JPH02122059A - Method for controlling holding zone temperature in alloying furnace - Google Patents

Abstract

PURPOSE:To easily adjust the holding time and holding temp. in a holding zone to a specified level by adjusting the flow rate of the dilution air to be introduced to a holding zone inlet zone after a heating zone to hold the holding zone at the desired alloying temp. plus the temp. corresponding to a decrease in the furnace temp. CONSTITUTION:A strip 3 is passed through a plating pot 1, plated, wiped by a wiper 2, heated to a specified temp. in the heating zone 5 of the alloying furnace 4, and then held at an alloying temp. in the holding zone 6 to alloy the plated metal. The holding zone 6 is separated by openable and closable partition members 13a-13c into >=2 zones 6a-6c in the traveling direction of the strip 3. The zones 6a-6c are separated into the number of the holding zone using zones in accordance with the desired holding time. A fan 7 or a damper 15 is controlled through a controller 18 in accordance with the number of zones, and the flow rate of the dilution air is adjusted so that the first zone is held at the desired alloying temp. plus the temp. corresponding to a decrease in the furnace temp. to the final holding zone. By this method, the holding temp. and time are strictly controlled, and a high-quality alloyed plated steel sheet is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a holding zone temperature control method for an alloying furnace in which an alloyed plating layer is formed by heating and holding a plated strip.

<Prior Art> Conventionally, in an alloying furnace, as shown in FIG. 4, a strip 3 plated by a plating bot 1 and having its coating amount controlled by a wiping device 2 enters an alloying furnace 4 and is processed. It is heated in a tropical zone 5, held at an alloying temperature in a holding zone 6, and then cooled.

Normally, the exhaust gas in the heating zone 5 is temperature-controlled by dilution air at a holding temperature (F6) and is exhausted at the outlet of the holding zone 6. 7 is a fan.

Further, as a galvanil furnace having a strip cooling means in the holding zone, for example, there is one disclosed in JP-A-60-159159, but in this structure, the holding zone is one zone, and the temperature of the holding zone is not adjustable. Even if there is, it is impossible to adjust the retention time.

In these alloying furnaces, if the threading speed changes due to some reason, such as the capacity of the plating pre-treatment furnace or the ability to control the amount of plating, or the target holding time changes due to a change in the composition of the plating layer. It is not possible to respond in a detailed manner when changes occur.

In conventional furnaces, the length of the holding band is constant, so if the threading speed changes, the holding time also changes, making it impossible to control the holding time.
The retention time cannot be controlled.

<Problem to be solved by the invention> Compared to non-alloyed plated steel sheets, alloyed plated steel sheets have superior surface coating adhesion and paintability, and are suitable for automobiles,
It is widely used mainly for home appliances.

In order to produce high-quality alloyed plated steel sheets, the heating temperature in the heating zone that causes the alloying reaction between the base iron and the plated metal, and the holding time in the holding zone that uniformizes the alloying are required. Needs to be strictly controlled.

However, when the retention band length is fixed, the required retention time and line speed are uniquely determined, and in a continuous line consisting of a plurality of equipment each having different processing speed capabilities, the predetermined retention time cannot necessarily be obtained.

Therefore, if the threading speed changes for some reason, or if the components of the plating layer change and the target holding time changes, the holding time will deviate significantly from the target and if the holding time becomes longer than the target, the alloying reaction will progress too much and the plate will burn out. This tends to cause powdering, which causes the alloyed layer to peel off.

On the other hand, if the holding time is too short, the alloying reaction will not proceed, resulting in insufficient baking or uneven baking, making the product unsuitable.

An object of the present invention is to provide a holding zone temperature control method for an alloying furnace that allows the holding time and holding temperature in the holding zone to be easily set or changed to predetermined levels.

Means for Solving the Problems> In order to achieve the above object, the present invention provides a heating zone for heating a plated strip, and a heating zone that is divided into two or more zones in the strip passing direction. In an alloying furnace equipped with a holding zone for maintaining a constant temperature, the temperature in the first zone is set to the target alloying temperature plus the amount of decrease in furnace temperature from the first zone to the final holding zone. A method for controlling temperature in an alloying furnace holding zone is provided, the method comprising adjusting the flow rate of dilution air introduced into the first zone.

The present invention will be explained in more detail below.

FIG. 1 is an explanatory diagram of an alloying furnace having a retaining zone divided into three zones to which the present invention is applied.

