Process to make miniaturized multipolar flame-propagation-resistant cables having a reduced emission of toxic and noxious gases and cables obtained thereby

The process of the invention to make miniaturized multipolar cables includes the steps of combining together a plurality of individually insulated conductors, inserting a filling in a pasty state and containing mineral fillers into the gaps existing between the conductors, partly hardening the filling and disposing the other cable components, in particular the sheath, around the conductors-filling assembly, and letting the filling become completely hard within the produced cable.

BACKGROUND OF THE INVENTION 
The present invention relates to a process to make miniaturized multipolar 
flame-propagation-resistant cables having a reduced emission of toxic and 
noxious gases. 
By the word "miniaturized", cables are intended in which the insulating 
layer thickness in the individual electrical conductors is included 
between 0.20 and 0.30 mm and the sheath thickness is included between 0.3 
and 0.8 mm. Examples of miniaturized cables are the object of AMT 551070 
specifications. 
By the expression "flame-propagation-resistant" it is intended to mean that 
the cables assembled together to form bundles, must comply with the 
requirements established by CEI (Comitato Elettrotecnico Italiano, Italian 
Electrotechnical Committee) rules 20-22-III. 
By the expression "reduced emission of toxic and noxious gases", it is 
intended to mean that the individual components of the cable when 
submitted to the tests established by CEI rule 20-37-II, give rise to an 
overall toxicity-index value of the cable, as hereinafter defined, lower 
than 3.5. 
Said overall toxicity index of the cable is the sum of the toxicity indices 
of the individual components, each of them being multiplied by the ratio 
of the weight that each said component has in the cable unit of length to 
the overall weight that all the components have in the cable unit of 
length. The present invention also refers to the cables obtained by the 
process in question. 
It is known that multipolar cables are cables provided, within one and the 
same sheath, with at least two and generally a plurality of electrical 
conductors which are individually insulated and assembled, being laid 
together for example. 
The known process is comprised of the steps of: 
combining together at least two and generally a plurality of electrical 
conductors which have been already individually insulated, i.e. already 
provided with an insulating layer of their own, said assembling being 
carried out for example by laying the conductors themselves together; 
inserting fillings into the gaps left between the conductors while they are 
being assembled, which fillings in the case of cables belonging to the 
flame-retardant cable class, are made of a practically fireproof material 
which therefore does not propagate flame, such as cables extruded from 
blends of polymeric materials highly charged with mineral fillers which, 
as such, do not propagate flame; and 
forming a sheath of a polymeric material about the assembly obtained by the 
preceding steps. 
While in known non-miniaturized multipolar low-voltage cables the conductor 
insulators have an average thickness of 0.82 mm, in miniaturized 
multipolar cables the insulator thickness is included between 0.20 and 
0.30 mm on an average. 
In the case of non-miniaturized cables no problem exists when polymeric 
material highly charged with mineral fillers is to be introduced by 
extrusion into the existing gaps between the assembled conductors. This is 
due to the fact that in non-miniaturized cables the thickness of the 
filling to be fitted into the gaps existing between the individual 
insulated conductors and around the assembly of same is of such a value 
that extrusion of the filling at relatively low temperatures is allowed 
without giving rise to discontinuities in the filling and/or important 
variations in the final diameter of the cable. On the contrary, the higher 
temperatures necessary for low-thickness (as in the case of miniaturized 
cables) extrusion of blends of polymeric materials highly charged with 
mineral fillers involves the presence of porosity in the filling itself 
caused by the emission of water vapour by desorption or decomposition of 
such hygroscopic mineral fillers. 
It should be noted in fact that in order to be able to extrude, for 
example, a polyolefin-based blend containing mineral fillers such as 
magnesium hydroxide or aluminium hydroxide in an amount of 40% by weight 
with respect to 100 parts by weight of polymer, the temperature to be 
reached during the extrusion for making the blend fluid enough so that 
gaps between the conductors can be properly filled, shall be about 
150.degree. C. 
