News

How to Repair Cooling Wall Damage After Carbon Bricks are Soaked in Water or Broken?

by

During the operation of the blast furnace, due to improper operation or different degrees of resistant material erosion, local cooling walls may burn out or wear and leak. Carbon bricks will undergo brittle fracture at a temperature of about 800°C. For cooling walls above the tuyere zone, the cooling walls can be quickly replaced by stopping the wind and lowering the material line or by emergency repair, and the lining can be hot-sprayed. Once the cooling wall in the furnace area leaks, the internal carbon bricks are soaked in water, or the carbon bricks are brittlely fractured, and heat conduction is blocked, there will be a risk of iron leakage from the furnace, causing major accidents. At present, the repair of carbon bricks in the furnace is generally to stop the furnace and clean the furnace. After replacing the cooling wall, carbon bricks are laid from the inside or high thermal conductivity materials are poured. The maintenance cycle lasting more than 20 days is inefficient and greatly affects the rhythm of blast furnace smelting.

Blast Furnaces Lining Construction
Blast Furnaces Lining Construction

In order to solve the defect of long repair period, a national new patent technology was developed – a repair method for damaged cooling staves and carbon bricks for blast furnace hearth after water immersion or brittle fracture. This repair method has the following characteristics:

  1. First, the furnace skin at the damaged cooling stave is cut off and the damaged cooling stave is removed, the damaged carbon bricks are removed, and a new cooling stave and a new furnace skin are installed. There is a gap between the new cooling stave and the surrounding cooling staves. The lower part of the new furnace skin is provided with a first grouting hole, the middle part is provided with a second grouting hole, and the top is provided with an exhaust hole.
  2. Second, the grouting pipe is passed through the first grouting hole and the new cooling stave in turn, and the pipe mouth is extended into the gap between the new cooling stave and the carbon brick after the gap between the surrounding cooling staves. The high thermal conductivity castable is injected through the grouting pipe at a certain pressure and begins to fill the gap between the new cooling stave and the carbon brick. During the injection process, the high thermal conductivity castable is injected into the gap between the new cooling stave and the surrounding cooling staves through the gap between the new cooling stave and the new furnace shell.
  3. Third, observe the filling situation from the second grouting hole. When the high thermal conductivity castable spreads to the same height as the second grouting hole, stop filling and seal the first grouting hole.
  4. Fourth, after the grouting pipe passes through the second grouting hole and the gap between the new cooling wall and the surrounding cooling wall in turn, the pipe mouth extends into the gap between the new cooling wall and the carbon brick. Pour the high thermal conductivity castable through the grouting pipe at a certain pressure and start filling the gap between the new cooling wall and the carbon brick. During the filling process, the high thermal conductivity castable is poured into the gap between the new cooling wall and the surrounding cooling wall into the gap between the new cooling wall and the new furnace shell.
  5. Fifth, observe the filling situation from the exhaust hole. When the high thermal conductivity castable spreads to the same height as the exhaust hole, stop filling. Seal the second grouting hole and the exhaust hole.

The repair method has achieved the following beneficial effects:

  • First, the repair cycle of damaged cooling walls and carbon bricks is greatly reduced, and the repair can be completed in only 1 day.
  • Second, it ensures that each layer of gaps is fully filled, thereby ensuring normal heat transfer and gap-free insulation.
  • Third, the maintenance cost is extremely low, and only normal grouting is required.
  • Fourth, the economic benefits of blast furnaces are greatly improved, and the market prospects are extremely broad.

Calculation and Laying Method of G-type Refractory Bricks for Lime Kiln

by

G1, G2, G3, G4, G5, G6, G7, G8 clay bricks and high alumina bricks, these types of refractory brick masonry circles need to be carefully calculated. At the beginning of kiln design, calculating the brick type and quantity required for G-size bricks often makes people dizzy. Today, we will bring you specific calculation methods and construction points to help you design furnace types, calculate purchase quantities and provide references for construction.

Lime kiln refractory brick Construction
Lime kiln refractory brick Construction

Calculation of the Amount of Furnace bottom Bricks

The volume of the bottom of the lime shaft kiln can be calculated by dividing the total volume of bricks by the volume of each brick. When calculating the number of bricks per layer, the horizontal cross-sectional area of ​​the furnace bottom bricks can be divided by the corresponding surface area of ​​each brick. Generally, a loss of 2% to 5% should also be considered. If the weight of the bricks needs to be calculated, the weight of each brick is multiplied by the number of bricks.

Calculation of the Amount of Ring Furnace Body

The other parts of the lime kiln are all ring cylinders or cones. Regardless of the upper and lower layers or the inner and outer layers, rings must be built, and wedge bricks must be used when building rings. If a ring of any diameter is built, wedge bricks and straight bricks must be used together. Generally, G-1 straight bricks are matched with G-3 or G-5 wedge bricks, and G-2 straight bricks are matched with G-4 or G-6 wedge bricks. Due to the different required ring diameters, the number of straight bricks and wedge bricks is also different.

If G-3, G-4, G-5, G-6 wedge bricks are used alone to build rings, the formula can be listed:

nx=(2πa)/(b-b1)

Where:

nx——Number of wedge bricks for building a ring, pieces;

a——Brick length, mm;

b——Width of the big end of the wedge brick, mm;

b1——Width of the small end of the wedge brick, mm.

From the above formula, we can know that the number n of wedge-shaped bricks used in each ring is only related to the width of the two ends of the wedge-shaped bricks and the length of the bricks, but has nothing to do with the diameter of the ring.

It can be concluded that:

Number of bricks needed to build a ring with G-3 is n=97

Number of bricks needed to build a ring with G-4 is n=87

Number of bricks needed to build a ring with G-5 is n=48

Number of bricks needed to build a ring with G-6 is n=54

At the same time, the inner diameters of the rings built with the above four wedge-shaped bricks are 4150mm, 3450mm, 1840mm, and 1897mm, respectively.

 

If you want to build a ring of any diameter, you need to use straight bricks and wedge bricks together. The number of straight bricks can be calculated by the following formula:

nz=(πd-nx*b1)/b

Where:

nz——Number of straight bricks, pieces;

nx——Number of wedge bricks, which is a constant after the brick type is determined;

b1——Width of the small end of the wedge brick, mm;

b——Width of the straight brick, mm;

d——Inner diameter of the ring, mm.

