U.S. patent number 3,728,424 [Application Number 05/065,563] was granted by the patent office on 1973-04-17 for method of making flat cables.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Ralf Rudiger Bauer.
United States Patent |
3,728,424 |
Bauer |
April 17, 1973 |
METHOD OF MAKING FLAT CABLES
Abstract
Method of making flat cables with plastics by extrusion. For
cooling, at least two cooling zones are provided. The width of the
flat cable is adjusted by setting the temperature difference of the
cooling zone, in which the cable sets, and of the preceding cooling
zone.
Inventors: |
Bauer; Ralf Rudiger
(Baden-Wuerttemberg, DT) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
5743522 |
Appl.
No.: |
05/065,563 |
Filed: |
August 19, 1970 |
Foreign Application Priority Data
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Aug 22, 1969 [DT] |
|
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P 19 42 784.0 |
|
Current U.S.
Class: |
264/40.6;
174/117F; 264/178R; 264/348; 264/171.16; 264/171.21; 264/237 |
Current CPC
Class: |
H01B
1/00 (20130101); H01B 13/14 (20130101); H01B
7/0823 (20130101); B29C 48/156 (20190201); B29C
48/08 (20190201); B29C 48/12 (20190201) |
Current International
Class: |
B29C
47/02 (20060101); H01B 1/00 (20060101); H01B
13/06 (20060101); H01B 13/14 (20060101); H01B
7/08 (20060101); B29f 003/10 (); B29c 025/00 () |
Field of
Search: |
;264/172,174,237,348,178,176,40 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,137,626 |
|
Dec 1968 |
|
GB |
|
1,113,728 |
|
Sep 1961 |
|
DT |
|
Primary Examiner: White; Robert F.
Assistant Examiner: Thurlow; Jeffery R.
Claims
I claim:
1. A method of making flat cables comprising moving a plurality of
spaced coplanar wire elements through an extrusion device;
coating said plurality of spaced coplanar wire elements with a
unitary plastic sheath by continuously extruding plastic onto said
moving coplanar wire elements;
passing said plastic covered wire elements after extrusion through
at least two successive cooling zones whereby said plastic is
cooled in the first zone and then is set and cooled in the second
zone; determining the width of said cable following cooling of said
cable in said second zone and regulating the difference in the
temperature of the flat cable entering the second cooling zone and
the temperature of the second cooling zone to provide a final
desired cable width.
2. A method in accordance with claim 1 in which said cable width is
increased by decreasing said temperature difference and decreased
by increasing said temperature difference.
3. A method in accordance with claim 1 which further comprises
passing said cable through a third cooling zone for cooling the
flat cable to a final temperature approaching an external
temperature;
determining the width of said cable at said final temperature of
said cable; and
regulating the temperature differential of said plastic material in
said first zone and the temperature of said second zone in response
to said width determination.
4. A method in accordance with claim 1 in which said plastic
material is selected from the class of materials comprising
polyethylene, polypropylene, copolymerizates of polyethylene and
polypropylene, polyvinyl chloride, silicone rubber, or fluorinated
ethylene propylene.
5. A method in accordance with claim 1 in which said plastic
material is non-crosslinked polyethylene.
6. A method of making flat cables in accordance with claim 1 in
which said control of said width dimension of said cable
includes
determining the width of said cable following cooling of said cable
in said second zone; and
regulating the temperature differential of said plastic material in
said first zone and the temperature of said second zone in response
to said width determination.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of making flat cables,
particularly a method of making flat electric cables in which
conductors are coated with plastic by extrusion.
2. Description of the Prior Art
Methods of and arrangements for extruding making of wires, stranded
wires, conductors and cables are known from the book
"Kunststoffextrudertechnik" (Plastics Extrusion Engineering) by
Gerhard Schenkel, published by Hanser Verlag Munich, 1963, chapter
X, pp. 354 - 373. On page 354 of the book by Gerhard Schenkel, it
is stated that the diameters of the wires to be coated range from
about 0.4 to 180 mm. Hitherto, any attempts at extruding flat
cables, which include more than 10 wires each having a diameter of
less than 0.3 mm, have been unsuccessful. Experience has shown that
extrusion by known methods results in the dimensions required not
being accurately observed. During extrusion variations in the
dimensions of the flat cable occur which are difficult to control
and which exceed the normal heat shrinkage of the plastics and the
tolerances applicable to microelectronics. The cause and effect of
these variations are only insufficiently known. MOreover, it is
practically impossible to size flat cables.
