Reason of casting refractory material for high temperature resistance

Casting refractory material, its main characteristic is high early strength, 3-7 days maximum compressive strength can reach more than 30MPa, and the disadvantage is the volume stability of temperature difference, the intensity decrease, the maximum fall by up to 40%, so the requirements for compressive strength must meet the design requirements and national standards.

The temperature reduces the strength of the main factors are: Casting reaches a certain temperature with low calcium and high alumina cement fireproof material in the heating furnace heating process (350 DEG C), dehydration, transformation of the hydrate started hydrate of cement stone structure, compactness and strength decreased, the volume of pouring material change, this time to the strength of castable the lowest point, after stabilizing. With the heating temperature up to 1100 DEG C, cement stone gradually sintering, casting crystalline refractory mullite crystal transformation. With the temperature rising, mullite crystal growing, a glass matrix liquid phase pouring material, forming a high temperature sintering shape, strength increase. At about 1300 DEG C, casting refractory material strength can reach more than 60MPa, a remarkable characteristic of refractory materials under high temperature condition for this is pouring.

Scientific analysis of castable “appears white hair” phenomenon and effective solution

Castable material in using process often can see high alumina cement castable appeared on the surface of hanging “frost”, “long hair” “powder” “powder” phenomenon. In the common refractory castable surface and water to have loose gelatinous precipitate. These “frost” is because the cement particle surface castable not hydrated in water, forming supersaturated solution, then precipitated alumina sol and hydrated calcium aluminate induced. In fact, “white box” is not affect castables performance, but too much can cause rough skin on the construction, affecting the appearance.

Reason of castable long white: containing alkali refractory raw material, such as calcined alum refractory aggregate in, calcination sticky superior, as calcium aluminates cement castable. All kinds of powder, such as a variety of fine powder, silicon powder and kyanite; there are also contains alkali additives, such as reducing agent, coagulant, explosion-proof toughness. These materials often contain a small amount of alkali, the alkali, some can be dissolved in water, especially the dispersing agent of alkali, almost all into the wood. These “base” by capillary hole to the hardening decent migration, arrives at the table and then, the formation of carbonate and C02 reaction in the air.

Solution for casting material surface “frost” phenomenon:

1. Choosing low alkali content of refractory materials;
2. As soon as possible out of the water, drying, carrier to eliminate sodium alkali, stranded in the construction of the body, not to migrate to the surface.
3. The castable airtight, covered with plastic film, thereby preventing the moisture with alkali to migrate to the surface.
4. Improve the refractory castable viscosity and rapid hardening (reduce sodium migration velocity).
5. Strengthen quality control, strict control of water, to prevent too much water.

Basic properties of refractory material for steel making

• 
  Refractory materials for converter

The furnace cap, tapping converter mouth, before and after the surface, the weld pool and the bottom are made of magnesia carbon brick; the trunnion and the slag line part using high strength magnesia carbon brick. Magnesia carbon brick in MgO content is 70 ~ 75%, the content of graphite is 16 ~ 20%, the bulk density is 2.8 ~ 2.9g/cm3,

the compressive strength of 25 ~ 30MPa.High strength magnesia carbon brick, with the elements of magnesia carbon brick, but the compressive strength of 30 ~ 42MPa.

• With refractory furnace

Furnace hearth, furnace slope and the molten pool for magnesia overall tie, or the use of magnesia carbon brick and tar bonded brick; hot and slag line area, the use of high-quality magnesia carbon brick; the furnace door on both sides and tapping El for magnesia brick, magnetite chrome brick; furnace cover for high alumina bricks or high alumina unfired brick.

• Refractories for UHP EAF

Ultra high power permanent lining for magnesium stone, door jamb magnesia chrome brick, slag line brick, hot spots for magnesia carbon brick, wall of the furnace for magnesia carbon brick, eccentric bottom and pool for magnesia brick, tapping into magnesia carbon brick, high alumina brick furnace cover, tapping hole filling is High-speed Rail dolomite filling material.

• Refractory materials used in open hearth furnace
  

The working conditions of various steel furnace can be seen, refractory material working environment is very bad, therefore, no matter what the use of refractory material, must have the following properties:

1. High temperature resistant has high refractoriness.
2. Erosion and erosion resistance to high temperature of molten steel and slag.
3. The steelmaking furnace for intermittent operation, requirements of the refractory material has good thermal shock resistance and spalling resistance.
4. Has high mechanical strength, impact can withstand the tilting and loading charge without damage.

