JPH01247986A - Control of temperature of crucible type molten metal holding furnace - Google Patents

Abstract

PURPOSE:To avoid a heater chamber from being heated or cooled more than necessity with respect to the amount of difference in the temperature of molten metal, by a method wherein heating is controlled by setting the range of the temperature of the heater chamber stepwisely with respect to the set value of the temperature of the molten metal. CONSTITUTION:The upper limit (tah2) and the lower limit (tal2) of the temperature (ta) of a heater chamber 4 are set with respect to the set value TmO of a molten metal temperature Tm, further, the upper limit (tah1) and the lower limit (tal1) of the temperature of the heater chamber are set stepwisely with respect to the allowable values Tmh, Tml of the set value TmO. The temperature (ta) of the heater chamber and the molten metal temperature Tm are detected by thermocouples 10, 8 respectively and the amount of difference is obtained from the molten metal temperature Tm and the set value TmO while theses detecting signals are operated to control the output of a heater 11 in an area B through PID control. The heater is put forcibly ON in an area A while the heater is forcibly put OFF in an area C. According to this method, the response property of temperature control may be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a temperature control method for a crucible-type molten metal holding furnace for maintaining molten metal in a crucible in a desired state.

(Prior Art) A crucible-type molten metal holding furnace is one in which a crucible made of metal or refractory is inserted into a furnace body, and a heater is attached around the crucible to heat the crucible. To control the temperature of the molten metal in the crucible by heating this heater, a temperature sensor is installed to detect the heater temperature or the ambient temperature around the crucible, or a temperature sensor is installed inside the molten metal. If the temperature sensor is in the molten metal, there is a possibility that the heater will be heated excessively, so an upper limit circuit or the like is added. In addition, as another method,
In Japanese Patent No. 1-157843, the heater is controlled at a predetermined temperature.

A method has been proposed in which the molten metal is cooled when the molten metal temperature rises above a set value. The heater was operated intermittently based on the data from these temperature sensors, and the temperature of the molten metal in the crucible was maintained in proportion to the deviation from the set value using PID control, etc., which took into account the differential and integral values of the deviation.

(Problems to be Solved by the Invention) However, since the heater and the crucible are not in close contact with each other and the heat from the heater is transmitted through the air and the crucible, there is a time delay in heat transfer. FIG. 6 illustrates the relationship between the molten metal temperature and the heater chamber temperature when a temperature sensor is provided for the molten metal.

Points A and B are the points of temperature change (disturbance) when molten metal is replenished or when the lid of the crucible is opened and oxides (slag) are removed.The heater is turned on in response to the temperature change at point A. heated. Then, when the upper limit temperature Tab of the heater reaches the set molten metal temperature Two, the heater is turned off, but the molten metal temperature rises due to the residual heat of the air and the crucible. Thereafter, when the molten metal temperature cools naturally and falls below the set molten metal temperature↑PengO, the heater is turned on, but the heater chamber temperature drops too low and the molten metal temperature decreases until it reaches equilibrium with the heater chamber temperature. Due to the presence of air in this way, in other words, the temperature sensor and the heat source are far apart, so the responsiveness of molten metal temperature control is poor.Moreover, when the molten metal is naturally cooled down to the set temperature, the heater Room temperature is too low. The same can be said for point B. However, the means disclosed in the above publication consumes a lot of energy.

An object of the present invention is to provide a temperature control method for a crucible-type molten metal holding furnace that can control the temperature of molten metal with a smaller deviation from a set value.

(Means for Solving the Problems) In order to achieve the above object, the present invention sets the first and lower limits of the heater chamber temperature ta heated by the heater to the molten metal temperature? + set value Two, further set the upper and lower limits of the heater chamber temperature in stages corresponding to the allowable value of the set value T intestine 0, detect the heater chamber temperature ta and the molten metal temperature Tm, Moreover, it is characterized in that the amount of deviation is determined from the molten metal temperature Tts and the set value ↑, and these detection signals are calculated to perform PID control of the heater output in the heater chamber.

(Function) When the heating temperature of the heat source is within the heating temperature range, the heat source is activated by a detection signal of molten metal temperature higher or lower than the set value, or a calculation signal of the amount of deviation (increase or decrease in temperature). Control and maintain the temperature of the molten metal. Note that if the heating temperature is outside the set range, the heat source is forcibly activated or stopped.

