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Table of Contents

A company has developed a new high-performance converter hot repair material. The developed carbon-bonded gunning material is far superior to ordinary gunning materials. It has good adhesion even if the brick surface is gunned to a temperature above 1300°C after slagging. It is a carbon-bonded gunning material corresponding to ultra-high temperature construction. The newly developed high-temperature pouring repair compound significantly shortens the hardening time, which helps shorten the repair time. These newly developed repair materials can significantly improve the thermal repair efficiency of converters.

Keywords: carbon bonded gunning compound; rapid hardening high temperature casting repair material; hardening time

Introduction

With the increase in steel demand in recent years, many steel plants are required to improve production efficiency. In the steelmaking process, the repair materials used in the repair parts of the converter, which is a particularly important piece of equipment, are shown in Table 1 and Figure 1. Carbon-bonded gunning material replaces conventional phosphate-bonded gunning material and is used near the slag line and tap hole. High-temperature pouring repair material is used for loading side walls and steel side walls, and gunning material is used for trunnion side walls where high-temperature pouring repair material cannot be used. Repairs using high-temperature pouring repair materials and carbon-bonded gunning materials are both effective repair methods. However, in order to improve production efficiency, it is required to further shorten the repair time. In response to this, the company is developing and promoting high-performance rapid-hardening high-temperature cast patching materials that significantly shorten the hardening time, as well as ultra-high-temperature construction-type carbon-bonded gunning compounds that adhere even in high-temperature areas above 1,300°C after slag removal.

Table 1 Representative BOF hot repair methods

repair arearequired performancerepair material
coneprotect wallPhosphate bonded gunning material
TapholeFast hardening and good durabilityHigh temperature cast repair material (water bonded or carbon bonded)
trunnionGood durability and high adhesion strengthCarbon bonded gunning materials, phosphate bonded gunning materials
Loading side wallFast hardening and good durabilityHigh temperature cast repair material (carbon bonded)

Figure 1 Schematic diagram of BOF thermal repair part

Corresponding to ultra-high temperature construction type carbon bonded gunning material

Table 2 shows the characteristics of carbon bonded gunning materials. Carbon-bonded gunning materials use special organic matter as a binder, so there is less generation of low-melting materials, inhibiting over-burning of carbon and slag intrusion. As a result, there is less peeling off during use and excellent durability. Unlike phosphate bonded gunning materials, one of its characteristics is that it does not contain phosphates and does not pollute molten steel.

Table 2 Comparison of properties of carbon-bonded and phosphate-bonded gunning materials

performanceCarbon bonded gunning materialPhosphate bonded gunning material
Gun spraying temperature/℃>800<1000
Durability/furnace4~82~4
RemarkGood durabilitygeneral purpose

The newly developed carbon bonded gunning material not only has good adhesion strength near 1000°C by using adhesion additives (new technology), but also greatly improves the adhesion in high temperature areas above 1300°C. According to this, it can be repaired after slag removal, which shortens the repair time. Moreover, it adheres firmly to the repair surface under high temperature and is not easy to peel off, reducing the number of repairs.

Table 3 shows the quality of carbon-bonded gunning materials developed for ultra-high temperature construction. The carbon content is increased in the order of JTM-M-168, JTM-M-207 and JTM-M-191, which improves the thermal shock resistance, is not easily wetted by slag and molten steel, and shows good durability. However, due to the increase in binder, the combustion hardening time tends to be prolonged. JTM-M-207 is a product that combines short-term combustion hardening properties with excellent durability.

In addition, Table 4 shows the actual performance of these products in industrial furnace applications. In industrial furnaces, good adhesion strength can also be confirmed on high-temperature repair surfaces of 1300 to 1500°C, which are difficult to repair with conventional carbon-bonded gunning materials. Compared with conventional carbon-bonded gunning materials, the durability is 2 to 2.5 times. The development of new repair materials will help extend the life of the converter and improve the operation rate.

