JP2012136402A - Method for producing high strength perlite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing high strength perlite which has a good foamed state, a large compression strength, and a remarkably high float-up remaining rate in pressurized water.SOLUTION: The method for producing high strength perlite includes: using, as a raw material, a pulverized substance of natural glassy rock having a water content of ≥2 mass% and adjusting the water content by preheating (first step); then lowering temperature to stabilize (second step); and foam firing the resulting raw material by heating it to a temperature at which foaming occurs (third step). In the first step, preheating is carried out preferably under such conditions that the difference between the temperature of the raw material and a peak temperature (maximum temperature in preheating) is 350-750°C, and the temperature raising speed to the peak temperature is 5-20 °C/s, and the water content of the powder of the raw material is adjusted to 0.7-1.6 mass%.

Description

The present invention relates to a method for producing pearlite that is widely used as a material such as a building material, a heat insulating material, and a soil improvement material. More specifically, natural glassy rocks, especially pearlite or pinestone rocks produced in Japan in large quantities, are low in water absorption and excellent in fluidity when mortarized, especially suitable for building materials. The present invention relates to a method for producing hard pearlite.

Perlite has been conventionally known as a hollow lightweight body produced from natural glassy rock. Perlite is made by heating raw particles such as pearlite and obsidian at a high temperature of 900 to 1300 ° C to foam the contained moisture into a hollow body. Widely used in

Conventional pearlite has a problem that if a raw material containing a large amount of water of crystallization is used, the surface becomes porous, resulting in high water absorption, making it unsuitable for lightweight aggregates. In view of this, a low water-absorbing pearlite having a large number of bubbles formed inside and an exterior wall that closes the opening of the bubbles has been developed (Patent Document 1: Japanese Patent Laid-Open No. 2008-1919).

Also, when heating and foaming raw rocks such as pearlite and obsidian, preheating is performed at a temperature lower than the softening point of the raw rock to avoid the formation of many open bubbles due to sudden foaming of the contained water. After that, spherical pearlite is known in which the water absorption rate is reduced by foaming and firing at a high temperature to form closed pores (Patent Document 2: Japanese Patent No. 3528390).

Further, using Shirasu ore powder, this was heated and dried to 350 to 500 ° C. to a moisture content of 1.46 to 2.90 mass%, and then fired to 980 to 1090 ° C. in an internal heating medium fluidized bed furnace. By doing so, a method of manufacturing a shirasu balloon with high strength and high sphericity is known. (Patent Document 3: JP 2010-64903 A)

The pearlite of Patent Document 1 is described as having a low water absorption rate and a floating rate of 80% because it has an outer shell that closes the opening of bubbles. Since these hollow particles have a large number of internal bubbles, the floating rate under normal pressure is high, but the internal bubbles are continuous bubbles and not independent bubbles (although there are partition walls in the internal space, the bubbles communicate with each other). However, if a crack occurs in the outer wall, water penetrates the entire particle through the communicating bubbles. For this reason, there is a problem that the floating rate in pressurized water is significantly reduced.

The pearlite of Patent Document 2 has a low water absorption rate because the internal bubbles are not open on the particle surface, but in many cases, the internal space of the particles is formed by large single bubbles and is compressed because there is no partition inside. The strength is low and cracks are likely to occur on the particle surface. Further, when cracks occur on the surface, the particles are easily filled with water. For this reason, the floating rate in pressurized water is significantly reduced.

The shirasu balloon of Patent Document 3 uses shirasu as a raw material, but when using a rock powder of pearlite or pine stone rock as a raw material, it is difficult to obtain good expanded particles by the dehydration heating method of Patent Document 3. There is a problem.

JP 2008-19149 A Japanese Patent No. 3528390 JP 2010-64903 A

It is said that perlite foams better when the moisture in the raw material is in the center. When Shirasu is used as a raw material, Shirasu is mainly a sandy volcanic deposit with volcanic ash deposited on it, and it is often used without crushing, and the particle surface is exposed to the outside air. Is relatively small, and the contained water is unevenly distributed in the center. Therefore, it is easy to foam well even if the heating rate of heat drying is slow. On the other hand, rhyolite materials such as pearlite and pine stone are crushed and made to an appropriate particle size, but the particle surface is exposed to the outside air for the first time by pulverization, so the distribution of water content is relatively uniform. Yes. Therefore, if the temperature rising rate for dehydration is slow, the water in the central part is also dehydrated, the amount of water is remarkably reduced, and there is a problem that foaming is not good. In addition, when the process proceeds to the firing step while maintaining the preheating temperature for dehydration, there is a problem that the distribution of the contained water is not sufficiently stable and foaming is not satisfactorily performed.

