JPH0978144A - Method for furnace purging in bell-type batch annealing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust purge gas quantity and purge time optimally by purging atmospheric gas based on the relation between the beforehand obtd. wt. of a material to be annealed and purge time of atmosphere with inert gas, in a bell-type batch annealing furnace using gaseous hydrogen-containing atmosphere. SOLUTION: At the time of batch-annealing a metallic coil, etc., in the bell type batch annealing furnace using gaseous hydrogen-containing atmosphere having explosiveness, in order to prevent the explosion of the hydrogen with gaseous oxygen in the air in the annealing furnace, after reducing the oxygen concn. to a prescribed value or lower by purging the air in the annealing furnace with the inert gas of Ar, etc., the Ar gas is purged with the hydrogen-containing gas as the annealing furnace atmospheric gas to start the annealing. In this case, the relation between the beforehand obtd. wt. of coil to be annealed and purge time with Ar gas which the annealing atmosphere becomes the explosive limit or lower, is decided and then, the oxygen content in the annealing atmosphere is reduced in little purge gas quantity and purge time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purging an inside of a bell type batch annealing furnace using an atmosphere gas containing explosive hydrogen gas.

[0002]

2. Description of the Related Art In a bell type batch annealing furnace, generally, as shown in FIG. 7, three to four stages of coils 2 to be annealed are stacked on a base 1 and an inner cover 3 and an outer cover 4 are mounted. Inner cover 3 and outer cover 4
A sealing device is installed in the lower part of the, and is automatically sealed by mounting the inner cover 3 and the outer cover 4. Before starting the annealing, oxygen in the annealing atmosphere gas is purged with an inert gas to prevent decarburization, explosion, and temper color.

Particularly, when an explosive gas such as hydrogen gas or ammonia decomposition gas is used as the annealing atmosphere gas, as shown in FIG. 8, the inner cover is covered with an inert gas such as nitrogen gas or argon gas for a predetermined time. After purging the gas in the inner cover 3 to reduce the oxygen concentration in the inner cover 3 to a predetermined concentration, an inert gas is purged with an annealing atmosphere gas, and a burner (not shown) of the outer cover 4 is ignited to start annealing. During annealing, heating, soaking, and cooling are one cycle while circulating the annealing atmosphere gas. After the annealing is completed, before the inner cover 3 is detached, the inner cover 3 is purged with an inert gas for a predetermined time in the same manner as before the annealing, and the annealing atmosphere gas in the inner cover 3 is adjusted to a predetermined concentration. After lowering, the inner cover 3 is detached and the coil 2 is extracted.

As a method for purging the bell-type batch annealing furnace in the furnace, an inner cover is put on a purging device, and when the inner cover put on the purging device is lifted, a space is created in the inner cover by the purging device. A method of injecting and confining a purging gas, and covering the coil placed on the base with an inner cover confining the purging gas (Japanese Patent Laid-Open No. 54-130408), before annealing in a bell-type annealing furnace. A method (Japanese Patent Laid-Open No. 59-38341) has been proposed in which gas purging is automatically performed via a solenoid valve that is closed after a predetermined time by a timer.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Patent No. 0408 can effectively perform the inside of the inner cover in a short time, but not only it is necessary to install a purging device having an outer shape slightly smaller than the inner space of the inner cover, but also the purging is performed. The inner cover containing the working gas must be moved to cover the coil placed on the base again, and air may enter the inner cover during this time, and it is explosive as an annealing atmosphere gas. When gas is used, after covering the coil placed on the base, the inner cover is again purged with an inert gas for a predetermined time to reduce the oxygen concentration in the inner cover 3 to a predetermined concentration. However, it is necessary to purge the inert gas with the annealing atmosphere gas, which complicates the operation itself.

Further, in the method disclosed in Japanese Patent Laid-Open No. 59-38341, the in-furnace purge time is set to a predetermined time by a timer, and the furnace volume is not taken into consideration for safety without considering the volume of the in-furnace coil. Since the purge time is determined on the assumption that the inside is empty, the coil is actually put in the furnace, so the gas purge is performed with a considerably large amount of gas. Therefore, in this method, there is a problem in the annealing efficiency by reducing the basic unit of the inert gas used for gas purging and the time required for purging.

On the other hand, as another method, it has been attempted to install an oxygen concentration meter and a hydrogen concentration meter in the furnace to optimize the flow rate and time of the purge gas, but it is expensive for each annealing furnace. A measuring device is required, and a large number of man-hours are required to manage the measuring device for maintaining accurate concentration measurement.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide an in-furnace purge method in a bell-type batch annealing furnace which can inexpensively optimize the purge gas amount and the purge time.

[0009]

Means for Solving the Problems The present inventors have conducted various tests and studies to achieve the above object. As a result, the relationship between the weight of the annealing coil and the purge time with an inert gas that is less than the explosion limit of hydrogen gas was obtained in advance for each annealing furnace, and this relationship was used to determine the pre-annealing and post-annealing based on the coil weight in the furnace. It was concluded that the purge gas amount and the purge time can be optimized by determining the in-furnace purge time, and the present invention was reached.

