JPS629166B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas jet cooling device for steel strips in continuous annealing equipment for mild steel plates, continuous annealing equipment for stainless steel plates, etc.

FIG. 1 shows a conventional gas jet cooling system that cools a traveling steel plate by jetting gas from a slit nozzle.

In Figure 1, the cooling gas supplied to headers 2 and 2' by blowers 1 and 1' is provided perpendicularly to a steel plate 4 running in the direction of the arrow between headers 2 and 2'. Slit nozzle 3
and 3' to cool the steel plate 4.

In this cooling device, as shown in Fig. 2, gas ejected from the slit nozzle groups 3 and 3' collides with the steel plate 4 and is then discharged through the gap between the steel plate 4 and the header in the direction of the edge of the steel plate 4 as shown by the arrow. Therefore, the closer the edge of the steel plate is, the faster the flow rate of the discharged gas becomes. Therefore, in the width direction of the steel plate, as shown in FIG. 3, the closer the steel plate is to the edge, the higher the heat transfer coefficient becomes, and the closer the steel plate is to the edge, the faster the cooling occurs. This results in non-uniform cooling in the width direction of the plate, which has the disadvantage of causing non-uniformity and deformation of the material.

In Figure 3, the horizontal axis is the distance Y from the center of the steel plate in the edge direction, and the vertical axis is the central heat transfer coefficient α.
The ratio of the heat transfer coefficient α at Y to ₀ is α/α _0. Based on the experimental data when the distance L between the steel plate 4 and the slit nozzles 3 and 3' in Fig. 1 is 100 mm, when the width of the steel plate is 1200 mm, the center Compared to this, the heat transfer coefficient at the edge portion is approximately 7% higher.

Further, as the distance L between the steel plate 4 and the slit nozzles 3 and 3' in FIG. 1 is reduced, the heat transfer coefficient increases and the cooling rate of the plate can be increased. Alternatively, a great advantage arises in that the length of the cooling zone can be shortened, but as L is made smaller, there are problems such as non-uniformity of the material due to non-uniform cooling and deformation of the steel plate, as well as this deformation and front and rear equipment. A problem arises in that the steel plate comes into contact with the nozzle surface due to vibration of the steel plate, unbalance of left and right header pressure, etc., and flaws occur on the surface.

Note that if the above L is made sufficiently large, the velocity of the gas discharged in the edge direction will be reduced, the heat transfer coefficient will be relatively uniform, and problems such as uneven cooling, deformation, and contact of the steel plate with the nozzle will be less likely to occur. The jet flow from the slit nozzle is attenuated by the time it collides with the steel plate, and the absolute value of the heat transfer coefficient becomes small, causing problems such as a decrease in the cooling rate and an increase in the required length of the cooling zone.

In addition, as illustrated in Japanese Patent Publication No. 55-1969 (see Figure 3 and the description in lines 15 to 13 from the bottom of column 5 on page 3), gas guide pipes (headers 2 and 2' of the present invention) Protective gas is injected into the strip running in the form of a gas jet through a slit cut into a group of gas jet nozzles arranged in parallel so as to protrude from both sides of the strip. There are known devices that take the device out of the furnace through If both are used separately, the effects of the present invention cannot be obtained and each has its own drawbacks.

In a gas jet cooling system equipped with a slit nozzle, the present invention aims to increase the cooling rate and shorten the length of the cooling system by increasing the distance between the steel plate and the nozzle (L in Figure 1).
It is an object of the present invention to provide a gas jet cooling device which can prevent the occurrence of flaws due to contact with a nozzle even if the material is made small, and which can alleviate uneven cooling and prevent unevenness and deformation of the material.

The structure of the device of the present invention is shown in FIG. In FIG. 4, the cooling gas supplied to the headers 2 and 2' provided on both sides of the steel plate 4 traveling in the direction of arrow A by the blowers 1 and 1' is supplied to the headers 2 and 2' provided on both sides of the steel plate 4 traveling in the direction of arrow A. After the jets from the nozzles 6 and 6' and the straight nozzles 5 and 5', which are also protruded by 1 on both sides, collide with the steel plate, the spaces B and D mainly exist on both sides of the straight nozzles 5 and 5'. is ejected through the paper in a direction perpendicular to the paper surface. x is the pitch of the nozzle.

