JPS636192Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a preheating furnace for metal plates such as steel plates, which uses exhaust gas from a heating furnace such as a subsequent heat treatment furnace as a heat source.

For example, as shown in Figure 1, steel plate c is 650
A heat treatment furnace a that heats to an arbitrary temperature between 930° C. and 930° C. and a preheating furnace b that preheats a steel plate c using the combustion exhaust gas of the heat treatment furnace a as a heat source are arranged as shown in the figure. The heat treatment furnace a placed after the preheating furnace b heats the steel plate c with a plurality of burners (not shown), and the exhaust gas is sent to the exhaust gas duct d.
The air is sucked and pressurized by a blower e along the way, and is divided into upper and lower parts and enters the preheating furnace b, as shown in the enlarged view of FIG. This preheating furnace b is surrounded by a heat insulating material h, has a roll i for conveying a steel plate c, and has a roll i for conveying a steel plate c.
An upper nozzle j is arranged above the nozzle j, and a lower nozzle k is arranged below the nozzle k. The exhaust gas is blown onto the surface of the steel plate as a high-speed jet from these nozzle groups, preheating the steel plate c, and is then radiated into the atmosphere from the chimney g through the flue f.

As in this example, it is well known that the method of preheating by blowing high-speed exhaust gas from a nozzle is called jet preheating, and the heat transfer coefficient at this time is expressed by the following formula.

α _n =0.286×[u _a x _o /ν] ^0.625 ×λ/x _oHere , α _n is the average heat transfer coefficient u _a =8.4u _j /2+H/D u _j =u (273+T ₁ /273) , D: Nozzle diameter (m) H: Distance between nozzle and object (m) u: Ejection speed (m/s) x _o : Nozzle pitch (m) ν: Kinematic viscosity coefficient (m ² /s) λ: Thermal conductivity (Kcal/mh°C) T ₁ : Nozzle gas temperature (°C) The thickness of the steel plate c in this example is in the range of 4.5 to 250 mm. The distance between the upper surface of roll i (referred to as the pass line) and upper nozzle j shown in Fig. 2 is H ₁ , and the lower nozzle k
Let the distance between the two points be _H2 . And the above H ₁ is the nozzle j
In order to protect the
Add mm. Since the above H ₂ only needs to take into account the deflection of the steel plate c, it should be 50 to 50, regardless of the plate thickness.
It is approximately 100mm.

Preheating is performed using this device, but when the steel plate c is thin, around 4.5 to 25 mm, this H ₁ becomes excessive, the effect of the jet is weakened, and the expected average heat transfer coefficient α _n
is not obtained.

In view of this point, a device for moving the upper nozzle group up and down in accordance with the thickness of the steel plate c was considered, but it was complicated and expensive, and was not very effective.

In this way, in the conventional preheating furnace b, the upper nozzle j
The above α _n changes, and especially for thin plate materials, the above α _n becomes too small. Further, there are disadvantages in that heat is not sufficiently transferred from the input exhaust gas to the steel plate c, and heat management is also difficult.

By using the lower nozzle as the main component, the present invention provides a preheating furnace with a stable and large average heat transfer coefficient, a sufficient preheating effect, and easy heat management. The purpose is to provide

Therefore, in a preheating furnace for steel plates, etc., which is installed in front of or in front of a heating furnace such as a heat treatment furnace and uses the exhaust gas of the heating furnace as a heat source, the present invention aims to adjust the exhaust gas flow rate to the upper nozzle/lower nozzle ≦0.3. The feature is that the upper nozzles are arranged sparsely and the lower nozzles are arranged densely.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 4 and 5.

Figure 4 shows the first embodiment of the present invention.
In the figure, 1 is a preheating furnace, 2 is a steel plate, 3 is an exhaust gas duct, 4 is a heat insulator, 5 is a day scroll, 6
is the upper nozzle, and 7 is the lower nozzle. That is, when compared with FIG. 3 which shows the conventional one, the roll i
is changed to a day scroll 5, and the ratio of the number of upper nozzles 6 to lower nozzles 7 is changed from 1:1 to 2:7. By doing this, firstly, the distance H ₂ between the lower nozzle 7 and the steel plate 2 remains unchanged, making it easier to manage the average heat transfer coefficient α _n described above, and
Since the distance H ₂ can be made small, the above α _n becomes large. Further, by using the day scroll 5 as the roll, the jet stream comes into contact with the steel plate 2 without being obstructed, so that the above α _n becomes large. In addition, as shown by reference numeral 2', in the case of a thick steel plate, since the upper part has the effect of mitigating the temperature drop, several nozzles are arranged and sprayed. The amount of exhaust gas from the upper nozzle 6 is within 30% of the amount from the lower nozzle 7.