The Applicant has observed that the possibility of applying fillings formed 
of polymeric materials containing high amounts of mineral fillers by 
extrusion, is limited to a minimum thickness of 0.5 mm. 
Therefore, the application of a filling by extrusion is to be excluded for 
miniaturized multipolar cables because in said cables the filling 
thickness between the conductors is on the order of 0.20-0.25 mm. 
However, in order to be able to make miniaturized multipolar 
flame-propagation resistant cables it is necessary to carry out filling of 
the gaps between the assembled conductors by a material resisting flame 
propagation or flame-retardant material. 
In a known solution it is provided that a glass rod or a glass-fibre cord 
is disposed into the gaps existing between the conductors combined 
together to form a cable. 
This known solution, however, has some drawbacks. If glass rods combined 
with the cable conductors are used as the filling, the cable flexibility 
is clearly reduced. In addition, the glass rod's brittleness makes the 
arrangement of said rods close to the conductors troublesome. 
If a glass-fibre cord is used as the filling, which cord may be optionally 
covered with a sheath of polymeric material, there is a risk that, due to 
breaking of some glass fibres in the cord, which fibres are very brittle 
being made of glass, said same glass fibres may project from the cord in 
the form of needles and consequently cause annoying injuries to the 
operators when they are assembling the cables with fittings such as 
connecting means or with appliances to be supplied power by the cable. 
In both cases, in addition, since it is necessary to carry out coupling of 
the glass rods or glass-fibre cords, the assembling operations are made 
more complicated because the number of components to combine together is 
twice that of the insulated conductors. 
Resorting to the use of section members of polymeric materials containing 
high amounts of mineral fillers in place of the glass rods or glass-fibre 
cords also involves the necessity, in addition to the complexity of the 
above mentioned assembling operation, to utilize section members having a 
very low tensile strength as compared with the tensile strength possessed 
by the insulated conductors, which will bring about the danger of breaking 
said section members while a cable is being manufactured. 
A solution similar to the one disclosed in U.S. Pat. No. 4,978,649, 
comprises introducing, at room temperature, blends of polymers having a 
high flowability at room temperature and capable of crosslinking in time 
still at room temperature, into multipolar cables already provided with a 
sheath for creating fillings between the assembled conductors, does not 
seem to be practicable. In fact the addition of the amounts of mineral 
fillers necessary to make the miniaturized cable flame retardant to the 
blends designed to form the fillings gives rise to such viscosity values 
in said blends that they cannot be pumped at room temperature into the 
gaps existing between the conductors and sheath in a cable. 
SUMMARY OF THE INVENTION 
In one aspect, the present invention relates to a process for making 
flexible miniaturized multipolar flame-propagation-resistant cables having 
a reduced emission of toxic and noxious gases, comprising the steps of: 
combining together at least two electrical conductors, individually covered 
with an insulating layer, gaps being defined between said conductors 
combined together, 
inserting a filling into at least one fraction of said gaps, 
applying a sheath surrounding the assembly formed of the conductors 
combined together and the filling inserted in the gaps defined between 
said conductors, characterized in that the step of filling the gaps 
defined between the conductors comprises the steps of: 
inserting a polymeric material containing dispersed mineral fillers into 
the gaps defined between the conductors immediately after they are 
combined together, at such an application temperature that the material is 
in a pasty state, with a viscosity lower than a predetermined value, 
increasing the viscosity of the polymeric material inserted into the gaps 
existing between the conductors until a value corresponding to a 
substantial stability of shape before application of the sheath, 
hardening (completing hardening of) the polymeric material after 
application of the sheath. 
Preferably, the mineral fillers are in an amount included between 40% and 
70% by weight of the overall weight of the blend, and they are selected 
from magnesium hydroxide and aluminium hydroxide. 
In particular, the viscosity of the polymeric material at said application 
temperature is such that it causes the substantial filling of all gaps 
defined between said conductors and, preferably, said viscosity measured 
at 25.degree. C. by a Brookfield viscometer A:4 V:2.5 is lower than, or 
equal to about 1100000 mPa.sec and more preferably, lower than or equal to 
about 500000 mPa.sec. Preferably, the application temperature of the 
polymeric material is room temperature. 
