Heating – Work feeding – agitating – discharging or conveying... – Having closure or seal for work feeder's entrance passage
Reexamination Certificate
1999-11-24
2001-02-20
Ferensic, Denise L. (Department: 3749)
Heating
Work feeding, agitating, discharging or conveying...
Having closure or seal for work feeder's entrance passage
C432S008000, C432S059000, C432S077000, C034S242000
Reexamination Certificate
active
06190164
ABSTRACT:
TECHNICAL FIELD
The present invention concerns a continuous heat treatment furnace and, more specifically, it relates to a continuous heat treatment furnace to be us ed for continuous heat treatment of metal strips such as strip-like materials, for example, of steel and aluminum and an operation method therefor.
BACKGROUND OF THE TECHNIQUES
In the present invention, “%” for hydrogen concentration means “% by volume” here and hereinafter.
The continuous heat treatment furnace is, basically, a facility for applying heat treatment of a predetermined heat pattern while continuously passing strip-like materials such as steel strips, which is constituted by successively disposing furnace zones each having a processing performance of heating/soaking/cooling (slow cooling and rapid cooling) in the order of treatment.
For example, a continuous heat treatment furnace for a cold-rolled steel strips comprises, as shown in
FIG. 4
, a heating zone
10
for heating a steel strip S to a predetermined temperature, or further soaking or further slowly cooling the same, a rapid cooling zone
11
for rapidly cooling in a predetermined temperature range and a cooling zone
12
for cooling it to a predetermined treatment completion temperature or averaging it before cooling, arranged and constituted in the order of treatment.
If the surface of materials is oxidized during heat treatment, the appearance of the products is deteriorated, so that the inside of the continuous heat treatment furnace is controlled to a non-oxidative atmosphere. In a continuous heat treatment furnace for steel strips, a mixed gas (HN gas) of a hydrogen gas and a nitrogen gas containing several % of hydrogen gas is generally used as an atmospheric gas.
When such HN gas is used, hydrogen contributed to reduction is consumed and formed into H
2
O along with the progress of the heat treatment, and the atmosphere inside the furnace can no more be kept to a non-oxidative state. Therefore, a discharge pipe and a supply pipe for the atmospheric gas are disposed to each of the furnace zones to discharge spent gases and supply fresh gases thereby keeping a predetermined hydrogen concentration in the furnace.
By the way, the composition of the atmospheric gas is not always identical for every furnace zone but, as described below, a composition of atmospheric gas different from others is sometimes adopted in a certain furnace zone depending on the characteristics to be provided to steel strips.
For example, for low carbon steel having a C content of from 0.01 to 0.02 wt %, a so-called overaging treatment of heating, soaking and then rapidly cooling a steel strip to solid-solubilize C in the steel to supersaturation and then keeping it at about 400° C. is conducted in order to improve the aging property. Rapid cooling technique in this case can include a gas jet cooling method of cooling/recycling an atmospheric gas by a heat exchanger, and blowing it as a high speed gas jet stream from gas jet chambers
13
as shown in
FIG. 4
to a steel strip, a roll cooling method of urging a cooling roll having coolants filled therein to a steel strip and a water cooling method or a mist cooling method of blowing water or mist to a steel strip. Among them, the gas jet cooling method can provide satisfactory appearance and shape to the steel strip after cooling and is less expensive in view of facilities compared with other methods.
However, the gas jet cooling method has a drawback of low cooling rate. In order to overcome the drawback, Japanese Patent Examined Publication Sho 55-1969, Japanese Patent Unexamined Publication Hei 6-346156 and Japanese Patent Unexamined Publication Hei 9-235626 have disclosed the use of an HN gas having a cooling performance enhanced by increasing a hydrogen concentration in a rapid cooling zone. Then, satisfactory rapid cooling at a cooling rate over 50° C./s is possible in the rapid cooling zone.
When using an atmospheric gas in a certain furnace zone different from that in other furnace zones, it is necessary to avoid mixing with atmospheric gases from those of other furnace zones. Therefore, sealing means are disposed at the boundary with other furnace zones.
Concrete structures or devices for known sealing means can include, for example, (A) a plurality of partition wall structures which also serve as processing chambers disposed to the boundary between each of atmospheric gases of different compositions and capable of supplying/discharging the atmospheric gases of different compositions (Japanese Patent Unexamined Publication Hei 5-125451), (B) a device for sliding contact of a seal member with a steel strip (Japanese Utility Model Examined Publication Sho 63-19316), (C) a device comprising a combination of sealing rolls, blow nozzles and sealing dampers (Japanese Patent Unexamined Publication Sho 59-133330), and (D) a roll-sealing device
4
comprising rolls rotating at the same speed as the passing speed of a material while putting the material between them from the front and back surfaces of the material as shown in FIG.
4
. Further, in a rapid cooling zone
11
of
FIG. 4
, a roll-sealing device
4
is disposed not only to the entrance and the exit but also to the exit at the upstream of the rapid cooling zone in which gas jet chambers
13
are disposed.
Among such sealing means, scratches are caused to the steel strip by contact with the sealing member in (B). This risk is particularly large under heat treatment condition of high passing speed. In (A) and (C), a consumption of atmospheric gas is worsened, since the flow rate of the sealing gas has always to be kept and, in addition, a gas flow rate at high accuracy is necessary for ensuring the sealing performance, to make the facility expensive. On the contrary, no scratches are caused to steel strips and the facility is inexpensive in (D).
As described above, in the rapid cooling zone of the continuous heat treatment furnace, it is advantageous to adopt a gas jet cooling method of using an HN gas at a higher hydrogen concentration than that in other furnace zones (heating zone, cooling zone or the like) and recycling/cooling and blowing the gas to the steel strips in view of the surface property of products and the cost for facilities. It is advantageous to adopt the roll-sealing device as the sealing means with the same viewpoint.
However, as actually shown in
FIG. 4
, when roll-sealing devices
4
are disposed before and after (at the entrance and exit) of the rapid cooling zone
11
to completely shield the atmospheric gas at high hydrogen concentration in the rapid cooling zone, a dynamic pressure is generated by the stream formed by the atmospheric gas at high hydrogen concentration blown to the strip material and flowing along the strip-like material in the rapid cooling zone (also called as an entrained stream). The dynamic pressure thus generated is interrupted by the roll-sealing devices to result in elevation of a static pressure in the vicinity of the roll-sealing devices. For example,
FIG. 5
shows the result of measurement for the static pressure (FIG.
5
(
a
)) and the hydrogen concentration in the atmospheric gas (FIG.
5
(
b
)) at points P
1
to P
9
in the rapid cooling zone and before and after the zone when a strip material having a 0.8 mm thickness and a 1250 mm width is passed through the continuous heat treatment furnace at a line speed of 400 mpm. As can be seen from FIG.
5
(
a
), large static pressure gaps are caused at some points. Therefore, the balance of the furnace pressures is lost in the rapid cooling zone and before and after of the zone to cause large gas streams, as a result, the atmospheric gas at a high hydrogen concentration in the rapid cooling zone is flown out of the rapid cooling zone, and the hydrogen concentration in the rapid cooling zone is lowered as shown in FIG.
5
(
b
). It is necessary to increase the amount of the HN gas at a high hydrogen concentration to be charged in order to compensate the lowering of the hydrogen concentration in the rapid cooling zone, which results in worsening of the RN gas
Iida Sachihiro
Samejima Ichiro
Ueno Naoto
Ferensic Denise L.
Kawasaki Steel Corporation
Lu Jiping
Young & Thompson
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