passes through zero when going from the positive half-cycle to the negative half-cycle or from the negative half-cycle to the positive half-cycle. The conduction cycle is changed within a certain period of time to change the output average power, thereby achieving the effect of regulating load power. The cycle refers to the time it takes for the AC to complete a complete change, that is, a sinusoidal waveform is called a cycle. The control output signal of the solid-state relay is a square wave.

[0034] Preferably, the thyristor module is a thyristor phase-shift trigger.

[0035] The thyristor phase-shift trigger in the present invention is a circuit for controlling the conduction moment of a thyristor (SCR), and uses the characteristics of the thyristor to control the magnitude of the output voltage by changing the phase of a trigger signal.

[0036] Specifically, phase-shift triggering means controlling the moment when the thyristor conducts by adjusting the phase of the trigger signal, thereby changing the effective value of the output. For example, within the frequency of the AC power supply, if the trigger signal is advanced or delayed relative to the voltage zero point, the power on the load can be adjusted.

[0037] The present invention has no special limitation on the specific structure or model of the thyristor module. The model or structure of the thyristor phase-shift trigger well known to those skilled in the art may be adopted, and may also be adjusted accordingly according to actual conditions, which will not be described in detail here.

[0038] Preferably, the heating control device also includes a temperature control instrument and a control system connected to the power regulation module.

[0039] The temperature control instrument in the present invention is a device for measuring and controlling temperature, which can monitor the temperature in real time and automatically adjust according to the set value to maintain a specific temperature range. There is no special limitation on the specific circuit and structure of the temperature control instrument, and a temperature control instrument familiar to those skilled in the art can be used.

[0040] The control system of the present invention can adjust the power regulation module and the transformer according to the temperature conditions obtained by the temperature control instrument and the current conditions in the circuit.

[0041] Preferably, the heating control device further comprises an ammeter, and two ends of the ammeter are electrically connected to the power regulating module and the heating element respectively.

[0042] Preferably, the voltage of the transformer is set to at least two levels.

[0043] The transformer of the present invention is set to at least two levels, wherein when the voltage of the transformer is set to two levels, the voltage of the first level is 60-70% of the voltage of the second level, so that the current value passing through the heating element can be changed by adjusting the transformer.

[0044] In a second aspect, the present invention provides a control method for extending the life of a heating element, wherein the control method is performed using the heating control device for extending the life of a heating element as described in the first aspect.

[0045] The control method for extending the life of a heating element provided in the second aspect of the present invention can significantly increase the service life of the heating element without having a negative impact on the production process.

[0046] Preferably, the control method comprises:

[0047] (1) In the initial service period of the heating element, the transformer is set to the first output voltage, and the power regulation module is adjusted to limit the output voltage so that the current passing through the heating element is the initial current I0;

[0048] (2) Determine whether the current is greater than the determination current. If so, proceed to step (3); if not, proceed to step (4);

[0049] (3) maintaining the current output voltage and power limit of the transformer and performing temperature-raising sintering, during which the current I1 passing through the heating element is monitored in real time; and repeating step (2) until the sintering process is completed, and ending the control after the sintering process is completed;

[0050] (4) Determine whether the power limit of the power regulation module reaches 100%; if not, proceed to step (5); if yes, proceed to step (6);

[0051] (5) upwardly adjusting the power limit of the power regulation module to increase the current, and repeating the current determination of step (2);

[0052] (6) Determine whether the transformer is in the second gear. If not, adjust the transformer to the second gear and loop back to step (2) to perform current determination. If yes, determine that the abnormality has ended and end control.

[0053] It is worth noting that the present invention can increase the current flowing through the heating element in the late oxidation stage of the heating element by adjusting the output voltage of the transformer, so that the voltage can be directly switched during the sintering process of the furnace, without wasting the sintering furnace, thereby ensuring the temperature increase effect during the sintering process. Moreover, the adjustment of the output voltage does not require replacement of the heating element or adjustment of the electric control module, and has little effect on the sintering process, and has broad application prospects.

[0054] Preferably, the resistance of the heating element is a first resistance R1, and the range of the first resistance R1 is 100-200% of the initial resistance R0 of the heating element at the beginning of service, for example, it can be 100%, 105%, 110%, 115%, 120%, 125%, 132%, 135%, 140%, 145%, 150%, 155%, 160%, 165%, 170%, 180%, 190% or 200%, etc.

