TITLE OF THE INVENTION
Unshaped refractory material
TECHNICAL FIELD
[0001]
The present invention relates to an unshaped (castable) refractory
material comprising an organic fiber and adapted to be installed with
the addition of water.
BACKGROUND ART
[0002]
An unshaped refractory material is used, for example, for a lining
of a ladle, a tundish, an iron runner of a blast furnace, or various
types of molten metal vessels, such as a vacuum degassing furnace.
By taking a casting method for installing a ladle lining as an example,
a process for installing an unshaped refractory material will be
described below.
[0003]
Firstly, an unshaped refractory material is kneaded together with
water added thereto to form a slurry. Then, the slurry is cast into
a space between an inner surface of a ladle and a core inserted in
the ladle, and cured until shape retainability is developed. A body
obtained by curing the cast slurry until development of shape
retainability will hereinafter be referred to as "installed body".
After completion of the curing, the core is removed, and the remaining
installed body is dried to serve as a lining.
[0004]
The drying of the installed body is performed by heating it using
a burner or microwaves. During the heating, water vapor is generated

from an inside of the installed body, and a resulting internal water
vapor pressure is likely to cause cracking or explosive spalling.
The occurrence of explosive spalling can be suppressed by drying the
installed body for a long period of time at a moderate temperature
rising rate. However, in view of enhancing an operating rate of the
ladle, it is desired to shorten the drying time.
[0005]
Therefore, a counterraeasure technique of incorporating organic
fibers into an unshaped refractory material has heretofore been
employed. The organic fibers are melted inside the installed body
by heat during the drying, and reduced in volume to form water vapor
venting holes in the installed body. Water vapor is dissipated from
the inside to outside of the installed body through an indefinitely
large number of fine venting holes formed by the organic fibers. This
makes it possible to ease a rise in internal water vapor pressure
of the installed body, thereby suppressing explosive spalling.
[0006]
The following Patent Document 1 mentions that the internal water
vapor pressure of the installed body sharply rises from about 200°C,
and therefore it is preferable to use a type of organic fiber which
is meltable at 180°C or less, i.e., at a temperature before the
internal water vapor pressure sharply rises. The Patent Document 1
cites, as an example of a low-melting-point raw material, vinylon,
polyethylene and polypropylene, and suggests that a vinylon fiber
is most preferable.
[0007]
The following Patent Documents 2 and 3 disclose specific examples
of an unshaped refractory material in which a polyethylene fiber is
selected as the explosive-spalling preventive organic fiber (see the

inventive examples 2 and 3 in the Patent Document 2, and the
comparative example 3 in the Patent Document 3) . The Patent Document
3 also mentions that a water content of the polyethylene fiber is
zero mass% (see upper right column on page 2 and Table 2 in the Patent
Document 3).
[0008]
The following Patent Document 4 cites low-density polyethylene
having a density of 0.93 g/cm3 or less, as a raw material for the
explosive-spalling preventive organic fiber. It is known that, among
various types of polyethylene, the low-density polyethylene has a
low melting point of 100 to 135°C.
LIST OF PRIOR ART DOCUMENTS
PATENT DOCUMENTS
[0009]
Patent Document 1: JP 61-010079A
Patent Document 2: JP 03-083869A
Patent Document 3: JP 03-265572A
Patent Document 4: JP 2008-120669A
SUMMARY OF THE INVENTION
TECHNICAL PROBLEM
[0010]
It has heretofore been simply believed that an organic fiber having
a lower melting point is more desirable as the explosive-spalling
preventive organic fiber. However, in some cases, explosive spalling
occurs even using low-melting-point organic fibers. As a result of
diligent researches, the inventors of this application have found
out that one major cause of the explosive spalling is water contained

