JP5143507B2 - Continuous heating furnace - Google Patents

Description

  The present invention relates to a heating furnace that continuously conveys steel and uniformly heats it.

  For example, as shown in FIG. 5, the heating furnace used for quenching and tempering heat treatment of steel pipes, etc. is a heating zone 1 heated by a burner 3, a soaking zone 2, and a steel pipe 8 by a walking beam 7 in the direction of the arrow. Then, it is continuously heated, held and heated to a predetermined temperature, and then removed from the furnace and subjected to quenching and tempering treatment.

  The steel tube is heated by controlling the temperature so that the ambient temperature in the furnace is set to a predetermined temperature and the specified temperature is reached. However, since the capacity of the furnace is large, a temperature difference is likely to occur between the burner 3 (hereinafter referred to as the ceiling 9) and the vicinity of the walking beam 7 (hereinafter referred to as the hearth 10) where the steel pipe 8 is conveyed. The uniform heating of the steel pipe 8 is difficult.

  Therefore, in order to reduce the temperature difference between the furnace atmosphere temperature near the ceiling 9 and the furnace floor 10, the combustion gas is stirred by the fan 4, or the furnace gas is covered with the baffle plate 5 to cover the combustion gas. It is devised that the combustion gas is uniformly applied to the steel pipe 8 that is conveyed by being circulated in the furnace or further provided with a slit plate having a large number of slits 6 in the baffle plate 5.

  Moreover, in patent document 1, the baffle board which provided the gas flow path between the ceiling and the hearth, and the baffle board closely_contact | adhered to the ceiling and the hearth are provided in the furnace width direction whole surface alternately by the advancing direction of a slab, A device has been devised to increase convective heat transfer due to gas flow.

However, even if the various measures described above are used, the ambient temperature in the vicinity of the hearth 10 is still uneven in the conveying direction of the steel pipe 8 due to the positional influence with the fan 4 and the like.
Japanese Patent Publication No. 01-35897

  This invention makes it a subject to provide the continuous heating furnace which solves the problem mentioned above and makes temperature distribution of a furnace length direction uniform.

  The heating furnace of the present invention has the following characteristics.

  The first invention is a heating furnace that continuously conveys and heats steel material, and heats and soaks the combustion burner, a fan that circulates the combustion exhaust gas in the furnace, and the steel material conveyance path so as to cover the combustion exhaust gas from the hearth. And a slit plate for rectifying the combustion exhaust gas at the lower part of the partition plate at the upper part of the steel material conveyance path, and the slit width of the slit plate varies in the steel material conveyance direction. It is a continuous heating furnace with excellent characteristics and furnace temperature distribution characteristics.

  2nd invention is 20-35% larger than the slit width of the steel material conveyance direction center part 25-30% length, and the steel material conveyance direction both ends, As described in 1st invention characterized by the above-mentioned. It is a continuous heating furnace with excellent temperature rise characteristics and furnace temperature distribution characteristics.

  Since the slit width was changed according to the steel material conveyance direction position, the flow of combustion exhaust gas from the ceiling direction to the hearth direction became smooth, and the furnace temperature distribution in the continuous heating furnace became uniform.

Embodiments of the present invention will be described below with reference to the drawings.
1. FIG. 5 is a diagram showing the overall structure of the continuous heating furnace of the present invention. The continuous furnace is composed of a heating zone 1 and a soaking zone 2. After the steel pipe 8 which is a heating material is inserted into the furnace from the heating zone 1 entry side (the left side in the figure), is transported in the direction of the arrow by the walking beam 7 and heated, and is maintained at the specified heating temperature in the soaking zone 2 It will be carried out.

  Although the inside of the furnace is heated by the combustion gas from the combustion burner 3, there is a distance between the ceiling 9 side and the furnace floor 10 side of the furnace. Occurs. Therefore, the combustion exhaust gas is forcibly circulated so that the atmosphere temperature in the vicinity of the steel pipe 8 on the walking beam 7 is as uneven as possible in the furnace width direction and the length direction.