[0055] Preferably, the voltage of the second gear is 1.2 to 2.0 times the voltage of the first gear, for example, it can be 1.2 times, 1.25 times, 1.3 times, 1.35 times, 1.4 times, 1.45 times, 1.5 times, 1.55 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times or 2.0 times, etc.

[0056] As the service time of the heating element increases, the heating element will age. A higher voltage is required to achieve the same current. Generally, the voltage of the first gear is set higher than the rated voltage of the heating element, and two gears are set. In this way, the heating element can still have a good sintering effect after the resistance increases, thereby extending the service life of the heating element.

[0057] Preferably, the rated voltage across the heating element is 75-85% of the lowest voltage of the transformer, for example, it may be 75%, 76%, 78%, 80%, 82%, 84% or 85%.

[0058] It is worth mentioning that when customizing the rated voltage at both ends of the heating element, a certain margin needs to be left. Generally, 1.2 to 1.5 times is the best. In this way, when adjusting the transformer's low-speed voltage to 80%, the resistance parameters are adjusted so that the heating element can pass the rated current. In this way, the heating element has an equivalent margin of 1.4 to 2.0 times, which lays the foundation for extending the service life of the heating element.

[0059] The present invention sets the transformer into two stages, which can reduce the adjustment pressure of the thyristor module on the one hand, and on the other hand, the voltage control of the transformer is more stable. The voltage of the transformer is adjusted during the sintering stage to correspond to the resistance value of the corresponding heating element, so that it has a current value equivalent to or even greater than the initial current I0, so as to ensure the sintering effect and improve the service life of the heating element.

[0060] During the adjustment process of power limitation, the adjustment may be performed according to a single increase of 10% to 20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0061] Preferably, the control method also includes: during the sintering process, according to the temperature data fed back by the temperature control instrument, adjusting the power regulation module to change the conduction angle of the waveform in the heating element input voltage or change the frequency of the waveform in the heating element input voltage, thereby adjusting the power limitation at both ends of the heating element until the temperature reaches the temperature preset by the temperature control instrument.

[0062] Preferably, the determination current is a rated current of the heating element.

[0063] Preferably, when the heating element is a silicon carbide rod, the determination current is 18 to 22 A, for example, it can be 18 A, 18.5 A, 19 A, 19.5 A, 20 A, 20.5 A, 21 A, 21.5 A or 22 A, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0064] Preferably, when the heating element is a silicon molybdenum rod, the determination current is 55 to 65 A, for example, it can be 55A, 56A, 57A, 58A, 59A, 60A, 61A, 62A, 63A, 64A or 65A, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0065] Preferably, when the heating element is a silicon carbide rod, the voltage of the first gear is 60-100V, for example, it can be 60V, 65V, 69V, 74V, 78V, 83V, 87V, 92V, 96V or 100V, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0066] Preferably, when the heating element is a silicon carbide rod, the voltage of the second gear is 100-150V, for example, it can be 100V, 106V, 112V, 117V, 123V, 128V, 134V, 139V, 145V or 150V, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0067] Preferably, when the heating element is a silicon molybdenum rod, the voltage of the first gear is 15-25V, for example, it can be 15V, 16V, 17V, 18V, 19V, 20V, 21V, 22V, 23V, 24V or 25V, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0068] Preferably, when the heating element is a silicon molybdenum rod, the voltage of the second gear is 25-40V, for example, it can be 25V, 26V, 28V, 30V, 32V, 33V, 35V, 38V or 40V, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0069] In a third aspect, the present invention provides a sintering furnace, comprising the heating control device for extending the life of the heating element as described in the first aspect.

[0070] The heating element in the sintering furnace provided by the present invention has a long service life and broad application prospects.

[0071] Preferably, the sintering furnace is a dental sintering furnace.

[0072] Compared with the prior art, the present invention has at least the following beneficial effects:

[0073] The heating control device and control method for extending the service life of the heating element provided by the present invention can increase the sintering life of the heating element from 200 heats to 800 heats without changing the electronic control module and the heating element, taking the silicon carbide heating element as an example, thereby increasing the service life of the sintering furnace and having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a circuit diagram for heating control using only a solid-state relay module.

[0075] Figure 2 Taking silicon carbide as an example, this is a schematic diagram showing how the resistance of the heating element changes with the furnace temperature.

[0076] Figure 3 It is a schematic diagram of a heating control device for extending the life of a heating element provided in Example 1 of the present invention.

