JPS597882A - Heat exchanger for cooling furnace body and its manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat exchanger for cooling the furnace body of a melting furnace such as a blast furnace or a heating furnace, and a method for manufacturing the same. The present invention relates to a heat exchanger and a method for manufacturing the same.

In recent years, as the furnace bodies of various heating furnaces and melting furnaces have become larger,
For the purpose of extending the life of the furnace body, a heat exchanger body with cooling bars and A1 cast inside the cast iron is placed between the furnace skin and the refractory, and water is passed through the cooling pipe. Furnace cooling methods that use water cooling or evaporative cooling are now being adopted. Improving the cooling efficiency of the furnace body is extremely important in extending the life of the refractories in the furnace, and various equipment has been developed and put into practice.

Conventionally, this type of heat exchanger for cooling the furnace body has been designed to improve the heat conduction between the cooling pipe and the cast iron casting material, as well as to improve the fusion properties between the two. It is known that the cooling pipe and the casting material are welded together by plating the outer surface, injecting molten cast iron as the casting material, and welding the cooling pipe and the casting material. However, when welding in this manner, cracks may occur in the cooling pipe due to the difference in the amount of expansion and contraction during casting between the cooling pipe and the casting material, resulting in a decrease in product yield. In addition, if a crack occurs in the casting due to thermal stress in the furnace after it is installed on the furnace wall, the crack in the casting material will propagate to the cooling pipe because the casting material and the cooling pipe are integrated by welding. This has caused problems such as cracks in the pipes, resulting in accidents such as water getting wet or water not being able to flow through the pipes.

Recently, in order to eliminate these drawbacks, so-called non-welded furnace bodies have been developed in which the cooling pipe and the casting material are made non-welded so that cracks that occur in the casting material do not lead to damage to the cooling pipe. Cooling heat exchangers have been developed and put into practical use. This non-welding type heat exchange specimen is
Use a casting material that has good thermal conductivity and improves cooling efficiency for the cast iron casting material, and protect the surface of the cooling pipe with a heat-resistant material to prevent welding with the cast iron casting material, thereby reducing the strength of the pipe. is prevented. Ordinary cast iron is mainly used as the casting material for such non-welded heat exchange specimens. Ordinary cast iron has a low solidification temperature, so it can be poured at low temperatures, so there is less risk of weakening the cooling pipe.Also, the fluidity of the molten metal makes casting work easier, and it has excellent thermal conductivity. It has excellent properties on the C-plane, making it a heat exchange material. However, ordinary cast iron has coarse flaky graphite in its solidified structure, resulting in poor mechanical strength and lack of heat resistance.Therefore, in a heat exchanger made of ordinary cast iron, the casting material is heated during operation. There is a problem that cracks are likely to occur and wear and tear is significant, thus shortening the life of the furnace body.

By the way, there is vermicular graphite cast iron, which is a high C1, high Si material like ordinary cast iron, has better mechanical properties than ordinary cast iron, and has particularly high heat resistance. Vermicular graphite PI iron has a caterpillar-like black ship shape, so there is less risk of the graphite becoming notched as in the case of flaky graphite, and therefore it has excellent mechanical properties such as tensile strength and elongation. , also has high heat resistance. 1. That is, FIG. 1 shows the results of measuring the mechanical properties of normal cast iron and vermicular graphite cast iron, which is a tough cast iron, used as casting materials for conventional heat exchangers over a range from room temperature to high temperature. From Figure 1, vermicular graphite cast iron has approximately twice the strength of ordinary cast iron not only at room temperature but also at high temperatures of 600°C. It seems that it is also excellent. However, although vermicular graphite cast iron has excellent hot strength, it has inferior fluidity compared to ordinary cast iron, so a high casting temperature is required. Therefore, when used as a casting material for cooling pipes, Experiments conducted by the present inventors have revealed that this leads to coarsening of crystal grains and a decrease in pipe strength.

This invention was made against the background of the above-mentioned circumstances, and was designed to be used as a heat exchanger for cooling the furnace body, with the casting as a whole having high strength and excellent heat resistance, while not causing a decrease in the strength of the cooling pipe. The object of the present invention is to provide a heat exchanger and a method for manufacturing the same.

In other words, this invention aims to utilize the advantages of the above-mentioned 1. normal cast iron and vermicular graphite cast iron, and at the same time compensate for their disadvantages. The present invention provides a heat exchanger having a two-layer structure in which ordinary cast iron is applied around a cooling pipe that requires thermal conductivity and low-temperature casting, and a method for manufacturing the same.

