Introduction
The card neck hanging wall is an important space separation device between the flat glass melting furnace, the melting part and the cooling part. Its main task is to prevent or reduce the influence of temperature and pressure fluctuations in the melting part on the cooling part, and to ensure the stability of glass forming in the cooling part.
Since the card neck hanging wall was introduced to China in the 1990s, after decades of digestion and absorption and technological innovation, its structural form and refractory configuration have shown several technological updates and iterations.
The structural form has undergone the evolution of a single set of T-shaped chain-type card-neck hanging wall, card-neck hanging flat-hanging group, and J-shaped hanging wall + card-neck hanging flat-hanging group.
The refractory configuration is gradually replaced by the original high-quality silica bricks by sintered mullite bricks and three-low mullite bricks. With the advent of the all-oxygen kiln, the high concentration of alkali steam in the all-oxygen kiln has put forward higher requirements for the alkali steam corrosion resistance of the refractory materials of the suspended wall; and the long kiln age (more than 12 years) and the high-quality glass Pursuing, it also has stricter and more stringent requirements on the performance of suspended wall refractory materials. Therefore, a new type of refractory material for card-neck hanging wall-the card-neck hanging wall brick with high alkali resistance and low creep has also emerged.
The following is a systematic introduction to the evolution of refractory materials for the card neck hanging wall.
The first generation of high-quality silica bricks
In the early days of the card neck hanging wall, the structure was mainly a single-group T-chain card neck hanging wall. The material was mainly made of high-quality silicon bricks. Most of the used parts were at the end of the card neck and in front of the independent gable wall in front of the cooling part.
High-quality silica bricks have excellent resistance to high temperature corrosion, the softening temperature under load can reach above 1680 ℃, and has good high temperature thermal stability, pressure resistance, wear resistance, melt erosion resistance and other characteristics.
However, the expansion coefficient of silica brick is large, and the maximum expansion can reach 15‰; this makes the requirement of loose top silk when the card neck hanging wall is baked in the kiln. The chain structure in which the card-neck hanging wall bricks are inserted into each other determines that the top wire of the card-neck hanging wall cannot be too loose, because too loose the top wire will cause the risk of the hanging wall to collapse. If the top wire is too tight, there is nowhere to release the expansion tension of the silicon brick, causing the card-neck hanging wall brick to be easily crushed, and there is also a risk of collapse. Because it is difficult to grasp the time node and amplitude of the loose top wire of the card neck hanging wall during the baking process, the lower surface of the silicon card neck hanging wall often opens (the top wire is too loose) or the ceiling wall is crushed and cracked (the top wire is too tight) The phenomenon.
Second generation sintered mullite brick
With the improvement of glass production technology and the need for convenient production and operation, the structure of the "short trellis + single-group T-chain type neck hanging wall" in the card neck area has gradually been adopted by the "card neck hanging and flat hanging wall group" or "J type". "Hanging wall + card neck hanging flat hanging group" replaced. The contact between the card neck hanging wall and the deep water bag, horizontal or vertical agitator is closer.
Although high-quality silica bricks have good thermal stability at high temperatures, their thermal shock resistance is poor. Exposure to water or large temperature fluctuations at high temperatures will cause the silica bricks to burst. And there are equipments such as deep-layer water bag, horizontal agitator or vertical agitator at the neck. These mechanical equipment, working in a high-temperature environment, are inseparable from the cooling of cooling water. In the process of replacing the card neck water bag and agitator, the space temperature in the area will fluctuate greatly; at the same time, it is difficult to ensure that the deep water bag and agitator will not leak water during the continuous production operation of the kiln age of 10 years or more. . Therefore, it is difficult to ensure that the card neck hanging wall will not be impacted by the cooling water, and the characteristics of high-quality silica bricks that encounter large temperature fluctuations or explode when exposed to water in high-temperature environments determine whether the card neck hanging wall uses high-quality silica bricks. Safe and secure.