 

Example: Try to use G-3 and G-1 bricks to build a ring with an inner diameter of 7.2 m. Find the number of wedge bricks and straight bricks required.

Solution:

nx=97 pieces

nz=(πd-nx*b1)/b=3.14*(7200-97*135)/150=65 pieces

Construction points of G-type bricks

When building a lime kiln, two types of bricks can be used to build rings of different diameters to adapt to the size of the furnace and the change of furnace diameter with height. Generally, refractory bricks G1 are matched with G3 or G5 wedge-shaped bricks, and refractory bricks G2 are matched with G4 or G6 wedge-shaped bricks. Due to the different ring diameters during the masonry process, the number of straight bricks and wedge-shaped bricks is also different.

When the inner lining of the lime kiln is built, the ring seams are required to be built with all staggered seams, and bricks must not be cut. If bricks must be cut, the cut surface must be smoothed. The thickness and staggered seams of the masonry are combined with different brick types with brick lengths of 230 mm and 345 mm. The thickness of the masonry can be increased or decreased by 115 mm and staggered seams can be achieved by matching. When the thickness change is less than 115 mm, the filler seams between the masonry and the furnace shell or the masonry and the cold wall can be used to adjust.

Of course, the specific dosage calculation and construction methods of the above methods are not fixed. It depends on the on-site furnace conditions and usage requirements.

Self-Baking Carbon Bricks for Calcium Carbide Furnaces

by

Self-baked carbon bricks for calcium carbide furnaces are made of high-temperature treated anthracite as the main raw material and are made through a high-frequency vibration molding process. They are used to build the bottom of large and medium-sized calcium carbide furnaces and the lining of the melting pool.

Self-Baking Carbon Bricks for Calcium Carbide Furnaces

Self-baked carbon bricks are divided into two categories according to the capacity of the calcium carbide furnace transformer. The first category is suitable for calcium carbide furnaces greater than or equal to 10000kVA, code-named TKZ-1. The second category is suitable for calcium carbide furnaces less than 10000kVA, code-named TKZ-2.

Surface quality of self-baked carbon bricks

  • 1) The surface of the carbon brick should be flat, and no local deformation, protrusions, cracks and oil defects are allowed.
  • 2) Corner missing: depth not greater than 10mm and not more than 1.
  • 3) Edge missing: length not greater than 50mm, depth not greater than 5mm and not more than 1.
  • 4) Distortion: not greater than 1mm on the masonry surface of the carbon brick.

The cross-sectional structure of the self-baked carbon brick should be uniform, without stratification, local looseness, voids and dry material defects.

Self-Baking Carbon Bricks for Calcium Carbide Furnaces
Self-Baking Carbon Bricks for Calcium Carbide Furnaces

Carbon Brick Standards and Performance Guide

Carbon Brick Size and Deviation:

  • The height tolerance of carbon bricks at the bottom and side of the furnace wall is ±3 mm, and the width tolerance is ±5 mm.
  • For carbon bricks without free end faces, the length tolerance is ±5 mm; for carbon bricks with free ends, the length tolerance is ±10 mm.

Carbon Brick Crack and Notch Standards:

  • The width of the crack on the carbon brick is less than 0.5 mm, the length is less than 200 mm, and there are no more than two cracks on each side.
  • The length of each side of the cross-edge crack is no more than 100 mm.
  • The width of the single notch and bee eye on the carbon brick shall not exceed 20 mm and the depth shall not exceed 10 mm.

Carbon brick size specifications:

  • 400*400*400-1800mm
  • 400*500*400-2500mm
  • 600*650*600-2000mm
  • 800*800*800-1900mm

The length can be customized according to customer needs, and various models and specifications of special-shaped carbon blocks and furnace mouth carbon blocks can be processed.

Performance requirements of carbon bricks:

  • Fixed carbon ≥50%
  • Silicon carbide content 15-22%
  • Volume density ≥1.7g/cm³
  • Apparent porosity ≤20%
  • Compressive strength ≥42MPa
  • Ash content ≤7%
  • Flexural strength 6.86MPa

Semi-graphite silicon carbide carbon bricks ensure efficient operation of your industrial furnaces! Contact the Rongsheng Manufacturer for detailed information.

What are the Formula, Proportion and Applicability of Refractory Plastics?

by

Refractory plastic is made of 70~80% granular and powdery materials, 10~25% plastic clay and other binders, and appropriate plasticizers. Refractory plastic is a hard mud paste and is an amorphous refractory material that maintains high plasticity for a long time.

Refractory Plastic Materials

Refractory plastics are mainly used in various heating furnaces that do not directly contact the molten material. The materials are mostly clay and high-alumina, but also silicon, magnesium, chromium, zircon, and silicon carbide. If classified by binder, there are clay-bonded, water glass-bonded, phosphate-bonded, sulfate-bonded plastics, etc.

Aggregates for Refractory Plastics

Aggregates for refractory plastics mainly include special-grade clay clinker, third-grade, second-grade, or first-grade alumina clinker, etc. The maximum particle size of the refractory aggregate is 10mm, and its particle grading is: 10~5mm, 33%~40%; 5~3mm, 28%~35%, less than 3mm, 28%~35%. It should be pointed out that particles of 0.5~0.09mm should be minimized or eliminated. The amount of aggregate is 55%~65%.

Refractory powder is generally made of special-grade, first-grade or second-grade alumina clinker. The fineness of ≤0.09mm should account for 95%, and the finer the better. It is strictly forbidden to use underburned materials or clay clinker as refractory powder. The amount of refractory powder is 20%~30%.

Rongsheng Refractory Plastics
Rongsheng Refractory Plastics

Performance of Refractory Plastics

In order to ensure smooth construction and normal use at high temperatures, refractory plastics should generally have the following basic properties: ① have a certain degree of plasticity to facilitate construction; ② have a certain shelf life to ensure that the molding performance remains unchanged during the specified storage period; ③ have a certain strength after room temperature curing to facilitate the removal of the frame or transportation after construction; ④ have a certain high temperature volume stability to prevent damage to the furnace lining structure due to excessive deformation.

Plasticity of Refractory Plastic

Since it is called refractory plastic, what does its plasticity have to do with?