In a preferred embodiment, the step of inserting the polymeric material in 
a pasty state into the gaps defined between the conductors is carried out 
by making the conductors, individually covered with an insulating layer 
and already assembled together, pass through a chamber containing said 
polymeric material at the pasty state maintained at said application 
temperature. 
In a preferred embodiment, the polymeric material to be introduced into the 
gaps defined between the conductors consists of a blend of a first polymer 
and a second polymer which is subjected to cold cross-linking by 
polyaddition. In particular the first polymer is polydimethyl siloxane 
having terminal vinyl groups, whereas the second polymer is a 
silicone-based polymer containing Si--H groups. 
Preferably, the increase in the viscosity of the polymeric material is 
achieved by heating to a predetermined temperature and, more preferably, 
said predetermined temperature is included between 170.degree. C. and 
180.degree. C. 
In a second aspect, the present invention relates to a miniaturized 
flexible multipolar flame-propagation-resistant cable having a reduced 
emission of toxic and noxious gases, which comprises: 
at least two individually insulated electric conductors combined together, 
a filling inserted into the gaps existing between said insulated conductors 
combined together, 
a sheath surrounding the assembly formed of the insulated conductors 
combined together and the filling, characterized in that the filling 
inserted into the gaps between the insulated conductors comprises a blend 
of a first polymer selected from polydimethyl siloxanes having terminal 
vinyl groups, a second polymer selected from silicones containing Si--H 
groups and mineral fillers selected from magnesium hydroxide and aluminium 
hydroxide, in an amount included between 40% and 70% by weight of the 
overall weight of the blend.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The process of the invention will be now described with the aid of FIG. 1. 
The first step in the process comprises in combining together at least two 
and in general a plurality of individually-insulated conductors, that is 
each provided with an electrically-insulating layer. Each conductor is 
stored on a reel. 
In the particular case of FIG. 1 four insulated conductors 1 are provided 
and they are stored on reels 2 freely rotating about their axis 3. 
Reels 2 are mounted on a rotating framework 4, the rotation of which takes 
place for example in the direction of arrow 5. In addition each reel 2 is 
mounted on a spindle 6 imposing rotation of each reel in a direction 
opposite to that of the framework 4 so that the insulated conductors are 
not subjected to twist stresses while the cable is being manufactured. 
Downstream of the reel 2 group there is a stationary assembling mould 3 
which carries out the operation of assembling or combining together the 
four insulated conductors putting them into mutual contact. 
In the particular embodiment shown in FIG. 1 the four insulated conductors 
1 are laid together having taken a helical configuration, due to the 
combined action exerted by the rotating framework and the stationary 
assembling mould. 
The assembled conductors obtained from the first processing step are 
submitted to the second step which comprises in inserting a pasty 
material, preferably of a polymeric nature, at an application temperature 
as below defined, into at least some of the gaps existing between the 
assembled conductors, which pasty material after undergoing a viscosity 
increase capable of giving rise to a partial hardening, will form a 
filling. 
By the term "application temperature" it is intended a temperature at which 
the material to be applied has a sufficient flowability so that it can 
fill the gaps provided for filling in a substantially complete manner 
without causing gas emissions, in particular water vapour emissions from 
the mineral fillers incorporated into the material to be applied. 
Preferably the "application temperature" is room temperature. The nature of 
said pasty material and the features of same will be set forth in more 
detail in the following. 
A particular embodiment of the second processing step, as shown in FIG. 1, 
comprises making the assembly of the conductors combined together pass 
through a chamber 7 filled with said pasty fluid which is at the 
application temperature, i.e. preferably room temperature. 
The pasty fluid is admitted to chamber 7, by pumping for example, through a 
duct 8. Within chamber 7 the pasty fluid incorporates the assembly of the 
conductors laid together filling the gaps existing therebetween. 
On coming out of chamber 7 the pasty fluid in excess is removed from the 
conductors by a gauged orifice by means of which a coating layer of 
predetermined thickness is formed around the assembly of the conductors 
laid together. 
