JP7831513B2 - Method for installing thermal insulation lining and method for manufacturing skid pipes - Google Patents

Description

This invention relates to an insulating lining for covering a cooling member, a method for installing the insulating lining, and a skid pipe.

In the hot rolling process within a steel mill, thin steel sheets are produced by heating steel slabs in a heating furnace and then rolling them. The heating furnace used in the hot rolling process is equipped with a platform called a skid, which holds the steel slabs, to transport them from the charging side to the discharge side. The skid is fitted with skid pipes called beams or posts. The steel slabs are placed on top of the skid pipes, and the skids move up, down, left, and right to transport the slabs. The skid pipes also have water-cooled pipes as cooling components. These water-cooled pipes are tubular components through which cooling water flows. Some of the energy supplied to the heating furnace when heating the steel slabs is also transferred to the cooling water flowing through the water-cooled pipes. Therefore, a highly insulating lining is installed around the water-cooled pipes.

As a method for applying highly insulating linings, a dry spray application method is known, in which the spray material is applied to the application surface. For example, Patent Document 1 discloses a dry spray application method in which powdered refractory raw materials are pumped to a nozzle, water is added at the nozzle, and the material is sprayed onto the application surface.

Japanese Patent Publication No. 2000-356475

However, applying the above insulation lining construction method to skid pipes results in the following problems:

In the dry spray application method described in Patent Document 1, the powder and water are mixed at the nozzle, which often results in uneven mixing. This leads to a problem where a large amount of dust is generated during spraying onto the water-cooled pipe, increasing rebound loss. On the other hand, if the powder and water are mixed before being pumped to the nozzle, problems such as clogging of the mixture before reaching the nozzle can occur, potentially worsening workability.

This invention was made to solve the above-mentioned problems of the prior art, and its objective is to provide an insulating lining, an insulating lining application method, and a skid pipe that can reduce rebound loss without worsening workability during spraying.

The thermal insulation lining according to the present invention, which advantageously solves the above problems, is configured as follows.

[1] An insulating lining covering the outer surface of a cooling member, comprising a sprayed refractory layer formed by spraying granules, which are produced by adding water to a refractory raw material, a flocculant, and a curing accelerator, toward the cooling member.
[2] In the above [1], the granulated material is an insulating lining in which the moisture content is 5 parts by mass or more and 10 parts by mass or less on the outside, with respect to 100 parts by mass of refractory raw material.
[3] In the above [1], the refractory raw material is an insulating lining containing one or more selected from _Al₂O₃ , _SiO₂ , _MgO , and CaO.
[4] The thermal insulation lining in which the particle size of the refractory raw material is less than 5 mm, as described in [3] above.
[5] In the above [1], the granules are an insulating lining in which the contact angle for evaluating the wettability of the granules is less than 90°.

The method for constructing the thermal insulation lining according to the present invention, which advantageously solves the above problems, is configured as follows.
[6] A method for applying an insulating lining to cover the outer periphery of a cooling member, comprising adding water to a refractory raw material, a flocculant, and a hardening accelerator to granulate, and then spraying the granulated material toward the cooling member to form a sprayed refractory layer on the outer periphery of the cooling member.

The skid pipe according to the present invention, which advantageously solves the above problems, is configured as follows.
[7] The thermal insulation lining described in any one of [1] to [5] above is a skid pipe formed in an annular structure around the cooling member.

According to this invention, a granular material containing water is produced by adding water to a refractory raw material, a flocculant, and a hardening accelerator and then granulating the mixture. By using this water-granulated material, it becomes unnecessary to add water to the granular material immediately before spraying, thus reducing rebound loss compared to the case where water is added immediately before spraying. Furthermore, because the granular material is granular, the risk of clogging before reaching the nozzle during pumping is reduced, thus suppressing deterioration of workability during spraying.

This is a diagram showing the cross-sectional structure of an insulating lining according to one embodiment of the present invention. This is an explanatory diagram showing the method for installing the thermal insulation lining according to the above embodiment. This is an explanatory diagram for evaluating the wettability of granulated material when it adheres to the surface of a component.