The present invention solves the above-mentioned conventional problems in the method for producing pearlite, and provides a high-strength pearlite having a good foamed state, a large compressive strength, and a remarkably high floating rate remaining in pressurized water. A method of manufacturing is provided.

The present invention relates to a method for producing high-strength pearlite having the following configuration.
[1] Using a natural vitreous rock pulverized material with a water content of 2% by mass or more as a raw material, pre-heating to adjust the water content (first step), then lowering the temperature to stabilize (second) After the step, a method for producing high-strength pearlite, which is heated to foaming and foamed and fired (third step).
[2] In the first step, from the raw material temperature to the peak temperature (maximum preheating temperature) is 350 ° C. to 750 ° C., and the preheating is performed at a rate of temperature increase to the peak temperature of 5 to 20 ° C./second, The manufacturing method as described in said [1] which adjusts the moisture content of a raw material powder to 0.7-1.6 mass%.
[3] The production method according to the above [1] or [2], wherein in the second step, the heating temperature of the raw material powder is lowered to a temperature range of 100 ° C. or higher and 150 ° C. or lower than the peak temperature.
[4] In the pre-heating in the first step, after heating to a peak temperature of 500 to 600 ° C. and holding in this temperature range for 20 to 40 seconds, the heating temperature is lowered to 150 to 500 ° C. in the second step. [1] The production method according to any one of [3] above.
[5] The production method according to any one of [1] to [4] above, wherein in the third step, the raw material powder is heated to 900 ° C. to 1200 ° C. and foamed.
[6] The production method according to any one of [1] to [5] above, wherein the natural glassy raw material is pearlite or pinestone.
[7] The manufacturing method according to any one of [1] to [6], wherein the first step and the second step are performed in a rotary kiln or an electric furnace, and the third step is performed in a fluidized bed firing furnace.

According to the method for producing pearlite of the present invention, a pulverized product of natural vitreous rock, in particular, a pulverized powder of pearlite or pinestone, is used as a raw material, dehydrated by preheating, stabilized, and then heated and foamed. It is possible to produce a high-strength pearlite that has a good foamed state, a high compressive strength, and a remarkably high floating ratio remaining in pressurized water.

Hereinafter, the present invention will be specifically described based on embodiments.
The production method of the present invention uses a natural glassy rock pulverized material having a water content of 2% by mass or more as a raw material, adjusts the water content by preheating and then lowers the temperature for stability. This is a method for producing high-strength pearlite, characterized in that after forming (second step), heating to foaming and foaming and firing (third step) are performed. Here, the amount of water was defined as the amount of water reduced when the pulverized raw material was heated from 100 ° C. to 1000 ° C.

[First step: Dehydration]
In the production method of the present invention, a pulverized product of natural glassy rock, for example, a pulverized powder of pearlite or pine oil can be used as a raw material. A pulverized natural glassy rock having a water content of 2% by mass or more is preheated to adjust the water content. If the water content is less than 2% by mass, the amount of water necessary for foaming is insufficient when dehydrating, and this is not preferable.

The preheating is preferably performed at a temperature rising rate of 5 to 20 ° C./second from the raw material temperature to the peak temperature (the maximum temperature for preheating). The raw material temperature is approximately room temperature. The peak temperature is the maximum temperature for preheating, and is suitably 350 ° C to 750 ° C, preferably 500 ° C to 600 ° C. When the peak temperature is lower than 350 ° C., the amount of water tends to be 1.7% by mass, and when the peak temperature is higher than 750 ° C., the amount of water tends to be less than 0.6% by mass.

If the heating rate of preheating is slower than 5 ° C / sec, the raw material is heated slowly, so the heating time until reaching the peak temperature is long and the amount of dehydration increases, so the water necessary for foaming is insufficient. It is not preferable. On the other hand, when the temperature increase rate of the preheating is higher than 20 ° C./second, a part of the raw material is vitrified, which is not preferable. After heating to peak temperature, it is good to hold | maintain at this temperature for 20 to 40 seconds.

The moisture of the raw material is dehydrated by this preheating, and the water content is preferably 0.7 to 1.6% by mass. If the amount of water after preheating is less than 0.7% by mass, the amount of water necessary for foaming is insufficient, such being undesirable. On the other hand, if the amount of water after preheating is more than 1.6% by mass, the foaming becomes excessive and the number of open bubbles increases, so that the hydrostatic pressure residual ratio decreases and the foam shape tends to be poor.

[Second step: Stabilization]
After the raw material is preheated to adjust the water content, the heating temperature is lowered and stabilized. The temperature range to be stabilized is 100 ° C. or higher and is preferably 150 ° C. or more lower than the peak temperature, preferably 200 ° C. or lower than the peak temperature. If the lower limit of the stabilization temperature is lower than 100 ° C., there is a concern that moisture in the air may be taken in, which is not preferable. On the other hand, if the difference between the upper limit of the stabilization temperature and the peak temperature is less than 150 ° C., the activity is too high to stabilize the moisture distribution inside the raw material, which is not preferable.

