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Fire resistant wall constructions are used in several different
connections, for example to partition-off different parts of a building,
to enclose a stairwell or staircase, to erect fireproof cabinets and
cupboards intended for storing equipment and assemblies which are
sensitive to high temperatures, for the construction of computer rooms,
etc.
In order for a wall to be considered fire resistant, it must be capable of
withstanding a given high external temperature for a given period of time
before the temperature of the wall interior exceeds a given level. Such
requirements vary, of course, from application to application.
Fire resistant walls are normally manufactured from concrete or
concrete-based materials, where in building applications walls are erected
with a thickness which is sufficient to prevent the interior temperature
of the wall from rising above a given level, when the outer surfaces of
the wall are subjected to high temperatures. Fire resistant walls that are
made of concrete are often heavy and expensive. Another drawback
encountered with concrete fire-resistant walls is that their weight often
renders it difficult to erect such walls in existing buildings. The need
to erect fire resistant walls may arise when part of a building is to
accommodate machinery and apparatus which is sensitive to high
temperatures, such as computer equipment. Another instance where fire
resistant walls constructed in accordance with known techniques are
difficult to erect is when movable walls are required, such as, for
example, concertina or folding partition walls in hotels, conference rooms
and public buildings, where the use of such walls is quite common. The
reason why such walls are difficult to install is because of the weight of
the concrete wall elements.
The maximum permitted temperature to which the interior of a so-called fire
resistant cupboard intended for storing data media, such as computer
discs, records, tapes, etc., can be heated when exposed to an external
temperature of 1000.degree. C. for a period of 2 hours is 50.degree. C.
The walls of such cupboards, or cabinets, are normally made of concrete,
with a layer of insulating material on one side of the concrete and plates
placed on both sides of the walls. The concrete wall is built to a
thickness such that the thermal conductivity of the concrete, in
combination with a certain transference of water from the concrete, will
ensure that the inner temperature of the wall, under the influence of the
insulating layer, will not exceed the aforesaid value under the conditions
mentioned.
The use of conventional concrete therefore results in a thick and heavy
wall, as beforementioned.
In order to obtain a temperature delay effect on the inside of a fire
resistant cupboard, it has been proposed to incorporate a phase converting
material in the cupboard wall, by which is meant a material which exhibits
endothermic phase conversion. This phase conversion shall take place at a
temperature which is beneath the maximum temperature to which the inner
wall surface can be allowed to reach.
Among other things, the International Application WO No. 82/00040 proposed
the use of glauber salt, i.e. sodium sulphate decahydrate, which has a
phase conversion temperature (melting temperature) of about 32.degree. C.,
and a further phase conversion temperature (vaporization of water of
crystallization) of about 100.degree. C.
Silicate compounds have also previously been used to obtain an endothermic
conversion, as disclosed, for example, in the German Published
Specification DE-OS No. 2413644. This publication teaches the combination
of a layer of silicate compound and a layer of mineral wool.
The U.S. Pat. Specification No, 4,413,869 teaches the use of gypsum,
mineral wool, and a mixture of a silicate compound in solid phase, and
gypsum in solid phase.
The use of a compound which undergoes endothermic conversion for the
purpose of delaying a rise in temperature above the level at which the
conversion takes place is therefore well known.
This phase conversion material, however, does not constitute a building
construction material per se, and hence the use of such materials must be
combined with supporting or load-bearing constructions.
The present invention eliminates the aforementioned drawbacks associated
with known techniques and provides a wall element of considerably smaller
thickness than known wall elements with which the same performance ability
is to be achieved.
The wall element is also considerably lighter than a concrete wall, and
hence the weight of a wall constructed with wall elements according to the
invention is much lighter than a wall constructed from conventional
concrete wall elements.
Thus, the present invention relates to a fire resistant wall construction
which incorporates a phase conversion material, the phase conversion of
which takes place at a lower level of temperature than a temperature level
which is hazardous to wood, paper etc., and which is characterized in that
the phase conversion material includes a mass produced from a mixture of
water glass in liquid phase, water and a binder, such as cement or the
like, said phase conversion material having a water content of such
magnitude that the endothermic reaction in the phase conversion process
constitutes essentially the vaporization of said water.
The invention will now be described in more detail with reference to the
accompanying drawing, in which FIG. 1 is a cross-sectional view of a wall
element according to a first embodiment in which the invention is
employed; FIG. 2 is a cross-sectional view of a wall element according to
a second embodiment in which the invention is employed; and FIG. 3 is a
cross-sectional view of a wall element according to a third embodiment in
which the invention is employed.
The present invention is based on an endeavour to obtain a construction
material which is suitable for use in fire resistant wall constructions
and which contains large quantities of water. When compared with other
phase conversion materials known in the present context, water is
essentially cost free while, at the same time, comparatively large
quantities of energy are required to raise the temperature of the water
from room temperature to a temperature in excess of 100.degree. C. In the
case of standard, conventional fire resistant wall constructions it is
desirable to use a phase conversion material with which phase conversion
takes place at a temperature lower than a temperature at which wood, paper
etc. is liable to ignite. This desideratum is fulfilled when water is
used.
One compound which can contain large quantities of water in gel form is
sodium silicate Na.sub.2 O.nSiO.sub.2.pH.sub.2 O. Water-glass is one such
compound. Water-glass absorbs large quantities of energy in a temperature
range slightly above 100.degree. C. Water-glass containing 60% water
increases its heat content by about 1900 kJ/kg from 20.degree. C. to
200.degree. C. Corresponding values for glauber salt are about 2000 kJ/kg.
The increase in the heat content of pure water over a temperature range of
20.degree. C. to 200.degree. C. is roughly 3000 kJ/kg. Thus, in the
present context water is more effective than solely water-glass or glauber
salt.
Water is thus particularly inexpensive and effective in use. The
disadvantage with water, of course, is that it can not, or in all events
should not be used in a free state, but must be bound.
According to the present invention there is used a phase conversion
material including a mass produced from a mixture of water-glass in liquid
phase, water and a binder, such as cement or the like, the phase
conversion material having a water content of such magnitude that the
endothermic reaction during the phase conversion process is consituted
essentially by vaporization of the water.
It has surprisingly been established that such a mass can be produced with
a water content as high as 80% or slightly thereabove. Depending upon its
water content, the mass varies from a gritty to a gel-like consistency.
According to one embodiment of the present invention, the phase conversion
material comprises a mass produced from a mixture of water-glass in liquid
phase, cement and water, in which the water is added in a quantity such
that the weight of added free water exceeds the total weight of
water-glass and cement, but is less than about three times the total
weight of water-glass and cement
The cement used is preferably Portland cement, although other kinds of
cement can be used. It has been found that masonry lime can be used
instead of cement.
In accordance with one preferred embodiment of the invention, the ratio
between the weight of cement and the weight of water-glass used,
preferably a water-glass containing 60% by weight water, is greater than
about 0.4.
Two mixing examples are given below. In both of these examples, the first
stage of the mixing process was to mix Portland cement with water. This
pre-mix served as a curing agent for the liquid water-glass, subsequent to
admixing said water-glass with the pre-mix.
EXAMPLE I
15 kg Portland cement and 65 kg water were mixed together to provide a
pre-mix, which was then admixed with 20 kg water-glass containing 60%
water. Within the space of one minute, the mixture had set to a relatively
solid, gel mass. The density of this mass was 1330 kg/m.sup.3. The mass
contained 77% water.
EXAMPLE II
80 kg Portland cement and 720 kg water were mixed together to form a
pre-mix, which was then admixed with 200 kg water-glass containing 60%
water. Within the space of six minutes the mixture had hardened to a
relatively solid, gel mass. The density of the mass was 1130 kg/m.sup.3.
Thus, the water content of the mass was as high as 84%.
The curing time, or setting time, for such masses is primarily influenced
by the proportion of Portland cement in the mixture. This curing time
decreases with increasing proportions of Portland cement. A short curing
time is normally beneficial with regard to the technical aspects of
production.
As beforementioned, the heat content of water increases by roughly
3000kJ/kg over a temperature range of 20.degree. C. to 200.degree. C.
The mass produced in accordance with Example II above increases its heat
content by about 2800 kJ/kg over the temperature range of 20.degree. C. to
200.degree. C. This increase in water content, in combination with the
fact that the mixture is particularly inexpensive, renders the mixture
particularly suited for use in the present context.
Since the mass has a low mechanical strength, a wall element cannot be
built solely from the mass, and hence the wall element must be stiffened
or reinforced in some way. The mass, however, is sufficiently strong to be
cast, and subsequent to hardening will retain its cast shape even when
subjected to a given load.
FIG. 3 illustrates an exemplifying embodiment of a simple wall construction
in which the present invention is applied. The reference 1 identifies a
wall element which incorporates the aforesaid mass, here referenced 2.
As will be evident from the aforegoing, it is possible to cast the
aforesaid mixture and therewith obtain a gel-like mass. However, because
of the high water content of the mass, which may reach to about 85%, it is
important to prevent the mass from drying-out. This can be achieved by
encasing the mass in an impervious casing, such as a plastic foil casing
3, for example a polypropylene foil, or a combination of metal sheet and
plastic foil or plastic tape. When manufacturing a wall construction
according to the invention, the mixture is therefore cast in plastic foil
bags 3 in a shape or form intended for the resultant wall element.
In order to obtain a wall element of sufficiently high mechanical strength,
the aforesaid bags, in accordance with one preferred embodiment, are
surrounded by thin plates 4,5 which define therebetween a cavity in which
the bags are placed. In this regard, the plate located nearest to the
ultimate outer surface 6 of the wall element is perforated with a
plurality of small holes 7, of which only a few are shown in FIG. 3. The
purpose of the holes is to permit steam to penetrate therethrough towards
the outer surface of the wall element when this outer surface is subjected
to a temperature of such magnitude as to cause the water in the mass to
vaporize, causing the bags 3 to burst as a result of the pressure
prevailing therein.
Alternatively, the aforesaid casing may comprise steel plates or plates
made of some other metal. In this case, the plates are connected together
along the corners thereof, or are connected by means of impervious plastic
tape to the wooden posts of a stud-work located between the plates. When
the wall element is heated to a temperature sufficiently high to vaporize
the water in the mass, the plastic tape will burst, enabling vaporized
water to escape from the cavity defined by the plates. In those instances
when the plates are connected to wooden battens, the battens are provided
with holes which are then sealed with an impervious plastic tape.
The embodiment illustrated in FIG. 3 includes a wooden batten 8, which
forms a spacer between the plates 4,5. The use of a wooden batten avoids
the formation of thermal bridges.
In accordance with one embodiment of the invention, illustrated in FIG. 1,
an insulating layer 9 of mineral wool is placed externally of the
perforated plate 4, in order to extend the time taken for the phase
conversion material 2 to become heated to the temperature prevailing on
the outer surface 6 of the wall element.
Naturally, the wall elements 1, 10,11 can be provided with suitable
internal and external cladding 12,13, to give the wall the desired
appearance. In the case of internal surfaces the cladding 12,13 may
comprise sheets of building material onto which wall-paper can be hung,
while in the case of external surfaces the cladding may have the form of
plaster or bricks.
The aforedescribed wall construction has been found to be particularly
effective. For example, in order to provide a two-hour delay before the
temperature of the inside 14 of the wall exceeds about 120.degree. C. when
the outer surface of the wall is heated to 1000.degree. C., the thickness
of the mass in the wall construction illustrated in FIG. 1 need only be
about 30 mm, with a mineral wool thickness of 20 mm. Thus, when using
building panels 12,13, the thickness of the entire wall is only about 60
mm. The plates 4,5 may have a thickness of 1 mm for example.
The present wall construction therefore eliminates the drawbacks mentioned
in the introduction.
In certain cases, such as in the walls of computer rooms or rooms which
accommodate other equipment sensitive to elevated temperatures, the
temperature on the inner surface 14 of the wall shall not exceed about
50.degree. C. under the aforementioned conditions.
When constructing walls for these purposes, the wall construction, in
accordance with a modification of the invention, also incorporates a
further phase conversion material, which is spaced from but parallel with
the firstmentioned phase conversion material, comprising the aforesaid
mass. This further phase conversion material is one with which the phase
conversion takes place at a lower temperature than the phase conversion of
the mass, namely at a temperature beneath 50.degree. C., this further
phase conversion material, in accordance with the invention, being placed
closer to the ultimate inner surface 14 of the wall construction.
One serious drawback with the known technique is that thick layers of
conventional insulating material must be used, together with relatively
thick layers of phase conversion material, due to the fact that there is
used solely one phase conversion material, the phase conversion of which
takes place at a temperature which is only slightly lower than the highest
permitted temperature, or equal thereto.
By combining a layer of said mass with a further phase conversion material
with which the phase conversion takes place at a lower temperature, only a
relatively small quantity of the further phase conversion material is
required while, at the same time, the total thickness of the wall is small
in comparison with the case when solely using the further phase conversion
material in combination with a thick layer of mineral wool insulation.
The further phase conversion material preferably comprises glauber salt. In
addition to being converted at a temperature of above 100.degree. C.,
glauber salt is also converted at a temperature of about 32.degree. C.
Thus, the heat content of glauber salt will increase by 240 kJ/kg over a
temperature range of 20.degree. C. to 50.degree. C., and consequently
glauber salt can be used efficiently nearest the inner surface of the
wall. Corresponding increases in the heat content over the temperature
range of 20.degree. C. to 50.degree. C. are also afforded by fixing salt
and paraffin.
The last mentioned application is exemplified in FIG. 2.
The further phase conversion material 15 is enclosed in bags 16 made of a
flexible and impervious material, preferably a three-ply plastic foil.
For the purpose of holding the bags 16 in position and to isolate said bags
from the firstmentioned phase conversion material, the cavity 17 between
the plates 5 and the cladding 13, forming the inner surface of the wall,
is filled with polyurethane foam 18 or the like, subsequent to positioning
the bags.
The wall 11 illustrated in FIG. 2 has been found to be extremely effective.
In order that the wall structure is able to withstand an external
temperature of 1000.degree. C. for two hours before the temperature of the
inner wall surface exceeds 50.degree. C., the thickness of the bags 16,
seen from right to left in FIG. 2, may be 10 mm when the total width of
the cavity 18 is 20 mm. The thickness of the bags 3 is then 30 mm and the
thickness of the mineral wool layer 9 is 20 mm.
When the surface temperature is 1000.degree. C., the heat will have
penetrated into the cavity 18 after a given period of time has lapsed.
Because a large quantity of this heat is lost in vaporizing the water
present in the mass 2, the temperature gradient will fall from
1000.degree. C. to approximately 100.degree. C. over the mineral wool
layer 9. In the final stage of a test, i.e. after a lapse of almost 2
hours, the temperature was held at a level of 100.degree. C. at the plate
5 outside the polyurethane layer. Because polyurethane foam has extremely
good heat insulating properties, only small quantities of heat are
transported therethrough.
Thus, the wall construction according to the invention is comparatively
thin in relation to wall elements constructed in accordance with
conventional techniques. Because the wall element is relatively thin it is
also relatively light in weight. The wall element is also relative
inexpensive.
Instead of arranging the bags 16 in the manner illustrated in FIG. 2, the
further phase conversion material may be collected at that location of the
space to be protected against excessively high temperatures at which the
quickest rise in temperature can be expected to occur.
Thus, containers containing bags of the further phase conversion material
can be placed in the ceiling of the room to be protected, such as small
rooms or various types of fire-proof cabinets. The effect produced hereby
fully corresponds with the aforementioned effect, since the phase
conversion of the further phase conversion material results in a lowering
of the air temperature in the room or space protected. The insulating
layer 18, preferably comprising polyurethane foam, is retained in this
embodiment.
In addition to walls of computer rooms, the last mentioned wall
construction may be used in the walls of document filing cabinets and
storage cabinets. In this case, the plates incorporated in the wall
element are utilized to secure different wall elements together. The door
of the cabinet is also constructed in accordance with the invention.
Folding walls of the aforesaid kind, for example, are suitably constructed
from a wall construction substantially in accordance with FIG. 3. In this
case, the claddings referenced 12 and 13 preferably have the form of
plates which are used load-carrying elements in the folding wall
structure.
It will be understood that the present invention can also be applied in
other connections where a fire resistant wall construction is required. In
addition, the mass according to the invention can be combined with other
materials than those described in the examples.
The invention shall not be considered to be limited to the aforedescribed
embodiments, and it will be understood that modifications can be carried
out within the scope of the following claims.
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