It is precisely because of the high temperature of the hanging wall of the card neck, the large fluctuation of the space temperature, the hidden danger of cooling water leakage, the collapse of the chain structure and the difficulty of grasping the loose top wire operation, etc., the shortcomings of using high-quality silica bricks as the card neck hanging wall It gradually revealed that collapse and explosion accidents also occurred from time to time. The selection of refractory materials for the card neck hanging wall has also started a new upgrade journey.
The suspended wall R&D engineers found that the sintered mullite brick with 72% alumina content has the following characteristics:
1. High operating temperature: the load soft temperature is 1650℃;
2. Good thermal shock resistance: water cooling at 1100℃, up to 15 times without bursting;
3. The expansion coefficient is low: the maximum is only 7‰, which is only one-half of the expansion coefficient of silica bricks.
The three physical and chemical performance indexes of this traditional sintered mullite brick, especially the latter two indexes, perfectly make up for the shortcomings of high-quality silica bricks as a refractory material for card neck hanging walls. Therefore, the card neck hanging wall bricks will soon be upgraded from high-quality silica bricks to sintered mullite bricks.
In the actual production and application process, sintered mullite bricks are used as the refractory material for the neck hanging wall, and its thermal shock resistance and high temperature corrosion resistance are very good. Has been fully recognized by the majority of users.
With the gradual promotion of the use of sintered mullite bricks as card-neck hanging wall bricks, kiln engineers have discovered that some of the card-neck hanging walls have undergone bulging deformation or even collapse in the actual use of about three years. Phenomenon. Although this situation is rare, once it occurs, it will cause irreversible damage to the card neck hanging wall.
After the suspended wall R&D team conducted multi-analysis and research on the suspended wall refractories and their use environment, it was found that this was mainly due to the high impurity content of sintered mullite bricks, especially the high eutectic oxides (such as Fe2O3), which caused high temperature creep resistance. Due to reduced performance.
Because there are many ways to synthesize mullite aggregates in sintered mullite bricks, such as high alumina bauxite to synthesize mullite, alumina powder and silica powder to synthesize mullite, etc. [1]. The properties of mullite aggregate synthesized by different raw materials and processes are also quite different. In particular, the content of impurities (such as eutectic oxide Fe2O3) is different, resulting in a great difference in high temperature creep properties [2].
For traditional sintered mullite bricks, neither national standards nor industry standards have set requirements on the technical index of high temperature creep. The requirements for the chemical composition of sintered mullite bricks Fe2O3≤0.3% in the standard are too broad. This leaves hidden dangers to the high-temperature performance of the card-neck hanging wall tiles.
In addition, the porosity of sintered mullite bricks, especially if the apparent porosity is too high (18%-20%), will cause more alkali vapor to penetrate into the open pores of the refractory bricks. The alkali vapor that penetrates into the pores chemically reacts with the mullite phase in the surrounding refractory bricks at high temperature to form nepheline. After the mullite turns into nepheline, the volume will increase by about 26%, which will cause the explosion and peeling of the refractory brick [3]. The nepheline that bursts off and falls into the molten glass will form stones, which will reduce the yield of the glass and affect the quality of the glass.
Therefore, although the traditional sintered mullite brick has the characteristics of good high temperature resistance, high thermal shock stability and low expansion coefficient. However, the two fatal defects of high temperature deformation and surface bursting determine that traditional sintered mullite bricks must be upgraded to fully adapt to the unique working environment of the neck part.
The third generation three low mullite bricks
How to make use of the superior thermal stability of sintered mullite bricks, while at the same time improving its high temperature creep resistance and reducing the occurrence of skin bursting? The hanging wall research and development team of China Building Materials Bengbu Glass Industry Design and Research Institute began a new upgrade of the hanging wall refractory materials.
Through joint efforts with relevant scientific research institutes and production cooperation units, a refractory material with unique performance and able to satisfy the unique working environment of the neck area-three low mullite bricks was born.
Compared with traditional sintered mullite bricks, its uniqueness lies in the "three lows and two highs", that is, "low iron, low porosity, low creep, high mullite phase and high aluminum content".