Refractory industry will develop to green

In the development of our domestic industry, basically can achieve energy-saving environmental protection industry is not a lot, but refractory industry today we say it is belongs to the field of energy development.

In this industry, refractory materials, various types of products  , such as refractory brick, refractory castable etc. products, however, these two products are able to do energy-saving green development. Now with the major industry continue to emerge,  the state pay more attention to the refractory material production, and the development trend is apparent.

In fact, for the resources of our country market, we must also understand some of it, like oil, coal and other natural resources are declining, and the state is always in search for new products to replace the natural resources, but not too ideal. But in the domestic resources are becoming scarce today, appear energy-saving environmental protection refractory material model,

let this situation has improved, the state has approved the development of this industry. Because the development of this industry can promote the sustainable development of the country, and to other industry has brought a lot of use.

For the development of refractory products green, low carbon, our country has not given up, and to make great improvement, the development strategy in the global green economy, only the development of refractory industry of our country mainly, to comprehensive economic in China has greatly improved, and perhaps one day as a big refractory materials can also be the global market.

How to shorten the unshaped refractory construction time

We know that usually heat treatment equipment (furnace) maintenance time is long, the entire construction time ordinary unshaped refractory takes a long time, which greatly affect the normal production of the enterprise, reduce the production efficiency. In order to solve this problem, Luoyang Yilong Refractories Co.,Ltd think of the following methods:

1.     We can add the composite explosion-proof agent of high explosion-proof performance;

2.     Add the compound water reducing agent to improve the operating performance, the main purpose is to reduce the amount of water, so that the material containing low content, decrease the burst risk in the process of drying;

3.    Using phosphate as binder, the curing time is faster than the cement, rapid hardening to achieve.

Through the above ways to resolve the construction time of heating furnace, the castable short construction time, baking temperature quickly, long service life, release time of only about 4h, and the drying time is shortened to 1-2 days, and conventional castables for 5-7 days compared to oven baking time, saving more than 3 days, can win the valuable production time enterprise.

High quality refractory castable can be used for furnace construction

Refractory castable is different from the refractory brick products, but the relationship between the two is very close, they are in many cases the common existence, also for some application industry is also very important products. Our country is the world export refractory products in most countries, but some countries sometimes from our domestic imports of some refractory castable, used in the production and processing of their national enterprises. Then the refractory castable in our country is mainly used in what industry or what the building?

This is what we say today's topic, some good quality, safe in refractory castable products can be used for the kiln and kiln construction, role, everyone is aware of the importance of our country, it is not the lack of. General a furnace life of approximately 5 to 10 years, some even up to 20 years, which is mainly composed of determine what? It is the quality of refractory castable. Only the quality of refractory castable is very high, and through the production process produced very strict, or more formal manufacturers, has many years of experience in production and operation, so it is worthy of widely accepted, at the same time for the kiln built, also has the very long life.

Kiln always have to face the environmental temperature, and the general material products can not do have a long life, but refractory castable is different, its appearance is to stand the test of time and temperature.

Solutions to refractory brick shedding used in boiler

Because the boiler pouring material and refractory material damage loss, seriously affect the safe operation of the unit, and even cause non stop accident unit.

In order to ensure the long-term safe operation of the boiler, take the following measures from the operation of the adjustment

• Ignition methods.

1. The ignition temperature process, control the bed temperature and the outlet of the furnace, cyclone separator leg temperature change rate of not more than 80 ℃ / h.
2. By adjusting the fuel door or throttle back to change the oil amount, strengthen with the wind, to maintain the best air fuel ratio, temperature less than 700 ℃ burner piping.
3.  Maintain a volume greater than the minimum fluidizing air flow rate, gas temperature rise faster, by increasing the rise velocity of two air control flue temperature does not exceed the specified value.
4. Bed temperature at 330 ～ 350 ℃ with coal feeding conditions using dynamic way to coal, while adding one or two times volume control the bed temperature and gas temperature from rising too fast, strict monitoring, control the bed temperature and gas temperature change, and the change trend of monitoring oxygen master advanced quantity control the quantity of coal. When the cyclone separator population temperature changes smoothly, gradually changed to continuous coal, used to add less, more in the way of increasing coal, so as to control the bed temperature of furnace outlet flue gas temperature and avoid large fluctuations, reduced the refractories shedding

•    Furnace measures

1. Boiler shutdown process, control the bed temperature, strict furnace exit flue gas temperature drop speed of not more than 80 ℃ / h.
   