in an organic fiber. This point will be described below.
[0011]
After production, organic fibers are not immediately combined in
an unshaped refractory material, but transported to an unshaped
refractory material plant and stored, whereafter the organic fibers
are put into a hopper exposed to atmospheric air, and kept in a standby
state until being mixed in an unshaped refractory material as a part
thereof. During the transportation and the storage, the organic
fibers are packed in a flexible container bag. However, in the case
where the flexible container bag is made of a moisture-permeable
material, water such as moisture in the air is likely to adhere to
the organic fibers. Moreover, during the standby state, water such
as moisture in the air is also likely to adhere to the organic fibers.
A period from the transportation to the standby is generally a total
of several days or more.
[0012]
Meanwhile, in an unshaped refractory material, a remainder other
than organic fibers comprises a refractory powder and a binder. In
an unshaped refractory material adapted to be installed with the
addition of water, a hydraulic (water-hardenable) binder such as
alumina cement is generally used as the binder. The refractory powder
comprises: a raw material having a hydratable property (hereinafter
referred to as "hydratable raw material"), such as a magnesia-based
raw material, a calcia-based raw material, or a dolomite-based raw
material; and an ultrafine powder, such as silica flour. As used here,
the term "hydration" means a phenomenon that a raw material reacts
with water to form a hydroxide.
[0013]
Therefore, in the produced unshaped refractory material, even

before water necessary for installation is added thereto, the organic
fibers having water adhering thereto are in contact with at least
one of the hydraulic binder, the hydratable raw material and the
ultrafine powder, and can serve as a water supply source therefor.
[0014]
Furthermore, the produced unshaped refractory material is not
immediately installed. Generally, in a process after an unshaped
refractory material is shipped from an unshaped refractory material
production plant in response to a prospect-based order passed to the
production plant, through until the unshaped refractory material is
installed with the addition of water at an installation site, the
unshaped refractory material undergoes a stock period, for example,
of about 5 days to about several months, in a situation where it is
packed in a flexible container bag.
[0015]
In this stock period, water contained in the organic fibers
accelerates degradation of the hydraulic binder, the hydratable raw
material or the ultrafine powder. More specifically, due to a contact
with the water, a hydration reaction in the hydraulic binder is
partially completed before the installation, so that hydration
reactivity of the hydraulic binder after the installation is
deteriorated, thereby causing deterioration in strength-imparting
function thereof. Further, the hydratable raw material is hydrated
through a contact with the water, so that it becomes structurally
crumbly due to volume expansion, which leads to deterioration in
strength after the installation. When the ultrafine powder is in
contact with the water, a temporal change occurs therein, maybe
because a surface of the ultrafine powder is hydroxylated, which leads
to deterioration in strength after the installation.

[0016]
Explosive spalling of an installed body occurs when an internal
water vapor pressure of the installed body becomes greater than the
strength of the installed body. As organic fibers have a lower melting
point, water vapor venting holes are formed at an earlier timing,
and therefore the internal water vapor pressure is less likely to
rise. However, if the strength of the installed body becomes
insufficient due to water contained in the organic fibers, the
installed body fails to withstand the internal water vapor pressure,
resulting in occurrence of explosive spalling.
[0017]
Each of the Patent Documents 1 to 4 discloses a test result
demonstrating an explosive-spalling preventing effect of organic
fibers recommended by each of them. However, all of the tests were
carried out on a laboratory basis, i.e., after preparing a sample
of an unshaped refractory material, the sample was immediately kneaded
together with water and then subjected to evaluation, so that an
influence of a factor, such as the stock period, in an actual process,
was not reflected. It has heretofore been unknown that water
contained in organic fibers becomes a factor hindering the
explosive-spalling preventing effect.
[0018]
The vinylon fiber used in the Patent Document 1 contains a large
amount of water. An official moisture regain of the vinylon fiber
is 5 mass%. Therefore, particularly when the stock period is
relatively long, the vinylon fiber fails to thoroughly produce the
explosive-spalling preventing effect.
[0019]
In general, an official moisture regain of an organic fiber means