The thermal insulation lining according to this embodiment will be described below.
<Insulating lining>
An insulating lining according to one embodiment of the present invention is an insulating lining that covers the outer surface of a cooling member, and includes a sprayed refractory layer formed by spraying granules, which are produced by adding water to a refractory raw material, a flocculant, and a curing accelerator, toward the cooling member.

In this embodiment, the insulating lining is for protecting the cooling element (hereinafter referred to as the water-cooled pipe) installed in the heating furnace. Cooling water at a temperature of approximately 40-50°C flows through the water-cooled pipe as the cooling medium.

As shown in Figure 1, the thermal insulation lining is provided to cover the outer circumference of the water-cooled pipe, which has multiple support members protruding from its outer surface. The thermal insulation lining in this embodiment consists of only one layer of sprayed refractory material. The sprayed refractory material layer is formed by spraying granular material toward the water-cooled pipe.

Here, the granulated material to be sprayed is prepared by adding water to refractory raw materials, a flocculant and a hardening accelerator, and a binder as an optional additive, and then granulating the mixture. Preferably, the granulated material has a water content of 5 to 10 parts by mass (on an external basis) per 100 parts by mass of refractory raw materials.

Unlike refractories, thermal insulation linings have a porous structure, making them more susceptible to rebound loss when their moisture content is low compared to refractories. Therefore, when spraying towards a water-cooling pipe, if the moisture content of the sprayed granules is less than 5 parts by mass, the amount of moisture is too low, and the sprayed material will not adhere to the water-cooling pipe, resulting in increased rebound loss. On the other hand, if the moisture content exceeds 10 parts by mass, the moisture content is too high, increasing the risk of clogging during pumping, and also increasing the amount of moisture that evaporates during drying. As a result, after drying, the porosity increases and densification does not occur, leading to a decrease in flexural and compressive strength and potentially reduced durability. Therefore, the moisture content is preferably between 5 and 10 parts by mass (outer coating) per 100 parts by mass of refractory raw material.

The moisture content of the sprayed granules is adjusted by the amount of water added during granulation. By setting the moisture content of the sprayed granules to between 5 and 10 parts by mass, the adhesion rate of the sprayed material to the water-cooled pipe can be increased without compromising workability, thereby reducing rebound loss. Furthermore, increasing the adhesion rate between the sprayed granules allows for layering to the desired thickness without detachment.

Specifically, it is preferable to adjust the moisture content of the granules so that the rebound loss when the granules are sprayed towards the water-cooling pipe is 25% or less.

Furthermore, the rebound loss was examined from the perspective of wettability regarding the adhesion of the granules to the surface of the material. Figure 3 is an explanatory diagram showing the relationship between the surface tension _γS of the solid, the surface tension _γL of the liquid, the contact angle θ of the liquid, and the interfacial tension _γSL of the solid and liquid when the granules adhere to the surface of the material. As a result of evaluating the adhesion of the granules, the contact angle θ was 40.6° under condition (a) and 76.8° under condition (b), and there were no problems with wettability in these cases. Under condition (c), the contact angle θ was 105.5°, and there was a problem with wettability. The rebound loss was 15% under condition (a), 20% under condition (b), and 30% under condition (c). Therefore, it was found that the smaller the contact angle θ is than 90°, the better the wettability and the less rebound loss can be reduced when sprayed. Therefore, in order to keep the rebound loss to 25% or less when the granules adhere to the water-cooling pipe, it is preferable that the contact angle θ used to evaluate the wettability of the granules be less than 90°.

By using such granules, the thickness of the sprayed refractory layer constituting the insulating lining (the layer thickness of the granules) can be made 50 mm or more, allowing the water-cooled pipes to be sufficiently insulated by a single layer of sprayed refractory material.

While known refractory raw materials can be used, it is preferable to include one or more selected from _Al₂O₃ , _SiO₂ , _MgO , and CaO, and more preferably to include all four of _Al₂O₃ , _SiO₂ , _MgO , and CaO. By using the four types of refractory raw materials, the range of composition and physical properties is broadened compared to cases where the refractory raw materials consist of one or two types, increasing versatility, as well as improving heat resistance, slag erosion resistance, and mechanical strength.