A method of manufacturing flat cables by extrusion is described in
DAS 1,075,695. By this known method, the insulation in the form of
a hose is extruded onto the wires passing the extrusion die
parallel to each other. Subsequently, at a reduced pressure in the
space between the nozzle and the hose the insulation is applied to
the conductors and bonded together. As satisfactory bonding of
thermoplastic necessitates the application of pressure, the results
obtained are not always perfect, which means that cavities result
on the bonding surface between the conductors. Such cavities are
undesirable, since the cable terminals thus produced are permeable
to moisture, contaminants or soldering agents.
Another method of manufacturing flat cables is described in U. S.
Pat. No. 3,082,292. According to the second paragraph of the patent
specification, this method was developed in view of the great
mechanical difficulties previously encountered in attempting to
coat more than two or three conductors in a single assembly. By the
method described in U. S. Pat. No. 3,082,292, two plastic strips
are initially produced by extrusion. In a bonding apparatus, these
strips are applied to the wires from both sides. Subsequently, the
assembly is heated and subjected to pressure, so that the two
plastic strips are fused together. After cooling, he edges of the
bonded strips are cut to a uniform width.
Although in the known laminating process, any cavities are filled
with plastics, since the two plastic strips are bonded together at
high temperature and pressure, the pressure applied may lead to the
position of the wires being changed, so that the electrical
properties such as the characteristic impedance and capacitance may
vary. Moreover, heating and bonding of the strips require a certain
period of time, so that the pay-off speed for flat cables produced
by the laminating process is very low. In practice, pay-off speeds
of 2.5 m per minute have been obtained.
German Pat. No. 1,047,276 describes a method of automatically
regulating the gauge and capacitance of plastics coated conductors.
In accordance with this known method, the speed at which the
conductor passes the screw press and the heating current for
preheating the conductor are automatically and reciprocally
adjusted as a function of the continuously measured gauge and
capacitance. This method is used for coating individual conductors,
preferably employing foam plastics. The known method is not
suitable for influencing the width of a flat cable, since the
adjustment provided extends in the first place to the gauge and
only to a limited degree to the width of the cable.
SUMMARY OF THE INVENTION
It is the object of this invention to provide an improved method by
which flat electric cables comprising a plurality of conductors can
be coated with plastics by extrusion.
It is also an object of this invention to provide a method of
making multiple conductor flat cables by extrusion in which
shrinkage can be controlled after extrusion so that dimensional
tolerances and expecially the required conductor spacings are
adhered to.
It is a further object of this invention to provide a method of
making multiple conductor flat cables by extrusion which is
relatively simple and economical and which is capable of
manufacture at speeds higher than heretofore obtainable by
laminating processes and in which precise dimensional control is
readily obtained.
Broadly, in accordance with this invention, the above as well as
other objects are obtained by extruding dielectric material in a
plastic state onto a plurality of space conductors, then cooling
the plastic material to a solid state in a controlled manner to
control the dimensions of the cable and the desired spacing of
conductors. Specifically, the plastic material is preferably
non-crosslinked polyethylene and control of the size of the plastic
mass is obtained by moving the encapsulated conductors through one
or more cooling zones in a manner which controls the dimensions of
the cable. More particularly, the temperature and/or the length of
a first cooling zone and/or the temperature of the second cooling
zone is/are so adjusted that the difference in the temperature of
the flat cable entering the second cooling zone and the temperature
of the second zone is increased as the width of the flat cable
increases and is decreased as the width of the flat cable
decreases.