The alloying furnace 4 is provided with a known heating zone 5 on the inlet side of the strip 3, and a holding zone 6 divided into three parts is connected to the outlet side of the heating zone 5.

The heating zone 5 is set to a predetermined temperature using a conventional method.

An air introduction pipe 8 is provided on the inlet side of the holding zone 6 to adjust the temperature of the exhaust gas introduced from the heating zone 5, and the amount of air introduced is controlled by a fan 7 and a damper 15. .

Exhaust ducts 9a, 9b, 9c and cutoff valves 10a, 10 are provided on the outlet side of each of the three divided zones 6a, 6b, 6c, respectively.
b, 10c are provided and connected to the connecting duct 11, so that the exhaust gas is dissipated from the exhaust pipe 12 to the outside of the retaining band 6.

Zone dividing members 13a, 13b, 13c are provided downstream of the openings of the respective exhaust ducts 9a, 9b, 9C, and cooling devices 14b and 14c are provided in the second zone 6b and third zone 6C, respectively. It is being

The zone dividing members 13a, 13b, 13c are as follows:
For example, a material such as a gas seal or a partition plate through which the strip 3 can pass and which can block the exhaust gas introduced from the heating zone 5 is used. Further, as the cooling devices 14b and 14c, a chamber or the like to which a cooling fluid such as air can be supplied is used.

The alloying furnace having a retaining zone consisting of three zones has been described above, but the greater the number of zones, the more precise control becomes possible, but the equipment cost also increases, so it is preferable to have about 3 to 4 zones.

Further, although a cooling device is not normally required in the first zone 6a, a cooling device may be provided if necessary.

16 is a thermometer that measures the temperature within the first zone 6a;
Reference numeral 7 denotes an air flow rate computing unit for dissection introduced into the first zone 6a, and 18 is a device that controls the air flow rate based on the calculation result of the computing unit 17.

The present invention provides a retaining band 6 divided into a plurality of zones as described above.
Each zone is used as a holding/cooling zone depending on the line speed, and the furnace temperature in the final holding zone is controlled to reach the target holding temperature.

The divided retaining zone 6 to which the present invention is applied tends to have a slightly lower degree of furnace insulation than the conventional single retaining zone, and it is necessary to consider the decrease in furnace temperature due to dissipated heat. Therefore, by inputting the target alloying temperature and the number of holding zones used as holding zones in advance into the calculator 17, the furnace temperature of the first zone 6a (
The required temperature) is calculated, and then compared with the furnace temperature of the first zone 6a measured by the thermometer 16, the dilution air flow rate is calculated to bring the furnace temperature of the first zone 6a to the required temperature. calculate.

Subsequently, the flow rate control device 18 is operated based on the result of the arithmetic unit 17 to control the rotation speed of the fan 7 or the damper 15.
By controlling the furnace temperature of the first zone 6a by adjusting the opening degree, the plate temperature at the exit of the final holding zone can be maintained at the target alloying temperature regardless of the number of holding zones used.

Note that the arithmetic unit 17 stores data necessary for the calculation, such as the amount of heat dissipated in each zone of the retention zone, the amount of heat dissipated corresponding to the number of retention zones used as the retention zone, and the first zone corresponding to the final retention zone exit temperature. The relationship between the furnace temperature in zone 6a and the relationship between the furnace temperature in zone 6a and the dilution air flow rate are previously determined manually, and the following calculations are performed.

(1) Calculation of the amount of heat dissipated in each zone QLl = AI xf (Tg) However, QLI・the amount of heat dissipated in the first zone (Kcal
/hour) A, ・Surface area of the first zone (m2) Tyo: Furnace temperature (substituted with target alloying temperature) ('C) (2) Number of retention zones used as retention zones or when N zones Calculation of the total dissipated heat ff1(Q,) Q4, (Kcau
/hr) = Σ QL (3) Calculation of furnace temperature drop ff1 (△Tt) at the exit of the final holding zone relative to the first zone △T, ('c) = Q+, /C, ·V.