Furthermore, it is preferable that the particle size of the aggregate in the refractory raw material is less than 5 mm. By making the particle size of the refractory raw material constituting the sprayed granules less than 5 mm, rebound loss during spraying of the granules can be reduced. Here, particle size refers to the maximum particle size of the aggregate. For example, a sieve with a mesh size of 5 mm can be used.

Furthermore, it is preferable that the refractory material includes fine particles in addition to aggregate with a particle size of less than 5 mm. Examples of fine particles include silica fine particles ( _SiO₂ ) or dolomite fine particles (MgO, CaO) with a particle size of less than 0.2 mm. By including fine particles in the refractory material in this way, rebound loss when spraying the granulated material can be reduced compared to a configuration in which the refractory material consists only of aggregate.

Examples of flocculants include alumina cement. Examples of hardening accelerators include alumina cement hydrate, lithium carbonate, and alkali metal hydroxides. Optional binders include alumina cement. It is preferable that the total amount of flocculant and hardening accelerator, applied externally, be between 5 and 11 parts by mass per 100 parts by mass of refractory raw material.

In the above embodiment, the thermal insulation lining was constructed using only one layer of sprayed refractory material. However, other thermal insulation layers may be provided. Specifically, for example, one layer of sprayed refractory material may be provided on the outside of the water-cooling pipe, a thermal insulation layer made of a microporous thermal insulation sheet may be provided on the outside of that, and another layer of sprayed refractory material may be provided on the outside of that thermal insulation layer. By constructing the thermal insulation layer with two or more layers, and sandwiching the microporous thermal insulation sheet from both sides with the sprayed refractory material layers, it is possible to enhance the thermal insulation performance of the thermal insulation layer while protecting the microporous thermal insulation sheet.

Furthermore, even when the thermal insulation lining is formed with two or more insulation layers, it is preferable that at least 50% of the total thickness of the thermal insulation lining is composed of a sprayed refractory layer, and more preferably 80% or more is composed of a sprayed refractory layer. By composing the majority of the thermal insulation lining with a sprayed refractory layer, the construction efficiency of the thermal insulation lining can be improved.

Next, the method for installing the thermal insulation lining according to this embodiment will be described.
<Installation method for thermal insulation lining>
The method for applying the heat insulating lining according to this embodiment involves adding water to a refractory raw material, a flocculant, and a hardening accelerator to granulate the material, and then spraying the granulated material toward a cooling member to form a sprayed refractory layer on the outer circumference of the cooling member.

When applying the thermal insulation lining, as shown in Figure 2, a dry sprayer is used to spray the granulated material towards the water-cooled pipe using air pressure, forming a sprayed refractory layer on the outside of the water-cooled pipe. The granulated material used is pre-granulated, consisting of refractory raw materials, a flocculant and a hardening accelerator, and optionally a binder, with water added. The granulation method is not particularly limited; for example, it can be granulated using a known granulator such as a rotary drum.

In typical dry spray application methods, unhumidified powder is compressed with air to the nozzle, where it is mixed with water before spraying. However, in this embodiment, since granulated material with added water is used, there is no need to mix the powder and water immediately before spraying, and the granulated material can be sprayed directly towards the water-cooled pipe.

In other words, since the refractory raw materials and water can be thoroughly mixed beforehand during granulation, this embodiment, compared to the conventional method of adding water to the powder immediately before spraying, is not affected by the amount of water added during spraying, generates less dust, and reduces rebound loss.

The above-described thermal insulation lining can be applied to skid pipes installed in heating furnaces. High thermal insulation is required around water-cooled pipes, and by forming the thermal insulation lining according to this embodiment in an annular structure around the water-cooled pipe, a skid pipe with high thermal insulation can be obtained.

