JPS5831371B2 - How to operate a continuous heat treatment furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a continuous heat treatment furnace equipped with a rapid heating furnace length section and a combustion heating furnace length section.

Heat treatment is an operation in which steel is heated to an appropriate temperature and then cooled at the required cooling rate to give it the desired properties.Heat treatment is classified into normalizing, quenching, and tempering, and the role of the heat treatment furnace is in rolling manufacturing. The purpose is to reheat the steel material to a predetermined temperature.

There are two types of continuous heat treatment furnaces: the radiant tube type, which indirectly heats the steel material by burning fuel in a radiant tube, and the direct-fired type, which heats the steel material directly in combustion gas from a fuel burner.

There is also an induction heating type continuous heat treatment furnace, but since the equipment cost is expensive, it is necessary to have a rapid heating furnace length section with a rapid heating means such as an induction heating device or a jet heating device, and the radiant tube or fuel burner mentioned above. A continuous heat treatment furnace consisting of a combustion heating furnace length section having a combustion heating means has been proposed.

For example, in conventional radiant tube formation for thick steel plates, the method of operating a direct-fired continuous heat treatment furnace is to determine the required temperature of the steel plate depending on the type of heat treatment, and then set the ambient temperature in the heating zone and soaking zone of the furnace. Then, the time in the furnace is determined according to the thickness of the steel plate, the conveyance speed of the steel plate in the furnace is set, and the temperature of the steel plate is raised to a predetermined required temperature and soaked.

For example, in actual heat treatment operations for thick steel plates, the treatment temperature (furnace extraction temperature) differs depending on the type of heat treatment such as normalizing and quenching, and even in tempering, the treatment temperature standard varies depending on the required material after treatment. ~700
over a range of °C.

Furthermore, the thickness of the steel plate to be treated ranges from 10 to 100 mm.

Also, in the heat treatment (annealing) of cold strip, the treatment temperature is 700-950℃, and the steel plate thickness is 0.3-3.0m.
/m range.

Therefore, before heat treatment, treated steel sheets are classified according to heat treatment temperature.

Furthermore, the steel plate groups classified according to the heat treatment temperature are classified according to plate thickness.

When sequentially charging groups of steel plates with different required temperatures and/or thicknesses into a continuous heat treatment furnace, the furnace temperature setting and/or in-furnace conveyance speed settings must be changed each time the above steel plate groups are charged. No.

Alternatively, if the subsequent steel plate group has the same required temperature as the preceding steel plate group but has a different plate thickness, the conveyance speed in the furnace must be corrected when charging the subsequent steel plate group, while the subsequent steel plate group has the same required temperature as the preceding steel plate group. Even if the plate thickness is the same as that of the group, if the required temperature is different,
When charging the subsequent steel plate group, it is necessary to change the furnace temperature setting.

The furnace temperature is determined by the required temperature, but for example, if the thickness changes in a group of steel plates separated by the required temperature, the in-furnace time T is calculated using equation 1 and the in-furnace conveyance speed is changed for each steel plate thickness. .

Furthermore, if the subsequent steel plate group has a different required temperature and plate thickness from the preceding steel plate group, the furnace temperature and in-furnace conveyance speed must be changed when charging the subsequent steel plate group.

If the furnace temperature or conveyance speed in the furnace is changed for the following steel plate group while there are still steel plates from the preceding steel plate group in the furnace, the temperature of the steel plates in the preceding steel plate group will be affected. The above-mentioned furnace temperature and speed settings are not changed and subsequent steel plates are not charged into the furnace until the following steel plates are extracted from the furnace.
The furnace is operated in an empty state, the last steel plate is extracted, the settings are changed, and the steel plate group is subsequently charged.

Therefore, the processing speed T/Hr decreases by the operating time of the empty furnace, and the heat retention energy of the furnace is wasted.

Also, in heat treatment (annealing) of cold strips, methods such as connecting dummy steel plates for adjustment are used.
It is inevitable that thermal energy will be wasted.

