JPH0480095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for cooling a strip in a continuous heat treatment furnace.

In a continuous heat treatment furnace, generally heating - soaking - rapid cooling -
(Reheating) - Perform overaging heat treatment. In the rapid cooling process, the cooling rate is increased as much as possible to ensure sufficient precipitation of solid solution carbon during overaging treatment, and the cooling end temperature is controlled near the overaging treatment temperature to prevent reheating for overaging treatment. The ideal is to eliminate the need for heat cycles.

Conventional rapid cooling methods include water jet immersion cooling, water-cooled roll contact cooling, and gas jet air cooling. However, all of these methods have advantages and disadvantages in obtaining the above-mentioned ideal thermal cycle.

The water jet immersion cooling method can achieve a cooling rate of 1500°C/second or more, and the material quality after annealing is extremely good.
However, due to the cooling rate, the cooling end temperature cannot be controlled much, and the strip is cooled to approximately room temperature (supercooling). As a result, reheating is required at the overaging treatment stage, which poses an energy problem.

Both the water-cooled roll contact cooling method and the gas jet air cooling method have lower cooling rates than the water jet immersion method, 100-250°C/sec and 10-50°C/sec, respectively.
Seconds. Therefore, it is relatively easy to control the cooling end temperature. However, since the cooling rate is slow, the overaging treatment to precipitate the solid solution carbon requires a long time, and there is a problem that the equipment becomes large.

The present invention was made to solve this problem, and utilizes the method of cooling high-temperature objects using hot water (Japanese Patent Publication No. 57-27926) proposed by the present inventors to achieve a relatively high cooling rate. It is an object of the present invention to provide a strip cooling method and a cooling device that can cool the strip at a high speed and easily control the final temperature.

That is, the first invention is characterized in that when the strip is heated and soaked and then rapidly cooled, the strip is passed horizontally or in a gently inclined manner, and hot water of 100° C. or higher is injected from a nozzle onto at least one side to cool the strip. The second invention is a threading roll that passes the strip horizontally or gently inclined after heating and soaking, and a heat exchanger that exchanges heat between the combustion exhaust gas after heating and soaking and the hot water used to cool the strip. It is characterized by comprising an exchanger and a nozzle that injects hot water of 100°C or higher reheated by the heat exchanger onto at least one side.

The present invention will be described below with reference to illustrative embodiments.

FIG. 1 is an explanatory diagram of the cooling device, and FIG. 2 is a sectional view taken along the - line in FIG. 1. This cooling device is
The strip 2 is guided into the cooling zone 1 to cool its lower surface. Sealing devices 3, 3 are provided at the inlet and outlet of the cooling zone 1, respectively, to prevent steam from entering other zones. Passing rolls 4 and 5 are provided at the plate. The passing rolls 4 and 5 are used to pass the strip 2 horizontally or in a gently inclined manner, and the interval between them corresponds to the cooling range when the hot water injected onto the strip 2 self-evaporates to form a gas-liquid two-phase flow. It corresponds to the maximum length.

Below the threading rolls 4, 5, hot water jetting nozzles 6 are arranged. This nozzle 6
A plurality of strips are installed in the longitudinal direction and the width direction of the strip 2 so as to face the lower surface of the strip 2. This nozzle 6 is connected to a hot water tank 10 via a supply pipe 9 equipped with a hot water supply cutoff valve 7 and a hot water flow rate adjustment valve 8.

Further, a hot water recovery tray 11 is provided below the nozzle 6. This tray 11 receives and collects droplets that did not evaporate among the droplets in the gas-liquid two-phase flow that collided with the lower surface of the strip.
It is connected to a heat exchanger 14 via a recovery pipe 13 equipped with a circulation pump 12 . The heat exchanger 14 exchanges heat between the collected droplets and the combustion exhaust gas after heating and soaking, and has a built-in heat transfer tube group (not shown) and is connected to the hot water tank 10. This hot water tank 10 is provided with a pressure regulating valve 15 that controls the temperature of hot water used for cooling.

Furthermore, a steam exhaust pipe 17 equipped with a regulating valve 16 is provided above the cooling zone 1 .
The steam exhaust pipe 17 controls the pressure in the cooling zone 1 and exhausts steam. Further, in the illustrated embodiment, a cooling water supply pipe 19 equipped with a regulating valve 18 is opened to the hot water recovery tray 11, but this may be opened to the hot water tank 10.