1. Compared with traditional mullite bricks, the iron oxide content of three-low mullite bricks is doubled, and the high temperature creep resistance is increased by more than three times. Thoroughly solve the problem of bulging and deformation of the card-neck suspended wall in a high temperature environment for a long time, and improve the safe use performance of the suspended wall;
2. The decrease of apparent porosity and the increase of alumina content and mullite phase in refractory materials improve the resistance to high temperature alkaline steam erosion of wall hanging bricks, and reduce the explosion of mullite bricks in high temperature alkaline steam environment. Possibility of peeling.
The improved triple-low mullite card-neck hanging wall bricks have been verified by use on more than 100 flat glass production lines. The high temperature stability and alkali vapor corrosion resistance have been greatly improved, which fully meets the requirements of air-combustion glass melting. The environment of the kiln.
Three-and-a-half generation new type high alkali resistance and low creep card neck hanging wall brick
As mentioned above, the improved sintered mullite bricks—three-low mullite bricks—can fully meet the environmental requirements of air-fired glass melting furnaces. But does the above-mentioned use effect still exist on the oxygen-assisted kiln used to produce soda-lime-silica glass?
We know that, because the combustion-supporting medium is pure oxygen, the combustion products in the air-assisted kiln also contain a large amount of non-combustible gas N2. The furnace with the same melting tonnage, the oxygen-assisted kiln The concentration of alkali vapor is 3 to 4 times higher than that of air-assisted kilns (depending on the type of fuel: burning natural gas is about 3 times, burning heavy oil is about 4 times). Therefore, the requirements for the anti-alkali performance of the card-neck hanging wall of the all-oxygen combustion-supporting kiln are more stringent.
Regardless of whether it is air-assisted combustion or oxygen-assisted combustion, since the hot spot temperature of the melting part of the glass melting furnace is about 1585℃, the water vapor in the combustion products at high temperatures exists in the form of hydroxyl (anions). The metal oxides in the molten glass actually exist in the form of ions (cations) and volatilize in the upper space of the furnace at high temperatures. Anion and cation chemically combine at high temperature to form new compounds. For example, the hydroxyl group combines with sodium ions to form sodium hydroxide, which is the reason for the existence of alkaline vapor at high temperature. Obviously, the concentration of alkaline steam in the oxygen-assisted kiln is much higher than that in the air-assisted kiln.
However, in the area of ??the sling, especially the orifice area of ??the deep water bag of the sling, due to the cooling effect of the cooling water of the deep water bag, the space temperature of the orifice area of ??the deep water bag is about 800 ℃, and the alkali vapor will liquefy. The liquid alkali will adhere to the surface of the refractory material of the card neck hanging wall, and penetrate into the interior of the refractory material through the opening pores. And in a high temperature environment, it reacts chemically with the refractory material with weak alkali resistance, which will damage the performance of the refractory material. Three-low mullite bricks can resist the corrosion of general alkali vapor, but in the environment of high-concentration alkali vapor in the all-oxygen combustion-supporting glass furnace, its performance is often unsatisfactory, and it is difficult to resist the chemical erosion and damage caused by high-concentration alkali vapor.
How to develop a hanging wall brick that has "high alkali resistance, low creep, low porosity, and good thermal shock resistance" at the same time, to meet the special needs of the deep water bag orifice area of ??the all-oxygen kiln? An urgent problem facing scientific researchers.
As the saying goes: the magic is one foot high, and the road is one foot high. There are always more solutions than difficulties!
After more than a year of hard work, the hanging wall R&D team of Bengbu Institute of China Building Materials Co., Ltd., together with the production and cooperation manufacturers, and with the strong support of relevant scientific research institutes, developed a new type of high-alkali-resistant and low-creep card neck with performance that exceeds the international standards of similar products. Hanging wall tiles". After repeated inspections by authoritative departments, the product has all-round excellent performance indicators of "high alkali resistance, low creep, low porosity and high thermal shock stability" (see Table 3 for product inspection indicators). Product indicators are especially superior to similar products in the world in terms of low creep and high thermal shock performance indicators. It is perfectly adapted to the deep water ladle area of ??the neck of a full-oxygen combustion-supporting glass melting furnace.