The plasticity of plastic has a direct impact on the characteristics of clay and the amount of clay added. It is also related to the amount of water added. Plasticity increases with the increase of water added. But it cannot be too high, generally 5~10%. To improve plasticity, it is necessary to control the amount of clay and water added in the plastic, and plasticizers can be added.

The role of plasticizers in refractory plastics: ① Increase the hygroscopicity of clay particles, so that clay particles are dispersed and coated with water film; ② Make clay particles sol; ③ Increase the electrostatic repulsion between clay particles and stabilize the sol; ④ Exclude ions that hinder solification from the system as insoluble salts; ⑤ Increase the viscosity of water in clay to form a solid water film, etc. Commonly used plasticizers are pulp waste liquid, cyclohexane acid, lignin sulfonate, lignin phosphate, lignin chromate, etc. At the same time, the binder used in refractory plastics also has a certain influence on plasticity.

Soft clay is an important raw material for refractory plastics, and the main performance characteristics of plastics also come from soft clay. In refractory plastics, soft clay not only acts as a binder, but also as a plasticizer and sintering agent. It has a great influence on the plasticity, water retention, construction, room temperature, and high-temperature refractory properties of refractory plastics. Therefore, the soft clay used to prepare refractory plastics should have good plasticity, hygroscopicity, moderate viscosity, refractoriness and sintering properties. From the perspective of molding and water retention, the best viscoplasticity is Guangxi clay and ash clay, the worst is Fuzhou clay, Jiaozuo clay, camphor clay, and purple wood clay can be used in combination. Its fineness: less than 0.09mm accounts for more than 85%, and the dosage is 10%~15%.

The chemical binder is aluminum sulfate solution with a density of 1.2~1.3g/cm³. After mixing with this binder, the material should be trapped for more than 16h. Because the sulfate in aluminum sulfate reacts with the iron in the powder to generate iron sulfate and release hydrogen, which causes the mud to bubble or swell, the material should be trapped. After drying, there is a light yellow precipitate on the surface of the refractory plastic, which is identified as iron alum by chemical and petrographic analysis. Its molecular formula is FeO·Al₂O₃·4SO₃·22H₂O.

The 18 crystal waters contained in the aluminum sulfate solution are mostly removed at about 134°C. At about 330°C, a small amount of crystal water is lost. The endothermic peak at 835°C is the decomposition of aluminum sulfate into Al₂O₃ and SO₃, and SO₃ escapes in gaseous form. Therefore, the organizational structure of the refractory plastic is slightly loose and the strength is reduced. The endothermic peak in the low temperature section of the iron alum differential thermal curve is caused by the discharge of crystal water. The endothermic peak at 752°C is caused by the decomposition of iron alum and the release of SO₃. It also affects the strength of the plastic.

The amount of foaming of refractory plastic is directly related to the purity, density and addition amount of aluminum sulfate. Generally speaking, when the purity is high, the density is high and the addition amount is large, the amount of foaming is also large. This is due to the large amount of sulfuric acid brought in. Therefore, under the premise of meeting the plasticity, construction and fire resistance of the refractory plastic, crude aluminum sulfate can be selected to prepare a low-density solution and minimize its dosage. The dosage of aluminum sulfate solution is generally 9%~13%.

The additives used in refractory plastics mainly include preservatives, plasticizers, reinforcing agents and preservatives. Its additives include spodumene powder (LiO₂·Al₂O₃·4SiO₂), lithium mica powder (LiO₂·Al₂O₃·3SiO₂) and bentonite and other sintering agents (also known as mineralizers), and expansion agents such as kyanite or sillimanite.

There are many types of admixtures for refractory plastics, including polyvinyl alcohol, dextrin, starch, carboxymethyl cellulose, citric acid, gluconic acid and ethyl silicate. The dosage of admixtures is generally less than 1%, and when it is greater than 1%, it also acts as a binder. Other admixtures include andalusite, sillimanite, zircon and alumina powder, and their dosage is generally greater than 3%.

The maximum particle size of refractory aggregate is 10mm, the moisture content of plastic is about 9%, and the plasticity index is 17%~30%. Sunan mud refers to the composite use of Suzhou mud and Nanjing mud. The former has a high sintering temperature, while the latter has a low sintering temperature due to the high content of low melting points. Special clay and I alum, etc., represent special clay clinker and I alumina clinker, respectively. I and II alum are I and II alumina clinkers, which are mixed in a ratio of 1:1 to make refractory powder. Admixtures are selected according to the use requirements of refractory plastics. For example, if construction is carried out immediately after production, preservatives may not be added.

Rongsheng Refractory Material Factory is a powerful manufacturer and seller of refractory materials. Rongsheng Factory, an environmentally friendly, fully automatic monolithic refractory material production line, specializes in providing monolithic refractory products for high-temperature industrial furnaces, including various refractory castables, high-strength wear-resistant plastics, wear-resistant ramming materials, etc. Contact Rongsheng for free samples and quotation information.

Setting Time of Low Cement Castable Refractory

by

The initial setting time of low-cement castable refractory materials is 40 minutes, and the final setting time does not exceed 8 hours. Factors affecting the setting time include material composition, ambient temperature, and humidity. Specifically:

  • ‌Material composition‌: The composition of refractory castables has a decisive influence on their setting time. For example, the higher the content of aluminate cement, the shorter the setting time; adding retarders can extend the setting time.
  • ‌Environmental temperature‌: The higher the temperature, the shorter the setting time. When constructing in a high-temperature environment, the temperature needs to be controlled to avoid affecting the setting time.
  • ‌Environmental humidity‌: Excessive humidity will cause condensation on the surface of refractory castables, affecting the setting effect. When constructing in a high humidity environment, measures such as strengthening ventilation and increasing the temperature are required.

In practical applications, accelerators or retarders can be added to adjust the initial and final setting times according to the construction conditions and temperature. Rongsheng Refractory Material Manufacturer can customize low-cement refractory castables according to actual working conditions and construction conditions. To purchase high-quality high-temperature industrial furnace lining refractory materials and customized refractory lining material solutions, please contact Rongsheng.