Specifically, the heat exchanger of the first invention consists of a first layer inside a high-temperature furnace made of vermicular graphite cast iron, and ordinary cast iron that is welded and bonded to this first layer and in which a cooling pipe is cast. It is characterized by having a second layer. Further, the method of the second invention, when manufacturing a heat exchanger for cooling a high-temperature furnace body in which a cooling pipe is cast with cast iron, provides a downward direction of the cooling pipe arranged in the mold from the position of the lower mold surface during casting. Inject the molten vermicular graphite cast iron to a position within the range of 20 to 50 mm, and then, when the molten vermicular graphite cast iron has solidified or has not yet solidified, pour the molten ordinary cast iron onto the vermicular graphite cast iron using the cooling vibrator. It is characterized by being poured so that it is cast.

Hereinafter, the heat exchanger of the present invention and its manufacturing method will be explained in more detail.

FIG. 2 shows an example of the heat exchanger of this invention,
The first layer 1, which corresponds to the inside of a high-temperature furnace such as a blast furnace, is made of vermicular cast iron, and the second layer 2, which corresponds to the outside of the furnace, is made of normal cast iron. A suitable number of cooling vibes 3 made of steel pipes or the like are wrapped around the second layer 2. To explain in more detail, the attachment of the second layer 2 to the outer wall of the furnace body (iron shell) is from the side corresponding to the ends 3A and 3B of the cooling vibe 3.
protrudes, and a plurality of refractory bricks 4 are encircled at predetermined intervals on the inner surface of the furnace of the first layer 1. However, this poem of Fire Brick 4 is not necessarily necessary.

As mentioned above, when the second layer 2 is attached to the outer wall of the furnace body, both ends of the cooling vibrator 3 protrude from the surface corresponding to the part, so the cooling vibrator 3 is installed on the upper mold side during the construction. , No. 111 are located on the lower mold side. That is, in manufacturing a heat exchanger having a two-layer structure as described above, first, molten vermicular graphite cast iron, which will become the first layer 1, is poured into a mold. At this time, it is desirable that the pouring temperature of the vermicular graphite cast iron be as low as possible within a temperature range that does not impair its fluidity.

Then, when the vermicular graphite cast iron has solidified from the lower mold surface and the upper surface has completely solidified, or when the upper surface is still in a molten state, the molten cast iron with excellent fluidity becomes No. 2!1I12. Gently pour the dredge into the first layer 1
At the same time, the cavity in the mold is filled with the molten cast iron flowing through the stand without causing any fusion with the cooling vibe 3, and the cooling vibe 3 is surrounded.

Here, as mentioned above, the width of the mixing area at the boundary between the vermicular graphite cast iron m'4 injected as No. 1111 and the normal cast iron injected as No. 211 is the width at the time when the injection of the second layer of normal n iron molten metal is started. Although it differs depending on the progress of solidification of the 1st w4 vermicular graphite spindle melt, the inventors experimentally measured the results and obtained the results shown in FIG. 3. In Fig. 3, the horizontal axis is the surface (distance ff) of the vermicular graphite cast iron injected as the first layer.
Each position in the vertical direction from o) is shown, and the vertical axis shows the mixing ratio of the first layer cast iron (vermicular graphite cast iron) at each position of the first layer and the second layer solidification completed poem.

In Fig. 3, numeral 5 indicates the mixing ratio when the second layer of ordinary cast iron is injected with the top surface of the first layer of vermicular graphite M fu solidified, and numeral 6 indicates the mixture ratio when the top surface of the first layer is not yet solidified. The mixing ratio is shown when the second skin melt is injected in the molten state of solidification. From the results shown in FIG. 3, it was found that the range where both materials are mixed at the boundary between the first layer and the second layer is about 40 to 8 Qmm. On the other hand, when the refractory brick 4 is cast, the distance from the top surface of the refractory brick 4 to the cooling vibe 3 is generally about 40 to 60 Il1m, although it varies depending on the conditions in which the heat exchanger is installed. When refractory bricks are not cast, the distance from the lower mold surface (i.e. furnace inner surface) to the cooling vibrator 3 is usually 55 mm.
The culm degree is 111m-120wII. As a result of comprehensive consideration of these values, the measurement results of the width of the mixed fFi region shown in Figure 3, the size of the casting, the placement position of the cooling vibrator, and the size of the void determined by the casting plan, the casting The distance between the top surface of vermicular graphite*a injected as the first layer 1 on the lower mold side and the cooling vibe 3 is 20 mm to 50 Il.
It has been found that lIm is desirable. ? F! ,
[In this way, the upper surface of the barge key 1 la graphite cast iron molten water to be injected as the first layer is positioned 20 below the cooling vibe 3.
By setting the position at ~50 mm, cast iron with a composition that is a mixture of two different types of molten iron does not appear on the refractory brick surface or the inner surface of the furnace, and at the same time, cast iron with a mixed structure appears around the cooling vibe. A structure that changes continuously from the vermicular graphite cast iron structure to the mixed cast iron structure to the normal cast iron structure is obtained from the inside surface of the furnace or the refractory brick surface to the periphery of the cooling vibe. In other words, a highly heat-resistant vermicular graphite cast iron structure is ensured on the inner surface of the furnace or the surface of the refractory I nongaster that is exposed to high temperatures, while Shintsu cast iron is used around the cooling vibrator where thermal conductivity is required. Organization is secured. In addition, if the top surface position of the first W4 is above the position 20 mm below the cooling part, a mixed structure of both materials may appear around the cooling vibe, which may reduce the thermal conductivity around the cooling vibe. On the other hand, if the top surface of the first layer is below the position 50mm below the cooling vibrator, a mixed structure may form on the inner surface of the furnace or the surface of the refractory bricks, which may impair the heat resistance of the surface. There is.