an amount of water contained in an internal structure of the organic
fiber.
[0020]
Although an official moisture regain of the polyethylene fiber
used in the Patent Documents 2 to 4 is zero mass%, water is likely
to adhere to a surface of the fiber during storage, as mentioned above.
Thus, a water content of the polyethylene fiber is not always zero
mass%. Explosive spalling is likely to occur due to water adhering
to the surface of the fiber.
[0021]
As used in this specification, the term "water content of an organic
fiber" means a sum of an amount of water contained in an internal
structure of the organic fiber and an amount of water adhering to
a surface of the organic fiber.
[0022]
It is an object of the present invention to provide an unshaped
refractory material which is less likely to undergo cracking and
explosive spalling during drying.
SOLUTION TO THE TECHNICAL PROBLEM
[0023]
According to one aspect of the present invention, there is provided
an unshaped refractory material which comprises an organic fiber and
adapted to be installed with the addition of water, wherein the organic
fiber is composed of a polyethylene fiber which has a water content
of less than 3 mass% and whose surface is coated with oil.
EFFECT OF THE INVENTION
[0024]

In order to prevent explosive spalling, it is necessary to keep
an internal water vapor pressure of an installed body from becoming
greater than a strength of the installed body, considering a balance
between the strength of the installed body and the internal water
vapor pressure of the installed body.
[0025]
In the organic fiber for use in the present invention, the water
content is as low as less than 3 mass%, and water is less likely to
adhere to the surface of the fiber because oil is applied to coat
the surface. Thus, the organic fiber for use in the present invention
is less likely to cause degradation of a remainder other than the
organic fibers in the unshaped refractory material even during a stock
period. Therefore, it becomes possible to prevent deterioration in
strength of the installed body in a drying process.
[0026]
Further, the organic fiber for use in the present invention is
made using polyethylene as a raw material. Among organic fibers each
having an official moisture regain satisfying the water content
defined in the appended claims, the polyethylene has a particularly
low melting point. Thus, the organic fiber for use in the present
invention is melted at an early stage after start of drying to form
a venting hole, so that it is also excellent in terms of an effect
of easing the internal water vapor pressure of the installed body.
[0027]
As above, it becomes possible to keep the internal water vapor
pressure of the installed body from becoming greater than the strength
of the installed body during drying, thereby preventing cracking and
explosive spalling in the installed body.

DESCRIPTION OF EMBODIMENTS
[0028]
In an embodiment of the present invention, an unshaped refractory
material comprises a refractory powder, a binder, and an organic
fiber.
[0029]
The present invention is directed to preventing degradation of
an unshaped refractory material due to water contained in the organic
fiber, and is of great significance, particularly, in a situation
where a remainder other than organic fibers in an unshaped refractory
material comprises a raw material which is more likely to undergo
degradation due to water. Specifically, the present invention is of
great significance, particularly, in a situation where an unshaped
refractory material comprises at least one of a hydratable raw
material as a refractory powder, an ultrafine powder as a refractory
powder, and a hydraulic binder as a binder.
[0030]
For example, the hydratable raw material may be one or more selected
from the group consisting of: a magnesia-based raw material such as
fused magnesia; a magnesia-silica based raw material such as olivine;
a calcia-based raw material such as calcia clinker; and a
dolomite-based raw material such as dolomite clinker. Particularly,
when a mixing amount of the hydratable raw material is 5 mass% or
more in terms of a ratio with respect to a total amount of the refractory
powder, degradation due to water contained in the organic fiber
becomes a concern.
[0031]
The ultrafine powder may be a powder having a mean particle size
of less than 10 urn, which includes: an amorphous silica ultrafine

