JPH0442867A - Low cement castable refractories - Google Patents

Abstract

PURPOSE:To improve strength and chipping resistance by adding a hot water soluble polyvinyl alcohol fiber as an constituting component of the subject low cement castable refractories. CONSTITUTION:With 67-89wt.% heat-resistant filler having a controlled particle size, 10-25wt.% one or more kinds of heat-resistant fine powder having <=10mum particle size, 1-8wt.% alumina cement, 0.01-0.5wt.% (outer percentage) dispersant and 0.05-1.0wt.% (outer percentage) hot water-soluble polyvinyl alcohol fiber are blended.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application> The present invention relates to improving the strength and explosion resistance of low cement castable refractories.

<Prior art and problems> Castable refractories generally contain 10% by weight or more of alumina cement as a binder;
There is a problem that dehydration causes strength deterioration in the intermediate temperature range of 1100°C, and a problem that CaO in alumina cement acts as a flux in the high temperature range of 1300°C or higher, reducing the heat resistance and corrosion resistance of castable refractories. It has been known.

In order to correct this problem, the amount of alumina cement added should be reduced to 10% by weight or less, and the particle size should be reduced to 10 μm.
Add the following ultrafine powder and add 0.0% dispersant. O1~0.
A low-cement castable refractory has been developed that can be constructed with low moisture content by adding 5% by weight and 96% by weight.

This type of low-cement castable is dense, high-strength, and has excellent heat resistance and corrosion resistance, but on the other hand, it has the disadvantage that it tends to explode or peel and collapse when subjected to rapid heating and drying. There is.

As a means to solve the above problem, JP-A-52-621
33, a method of adding organic fibers as proposed in JP-A-59-190278, or JP-A-58-784.
There are methods such as adding metallic aluminum proposed in No. 77, but although they can improve the explosion resistance, they have the disadvantage of worsening the structure of the constructed body, so they are not satisfactory.

<Means for Solving the Problems> The present invention solves the above-mentioned conventional drawbacks by adding hot water-soluble polyvinyl alcohol fibers.

Its characteristics include 67-89% by weight of refractory aggregate with particle size adjustment, 10-25% by weight of one or more types of ultrafine refractory powder with a particle size of lOμ or less, and 1-8% by weight of alumina cement. Weight %, dispersant is 0. O1-0.5% by weight
, hot water soluble polyvinyl alcohol fiber is 0°0 on the outside.
It is a low cement castable refractory consisting of 5 to 1.0% by weight.

<Function> Hereinafter, the low cement castable of the present invention will be explained in detail.

The refractory aggregates with particle size adjustment used in the present invention include fused alumina, fused mullite, sintered alumina, synthetic mullite,
High alumina raw materials such as bauxite, sillimanite, and clay shale, silicic raw materials such as silica stone, loite, and chamotte, basic raw materials such as magnesia clinker-chromite, and spinel, and other materials such as zircon, zirconia, silicon carbide,
One or more types of materials generally used as refractory materials such as graphite account for 67 to 89% by weight.

The refractory ultrafine powder contains 10 to 25% by weight of one or more of alumina, clay, silica flour, titania, and chromium oxide, each having a particle size of 10 μm or less, preferably 3 μm or less. 10
If the amount is less than % by weight, the fluidity will be insufficient and a constructed body with high density and high strength will not be obtained. If it exceeds 25% by weight, the resistance when mixed with water increases, making pouring construction difficult.

In addition, heat shrinkage becomes large, leading to a problem of reduced heat resistance.

As the alumina cement, commercially available electrified high alumina cement super, electrified high alumina cement, Alcoa CA-25, Sekar 250, etc. can be used.

The addition amount is preferably 1 to 8% by weight. If b1 weight is less than 96%, sufficient strength cannot be obtained. Adding more than 8% by weight increases the amount of alumina cement that remains unhydrated, which is useless for the purpose of developing strength. Also, excess alumina cement is C
The amount of aO component is increased to reduce the corrosion resistance of castable refractories.

The dispersant disperses alumina cement and ultrafine refractory powder to reduce water and improve the fluidity of castable refractories.

For example, sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, sodium borate, soda carbonate, etc. are used. The amount added is 0.01 to 0.5% by weight.

If it is less than 0.01% by weight, the dispersibility of alumina cement and refractory ultrafine powder will be poor, reducing the strength of the castable refractory. If it exceeds 0.5% by weight, the dispersed particles will re-agglomerate and increase in viscosity.

The purpose of using hot water-soluble polyvinyl alcohol fibers can be broadly classified as follows.

■ To improve the structure and strength of low-cement castables at normal and intermediate temperatures.

■ To prevent the breathing phenomenon of low cement castable construction bodies.

■ Improving the explosion resistance of low cement castable construction bodies during heat drying.

■ Expanding the suitable moisture range for low cement castables.

Each will be explained in detail below.

Regarding (2), the addition of hot water-soluble polyvinyl alcohol fibers has the effect of making the structure of the low-cement castable construction body dense and increasing its strength in the room temperature and intermediate temperature ranges.