Also, vermiki kola as the first layer! ? , mixed area near the joint surface of leaded cast iron and ordinary cast iron as the second layer)
As shown in the actual eggplant examples described below, it was confirmed that there was no occurrence of poor welding or cast iron defects, and there was no decrease in strength due to chilling of the structure.

In the vermicular cast iron used for the first layer, it is sufficient that the graphite crystallized in the matrix has a caterpillar shape (vermicular shape), which is between a flake and a spherical shape, and its components are usually Carbon saturation within the range of Ca, 1 to 3.9% (weight %, same hereinafter), Si 2.2 to 2.6%, and at a eutectic level of cast iron. Carbon saturation SC1, that is, 5c = C (%) / (4,23-9i (%)/3.
2) so that the value of C is within the range of 0.90 to 1.10.
and Si, and improve graphite spheroidizing ability to vermicularize crystallized graphite, or add one or more of 49 alloy, Ca alloy, and Ca alloy to cast iron before casting the molten metal. 4fI O,010~0.025% inside
, CaO0002~0.005%, Q90,010
~0.020% of one or more types in a total amount of 0.020%.
It is sufficient if the content is 0.025% or less. These component ranges are determined primarily from the viewpoint of sufficiently graphitizing the carbon and preventing the graphite from becoming excessively spheroidally purified and increasing the proportion of spheroidal graphite as in ductile cast iron.

The vermicular graphite cast iron used as the first layer is
Unlike ductile cast iron, which has a spheroidal graphite structure,
There are few sideways in cast-in poems.

Therefore, there is no need to install a particularly large riser, and the yield of γJ products is as good as in the case of mountain cast iron.

Specific examples of this invention will be described below.

EXAMPLE As shown in FIG. 2, a heat exchanger for cooling the furnace body was manufactured, which was made of two layers of 1.2 1i iron, with refractory bricks 4 rotted on the lower surface of the casting mold corresponding to the inside of the furnace. At this time, the size of the entire heat exchanger is 900mm in width and 1800!11111 in fi.
．． The thickness was 300 mm, the weight fR was 2850 kg, the diameter of the cooling vibrator to be filled was 60.5 mm, and the gap between the refractory brick and the cooling vibrator was 60 n+m. Injected as the first layer 1 of the two-layer structure, the chemical composition of the vermicular graphite cast iron melt is C3.47%, S+:? , 5196, ToAn
0.78%, PO, 033%, 30.010%, 1g
The remaining 0.019% is ``e''.In addition, this 8th grade was prepared by adding Fe -9i -) and (f1 alloy to make the graphite shape vermicular (worm-like) and measure its strength] - before casting. On the other hand, the chemical composition of the ordinary cast iron injected as the second H2 is C3, 57%, 3i 1.78%, M
n O, 54%, PO, 045%, SO, 014%,
The rest were FC. Vermicular graphite #1
Cast iron is cast until the top of the molten metal reaches a position equivalent to half the distance from the top of the refractory brick to the cooling vibrator, that is, 30 mWl below the cooling pipe.
I had coagulation progressing from below. The salinity of the molten vermicular graphite cast iron that forms this first layer is 1250.
℃~1280℃ 11 Then vermicular graphite was injected as the first layer v! When the top surface of the iron is unsolidified,
Gently pour a layer of Sui Tong special iron molten metal onto the vermicular graphite cast iron, combine both molten metals, fill the area around the cooling vibe, fill the void up to the top of the mold, and solidify. I let it happen. The pouring temperature of the molten ordinary cast iron used as the second layer was set to be as low as possible (approximately ℃) within a range C that does not impair its fluidity.

FIGS. 4 to 6 show examples of the results of examining the microscopic silkiness of each part of the cast parts of the 2WIW4 furnace cooling heat exchanger manufactured in this manner at 50 times magnification.