Specifically, for example, when the preheating peak temperature in the first step is 500 to 600 ° C, the stabilization temperature in the second step is 150 ° C to 500 ° C, preferably 200 ° C to 400 ° C. good.

[Third step: Foaming]
After the stabilization, the raw material is heated and fired at 900 ° C. to 1200 ° C. to be foamed. When the firing temperature is lower than 900 ° C., there are many cases where sufficient foaming cannot be performed, which is not preferable. On the other hand, if the firing temperature exceeds 1200 ° C., the raw material may be completely melted, which is not preferable.

The first step and the second step may be performed in a rotary kiln or an electric furnace, and the third step may be performed in a fluidized bed firing furnace. After foaming and firing, the foam is selected with water, and unfoamed material and the like are removed by a sorting means such as airflow diversion to obtain the desired hard spherical pearlite.

The Example of this invention is shown with a comparative example. In addition, the moisture content, the hydrostatic pressure residual ratio, and the bulk density were measured by the following methods.
〔amount of water〕
Dry the raw material in a dryer at about 100 ° C until a constant weight is obtained. This dried raw material is put in a crucible and a sample mass A is weighed. This is heated in an electric furnace at about 1000 ° C. until a constant weight is obtained, and the sample mass B after heating is weighed. From the obtained sample mass, (A−B) / A × 100% was calculated, and this value was taken as the moisture content.
[Remaining hydrostatic pressure levitation rate]
The sample is put into a pressurized container filled with water together with the sample container, and pressurized at 8 MPa for 1 minute. After pressurization, the entire amount of the pressurized sample is taken out and placed in a graduated cylinder, and 200 ml of water is added and left to stand. When the turbidity of water disappears after standing, the volume of the sample particles floating is measured by a method according to the above method for measuring the floating rate, and is set as a pressurized floating rate (floating rate) W2 under a pressure of 8 MPa. A sample having the same amount as the pressurized sample is measured by the same measurement method except that the sample is not pressurized and is at normal pressure, and is defined as a non-pressurized floating rate (floating rate) W1. The hydrostatic pressure levitation residual rate was calculated based on the formula of pressurized sample buoyancy rate W2 / non-pressurized levitation rate W1 × 100.
〔The bulk density〕
A sample is filled into a container with a constant volume S (cm ³ ), the portion protruding from the opening is ground, the total weight G1 is measured, and the weight G2 of the container is subtracted from this to obtain the powder weight G3 (g). The powder weight G3 [G3 / S] g / cm ³ with respect to the volume S was defined as the bulk density.
[Shape] The shape was determined with the naked eye.

[Example 1]
Pearlite with a water content of 2.9% and an average particle size of 120 μm (hereinafter referred to as “raw material A”) was preheated in a rotary kiln at a heating rate of 5 ° C./second, a peak temperature of 600 ° C., and a holding time of 30 seconds (first Step) The water content was adjusted to 0.7%. Next, after the heating temperature was lowered (second step), the heating temperature was raised and foaming firing (third step) was performed at 1050 ° C. After classification, the bulk density and hydrostatic pressure residual ratio of the foam were measured to determine the shape. The results are shown in Table 1.
When cooling at a temperature 200 to 450 ° C. lower than the peak temperature of preheating, the proportion of amorphous non-spherical particles decreases, and the hydrostatic pressure residual rate increases dramatically (A3, A4). On the other hand, in the sample (A1) in which the temperature is not lowered at all from the peak temperature, or in the sample (A2) in which the temperature difference from the peak temperature is 100 ° C., the ratio of amorphous non-spherical particles increases. When the stabilization temperature is lower than 100 ° C., the proportion of amorphous non-spherical particles increases, and the hydrostatic pressure residual ratio decreases dramatically (A5). Accordingly, the stabilization temperature after the preheating is 150 ° C. or more, preferably 200 ° C. or more lower than the preheating peak temperature.

[Example 2]
The raw material A was preheated in a rotary kiln by changing the rate of temperature rise and the peak temperature (holding time 30 seconds). Next, after the temperature was lowered to the stabilization temperature, foam firing was performed at a firing temperature of 1050 ° C. After classification, the bulk density and hydrostatic pressure residual ratio of the foam were measured to determine the shape. The results are shown in Table 2.
Even if the stabilization temperature is the same, if the difference between the peak temperature of the preheating and the stabilization temperature is 100 ° C., excessive foaming occurs in the foamed particles, and the number of amorphous non-spherical particles increases (A7). On the other hand, samples (A6, A8) having a difference between the preheating peak temperature and the stabilization temperature of 200 ° C. or higher have a high hydrostatic pressure residual rate.