[0077] Figure 4 Schematic diagram of a double-threaded silicon carbide rod provided in Example 1 of the present invention.

[0078] Figure 5 It is a schematic diagram of the change of current with furnace temperature under different voltages provided in Example 1 of the present invention.

[0079] Figure 6 It is a schematic diagram of adjusting the conduction angle of the thyristor module in the early and late service stages provided by Example 1 of the present invention.

[0080] Figure 7 This is a flow chart of a heating control method for extending the life of a heating element provided in Example 1 of the present invention.

[0081] Figure 8 This is a schematic diagram of a heating control device for extending the life of a heating element provided in Example 3 of the present invention.

[0082] Fig. 9 This is a flow chart of a heating control method for extending the life of a heating element provided in Example 3 of the present invention.

[0083] Fig.10It is a schematic diagram of adjusting the frequency of the solid-state relay provided in Example 3 of the present invention.

[0084] In the figure, 1. transformer; 11. first end of transformer; 12. second end of transformer; 13. third end of transformer; 14. fourth end of transformer; 2. temperature control instrument; 21. first end of temperature control instrument; 22. second end of temperature control instrument; 3. power regulation module; 31. power regulation input end; 32. power regulation output end; 4. ammeter; 5. heating element; 6. control system. DETAILED DESCRIPTION

[0085] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0086] It should be understood that, in the description of the present invention, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0087] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0088] Example 1

[0089] This specific embodiment provides a heating control device that extends the life of the heating element. Figure 4 The heating control device includes a heating element 5, an AC power supply, a transformer 1 and a power adjustment module 3.

[0090] The power regulation module 3 is a thyristor module.

[0091] The AC power supply is used to provide power, and the AC power supply transmits current to the heating element 5 through the transformer 1; the power adjustment input terminal 31 is electrically connected to the transformer 1, and the power adjustment output terminal 32 is electrically connected to the heating element 5; the thyristor module is used to adjust the conduction angle of the waveform in the input voltage of the heating element 5; the heating element 5 is used for heating and temperature rise, and the heating element 5 is a silicon carbide rod. The silicon carbide rod is a double-threaded silicon carbide rod.

[0092] The transformer 1 includes a primary coil and a secondary coil coupled to each other, the primary coil is connected to the AC power source, and the secondary coil is connected to the heating element 5 .

[0093] See also Figure 3 , the number of the double-threaded silicon carbide rod is single. The outer diameter of the double-threaded silicon carbide rod is 75 mm. The double-threaded silicon carbide rod has a hollow hole, and the diameter of the hollow hole is 55 mm. The spacing between the spiral notches in the double-threaded silicon carbide rod is 3.5 mm. The double-threaded silicon carbide rod includes a threaded hot end and a tubular cold end located at one end of the threaded hot end.

[0094] The thyristor module is a thyristor phase-shift trigger. The heating control device also includes a temperature control instrument 2 and a control system 6 connected to the thyristor module. The temperature control instrument first end 21 and the temperature control instrument second end 22 of the temperature control instrument 2 are respectively connected to the two ends of the power adjustment module 3.

[0095] The heating control device further comprises an ammeter 4 , and two ends of the ammeter 4 are electrically connected to the thyristor module and the heating element 5 respectively.

[0096] The voltage of the transformer 1 is set to at least two levels.

[0097] Among them, the current flows from the L pole into the first end 11 of the transformer, the first end 11 of the transformer is the input end, and the third end 13 of the transformer is the output end of the variable gear. The current flows into the power adjustment input end 31 through this, flows out from the power adjustment output end 32 through the ammeter 44 and is input into the heating element 55 for heating, and the return value is output from the heating element 55 to the fourth end 14 of the transformer, and the second end 12 of the transformer senses the current flowing back to the N pole.

[0098] This specific embodiment also provides a control method for extending the life of the heating element, see Figure 7 , the control method comprises:

[0099] (1) In the initial service period of the heating element, the transformer is set to the first output voltage, and the thyristor module is adjusted to limit the output voltage so that the current passing through the heating element is the initial current I0;

[0100] (2) Determine whether the current is greater than the determination current (20A). If so, proceed to step (3); if not, proceed to step (4);

[0101] (3) maintaining the current output voltage and power limit of the transformer and performing temperature-raising sintering, during which the current I1 passing through the heating element is monitored in real time; and repeating step (2) until the sintering process is completed, and ending the control after the sintering process is completed;

[0102] (4) Determine whether the power limit of the thyristor module reaches 100%; if not, proceed to step (5); if yes, proceed to step (6);

[0103] (5) adjusting the power limit of the thyristor module upward to increase the current, and repeating the current determination in step (2);

[0104] (6) Determine whether the transformer is in the second gear. If not, adjust the transformer to the second gear and loop back to step (2) to perform current determination. If yes, determine that the abnormality has ended and end control.