High adhesion strength under high temperature conditions

Less peeling due to low shrinkage value

Low slag wetting and high corrosion resistance

Phosphate free

Conventional gunning equipment can be used

Table 3 Characteristics of carbon-bonded gunning materials for high-temperature construction​

Trade nameJTM-M-168 JTM-M-207JTM-M-191
Chemical composition/%   
MgO847877
C7913
Particle size distribution   
Maximum size/mm333
>1.0mm/%282828
<0.075mm/%383838
Physical properties after 1000℃   
Apparent porosity/%303132
Bulk density/(g·cm-³)2.82.82.8

Table 4 Use performance of carbon bonded gunning materials

Repair parttrunnion side
Temperature/°C1000~12001.3001500
Mixing consumption per unit time/kg200~1000  
Durability/furnace   
Regular products2~52~30
Newly developed products5~105~71~2
Actual use itemsJTM-M-207JTM-M-207JTM-M-191

Rapid hardening high temperature pouring repair material

Table 5 shows the characteristics of high-temperature pouring repair materials for converter repair. According to the classification of binders, high-temperature cast repair materials can be roughly divided into three types: water-based, phenolic resin-based and asphalt-based. Compared with the asphalt system, the adhesion strength of the water-based and phenolic resin-based systems is slightly lower, so the durability is also lower than that of the asphalt-based systems. There are wet type and powder type in the asphalt system, and the material properties are the same. However, the powder type has good storage properties in the converter operating area, that is, it is not easy to change over time, so the powder type has now become the mainstream. Figure 2 is the repair method of high-temperature pouring repair material. The repair of high-temperature pouring repair material is carried out after steel tapping and slag discharge. Generally, the repair material is put into the converter through a scrap steel chute. The input high-temperature pouring repair material flows while burning, covering and filling the damaged parts of the refractory bricks on the charging side, furnace bottom, and tapping side for repair. Therefore, it is required that the high-temperature pouring repair material should have the characteristics of quickly flowing to the damaged part and quickly extinguishing the flame and hardening. Figure 3 is a comparison of the hardening time and fluidity between the developed product and conventional products. Hardening time and fluidity are important properties of high-temperature cast repair materials. However, generally as the hardening time becomes shorter, the fluidity also tends to decrease. By studying the type and amount of asphalt, combustion accelerators, and particle size composition, the developed product achieves short-time hardening and high fluidity. Compared with the fluidity of the equivalent conventional product (FRX-M90-D58), the laboratory hardening time of the newly developed rapid-hardening high-temperature castable (FRX-M90-D110) is shortened by about 30%. Table 6 shows the quality of rapid hardening high temperature cast repair materials. The actual application results of industrial furnaces are shown in Table 7. In industrial furnaces, select the most suitable product based on operating conditions (guaranteed repair time). Compared with conventional products, it is confirmed that the hardening time of the developed product is shortened by approximately 30% to 60%. Because of its high fluidity and short-time hardening, the fast-hardening high-temperature pouring repair material is used in various factories and has contributed to improving the converter operating rate and has been well received.

Table 5 Classification of high temperature cast repair materials

Classification  Anhydrous binder systemWater system
Phenolic resin systemAsphalt system
moist typePowder type
Liquidity
Adhesion
hardening timeOOO
DurabilityOO△~X
RemarkHigh feesPoor storageOverall performance is more popular

Note: Good ◎…O…△…×Poor.

Table 6 Typical properties of rapid hardening high temperature cast repair materials

Trade name Newly developed productsRapid hardening
FRX-M90-D104FRX-M90- D110FRX-M90-D58
chemical components/%   
MgO777577
CaO0.80.70.8
C7.67.27.6
Pouring at 1000℃   
Apparent porosity/%25.525.325.7
Bulk density/(g·cm-³)2.462.472.42
Adhesion strength/MPa2.62.32.5
Thermal mobility index/-10098100
Hardening time index/-8870100

Table 7 Performance of industrial furnace application of rapid hardening high temperature cast repair materials

userFactory AFactory BFactory C-aFactory C-b
Converter repair partsLoading department  bottomLoading part, tap holeLoading part, bottom
Repair temperature/℃1300  120014001100
Usage/kg700    900700500
Hardening time/min    
Regular products40     452035
Improved product(D104)20     301025
Improved product(D110)10     20515
Durability/furnace7~8    5~65~67~10

Figure 2 Repair method of high temperature pouring repair material

Figure 3 Hardening time and fluidity of newly developed repair materials

Future directions

As mentioned above, combining carbon-bonded gunning materials corresponding to ultra-high temperature construction and rapid hardening high-temperature pouring repair materials can significantly improve the thermal repair efficiency of the converter. In addition, as one of the measures to reduce the environmental load, refractory materials have recently begun to be recycled, and the company has also developed ultra-high-temperature carbon-bonded gunning materials and rapid-hardening high-temperature cast repair materials using MgO-C bricks after use in converters. . It is believed that the use of these recycled products will be expanded in the future.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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