Next, the method of the present invention will be explained based on the cooling device configured as described above.

The heated and soaked strip 2 is turned down and introduced into the cooling zone 1, where it is formed into a horizontal or gently inclined shape between passing rolls 4 and 5. Hot water of 100°C or higher is injected from the nozzle 6 onto the lower surface of the strip 2 in this state. The injected hot water flashes, a portion of which becomes the above-mentioned water, and the remaining hot water becomes sheared fine droplets by the steam, which is further accelerated by the steam and collides with the lower surface of the strip while remaining at a high temperature. At this time, the fine droplets are
Due to the high temperature, the strip 2 tends to evaporate due to the heat it retains on the surface of the strip. The evaporated steam is immediately removed from the surface of the strip 2 by the high-speed steam flashed when the nozzle jets out. Therefore, the latent heat of vaporization effectively contributes to cooling.

The thus cooled strip 2 is turned up and sent to an overaging treatment zone (not shown). In addition, among the droplets in the gas-liquid two-phase flow that collided with the lower surface of the strip, the droplets that did not evaporate were removed from the cooling water supply pipe 1.
The hot water recovery tray 11 receives the water together with the cooling water from the hot water recovery system 9 . The collected droplets are sent to the heat exchanger 14 by the circulation pump 12, where they are reheated by exchanging heat with the combustion exhaust gas after heating and soaking. After this hot water tank 10
Return to In the hot water tank 10, the pressure in the hot water tank 10 is controlled by the pressure regulating valve 15 to control the hot water temperature, and the hot water supply cutoff valve 7 and the hot water flow rate regulating valve 8 are adjusted to reach 100°C. A predetermined amount of the above hot water is self-injected from the nozzle.

However, according to this invention, since the high-speed gas-liquid two-phase flow containing high-temperature fine droplets impinges uniformly over a wide area on the bottom surface of the strip, the average cooling capacity of the bottom surface of the strip is greater than that achieved by conventional gas jet cooling. In fact, it is possible to achieve a rapid cooling rate of about 400 to 500°C/sec, and the amount of cooling water is about 1/10 that of other cooling methods, such as water jet immersion cooling or laminar flow cooling. . Furthermore, since cooling is performed from the bottom surface, the droplets after colliding with the strip ride on the top surface of the strip and leave the strip without staying, making temperature control easy. Therefore, the cooling completion speed can be controlled arbitrarily; for example, a strip heated to about 700 to 800°C can be
It can be cooled to about 500°C and sent to the next process such as overaging treatment.

In addition, the colliding gas-liquid two-phase flow is at a high temperature, so even if cooling water adheres to the strip, it will evaporate immediately.
At the end of cooling, the strip becomes dry. Therefore, this method does not require a cooling water purge to control the wetting pattern, which is required in other cooling methods, such as laminar flow cooling. In particular, when controlling the strip temperature at the end of cooling by controlling the length of the cooling zone when the strip thickness and line speed change, the laminar flow cooling method described above requires a large number of purge nozzles for controlling the wetting pattern. , is completely unnecessary in this invention, and its control system is also simple.

Furthermore, when cooling the bottom surface of the strip using the laminar flow cooling method described above, the cooling water may flow irregularly from the strip edge to the top surface, causing uneven cooling, so countermeasures such as installing a purge nozzle on the top surface may be taken. It becomes necessary. In contrast, in the present invention, only the evaporated steam comes into contact with the
The above measures become unnecessary.

Furthermore, most of the hot water used as a cooling medium is recycled and degassed during that time. Therefore, according to the present invention, the steam oxide film formed on the strip surface is lighter than in other cooling methods that use cooling water, reducing the load during intermediate pickling or final pickling, and improving product quality. Improves surface quality.

Note that the present invention is not limited to the embodiments shown in FIGS. 1 and 2, but may be as shown in FIG. 3. In this cooling device, the steam generated by cooling the strip 2 is guided to the condenser 20 using a regulating valve 16, and the condensed water after condensation is returned to the hot water recovery tray 11 using a circulation regulating valve 18. It is something. This cooling device can be used without replenishing cooling water.