However, C3: Specific heat of gas in the holding zone (N can /Nm'℃) V□: f (Q, , T,): Gas flow rate in the holding zone (Nm'/hr) Q,・Amount of combustion in the heating zone (Nm'/hr) caIL/hr) (4) Calculation of the furnace temperature and required temperature of the first zone to be set (T) = T, +ΔT, where Ts: target alloying temperature (°C) controlled based on the above calculation. Setting furnace temperature for the first zone (required temperature: T)
The temperature in each zone from ('C) to the final retention zone outlet temperature (1) is as shown in the schematic diagram in Figure 2 depending on the number of retention zones used as one retention zone. However,
(2) is the case where the number of holding zones used as the holding band is 1 zone, and (2) to (2) are the cases where the number of holding zones is 2, 3, and 4 zones, respectively. In the case of (1) to (2), the required temperature T is in addition to T8 by the amount lowered by the furnace temperature and grazing heat between the exit of the first zone and the exit of each final holding zone. The amount to be added is calculated using the above-mentioned formula, and its control is performed as described above.

In addition, the relationship between the strip passing time and the strip temperature through the alloying furnace in which the present invention is applied is as shown in FIG. where the target alloying temperature (T, ) and T
, +lO (shaded area in the figure), and the holding time can be kept constant regardless of the sheet passing speed.
In the conventional heat pattern, the holding time in the holding band changes depending on the sheet passing speed, and varies within the range T of ±20° C. as shown by the broken line (■) at low speed and If at high speed. Although the present invention has been described above using control by an arithmetic unit, the same effect can be obtained by controlling by a table obtained by suitably simplifying each of the above calculations.

Next, an example of the operation of selectively using each zone of the retaining zone of the alloying furnace to which the present invention is applied will be explained.

In the alloying furnace shown in FIG. 1, after the strip 3 is immersed in the plating bot 1, excess plating is wiped off by a wiping device M2, and the plating thickness is adjusted to a predetermined thickness.

Subsequently, in order to undergo alloying treatment, it is heated to a predetermined temperature in a heating zone 5, and is kept heated in a holding zone 6 for a necessary time.

Here, when all of the first to third zones 6a, 6b, 6c are used as retention bands, the cutoff valves 10a, 10b are left idle, 10c is opened, and the zone dividing members 13a, 13b are
is not used and left in the open state, and only 13c is used to shut off the temperature-controlled exhaust gas from the exhaust duct 9c to the exhaust pipe 12 via the first to third sones 6a, 6b, and 6c. It can be discharged after a period of time.

In addition, when the threading speed decreases or the target holding time becomes shorter, the number of zones to be used as the holding band can be determined from the threading speed and holding time. When used as a retention band, shutoff valve 10
b is open, loa and 10c are closed, zone dividing members 13a and 13c are not used and are in the open state, and only 13b is used to shut off the temperature-controlled exhaust gas. Exhaust duct 9b via zones 6a and 6b
This is achieved by discharging the air through the discharge pipe 12. This third zone 6c is supplied with cooling fluid from the cooling device 14c and is used as a cooling zone.

If the retention length can be further shortened, the second and third zones 6
b, 6c as a cooling zone, the cooling device 14b
, 14c, and the zone dividing member 13
It is sufficient to set the shut-off state using the exhaust gas duct 9a, and let lJt of exhaust gas be discharged from the exhaust duct 9a through the exhaust pipe 12.

Depending on the number of retention zones selected as described above,
The required temperature of the first zone is appropriately controlled by the formula described above so that the final holding zone is at the target alloying temperature.

<Example> The present invention will be specifically explained below based on Examples.

(Example 1) A galvanized steel strip (width 1200 mm, thickness 0.9 mm) plated to a coating weight of 60 g/m2 was passed through a heating zone set at a furnace temperature of 1100°C, It was introduced into a zone divided into zones.

The holding time required to make the alloying uniform in the plating layer of this steel plate is 10 seconds, and the effective length of each zone of the holding band is 5 seconds.
[m], the zone dividing member was a gas seal.

The amount of heat dissipated in each zone, the amount of furnace temperature decrease at the exit of each zone, and the target alloying temperature were as shown in Table 1.

First, since the line speed was initially 90 [mpm], the gas seal on the outlet side of the third zone was used to shut off the gas seal, and the first to third zones were connected to the retaining belt and the fourth zone from the inlet side of the retaining belt.
The zone was used as a cooling zone. 1st zone temperature 5
60°C was manually input to the computer, the dilution air flow rate was adjusted based on the calculation result, the temperature in the first zone was controlled to 560°C, and the strip was threaded. The strip temperature at the third zone exit was maintained at 553°C.