Furthermore, if there is a sudden temperature change within the heating temperature range, the molten metal temperature is determined to be high or low and whether it was rising or falling, and it is determined whether the heat source should be activated or stopped.

(Example) An example of the method of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 shows an apparatus for carrying out the method of the invention.

This device consists of a temperature sensor placed in the holding furnace and a control device that controls the heater using this temperature detection signal.
In the figure, a holding furnace 1 is one in which a crucible 2 made of metal or refractory is inserted into a heater chamber 4 which is provided with a furnace body 3 and has an upward opening. The crucible 2 is filled with molten metal 5 and sealed with a furnace lid 6. The seven rungs 2a formed on the edge of the crucible 2 support the crucible 2 from the furnace body 3 and hermetically seal the heater chamber 4.

A thermocouple 8 covered by a protective tube 7 is immersed in the molten metal 5, and is fitted and supported by the furnace lid 6. A protective tube 9 is provided in the heater chamber 4 to protrude from the side wall of the furnace body 3, and a thermocouple 10 is inserted into the protective tube 9. A heater 11 for heating the crucible 2 is arranged on the peripheral wall of the heater chamber 4 of the furnace body 3, and a control circuit 12 for adjusting the output of the heater.
is connected to a final stage element such as a thyristor 13.

The thermocouple 8 is connected to the control circuit 12 via the molten metal temperature controller 14.
It is connected to the. Similarly, the thermocouple 10 is also connected to the control circuit 12 via the heater room temperature controller 15 .

The molten metal temperature controller 14 receives the detection signal from the thermocouple 18 and outputs a PID signal calculated from the amount of deviation from the molten metal temperature set value Two, its rate of change, etc.
When the upper limit temperature Tmh and lower limit temperature T1, which are the allowable values of o, are exceeded, a molten metal upper limit signal and a molten metal lower limit signal are output, respectively.

The heater room temperature controller 15 receives the detection signal from the thermocouple 10 and determines the lower limit temperature TALL, which determines the heating temperature range.
ta12 (tall < ta12) or upper limit temperature tah1. tah2 (tahl > tah
2), the respective signals are output.

Here, the L limit temperature of the heater room temperature tab4, tah2
, how to determine the lower limit temperatures ta11 and ta12 will be shown.

Upper limit temperature tahl and lower limit temperature ta of heater room temperature ta
ll is appropriately set within a range in which the molten metal temperature Tm quickly recovers when affected by a relatively large disturbance expected in this control system, and does not significantly overshoot the molten metal temperature set value Two. Also, the heater room temperature ta
The upper limit temperature tah2 and the lower limit temperature ta12 are the heater chamber temperature range in which the balance of heat is balanced in the absence of large disturbances. In this way, the northern and lower limits of the heater room temperature are set in stages. Since this equilibrium temperature is affected by changes in the amount of molten metal 5 and the thermal conductivity of the crucible 2, the highest temperature is tah2 and the lowest temperature ta12.

The upper limit temperature Tmh of the molten metal temperature Ts is such that the molten metal temperature TII is the set value Two, and the heater chamber temperature ta is the upper limit temperature t.
At ah2, the temperature is set within a range in which the molten metal temperature Tm does not exceed this while the heater output is decreasing. Lower limit temperature T
Similarly, in case 1, when the molten metal temperature ↑1 is the set value Ta+o and the heater room temperature ta is the lower limit temperature ta12, the molten metal temperature T+s does not fall below this lower limit temperature ↑ml while the heater output is rising. Set in range.

Specifically, as an example, a graphite crucible 1 is placed in a container A1.
When storing molten metal, set the molten metal temperature setting value T + ao to 70
When the upper limit temperature ↑IIh is set to 0°C, the upper limit temperature ↑ IIh is set to 705°C, and the lower limit temperature Tml is set to 685°C, the heater chamber temperature setting value is the lower limit temperature tall, and ta12 is [i80°C.

720℃, upper limit temperature tah1, tah2 800
The temperature was 740°C.

Next, the method of the present invention carried out based on the temperature thus determined will be explained with reference to the flowchart of FIG.