[0105] Specifically, the rated voltage of a single double-threaded silicon carbide rod is 60V, and the voltage of the transformer is set to two levels, with the first level and the second level being 80V and 120V respectively.

[0106] During the sintering process, according to the temperature data fed back by the temperature control instrument, the thyristor module is adjusted to change the conduction angle of the waveform in the input voltage of the heating element, thereby adjusting the equivalent voltage and equivalent power at both ends of the heating element to adjust the power limit until the temperature reaches the preset temperature of the temperature control instrument.

[0107] Optionally, for the adjustment of the conduction angle in this specific implementation mode, see Figure 6 , Figure 6 The left side shows the voltage waveform in the early stage of service. The shaded area is the effective heating power of the heating element. In the early stage of service, the resistance of the heating element is small and the equivalent voltage applied to the heating element is large, so the conduction angle of the thyristor module is relatively small, that is, the time when the horizontal axis of the shaded area is on; in the later stage of service, after the heating element ages, the resistance becomes larger and the equivalent voltage becomes smaller, such as Figure 6 On the right side, in order to achieve the effective heating power in the early stage of service, it is necessary to increase the conduction time of the thyristor and lengthen the on time so that the shadow areas of the left and right waveforms are the same, so that the sintering furnace using the aged heating element has the same heating capacity as the initial unaged heating element, thereby extending the service life of the heating element.

[0108] During the adjustment process of the present invention, since the cold resistance of the heating element at room temperature is very large, it is not suitable to operate at full power. The power needs to be adjusted step by step to give the heating element and the furnace a certain adaptation time to reduce the difference between the cold and hot stress on the surface of the heating element. The current is detected to determine whether it is greater than 20A. If it is greater than 20A, it indicates that the resistance of the heating element is good, and the power limit is further adjusted upward to 25%. If it is less than 20A, it indicates that the heating element has a certain degree of aging. After switching the transformer to 120V, the power limit is 25%.

[0109] Through such regulation, the present invention can directly detect the aging condition of the heating element during the production process and make adjustments in real time.

[0110] from Figure 5 It can be seen that in the early stage of the sintering furnace, when the resistance of the heating element has not been oxidized, the resistance value is small, and the transformer uses 80V output. For specific current, see Figure 5 The solid line, the silicon carbon rod resistance is oxidized in the later stage, the current under the same voltage can no longer meet the heating demand, the transformer is switched to 120V, the specific current is shown in Figure 5 From the dotted line, we can see that the current of the silicon carbon rod has been significantly improved, ensuring the normal heating rate of the furnace.

[0111] In summary, the control method and control structure for extending the life of the heating element provided in this embodiment select a single reaction-sintered large-aperture double-threaded silicon carbide rod, which eliminates the situation where the resistance of multiple silicon carbide rods does not match during the aging process. The reaction sintering process makes the internal pores of the silicon carbide rod smaller, reducing the oxidation reaction with the air, and setting the rated voltage of the heating element at 80% of the lowest rated output voltage of the transformer. The thyristor phase-shift trigger is used. During the normal sintering process, the power is adjusted step by step so that when the transformer outputs 80%, the heating element can work normally. When the heating element ages, it outputs 100% of the lowest rated output voltage to increase the working voltage at both ends of the heating element; when the heating element further ages, the voltage is switched and the voltage is increased again, thereby increasing the working current of the heating element, breaking the balance point of alternating hot and cold, so that the sintering furnace is heated again to reach the required sintering temperature, thereby increasing the service life of the sintering furnace.

[0112] Example 2

[0113] This specific embodiment provides a heating control device for extending the life of a heating element, which is basically the same as Example 1, and differs from Example 1 in that:

[0114] The silicon carbide rod is a single-threaded silicon carbide rod. The outer diameter of the single-threaded silicon carbide rod is 80 mm. The single-threaded silicon carbide rod has a hollow hole, and the diameter of the hollow hole is 55 mm. The spacing between the spiral notches in the single-threaded silicon carbide rod is 6 mm.