The effects of this embodiment will be described in detail below based on the examples, but the present invention is not limited to these examples.
As an example of this embodiment, in the case of an insulating lining for a water-cooled pipe installed in a heating furnace, the optimal specifications for the spraying method were investigated, assuming that the insulating lining consists of one layer and has a total thickness of 100 mm.

First, for Test No. 1-1, a granulated material was prepared by adding water to refractory raw materials, a coagulant, and a hardening accelerator and then granulating the mixture. For Test No. 1-2, an ungranulated material was prepared without adding water and granulation. For the granulated material in Test No. 1-1, the mixture was sprayed directly from the nozzle of a dry spraying machine without mixing in any mixing water. For the ungranulated material in Test No. 1-2, the mixing water was mixed in from the nozzle before spraying, and the rebound loss after spraying was compared.

Table 1 shows the results. In Test No. 1-1, the rebound loss when granulated material was sprayed was 15%, while in Test No. 1-2, the rebound loss when ungranulated material was sprayed was 30%.

Next, the moisture content of the granulated material was examined. The results are shown in Table 2. As shown in Test No. 1-1 and Tests No. 2-2 to 2-4, when the moisture content of the granulated material was between 5 and 10 parts by mass, the rebound loss could be suppressed to 25% or less, and the granules could be pumped without clogging.

Furthermore, the adhesion rate between granules increased, allowing for lamination to the specified thickness without detachment. On the other hand, as in Test No. 2-1, when the moisture content was less than 5 parts by mass, the low moisture content resulted in a reduced adhesion rate of the sprayed granules, exceeding a rebound loss of 25%. Also, as in Test No. 2-5, when the moisture content exceeded 10 parts by mass, the excessive moisture content caused clogging during granule transport, significantly increasing the porosity of the sprayed material and preventing densification. Increasing the air pressure was necessary to resolve this clogging, resulting in higher costs compared to other test conditions.

Furthermore, the composition of _the refractory raw materials used as granules was investigated. The results are shown in Table 3. As in Test No. 1-1, when the refractory raw material consisted of four types: _Al₂O₃ , _SiO₂ , _MgO , and CaO, the compressive strength and flexural strength of the sprayed refractory layer were high. As in Tests No. 3-1 to 3-4, when the refractory raw material consisted of any three types: _Al₂O₃ , _SiO₂ , MgO, and CaO, the compressive strength and flexural strength were slightly lower compared to Test No. 1-1. As in Tests No. 3-5 to 3-6, when the refractory raw material consisted of two types, the compressive strength and flexural strength were further lower compared to Test No. 1-1.

Next, we investigated the maximum particle size of the aggregate used as the refractory raw material for the granulated material. The results are shown in Table 4. As shown in Test No. 4-1, when the maximum aggregate particle size was 5 mm or larger, the rebound loss increased compared to when the maximum aggregate particle size was less than 5 mm.

1. Water-cooled pipes 2. Sprayed refractory layer 3. Support material 4. Cooling water 5. Dry spraying machine (air)
6. Granulated material 7. Nozzle section θ Contact angle γ _S Surface tension of solid γ _L Surface tension of liquid γ _SL Interfacial tension between solid and liquid

Claims (5)

A method for installing an insulating lining that covers the outer circumference of a cooling component,
In the process of adding water to refractory raw materials, a flocculant, and a hardening accelerator to granulate them , and then spraying the granulated material toward the cooling member to form a sprayed refractory layer on the outer circumference of the cooling member ,
The aforementioned granules have a moisture content of 5 to 10 parts by mass when applied externally, relative to 100 parts by mass of refractory raw material , in a method for constructing an insulating lining. The method for constructing an insulating lining according to claim 1, wherein the refractory raw material contains one or more selected from _Al₂O₃ , _SiO₂ , MgO _, and CaO. The method for installing the thermal insulation lining according to claim 2 , wherein the particle size of the refractory material is less than 5 mm. The method for installing an insulating lining according to claim 1, wherein the granules have a contact angle of less than 90° for evaluating the wettability of the granules. A method for manufacturing a skid pipe, comprising forming an annular thermal insulation lining around the cooling member using the method for constructing a thermal insulation lining according to any one of claims 1 to 4.