Downstream of chamber 7 the third step of the process takes place and it 
consists in performing a partial hardening of the pasty material applied 
to the assembly of insulated conductors laid together so as to give them a 
substantial stability of shape. 
By the expression "substantial stability of shape" it is intended that the 
viscosity of the material applied in a pasty state increases to such an 
extent that the material does not drip any longer under its own weight 
during the period elapsing from when it is applied to when the formation 
of the sheath about the cable occurs. 
Taking into account the specific materials to be used for forming the 
fillings and the selected technique for carrying out said partial 
hardening of the pasty material, a person of ordinary skill in the art, 
based on the available knowledge of the materials and the above 
indications, will be able to establish the appropriate viscosity increase 
without further instructions. 
A particular embodiment of the third step in question consists in heating 
the outer surface of the pasty material layer by a hot air blow, emitted 
by a fan 9 for example, so that an increase in the viscosity of said layer 
due to partial cross-linking and therefore a hardening of same is caused 
to such an extent that said material is prevented from undergoing 
substantial deformations and variations in the shape it has received from 
the gauged orifice located at the chamber 7 exit, as hereinafter defined. 
The temperature value of the air blown onto the outer surface of the 
applied pasty material as well as the quantity of this hot air depends on 
the nature of the pasty material employed and therefore a person skilled 
in the art, based on his knowledge of the composition, will be able to 
establish this value without any particular instructions. Then the 
assembly of the insulated conductors laid together and to which the pasty 
material has been applied are submitted to the fourth step of the process 
which comprises applying a sheath made of a plastic material for example, 
and obtained by means of extrusion for example by an extruder 10, as shown 
in FIG. 1. 
A reel not shown, on which the cable is stored, is located downstream of 
chamber 7. 
The fourth step can be preceded by a lapping step during which a cover 
tape, of plastic material for example, is applied to the assembly of 
insulated conductors laid together and having the partly-hardened pasty 
material applied thereto. 
This operation may be carried out for example, as shown in FIG. 1, by a 
lapping machine provided with a spool 11 on which a tape 12 is stored, 
which spool is rotated around the assembly of the conductors laid 
togegher. 
Another optional step to be executed between the lapping step and that 
involving formation of the sheath comprises applying a screen of braided 
copper wires. For this operation (not shown in FIG. 1) means known per se 
and therefore not further described is employed. 
According to an alternative embodiment of the invention (not shown), for 
carrying into effect the process of the invention, the framework 4 is 
stationary and also stationary are spindles 6, whereas the assembly of the 
conductors combined together rotates about the longitudinal axis of same 
following rotation about this axis of the reel, not shown in FIG. 1, on 
which the produced cable is stored. 
A particular cable obtained by the above described process and falling 
within the scope of the present invention as well, is shown in FIG. 2, in 
a sectional view at right angles to the axis of same. Starting from the 
centre and going towards the external portion, the cable has four 
electrical conductors 13 in the form of cords formed of copper wires each 
provided with an insulator means consisting of a layer of an extruded 
polymeric material as stated in AMT 551070 specification relating to 
miniaturized cables. 
Provided around the assembly of the four insulated conductors is a filling 
of polymeric material applied according to the process of the present 
invention as previously described and the composition of which will be 
detailed later on. 
To the ends of the present invention, by gaps defined between the insulated 
conductors, to be filled with polymeric material in a pasty state, it is 
intended the star-shaped spaces defined between the outwardly-facing 
conductor surfaces and an external cylindrical surface enclosing all the 
insulated conductors, tangent to or external of said conductors. 
As shown in FIG. 2, this polymeric material fills the gaps 15 existing 
between the insulated conductors, preferably but not necessarily without 
occupying the radially innermost space 16, and forms a cylindrical 
envelope about the assembly of same. 
Disposed over the external cylindrical surface of the filling material is a 
lapping tape 17 applied by overlapping each winding with the edge of the 
preceding winding. 