[0115] This specific embodiment also provides a control method for extending the life of a heating element, and the control method is different from that of Example 1 in that:

[0116] Specifically, the rated voltage of a single single-threaded silicon carbide rod is 70V, and the voltage of the transformer is set to two levels, with the first level and the second level being 80V and 130V respectively.

[0117] During the sintering process, according to the temperature data fed back by the temperature control instrument, the thyristor module is adjusted to change the conduction angle of the waveform in the input voltage of the heating element, thereby adjusting the equivalent voltage and equivalent power at both ends of the heating element until the temperature reaches the preset temperature of the temperature control instrument.

[0118] The control method and control structure of a single single-threaded silicon carbide rod provided in this embodiment uses a single reaction-sintered large-aperture single-threaded silicon carbide rod, which eliminates the situation where the resistance of multiple silicon carbide rods does not match during the aging process. The reaction sintering process makes the internal pores of the silicon carbide rod smaller, reducing the oxidation reaction with the air. In addition, the rated voltage of the heating element is set lower than the lowest rated output voltage of the transformer, leaving a margin for subsequent adjustments, and a two-stage transformer control measure is adopted to increase the working current of the heating element step by step, breaking the balance point of alternating hot and cold, so that the sintering furnace heats up again to reach the required sintering temperature, thereby increasing the service life of the sintering furnace; and in the normal sintering process, a thyristor phase-shift trigger is used to adjust the power step by step to ensure that the heating element can work normally.

[0119] In embodiments 2 to 3, a thyristor module is used for adjustment, which has the advantages of small fluctuation, relatively smooth output current and voltage, and stronger low-frequency anti-interference ability.

[0120] Example 3

[0121] This specific embodiment provides a heating control device for extending the life of a heating element, which is basically the same as Example 1, see Figure 8 , which is different from Example 1 in that:

[0122] The power regulation module is a solid-state relay.

[0123] The heating element is a solid U-shaped silicon-molybdenum rod. The diameter of the solid U-shaped silicon-molybdenum rod is 75 mm.

[0124] This specific embodiment also provides a control method for extending the life of the heating element, see Fig. 9 , the control method comprises:

[0125] (1) In the initial service period of the heating element, the transformer is set to the first output voltage, and the solid-state relay is adjusted to limit the output voltage so that the current passing through the heating element is the initial current I0;

[0126] (2) Determine whether the current is greater than the determination current (60A). If so, proceed to step (3); if not, proceed to step (4);

[0127] (3) maintaining the current output voltage and power limit of the transformer and performing temperature-raising sintering, during which the current I1 passing through the heating element is monitored in real time; and repeating step (2) until the sintering process is completed, and ending the control after the sintering process is completed;

[0128] (4) Determine whether the power limit of the solid-state relay reaches 100%; if not, proceed to step (5); if yes, proceed to step (6);

[0129] (5) adjusting the power limit of the solid-state relay upward to increase the current, and repeating the current determination of step (2);

[0130] (6) Determine whether the transformer is in the second gear. If not, adjust the transformer to the second gear and loop back to step (2) to perform current determination. If yes, determine that the abnormality has ended and end control.

[0131] Specifically, the rated voltage of the solid U-shaped silicon molybdenum rod is 15V, and the voltage of the transformer is set to two levels, with the first level and the second level being 20V and 30V respectively.

[0132] During the sintering process, according to the temperature data fed back by the temperature control instrument, the solid-state relay is adjusted to change the frequency of the waveform in the input voltage of the heating element, thereby adjusting the equivalent voltage and equivalent power at both ends of the heating element to adjust the power limit until the temperature reaches the preset temperature of the temperature control instrument.

[0133] Optionally, for the adjustment of the frequency in this specific embodiment, see Fig.10 , Fig.10 The shaded area is the effective heating power of the heating element, where 100% power, 50% power limit and 25% power limit are shown in the figure. Fig.10 As shown in the figure, in the early stage of service, the resistance of the heating element is small and the equivalent voltage applied to the heating element is large, so the frequency of the 25% power limit on the far left can be used for adjustment; in the later stage of service, after the heating element ages, the resistance becomes larger and the equivalent voltage becomes smaller, as shown in the figure. Fig.10 On the left, in order to achieve the effective heating power in the early stage of service, it is necessary to increase the power and lengthen the connection time so that the sintering furnace using the aged heating element has the same heating capacity as the initial non-aged heating element, thereby extending the service life of the heating element.