The above problem could be solved by having a dedicated furnace for each required temperature and sheet thickness, but this cannot be used because of the high equipment cost.

Conventional radiant tube formation involves a direct-fired continuous heat treatment furnace, as well as a rapid heating furnace length section having a rapid heating means such as an induction heating device or a jet heating device as described above, and the radiant tube or fuel burner. A continuous heat treatment furnace consisting of a combustion heating furnace length section having a combustion heating means such as It has not been.

The present invention was made in view of the above-mentioned circumstances, and is a rapid heating furnace that reduces the empty furnace state caused by differences in steel plate dimensions and heat treatment temperatures in conventional heat treatment furnaces, improves processing speed, and saves energy. An object of the present invention is to provide a method for operating a continuous heat treatment furnace equipped with a long section and a combustion heating furnace long section.

The operating method of the heat treatment furnace of the present invention will be explained below with reference to the drawings, taking the case of steel plates as an example.

Fig. 1 is composed of a rapid heating furnace length section 2 in which an induction heating device 1 is provided in the furnace length section on the steel plate charging side, and a combustion heating furnace length section 4 in which a radiant tube 3 is provided in the remaining furnace length section. This figure shows a continuous heat treatment furnace 5 in which steel plates 7 and 8 are transferred by table rollers 6.

The induction heating device 1 includes a coil 1a and a temperature controller 1.
It consists of b.

9 and 10 are heating zones and soaking zones of the combustion heating furnace length section 4; 11 and 12 are furnace temperature detectors for the zones 9 and 10;
3 is a thermometer that detects the temperature of the steel plate at the outlet of the heating zone 9; 14;
is a detector located just before the charging port of the heat treatment furnace 5 that has both a steel plate charging detection function and a charging steel plate temperature detection function (detects the temperature of the charged steel plate when the steel plate is inserted in a hot state). , 15 are calculators, 16 and 17 are control valves that independently adjust the amount of fuel to the radiant tubes 3 in the heating zone 9 and the soaking zone 10, and 18 and 19 are control valves 16 and 17 by instructions ◆ from the computer 15. It is a temperature controller to control.

First, an operating method will be described in which steel plates of various thicknesses with a constant required steel plate temperature are continuously charged and heat treated.

This operating method is most effective in heat treatments such as normalizing and quenching where the processing temperature (required temperature) range is small depending on the required material after treatment, and in dedicated furnaces for different required temperatures.

The calculator 15, which has been given dimensional information of the steel plate to be processed from an information input device (not shown), first calculates the minimum thickness steel plate (reference steel plate) 7 that is most likely to be heated among various thickness steel plates with a constant required steel plate temperature. Assuming that the temperature is raised in the combustion heating furnace long section 4 without being heated by the induction heating device 1 of the rapid heating furnace long section 2 (or by giving a constant heating degree even if heated), the steel sheet temperature is lower than the above-mentioned required temperature in the furnace. Find the temperature θm.

Next, the above furnace temperature θm, the above minimum steel plate thickness t, and the (1st
) is used to find the furnace residence time T of the combustion heating furnace length section 4, and determine the in-furnace conveyance speed (2).

Then, the calculator 15 gives the above-mentioned furnace conveyance speed as a target value to a table speed controller (not shown) of the table roller 6, and sets the above-mentioned furnace temperature θm to a table speed controller (not shown) of the table roller 6.
is given as the target value.

Fuel is fed into the radiant tube 3 via the fuel control valve 16.17 by the temperature controller 18.19 and combusted, and the furnace temperature is detected by the furnace temperature detectors 11 and 12 and fed back to the temperature controller 18.19. , the furnace temperature is controlled to the target value.

The steel plates 7 are successively charged into the furnace 5 in this state.
, 7.7 are heated to a predetermined required temperature in the furnace length section 4 without being heated in the rapid heating furnace length section 2, and are sequentially extracted.