A screen 18 is present over the lapping tape and it consists of one or more 
layers formed of braided copper wires. 
A sheath of polymeric material 19 applied by extrusion is disposed over the 
assembly formed of the previously described elements. 
As previously said, the filling in the gaps 15 between the conductors is 
formed of a polymeric material applied thereto in a pasty state, at an 
application temperature that in this particular case is room temperature, 
which material quickly becomes partly hard by incipient cross-linking by 
means of heating immediately after it has been applied, so as to increase 
viscosity to such a value that deformation of same is prevented, the 
material acquiring a stability of shape that will enable application of 
the external cable components to be carried out. 
In the particular case in question "stability of shape" means that between 
the exit from the gauged orifice of chamber 7 at which the filling 
material forms a perfectly cylindrical envelope and the position at which 
the sheath is applied, the dimensional variation that can take place in 
the external surface of the cylindrical envelope must not exceed 20% and 
preferably must not exceed 10% of the gauged orifice diameter. 
Described hereinafter is an appropriate material for a preferred embodiment 
of the invention. The material in question is a two-polymer-based blend in 
which the two polymers are susceptible of cold cross-linking by 
polyaddition and contain mineral fillers in an amount included between 40% 
and 70% by weight of the overall weight of the polymer blend. 
One of these two polymers is a polydimethyl siloxane containing terminal 
vinyl groups, the second polymer being a silicone-based polymer containing 
Si--H groups and the mineral fillers are selected from magnesium hydroxide 
and aluminium hydroxide. 
More specifically, the first polymer, that is polydimethyl siloxane 
containing terminal vinyl groups, used for the experimental tests has a 
viscosity at 25.degree. C. of 6400 mPa.sec measured by a Brookfield 
viscometer utilizing a spindle RV7 rotated at a speed of 2.5 rpm, whereas 
the second polymer, that is the silicone-based polymer containing Si--H 
groups, has a viscosity of 4800 mPa.sec measured with a Brookfield 
viscometer using a spindle RV7 rotated at a speed of 2.5 rpm. 
The utilized mineral filler is magnesium hydroxide. 
Experimental examples providing the use of a mineral filler comprising of 
aluminium hydroxide are not expressly reproduced in that they are exactly 
the same as those obtained by the use of magnesium hydroxide as the 
filling. 
The mineral filler, that is magnesium hydroxide, was admixed with the first 
polymer by a mixer and in the mixture also a chloroplatinic-acid and 
divinyl-tetramethyl-siloxane compound acting as a catalyst for the 
polyaddition reaction of the two polymers was added. 
For the group consisting of the first polymer, the mineral filler and the 
catalyst, hereinafter referred to as component A, formulations having the 
following compositions were prepared: 
______________________________________ 
first polymer Mg(OH).sub.2 
above cited catalyst 
parts by weight parts by weight ppm 
______________________________________ 
A1 100 50 20 
A2 100 85 20 
A3 100 160 20 
A4 100 320 20 
A5 100 400 20 
______________________________________ 
The second polymer, that is the silicone-based polymer containing Si--H 
groups, forms component B by itself. 
With components A1, A2, A3, A4, A5 and component B five blends were 
prepared by addition of one part by weight of component B to 10 parts by 
weight of each of said components A. 
Mixing was carried out with an electric mixer under stirring at 23.degree. 
C. over a period of ten minutes, the mixer rotating at such a speed that 
the introduction of air bubbles in the mixture was avoided. 
The obtained blends had the following viscosities, measured with a 
Brookfield viscometer using a spindle RV7, the rotation speed of said 
spindle being 2.5 rpm: 
______________________________________ 
Viscosity after 15 m from 
Type of blend preparation (m Pa .cndot. sec) Mg(OH).sub.2 
______________________________________ 
A1 + B 83000 30% by weight 
A2 + B 185000 41% by weight 
A3 + B 307200 55% by weight 
A4 + B 970000 70% by weight 
A5 + B 1220000 73% by weight 
______________________________________ 
It was first of all observed that with blend A5, that is a blend containing 
73% by weight of magnesium hydroxide, it is impossible to make a cable 
having acceptable features in that at room temperature the viscosity of 
this blend is very high and does not offer the assurance of a complete 
filling of the gaps between the conductors. 
