Apparatus for treating materials in the form of continuous lengths

In a method of treating coated or uncoated materials made of natural or synthetic polymers in the form of continuous lengths to improve the quality of the material, the material is subjected to a series of processing steps, one of which is a cooling step in which the material is cooled by means of a cooling medium at extremely low temperature, such as a liquefied gas, for example, liquid nitrogen. Such cooling after a drying or heat-setting operation prevents creasing of the material when it is folded to form a stack. Apparatus for carrying out the method comprises a conveyor (2) for the length of material (1) and at least one blast nozzle head (3) provided with a plurality of blast nozzles (5) past which the material is conveyed, and connected to a source of cooling medium through suitable delivery means.

FIELD OF THE INVENTION 
The present invention relates to an apparatus for treating coated or 
uncoated materials in the form of continuous lengths made of natural or 
synthetic polymers to improve their quality, wherein the materials are 
cooled inter alia in the course of several processing steps, optionally 
while the width of the material is controlled. 
BACKGROUND OF THE INVENTION 
Examples of suitable materials for the treatment with the apparatus of the 
invention include textiles, paper, leather, plastic films, wood, rubber, 
vulcanized fibers, emery cloth, and the like. As is well known, when 
producing lengths of such materials, it is often necessary to cool them in 
the course of various other processing operations, such as after a drying 
operation or a heat-setting operation, for example, so as to permit 
continuous further processing and to ensure that the material is of high 
quality. 
For example, it is customary to dry or heat-set composite fabrics 
containing synthetic fibers at speeds of from 100 to 150 m/minute, the 
lengths of fabric emerging from the heating chamber at temperatures of 
between 75.degree. C. and 110.degree. C. at these speeds. If the lengths 
of material were to be folded and stored at such temperatures, the 
intrinsic weight of the stack could produce creases and kinks which would 
impair the quality of the material if it was piled unsuitably. However, 
such creasing can usually be avoided if the lengths of material are cooled 
down at least to room temperature, before being folded. Apart from this, 
the quality of the lengths of material can be improved by cooling if, 
during such heat-treatment operations, the length of material are kept 
taut widthwise (in the direction of their width) by means of spiked 
chains, clamps, or the like, so as to maintain dimensional stability; this 
dimensional stability can be much better maintained after a heat 
treatment, if the lengths of material are cooled immediately after the 
heat-treatment, possibly also while the width of the material is 
controlled. 
Hitherto, in most cases, the lengths of material have been cooled by 
blowing fresh air over them. In addition, particularly when permeable 
materials are involved, arrangements have been used in which fresh air is 
drawn through the length of material by means of a vacuum with the aid of 
suction nozzle heads past which the length of material is led, or with the 
aid of perforated drums over which the length of material is passed. 
However, with these cooling systems, large quantities of air have to be 
pumped to obtain a satisfactory cooling effect given the short cooling 
time available with the high speeds used during the processing operations. 
This leads to high energy costs which are quite unjustifiable economically 
in many cases. Consequently, use has already been made of cooling systems 
in which the air is cooled in heat exchangers, for example, by means of 
cooling water, and only then brought into contact with the length of 
material. But, even with such cooling systems, substantial amounts of 
energy often have to be used in order to obtain a cooling speed 
corresponding to the speed of the individual processing operations. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide an apparatus for 
treating materials in the form of continuous lengths made of natural or 
synthetic polymers. 
Another object is to provide an apparatus by means of which intensive 
cooling of lengths of material can be achieved in a simple fashion, and 
with which the cooling process can readily be matched to the speed at 
which individual processing operations take place. 
SUMMARY OF THE INVENTION 
According to one aspect of the invention, there is provided a method of 
treating coated or uncoated materials made of natural or synthetic 
polymers to improve the quality thereof, in which the material in the form 
of a continuous length is subjected to a plurality of successive 
processing steps including a cooling step in which the material is cooled 
by means of a cooling medium at extremely low temperatures. Preferably, 
the cooling medium is a liquefied gas. 
The use of a very cold cooling medium (i.e. a temperature considerably 
below normal atmospheric temperature) makes it possible to ensure a very 
rapid and intensive cooling of the material in a continuous process in 
which as the lengths of material undergo a series of processing steps. 
During cooling, the lengths of material can be held taut widthwise by 
suitable means, such as spiked chains or clamps, so that dimensional 
stability can also be maintained during the cooling process; this 
dimensional stability will then stay constant after the cooling step. 
Liquid nitrogen is a particularly suitable and advantageous cooling medium 
of extremely low temperature. It can be brought into heat exchange with 
the length of material to be cooled at a temperature of -196.degree. C. 
and vaporizes in the process. The cold gas so produced can be directed 
against the length of material being cooled so as to remove a considerable 
amount of heat from the length of material in this way before the actual 
shock-cooling with the liquefied gas. 
Apart from spraying the cooling medium directly onto the material to be 
cooled, it is also possible to mix the cooling medium with a gas, such as 
air, for example, and to bring this mixture into contact with the length 
of material. Which of the cooling methods is used depends primarily on the 
preceding process steps which the length of material has undergone and the 
temperatures thereof. 
It is particularly advantageous to cool the lengths of material in this way 
using a cooling medium at extremely low temperature after the materials 
have undergone a heat-treatment and/or humidifying process. After 
heat-treatment, needed, for example, to dry the length of material, this 
at once ensures intensive cooling of the length of material so that this 
can undergo further processing without the risk of creasing and varying 
dimensional stability which is particularly high when the material is hot. 
After a length of material has been humidified, an operation which is 
particularly necessary for woven and knitted fabrics to prevent them from 
drying out, this kind of cooling makes it possible to conserve the 
moisture introduced in the core of the fibers by freezing. As a result of 
the presence of a frozen film of water on the surface of the fabric, 
virtually none of the moisture is lost through evaporation when the fabric 
is folded to form a stack and the moisture initially present in the form 
of a surface film penetrates into the centers of the fibers more easily as 
the fabric is defrosted. 
In accordance with a further aspect of the invention, apparatus for 
carrying out the method comprises a conveyor, on which the materials are 
placed, if desired, fixed as regards their width, and a cooling system, 
which comprises at least one blast nozzle head, provided at one side with 
a plurality of blast nozzles, past which the conveyor moves, the or each 
blast nozzle head being connected to a source of a cooling medium at 
extremely low temperatures through a feeding means and a piping system. 
The conveyor may be in the form of an endless belt which may be perforated, 
if required. Alternatively, the conveyor could merely be in the form of a 
pair of spiked chains or clamps laterally separated by a distance equal to 
the width of the material and by which the length of material is secured, 
so that it can be moved past the blast nozzle heads unsupported and the 
cooling medium can be brought into contact with the length of material 
without interference by a conveyor belt. 
Preferably, the blast nozzles and the delivery arrangement are so designed 
that the cooling medium leaves the outlet of the nozzle at a speed of 20 
to 60 m/sec., in particular 30 to 50 m/sec. If such a flow rate for the 
cooling medium is maintained at the outlet of the blast nozzle, uniform 
and intensive cooling of the length of material is ensured at the 
conveying speeds normally used for all the process steps. 
The cooling system comprising the blast nozzle heads is preferably so 
constructed that all the blast nozzle heads have at least one associated 
extractor head, connected to the feeding means and located opposite to the 
side of the blast nozzle head provided with the nozzles. The conveyor 
feeds the length of material between the blast nozzle heads and the 
extractor heads, so that the cooling medium coming from the blast nozzle 
heads can be sucked away by means of the extractor heads after cooling the 
length of material, and then returned to the feeding means. In this way, 
the cryogenic energy still present in the cooling medium after cooling the 
length of material can be re-used to cool a length of material and the 
cooling medium circuit formed by the extractor heads and the return line 
to the feeding means only has to be supplied with sufficient fresh cooling 
medium from the cooling medium source to offset the cryogenic energy lost 
in heat exchange with the length of material. Excess cooling medium is 
sucked up through the gap provided between the blast nozzle heads and the 
extractor heads for the passage of the conveyor and the length of 
material. The blast nozzle heads and the extractor heads can be arranged 
so that each blast nozzle head has its own extractor head located opposite 
to it, or so that a single extractor head is located opposite to a 
plurality of blast nozzle heads mounted side by side. 
Instead of using extractor heads, in an alternative embodiment of the 
invention, pairs of blast nozzle heads are arranged in the cooling system 
with their nozzle sides facing one another, the conveyor carrying the 
length of material being passed between the facing sides of the blast 
nozzle heads. Compared with the first embodiment described above, this 
cooling arrangement has the advantage that the cooling medium can be 
directed onto the length of material both from above and below, thereby 
increasing the total cooling effect. One way of reutilizing the cooling 
medium in this form of apparatus is for the cooling arrangement to include 
a thermally insulated tunnel in which the blast nozzle heads are arranged. 
The cooling medium emerging through the gap between the facing blast 
nozzle heads can then be collected in the cooling tunnel, withdrawn 
therefrom and returned to the cooling medium feeding means. The cooling 
tunnel can also serve to provide thermal insulation for the cooling system 
as a whole. If no cooling tunnel is provided, it is always desirable for 
all the parts of the cooling system and feeding means to have thermally 
insulated walls. 
For the distribution of the cooling medium to the individual blast nozzles 
in the blast nozzle heads, it is advantageous if the blast nozzle heads 
are provided with internal gas ducting walls. This is a simple way of 
ensuring uniform distribution of the cooling medium over the entire width 
of the length of material. 
In order that, in certain cooling applications where the lengths of 
material require particularly intensive cooling, the cooling medium can be 
mixed with a convection carrier such as air for example, prior to 
directing it onto the length of material, it is expedient for the feeding 
means to include a mixing chamber and a compressor attached thereto, and 
for atomizer nozzles for the cooling medium to be arranged in the mixing 
chamber. The two media are then mixed together in the mixing chamber, the 
compressor supplying fresh and/or recirculated air from the cooling medium 
circuit to the mixing chamber. To ensure thorough mixing of the cooling 
medium and the convection carrier, the atomizer nozzles should be so 
directed that the cooling medium is sprayed against the direction of flow 
of the convection carrier. The mixing chamber can be located between the 
compressor and the blast nozzle head or in front of the compressor intake. 
If air is used as the convection carrier, the relative humidity of the air 
rises as the temperature falls due to the introduction of the cooling 
medium, until excess water vapor is precipitated in droplet form when the 
dewpoint has been passed. Since humidification is undesirable with many 
materials, such as paper, for example, it is thus advantageous, when 
handling such materials, to locate at least one vapor trap in the mixing 
chamber downstream of the atomizer nozzles in the direction of flow and to 
separate the water vapor that forms by this means. 
To allow processing to take place continuously after the length of material 
has undergone a heat-treatment operation, it is advantageous, for the 
cooling arrangement to be located at the end of a horizontal and/or 
multi-stage drying installation and/or a heat-setting installation, at 
which the length of material is discharged. In this way, the arrangement 
can be attached to existing drying and/or heat-setting installations 
without changing the overall size, since when an extremely cold cooling 
medium is used in accordance with the invention, satisfactory cooling of 
the length of material to be processed can be achieved with a cooling 
system which is very short, viewed in the operational flow direction. For 
example, an active cooling path about 1 m in length is sufficient to cool 
a length of material emerging from the drying or heat-setting installation 
at a speed of 150 m/min., at a temperature of 70.degree. C., down to a 
temperature of 20.degree. C. This sort of space is available behind any 
horizontal drying installation, so the conveying means of this 
installation can also be used to carry the length of material through the 
cooling system and the length of material, controlled as regards its width 
in the same way as for its passage through the horizontal drying 
installation, can be cooled down to room temperature and fixed. In this 
case, it is expedient to measure continuously the temperature of the 
material at the outlet of the installation and to regulate the amount of 
extremely cold cooling medium delivered so as to obtain a given 
temperature level for a particular material, thereby obtaining an 
automatic control by which any unnecessary over-cooling of the length of 
material is avoided.

SPECIFIC DESCRIPTION 
In all the Figures, a length of material 1 which is to be cooled is moved 
on a conveyor 2 through a cooling arrangement including one or more blast 
nozzle heads 3. The conveyor 2 may be in the form of two chains having 
spikes or clamps running along them and laterally separated by a space 
corresponding to the width of the length of material. Referring now to 
FIG. 1, the cooling arrangement comprises a blast nozzle head 3 having a 
plurality of blast nozzles 5 and an extractor head 4 located opposite the 
blast nozzle head 3 the conveyor 2 and the material to be cooled passing 
between the two heads 3 and 4, and means for delivering cooling medium at 
an extremely low temperatures, such as liquid nitrogen, for example, to 
the blast nozzle head 3. The delivery means comprises a compressor 6, a 
mixing chamber 7 and a piping system 8 connecting the output of the 
compressor 6 via the mixing chamber 7 to the blast nozzle head 3 and 
connecting the extractor head 4 to the intake of the compressor 6. A 
delivery pipe 9, which is connected to a source of cooling medium (not 
shown) and carries a plurality of atomizer nozzles 10 within the mixing 
chamber 7, is fixed to the mixing chamber 7. The piping system 8, the 
blast nozzle head 3 and the extractor head 4 are all provided with a 
thermally insulating covering 12. 
The cooling medium delivered through the feed pipe 9 is mixed with the 
fresh or recirculated air delivered by the compressor 6 into the mixing 
chamber 7. For this purpose, the extremely cold cooling-medium present in 
the form of a liquefied gas, is sprayed preferably against the stream of 
air by means of the atomizer nozzles 10, so as to ensure thorough mixing 
of the air and the liquid cooling medium. In condensate forming as the air 
is cooled is filtered out by means of a vapor trap 11 disposed downstream 
of the atomizer nozzles 10 in the direction of air flow. The mixture of 
fresh air and extremely cold gas so formed is then distributed evenly over 
the length of material 1 through the blast nozzles 5 of the blast nozzle 
head 3 and, after heat exchange with the material 1, some of it is 
returned to the compressor 6 through the extractor head 4. Only a very 
small portion is lost through the gap provided between the blast nozzle 
head 3 and the extractor head 4 for the passage of the conveyor 2. To 
ensure uniform distribution of the cooling medium over the length of 
material 1, the blast nozzles 5 preferably take the form of nozzles with a 
hole or slit and the blast nozzle head 3 contains gas ducting walls 13 
which distribute the cooling medium evenly to all the blast nozzles 5. 
The apparatus shown in FIG. 2 differs from that shown in FIG. 1 in that the 
extractor head 4 is replaced by a further blast nozzle head 3 so that in 
this case the length of material 1 being cooled is brought into contact 
with a cooling medium both from above and from below. In this case, both 
the blast nozzle heads 3 are connected to the mixing chamber 7 via the 
piping system 8 and the compressor 6 only supplies fresh air to the mixing 
chamber 7. 
In the treatment installation shown in FIG. 3, the cooling apparatus in 
accordance with the invention is located at the material discharge end of 
a horizontal drying and/or heat-setting plant 14, the conveyor 2 and the 
cooling arrangement being shown from the side in contrast to the view of 
FIGS. 1 and 2, where it is shown in transverse section. In this case, the 
cooling system consists of three blast nozzle heads 3 which are connected 
one behind another and located in a thermally insulated and almost 
completely closed cooling tunnel 15. The blast nozzle heads 3 located 
above the conveyor 2 can have either extractor heads 4 or further blast 
nozzle heads 3 located opposite them on the underside of the conveyor 2, 
as in the arrangements shown in FIGS. 1 and 2 respectively. In the latter 
case, the cooling tunnel 15 may be provided with a gas discharge line 
which is connected to the intake side of a compressor connected to the 
blast nozzle heads 3. 
The enlarged cooling area produced by connecting a plurality of blast 
nozzle heads one behind another allows increased cooling of the length of 
material as compared with arrangements using a single blast nozzle head 3 
so that the intensity of the cooling effect can be tailored in accordance 
with the preceding processing operation which the length of material has 
undergone, by selection of the number of blast nozzle heads used, and by 
the choice of a cooling system with blast nozzle heads and extractor 
heads, or with blast nozzle heads alone. 
Apart from using a mixing chamber to mix the extremely cold gas which is 
used as the cooling medium with the convection carrier e.g. air, it is 
also possible to spray the extremely cold gas used as the cooling medium 
directly through the blast nozzle heads onto the material, giving yet 
another variation in the cooling intensity produced. In every case, the 
shape of the blast nozzles and the distance between the mouths of the 
nozzles and the length of material have a decisive influence on the 
outcome of the heat transfer process.