JPH03247568A - Heat insulating monolithic refractory - Google Patents

Abstract

PURPOSE:To enhance strength, refractoriness, heat insulating property, work efficiency and safety by impregnating specified lightweight aggregate with a water insoluble thermosetting liq. material or coating the aggregate with the liq. material. CONSTITUTION:Magnesia-based lightweight aggregate contg. 95% MgO, <=20% Al2O3 and about 1% SiO2+B2O3 and having 0.1-4mm diameter and 10-50mum average pore diameter is prepd. A water insoluble thermosetting liq. material such as phenol resin is impregnated into the aggregate by 5-10% or the aggregate is coated with the liq. material and drying is carried out to obtain refractory lightweight aggregate. This aggregate is then mixed with castable alumina and 6-15% water.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a monolithic refractory that enhances the fireproof and heat insulating function of a permanent layer in the lining structure of various industrial furnaces, and has particularly excellent strength, fire resistance, and heat insulation properties. , regarding a heat-insulating monolithic refractory that can significantly improve workability and safety.

Conventional technology In general, in kilns at temperatures of 1200°C or higher, fireproof insulating bricks are used as the lining for the furnace walls to prevent heat radiation loss, and various types of insulating castables are used as lining materials for hot spray repairs. ing.

The insulation of monolithic refractories, such as insulating castables, is classified into two types: (1) Foaming agent added type and (2) Light aggregate type, similar to that of regular fired bricks.

■The foaming agent-added type is a material that is solidified after foaming the blended water by adding a surfactant, and ■The lightweight aggregate type is a material that is made of aggregate that has been foamed or porously modified through heat treatment, etc. This is the material used. Note that, in boards different from fired bricks, there are insulating materials to which materials that expand significantly at low temperatures, such as mica and vermiculite, are added.

These insulating castables have numerous natural or artificial pores inside them, so they generally have a low bulk specific gravity and low compressive strength, so their field of application is narrower than that of ordinary refractories, and in the case of porous aggregates, Due to its low melting point, it is typically used at temperatures below 1400°C, making its range of use even narrower.

In addition, lightweight aggregate types tend to absorb a lot of added moisture or inorganic binders, which not only takes a long time to dry, but also acts as a heat insulator during the drying process, allowing heat to flow from the heating surface into the interior. There were problems with workability and safety, such as poor heat transfer, uneven dehydration of adhering water or crystallized water, and the risk of steam explosion during the drying and preheating stages.

As a countermeasure against this, when a surfactant is used in combination, although a water-reducing effect can be obtained, the strength may be uneven due to the reaction between the surfactant and the binder or the aggregation of foamed air bubbles during the solidification process, making it difficult to form a molded product. often lacks stability.

On the other hand, the permanent layer in the lining structure has not only a simple heat insulating function but also a safety lining function to prevent problems such as steel leakage when the wear layer is partially damaged.

However, since basic refractories have a high melting point and high thermal conductivity, there are no materials with high fireproof and heat-insulating properties, and the reality is that they compensate for their heat-insulating properties with their thickness.

Recently, high alumina or basic lining construction has been frequently used for molten steel ladles, etc., with the aim of improving steel quality and extending the life of the ladle.However, both high alumina and basic refractory materials are Due to its high conductivity, it dissipates a large amount of heat, has a high durability temperature for the permanent layer, and has the problem of significantly lowering the temperature of molten steel.

Problems to be Solved by the Invention When using monolithic refractories to insulate the permanent layer of molten steel ladles, etc., which require particularly high insulation in the steel process, conventional fire-resistant lightweight aggregates (e.g. lightweight chamotte) Aggregate) is porous and easily adsorbs moisture and binder, which reduces its heat insulation properties and causes oversintering.It also has poor fire resistance because it contains dust, and the aggregate itself is damaged during the drying and preheating process. Due to the heat insulating effect, problems arise such as the risk of steam explosion due to residual adhered water and crystallized water.

The present invention has been made to solve these conventional problems, and aims to provide a monolithic refractory having excellent strength and fireproof heat insulation properties in the permanent layer of various types of furnaces.