That is, a fan 4 for sending combustion exhaust gas from the ceiling 9 side to the walking beam 7 side and a partition plate 5 for guiding the combustion exhaust gas from the furnace floor 10 side to the fan 4 side of the ceiling 9 are installed at the upper part of the conveying path of the steel pipe 8. Yes. Further, slit plates 6 are installed in the furnace width direction and the furnace length direction so that the combustion exhaust gas sent out from the fan 4 does not hit the steel pipe 8 locally. The combustion exhaust gas reaches the steel pipe 8 via a slit groove provided in the slit plate 6.
2. Next, it will be described that the uniformity of the temperature in the furnace is affected by the arrangement method of the slit grooves of the slit plate 6.

  FIG. 2 explains the influence on the ambient temperature in the vicinity of the steel pipe when the slit width and the slit width range (length ratio) are changed. The reference numerals in FIG. 2 refer to FIG. 1, and the slit width is represented by St as the slit width on the furnace entrance side, Sm as the slit width at the center of the furnace, and Se as the slit width at the furnace outlet side. The furnace length direction length range of each slit width is indicated as lt, the range corresponding to the slit width St, lm as the range corresponding to the slit width Sm, and le as the range corresponding to the slit width Se. In addition, lt, lm, and le are represented by the length ratio with respect to the furnace total length lo.

  In Comparative Example 1 and Comparative Example 2, the slit width is fixed to 10 mm over the entire length of the furnace, and the flow rate of the combustion exhaust gas is 14 m / sec and 20 m / sec. The results are shown in FIGS. 3A and 3B, in which the temperature near the center of the heating zone is lower than the planned temperature. The distribution of the low temperature part is shown in FIG. It can be seen that the low temperature part is widely distributed from the center of the heating zone to the furnace entrance side.

  On the other hand, in Invention Example 1 and Invention Example 2, the flow rate of the combustion exhaust gas is constant at 20 m / sec, and in Invention Example 1, the slit width Sm at the furnace center is 10 mm, the furnace entrance side slit width St is 7.5 mm, and the furnace outlet This is an example in which the side slit width Se is 7.5 mm, the Sm length direction range lm is 25%, and the St and Se length direction ranges lt and le are both 37.5%.

  Invention Example 2 has a slit width Sm of 12 mm at the center of the furnace, a furnace entrance side slit width St of 10 mm, a furnace exit side slit width Se of 10 mm, an Sm length direction range lm of 30%, and a length of St, Se. In this example, both the vertical ranges lt and le are set to 35%.

  In the example of the present invention, as shown in FIG. 1, the distribution of the low temperature portion is remarkably reduced in the center of the furnace as compared with Comparative Examples 1 and 2, and the temperature in the center of the furnace is as shown in FIG. It is higher than that of the comparative example, and has a uniform temperature distribution from the furnace center to the furnace exit side.

Thereby, since the temperature of the center part of the furnace length of Invention Examples 1 and 2 increased, the amount of energy input to the material to be heated increased from the furnace entrance side to the furnace center part. Since the rate of temperature increase is increased and the time for reaching the predetermined soaking temperature is also increased, the productivity of the heat treatment is improved.
Furthermore, it can be seen that the invention example 2 in which the range lm in which the slit width Sm at the center of the furnace is 12 mm is 30%, the ambient temperature is shifted to a higher temperature side than the invention example 1.

  Although the present invention has been described for the case of a steel pipe, the same equipment and heating method can be applied to a continuous heating furnace for steel plates.

It is a figure explaining the temperature distribution of the heating furnace which has the slit width of the example of the present invention. It is a figure which shows a hearth side furnace temperature measurement result. It is a graph which shows a hearth side furnace temperature measurement result. It is a figure explaining the temperature distribution of the heating furnace which has the slit width of a comparative example. It is a figure explaining the steel material conveyance direction sectional structure of a continuous heating furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating zone 2 Soaking zone 3 Burner 4 Fan 5 Partition plate 6 Slit plate 7 Walking beam 8 Steel pipe 9 Ceiling 10 Hearth

Claims (1)

A heating furnace that continuously heats and soaks steel material, a combustion burner, a fan that circulates the combustion exhaust gas in the furnace, a partition plate that covers the steel material conveyance path and guides the combustion exhaust gas from the hearth to the ceiling, A slit plate that rectifies the combustion exhaust gas at the lower part of the partition plate at the upper part of the steel material conveying path has a slit width that is located in the length range of 25 to 30% of the central part in the steel material conveying direction. A continuous heating furnace having excellent temperature rise characteristics and furnace temperature distribution characteristics characterized by being 20 to 35% larger than the width of the slits at both ends in the direction .

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