Example 3
The raw material A was preheated in a rotary kiln (heating rate 5 ° C./second, peak temperature 600 ° C., holding time 30 seconds), and the water content was adjusted to 1.1 mass%. Next, after the temperature was lowered to the stabilization temperature of 300 ° C., the firing temperature was changed to perform foaming firing. After classification, the bulk density and hydrostatic pressure residual ratio of the foam were measured to determine the shape. The results are shown in Table 3.
If the firing temperature is 900 to 1200 ° C., the shape is good and the hydrostatic pressure residual rate is high (A9 to A11). If the firing temperature is higher (1350 ° C.), it will melt (A12).

Example 4
The raw material A was preheated in a rotary kiln by changing the heating rate, peak temperature, and holding time. Next, after the temperature was lowered by 300 ° C. from the peak temperature of the preheating as the stabilization temperature, foam firing was performed at a firing temperature of 1050 ° C. After classification, the bulk density and hydrostatic pressure residual ratio of the foam were measured to determine the shape. The results are shown in Table 4.

At a heating rate of 3 ° C./second, the water content becomes as small as 0.4% by mass and does not foam even when heated and fired (A13). On the other hand, when the rate of temperature increase is 30 ° C./second, the water content becomes as large as 2.1% by mass, and when this is heated and fired, the proportion of amorphous non-spherical particles in the expanded particles increases (A14). Further, when the preheating peak temperature is as low as 300 ° C., the water content becomes as large as 2.6% by mass, so that the shape of the foam becomes poor and the hydrostatic pressure residual rate is small (A15). When the peak temperature of the preheating is 800 ° C., the water content is dehydrated to 0.6% by mass even at a rate of temperature increase of 26 ° C./second, so that no foaming occurs (A16). No foaming occurs at a rate of temperature increase of 3 ° C./second even when the water content after preheating is 0.5 mass% (A17). Accordingly, the heating rate for preheating is preferably 5 to 20 ° C./second, and the water content is preferably 0.7 to 1.6 mass%.

Example 5
Pearlite (raw material B) having a moisture content of 2.2 mass% and an average particle size of 120 μm was preheated in a rotary kiln by changing the heating rate (maximum temperature 600 ° C., holding time 30 seconds). After the stabilization temperature was lowered by 300 ° C. from the preheating peak temperature, foam firing was performed at a firing temperature of 1050 ° C. After classification, after classification, the bulk density and hydrostatic pressure residual ratio of the foam were measured, and the shape was determined. The results are shown in Table 5.
Even if the raw material has a different water content before preheating, if the water content is adjusted to 0.7 to 1.6% by mass by preheating and stabilized by lowering the preheating peak temperature by 300 ° C., the shape becomes The hydrostatic pressure residual rate is also good (B1, B2).

Pearlite (raw material C) having a water content of 1.5% by mass and an average particle size of 120 μm was subjected to foam firing by performing one-stage firing (firing temperature of 1,050 ° C.) without performing preheating. After classification, after classification, the bulk density and hydrostatic pressure residual ratio of the foam were measured, and the shape was determined. The results are shown in Table 6.
In one-step firing without a stabilization step, the proportion of amorphous non-spherical particles increases even when the moisture content of the raw material is 1.5% by mass, and the hydrostatic pressure residual rate is small (C).

Claims (7)

Using a pulverized natural glassy rock having a water content of 2% by mass or more as a raw material, preheating was performed to adjust the water content (first step), and then the temperature was lowered and stabilized (second step). A method for producing high-strength pearlite, which is heated to foaming and then fired by foaming (third step). In the first step, from the raw material temperature to the peak temperature (maximum preheating temperature) is 350 ° C. to 750 ° C., preheating is performed at a rate of temperature increase to the peak temperature of 5 to 20 ° C./second, The production method according to claim 1, wherein the water content is adjusted to 0.7 to 1.6 mass%.
The manufacturing method according to claim 1 or 2, wherein in the second step, the heating temperature of the raw material powder is lowered to a temperature range of 100 ° C or higher and 150 ° C or lower than the peak temperature.
The preheating in the first step is heated to a peak temperature of 500 to 600 ° C, held in this temperature range for 20 to 40 seconds, and then the heating temperature is lowered to 150 to 500 ° C in the second step. The manufacturing method in any one of Claim 3.
The manufacturing method according to any one of claims 1 to 4, wherein in the third step, the raw material powder is heated to 900 ° C to 1200 ° C to be foamed.
The manufacturing method according to any one of claims 1 to 5, wherein the natural glassy raw material is pearlite or pine stone.
The manufacturing method according to any one of claims 1 to 61, wherein the first step and the second step are performed in a rotary kiln or an electric furnace, and the third step is performed in a fluidized bed firing furnace.