JPS5970714A - Heating method in heat treatment furnace - Google Patents

Abstract

PURPOSE:To control securely the temp. in a heat treatment furnace with a reduction in required energy cost by providing electric heaters and a burner in combination in the furnace, supplying the prescribed quantity of the required quantity of heat with the burner and controlling the heaters to maintain the specified temp. in the furnace. CONSTITUTION:A required set temp. T deg.C is inputted to a temp. controller 11, and and a furnace 3 is heated up to the temp. T deg.C by starting a fan 7, igniting a burner 8 and energizing electric heaters 9. Since the furnace 3 is cold in the beginning when the heating is started, the burner 8 is operated to burn at a high level while the electric power to be supplied to the heaters 9 is increased. The heating period operates on the largest electric power but if several tens % of the required quantity of heat is supplied by the burner 8, the max. power can be decreased largely and since the heating time is shortened, the total energy cost required for the heating is economized. A power control board 10 decreases the power supply to the heaters 9 in accordance with the result of comparison between the signal from the thermocouple 12 of a controller 11 and a set value when the temp. in the furnace is approximate to the T deg.C. The heaters 9 are controlled by the board 10 and the burner 8 is put into the combustion state at a low level when the furnace temp. attains the T deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating method in a heat treatment furnace such as a quenching furnace or a tempering furnace.

Conventionally, heat treatment furnaces for various metal products have been known, including those that use a burner such as a heavy oil burner or gas burner as the heating device, and those that use an electric heater as the heating device. Each has advantages and disadvantages, and each is used depending on the object to be heat treated and the required heat treatment conditions. For example, when heat treating aluminum castings or aluminum alloy castings, it may be necessary to maintain the heating temperature within a range of approximately ±5°C from the desired temperature. In this case, a heat treatment furnace using an electric heater as a heating device is preferable. On the other hand, from the point of view of energy cost, the fact is that the electric power cost is extremely high, so a heat treatment furnace using a burner as a heating device is preferable. Generally speaking, for example, in the case of cast parts for automobiles, the walls are made thinner to reduce weight, so it may not be possible to apply sufficient vibration and shock during the core sand removal process. When the object is a component, it is desirable to bake core sand containing thermosetting resin in the heat treatment process, but in a heat treatment furnace that uses a burner as a heating device, the oxygen concentration in the furnace decreases. There are cases where the core sand cannot be baked sufficiently, so from the viewpoint of sufficiently baking the core sand, a heat treatment furnace using an electric heater as a heating device is preferable.

However, in the past, it was common to heat with either an electric heater or a burner, and the reality is that it is impossible to satisfy either of the conflicting requirements mentioned above. When aluminum alloy castings are heat treated, they are heated exclusively by electric heaters, which requires a large amount of energy cost.

This invention was made in view of the above circumstances, and it is possible to easily and accurately control the temperature inside the furnace, and also to reliably burn the core sand attached to the object. The object of the present invention is to provide a heating method in a heat treatment furnace that can reduce energy costs. The feature of this invention is that the burner is fixedly combusted so that the calorific value is constant, and a predetermined proportion of the required heat is supplied into the furnace, while the remainder of the required heat is supplied by the electric heater. Moreover, the heat amount of the electric heater is controlled so that the temperature inside the furnace is constant.

The present invention will be described in detail below based on examples.

First, to explain the apparatus for implementing the method of the present invention, FIG. 1 is a schematic cross-sectional view showing an example of a hot air circulation type continuous heat treatment furnace configured to implement the method of the present invention. Conveyor 2 that conveys 1
is provided in category 3, and a baffle 4 is provided in category 3 to cover the heat-treated product basket 1 on the conveyor 2. Hot air currents 5 are formed on the left and right side walls of the baffle 4, and the ceiling of the baffle 4 has a suction port opened toward the inside of the panfur 4 and the furnace 3.
A circulation fan 7 driven by a motor 6 provided on the upper part of the baffle 4 is provided, so that the gas in the group 3 is circulated between the inside and outside of the baffle 4 by the circulation fan 7.