Rongsheng Low Cement Castable
Rongsheng Low Cement Castable

Solidification and Use Effect of Refractory Castables

Refractory castables are a kind of refractory materials widely used in high-temperature industrial fields such as metallurgy, petroleum, chemical industry, and electric power. It has excellent high-temperature performance, corrosion resistance, wear resistance and other characteristics, and can effectively protect equipment from damage caused by high temperature and chemical corrosion. However, when using refractory castables, we often encounter a problem: How long does it take for refractory castables to solidify? Will it affect its use effect if it solidifies too early or too late?

First, let’s understand the solidification process of refractory castables. When refractory castables are cast on equipment or structures, they will gradually solidify over a certain period of time. This process is mainly affected by factors such as material composition, construction conditions, ambient temperature and humidity.

Generally speaking, the solidification time of refractory castables can be divided into two stages: initial setting and final setting. Initial setting refers to the time when the castable begins to lose fluidity and hardens on the surface; while final setting refers to the time when the castable completely loses fluidity and reaches complete hardening.

So, how long does it take for refractory castables to solidify? There is no fixed answer to this, because different refractory castable formulas and construction conditions will lead to different solidification times. Generally speaking, the initial setting time is from a few hours to more than ten hours, while the final setting time may take several days or even longer.

In order to ensure the construction quality and use effect of refractory castables, we need to pay attention to the following points:

  1. Before construction, the refractory castables should be fully stirred and mixed to ensure that its components are evenly distributed.
  2. During the construction process, the construction temperature and humidity should be controlled to avoid the castables from being disturbed by external factors.
  3. After the pouring is completed, the castables should be cured and insulated in time to ensure their normal solidification.

In short, the solidification time of refractory castables is affected by many factors and needs to be judged and adjusted according to the actual situation. At the same time, attention should be paid to details during the construction process to ensure the construction quality and use effect.

Rongsheng Lightweight Refractory Insulation Brick Manufacturer – Mullite Insulation Brick

by

Lightweight thermal insulation refractory materials. The common characteristics of this type of material are low bulk density, light weight and low thermal conductivity. Rongsheng lightweight refractory insulation brick manufacturer, refractory insulation bricks, use temperature between 1000 ~ 1500 ℃, mainly lightweight clay bricks, lightweight silica bricks, lightweight high alumina bricks, etc. High temperature insulation bricks, use temperature above 1500 ℃, and can be directly used as the lining of high temperature kilns, mainly lightweight corundum bricks, alumina hollow ball products and zirconia hollow ball products. This article mainly introduces mullite insulation bricks. Contact Rongsheng for more information.

Rongsheng Mullite Insulation Brick Manufacturer
Rongsheng Mullite Insulation Brick Manufacturer

Mullite Insulation Brick

Lightweight mullite brick is a new type of energy-saving refractory material that can directly contact the flame and has the characteristics of high temperature resistance, high thermal shock stability, high strength, and low thermal conductivity. Mullite insulation bricks are widely used in the lining, furnace door bricks, kiln car bricks, etc. of ceramic roller kilns, shuttle kilns, cracking furnaces, hot air furnaces and various electric furnaces. The advantages are high purity, low impurity content, high temperature resistance, direct contact with flames, resistance to various atmosphere corrosion, low thermal conductivity, low heat melting, high strength, and excellent thermal shock resistance, high dimensional accuracy, and can be cut at will. The body density can be between 0.5 0.6 0.8 0.9 1.0 1.2 1.5 according to user requirements. It acts on high-temperature kilns and directly contacts the flame. It has good insulation effect, high compressive strength, and low thermal conductivity. It is suitable for electric kiln insulation, various high-temperature rotary kilns, tunnel kilns, nitriding gas kilns, etc. The crystals of fused mullite are larger than those of sintered mullite, and its thermal shock resistance is better than that of sintered products. Their high temperature performance mainly depends on the content of alumina and the uniformity of the distribution of mullite phase and glass. 1400 degree mullite bricks are mainly used for the top of hot blast furnace, blast furnace body and bottom, glass melting furnace regenerator, ceramic sintering kiln, dead corner lining of petroleum cracking system, etc.

JM23 lightweight mullite brick is a high-temperature resistant and energy-saving lightweight refractory material produced by Rongsheng Refractory Material Factory. Lightweight mullite brick has light weight and good thermal insulation effect. It is a high-quality high-purity refractory powder. According to the required specific gravity of the product, organic composite fillers are added, vacuum extruded and sintered at high temperature to form lightweight mullite products. Rongsheng manufacturers can customize different specifications of lightweight mullite bricks according to the actual working conditions of high-temperature industrial furnaces, and the content of alumina ranges from 50% to 80%.

Low Iron JM23 JM26 JM28 Mullite Insulation Bricks
Low Iron JM23 JM26 JM28 Mullite Insulation Bricks

Characteristics of Mullite Lightweight Insulation Bricks

High temperature resistance can reach above 1790℃. The load softening start temperature is 1600-1700℃, and the compressive strength at room temperature is 70-260MPa. Good thermal shock resistance, high strength, low high-temperature creep rate, low expansion coefficient, small thermal coefficient, and resistance to acidic slag erosion. It can also greatly reduce the weight of the high-temperature furnace body, transform the structure, save materials, save energy, and improve production efficiency.

Lightweight mullite bricks are made of imported plate-shaped corundum and high-purity fused corundum as the main raw materials. They are made by mixing, drying, forming and firing in a high-temperature shuttle kiln using advanced ultrafine powder adding technology. Lightweight mullite bricks are widely used in equipment such as residual oil gasification furnaces, synthetic ammonia second-stage reforming furnaces, carbon black reactors and refractory kilns. The product’s dimensions, physical and chemical indicators and service life all meet customer requirements.

According to the chemical structure of lightweight mullite bricks, its outstanding performance is as follows:

  • 1. Low heat melting. Due to low thermal conductivity, mullite series lightweight insulation bricks accumulate very little heat energy, and the energy saving effect is obvious in intermittent operation.
  • 2. Low thermal conductivity, with good thermal insulation effect.
  • 3. Low impurity content has very low content of oxides such as iron and alkali metals. Therefore, the refractoriness is high, and the high aluminum content enables it to maintain good performance under reducing atmosphere.
  • 4. High hot compressive strength.
  • 5. It can be processed into special shapes to reduce the number of bricks and masonry joints.
  • 6. The appearance size is precise, which speeds up the masonry speed and reduces the use of refractory mud. The strength and stability of the masonry are guaranteed, thereby extending the life of the lining.