Figure 5 shows an enlarged view of the gas-cussion type nozzles 6, 6', in which the tips of the two straight nozzles are bent inward at an angle β (usually 30 to 45 degrees), and the inner side forming the nozzle is A back plate c that closes the surface is attached to form a quasi-closed space with the jets a and b from the nozzles, this back plate c, and the steel plate 4, and a high pressure is maintained within this space. Therefore, the smaller the distance L between the steel plate 4 and the tips of the nozzles 6 and 6', the smaller the attenuation of the flow velocity of the jets a and b, so that a larger force can be maintained in this space as described below.

FIG. 6 shows the traveling direction A of the steel plate 4 on the front side of the device of the present invention.
Figure 2 shows a pressure distribution diagram at . This is the distribution of force applied to the steel plate 4 by this device, and is data when only the nozzles 5 and 6 on one side are used and the distances between the nozzle tip and the steel plate are 5 mm, 20 mm, and 100 mm. As a result, the steel plate 4 is subjected to a much larger force on the front surface of the gas-cussion type nozzle 6 than on the front surface of the straight nozzle 5, and the smaller the distance between the nozzle 6 and the steel plate 4, the greater the force. I understand that you can receive it. This is illustrated in FIG. 7. This is the average pressure P _A between the front surface m ₁ of the gas union nozzle 6 in FIG.
(Kg/m ² ) and the average pressure P _B between the straight nozzle 5 front surface m ₂ (Kg/m ₂ and the distance between the nozzle and the steel plate)
This shows the relationship between Zn.

From Figure 7, for example, L = 50mm under regular threading conditions.
That is, if the gap between the gas union nozzles 6 and 6' facing each other with the steel plate 4 in between is designed to be 100 mm, when the steel plate 4 approaches one of the nozzles 6 or 6' for some reason, the nozzle 5 in FIG. If you approach the side _up to _{10mm from}
+P ₉₀ ', and this difference pushes the steel plate 4 back toward the nozzle 6'. This difference in force increases rapidly as the steel plate 4 approaches one of the nozzles 6, 6'.
The force that tries to push it back increases rapidly, which has the effect of preventing it from coming into contact with the nozzle 6 or 6'.

FIG. 8 shows the heat transfer coefficient distribution in the width direction of the steel plate 4. As in FIG. 3, the horizontal axis is the distance Y from the center of the steel plate 4 in the edge direction, and the vertical axis is the heat transfer coefficient α at the center.The ratio α/ of the heat transfer coefficient α at Y to ₀
α is taken as ₀ . At this time, l is 200mm,
x is 450mm. In FIG. 8, e indicates the data of the gas cushion nozzles 6 and 6', f indicates the data of the straight nozzles 3 and 3', and g indicates the average of these data. The gas union nozzles 6 and 6' have the same tendency or width as the conventional device shown in Figure 1.
Although the edges of a 1.2 m steel plate are about 7% higher than the center, the straight nozzle section has a gas discharge passage, so it shows an almost uniform heat transfer coefficient distribution in the width direction of the plate. From these results, it can be seen that the average heat transfer coefficient distribution for the entire device of the present invention is an area average of these, and is much more uniform than that of the conventional device. In other words, if the gas cushion nozzles 6, 6' and the straight nozzles 5, 5' are arranged alternately at equal pitch x as shown in Fig. 4, the area of the gas cushion nozzles 6, 6' will be 1 of the total. /3 or less, and the increase in heat transfer coefficient at the edge of the device of the present invention as a whole is 7% x 1/3 compared to 7% of the conventional device, taking the aforementioned 1.2m wide steel plate as an example.
3 or less, about 2%, which has the effect of allowing substantially uniform cooling in the width direction of the plate.

Note that arranging only the straight nozzles 5, 5' that protrude by a distance l from the headers 2, 2' shown in FIG. 4 is more advantageous than the apparatus of the present invention in terms of making the heat transfer coefficient uniform in the width direction of the plate. P _B and Zn shown in Figure 7
As can be seen from the relationship, the change in P _B with respect to the change in Zn is extremely small, and when Zn becomes extremely small, the force tends to decrease. Even if the steel plate 4 approaches the nozzle 5 or 5' due to the above-mentioned methods, the force to push it back is very small and it easily comes into contact with the nozzle 5 or 5', causing a flaw.

On the other hand, if only the gas union nozzles 6, 6' are used, the vibration of the steel plate 4, header 2,
Although the effect of preventing contact with the nozzle 6 or 6' due to the unbalance of the pressure of , prevention of deformation cannot be achieved.