In other words, the microscopic surface phase in Fig. 4 is the first layer C.
This shows the brightness of the injected vermicular graphite cast iron near the inner surface of the furnace after solidification. Here, the graphite shape is caterpillar-like, and there are no casting defects such as internal shrinkage cavities.
It is clear that the casting is one of the strongest in the world, and the microscopic photograph in Figure 5 shows the cooling pipe corresponding to the joint surface of the first layer and the second layer. Lower 30FI
I! The structure of the casting in I is shown, and the chemical composition is found to be a 50% mixture of both dippings as a result of chemical analysis. It was found that the graphite shape in the part corresponding to the flat culm of the vermicular graphite tsuba iron molten slag and the Huitong cast iron was a mixture of caterpillar-like and flake-like shapes, and the graphite shape was collapsed.

On the other hand, microscope 1 with 6 diagrams! The structure photograph shows the structure of the casting around the casting cooling vibe, and shows a coarse flaky graphite cast iron structure.

In this way, as the first layer, vermicular graphite cast iron,
If ordinary cast iron is successively cast as the second M, and both are combined in the mold to produce a heat exchanger, the structure of the cast part will be continuous from the inside of the furnace where heat-resistant strength is required to the area around the cooling vibe. There are no defects such as poor bonding or chilling, and it is similar to conventional casting materials. It was confirmed that no welding occurred between the casting material and the cooling pipe, similar to the case with heat exchangers whose cast parts were integrally formed using iron.

Furthermore, the mechanical strength of each part of the cast part of the heat exchanger having the above structure was determined as follows. °In other words, the tensile strength of the vermicular graphite cast iron part corresponding to the inside of the furnace is 37
．． 4kg/mJ, elongation is 3.2%, and the tensile strength of the iron part around the cooling pipe is 11.8k Q, / -
A value of 1 elongation of 0.7% was obtained, and the strength of the portion corresponding to the inside of the furnace was sufficiently improved. As for the mechanical properties of the position corresponding to the boundary between the first layer molten metal and the second layer molten metal, the tensile strength is 26.3k (+/aJ), and the elongation is 16.6. It was also found that the level of quantitative strength was medium.

As is clear from the above description, the heat exchanger for cooling the furnace body of the present invention is made of vermicular graphite cast iron, which has excellent strength and heat resistance, even in the inner part of the furnace that is exposed to high temperatures. Since it is cast in ordinary cast iron that has excellent thermal conductivity and good fluidity of the molten metal and can be cast at low temperatures, it is possible to prevent welding between the cooling parve and the same as before. In addition, it does not cause a decrease in the strength of the cooling pipe during casting, and is strong against heat effects from inside the furnace during use. It has various advantages such as less chance of leakage and accidents. Moreover, if the method of manufacturing the heat exchanger IFI of this invention is used, it will be excellent as described above! In addition to being able to actually manufacture a heat exchanger that meets the requirements of 11 properties, it is not necessary to install particularly large presses as in conventional heat exchanger manufacturing, making it easy to make, unmold, and finish the work. It has some excellent advantages, such as not causing a decrease in product yield.

[Brief explanation of drawings]

FIG. 1 is a graph showing the strength changes of various cast iron materials at high temperatures; FIG. The figure is a graph showing the change in the mixing ratio when the 21st WI shoulder of different harvests is injected onto the first layer in manufacturing the heat exchanger of the present invention. Figure 5 is a photograph of the solidification structure of the vermicular graphite cast iron material injected as I, Figure 5 is a photograph of the solidification structure of the mixed part of vermicular graphite cast iron and normal cast iron, and Figure 6 is
This is a photograph of the solidification structure of ordinary cast iron material injected as a layer. 1...First layer, 2...Second layer, 3...Cooling pipe. Applicant Kawasaki Steel Co., Ltd. agent Patent attorney Takehisa Toyota (one idiot) aIs I Figure 2 B / l ('C) Figure 3 Figure 41 So1

Claims (2)

[Claims] (1) It is characterized by having a first layer on the inside of the furnace made of vermicular graphite cast iron, and a second layer made of ordinary cast iron that is welded to this first layer and in which a cooling pipe is cast. A heat exchanger for cooling the furnace body. (2) When manufacturing a heat exchanger for cooling a furnace body in which a cooling pipe is cast with cast iron, a distance of 520 to 5 Qmm below the cooling pipe placed in the mold from the position of the lower mold surface during casting. Inject the vermicular graphite cast iron melt field to the position within the range. Afterwards, when the vermicular graphite cast iron is completely solidified or not yet solidified, molten ordinary cast iron is injected onto the vermicular graphite cast iron so that the cooling pipe is cast over the vermicular graphite cast iron. manufacturing method.