Application Scope of Mullite Insulation Bricks

Mainly used for high-temperature metallurgical hot blast furnaces above 1400℃, parts of torpedo cars impacted by molten iron, slag lines, furnace roofs of steelmaking arc furnaces, material channels of glass melting furnaces, regenerator arches, and upper structures. Ceramic sintering kilns, ceramic roller kilns, tunnel kilns, electric porcelain drawer kilns, and dead-angle furnace linings of petroleum cracking systems. Linings of glass crucible kilns and various electric furnaces, and the walls of clarifiers, which can directly contact the flame.

Selection of Refractory Aggregate and Powder for Ultra-Low Cement Castables for Iron Troughs

by

In the preparation process of ultra-low cement refractory castables for the blast furnace tapping channel, the selection of refractory aggregates and refractory powders is very important. Only by selecting suitable refractory aggregates and powders, reasonably preparing them, and using them in proper amounts can they play their greatest role. Rongsheng refractory material manufacturer, an advanced fully automatic amorphous refractory castable factory, specializes in providing long-life refractory castable products for high-temperature industrial furnaces. Contact Rongsheng to get a free quote for ultra-low cement castables for tapping channels.

Selection and grading of refractory aggregates for ultra-low cement castables for iron trenches

In ultra-low cement refractory materials, the amount of refractory aggregate is generally 68% to 72%, which acts as a skeleton and can significantly affect the performance of the refractory castable lining. The thickness of the lining and the construction and production methods are different, and the critical particle size of the refractory aggregate is also different. At present, the critical particle size of refractory aggregates tends to decrease, and 8mm or 5mm is generally used. The preparation of iron ditch refractory castables usually adopts three-level gradation or four-level gradation. The particle gradation is as follows: 8~5mm 40%~60%, 5~1.2mm 10%~30%, 1.2~0.15mm 20%~40%. Or 5~3mm 40%~60%, 3~1mm 20%~30%, 1~0.15mm 15%~25%. Different types of refractory aggregates have different properties of the prepared ultra-low cement castables.

Ultra Low-Cement Castable Precast Shapes for Iron Trough
Ultra Low-Cement Castable Precast Shapes for Iron Trough

The influence of aggregate type and quality on the properties of castables. Different types of refractory aggregates have different drying compressive strengths of castables. That is, the quality of refractory aggregate directly affects its performance. Because good aggregate has low porosity and low water absorption, the castable requires less water and its performance can be improved.

Preparation of refractory powder for iron ditch castables

Refractory powder is the matrix material of amorphous refractory materials, which plays the role of filling aggregate gaps and improving construction and workability.

Refractory powder for iron ditch castables includes fused corundum powder, SiC powder, and carbon materials, among which the amount of fused corundum powder is 5% to 10%. The amount of ultrafine powder should be determined according to the experience of its variety, generally 5% to 15%. Among them, the appropriate amount of active SiO2 ultrafine powder is 5% to 7%, and the amount of other ultrafine powders is 7% to 10%.

Use of active SiO2 ultrafine powder and α-Al2O3 ultrafine powder

In ultra-low cement refractory castables, the basic mechanism of action of ultrafine powder is filling. In ultra-low cement refractory castables, various ultrafine powders can form colloidal particles in water. When a dispersant is present, the double electric layer formed on the surface of the particles overlaps to generate electrostatic repulsion, which prevents adsorption and flocculation between particles. At the same time, the dispersant is adsorbed around the particles to form a solvent layer, thereby increasing the fluidity of the castable.

The ultrafine powders used in Tiegou refractory castables mainly include active SiO2 powder and α-Al2O3 powder. The content of their components is 93.2% and >90%, respectively, and the particle size distribution <1.0μm should be >70%.

There are two types of SiO2 ultrafine powder. One is made of high-purity silica, and the other is a by-product of producing metallic silicon or ferrosilicon. The former is granular and inactive, while the latter is hollow spherical and active, does not agglomerate, and has good dispersibility and filling properties. It reacts with volcanic ash at room temperature and reacts with Al2O3 to form mullite at high temperature, which is beneficial to improving the strength of the castable.

α-Al2O3 ultrafine powder is made by calcining industrial alumina. Its characteristics are good dispersibility, small particles, easy sintering at high temperature and small volume effect.

Active SiO2 is added to ultra-low cement refractory castables. When the temperature is higher than 900°C, it reacts with Al2O3 in powder or cement. Mullitization is gradually formed, producing a volume effect, offsetting part of the volume shrinkage of the refractory castable, and promoting the improvement of strength. Adding α-Al2O3 ultrafine powder can cause calcium aluminate to form more calcium hexaaluminate (CA6) at high temperatures, as well as a small amount of mullite, anorthite, etc. The molar volumes of these minerals are relatively large, which prevents their volume from shrinking. Microscopic observation confirmed that the main crystal phase CA6 is a small columnar and needle-shaped crystal, and the anorthite is a small columnar crystal, which together form a small columnar and needle-shaped cross-skeleton structure, which is relatively strong and dense. Therefore, the strength of the castable can be significantly increased.

As the amount of ultrafine powder increases, the effect of cohesion and bonding increases, the strength increases, the volume density increases, and the apparent porosity decreases. However, increasing the dosage of SiO2 ultrafine powder will reduce the Al2O3 content in the castable. At the same time, the increase of free quartz will inevitably lead to a decrease in the slag resistance of the castable. Experiments have proven that when the dosage of SiO2 ultrafine powder is about 5%, the slag resistance is the best. In addition, adding more ultrafine powder will cause uneven shrinkage of the castable after high-temperature sintering, resulting in a significant decrease in strength.

Effect of ultrafine powder on the flexural strength of ultra-low cement castables. The ultrafine powder mixed with equal amounts of active SiO2 and α-Al2O3 has the highest strength. In fact, in ultra-low cement refractory castables, not only the fineness of the ultra-fine powder plays a role, but also its shape and activity. For example, SiO2 powder is silica fume, which is spherical and active, although slightly thicker. However, its filling and water-reducing properties are better than granular inactive α-Al2O3. Therefore, the dosage of active SiO2 ultrafine powder can also be less.