Therefore, applying this material to the mouth of the burner nozzle of a cement kiln will stabilize the anchor stud area and extend its service life. Regarding (2), conventionally, low cement castables have had the problem of fine powder gathering on the construction surface due to the breathing phenomenon, causing abnormal shrinkage when exposed to heat and lowering corrosion resistance more than expected. Hot water-soluble polyvinyl alcohol fibers have hydrophilic groups on their surfaces, have a low specific gravity, and have very good dispersibility, so they can prevent the breathing phenomenon. It is said that the fibrous shape is also effective. The improvement in explosion resistance (ii) is due to the fact that hot water-soluble polyvinyl alcohol fibers dissolve during heating and drying to form ventilation voids. Concerning the suitable moisture range (2), the suitable moisture range for low cement castables was narrower than before, at around 1%. If water exceeding this suitable range is added, the strength of the constructed structure will drop sharply, so careful attention must be paid to the amount of water added.

Hot water soluble polyvinyl alcohol fiber has water retention capacity,
The suitable moisture range can be expanded to approximately 2%, making it an easy-to-use material.

The hot water soluble polyvinyl alcohol fiber having the above-mentioned functions has a diameter of 1 to 30 μm and a length of 2 to 10 μm.
wm, and those having a dissolution temperature in water of 40 to 90°C can be preferably used.

The diameter of the warm water soluble polyvinyl alcohol fiber is 1 μm.
If it is less than that, the ventilation voids formed are too small to be useful in preventing steam explosion. Furthermore, if the thickness is greater than 30μ, the structure becomes porous, causing a problem of lowering corrosion resistance.

If the length of the hot water-soluble polyvinyl alcohol fiber is less than 21, the effect of preventing the breathing phenomenon is small, and the ventilation voids are not continuous, so the effect of preventing explosion is poor.

Furthermore, if the melting temperature of the hot water-soluble polyvinyl alcohol fiber is less than 40° C., it will dissolve during crosstalk, making it impossible to form desired ventilation voids. It also increases the viscosity during crosstalk and deteriorates the structure. If the melting temperature is 90°C or higher, the effect of preventing the breathing phenomenon and the function of widening the suitable moisture range will be impaired.

In addition, as a refractory with improved explosion resistance using hot water-soluble polyvinyl alcohol fibers, Japanese Patent Application Laid-open No. 1-22427
There is No. 4. This is a sprayed large refractory that is constructed with an amount of added water of approximately 20%, whereas the present invention relates to a low cement castable refractory that is constructed with an amount of added water of approximately 7%. While sprayed large-sized materials become dense and strong with the help of spraying pressure, low-cement castables reduce the amount of added water as much as possible through the action of a dispersant, and become dense and strong due to the cohesive force of alumina cement. It is. The polyvinyl alcohol fibers used in the present invention are used for the purpose of improving the dispersibility of ultrafine powder and alumina cement by assisting the function of a dispersant, thereby making the construction body denser and stronger. Ordinary low-cement castable refractories tend to explode if they are made dense and high-strength, but when polyvinyl alcohol fibers are added to low-cement castable refractories as in the present invention, they become dense and high-strength. It also has the great advantage of not being prone to explosions. Furthermore, the effect of preventing the breathing phenomenon that occurs in the present invention due to the use of polyvinyl alcohol fibers is a unique and necessary characteristic of cast-in refractories, but is not a problem in spray-refractory refractories.

<Example> Next, the features of the present invention will be specifically explained using examples.

Castable refractories are manufactured using the blending ratio shown in Table 1,
When its physical property values were measured, the results shown in the same table were obtained. At the ambient temperature shown in Table 1, the amounts of water added were added and kneaded, and the pot life, curing time, apparent porosity, bending strength, and explosion resistance were measured by the following methods.

■Pot life is the time when construction is no longer possible after mixing with water.

■Curing time is the time required to make it possible to remove the frame after kneading with water.

■ Apparent porosity is 40x40x160m by vibration molding.
A test bed of s+ was molded and JIS-R2 after heat treatment at each temperature.
Measurements were made based on 205.

■ For bending strength, prepare test pieces using the same method as in the previous section, and use JI
It was measured by Snowan 100 scale based on S-R2553.

■ The test piece for explosion resistance test is 100 x too x
Vibration molding was performed using a 100-inch mold, and after 24 hours of curing, it was immediately put into an electric furnace at each test temperature and held for 30 minutes. Those that exploded were rated X, and those that did not explode were rated O.

In Table 1, Comparative Example 1 is a normal castable in which the amount of alumina cement added is 10% by weight or more. Comparative example 2
．． No. 3 is a low cement castable with no explosion prevention additive added. Comparative Examples 4.5.6 are conventional low cement castable refractories with the addition of metallic aluminum or vinylon fibers as detonation inhibitors. Examples 1-5 are low cement castable refractories loaded with polyvinyl alcohol fibers according to the present invention. The following is clear when compared with the comparative example.

■ Adding polyvinyl alcohol fibers tends to shorten the curing time. At low temperatures of 5° C., the curing time of conventional low cement castable refractories is more than 24 hours, or can be reduced to less than 24 hours with the present invention.

■ By adding polyvinyl alcohol fiber,
The apparent porosity of low-cement castable refractories after 24-hour curing and drying at 110°C can be lowered and the bending strength can be improved.

■ The explosion resistance of low cement castables can be improved by adding polyvinyl alcohol fibers.

<Effects of the Invention> As described above, according to the present invention, it is possible to shorten the curing time and obtain a dense and high-strength construction body without impairing the explosion resistance of a low-cement castable.

Claims (1)

[Claims] 87-89% by weight of refractory aggregate with particle size adjustment, 10-2% of one or more refractory ultrafine powders with a particle size of 10μ or less
5% by weight, alumina cement from 1 to 8% by weight, dispersant from 0.01 to 0.5% by weight, and hot water soluble polyvinyl alcohol fiber from 0.05 to 1.0% by weight. thing.