Next, even if the detector 14 confirms that the steel plate 8 has the same required temperature as the steel plate 1 but is thicker, the conveyance speed (■) is kept constant without changing, and the long portion of the combustion heating furnace of the steel plate 8 is The in-furnace time T at 4 is fixed.

Furnace temperature θm is also fixed.

Even if the steel plate 8 is inserted into the furnace as it is, the required temperature will not be reached at the furnace outlet, so when the steel plate 8 is confirmed by the detector 14, the calculator 15 transports the furnace length section 4 at the furnace temperature θm at a speed V. The degree of heating (amount of temperature rise) of the steel plate 8 in the rapid heating furnace length portion 2 required to reach the required temperature is calculated from the following equation (2).

Here, the in-furnace time T is a constant value previously determined by equation (1), and the steel plate thickness t, specific heat Cp, and density ρ in the functional equation of the heat transfer condition α are input as information to the calculator 15. Appropriate values for the heat transfer coefficient are determined from past performance data for each plate thickness or furnace temperature, and are stored in the computer 15.

Note that the same calculation is performed when a constant heating degree is applied in the rapid heating furnace length section 2.

In this way, the computer 15 calculates the required steel plate temperature θ at the outlet of the rapid heating furnace long section 2 or the inlet of the combustion heating furnace long section 4.

Once obtained, the calculator 15 calculates the dimensions of the steel plate 6, the moving speed (■), the charging temperature of the steel plate 6 to the long part of the rapid heating furnace, and the temperature θ.
.

The input power of the induction heating coil 1a is calculated from the above, and the power reference signal is sent to the temperature controller 1-.

-ra 1b, whereby the induction heating device 1 heats the steel plate 6 to a temperature θ.

Induction heating is performed to achieve the desired temperature. In this way, when continuously charging and heat-treating steel plates of various thicknesses with a constant required steel plate temperature,
Determine the furnace temperature of the long part of the combustion heating furnace from the required temperature of the steel sheet, and determine the conveyance speed in the furnace from the minimum thickness steel sheet dimension among the steel sheets scheduled to be charged and the above furnace temperature. According to the operation method of fixing the conveyance speed and adjusting the amount of heating at the long part of the rapid heating furnace according to the thickness of the steel plate, it is possible to continuously insert sheets of different thicknesses at a constant conveyance speed in the furnace. , the interval between steel plates with different thicknesses, or the interval between the last steel plate of the preceding steel plate group and the most advanced steel plate of the following steel plate group between steel plate groups of different plate thicknesses, for changing the conveyance speed setting when changing the plate thickness. There is no need to take
Heat retention is eliminated, and unnecessary energy loss during that time is eliminated, resulting in energy savings.

In addition, since the conveyance speed in the furnace is determined based on the steel plate with the minimum thickness among the steel plates scheduled to be charged, and there is no need to maintain a gap between the steel plates, the processing speed T/Hr is also improved, and as a result, the processing speed T/Hr is improved. Thermal efficiency per weight is also improved, and the unit heat consumption is also improved.

The above describes the operation method when steel plates of various thicknesses are continuously charged while the required steel plate temperature is constant. , When the required temperature of the steel plate must also be changed depending on the required material, that is, the steel plate is composed of multiple steel plates of various thicknesses with different required temperatures, and a plurality of groups of steel plates with different required temperatures are successively inserted and heat treated. We will explain how to operate a continuous heat treatment furnace in this case.

The feature of this operating method is that the continuous heat treatment furnace is equipped with a rapid heating section and a long section of the combustion heating furnace consisting of a heating zone and a soaking zone. When the plurality of steel plate groups having different required temperatures are sequentially inserted and heat treated, the furnace temperature of the heating zone of the combustion furnace length is determined from the maximum required temperature of the plurality of steel plate groups to be charged, and the above furnace temperature is determined. The conveyance speed in the furnace is determined based on the minimum thickness steel sheet size in the group of steel sheets with the minimum required temperature, the furnace temperature and conveyance speed are kept constant, and the length of the combustion heating furnace is determined according to the required temperature of the group of steel sheets. In addition to adjusting the furnace temperature in the soaking zone of the rapid heating furnace, the amount of heating in the long section of the rapid heating furnace is adjusted according to the thickness of the steel plates in the steel plate group.