Furthermore, the present invention is not limited to cooling the lower surface of the strip, but can also be applied to cooling the upper surface or both upper and lower surfaces of the strip.

Next, an example in which the present invention is specifically applied to a continuous heat treatment furnace will be shown below.

[Specifications and operational results]

Strip size 1200mmW x 0.8mmt Speed 350m/min Cooling start temperature 600℃ Cooling end temperature 400℃ Cooling equipment Zone length 3000mm Distance between strip and nozzle 250mm Nozzle Flat spray nozzle Nozzle arrangement Strip running direction 125mm pitch x 24 pieces Strip width direction Strip One each 300mm on both sides from the center of width Nozzle supply hot water temperature 145℃ Nozzle supply hot water amount 20/min Makeup water amount 9.2 ^T /H Heat exchanger for hot water reheating Heat exchanger tube for hot water reheating 42.7φ×3.2 t Arrangement 110mm pitch, 99 rows x 11 stages Duct size 3000mm x 1320mm cross section, length 10890mm Hot water flow rate 57600Kg/h Inlet hot water temperature 80℃ Outlet hot water temperature 145℃ Exhaust gas flow rate 74000Nm ² /h Inlet exhaust gas temperature 480℃ Outlet 〃 334℃ In the above, the strip thickness is 1.6mmt.
In this case, the stripping speed was halved due to the lack of heating and soaking ability, so it was possible to stop cooling from 600°C to 400°C without changing the cooling conditions. In addition, when the plate thickness is 0.4 mmt, the cooling zone length is halved by stopping spraying from half of the strip running direction nozzles on the strip passing roll 4 side.
It was possible to stop the cooling from 600℃ to 400℃.

If the plate thickness is to be reduced, in addition to the method described above, the flow rate regulating valve 8 of each nozzle may be adjusted to reduce the amount of hot water ejected to reduce the heat transfer between the strip and the cooling medium. Alternatively, a method of alternately arranging ejection stop nozzles and ejection nozzles may be used. These methods are effective because the cooling rate of the plate is kept almost constant regardless of the plate thickness, and it is unnecessary to change the alloy composition for each plate thickness due to the material of the product.

As explained above, according to the present invention, the strip is cooled with hot water of 100°C or higher, that is, a gas-liquid two-phase flow consisting of high-temperature fine droplets and water vapor. Sufficient precipitation of solid solution carbon during treatment can be ensured. In addition, since the droplets after colliding with the strip leave the strip without stagnation, temperature control becomes easy, and there are significant effects such as no need for reheating in the overaging treatment stage.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a cooling device showing an embodiment of the present invention, FIG. 2 is a sectional view taken along the line - in FIG. 1,
FIG. 3 is an explanatory diagram of a cooling device showing another embodiment of the present invention. 1... Cooling zone, 2... Strip, 3...
Sealing device, 4, 5... Threading roll, 6... Nozzle for hot water jetting, 7... Hot water supply cutoff valve, 8... Hot water flow rate adjustment valve, 9... Supply pipe, 10... Hot water Tank, 11...Hot water recovery tray, 12...Circulation pump, 13...Recovery pipe, 14...Heat exchanger, 15
...Pressure regulating valve, 16...Adjusting valve, 17...Steam exhaust pipe, 18...Adjusting valve, 19...Cooling water supply pipe, 20...Condenser.

Claims (1)

[Claims] 1. When the strip is heated and soaked and then rapidly cooled, the strip is passed horizontally or at a gentle slope, and hot water of 100°C or higher is injected from a nozzle onto at least one side of the strip to cool it. strip cooling method in a continuous heat treatment furnace. 2. The strip cooling method in a continuous heat treatment furnace according to claim 1, wherein hot water of 100°C or higher is obtained by reheating the hot water used for cooling by exchanging heat with the combustion exhaust gas after strip heating and soaking. 3. A threading roll that passes the strip horizontally or with a gentle slope after heating and soaking, a heat exchanger that exchanges heat between the combustion exhaust gas after heating and soaking and the hot water used to cool the strip, and 100℃ reheated by exchanger
A strip cooling device for a continuous heat treatment furnace, comprising a nozzle for injecting hot water as described above onto at least one side.