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular
description of a preferred embodiment of the invention, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an embodiment of a flat cable manufactured in
accordance with the method of the invention;
FIG. 2 illustrates an apparatus useable for practicing the method
of the present invention;
FIG. 3 shows certain details of an extrusion press useable in the
apparatus shown in FIG. 2;
FIG. 4 shows details of a width measuring device useful in the
apparatus shown in FIG. 2;
FIG. 5 illustrates width shrinkage of a flat cable during cooling;
and
FIG. 6 is a chart showing how the width of the flat cable is
influenced by the method in accordance with the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 is the cross-sectional view of a flat cable produced to the
method in accordance with the invention. The width of this cable is
29.2 mm and the gauge 0.7 mm. Each of the 60 wires arranged side by
side in the flat cable has a diameter of 0.18 mm. The signal wires
are identified by numeral 1. One ground wire 2 each is arranged on
both sides of a signal wire for screening the latter. During
extrusion of the cable through the suitably shaped nozzle, grooves
3 are formed in all those places on the cable surface where there
are no wires. In the case of the preferred embodiment, polyethylene
is used for plastics making the wires; also suitable for this
purpose are polypropylene, polyethylene and polypropylene
copolymerizates, polyvinyl chloride, silicone rubber or fluorinated
ethylene propylene.
FIG. 2 shows an arrangement, by means of which the method in
accordance with the invention is applied. The wires and
subsequently the flat cable pass the arrangement shown in FIG. 2
from left to right. The wires 10 for the flat cable are taken off
the rollers 11 which are mounted in a pay-off frame 12. The rear
side of the pay-off frame 12 is provided with the same number of
rollers as the front side, but the former rollers are not visible
in FIG. 2. For manufacturing a flat cable comprising 60 wires, each
side of the pay-off frame 12 would have to be equipped with 30
rollers, of which, for the sake of simplicity, only a limited
number is shown. In order to keep the wires 10 tensioned, rollers
11 are continuously decelerated, preferably using a shoe brake.
Sagging of the wires in the case of sudden stoppages is avoided by
means of spiral springs arranged between the rollers 11 and the
brakes and which try to turn the rollers against the pay-off
direction. Deflector rollers 14 and 15 serve to preliminarily
adjust wires 10. Subsequently, the wires pass onto a roller 16,
which is notched on its circumference for guiding the wires. Wires
10 are then guided between electric contact plates which produce a
signal in the event any of the wires rupture. Subsequently, the
wires pass a further roller 18, which similar to roller 16, is
provided with guiding notches. Wires 10 are forced against roller
18 by means of a rubber back-up roller 19. In the area between
roller 16 and roller 18 the spacing of the wires exceeds that in
the flat cable; in a comb-shaped guide 20 the wires are assembled
to their final spacing in the flat cable.
Then wires 10 enter from the left the angle extrusion head 21 of an
extrusion press 22. An enlarged perspective view of the extrusion
press is shown in FIG. 3 to render the function of this machine
readily understandable. The granulated plastics, such as, for
example, polyethylene, are fed into a funnel 23. For preheating the
granulate, funnel 23 is provided with a fan 24 which takes in its
operating air via a tube 25. After having been heated in heater 26,
the air is discharged into funnel 23 via tube 27. The preheated
granulate is fed to the screw press. The screw press consists of a
heated hollow cylinder 28 in which the screw 29, transferring the
plastic material in the direction of the die 21, rotates. Screw 29
is driven by an electric motor of which only the covering is
visible in the bottom part of the extruder. Heating, compression
and friction of the granulate result in a compound which becomes
increasingly plastic in the direction of the die 21. The die 21
employed is an angle extrusion head as is mostly used for coating
wires. In the angle extrusion head 21 a path 30, which forms the
extension of the hollow cylinder 28, is split into two paths 31, 32
which are both deflected through an angle of 90.degree. and which
then from above and below converge in the direction of the wires 10
which are led in parallel to each other. At the point of
convergence of the plastic compound emerging from paths 31 and 32
the wires are densely surrounded with plastic material. On the
right output of angle extrusion head 21 nozzle 33 is arranged, the
cross-section of which exceeds that of the finished cable by the
shrinkage in volume (e.g. by about 10 percent with regard o the
width and gauge). Longitudinal shrinkage of the flat cable is
prevented by the wires. The screw output, which can be adjusted as
a function of the number of revolutions of the screw, is chosen so
that the plastic material leaves nozzle 33 at the same speed at
which the wires 10 are taken off. In the case of polyethylene, for
example, the plastic material upon leaving the nozzle has a
temperature of about 200.degree.C.