It was also observed that, for all blends of components A1, A2, A3, A4 with 
component B kept at 23.degree. C., the time after which the obtained 
product had reached such a viscosity that application of same was 
inhibited (approximately &gt;1500000 mPa.sec), is about 90 minutes. 
To the ends of the present invention an appropriate viscosity of the 
overall polymeric blend at the application temperature is believed to be 
preferably lower than or equal to 1100000 mPa.sec and, more preferably, 
lower than or equal to 500000 mPa.sec. 
It was also observed that for each blend the required time at 23.degree. C. 
for reaching a complete hardening is about 8 hours. 
Using the blends containing 30, 41, 55 and 70% by weight of magnesium 
hydroxide respectively, four cables were made having the structure shown 
in FIG. 2 which has been previously described. 
The four cables have the same sizes and differ from each other exclusively 
for the different type of blend used to make the cable filling. 
The dimensional features of the cables, their components and the material 
of the latter are now reproduced and their features correspond to a 
particular case contained in AMT 551070 specifications. 
The cable conductors have a section of 0.6 mm.sup.2 and are formed of 19 
copper wires with a diameter of 0.2 mm. 
The insulating layer of the conductors has a thickness of 0.25 mm. For this 
insulating layer a polybutylene terephthalate-based blend was selected 
which was applied by extrusion to the conductor. The blend contained a 
silicone etherimide copolymer, a brominated additive having a content of 
3.5% by weight of bromine, antimony(III) oxide and stabilizers of a type 
known per se. 
The tape used to form layer 17 of FIG. 2 is a tape of polyethylene 
terephthalate of a thickness of 20 82 m. 
This layer is formed by wrapping a single tape and this wrapping is carried 
out with an overlap of 50%. 
The different filling blends differentiating the cables from one another 
were applied under the same conditions and following the same modalities. 
In particular, the blends were applied to the four insulated conductors, 
already laid together, by mixing, at 23.degree. C., the components (A1, 
A2, A3, A4 with component B) stored into separate tanks, immediately 
before their application, sending said components by metering pumps having 
volumetric counters to a mixer and directly loading the blend to the 
application apparatus. 
When coming out of the apparatus carrying out application of the filling, 
said conductors have a continuous layer of a thickness of 0.25 mm formed 
around them at the radially outermost area thereof. 
Immediately downstream of the filling-applying apparatus heating of said 
filling is carried out by hot air. 
In the particular embodiment of the cables under examination the hot air 
jet employed has a flow rate of 400-500 l/minute and the temperature of 
said air was selected such that the whole external surface of the applied 
filling could have a temperature included between 170.degree. C. and 
180.degree. C. for a period of some seconds. 
At a position radially external of the lapping tape there is a copper-wire 
screen and more particularly a screen comprising braided copper wires of a 
diameter of 0.2 mm. 
Located over the copper-wire screen is the cable sheath. This sheath has a 
thickness of 0.6 mm and is formed of a base blend which is subsequently 
set by means of vinylsilanes. 
The base blend consists of: 
100 parts by weight of an ethylene vinylacetate copolymer, 
130 parts by weight of magnesiun hydroxide, 
5 parts by weight of stabilizers of a type known per se and appropriate for 
blends of polymeric materials. 
This base blend was set by means of vinylsilanes known per se in an 
appropriate double-screw, extruded about the cable by addition of tin 
dibutyl laurate as the catalyst and link-crosslinked by dipping the cable 
into water at 80.degree. C. over a period of 16 hours after sealing the 
cable ends. 
In addition to the four cables differing from each other for the filling 
material composition alone, a fifth cable was made which differs from the 
others exclusively in that the filling material is absent. 
The cables in question (those containing the filling and the filling-free 
cable) were submitted to the flame- propagation test prescribed by rule 
CEI 20-20/III. 