powder such as silica flour; an alumina ultrafine powder such as
calcined alumina; clay; and a titania ultrafine powder. Particularly,
the silica flour is more likely to undergo degradation due to moisture.
In this specification, the aforementioned hydratable raw material
is excluded from a concept of the ultrafine powder. Particularly,
when a mixing amount of the ultrafine powder is 5 mass% or more in
terms of a ratio with respect to the total amount of the refractory
powder, degradation due to water contained in the organic fiber
becomes a concern.
[0032]
As used in this specification, the term "mean particle size" means
a mean volume particle size which is a medium value of a particle
size distribution measured by a laser diffraction scattering type
particle size distribution measuring apparatus.
[0033]
For example, the hydraulic binder includes alumina cement,
hydraulic alumina (ρ-alumina), Portland cement, and light burnt
magnesia. Particularly, when a mixing amount of the hydraulic binder
is 1 mass% or more in terms of a ratio with respect to and in addition
to the total amount of the refractory powder, degradation due to water
contained in the organic fiber becomes a concern.
[0034]
The organic fiber is composed of a polyethylene fiber which has
a water content of less than 3 mass% and whose surface is coated with
oil. The water content of the organic fiber is preferably 2 mass%
or less, more preferably 1.5 mass% or less.
[0035]
As used in this specification, the term "polyethylene" has a
concept which encompasses not only ethylene homopolymer but also

ethylene-comonomer copolymer.
[0036]
The water content is defined as follows:
Water content (mass%) = (a total mass of an organic fiber
including water - a mass of the organic fiber excluding water) / the
mass of the organic fiber excluding water × 100
[0037]
The polyethylene fiber has an official moisture regain of zero
mass%, i.e., no water is contained in an internal structure of the
fiber. That is, the situation where the polyethylene fiber has a water
content of less than 3 mass% means that an amount of water adhering
to the surface of the polyethylene fiber is less than 3 mass%.
[0038]
In addition to the polyethylene fiber, an organic fiber having
a low official moisture regain includes a polypropylene fiber, a
polyvinyl chloride fiber, and a polyester fiber. Among them, the
polyethylene fiber has a lowest melting point. Thus, the
polyethylene fiber is capable of being melted at an early stage after
start of drying to form a venting hole, so that it is excellent in
terms of an effect of easing an internal water vapor pressure of an
installed body. For example, the polyethylene fiber has a melting
point of 100 to 135°C.
[0039]
For example, the oil includes: mineral oil; vegetal oil such as
castor oil; isotridecyl stearate; POE oleyl ether; POE nonylphenyl
ether; sodium lauryl sulfonate; and potassium POE lauryl ether
phosphate. These may be applied independently or in the form of a
combination of two or more of them.
[0040]

The oil has an effect of preventing moisture in the air from
adhering to the surface of the polyethylene fiber. Therefore, the
polyethylene fiber coated with the oil is less likely to cause
degradation of the remainder other than the organic fibers in the
unshaped refractory material, even if it undergoes a stock period,
i.e., exposure to the air, before incorporation into the unshaped
refractory material. This makes it possible to prevent deterioration
in strength of the installed body during drying.
[0041]
While a coating amount of oil to the polyethylene fiber is not
particularly limited, it is preferably set in the range of 1 to 5
mass%. When the oil coating amount is set to 1 mass% or more, it
becomes possible to further ensure the effect of preventing moisture
from adhering to the surface of the fiber. Further, when the oil
coating amount is kept within 5 mass%, it becomes possible to prevent
deterioration in handling or working performance of the fiber due
to the oil.
[0042]
The oil coating amount is defined as follows:
Oil coating amount (mass%) = a mass of oil applied to coat
an organic fiber / a total mass of the organic fiber including the
oil × 100
[0043]
A method of producing the polyethylene fiber for use in the present
invention is not particularly limited. For example, the polyethylene
fiber coated with oil can be continuously obtained by providing an
oil coating process after a process of subjecting polyethylene to
melt-spinning to form a fiber and subjecting the fiber to the hot
stretching. Alternatively, the polyethylene fiber usable in the