Effect of ultrafine powder dosage on the compressive strength of castables. As the amount of ultrafine powder increases, the compressive strength increases after sintering at 1600°C. When the dosage of SiO2 ultrafine powder is about 5%, the dosage of Al2O3 ultrafine powder is about 7%. At this time, the compressive strength is high and other properties are also excellent.

Use of silicon carbide and carbon materials

SiC and carbon materials should be added to the iron trench refractory castable to improve its slag resistance and thermal shock stability. Tests and use have shown that the grade and amount of SiC and carbon materials have a great influence on the performance of the castable. The grade and amount should be reasonably selected according to the size of the blast furnace and the different parts of use.

In the iron trench refractory castable, silicon carbide plays a filling role and forms the matrix of the iron trench material. Therefore, the particle size should be <3.4mm, of which <0.15mm should account for more than 60%. The particle size of the carbon material should also be less than 0.3mm.

Due to the addition of SiC and carbon materials, the oxidation resistance of the castable is reduced. To improve the oxidation resistance of the castable, metal aluminum powder and metal silicon powder can be added at the same time. In this way, metal silicon and aluminum react with carbon at high temperatures to generate SiC and Al4C3. The castable’s structure and surface are made denser, its oxidation resistance is improved, and the castable’s strength is also improved.

Factors Affecting the Performance of Refractory Castables

by

There are many varieties of refractory castables, with different mix proportions, different performances, different construction methods, and different maintenance systems. Rongsheng Refractory Material Factory has found that there are many factors that affect the performance of refractory castables based on their production and sales experience over the years. The specific ones are as follows.

Application Fields of Refractory Castables
Application Fields of Refractory Castables

  1. Amount of cement

Cement is one of the important components of refractory castables. It is an important material that determines strength and also affects other properties. Different types of cement and their dosage have different effects on performance. For example, CA-50 cement high-alumina refractory castables, refractory aggregates and powders are both secondary alumina clinker, and the amount of water added is 10%. With the increase of cement dosage, the compressive strength at room temperature will increase. The compressive strength after burning at 1200℃ is 40%~65% lower than the drying compressive strength. The refractoriness and load softening temperature continue to decrease, and the linear shrinkage after burning also increases. This is because CA-50 cement has a high impurity content and low refractoriness. When the dosage increases, the amount of liquid phase in the heating process of the castable is large, resulting in a decrease in performance. Therefore, under the condition of ensuring the strength at room temperature, the amount of CA-50 cement should be minimized to improve the high-temperature performance of the refractory castable. When the amount of cement is reduced, the refractory powder should be appropriately increased so that the combined amount of cement and powder can fully wrap the refractory aggregate and the refractory castable can achieve the maximum density. The commonly used cement dosage is 10%~15%.

  1. Water addition

Different types of aluminate cement can produce different refractory castables. The same type of cement can also be used to make multiple types of refractory castables. When the mix ratio and process conditions of refractory castables are the same, the influence of water dosage on the performance of refractory castables is basically the same. Taking CA-50 cement high-alumina refractory castable as an example, the influence of water dosage on the performance of castables is that refractory aggregate and powder are both secondary alumina clinker, aggregate is 70% of the total material <15mm, powder and cement are 15% each. After the initial setting of the molding, the mold is removed after wet curing for 1d, and then standard curing is carried out for 2d to test various properties. As the amount of water used in the castable increases, various properties generally decrease significantly. The compressive strength at room temperature decreases by 27%~35%, the drying compressive strength decreases to 19.1MPa, the compressive strength after burning decreases by about 40%, and the high temperature compressive strength decreases by about 57%. The load softening temperature dropped from 1400℃ to 1250℃, and the post-firing line change dropped from -0.38% to -0.96%. The apparent porosity increased from 19% to 23%, and the bulk density dropped from 2.29g/cm3 to 2.17g/cm3. That is to say, the selection of water dosage (or water-cement ratio) is very important when preparing aluminate cement refractory castables. When the amount of water is large, after heating, the water escapes, the pores increase, the structure becomes loose, and various properties are reduced comprehensively. Therefore, under the condition of ensuring its construction and workability, the amount of water in the mixture should be minimized. Under the premise of not adding water reducing agent, the appropriate water dosage of aluminate cement refractory castable is 10%~13%.

It should be pointed out that when the mix ratio and production process of refractory castables are basically the same, there is an optimal value for its water dosage. Therefore, when constructing and making aluminate cement refractory castables, they should be tried and mixed first to select the best fluidity. Compare the strength at room temperature and determine the optimal amount of water before production and construction can begin.

  1. Refractory powder

Refractory castables are generally mixed with appropriate refractory powder. Its functions: (1) Reduce cement consumption, reduce costs and increase operating temperature. (2) Refractory powder can play a role in infertility, and can participate in reactions at high temperatures to form high-temperature resistant minerals to improve refractory performance. (3) The addition of refractory oxide ultrafine powder can reduce the amount of water, form high-temperature resistant minerals at high temperatures or enhance sintering properties, so it can improve the performance of castables. The type, fineness and dosage of refractory powder are important factors affecting the performance of castables.

The fineness of refractory powder directly affects the strength, bulk density and apparent porosity of refractory castables. Generally speaking, the finer the refractory powder, the better the performance of the refractory castable. When ultrafine powder is used to replace part of the refractory powder, its bulk density increases, its apparent porosity is low, and its strength is significantly improved.

  1. Refractory Aggregate

Refractory aggregate is one of the important components of refractory castables. Its variety, grade, maximum particle size and particle grading are the main factors affecting performance. The influence of refractory aggregate variety on the performance of refractory castables. In addition, the grade, impurity content and sintering quality of refractory aggregate also affect its performance. For example, when alumina clinker is used as refractory aggregate, as the Al2O3 content increases, that is, the grade improves, the refractoriness and load softening temperature of the castable increase, and the linear change after burning decreases. When the material is under-burned or has a high impurity content, its refractoriness and load softening temperature decrease, and the linear shrinkage after burning is large. Therefore, only by selecting suitable refractory aggregates with good sintering and high purity can high-performance refractory castables be prepared.

The more irregular the shape of the refractory aggregate particles, the better, and try not to use long flake materials. Its maximum particle size should be determined according to the thickness of the lining. Once the maximum particle size of the refractory aggregate is determined, its particle grading has a significant impact on the performance of the refractory castable.