The present operating method will be explained above with reference to FIG.

In FIG. 1, information such as processing temperature and plate thickness regarding a group of treated steel plates to be charged is given from an input device (not shown).

Then, the calculator 15 selects the steel plate group having the lowest treatment temperature and the steel plate group having the highest treatment temperature among the steel plate group to be charged, and also selects the steel plate with the minimum thickness among the steel plate group having the minimum treatment temperature.

Then, select an appropriate value equal to or higher than the furnace temperature of the soaking zone 10 of the combustion heating furnace length section 4 determined from the maximum processing temperature, and set this as the furnace temperature of the heating zone 9 of the furnace length section 4. Fix it.

This furnace temperature is not changed during the charging operation of the group of treated steel sheets scheduled to be charged.

Next, from the furnace temperature of the zone 9 and the dimensions of the steel plate (reference steel plate) with the minimum thickness that minimizes the in-furnace time of the furnace length section 4 among the steel plate group with the minimum treatment temperature, the (1) The time in the furnace of the above-mentioned steel plate is calculated using the formula, and the conveyance speed in the furnace, that is, the table speed of the table roller 6 is determined from this.

This in-furnace conveyance speed is not changed during the charging process of the group of treated steel plates scheduled to be charged.

On the other hand, since the furnace temperature of the soaking zone 10 of the furnace length section 4 is determined by the processing temperature of each steel plate group, the setting is changed for each steel plate group.

The timing of this setting change will be described later.

Now, if a steel plate with a large thickness is heated in a group of steel plates treated at the same processing temperature, unless it is heated in the rapid heating furnace length section 2, it will be necessary to extend the furnace time in the furnace length section 4. The steel plate temperature required at the outlet of the furnace length section 2 in order to fix the furnace temperature in the heating zone soaking zone of section 4 and achieve the above-mentioned same treatment temperature at the extraction port or heating zone outlet of the furnace is determined by ) and calculate it by substituting the formula.

Then, the power input to the induction heating coil is calculated from the dimensional movement speed of the steel plate and the above-mentioned required temperature.

This calculation is performed for each steel plate in the steel plate group grouped at each treatment temperature.

Further, this calculation timing may be performed at the time of calculating the above-mentioned furnace temperature and conveyance speed, or may be performed for each steel plate group immediately before charging.

The induction heating device 1 of the rapid heating furnace section 2 applies a predetermined heating degree to each steel plate in the group of steel plates treated at the same processing temperature.

In FIG. 1, it is assumed that the preceding steel plate group e and the succeeding steel plate group f have different processing temperatures.

Then, when the first steel plate 8 of the subsequent steel plate group f is detected by the detector 14, the set conveyance speed and the furnace temperature of the heating zone 9 of the furnace length section 4 are not changed, and the speed and the soaking zone 10 are the same. Based on the time required to change the setting of the furnace temperature, in order to provide the minimum necessary gap between the last steel plate of the preceding steel plate group e and the leading steel plate of the succeeding steel plate group f, the steel plate group f is changed for the necessary time to change the setting. The leading steel plate is stopped on the charging side table of the furnace 5.

The furnace temperature setting change time of this soaking zone 10 is such that the charging schedule for the steel plate groups to be charged is changed from the steel plate group with the minimum processing temperature to the steel plate group with the highest processing temperature so that the difference in setting temperature is minimized. If you do this, the setting change time will be minimized, and
The empty furnace length is minimized.

Note that it is faster to raise the furnace temperature than to lower it.