First, the molten metal temperature T is detected and it is determined whether it is within the allowable value (steps 1 and 2.3), and then the heater chamber temperature T is determined.
It is determined whether a is within the northern limit temperature tah2 and the lower limit temperature talz (step 4.5). When these conditions are satisfied, the PID control W (step 6) is performed. Also,
When the molten metal temperature Trn is out of the allowable value, if the heater chamber temperature ta is higher than the upper limit temperature taJ, the heater is forcibly stopped (step 7.8), and if the heater chamber temperature ta is lower than the lower limit temperature tall, the heater is forcibly stopped. (step 9.10), otherwise P
Perform ID control. Note that even if the molten metal temperature Tm is within the allowable range, if the heater chamber temperature ta is higher than the upper limit temperature tah2, the heater is stopped (Step 4.8), and the lower limit temperature ta1
If the temperature is lower than 2, the heater is activated (
Steps 5, 10).

The operation status of the heater controlled in this way is divided into three regions A, B, and C as shown in Figure 3.A region where the heater is forcibly turned on, and a region where the heater is forced into the PID region.
Area B to control.

Area C is shown where the heater is forcibly turned off.

Next, in Fig. 4, when the molten metal temperature TI suddenly decreases from the equilibrium state (point A), even if the molten metal temperature Tm is in the middle of rising or falling, the amount of deviation of the molten metal temperature Tm and its rate of change, etc. According to the calculated PID signal, the heater chamber temperature ta is heated to rise. When the upper limit temperature tah1 of the range of heater chamber temperature ta is reached, the heater chamber temperature ta remains constant until the molten metal temperature Tm reaches the lower limit temperature Two of the allowable range, and cannot exceed the upper limit temperature tah1 set in one step. Not after that.

The molten metal temperature Tm is PID-controlled within a narrow range of upper limit temperature tah2 and lower limit temperature ta12 of the heater chamber temperature. Also,
PID control is performed in the same way when the molten metal temperature ↑1 rises rapidly.

FIG. 5 shows the distribution of PID control in another embodiment. In this method, the permissible value of the molten metal temperature Tm is divided into two stages, and the control range of the heater chamber temperature is divided into three stages, so the molten metal temperature Tm can be controlled more precisely, and the amplitude can be reduced efficiently against disturbances. can converge to the waveform of

(Effects of the Invention) The method of the present invention sets the molten metal temperature as described below and heats the molten metal by setting the temperature range of the heater chamber in stages. There is no heating or cooling of the room temperature.Therefore, in the case of sudden temperature rises of the molten metal, the lower limit of the heater room temperature is determined, so the molten metal will not be cooled too much. When raising the room temperature, since the upper limit temperature is set, the heating temperature is lower than in the past, the amount of heat loss is reduced, and therefore the energy for holding the molten metal can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a temperature control device for carrying out the method of the present invention, Fig. 2 is a flowchart showing the method of the present invention, and Fig. 3 is a diagram of the molten metal temperature for illustrating the classification of temperature control by the method of the present invention. The figure which shows the relationship between the range and the range of heater room temperature. FIG. 4 is a diagram showing the operating characteristics of temperature control of this device. Fig. 5 is a diagram showing the relationship between the molten metal temperature range and the heater chamber temperature range for classifying the temperature control according to another embodiment, and Fig. 6 is a diagram showing the operating characteristics of conventional temperature control. be. G... Molten metal temperature Two... Molten metal temperature setting value t
a... Heater room temperature patent applicant Toyota Motor Corporation (and 2 others) Figure Tm1. Enthusiasm warm summer Tmo... 8 corner i shop setting q tO...shi - evening view zi Sai 2 figure 3 P5't te kun hire tQ figure 4 heat word on introduction addition figure 5 ko - Ta! Easy to counterfeit 26 diagram heater! Temperature tQ tah

Claims (1)

[Claims] (1) The heating temperature range for heating the crucible is set in stages according to the allowable value of the set value for the set value of the molten metal temperature, and the molten metal temperature and the heating temperature are detected within this range. A temperature control method for a crucible-type molten metal holding furnace, characterized in that the amount of deviation in the temperature of the molten metal is determined, and the output of the heat source is controlled based on this detection signal and the deviation value.