  1. Additives

Common additives used in refractory castables are generally divided into water reducers, setting accelerators and setting retarders. In addition, sintering agents and expansion agents are also added. It should be noted that the refractory cement used in refractory castables is different, and the selected additives and their dosage are also different, which should generally be determined by experiment.

  1. Maintenance system

Maintenance systems are divided into standard maintenance, natural maintenance, wet maintenance, steam maintenance, water maintenance and dry maintenance.

The technical team of Rongsheng manufacturer reminds that when constructing amorphous refractory castables, they must be constructed strictly in accordance with the construction instructions. Strictly control the amount of water added. Choose experienced construction workers. To ensure the efficient construction quality. If there are any problems with the construction of refractory castables, technical formula adjustment, etc., please let us know. We can customize refractory lining material solutions according to your actual working conditions.

What is the Difference between Low Cement Castable and Ordinary Refractory Castable?

by

The low cement series refractory castables are developed on the basis of clay-combined refractory castables. According to their content characteristics, they are mainly divided into low cement refractory castables, ultra-low cement refractory castables, and cement-free refractory castables.

The main characteristics of low cement series refractory castables are high volume density, low porosity, high compressive strength, good wear resistance, good thermal shock resistance and strong erosion resistance. In terms of construction, the advantages of low cement refractory castables are strong volume stability and low water consumption in construction. Because of these, low cement refractory castables are widely used.

Rongsheng Low Cement Castable
Rongsheng Low Cement Castable

Classification of Low-Cement Series Refractory Castables

There is no national standard or industry standard for this product in the industry. Therefore, manufacturers have many names for this type of product, some are called dense high-strength refractory castables, some are called low-porosity refractory castables, and some are called low-moisture refractory castables based on the characteristic of low water addition during construction. In foreign countries, the United States classifies low-cement series products according to the calcium oxide content in the castable. Traditional cement castables (calcium oxide content greater than 2.5), low-cement castables (calcium oxide content between 1.0 and 2.5), ultra-low cement castables (calcium oxide content between 0.2 and 1.0), cement-free or ultra-fine powder castables (calcium oxide content less than 0.2).

According to the material of its main raw materials, it is divided into mullite low cement castable, corundum low cement castable, spinel low cement castable, aluminum silicate low cement castable, high aluminum low cement castable, etc.

According to its scope of use, it is divided into ladle refractory castable, iron ditch refractory castable, etc. Different parts of use can directly name the low cement refractory castable.

Compared with traditional aluminate cement castables, low cement refractory castables have a lower cement content. Generally, the cement content of low cement series products is less than 4%, and the water content is less than 11%.

Low-Cement Steel Fiber Reinforced Castable
Low-Cement Steel Fiber Reinforced Castable

What are the Differences between Low-Cement Castables and Ordinary Refractory Castables?

Low-cement castables have the characteristics of high density, low porosity, high strength, low wear, thermal shock resistance and erosion resistance. They are mainly used in metallurgy, electric power, petroleum, chemical industry and various silicate kilns. Such as some components of off-furnace refining devices, off-furnace refining bag covers, electric furnace top linings, heating furnace soaking furnace linings, annealing furnace linings, tundish linings, steel tapping troughs, high-temperature burners and blast furnace iron tapping ditch covers, iron ladle linings, etc.

Low-cement castables have high fluidity. They are used as industrial furnace linings. On-site pouring, smearing and ramming construction methods can be used.

Low cement castables are similar to ordinary refractory castables. They are all composed of refractory aggregates, refractory fine powders and binders. The difference is that in the matrix composed of refractory fine powders and binders, fine powders are used to replace part or all of the alumina cement. A small amount of dispersant is added to evenly disperse the fine powders between the aggregate particles and fill them in the submicron-level gaps, thus forming a uniform and dense organizational structure. The key to this type of castable is the introduction of fine powders and their dispersion technology. In the field of amorphous refractory materials, ordinary cement castables have low medium-temperature strength and poor spalling resistance. The clay-bonded castables introduced in the early 1970s, although the medium-temperature strength has been improved, the room-temperature strength is much lower than that of ordinary cement castables. They cannot meet the needs of industrial furnaces and thermal equipment for refractory materials. In order to change this situation, low-cement high-strength refractory castables have been developed at home and abroad in recent years.

The main uses and advantages of low-cement castables. The use temperature of low cement castables and ultra-low cement castables is higher than that of ordinary refractory castables of the same material. The use temperature of low cement castables and ultra-low cement castables is higher than that of ordinary refractory castables of the same material.

Rongsheng Refractory Material Factory, environmentally friendly fully automatic monolithic refractory material production line, specializes in providing high-quality monolithic refractory material lining for high-temperature industrial furnace lining. Low cement castables, ultra-low or no cement castables, use micro powders with the same or similar chemical composition as the main material to replace most or all cement. Scientifically optimize factors such as particle grading, micro powder, particle morphology, etc., and add a small amount of dispersant (water reducer) and appropriate amount of retarder and other composite admixtures. Contact Rongsheng for free samples and quotes.

Low-Cement Castable Refractory Factory
RS Low-Cement Castable Refractory Factory

Physical and Chemical Properties of Ultra-Low Cement Castables

Ultra-low cement castables are a common category of refractory castables for cement kilns. Due to the continuous updating of technology in recent years, the problems of slow setting, hardening and low dry strength have been solved, and the problem of excessive strength after burning has been solved. Ultra-low cement refractory castables with excellent performance have been developed. The physical and chemical performance indicators of ultra-low cement castables made with the introduction of 0.5% CaO are as follows.

The flexural strength of ultra-low cement refractory castables after drying at 110°C is 9.8MPa and the compressive strength is 78MPa. After sintering at 1100°C, the flexural strength is 21MPa and the compressive strength is 155MPa. After sintering at 1500°C, the flexural strength is 18MPa, the compressive strength is 149MPa, and the line change after burning is 0.02%. These properties fully meet the requirements of cement companies. This ultra-low cement refractory castable is made of active calcium aluminate cement. If ordinary pure calcium aluminate cement is used with silica sol or diluted chain sol as an auxiliary binder, ultra-low cement refractory castables with similar properties can also be produced.