When the required time for setting changes has elapsed, the leading steel plate of the succeeding steel plate group f is inserted into the furnace while maintaining the gap with the trailing steel plate of the preceding steel plate group e, and each steel plate of the steel plate group f is successively inserted thereafter. do.

The steel plates of different thicknesses of the steel plate group f are heated by the induction heating device 1 of the rapid heating furnace long section 2 so as to reach the processing temperature at the entrance of the soaking zone 10.

When the trailing steel plate of the preceding steel plate group e passes through the furnace while maintaining a gap and passes through the soaking zone 10 and is extracted, the furnace temperature of the soaking zone 10 is immediately changed to the furnace temperature for the succeeding steel plate group f. Let's do it.

This is executed by the computer 5 giving a signal to the temperature controller 19.

Similar operations are performed for the joints of steel plate groups having different treatment temperatures, and the steel plate groups with the highest treatment temperature are sequentially charged, allowing operation with a constant furnace time.

As described above, by adjusting the heating amount in the long part of the rapid heating furnace according to the change in the thickness of the steel sheet group, and adjusting the furnace temperature in the soaking zone according to the change in the processing temperature of the steel sheet group, each steel sheet can be heated. The in-furnace time is constant, and the above-mentioned in-furnace time is determined by the furnace temperature of the heating zone determined from the maximum processing temperature of the plurality of steel plate groups scheduled to be charged, and the steel plate size of the minimum thickness of the steel plate group with the lowest processing temperature. Since the minimum time is more defined, the processing speed T/Hr is improved, and since only the minimum air gap is created, energy is saved.

The operating method detailed above has the following effects in addition to the effects of energy saving and improvement of processing speed.

■ When retaining heat in the furnace, energy loss in the rapid heating furnace length can be reduced to zero.

■ The furnace length is short and equipment costs are low.

■ All heat treatments such as temper linking, normalizing zinc, and quenching can be easily carried out in one furnace, and all the heat treatments can be carried out by a single person without the need of a skilled worker.

■ The number of classifications by heat treatment temperature and steel plate size is reduced, making it easier to pile up steel plates before treatment.

In the explanation of the above examples, the operation mode was explained under the condition that the standard steel plate is not heated in the long part of the rapid heating furnace, but the standard steel plate is heated to a constant degree, that is, all the steel plates are On the other hand, it can be similarly operated under the condition of providing a constant heating degree.

In addition, although the embodiment has been explained using a continuous heat treatment furnace that uses an induction heating device as a rapid heating means, since there is no scale generation at low temperatures, a continuous heat treatment furnace using a jet heating device g as a rapid heating means is used as shown in Fig. 2. The operating method of the present invention can be similarly applied to a type heat treatment furnace.

In addition, in the examples, for steel plates whose heating capacity exceeds the heating capacity of the rapid heating means of the rapid heating furnace long section, a steel plate that fixes the furnace temperature and in-furnace conveyance speed of the combustion heating furnace long section or the heating zone of the furnace long section is used. Of course, it is not added as a steel plate group or steel plate group, but is handled separately as another steel plate group.

Next, a case where the rapid heating section is provided on the outlet side (later stage) of the combustion heating section will be described.

As described above, an induction heating device or a jet heating device is used for this rapid heating section.

As mentioned above, the advantage of a continuous heat treatment furnace with a rapid heating section installed on the exit side is that this rapid heating section can control the temperature in response to changes in the thickness of the steel material and changes in the required temperature, thereby controlling the table speed and the set furnace temperature of the combustion heating section. It is a hot topic that it can be made constant, reducing wasted time, improving productivity and saving energy.

In addition, in combination continuous heat treatment furnaces in which the latter stage is a combustion-type heating furnace length, and in conventional continuous heat treatment furnaces in which all furnaces are combustion-type furnace lengths, the temperature of the steel material is increased per unit time at the initial stage of temperature rise. The amount of temperature increase is relatively large, but in the latter half of the temperature increase, the amount of temperature increase per unit time is small and the heating time becomes long.