Means for Solving the Problem The inventor focused on porous magnesia clinker for water quality adjustment, and added paraffin to talin heated to 100°C, impregnated and cooled, and porous clinker with alumina. The following was discovered from the amorphous construction body obtained by mixing castable (binder: alumina cement), adding an appropriate amount of water, kneading, curing and drying.

(1) When porous clinker is coated with a water-insoluble thermoplastic material, equivalent strength can be obtained with reduced amounts of added water and binder.

(2) The strength and heat insulation properties of the aggregate for monolithic refractories are more stable if they do not contain fine particles with a particle size of less than 1 mm.

(3) By using aggregate coated with a water-insoluble thermoplastic material, the added moisture is sufficiently dried and the risk of steam explosion is eliminated.

(4) A thermosetting material is effective as the covering material.

(5) As an aggregate, the clinker dries faster than hollow alumina poles, and has excellent fire resistance and high strength.

This invention was discovered based on the above findings, and its gist is that the particle size is 1 nv or more and 4+ nm or less, and the average pore size is 10 to 50 nm.
It is an insulating monolithic refractory made from magnesia lightweight aggregate with μm pores impregnated or coated with a water-insoluble thermosetting liquid. is a heat insulating monolithic refractory using porous magnesia with a MgO content of 95% and containing 20% or less of Al2O3.

Function The aggregate used in this invention is limited to porous magnesia-based aggregate with a melting point of 2700°C or higher (A
It has a high specific heat (I, 0, 2050℃) and a low specific heat (A
Since l to s > M g O), drying properties are good, and secondary spinel (MgO•AI toj) is formed around the highly active MgO aggregate, resulting in high strength.

As the porous magnesia-based lightweight aggregate, it is preferable to use a by-product of seawater magnesia, which has high fire resistance with Mg 095% and 5iQs and B and O contents of about 1% each.

Note that the content of AlzO3 is limited to 20% or less because 20% is the stoichiometric upper limit in order to make it possible to form spinel with high strength.

This refractory aggregate has 0 bores with an average pore diameter of 10 to 50 μm.
．． Contains 5cc/g and has a bulk specific gravity of 1.5 to 1.7
extremely low and highly active. Therefore, it has the characteristics of low thermal conductivity and low thermal expansion.

The reason why the particle size of this refractory aggregate is limited to 0.1 to 4 mm is that the strength and heat insulation properties are more stable if the fine particle region of less than 0.1 mm is excluded.

In other words, by eliminating fine particles with a large specific surface area, it is possible to further reduce the amount of water that adheres to the particle surface when forming pseudoparticles, and because the particle size distribution is not closest packed, the amount of pores can be relatively reduced. This increases the strength and insulation properties.

Note that the upper limit of the particle size of the aggregate is limited to 4 mm, which indicates the upper limit of the particle size of ordinary monolithic refractories, and also indicates the limit in terms of the crush resistance of the aggregate itself.

As a liquid material used for pre-treatment of magnesia-based lightweight aggregate,
We limited it to water-insoluble and thermosetting materials because they do not dissolve with water-soluble binders, have a lower vapor pressure than water, do not deteriorate due to evaporation, and are suitable for use before adding water during crosstalk. This is because it has properties such as being fixed in the aggregate during processing and not penetrating into the matrix powder.

As the water-insoluble thermosetting liquid material, synthetic resins such as phenol resins and furan resins, and organic substances such as paraffin or pitch having a melting point of 100° C. or higher are suitable.

As a method of impregnating the lightweight aggregate with the liquid substance or a method of coating the aggregate with the liquid substance, a method of adding the liquid substance to the fire-resistant lightweight aggregate, mixing it, and drying it can be used.

When fire-resistant lightweight aggregate is impregnated or coated with the liquid and used as a raw material, moisture and binder are prevented from entering into the bore of the aggregate during crosstalk. The same strength can be obtained even if the amount of binder added is reduced.

Further, by preventing moisture from entering (absorbing) into the aggregate, a molded article with low moisture content can be obtained, and as a result, steam explosion does not occur.

The amount of liquid added to the fire-resistant lightweight aggregate is 5 to 10, which is the construction moisture content of currently commercially available castables.
% is fine. In other words, if it is less than 5%, the impregnation or coating effect cannot be obtained and the water repellency of the aggregate cannot be ensured, while if it exceeds 10%, a large amount of gas will be generated during the heating process such as firing, which will interfere with the work. be.