present invention can also be obtained by producing a polyethylene
fiber coated with no oil, in a conventional manner, and then coating
the polyethylene fiber with oil. In this case, before the oil coating,
it is preferable to perform drying for reducing a water content of
the fiber to less than 3 mass%. For example, a method for the oil
coating includes application, spraying, and immersion.
[0044]
The polyethylene is broadly classified by density into
high-density polyethylene (HDPE) and low-density polyethylene (LDPE)
both of whose official moisture regains are zero mass% . In the present
invention, the low-density polyethylene is more preferable.
According to JIS K6922, the low-density polyethylene means
polyethylene having a density of 0.910 to 0.929 g/cm3. However, as
used in this specification, the term "low-density polyethylene" means
polyethylene having a density of 0.929 g/cm3 or less. Further, the
term "high-density polyethylene" means polyethylene having a density
of greater than that of the low-density polyethylene.
[0045]
The low-density polyethylene has a relatively low melting point
because of its relatively low density. Therefore, the low-density
polyethylene can form a venting hole at an earlier timing in the drying
process, so that it is particularly excellent in terms of the effect
of easing an internal water vapor pressure of an installed body.
Specifically, the melting point of the low-density polyethylene is
in the range of 90 to 135°C.
[0046]
Further, as compared to the high-density polyethylene, the
rbw-density polyethylene is soft and flexible. Thus, under a
condition that an amount of water to be added to the unshaped

refractory material is constant, a low-density polyethylene fiber
tends to be able to enhance fluidity of a slurry, as compared to the
case of using a high-density polyethylene fiber. A slurry having
higher fluidity can be charged in a space defined by a formwork more
closely and fully.
[0047]
The low-density polyethylene is classified into
high-pressure-processed low-density polyethylene, and linear
low-density polyethylene (LLDPE) . In the present invention, the
linear low-density polyethylene is more preferable. As compared to
the high-pressure-processed low-density polyethylene, the linear
low-density polyethylene is excellent in tension strength, and
therefore less likely to break into fragments during kneading.
Supposing that the organic fiber breaks into fragments during kneading,
each venting hole formed in a drying process naturally becomes shorter,
causing deterioration in ventilation performance of an installed body.
In contrast, the organic fiber which is less likely to break into
fragments during kneading is capable of preventing deterioration in
ventilation performance of an installed body, so that the organic
fiber can thoroughly produce an explosive-spalling preventing effect.
[0048]
It is considered that a mixing amount of the polyethylene fiber
is naturally determined according to common technical knowledge of
those skilled in the art. For example, the mixing amount of the
polyethylene fiber may be set in the range of 0.01 to 1 mass% in terms
of a ratio with respect to and in addition to 100 mass% of the refractory
powder.
[0049]
A diameter of the polyethylene fiber is not particularly limited.

For example, the diameter may be set in the range of 1 to 100 μm.
When the diameter is set to 1 μm or more, a ventilation resistance
of each venting hole formed in an installed body is particularly
reduced. When the diameter is set to 100 um or less, it becomes
possible to ensure a sufficient number of fibers even when the mixing
amount is set in the range of 0.01 to 1 mass%, thereby particularly
improving an effect of decreasing air permeability of an installed
body. Preferably, the diameter is set in the range of 1 to 50 μm.
[0050]
A length of the polyethylene fiber is not particularly limited.
For example, the length may be set in the range of 1 to 20 mm. When
the length is set to 1 mm or more, it becomes possible to suppress
a sharp increase in cutting cost, and improve continuity of a venting
hole. When the length is set to 20 mm or less, deterioration in
fluidity of a slurry obtained by kneading the unshaped refractory
material together with water becomes less likely to occur.
[0051]
Although the present invention has been described based on one
embodiment thereof, the present invention is not limited thereto.
[0052]
It is to be understood that the refractory powder may comprise
a raw material having no hydratable property, which includes: an
alumina-based raw material such as fused alumina or bauxite; a
silica-based raw material such as silica stone; an alumina-silica
based raw material such as kyanite, andalusite or chamotte; a
zircon-based raw material; silicon carbide; and a carbon-based raw
material.
[0053]
It is to be understood that the binder may comprises a binder having