From the data in the above table, it can be seen that the new type of high-alkali-resistant and low-creep card-neck hanging wall bricks, although the same as the three-low mullite bricks, belong to the "alkali-resistant first-class". But using "GB/T14983-2008 Method Three" to carry out the anti-alkali comparison test, it can be seen that:
In the same temperature and the same concentration of alkali vapor environment, the quality change rate of the new type high alkali resistance and low creep card neck hanging wall brick is only one third of that of the three low mullite bricks. In other words, the new type of high alkali resistance and low creep card-neck hanging wall bricks has three times the alkali steam erosion resistance of three-low mullite bricks. Moreover, the new type of high-alkali-resistant and low-creep card-neck hanging wall bricks has a lower high-temperature creep rate, lower apparent porosity, and good thermal shock resistance (water cooling at 1100°C, no cracking for more than 10 times). It is very suitable for use in high temperature and high alkali steam environment.
So why not call it the fourth generation, but the three and a half generations? The main consideration is that the new type of hanging wall bricks is only a partial replacement of three-low mullite bricks, rather than a complete replacement.
On the one hand, in the neck area of ??the oxygen-combustion glass melting furnace, due to the influence of the cooling water of the neck's deep water bag, the temperature in the deep water bag space area is low, and the alkali vapor is easy to liquefy. Coupled with the barrier of the hanging wall behind the deep water bag, it is difficult for the alkali vapor to diffuse to the back half of the neck area. Therefore, in the neck area, the most severe part of alkali vapor erosion is the neck area of ??the deep water pack. As long as the new high-alkali-resistant and low-creep card-neck hanging wall bricks are used in this area to replace the three-low mullite bricks, the special use environment needs of the card-neck area can be met. In other areas of the card neck, the three-low mullite bricks can fully meet the requirements of use and do not need to be replaced.
On the other hand, this new type of high-alkali-resistant and low-creep card-neck hanging wall brick has very high requirements on raw materials and technology in the manufacturing process, so the production cost is expensive, and the price is much higher than the three-low mullite brick. If all the card-neck hanging and flat hanger sets adopt this new type of card-neck hanging wall bricks, the investment cost of the card-neck hanging wall will increase exponentially, resulting in waste.
Therefore, considering the environmental characteristics of the collar area and the cost-effectiveness of refractory material configuration, we only need to adopt a new type of high alkali resistance and low creep card in the deep water bag orifice area (front and rear hanging walls and top cover) of the oxygen-supported glass furnace. The neck hanging wall bricks, and the three-low mullite bricks are still used in other parts of the neck. This combination has the best effect and the highest cost performance. It is the best option for the card neck.
This combination is also a recommended option for sling-neck refractory materials for the production of high-quality glass and glass melting furnaces with a long furnace age (more than 12 years).
Summary
The card neck hanging wall was introduced to China in the 1990s. Through the continuous improvement of several generations of hanging wall R&D engineers and production technicians, the performance index of the card neck hanging wall refractory has made a qualitative leap. Especially in terms of high temperature stability, alkali corrosion resistance and thermal shock resistance of refractories, the generational optimization is more significant. It fully demonstrated the R&D and innovation capabilities and equipment manufacturing capabilities of Chinese float technology workers.
Every time the card neck hanging wall refractory is updated, it focuses on solving the problem of one or several physical and chemical properties of the hanging wall refractory material, which is not compatible with the production environment of the glass melting furnace. The upgrading of the card neck hanging wall refractory material, in summary, has the following characteristics:
Judging from the current professional experience and technical cognition, the third-generation and a half products can basically meet the environmental needs of the neck area of ??the full range of glass melting furnaces. However, scientific exploration is endless. With the advancement of glass production technology and process improvement, the requirements for the performance of the suspended wall refractory material in the neck area will become higher and higher. Perhaps there will be more room for improvement in the performance of the refractory material of the card neck hanging wall, and there will be technical updates and iterations of the fourth and fifth generations. This will be a big test for both technology research and development and manufacturing.