After having left nozzle 33, the flat cable 34, which at that stage
is still plastic, passes a first cooling zone 35 which is formed by
the surrounding air. This cooling zone may be some 40 cm long.
Through an aperture 36 the flat cable enters a cooling tank 37,
which preferably takes the form of a water cooling tank. The
cooling tank 37 comprises two cooling zones 38 and 39. The water,
as it comes out of the main, is led to cooling zone 39 via an inlet
tube 40. The front part of cooling zone 39 is designed as an
overflow. The water overflowing from cooling zone 39 enters cooling
zone 38. The front part of cooling zone 38 is also provided with an
overflow. The water overflowing from this zone accumulates in basin
41 and is subsequently discharged via tube 42. Through an aperture
43, which is sealed by brushes positioned above and below the flat
cable 34, the latter enters the second cooling zone 38. As will be
described below, the temperature of cooling zone 38 is set to a
nominal value. In the case of the present embodiment, the
temperature of cooling zone 38 is, for example, 80.degree.C. This
temperature is generated by means of a heating coil 44. In order to
ensure that this water temperature is kept as accurately as
possible, the water is agitated by means of a circulating unit 45
which consists of a motor-driven propeller. In cooling zone 38 the
flat cable is guided by means of two rollers 46. Cooling zone 39 is
provided with three further rollers 47, of which the first one is
so positioned in relation to the overflow that the flat cable is
transferred to the second cooling zone 39 above the overflow. As
has been previously stated, the water in cooling zone 39 has the
temperature at which it leaves the main. This temperature is not
critical. The flat cable is led out of cooling zone 39 through a
foam plastic coated aperture 48, by means of which any water still
adhering to the cable is wiped off.
Behind cooling tank 37 a width measuring device 49 is provided
which takes the form of a feeler roll measuring unit. Needless to
say, the feeler roll measuring unit can be replaced by any other
measuring device, such as, for example, a measuring device working
to the pneumatic principle. Details of the width measuring device
49 are shown in FIG. 4. The actual measuring device is arranged on
a frame 50. The flat cable passes between two rollers 51 and 52.
The two rollers are resiliently mounted, so that they are laterally
moved by the lateral edges of flat cable 34. This lateral movement
is transferred to pin 53 and can be indicated by means of a
measuring instrument 54. Thus, measuring instrument 54 indicates
the width of the flat cable. Moreover, a circuit 55 is provided
which converts the mechanical deflection of pin 53 into an electric
signal on lines 56. The mechanical deflection of pin 53 can be
converted into an electric signal in one of several manners. So,
for example, pin 53 can be employed to change the tap of a
potentiometer, thus causing an electric current to be changed. Pin
53 can also be used to change the capacitance of a measuring bridge
capacitor, whereby the change in capacitance affects a signal. If
necessary, these signals can be amplified. Devices for converting
mechanical movements into electric signles are, for example,
described in the book "Control Engineers Handbook" published by
Truxal, McGraw Hill Book Company, Inc., 1958, chapter 17 "Signal
Transducers".
Lines 56 are connected to a regulating device 57, by means of which
to the method in accordance with the invention, the heating voltage
of the heating coil 43 is so regulated that as the width of the
flat cable on the feeler roll measuring device 49 increases, the
temperature of cooling zone 38 is reduced, while the temperature of
cooling zone 38 is increased as the width on feeler roll measuring
device 49 decreases. The temperature of cooling zone 38 can also be
set by hand. Manual adjustment of the temperature is effected in
accordance with the deflection of the pointer indicator 54 on the
feeler roll measuring device. How the temperature of cooling zone
38 affects the width of flat calbe 34 is described below by means
of FIGS. 5 and 6.