Furthermore, a burner 8 such as a heavy oil burner or a gas nozzle is installed on the side wall of the furnace 3 toward the inside of the furnace 3, more precisely between the baffle 4 and the furnace wall, and is further installed on the ceiling of the furnace 3. , an electric heater 9 is provided hanging down inside the casing 3. The electric heater 9 is connected to a power control panel 10 for controlling the amount of heat generated, and a temperature controller 11 is further connected to the power control panel 10. The temperature controller 11 has a function of inputting a predetermined set temperature and a function of comparing and calculating an input signal from a predetermined temperature detector and the set temperature and outputting the result. A thermal lightning pair 12 is inserted inside the baffle 4 as a container. Therefore, the temperature controller 11 compares and calculates the signal output by the thermal lightning pair 12 according to the temperature inside the baffle 4 and the set value corresponding to a predetermined set temperature, and outputs the result. The power charge t[li! 10
is operated to control the amount of heat generated by the electric heater 9.

Next, the heating method in the heat treatment furnace configured as described above, that is, the present invention will be explained in detail.

First, input a desired set temperature rIT°C (for example, 500°C) into the temperature controller 11, operate the circulation fan 7, ignite the burner 8 in this state, and energize the electric heater 9 to generate heat. . Fig. 2 <A) is a diagram showing the transition of the temperature inside the furnace, and Fig. 2 (B) is a diagram showing the calorific value of the burner 8 and the electric heater 9. Since it is cooled to about room temperature, it is necessary to raise the temperature of the furnace 3 to the set temperature T℃ before heat treatment. Therefore, at the beginning of heating, the burner 8 is burned at a high level to generate a large amount of heat (and The amount of power supplied to the electric heater 9 is increased to increase its calorific value.The electric power during this heating period becomes the maximum electric power, but several tens of percent, for example 20 to 70%, of the amount of heat required for heating is supplied to the burner 8. By supplying electricity by heating, the maximum power can be significantly lowered compared to the case of heating only with electric heaters, and therefore the contract power can be lowered in the case of power purchase, which greatly contributes to lower running costs. On the other hand, if electricity is used up to the limit of the existing contract electricity in the heating process, the amount of heat generated by burner 8 will be added, so the heating time can be shortened, and therefore the electricity consumption will be reduced. Even if the energy cost consumed by the burner 8 is taken into account, the total energy cost required for temperature increase can be reduced.

As a result of heating the inside of the furnace 3 as described above, when the internal temperature of the furnace 3 reaches close to the set temperature T°C, the temperature changes from the thermocouple 12 in the temperature controller 11 due to local temperature variations. Since the power control panel 10 reduces the power supplied to the electric heater 9 based on the comparison result between the input signal and the set value, the heat generation R of the electric heater 9 is temporarily reduced. That is, the internal temperature of the furnace 3 is controlled by controlling the calorific value of the electric heater 9, and as a result, when the entire inside of the furnace 3 reaches the set temperature T°C, the electric heater 9 is controlled by the power consumption board 10 and its temperature is increased. The calorific value decreases significantly, and at the same time, burner 8 is switched to a low-level combustion state,
In this state, the heat-treated product is placed in the basket 1 and fed into the casing 3, thereby heating, that is, running the heat-treated product. Therefore, even during running, heating is performed by the burner 8 and the electric heater 9, but the combustion in the burner 8 in this case is fixed combustion at a low level and with a constant calorific value. Low level combustion here refers to the secondary air to burner 8 and the furnace 3 of the heat treated product.
This is a combustion state in which the 02 concentration within Class 3 becomes 15% or more due to outside air entering the Class 3 interior when the door is opened and closed during loading and unloading.

In other words, according to the experiments of the present inventors, in order to burn off the core sand adhering to the heat-treated product,
This is because it is sufficient that the degree of 1 degree is at least about 15%. Figure 3 shows 021 in class 3 in the experiment conducted by the inventors.
It shows the change in degree.

By the way, during running, outside air enters when the door is opened and closed to carry in and take out heat-treated products, new heat-treated products at a temperature as low as air temperature are brought in, heated heat-treated products are carried out, and heat-treated products are removed from the furnace wall. Furnace 3 due to heat radiation, etc.
The internal temperature of decreases, but when the decrease in internal temperature occurs,
The temperature controller 11 compares the input signal from the thermal lightning pair 12 with a set value and outputs a signal, and the power control panel 10 increases the power indication supplied to the electric heater 9 based on the output signal, so that the furnace 3 The inside of the furnace 3 is heated more than before, and as a result, the internal temperature of the furnace 3 is kept almost constant at the set temperature T°C. That is, even during running, the internal temperature of the furnace 3 is controlled by controlling the amount of heat generated by the electric heater 9.