no hydraulic (water-hardenable) property, which includes: anorganic
binder such as pitch, tar or resin; silica sol; silicate; and phosphate .
Further, the binder is not essential. That is, the unshaped
refractory material of the present invention may be devoid of the
binder.
[0054]
Further, it is to be understood that the unshaped refractory
material of the present invention may comprise one or more additives
selected from the group, for example, of dispersant, aluminum lactate,
metal powder, thickener, antioxidant, low-melting-point glass, and
curing time regulator.
[0055]
An installation method for the unshaped refractory material of
the present invention is not particularly limited as long as it is
installed with the addition of water. Typically, it includes a
casting method, a vibrating trowel-based method, a wet spraying method,
and a dry spraying method. In the casting method, the vibrating
trowel-based method and the wet spraying method, the unshaped
refractory material of the present invention is preliminarily kneaded
together with water to form a slurry. In the dry spraying method,
the unshaped refractory material of the present invention is carried
by an air stream toward a nozzle through a carrier pipe, and water
is added thereto in at least one of the carrier pipe and the nozzle.
In some cases, water is added at a plurality of positions in the carrier
pipe. In either installation method, as long as the unshaped
refractory material is installed with the addition of water, it is
essential to provide a drying process for reducing the water by
heating.


* A numerical value in parentheses indicates a ratio (mass%) with
EXAMPLES
[0056]
Table 1 represents a specific example of an unshaped refractory
material. In Table 1, seawater magnesia falls under the category of
the hydratable raw material. Silica flour and calcined alumina fall
under the category of the ultrafine powder, and alumina cement falls
under the category of the hydraulic binder. Based on a mixture in
Table 1, a type of organic fiber was variously changed.
[0057]

respect to and in addition to a total amount of the refractory powder.
[0058]
Table 2 represents a water content and an oil content of each
organic fiber used in the composition in Table 1, and an evaluation
result of each unshaped refractory material.

[0060]
All of the organic fibers in Table 2 were formed in a common shape
having a diameter of 10 to 20 μm and a length of 3 to 5 mm.
[0061]
The water content was calculated by the following formula using
values measured by a hot-air drying method:
water content (mass%) = (a mass of a sample - an absolute dry
mass of the sample) / the absolute dry mass of the sample × 100, where
the absolute dry mass of the sample represents a constant mass after
the sample is left in a hot-air dryer maintained at a temperature
of 105°C ± 2°C.
A test was performed twice per sample, and an average of two test
values is presented in Table 2.
[0062]
The oil content was calculated by the following formula using
values measured by a method which comprises: extracting oil onto a
tray by a rapid residual fat/oil extraction apparatus (produced by
Tokai Keiki Co., Ltd), using a solution prepared by mixing propanol
and hexane at a ratio of 1 : 2, and removing the solvent therefrom:
oil content (mass%) = (a mass of the tray after the oil
extraction - a mass of the tray before the oil extraction) / an amount
of a sample × 100
A test was performed twice per sample, and an average of two test
values is presented in Table 2.
[0063]
The evaluation was performed in the following manner. First of
all, organic fibers were left in a situation where moisture adheres
to surfaces thereof, specifically, in a space having a humidity of
75 to 85% for 5 days. Then, the organic fibers were mixed with a

remainder of the composition in Table 1 to obtain an unshaped
refractory material. The obtained unshaped refractory material was
put in a vinyl bag, and left for one week. Then, water was added in
an amount of 6 mass% with respect to and in addition to 100 mass%
of the unshaped refractory material, and the mixture was kneaded to
form a slurry. The obtained slurry was cast into a formwork, and cured.
Then, a sample of the installed body was subjected to an autoclave
treatment at 150°C for 6 hours, and subjected to a measurement.
[0064]
The post-curing strength was evaluated by bending strength and
rated on a scale of ×, ∆, o and ⌾. A larger bending strength allows
an installed body to withstand a higher internal water vapor pressure,
so that explosive spalling becomes less likely to occur. The bending
strength was measured using each sample, according to the rule of
JIS-R2553.
[0065]
The ventilation performance was evaluated by a ventilation rate
of the sample and rated on a scale of ×, ∆, o, ⌾ and ⌾⌾. A high
ventilation rate allows water vapor to become less likely to be
confined inside an installed body, so that explosive spalling becomes
less likely to occur. The ventilation rate u (cm2 / (cm H2O • sec))
is defined as follows:
u = Q x (L / S) x (1 /p1 - p2)
In the above formula, Q represents a volume (craVsec) of air
transmitted through the sample per unit time, and was measured by
an air-leak tester (LS-1821 produced by Cosmo instruments Co. , Ltd. ) .
Further, S represents a cross-sectional are (cm2) of the sample, and
L represents a thickness (cm) of the sample. P1 represents a pressure