2. Slide stop, bed temperature and steam temperature, steam synchronization downhill, by adding one or two times volume decreased bed temperature, to avoid the high bed temperature shutdown period. When the bed temperature below 550 ℃ and the decreasing speed stop to the coal will be a volume is reduced to the minimum fluidizing air flow rate, the two volume is reduced to the minimum, avoid bed temperature drops too fast.
3. Boiler flameout, bed temperature should stop one or two wind turbines operating in more than 400 ℃, prevent the abrupt cooling, fan ventilation and stop running.
4. Fan stops running 4h, bed temperature below 400 ℃ can start fan cooling.

In the boiler start stop, peak shaving, machine breakdown and unit load rejection, strict control of smoke temperature change rate, thus pouring material and refractory protection is not damaged

Hot air furnace drying、 insulation and cold furnace technology

1.  Drying technology of blast furnace and hot blast stove

At present, various kinds of stove of different types, different kinds of refractory material, and the combustion media of different types are a good way to solve the problem of oven.

2.  Long period of silica brick hot furnace insulation technology

Heat insulation furnace, especially thermal insulation brick stove, hot blast stove is shut down or need to repair in blast furnace. How to keep the brick masonry temperature not lower than 600 ℃, while the exhaust temperature is not higher than 400 ℃. According to the site and equipment maintenance shutdown of length and time, using different methods of thermal insulation. The first uses the combustion and keep the roof temperature, air cooling, and the control of exhaust temperature approach called "burning heating, air cooling heat preservation method". The heat preservation method is an effective measure of silica brick hot furnace insulation. No matter how long the blast furnace shutdown time, this method applies.

3.  Silica brick hot stove cool stove reproduction technology

Cool furnace brick stove: brick has good performance of high temperature and low temperature (600 ℃) instability. In the past, silica brick hot blast stove once put into production, can no longer be cooled to 600 ℃,

otherwise it will suddenly shrink, rupture and collapse of brick masonry. The experimental study of a large number of internal and external, cold furnace brick stove, there are two kinds of methods are: natural slow furnace cooling and rapid cooling furnace.

Silica brick for hot blast stove, natural corrosion cold furnace is successful, but because the relationship between the natural period, slow cooling time, do try to quickly cool furnace. A steel mill blast furnace brick in hot blast stove was fast cooling furnace, with 14 days of the furnace successfully to cool down. And successfully repeated reproduction. Fast cooling furnace is very successful, breaking the "firebrick in hot blast stove life goods" argument, that silica brick hot furnace fast cooling furnace is feasible "indicates the possibility and inevitability of silica brick hot blast stove cross generation".

Selection of refractories used in industrial furnace lining:

Refractory and heat insulation material selection of appropriate lining; reasonable structure,

high quality construction, is to improve the thermal performance of the stove and an important factor to improve the service life of lining.

Industrial furnace firebrick main ingredients commonly used is a mixture of SiO2 and Al2O3, impurities can make bricks softening at high temperature, so the highest use temperature lining often limited in 1350 ℃. High alumina brick such as the use of Al2O3 containing greater than 60%, the maximum temperature can reach 1450 ℃ is lining and magnesia brick, magnesia alumina brick; the temperature can reach 1500 ℃, is the excellent material for alkali resistant, so much for the masonry heater. Zirconium corundum brick is abrasion resistant and capacity scale erosion, suitable for sliding track bricks used for continuous heating furnace. Silicon carbide has high strength and good thermal conductivity at high temperature, suitable for the radiation plate less oxidation or non oxidation heating furnace. The basic component, and Fe2O3 component of not more than 1% anti carburizing bricks to SiO2 and Al2O3 resistance, good performance in reducing atmosphere, is a good material for controlled atmosphere furnace.

With the advent of lightweight and ultra lightweight refractory materials, industrial furnace lining inner to refractory fiber or light refractory brick, because this kind of material with refractory and heat insulation performance, especially with low thermal conductivity, heat capacity of small, good thermal stability etc., can significantly speed up the furnace temperature and improve temperature uniformity, and the effect of energy saving is also very remarkable.

Precast blocks are made of various refractory precast refractory plastic and with different properties into different shapes, or on the site directly rammed lining, can shorten the construction period and enhancing the integrity and sealing furnace.

Measures to solve the refractory brick damage

Analysis of mechanism and causes of damage of refractory bricks, take corresponding countermeasure and measure according to these reasons, eliminate the factors of refractory brick damage, so as to achieve the purpose of extending service life of refractory brick.