FIG. 5 shows a second embodiment of the present invention.
This is suitable when the steel plate 2 is thin. That is, the fourth
The upper nozzle 6 in the figure is omitted to lower the ceiling, and the lower nozzle 7 inside the furnace is insulated. Furthermore, a heat storage body 8 is provided above the steel plate 2, that is, below the heat insulating material 4 on the ceiling of the preheating furnace 1. This heat storage body 8 is made of refractory bricks with a bulk specific gravity exceeding 0.5. That is,
In recent years, ceramic fiber or board with a bulk specific gravity of 0.1 has been frequently used as insulation material 4.
In this case, the amount of heat storage is too small, and the temperature of the heat insulating material 4 above the steel plate 2 decreases, and after a certain period of time, the heat below the steel plate 2 begins to actively move from the upper surface to the heat insulating material 4. In Fig. 5, when the furnace is empty and no steel plate 2 is present, the gas blown out from the lower nozzle 7 is sufficiently heated and stored, and the upper surface of the steel plate 2 to be fed next is given heat, and It is made difficult to absorb heat from the steel plate 2 even after a certain period of time.

FIG. 6 is an experimental temperature rise curve diagram when the steel plate c is preheated by the conventional preheating furnace b shown in FIG. In the figure, the solid line curve M ₁ is the temperature at the lower surface of the steel plate, and the dotted line curve M ₂ is the temperature at the center of the steel plate. Although the temperature of the upper surface of the steel plate is not shown, it is just between _M1 and _M2 . That is, the relationship was such that temperature M ₁ of the lower surface of the steel plate>temperature of the upper surface of the steel plate>temperature _M2 of the center of the steel plate.

The conditions for the experiment shown in Figure 6 are as follows: Steel plate thickness: 19mm Nozzle pitch: 500mm Distance between upper nozzle and steel plate: 350mm Distance between lower nozzle and steel plate: 100mm Nozzle inner diameter: 27mm Nozzle jet velocity: 22/Nm/s Exhaust gas temperature: 320℃ It is.

FIG. 7 is an experimental temperature rise curve diagram when the steel plate 2 is preheated by the preheating furnace 1 of the second embodiment of the present invention shown in FIG. In the same figure, the solid line curve M ₃ is the temperature of the lower surface of the steel plate, and the dotted line curve M ₄ is the temperature of the upper surface of the steel plate. Since the total number of nozzles and nozzle pitch in Fig. 5 are different from those in Fig. 3, in order to facilitate comparison with Fig. 6, Fig. It was taken as the inner diameter of the nozzle.

In other words, the conditions for the experiment in Figure 7 are as follows: Steel plate thickness: 19mm Nozzle pitch: 250mm Upper nozzle: None (with upper heat storage element) Distance between nozzle and steel plate: 100mm Nozzle inner diameter: 29mm Nozzle jet speed: 22Nm/s Exhaust gas temperature: 320℃ It is.

As is clear from FIG. 6 and FIG. 7, when the amount of exhaust gas used is the same, the temperature rise characteristics of the steel plates are almost the same.

In this way, the preheating furnace of the present invention mainly uses the lower nozzle, so the average heat transfer coefficient _αn is stable and a large value can be obtained, and heat management is easy. In addition, although the heating is mainly performed on one side of the lower surface,
A preheating effect similar to that of double-sided heating is obtained, and damage to nozzles is reduced. In particular, when the upper nozzle is eliminated and the furnace roof is lowered, the equipment becomes significantly simpler.

[Brief explanation of drawings]

Figure 1 is a side view showing an example of the arrangement of a conventional preheating furnace and heat treatment furnace, Figure 2 is an enlarged cross-sectional side view of the preheating furnace in Figure 1, and Figure 3 is a cutting line in Figure 2. A-
4 is a sectional front view taken along line A, FIG. 4 is a sectional front view showing the first embodiment of the present invention, FIG. 5 is a sectional front view showing the second embodiment of the present invention, and FIG. 6 is FIG. FIG. 7 is an explanatory diagram of the steel plate temperature increase due to the preheating furnace of FIG. 5. FIG. 1... Preheating furnace, 2... Steel plate, 3... Exhaust gas duct, 4... Insulation material, 5... Day scroll, 6...
...Upper nozzle, 7...Lower nozzle, 8...Heat storage body.

Claims (1)

[Scope of Claim for Utility Model Registration] In a preheating furnace for metal plates that uses exhaust gas from a subsequent heating furnace as a heat source, the lower nozzles that blow the exhaust gas are arranged more densely than the upper nozzles, and the flow rate of the exhaust gas is higher. A preheating furnace characterized by maintaining a relationship of nozzle/lower nozzle≦0.3.