(cm H2O) when air enters the sample, and P2 represents an atmospheric
pressure (cm H2O) .
[0066]
In the inventive sample 1 using a high-density polyethylene fiber
having a density of 0.94 g/cm3, the polyethylene fiber is coated with
oil, so that the water content is low to provide an excellent
post-curing strength. The ventilation performance is within an
acceptable range although it is inferior to those of the low-density
polyethylene fibers in the inventive samples 2 to 5. Therefore, it
can be said that the inventive sample 1 is excellent in the
explosive-spalling preventing effect.
[0067]
The inventive sample 2 using a low-density polyethylene fiber as
the polyethylene fiber is superior to the inventive sample 1 in terms
of the ventilation rate. Further, as compared to the inventive sample
1, the inventive sample 2 has a lower oil content and a higher water
content, so that the post-curing strength is inferior to the inventive
sample 1 but is still excellent.
[0068]
In the inventive samples 3 and 4 where the oil content is increased
as compared to the inventive sample 2, the water content is reduced
to provide an excellent post-curing strength. The results of the
inventive samples 2 to 4 show that the water content is dependent
on the oil content.
[0069]
In the inventive sample 5 using a linear low-density polyethylene
fiber as the polyethylene fiber, the ventilation performance is
enhanced as compared to the inventive sample 4. Although not sure,
it is assumed that this is because the linear low-density polyethylene

fiber is excellent in tension strength among various low-density
polyethylene fibers, and is less likely to break into fragments during
kneading. That is, the organic fibers are less likely to break into
fragments during kneading, so that it becomes possible to prevent
deterioration in ventilation performance of an installed body,
thereby allowing the organic fiber to thoroughly produce the
explosive-spalling preventing effect.
[0070]
In the comparative sample 1 using a polyethylene fiber devoid of
oil, although the ventilation performance is within an acceptable
range because the polyethylene fiber has a low melting point, the
post-curing strength becomes insufficient due to a large water content.
Thus, in the comparative sample 1, there are concerns about explosive
spalling. Comparing the comparative sample 1 with the inventive
sample 1, it is proven that the post-curing strength of the installed
body is lowered along with an increase in the water content of the
organic fiber. In order to prevent explosive spalling, it is
necessary that the water content of the polyethylene fiber is less
than 3 mass%.
[0071]
In the comparative sample 2 using a low-density polyethylene fiber
devoid of oil, although the ventilation performance is excellent,
the post-curing strength becomes insufficient due to a large water
content, raising a concern about explosive spalling.
[0072]
In the comparative samples 3, 4 and 5 using a polypropylene fiber,
a polyester fiber and a polyvinyl chloride, respectively, although
the requirement of the present invention is satisfied when focusing
on only the water content, the ventilation performance is deteriorated

due to a high melting point, thereby leading to a high probability
of causing explosive spalling.
{0073]
In the comparative sample 6 using a vinylon fiber, although the
vinylon fiber is melted in a hot water, it forms a film over the surface
of the installed body, causing deterioration in ventilation
performance. Moreover, the vinylon fiber has a relatively high water
content, so that the post-curing strength is relatively low.
[0074]
As above, although the present invention has been described based
on a specific embodiment, the present invention is not limited thereto.
For example, it is to be understood that various changes and
modifications will be apparent to those skilled in the art.

We Claim:
1. An unshaped refractory material comprising an organic fiber and
adapted to be installed with the addition of water, wherein the organic
fiber is composed of a polyethylene fiber which has a water content
of less than 3 mass% and whose surface is coated with oil.
2. The unshaped refractory material as defined in claim 1, wherein
the polyethylene is low-density polyethylene.