In other words, according to the present invention, a so-called gas-cussion type nozzle is provided, in which the smaller the distance between the steel plate and the nozzle, the faster the force of the jet acting on the steel plate becomes. By arranging at least one straight type nozzle having a cooling gas discharge passage, uneven cooling of the steel plate can be significantly alleviated even in equipment where the distance between the steel plate and the nozzle (L in Figure 1) is set small. It will be possible to prevent contact with

Therefore, the following effects can be obtained with the apparatus of the present invention.

(1) Shaking of the steel plate caused by the equipment before and after the cooling device,
It is possible to prevent the steel plate from coming into contact with the nozzle due to unbalanced header pressure.

(2) Since the change in heat transfer coefficient in the width direction of the steel plate can be reduced, uniform cooling can be achieved, and deformation caused by non-uniformity of the material and non-uniform cooling can be prevented.

(3) From (1) and (2), it is possible to design a design that reduces the distance between the nozzle and the steel plate, which increases the heat transfer coefficient (i.e., increases the cooling rate, shortens the cooling device, and reduces the capacity of the blower. Can).

In addition to the structure shown in Fig. 4, the structure of the device of the present invention may be as shown in Figs. 9, 10, 11, and 12 (the numbering in Figs. Other than that, follow Figure 4).

The one shown in FIG. 9 uses trapezoidal blocks 7, 7' in the structure of the gas cushion nozzles 6 and 6', and exhibits the same function and effect as in FIG. 4.

What is shown in Fig. 10 is the gas cushion nozzle 6.
and straight nozzles 5 arranged on both sides of 6′,
5' is increased to two, which is more advantageous than those shown in FIGS. 4 and 9 in terms of uniform cooling of the steel plate 4 in the width direction, but the force of the jet acting on the steel plate 4 as a whole is It decreases as the number of gas jets decreases.

The one shown in Fig. 11 is the one in which the two straight nozzles 5, 5' shown in Fig. 4 are replaced with one gas union nozzle 6, 6'; This is replaced by one gas cushion nozzle 6, 6', and the slit width d of the gas cushion nozzle is 1/2 of that shown in FIGS. 4, 9, and 10. The force per unit area in front of the nozzles 6, 6' is the same as that of the other nozzles, but since the area ratio occupied by the gas union nozzles 6, 6' increases, the force acting on the steel plate 4 as a whole increases, and the force acting on the steel plate 4 increases. It is slightly inferior in terms of uniform cooling in the width direction of the plate.

In this way, the combination of the gas cushion nozzle and the straight nozzle may be selected based on conditions that take into account uniform cooling of the steel plate and prevention of contact with the nozzle.

Also, the header shown in FIG. 12 has headers 2 and 11, in contrast to the ones shown in FIGS.
It has a structure having an angle β directly from 2', and has the same effect as the one in FIGS. 4 and 9.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional gas jet cooling device, Figure 2 is a plan view showing the flow of cooling gas through the nozzle group of the device in Figure 1, and Figure 3 is a view from the center of the steel plate in Figure 2 to the edge direction. 4 is a sectional view of a jet cooling device according to the present invention, FIG. 5 is an enlarged sectional view of a gas cushion type nozzle, and FIG. Pressure distribution diagram. Figure 7 is a curve diagram showing the strength of pressure applied to the steel plate when the steel plate approaches one nozzle in the apparatus of the present invention. Figure 8 is a curve diagram showing the strength of the pressure applied to the steel plate in the apparatus of the present invention in the width direction of the steel plate. The heat transfer coefficient distribution diagrams of FIGS. 9 to 12 are cross-sectional views of various modifications of the device of the invention. 1, 1'... Blower, 2, 2'... Header, 3, 3'
...Slit nozzle, 4...Steel plate, 5,5'...Straight nozzle, 6,6'...Gas cut nozzle.

Claims (1)

[Claims] 1. In a gas jet cooling device for a steel strip such as a continuous annealing facility for mild steel plates or a continuous annealing facility for stainless steel plates, there is a cooling gas supply header provided on both sides of a traveling steel plate, and a cooling gas supply header that protrudes from the header and is inclined to the plane of the steel plate. a plurality of cushion-type nozzles that inject gas from the front and rear of the running surface; and at least one straight-type nozzle that protrudes from the header and has a discharge passage for cooling gas after colliding with the steel plate and is disposed on both sides of each cushion. A steel strip gas jet cooling device, characterized in that it has: