Device for double encasing a strand of material containing one or more waveguides

A device for encasing a rope-like strand containing one or more light waveguides, which device includes two extruders situated one after the other characterized by a fluid cooling device positioned between the two extruders for applying a cooling fluid to the external surface of a first layer applied by the first extruder to cool it prior to extruding a second layer thereon. The cooling device enables increasing the rate of travel of the rope-like strand during the extruding operation.

BACKGROUND OF THE INVENTION 
The present invention is directed to a device for double encasing a 
rope-like material containing one or more light waveguides which have been 
stranded together. The device utilizes two extruders which are spaced to 
extrude a first layer onto the rope-like material and then subsequently 
extrude a second layer onto the first layer. 
It is known that two sheathing layers can be successively applied by 
extruders when cladding rope-like material containing one or more light 
waveguides. An example is disclosed in U.S. Pat. No. 4,414,165 which was 
based on the German application No. 31 11 963. As disclosed in this U.S. 
Pat. No. 4,414,165, whose disclosure is incorporated by reference thereto, 
a filling compound which provides a cooling effect and thereby shortens 
the stretching cone for the extrusion nozzles is applied before the 
application of the inside or inner sheath or cladding. In many cases 
however, it is desirable to increase the working speed, for example, the 
rate of passage of the bundle of optical fibers to such a degree that an 
adequate solidification can no longer be achieved by using such cooling 
measures in the brief time available unless unnecessarily great distances 
are provided between the first and second extruder. However, increasing 
the distance between the first and second extruder has proven extremely 
unfavorable because of the great space requirement among other things and 
moreover due to the over-stressing of the mechanical stability of the 
yet-unhardened cladding layers or sheaths. 
SUMMARY OF THE INVENTION 
The object of the present invention is to improve an apparatus for 
extruding an inner and an outer sheath or cladding onto a rope-like strand 
containing one or more light waveguides so that the work can be carried 
out with a higher output rate and which apparatus assures that the inner 
sheath has already sufficiently solidified when the second sheath is 
extruded thereon. In accordance with the invention, this object is 
achieved by an improvement in a device for double encasing a rope-like 
strand containing one or more light waveguides, said device having two 
extruders spaced along the path of movement for the rope-like strand. The 
improvements are that a cooling means for externally applying a cooling 
fluid to an outer surface of a first layer of cladding or sheath material 
is positioned between the first and second extruders. 
Because the fluid cooling occurs from the outside, adequately high 
quantities of the coolant, which are also correspondingly selected in 
terms of their temperature, can be supplied to the still-soft sheath and a 
rapid solidification will therefore occur. In known apparatus by contrast, 
the cooling depends only on the condition and the temperature of the 
filling compound and to a certain degree on the externally acting cooling 
air. Both, however, cannot be kept arbitrarily cooled without further ado 
because, for example, the filling compounds below certain temperatures 
become too viscous and thus become hard to process and the coefficient of 
heat transmission for the cooling air is extremely low. In addition, the 
light waveguides or, respectively, the group of light waveguides is not 
surrounded with an arbitrarily coolable filling compound in all cases. 
Above all else, the present invention is also employable for horizontally 
functioning light waveguide bundles or, respectively, light waveguide 
strands. 
The improved device also achieves a greater cooling in that the distance 
between extruders can be selected to be relatively large because the 
solidification of the applied first sheath can be very quickly executed 
and thus the second extruder can be positioned at a greater distance from 
the first. Space is thus created for the cooling device and for the 
following drying device or means. The surface of the first sheath must be 
absolutely coolant-free or dry before the second coating can be applied. 
Instead of utilizing ordinary water, other more quickly evaporating agents 
can be utilized for cooling, for example, alcohol, whose vapors, of 
course, must be suctioned off. Thus, the cooling material can be selected 
from a group of materials consisting of water, alcohol and mixtures of 
water and alcohol. 
In further developments of the invention, the cooling means includes at 
least one annular nozzle having an inner diameter through which the 
rope-like strand of material with the first or inner sheath passes. The 
nozzle has a cylindrical shape and is provided with a plurality of 
radially inwardly extending apertures through which the cooling medium or 
fluid will flow to entirely cover the outer surface of the inner sheath or 
layer. Subsequent to passing through the cooling means, the cooled sheath 
will pass through an extraction means or device for removing any of the 
fluid therefrom prior to reaching the second extruding device. 
As mentioned hereinabove, the improvements of the present invention enable 
placing the extruders to operate on a horizontally traveling strand or 
cable. The distance between the two extruders of the device is preferably 
more than 0.5 meters and is preferably in a range of 0.5 meters to 2 
meters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The principles of the present invention are particularly useful in a device 
illustrated in FIGS. 1 and 2 which extrudes an inner or first sheath or 
cladding layer on a cable or strand of one or more waveguides and 
subsequently extrudes a second or outer cladding layer or sheath on the 
first sheath. The device as illustrated in FIGS. 1 and 2 includes a 
pay-out stand AG, which is equipped with supply reels VS11, VS12, VS21 and 
VS22 (only four are shown for purposes of illustration). As illustrated, 
light waveguide leads such as optical fibers AF1 and AF2 are removed from 
the reels VS11 and VS22 and are combined into a bundle or strand AB of 
waveguides. Instead of such a bundle of waveguides, however, a single 
light waveguide can also be treated in the device of the present 
invention. 
The bundle AB of waveguides, which can be stranded together in a rope-like 
manner or can consist of a single waveguide, is pre-moistened with a 
filling compound under certain conditions and then proceeds to a first 
extruder EX1 which will extrude a first sheath or cladding layer of 
plastic material on the bundle AB. The bundle with the first layer leaving 
the extruder EX1 is referenced ABC. After having the first coating or 
sheath applied by the extruder EX1, the bundle ABC will then have a second 
coating or sheath applied by a second extruder EX2 to form a bundle having 
two sheaths which is indicated at ABCC. In order to apply the second 
sheath or cladding, the first applied sheath must have become sufficiently 
solidified. To this end, a cooling device KE is interposed between the 
output of the first extruder EX1 and the input to the extruder EX2. The 
cooling apparatus KE is constructed so that it externally withdraws as 
much heat as possible from the extruded sheath or cladding applied by the 
extruder EX1 over a very short length of travel of the coated bundle or 
strand ABC. 
The cooling apparatus KE includes a plurality of annular nozzles RD1, RD2 
and RD3, which are positioned one after another so that the bundle ABC 
with the single extruded casing passes in succession through each of these 
nozzles before reaching the second extruder. A fluid medium, preferably 
water, is employed as the coolant and this is supplied to each of the 
annular nozzles RD1-RD3 by appropriate connecting lines AD1-AD3. The 
cooling fluid flowing off of the bundle ABC from each of the nozzles is 
collected in a vessel or pan BT and returned to a reservoir VS. 
Appropriate pumps, which are not shown in detail, are provided in the exit 
ports for the reservoir VS and these pumps are respectively allocated one 
to each of the connecting lines AD1-AD3. If necessary, the circulation 
arrangement, which is a closed system that includes the lines AD1-AD3, the 
pan BT and reservoir VS, can have an additional cooling device. This 
additional cooling device enables artifically holding the cooling medium 
at a lower temperature. As a result of the cooling of the bundle ABC 
having the single cladding, the first sheath applied by the extruder EX is 
so greatly cooled within a short path that the distance between the 
extruder EX1 and EX2 can be arbitrarily selected and a high output speed 
or rate at the extruders is obtainable. 
In order to guarantee disruption-free extrusion of the second sheathing 
layer to be applied on the first sheathing layer of the bundle ABC by the 
extruder EX2, an extraction device or means WA which removes drop-like 
residue of the fluid is expediently present and positioned between the 
last nozzle RD and the entrance to the second extruder EX2. It should be 
noted that a complete drying is not absolutely necessary because the 
sheathing applied by the extruder EX1 is still warm enough in the region 
of the extraction device WA that the remaining moisture will dry very 
quickly. A thickness measuring device DM can also be provided to precede 
the extruder EX2. More rapid evaporating agents such as alcohol which can 
be either methyl, ethyl, propanol, glycol, etc. can be employed for an 
especially intense intermediate cooling. In addition, mixtures of water 
and alcohol are also possible. The rope-like material ABCC obtained at the 
output of the extruder EX2 will be double encased and is further processed 
in a known way after being discharged from this extruder. This further 
processing will include winding or depositing the doubly encased rope-like 
strand ABCC on suitable drums or reels or coiling the strand on suitable 
dishes or supports. 
Each of the annular nozzles RD1 through RD3 is advantageously composed of 
two half shells of which one, namely, the lower half shell is shown in 
greater detail in FIG. 3. The lower half shell is composed of an outer 
half cylinder AZ and a concentrically disposed inner half cylinder IZ with 
end walls such as SF to form an annular hollow member. When two half 
shells are put together, the construction of the end walls and the inner 
cylinder IZ are such to provide a cylindrical transit opening DO, which is 
of a size so that the incoming, singly encased strand ABC shown in 
dot-dash lines can be conducted through the nozzle without brushing 
against the inside walls of the transit opening DO. Every annular nozzle 
comprises a connecting sleeve AS to which the associated connecting line 
such as AD1 is connected. The supplied coolant first flows into the 
cylindrical annular zone between the outside jacket AZ and inside 
cylindrical jacket IZ and then proceeds through a plurality of nozzle 
apertures or orifices DS1-DS4 into the transit opening DO. The fluid will 
thus create a flow that will cover all outer surfaces of the encased 
strand ABC passing therethrough and this fluid will then emerge from the 
nozzle RD1 at one of the end faces such as the end face SF as indicated by 
the arrows. In this way, the singly encased strand ABC is protected 
against any mechanical contact with the annular nozzle RD1 and is 
simultaneously carried by the coolant. This has the advantage that the 
singly encased strand ABC is not mechanically stressed because practically 
no friction occurs during its passage through the opening DO. The cooling 
effect is also improved so that an adequate lowering of the temperature of 
the sheath applied by the extruder EX1 can be obtained in a relatively 
short space and with a high rate of speed for movement of the encased 
cable or strand ABC. 
This type of managing for the singly encased or sheath rope-like strand or 
cable in a coolant flowing past in an axial direction in the region of the 
annular nozzle also offers the possibility of constructing an extruding 
arrangement where the cable is moving in a horizontal direction even when 
the leads such as AF1 and AF2 are not all too stiff. It is also not 
necessary that the sheath, which is being applied by the extruder EX1, be 
particularly thick or stiff. Because the sheath or cladding applied by the 
extruder EX1 is already quickly and adequately solidified by the cooling 
device KE immediately following the discharge from the extruder EX1, an 
unavoidable great sag is avoided. Moreover, the frictional forces are 
avoided as a consequence of the strand floating on the coolant. 
It is possible to realize a speed in the device in the range of 10 to 200 
meters per minute and to thereby select the distance between the extruders 
EX1 and EX2 to be up to a number of meters. Preferably, the distance is 
more than one-half meter and preferably falls in a range of 0.5 to 2 
meters. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that we wish to embody within the scope 
of the patent granted hereon, all such modifications as reasonably and 
properly come within the scope of our contribution to the art.