For taking off the finished flat cable, a take-off 58 is arranged
behind the feeler roll measuring device 49, which comprises two
tractors 59 and 60. The two tractors, embodied by two rubber bands
which revolve around two rollers each, are driven by an electric
motor, not shown. Finally, a coiling device 61 is provided behind
the take-off 58. The coiling device 61 is driven by means of an
electric motor, not shown, which can be decelerated to
standstill.
The shrinkage of the flat cable is shown in FIG. 5 which is a plan
view of the cable. In order to render the shrinking process readily
understandable, the amounts of shrinkage encountered are shown in
exaggerated form.
The dotted lines 72 define the outer edge of an extruded plastic
strip without wires. In the area of air cooling zone 35, cooling
and shrinkage of this strip are relatively insignificant. Upon
entering water cooling zone 38 at line 70, the plastic strip is
cooled relatively intensely, which results in a bend at this line
the material shrinks considerably. Depending upon the temperature
of cooling zone 35, the plastic strip will shrink more or less
heavily in this area. The total shrinkage of a plastic strip
without longitudinal wires is invariably the same, irrespective of
whether the temperature in cooling zone 35 is high or low. Beyond
the straight line 71 the plastics are set, whereby it is negligible
that freezing occurs over a wider area. Shrinkage beyond line 71 is
almost excusively attributable to the coefficient of thermal
expansion.
The shrinkage of a flat cable is slightly different from that
experienced with a plastic strip (dotted line 72). The flat cable
is designated by the unbroken line 73. It is readily recognizable
that the shrinkage plot is not bent at the entry 70 to the second
cooling zone, since the tensile stress of the wires prevent any
abrupt change in width while the material is in a plastic state,
and that the heavy shrinkage in the first cooling zone, caused by
the wires, results in a more pronounced reduction in width behind
the nozzle than in the case of a plastic strip.
The diagram of FIG. 6 serves to explain in detail how the shrinkage
of a plastic strip with and without wires proceeds and how the
width B of an extruded flat cable is influenced by changing the
temperature of the second cooling zone 38. In the diagram of FIG. 6
width B, during cooling, is shown on the abscissa with respect to
the spacing A from the nozzle outlet. The three cooling zones, the
first zone 35, the second 38, and the third 39, are defined in
relation to each other by vertical lines 100, 101, and 102. First
of all are considered the dotted plots which represent the
reduction in width of an extruded plastic strip (without wires).
Plot section 103 shows how the width of the extruded plastic strip
decreases in the first cooling zone, the air cooling zone 35. At a
cooling water temperature of 80.degree.C of the second cooling zone
38 the width of the platic strip decreases in accordance with the
dotted plot 104. If the cooling water temperature of the second
cooling zone 38 is lower than that of the first, say, for example,
50.degree.C, the reduction in width in cooling zone 38 proceeds in
accordance with plot 105. At the straight line 100, the point where
the plastic strips enter cooling basin 23, the width plot is bent.
Plots 104 and 105 are proportional to the amount of cooling. Points
108 and 109 are the freezing points. Beyond these points the
plastics are set over their full cross-sectional area. In some
areas setting occurs more rapidly. Beyond freezing points 108 and
109, shrinkage of the plastics is mainly governed by the
coefficient of thermal expansion and only to a very limited degree
by crystallization. The degree of crystallization depends upon the
temperature of cooling zone 38. Subsequent crystallization is
encountered as long as one week after cooling, producing a
negligible shrinkage of some 2 percent.degree. in the width and
gauge of the material.
Straight line 101 defines the entry to cooling zone 39. In the
embodiment the temperature of this cooling zone is assumed to be
20.degree.C. The width of the plastic strip proceeds along the
dotted plot 106 if the temperature of cooling zone 38 is
80.degree.C and along plot 107 if the temperature is 50.degree.C.