Therefore, by performing rapid heating in the latter half of the temperature rise, the overall temperature rise time can be shortened, productivity can be further improved, or the furnace length per unit production can be shortened.

These things also save energy.

A method of operating a continuous heat treatment furnace equipped with rapid heating equipment in the latter stage will be described below.

Now, when sequentially and continuously inserting each steel plate group including steel plates with different required temperatures and/or thicknesses, for example, a steel plate group consisting of a plurality of steel plates with different required temperatures and thicknesses, first, the in-furnace conveyance speed of the heat treatment furnace is , the furnace temperature of the combustion heating furnace length is set and fixed.

The method of intercepting this steel plate group and the method of setting and fixing the speed and furnace temperature are as follows.

This table speed is roughly determined from the furnace time of the thin steel plate group, and the furnace temperature is also set approximately to the final required temperature value of the steel plates in the steel plate group to be processed.
The table speed and set furnace temperature are ultimately determined from the interrelationship with the thickness of each steel plate in the steel plate group, initial temperature, final required temperature, and heating capacity of the rapid heating section.

Of course, based on these mutual relationships, steel plates that can be heat treated with a constant table speed and set furnace temperature are predicted and grouped into steel plate groups.

Steel plates that cannot be heat treated at the fixed speed and furnace temperature mentioned above are treated as a separate steel plate group.

Now, it is assumed that the steel plates of the specified thickness of the steel plate group can be processed without being heated in the long part of the rapid heating furnace by operating under the specified furnace temperature and table speed.

In the present invention, the table speed and furnace temperature are kept constant even if a steel plate with a thickness greater than the thickness of the steel plate in the steel plate group comes in, but under these conditions, the temperature of the steel plate cannot be raised completely in the long part of the combustion heating furnace. The inlet temperature of the rapid heating section is detected, or it is determined by predictive calculation based on the in-furnace time of the combustion heating section, furnace temperature, and steel material dimensions.In other words, the inlet temperature of the rapid heating section is detected, and the in-furnace time of the rapid heating section and the outlet demand are calculated. Temperature control is performed in the rapid heating section.

In this way, as in the case of the previous embodiment in which the rapid heating section was provided on the inlet side of the combustion heating section, there is no wasted time due to changes in table speed or furnace temperature due to changes in plate thickness, improving productivity and saving energy. can be measured.

Note that there are steel plate groups including steel plates with different required temperatures and/or thicknesses, and the same operation mode can be adopted for these steel plate groups.

Although the above specific explanation has been made using a thick steel plate as an example, the concept of the present invention can be similarly adopted even in the case of cold slip heat treatment (annealing) of a small steel plate, just by increasing the length of the steel plate.

[Brief explanation of drawings]

Figure 1.2 is an explanatory diagram of the operating method of the present invention. 1...Induction heating device, 2...Rapid heating furnace length, 3...Radiant tube, 4...
... Fuel heating furnace length section, 5 ... Continuous heat treatment furnace, 6 ... Table roller, 7, 8 ...
Steel plate, 9... Heating zone, 10... Soaking zone, 11, 12... Furnace temperature detector, 13...
・Steel plate thermometer, 14...Detector, 15...
... Computer, 16°17 ... Control valve, 18,1
9...Temperature controller, 20...Jet heating device, 21...Burner.

Claims (1)

[Claims] 1 In a continuous heat treatment furnace equipped with a rapid heating furnace length section and a combustion heating furnace length section, when steel plates of various thicknesses with a constant required steel plate temperature are continuously charged and heat treated, the above required temperature is Set the furnace temperature of the long part of the above-mentioned combustion heating furnace from the above, set the steel plate dimension of the minimum thickness among the steel plate groups to be charged, and the furnace conveyance speed based on the above furnace temperature, and set the furnace conveyance speed for each of the above steel plate groups. A method for operating a continuous heat treatment furnace, characterized in that the amount of heating in the rapid heating furnace length is adjusted according to the thickness of the steel plate.