Cause of refractory brick physical damage and chemical damage ash and kiln skin erosion thin, mechanical damage and the refractory brick masonry quality. That is to say to extend the service life of refractory bricks in burning zone, in addition to select suitable suppliers, shall be laid a good grasp of building quality,

maintain the skin at the kiln kiln during operation. Measures of is:

1. Grasp the quality of refractory brick masonry.

• Cement ratio and dilute the appropriate thick. Specific detection method is easy to spread the cement shop into the brick, and can not flow. Too thick is not easy to spread too thin, is easy to flow; two is in a brick on the fire clay, pressure on another brick slightly strong kneading, and then lift up the brick body, the brick below belt, that the proper proportion of cement.
• The front of refractory brick to be close to the cylinder. Between the brick and the cylinder body cannot pad fire clay and other debris. In the pool of fireclay brick, in front stretcher rectangular to leave 1-2 cm position does not stand in the cement, upward pressure brick, end close to the cylinder pressure to the fireclay, knead move, make cement covered the face brick, a small amount of excess cement extruded from the bricks and the small end of the big two, brick end matter stick cylinder. Brick joints cannot be greater than 1.5mm. Check brick facet, row not up, wrapping phenomenon.
• The top tight top bar. In half of the circumference of the masonry, with top carry to brick top tight, rotary kiln bricks on the other half of the week, when the top bar must be the top tight. Between the brick and the top bar end to pad body, to avoid damaging the refractory brick. Method to check whether the roof top bar tension is, when the top bar with the rotation of the cylinder to check the cylinder top brick not flagging lock position, if the sagging phenomenon, in the kiln and kiln refractory during the relative displacement caused by mechanical damage to the firebrick.
  

2.   hang up and maintain the good kiln crust. In the hanging and protect the kiln crust, mainly take the following measures

• For kiln operation training and guidance. Before ignition, special arrangements for the time of kiln operation training. Clearly pointed out that in any case, hang up and maintain good kiln crust is mainly the responsibility of kiln. At the same time about operating method under different conditions to them, in the actual operation, according to the kiln to give operation guidance and comments in a timely manner, to carry out technical exchanges between operations, and constantly improve the technological level of operation.
• Coal injection pipe reasonable position, with slightly lower guests’ glasses emblem.
• Improve technology status.
• Proper proportioning solution: the quantity of liquid phase resistance is suitable in 22-24%. Too low is not easy to hang kiln skin, too much can narrow the range of sintering temperature, silicate minerals reduce, not conducive to the operation and improve the quality of clinker.

The latest achievements of refractories development

With technology developing, our refractories industry has made ​​great development, but also promoted the development of refractory materials. Domestic refractory materials has made tremendous development.

Specific features:

1. Instead of using natural bauxite alumina industry, has developed a new type of sub-soil just white.
2. The use of flotation and other measures to produce high purity magnesia;
3. Jiangsu, Heilongjiang, dressing made ​​great achievements;
4. Luoyang Yilong Refractory Co., can produce high-quality bauxite
5. The use of Gollum in Qinghai Salt Lake Brine manufacturing high purity magnesia;
6. The use of light burned magnesia mixed with high-alumina spinel synthetic magnesium shovel;
7. High bauxite increased purity;
8. Xinjiang, Tibet and other processing results achieved unprecedented progress;

During this period, China has introduced from abroad advanced production technology and equipment, but also improves the overall level of China's refractories industry. Owing to the continuous development of refractories, refractory industry that makes our country has made tremendous progress.

Introduction and application of Aluminum silicate fiber tiles

Aluminum silicate fibertiles (ceramic fiber tiles) divided into low temperature ceramic fiber brick and high temperature ceramic fiber brick;

using temperature between 800-1400 degrees. The main raw material for the aluminum silicate fiber cotton, using vacuum suction filtration molding production process, and add silica, aluminum phosphate inorganic binder, whose role is to ensure that the high-temperature strength of the products.

Aluminosilicate refractory fibers have excellent slag resistance and thermal shock resistance. Comparison with magnesium carbon refractories, refractory ceramic fiber has better anti-TiO2 slag alkali corrosion and corrosion. In addition, aluminum silicate fiber tiles also has low thermal conductivity, heat capacity, excellent chemical stability, excellent sound absorption, soft, flexible, easy construction, cutting and processing characteristics.

Aluminosilicate refractory fibers have excellent slag resistance and thermal shock resistance.

Comparison with magnesium carbon refractories, refractory ceramic fiber has better anti-TiO2 corrosion and slag alkali corrosion. In addition, ceramic fiber tiles also has low thermal conductivity, heat capacity, excellent chemical stability, excellent sound absorption, soft, flexible, easy construction, cutting and processing characteristics.