A water-soluble inorganic binder is used as the binder.

It is sufficient to add an amount of moisture of 6 to 15%, but the consistency is mainly used as an index and is applied by pouring or vibration molding to a consistency of 200 to 250.

The construction method is to knead each material, fill it between the steel shell and core, and remove it from the mold after curing.In addition, if the wear layer is lined with amorphous refractories, it is dried with warm air at about 300℃. Lining later.

Examples Example 1 Porous magnesia aggregate with a particle size of 2.5 mmφ to 0.1 mmφ was preheated to 150°C, 6.5% of novolac type phenolic resin with a softening point of 75°C was added to the aggregate, and heated for 10 minutes. After stirring and mixing, the mixture was air-cooled and dried to obtain an aggregate whose surface was coated with the resin.

This pre-treated aggregate and alumina aggregate (corundum grains)
Mix at a ratio of 0:10 and add alumina cement to this.
(Add 7.5% (constant) of untreated water, add water to give a certain fluidity (consistency 280), and spread it 200 m vertically.
The molded product was poured into a metal frame measuring 200 mm wide x 100 mm high, dried with hot air at 100° C. for 24 hours, and fired at 800° C. for 3 hours, and the properties of the obtained molded body were investigated. The results are shown in Table 1 together with the particle size blend ratio.

In addition, the comparative examples in Table 1 are those that used the pretreated aggregate of the present invention and contained many fine particles outside the particle size range, and those that were composed only of untreated aggregate. It is an insulating castable made of lightweight chamotte aggregate, and is used for lining hot metal gutters, etc. In addition, the compressive strength and thermal conductivity ratio are expressed as a ratio of the measured values of the conventional example.

From the results in Table 1, the monolithic refractory of the present invention has a thickness of 0.1 mm.
It can be seen that both the compressive strength and the thermal conductivity ratio are excellent not only in cases where no fine particles are contained, but also in cases where a small amount of fine particles are contained.

On the other hand, even if the same pretreated aggregate is used, the particle size is 0.1
Comparative Example I, in which a large amount of fine particles less than mm in size was blended, had an inferior thermal conductivity ratio, and Comparative Examples 2.3, in which no pretreated aggregate was used, had inferior compressive strength and thermal conductive ratio.

Example 2 The same porous magnesia aggregate as Example 1 had a softening point of 128°C.
The pretreated aggregate obtained by adding 5% of petroleum pitch and impregnating it while heating and mixing, and the calcined alumina aggregate were mixed with the sample NO and C in Table 1, and an aluminum phosphate aqueous solution was mixed. Pour it into the bottom of a 70 ton capacity ladle as a binder (
After curing for 15 hours, unfired bricks with an A I depth of 0-78% were lined with unfired bricks having an A I depth of 0-78%, dried, preheated, and used for operation.

After the start of operation, the maximum value of the temperature rise of the steel skin of the receiving steel is measured for 33 to 35 hours, and the average value is A I! Os75
As a result of comparison with the average value of a conventional ladle using % high alumina castable (moisture 13%), the average receiving temperature was 16%.
Compared to 80°C, the average temperature of the conventional ladle was 325°C, whereas the average temperature of the bottom of the ladle according to the present invention was as low as 312°C, confirming that the amount of heat dissipation was significantly reduced. .

As explained in detail below, the insulating monolithic refractory of the present invention has superior heat insulating properties and fire resistance compared to conventional insulating castables,
It also has the effect of enabling highly safe construction with less chance of steam explosion, and is extremely useful as an insulation construction material for permanent layers such as molten steel ladles, which require particularly high insulation.

Claims (1)

[Scope of Claims] 1. A heat-insulating monolithic refractory made from magnesia-based lightweight aggregate, which has pores with a grain size of 0.1 mm or more and 4 mm or less and an average pore diameter of 10 to 50 μm. A heat-insulating monolithic refractory characterized by being made from a material impregnated or coated with a water-soluble thermosetting liquid material. 2. The insulating monolithic refractory according to claim 1, wherein the lightweight aggregate is porous magnesia with an MgO content of 95% and contains 20% or less of Al_2O_3.