Magnesia Refractory Castable in Rongsheng Refractory Manufacturer

by

Magnesia refractory castable is a castable refractory material with magnesium oxide (MgO) as the main component. According to the material, it can be divided into: alkaline castables such as magnesia, alumina-magnesia, spinel, magnesium-chromium, magnesia-silica and magnesia-carbon. Magnesite (periclase) refractory castables are prepared from fused magnesia or sintered magnesia aggregates and fine powder.

High-Quality Alumina Magnesia Refractory Castable
High-Quality Alumina Magnesia Refractory Castable

Magnesium Refractory Castables with Different Properties

The magnesia refractory castable combined with high alumina cement has the advantages of high purity, small linear change rate after burning, and high load softening temperature. However, as the heat treatment temperature increases, especially between 400 and 1200°C, the magnesium hydroxide generated by the hydration of magnesia loses its cementing effect due to dehydration, and the combination of refractory aggregate and powder becomes loose and peels off.

The magnesia refractory castable combined with water glass has the advantages of high strength and strong resistance to alkali and sodium salt molten corrosion. However, due to the use of water glass as a binding agent, a large amount of Na2O (or K2O) and SiO2 are brought in, which greatly reduces the fire resistance and load softening temperature of magnesia refractory castables. This limits the maximum service temperature of water glass bonded castables.

The magnesia refractory castable combined with polyphosphate has the advantages of high strength after burning, small decrease in strength as the heat treatment temperature increases, high softening temperature under load, and good thermal shock resistance. However, at high temperatures (above 1400°C), the strength of magnesia castables decreases due to the large amount of P2O3 volatilization. Generally speaking, sodium polyphosphate is used as the binder for magnesium castables.

Commonly used ones include sodium tripolyphosphate, sodium hexametaphosphate, etc. The degree of polymerization of polyphosphate and the content of P2O3 have a great influence on the strength of castables. When the average polymerization degree of polyphosphate is 24, the castable has the greatest strength. In addition, in order to improve the high-temperature strength of magnesia refractory castables, add an appropriate amount of calcium-containing materials (such as calcium carbonate, etc.). In order to generate the Na2O·2CaO·P2O5 phase with high collective strength and stable existence at high temperature.

However, no matter which of the above-mentioned binders is used, it is difficult to overcome the problem of easy hydration of magnesia refractory castables, and cracks are prone to occur during the drying process. Adding an appropriate amount of silica ultrafine powder can overcome hydration problems.

Magnesium Chromium Castable Refractory
Magnesium Chromium Castable Refractory

Advantages of Ultrafine Powder Combined Magnesium Refractory Castables

Ultrafine powder combined with magnesium refractory castables were successfully developed around 1990. They have good resistance to slag erosion, less pollution to molten steel and have a purification effect. However, due to the presence of magnesium oxide, the resistance to slag permeability and thermal shock resistance is reduced. At the same time, the low medium temperature strength and easy water absorption and powderization affect the promotion and use of castables.

In recent years, a lot of effective work has been done in the research and improvement of the varieties and performance of ultrafine powder combined with magnesium refractory castables. Its varieties have increased and its defects have been improved. It has also been used in thermal equipment such as ladle slag line, tundish working lining and slag weir, non-ferrous metallurgical Ausmelt furnace and slag depletion furnace, with good results.

The varieties of superfine powder combined with magnesia refractory castables include magnesia, magnesia chromium, magnesia spinel and magnesia calcium. The first three castables developed earlier, faster and more practical, and the latter magnesia calcium refractory castable is under development. The key is to solve problems such as hydration.

The refractory aggregates of superfine powder combined with magnesia refractory castables include fused or high-purity magnesia, high-quality magnesia, brick-making magnesia and metallurgical magnesia. Refractory powders include magnesia powder, chromite powder, aluminum magnesium spinel powder, Cr2O3 and a-Al2O3 and other superfine powders, and uf-SiO2 powder is used as a binder, and admixtures and explosion-proof agents are added.

Magnesium Castable Refractory in Rongsheng Company
Magnesium Castable Refractory in Rongsheng Company

Magnesia Cement Refractory Castables

Magnesia cement mainly includes periclase cement and periclase-spinel cement, which are made by grinding highly recrystallized sintered magnesia sand. Its setting and hardening mechanism is mainly the hydration reaction of magnesium oxide and the crystallization of magnesium hydroxide. The reaction formula of cement is:

MgO+H2O——Mg(OH)2

However, the hydration rate of periclase cement is slow. Therefore, tempering agents such as magnesium chloride, magnesium sulfate and magnesium nitrate should be added to promote its hydration and crystallization. It is well known that the solubility of magnesium hydroxide in water is very small, and its gel is difficult to crystallize into large particles. When the tempering agent is added, the boiling point of the tempering water is increased, the solubility of magnesium hydroxide is increased, and the crystallization and growth of magnesium hydroxide gel are accelerated. This needle-shaped brucite crystal cross-grows, which makes the magnesia cement refractory castable gain strength. The effect of magnesium chloride as a blending agent is better than that of magnesium sulfate and other blending agents because magnesium chloride as a blending agent also generates magnesium oxychloride which gradually crystallizes and promotes the coagulation and hardening of cement.

This type of refractory castable is air-hardening and should be naturally cured after molding without watering.

For example, the mix ratio of refractory castables combined with magnesia cement is that the refractory aggregate is metallurgical magnesia sand aggregate, chromium slag and cement, iron powder, and magnesium chloride solution and magnesium sulfate solution are added with iron powder to act as mineralizers or sintering agents.

The drying strength of periclase cement refractory castable is relatively high. However. At about 400℃, the strength begins to decrease due to the decomposition of magnesium hydroxide. As the heating temperature increases, the organizational structure becomes loose and the strength continues to decrease. When the temperature reaches 1000~1200℃, it has not yet been sintered, and the strength is reduced to the lowest point, only 2.5-9.3MPa. When it exceeds 1200℃, the strength rises slightly due to the recrystallization of magnesium oxide. At about 1400℃, solid phase reaction begins, and the strength increases, which is about 25% of the drying strength. When iron powder and chromium slag are added, the sintering of periclase can be promoted, and the medium-temperature strength is improved.

To purchase high-quality magnesium refractory castables, please choose Rongsheng Refractory Material Factory. The product quality is reliable and the performance is guaranteed.

China Rongsheng Refractory Manufacturing
Contact Us

    Get Latest Quotation