Plots 106 and 107 converge. Thus, the plastic strip has a uniform
width under identical environmental and material conditions, which
is independent of how cooling is effected, i.e. in this case of
whether the temperature of cooling zone 38 is 80.degree. or
50.degree.C.
Details of the reduction in width of a flat cable during cooling
after extrusion are given below. In FIG. 6 the width plots of the
flat cable are represented by unbroken lines. After the plastics
have set, the reduction in width of the flat cable proceeds
parallel to the reduction in width of the plastic strip. At a
temperature of 80.degree.C in the second cooling zone 38, the width
of the flat cable corresponds to plot 110 and after entry into the
third cooling zone 39 to plot 111. Correspondingly, the width of a
flat cable cooled to 50.degree.C in the second cooling zone 38
decreases beyond the freezing point according to plot 112 and in
cooling zone 39 to plot 113. Plots 110 and 111 are shifted
downwards in relation to plots 104 and 106 and plots 112 and 113
with respect to plots 105 and 107. This is due to the wires being
pressed together in cooling zone 38 during cooling, which results
in the width of the flat cable, which is in a plastic state in
cooling zone 35, being reduced. The different widths in this area
are represented by plots 114 and 115. The reduction in width is
more pronounced, the more intense the cooling in the second cooling
zone 38, i.e. the more marked the bend at the straight line 100.
Freezing points 116 and 117 of the flat cable are below freezing
points 108 and 109 which apply to plastic strip.
The difference between freezing points 117 and 109 is more
pronounced than between freezing points 116 and 108. As beyond the
freezing points the plots for plastic strips and flat cables
proceed parallel to each other under identical cooling conditions,
different widths for the flat cable result on the straight line 102
upon completion of cooling. The cable is narrower the heavier the
cooling in the second cooling zone 38. This phenomenon, which is
not encountered with plastic strip, is utilized in accordance with
the invention for adjusting the width of the flat cable to a
constant width. By controlling the temperature of the second
cooling zone 38, variations in material and temperatures in the
extruder, different output speeds and environmental influences,
such as room temperature, humidity, etc. can be compensated
for.
The influence of the temperature of cooling zone 38 on the final
width of the cable can also be readily physically explained by
means of FIG. 6. While the actual nozzle outlet of the extruder in
FIG. 6 is at abscissa 0, one can imagine a virtual nozzle in the
area of the first cooling zone in which the flat cable is still in
a plastic state. Assuming the virtual nozzle is located near the
vertical 100. At this vertical the width 114 or 115 of the flat
cable differs considerably, which is due to the wires being forced
together by the varying amounts of shrinkage in the second cooling
zone 38. This interaction produces an effect similar to that
obtainable by a real nozzle with variable cross-section. These
conditions, in particular the variations in temperature in the
second cooling zone, are shown in exaggerated form in FIG. 6. In
actual fact, the cooling water temperatures in an arrangement
according to the invention differ only slightly, for example, by
3.degree.C. In an extruder working to the method in accordance with
the invention and which is employed for extruding 60-core
polyethylene flat cables having a final width of 29.2 mm, the
temperature of the controlled cooling zone is about 80.degree.C,
this value being accurately regulable within a tolerance of
0.5.degree.C.
In general, it can be said that the reduction in width of the cable
in the area of cooling zone 35 is pronounced and the final
dimensions of the cable are smaller, the more marked the bent of
the cooling plot of a strip without wires is under similar cooling
conditions above the freezing temperature. The angle of this bent
can also be influenced in a manner other than is described in the
above example where the temperature of the second cooling zone, in
which the plastics set, is changed. The angle of the bent can also
be altered by changing the length of the first cooling zone 35.
This results in the temperature of the flat cable being changed
upon entry into the second cooling zone 38. The temperature of the
flat cable upon entry into the second cooling zone can also be
influenced by changing the temperature of the first cooling zone 35
(e.g. by altering the air temperature of the air flow). Finally, it
is also possible to change these parameters simultaneously.
The invention is not only suitable for cooling systems consisting
of air and water cooling zones, but may also be utilized for
systems employing different cooling speeds before the freezing
point of the plastics.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *