JPH0614895U - Gas carburizing furnace - Google Patents

Abstract

(57) [Summary] [Structure] Addition of water to a mixture of 30 to 70% by weight of heat-resistant inorganic fiber, 0 to 50% by weight of iron-free refractory inorganic powder, and 10 to 30% by weight of colloidal silica to form a brick shape. Inorganic fibrous refractory heat-insulating bricks, which were formed by firing at 1200 to 1400 ° C., were used for the inner wall of the furnace. [Effect] Since the refractory insulation brick used for the lining does not cause cracks due to carbon particle growth, continuous operation is possible for a long time, and maintenance costs are low. Since it is also excellent in terms of heat insulation performance, it is possible to reduce the size of the furnace by reducing the thickness of the inner wall made of refractory insulation bricks as compared with the conventional gas carburizing furnace.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a gas carburizing furnace.

[0002]

[Prior art]

 A gas carburizing furnace for gas carburizing steel products is filled with high-temperature atmospheric gas containing carbon monoxide and hydrogen as main components. For this reason, it is necessary that the refractory insulation bricks used for the inner wall of the gas carburizing furnace should not easily be altered or deteriorated by the atmospheric gas.

When a general refractory heat-insulating brick made from clay minerals is used in a gas carburizing furnace, the reaction of 2CO → C + CO ₂ occurs at a temperature near 420 to 470 ° C. due to the catalytic action of iron oxide in the lenght. It is known. When the carbon generated by this reaction deposits and grows around the iron particles, the expansion pressure causes the bricks to crack and eventually collapse. For this reason, it is desirable that the refractory insulation bricks for gas carburizing furnaces have as low an iron content as possible, but in refractory insulation bricks produced from clay minerals, the iron content from the raw materials cannot be avoided and the iron oxide content is high. It is difficult to get one with less.

[0004]

[Problems to be solved by the device]

 The purpose of the present invention is to line up with a refractory insulation brick that has a very low content of iron oxide, which is a catalyst for the above-mentioned carbon production reaction, and has excellent heat resistance and heat insulation properties, which makes it superior to conventional furnaces. An object is to provide a gas carburizing furnace that exhibits durability and high thermal efficiency.

[0005]

[Means for Solving the Problems]

 The gas carburizing furnace successfully provided by the present invention has a furnace inner wall of 30 to 70% by weight of heat resistant inorganic fiber, 0 to 50% by weight of iron-free refractory inorganic powder, and 10 to 30% by weight of colloidal silica. It is made of an inorganic fibrous refractory brick obtained by adding water to a mixture consisting of the above to form a brick and firing it at 1200 to 1400 ° C.

[0006]

[Action]

 The inorganic fibrous refractory insulation brick used in the present invention does not use clay minerals at all, and is manufactured using heat resistant inorganic fibers, iron-free refractory inorganic powder, colloidal silica, etc. as raw materials. A refractory insulation brick with an extremely low iron content can be obtained, and iron oxide content of less than 0.1% by weight can be easily obtained. As a result, contact with hot carbon monoxide does not produce carbon therefrom. Therefore, the above-mentioned deterioration and collapse due to the growth of carbon particles do not occur. In addition, since it contains inorganic fibers at a high rate, it is lightweight and has high strength, and it is also excellent in the basic performance required as a refractory insulation brick, and has a low thermal conductivity and a temperature dependent thermal conductivity. There is almost no fluctuation. For this reason, if the furnace wall has the same heat insulation performance, the brick layer can be made thinner than when using conventional refractory insulation bricks, which enables downsizing of the furnace.

Explaining the method for producing this inorganic fibrous refractory brick, the main raw material inorganic fibers are ceramic fibers having good heat resistance such as aluminosilicate fibers, alumina fibers, siliceous fibers and mullite fibers. Can be used. The inorganic fiber may be a short fiber that is cut into short pieces, but if it is processed into granular cotton, bricks with excellent thermal shock resistance can be obtained. In order to form granular cotton, inorganic fibers are cut and crushed between the rotating blades that are meshed in a comb shape, then crushed and pulverized while rolling on a rotary sieve, and finally sieved to a predetermined particle size. The preferred diameter of the granular cotton is about 1-10 mm.

To this, a suitable amount of colloidal silica and refractory inorganic powder (suitable particle size of about 1 to 50 μm) that does not contain iron, such as alumina, mullite, steatite, forsterite, and zirconia, are mixed. A suitable compounding ratio is 30 to 70% by weight of inorganic fiber, 0 to 50% by weight of refractory inorganic powder, and 10 to 30% by weight of colloidal silica per product weight. Inorganic fiber, inorganic powder and binder are added with water and mixed until uniform. If granular cotton is used, be careful not to mix it too much and disintegrate it into single fibers. The appropriate amount of water is about 25 to 1000% by weight based on the total solids.

Once a homogeneous pasty mixture is obtained, it is placed in a mold and dehydrated into a slab. The pressing pressure is preferably adjusted in the range of about ^{2 to 5} kgf / cm ² so that the bulk specific gravity of the final product is about 0.7 to 1.1. The obtained slab-shaped molded product is sufficiently dried at about 110 to 140 ° C and then calcined at 1200 to 1400 ° C to form a siliceous matrix derived from colloidal silica. After that, it is cut into bricks to obtain refractory insulation bricks. No special structure is required for the entire gas carburizing furnace, except that the inner wall of the furnace is constructed using the above-mentioned inorganic fiber fireproof insulation brick. The outside of the brick can be placed with any insulation.

[0010]

【Example】

 100 parts by weight of granular cotton of aluminosilicate fiber (average particle size 5 to 10 mm), 85 parts by weight of alumina powder (average particle size 4 to 5 μm), and 50 parts by weight of colloidal silica, 100 parts by weight of water and carboxymethyl cellulose (serogen). 4H) 5 parts by weight, press-molded, dried, and fired at 1300 ° C. to produce an inorganic fiber fireproof heat-resistant brick (bulk specific gravity: 0.76).

A gas carburizing furnace as shown in FIG. 1 was manufactured by using this refractory insulation brick for the inner wall. In the figure, the refractory heat-insulating bricks were used for all linings except the bottom wall portion 3, such as the side wall 1 (four circumferences), the ceiling portion 2 and the lining 5 of the door 4 for loading and unloading the object S. The outer wall 6 is made of a steel plate. The basic structure of the furnace is well-known, and an atmospheric gas inlet 7 is provided on the side wall 1 at the back of the front face, and a fan 8 for stirring the atmospheric gas and a thermometer 9 are provided in the ceiling part 2. The heaters 10 for heating are arranged in contact with the left and right side walls at equal intervals. Table 1 shows the iron oxide content, density and thermal conductivity of this refractory insulation brick. For comparison, the performance values of refractory insulation bricks (corresponding to JIS / B class 4) that have been used in gas carburizing furnaces are also shown in the table.

[0012]

[Table 1] Example Used product Conventional product Iron oxide content (% by weight) 0.05 0.80 Density (g / cm ³ ) 0.76 0.75 Thermal conductivity (kcal / m · h · ° C) 400 ℃ 0.21 0.22 600 ℃ 0.21 0.26 700 ℃ 0.21 0.28 800 ℃ 0.21 0.32

As is clear from Table 1, the inorganic fiber refractory insulating agar used in the above gas carburizing furnace does not substantially contain iron oxide and carbon does not deposit during use, so that cracks due to carbon particle growth occur. It was usable for a long period of time with almost no occurrence. In addition, the inorganic fiber refractory insulation brick used in the gas carburizing furnace has a low thermal conductivity, and the thermal conductivity hardly changes with temperature up to 800 ° C, and thus it is also excellent in thermal insulation performance.

[0014]

[Effect of device]

 Since the gas carburizing furnace of the present invention is lined with an inorganic fiber refractory insulating brick that does not cause cracks due to carbon particle growth, the conventional gas carburizing furnace lined with a fireproof insulating range made of clay mineral is used. It can be operated continuously for a longer period of time, and maintenance costs are lower. In addition, since the inorganic fiber fireproof heat insulating lag used in the gas carburizing furnace of the present invention is also excellent in terms of heat insulating performance, the inner wall thickness of the fireproof heat insulating brick is thinner than that of the conventional gas carburizing furnace. Thus, the furnace can be downsized.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Explanation of symbols]

 1: Side wall 2: Ceiling part 4: Door 6: Outer wall 7: Atmosphere gas inlet port 8: Fan 10: Heater

Claims (1)

[Scope of utility model registration request] 1. In a gas carburizing furnace, the inner wall of the furnace is a mixture of 30 to 70% by weight of heat-resistant inorganic fibers, 0 to 50% by weight of iron-free refractory inorganic powder, and 10 to 30% by weight of colloidal silica. Add water to form a brick, 12
A gas carburizing furnace comprising an inorganic fibrous refractory heat-insulating brick fired at 00 to 1400 ° C.