Therefore, it is generally difficult to delicately control the calorific value of the burner 8, and in addition to this, it is necessary to control the secondary air of the burner 8 in order to adjust the 02 concentration within Class 3, but the method of this invention As described above, since the burner 8 is set to fixed combustion and the temperature 1iIJ t[I is controlled by controlling the calorific value of the electric heater 9, the internal temperature of the furnace 3 can be controlled easily and accurately. Furthermore, by installing the burner 8, a heat source with a lower energy unit price than electricity is used in combination, so the total energy cost can be kept low.

In addition, although a continuous heat treatment furnace was used as an example in the above example,
Of course, the present invention can also be applied to a batch type heat treatment furnace.

As is clear from the above description, according to the heating method of the present invention, the burner is fixedly combusted so that the calorific value is constant, and a predetermined proportion of the required heat is supplied into the furnace. The remainder is supplied by an electric heater, and the amount of heat from the electric heater is controlled so that the temperature inside the furnace remains constant.Since temperature control is performed electrically, the internal temperature of the furnace can be easily and accurately adjusted. Furthermore, since energy sources such as heavy oil and LPG, which have lower energy unit costs than electricity, are used in addition to electricity, the total required energy cost can be lowered, and at the same time, the combustion state of the burner can be kept below a predetermined level. By doing so, the core sand can be burnt off well. In addition, a large amount of heat is required to raise the temperature at the beginning of heating, but by using the method of this invention in combination with a burner, the required electric power tube can be significantly reduced compared to the conventional method, so in the case of electricity purchase. The contract power can be kept low, and at the same time, the required heating time is shortened, so power consumption is reduced, and from these points of view as well, the required energy cost can be reduced. Furthermore, by installing a burner, the internal pressure of the furnace becomes a positive pressure that is slightly higher than atmospheric pressure, which reduces the amount of air that enters the furnace when the door is opened and closed, thus making the temperature distribution inside the furnace more uniform. I can do it.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view showing an example of a heat treatment furnace for carrying out the method of the present invention, Figure 2 (A> is a diagram showing changes in the internal temperature of the furnace, and Figure 2 (B) is an electric heater. Fig. 3 is a diagram showing the transition of the calorific value between the burner and the burner, and Fig. 3 is a diagram showing the transition of 02m degrees inside the furnace. 3...furnace, 8...burner, 9...N heat heater , 10...Electricity charge m+ panel, 11...Temperature controller,
12...Thermocouple. Applicant Toyota Motor Corporation Representative Patent Attorney Yutaka 1) Hisashi Take (and 1 other person) Amendment to Figure 1 Procedures (Voluntary) November 29, 1980! Commissioner of the Japan Patent Office Kazuo Wakasugi1, Indication of the case, Patent Application No. 180255 of 19802, Title of the invention: Heating method in a heat treatment furnace3, Relationship with the amended person case Address of the patent applicant: Toyota City, Aichi Prefecture Toyota Town 1 name (
320) l-Yota Jidosha Co., Ltd. 4, Agent address: 3-4-18-5, Mita, Minato-ku, Tokyo, ``Detailed description of the invention'' column 6 of the statement of subject matter of the amendment, Statement of contents of the amendment In the fourth line of page 2, "of these types" is corrected to "of these types."

Claims (2)

[Claims] (1) An electric heater is installed in the heat treatment furnace, and a burner is installed facing the inside of the heat treatment furnace, and the burner is fixedly burned so that its calorific value remains constant to generate a predetermined amount of heat out of the required amount of heat. While supplying heat into the furnace, the electric heater and the burner heat the inside of the furnace by supplying the remainder of the required amount of heat by the electric heater and controlling the amount of heat generated by the electric heater to keep the furnace temperature constant. A heating method in a heat treatment furnace characterized by: (2) A heating method in a heat treatment furnace according to claim 1, characterized in that the burner is operated in a fixed manner so that the oxygen concentration in the heat treatment furnace becomes 15% or more.