Aluminum silicate fiber tiles are mainly used in the construction of various chemical transformation furnaces and furnace linings, construction safety, convenience, while improving the quality of the lining inside the furnace and conversion work has played a crucial role.

Recent Status of graphite industry

Graphite is most common in marble, schist or gneiss, due to its special structure, with many features high temperature resistance, thermal shock resistance, electrical conductivity, lubricity, chemical stability and plasticity,

is the modern industrial and military high, new, sharp technological developments are an important strategic resource. Experts had said, "The 20th century was the century of silicon, the 21st century will be the century of carbon."

From the distribution of resources situation exists, Asia, Europe, Africa, the Americas, Oceania has a graphite deposit, but the Asian production of graphite most. According to USGS statistics, the world's graphite resources proved reserves of approximately 84 million tons, of which China reserves of 64 million tons, accounting for 74% of the world's total reserves. 2010 global production of about 925,000 tons, of which China output of 600,000 tons, accounting for 64.9% of global output. Due to the lack of regulatory industry disorderly competition leads to serious waste of resources. However, this situation is expected with the implementation of access conditions change.

According to the U.S. Geological Survey, in 2011 the major downstream industry needs in the graphite refractory crucible 33% (China more than 40%), casting and steel manufacturing accounted for 26%, 7% of the brake lining, battery and lubricant 5%, 29% for other purposes.Access conditions put forward, "Twelve Five" period, based on domestic demand, and strictly control the incremental, focusing on optimizing inventory, actively adjusting structure, promoting mergers and acquisitions, increased industrial concentration. 

Five main quality indicators of refractory

• Refractoriness

Refractory nature in the course, resist high temperature without melting, called refractoriness.

Refractoriness refractory given temperature limit used is an important indicator of assessing the merits of the refractory quality.

• Thermal shock resistance

Refractory resist drastic temperature changes without cracking or peeling ability, called thermal shock resistance. This cyclical nature of the furnace heating and cooling operations is important.

• High-temperature structural strength

    At a high temperature and a certain load is applied to the refractory deformation temperature from the start of the deformation to some extent, the structure is called a high temperature or high strength load softening temperature. It is the ability of the refractory temperature and the load resistance while being deformed under the action of this nature and by the selection of a high temperature furnace under the building material force is important.

• Volume stability at high temperatures

    Refractory material for a long time under high temperature, resulting involume expansion, the expansion is called the residual.

Size refractory residual swelling, reflecting the quality of the high temperature volume stability: the smaller the residual deformation, volume stability, the better; contrary, the worse the stability of the volume, the more likely to cause deformation or damage to the masonry.

• Lag resistance

    Ability to resist the erosion of refractories and slag of molten material in

the course of soot and other damage without being called a slag resistance. Slag resistance is an important indicator of the refractory nature of the work you are, the higher the better ability of anti-slag. Good slag resistance refractory high life.

Advantages of castable in refractory material

General portland cement concrete can not withstand high temperature operating conditions, precipitation of calcium hydroxide in the hydration process, it becomes calcium oxide at high temperatures; As aggregate of limestone under high temperature thermal decomposition, strength destroyed.strength destroyed.

Ordinary concrete can only be used below 300 ℃ low temperature parts of the foundation and chimney stove. The castable temperature up to 900 ℃ or more.

Compared with other refractory castable has some distinctive features:

(1)Castable has almost same refractoriness with the firebrick, but because castable without sintering, the larger contraction when heated first time, so the load is slightly lower than the softening point firebrick. Nevertheless, a measure of overall performance is better than firebrick.

(2) As the effect of low temperature cementation materials, castable has high temperature compressive strength. and because masonry's good integrity, furnace air tightness, not easily deformed, outside the furnace shell plate can be canceled, stoves resistance to mechanical vibration and shock performance is better than brick masonry. For example, the upper sidewall of soaking furnace, where mechanical abrasion and impact are more severe, life expectancy increased by several times than brick.

(3)Good thermal stability, most or all of the aggregate are clinker,;expansion and contraction of cementing material phase offset,

Relatively speaking,the thermal expansion of masonry is smaller than a brick, thermal stress is also small. And there are a variety of mesh, needle and chain crystalline phase structures, a strong resistance to temperature.For example, to pouring soaking furnace mouth and lid. Life expectancy to a year and a half.

(4)The production process is simple, eliminating the complex steps of brick making. Castable can be made into a variety of prefabricated blocks, and to mechanized construction, brickwork greatly accelerate the speed and improve the efficiency of more than ten times higher than bricklaying. Waste bricks can also use as aggregate, waste for profit.