That is, according to the present invention, in the method of purging the inside of a bell-type batch annealing furnace using an explosive atmosphere gas with an inert gas before and after annealing, the annealing coil weight and the explosion limit or less are set in advance for each annealing furnace. The purge time with an inert gas is calculated in advance, and the furnace purge time before and after annealing is determined based on the coil weight in the furnace using this relationship. It is a purging method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION According to the method of the present invention, in the purging of a bell type batch annealing furnace using an explosive atmosphere gas with an inert gas before and after annealing, in the purging with an inert gas before annealing, The relationship between the purge time and the oxygen concentration is obtained in advance for each coil loading weight in the annealing furnace, and this relationship is used to determine the purge time that will be less than or equal to the explosion limit even if the atmosphere gas having an explosive property is substituted. . When purging the inside of the furnace with an inert gas after annealing, the relationship between the purge time and the hydrogen concentration is calculated in advance for each coil loading weight in the annealing furnace, and even if it is mixed with air using this relationship, the explosion limit By determining the purge time as follows, it is possible to reliably prevent gas explosion, optimize the purge gas amount and purge time, reduce the gas basic unit of the inert gas, and reduce the purge time. By shortening, the total annealing time can be shortened and the annealing efficiency can be improved.

For example, in a bell-type batch annealing furnace with a maximum coil throughput of 100 Ton, in the case of purging with an inert gas before annealing without coil loading, there is a relationship between the oxygen concentration in the furnace and the purge time with an inert gas. , As shown in FIG. The relationship between the coil weight and the purge time is as shown in FIG. Therefore, for example, when hydrogen gas is used as the explosive atmosphere gas, the purge time is T time if the oxygen concentration that is below the explosion limit even if it is replaced with hydrogen gas is α%. If the coil weight inside is 50 Ton, for example, the purge time T is corrected to (T-t) based on FIG.

Further, in the purging in the furnace with the inert gas after annealing, the relationship between the oxygen concentration in the furnace and the purging time with the inert gas is as shown in FIG. The relationship between the coil weight and the purge time in this case is as shown in FIG. Therefore, if the hydrogen concentration that is below the explosion limit even if the inner cover is detached and mixed with air is β%, the purge time will be Ta, so if the coil weight in the furnace, for example, 50 Ton, Based on the above, the purge time Ta is corrected to (Ta-ta).

From the above results, for example, in a bell-type batch annealing furnace having a maximum coil throughput of 100 Ton, if the relationship between the annealing coil weight and the gas purge time is obtained in advance as shown in FIGS. The gas purge time can be determined immediately according to

[0015]

[Example] In a bell-type batch annealing furnace using hydrogen gas as an atmosphere gas having a maximum coil throughput of 100 Ton, the air in the inner cover before annealing was 80 Nm ³ / H.
After purging with nitrogen gas of r, purging nitrogen gas with hydrogen gas to start annealing, and after purging the hydrogen gas in the inner cover with nitrogen gas of 80 Nm ³ / Hr after completion of annealing, detach the inner cover. In repeating the process, the gas purging time with nitrogen gas of 80 Nm ³ / Hr before and after annealing was determined based on the coil weight in the furnace based on FIGS. 5 and 6, and the gas purged example of the present invention and the coil weight in the furnace were determined. Regardless of the condition, the air in the inner cover before annealing is purged with 80 Nm ³ / Hr of nitrogen gas for 1 hour, then nitrogen gas is purged with hydrogen gas to start annealing, and the hydrogen gas in the inner cover after annealing is completed. for each comparative example 1 hour purge with nitrogen gas at 80 Nm ³ / hr, and the amount of nitrogen gas for purging and during gas purging They were compared with annealing times 10 times.

As a result, in the example of the present invention, the amount of nitrogen gas used for purging and the gas purging time can be reduced by about 30% as compared with the comparative example, and the basic gas unit for purging and the annealing efficiency can be improved. I was able to.

[0017]

As described above, according to the method of the present invention, it is possible to optimally perform the gas purging before and after annealing in a bell-type batch annealing furnace using an explosive atmosphere gas without installing expensive equipment. In addition, it is possible to reduce the basic unit of purge gas and improve the annealing efficiency by shortening the purge time.

[Brief description of drawings]

FIG. 1 is a graph showing an example of the relationship between gas purge time before annealing and oxygen concentration.

FIG. 2 is a graph showing an example of the relationship between the coil weight and the gas purge time before annealing.

FIG. 3 is a graph showing an example of the relationship between the gas purge time after annealing and the oxygen concentration.

FIG. 4 is a graph showing an example of the relationship between the coil weight and the gas purge time after annealing.

FIG. 5 is a graph showing an example of a relationship between a coil weight, a gas purge time before annealing, and a gas purge amount.

FIG. 6 is a graph showing an example of the relationship between the coil weight, the gas purge time after annealing, and the gas purge amount.

FIG. 7 is a schematic explanatory view of a bell-type batch annealing furnace.

FIG. 8 is an explanatory diagram of a purging method for a bell-type batch annealing furnace that uses an explosive atmosphere gas.

[Explanation of symbols]

 1 Base 2 Coil 3 Inner cover 4 Outer cover

Claims (1)

[Claims] 1. A method of purging in a furnace with an inert gas before and after annealing in a bell-type batch annealing furnace using an explosive atmosphere gas, in which the annealing coil weight and the gas explosion limit are not exceeded in advance for each annealing furnace. A method for purging in a furnace in a bell-type batch annealing furnace characterized in that the purging time by an active gas is obtained and the purging time before and after annealing is determined based on the coil weight in the furnace using this relation. .