[0134] The control method and control structure of the silicon-molybdenum rod provided in this embodiment select the rated voltage of the heating element to be set lower than the lowest rated output voltage of the transformer, leaving a margin for subsequent adjustment, and adopting a two-stage transformer control measure to increase the working current of the heating element step by step, breaking the balance point of alternating hot and cold, so that the sintering furnace is heated again to reach the required sintering temperature, thereby increasing the service life of the sintering furnace; and in the normal sintering process, a solid-state relay is used to adjust the power step by step to ensure that the heating element can work normally.

[0135] This specific embodiment also provides a sintering furnace, which includes any one of the above-mentioned heating control devices for extending the life of the heating element.

[0136] The heating element in the sintering furnace provided by the present invention has a long service life and broad application prospects.

[0137] Preferably, the sintering furnace is a dental sintering furnace.

[0138] The present invention illustrates the detailed features of the present invention through the above embodiments, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvement to the present invention, equivalent replacement of the technical features selected by the present invention, addition of auxiliary technical features, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A heating control device for extending the life of a heating element, characterized in that: The heating control device includes a heating element, an AC power supply, a transformer and a power adjustment module; The AC power source is used to provide electric power; and the AC power source transmits electric current to the heating element through a transformer; The input end of the power regulating module is electrically connected to the transformer, and the output end of the power regulating module is electrically connected to the heating element; the power regulating module is used to adjust the conduction angle of the waveform in the input voltage of the heating element, and / or to adjust the frequency of the waveform in the input voltage of the heating element; The heating element is used for heating and increasing the temperature.

2. The heating control device according to claim 1, characterized in that: The transformer includes a primary coil and a secondary coil coupled to each other, the primary coil is connected to the AC power source, and the secondary coil is connected to the heating element.

3. The heating control device according to claim 1 or 2, characterized in that: The heating element includes any one of a silicon carbon rod, a silicon molybdenum rod or a resistance wire, or a combination of at least two of them.

4. The heating control device according to claim 1, characterized in that: The power regulation module includes a solid-state relay and / or a thyristor module; The thyristor module is a thyristor phase-shift trigger; And / or, the heating control device also includes a temperature control instrument and a control system connected to the power regulation module.

5. The heating control device according to claim 1, characterized in that: The heating control device further comprises an ammeter, and two ends of the ammeter are electrically connected to the power adjustment module and the heating element respectively; And / or, the voltage of the transformer is set to at least two levels.

6. A control method for extending the life of a heating element, characterized in that: The control method is carried out by using the heating control device for extending the life of the heating element as described in any one of claims 1 to 5.

7. The control method according to claim 6, characterized in that: The control method comprises: (1) In the initial service period of the heating element, the transformer is set to the first output voltage, and the power regulation module is adjusted to limit the output voltage so that the current passing through the heating element is the initial current I0; (2) Determine whether the current is greater than the determination current. If so, proceed to step (3); if not, proceed to step (4); (3) maintaining the current output voltage and power limit of the transformer and performing temperature-raising sintering, during which the current I1 passing through the heating element is monitored in real time; and repeating step (2) until the sintering process is completed, and ending the control after the sintering process is completed; (4) Determine whether the power limit of the power regulation module reaches 100%; if not, proceed to step (5); if yes, proceed to step (6); (5) upwardly adjusting the power limit of the power regulation module to increase the current, and repeating the current determination of step (2); (6) Determine whether the transformer is in the second gear. If not, adjust the transformer to the second gear and loop back to step (2) to perform current determination. If yes, determine that the abnormality has ended and end control.

8. The control method according to claim 7, characterized in that: In the later stage of service, the resistance of the heating element is a first resistance R1, and the range of the first resistance R1 is 100-200% of the initial resistance R0 of the heating element in the early stage of service; The voltage of the second gear is 1.2 to 2.0 times the voltage of the first gear.

9. The control method according to claim 7 or 8, characterized in that: The control method also includes: during the sintering process, according to the temperature data fed back by the temperature control instrument, adjusting the power regulation module to change the conduction angle of the waveform in the heating element input voltage or the frequency of the waveform in the heating element input voltage, thereby limiting the power at both ends of the heating element until the temperature reaches the temperature preset by the temperature control instrument.

10. A sintering furnace, characterized in that: The sintering furnace comprises the heating control device for extending the life of the heating element according to any one of claims 1 to 5.

Images