Next, since the line speed was 60 [m p m], the gas seal on the outlet side of the second zone was used to shut off the gas, and the first and second zones were placed in a holding band, and the third and fourth zones were placed in a shut-off state. It was used with a cooling zone.

The temperature of the first zone, 555° C., was input manually to the calculator, and the temperature of the first zone was controlled to 555° C. based on the calculation result, and the strip was threaded. The strip temperature at the second zone exit was maintained at 551°C.

In this way, by using each zone of the holding zone as a holding/cooling zone and controlling the temperature of the first zone, the required holding time can be properly maintained without being too long or short, and the strip temperature at the exit of the final holding zone can be brought to the target alloying temperature. I was able to hold it.

That is, when a conventional furnace is used, the holding time of the holding band varies depending on the line speed because the holding band length cannot be changed.

So, by changing the temperature of the heating zone, it is possible to prevent overcooking and undercooking. The company was operating in a sloppy manner.

In contrast, in the embodiment, each zone of the holding zone can be used as a holding/cooling zone depending on the line speed, and the furnace temperature of the holding zone used as the holding zone can be set to the target alloying temperature T. In addition, even if the line speed changes, by using each zone of the holding zone properly, the strip holding time in the holding zone can always be kept at the target holding time, and when using a conventional furnace, powdering (due to overheating) Although 0.5 wt% of defective products such as poor quality were generated, in the above example, there was no occurrence of over-baking or under-baking, and high quality alloyed plated steel sheets were obtained.

<Effects of the Invention> Since the present invention is configured as explained above, it is possible to heat the material to the optimum alloying temperature in the heating zone and then hold it at the target alloying temperature in the holding zone for a target time. Therefore, even when the line speed is changed due to a change in strip thickness, etc., the holding zone length is instantly changed according to the change in the learn speed, and the temperature at the exit of the final holding zone is controlled to the target alloying temperature. It is now possible to hold the temperature for the target time, and there is no need to change the heating temperature in the heating zone. In addition, even if the target retention time changes due to changes in components in the plating, such as the concentration of Aρ, which has a large effect on the alloying rate, the retention zone length can be changed instantly without changing the heating zone capacity. This allows the holding time to be varied and the temperature at the exit of the final holding zone to be controlled to the target alloying temperature.

Therefore, defects that occurred during the time required for the thermal response of the retention zone during operational changes no longer occur.

Furthermore, according to the present invention, overheating and temperature drop of the strip in the retention zone can be prevented, and the retention time and temperature in the retention zone can be reduced to IT! It became possible to closely control L, easily producing high quality alloyed plated steel sheets, and reducing the defective rate from 0.5*t% to 0.2wt%.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an alloying furnace having a retaining zone divided into three zones, in which the present invention is applied. FIG. 2 is a schematic diagram showing the relationship between the number of retention zones used as retention zones and the temperature within each zone. FIG. 3 is a graph showing the relationship between strip passage time and strip temperature. FIG. 4 is a diagram showing an outline of a conventional alloying furnace. Explanation of symbols 1... Meggi pot, 2... Wiping device, 3... Strip, 4...
Alloying furnace, 5... Heating zone, 6... Zone, 6a... First zone, 6b... Second zone, 6c... Third zone, 7... Fan, 8...・Air introduction pipe, 9a, 9b, 9c - Exhaust duct, 10a, 10b, 10c'' - Shutoff valve, 11... Connection duct, 12... Discharge pipe, 13a, 13b, 13c... Zone division Members, 4a, 14b, 14c...Cooling device, 5...
- Damper 6...Thermometer, 7...Air flow rate calculator for dilution, 8...Flow rate control device FIG, 1 FIG. N1) r-7 ) 硲2 NO/ ]φ43・NO/ 1A4 ZONE FIG, 3 Stroke 1 Lube street clear space (O7) FI G, 4

Claims (1)

[Claims] (1) In an alloying furnace equipped with a heating zone for heating the plated strip and a holding zone for maintaining the temperature at a constant temperature, the zone is divided into two or more zones in the strip passing direction. The temperature of one zone is the first to the target alloying temperature.
A method for controlling temperature in an alloying furnace holding zone, the method comprising adjusting the flow rate of diluting air introduced into the first zone so that the temperature is the sum of the furnace temperature reduction amount from the zone to the final holding zone.