For each test, bundles of cable lengths 3.5 m long were used in a number 
sufficient to form a volume of 1.5 dm.sup.3 of non metallic material. As a 
result, bundles of 71 cable lengths were used for cables provided with 
filling and a bundle of 123 cable lengths for unfilled cable. 
Each cable bundle was disposed upright in a furnace as prescribed by the 
rule in question and flame was applied to the bundle base for a period of 
20 minutes. The flame was obtained by combustion of air and propane, the 
propane flow rate being of 996 l/hour and the air flow rate of 4600 
l/hour. 
During the tests the temperature outside the furnace was 24.degree. C., the 
sky was clear and the wind was running at a speed of 3 m/sec, all of the 
above values falling within those allowed by the rule in question. 
Cables passing the flame-propagation-resistance test are then submitted to 
determination of the toxicity index for the gases generated during 
combustion. 
This determination of the toxicity index for the gases generated during 
combustion was carried out following the modalities briefly described 
hereinafter and as provided by CEI 20-37 II rule. 
The results obtained with the flame-propagation-resistance test are 
reproduced in the following table. 
______________________________________ 
Max. height of 
Elapsed time from length submit. 
Type of Mg(OH).sub.2 in flame application to combustion 
cable filling (minutes) (m) 
______________________________________ 
Cable I absent 9 2.5 
Cable II 30% 10 2.5 
Cable III 41% 20 1.4 
Cable IV 55% 20 1.2 
Cable V 70% 20 1.3 
______________________________________ 
As viewed from the table, only cables III, IV and V passed the 
flame-propagation-resistance test and only said cables were subsequently 
submitted to the tests for determining the toxicity index for the 
generated gases, following the combustion modalities prescribed by CEI 
20-37 II rule. 
For the purpose, from the components of each cable the non-metallic 
materials were removed, i.e.: conductor insulator, filling, tape wrapped 
around the filling, cable sheath. These materials were chopped to form 
powders. For the powders of each cable component, the toxicity factors, 
that is the ratios between the real amount of the particular gases 
generated (specified in the following) and the reference concentration for 
each of said gases, i.e. the amount of gas that would be mortal for men 
after an exposure of 30 minutes were determined. 
Then the percent weights of each cable component were determined per unit 
of length of the cable itself. 
The overall toxicity indices for each cable were obtained by summing the 
products of the toxicity indices of the individual components by the 
percent ratios by weight of said components to the total weight of the 
components per unit of length of the cable. 
Practically the following formula was used in which the abbreviation ITC 
means "toxicity index": 
EQU ITC.sub.cable =(% sheath weight.times.ITC.sub.sheath)+(% tape 
weight.times.ITC.sub.tape)+(% filling weight.times.ITC.sub.filling)+(% 
insulator weight.times.ITC.sub.insulator). 
The toxicity indices obtained for the cables submitted to the test are 
reproduced in the following table, where one can see that all the cables 
have a toxicity index lower than 3.5. 
______________________________________ 
CABLE III 
CABLE IV CABLE V 
______________________________________ 
sheath ITC 2.3 2.3 2.3 
wt % 48.8 47.8 46.84 
tape ITC 3.5 3.5 3.5 
wt % 0.54 0.53 0.51 
filling ITC 2.1 1.7 1.5 
wt % 31.4 32.86 34.24 
insulator ITC 7.2 7.3 7.3 
wt % 19.2 18.8 18.4 
Cable ITC in all 3.2 3.04 2.95 
______________________________________ 
The different components were also submitted to determination of the amount 
of corrosive hydrogen halides emitted during the combustion according to 
CEI 20-37-I specification and it was found that the hydrogen chloride 
values expressed in % for the insulator were lower than 1%, whereas for 
all other cable components the value for said acid was substantially zero 
and at all events of an undetectable amount. 
The above experimental tests clearly show that with the process of the 
invention the intended aim is achieved, that is miniaturized 
flame-propagation-resistant cables are manufactured which are provided 
with a filling charged with mineral fillers and having a low emission of 
toxic and noxious gases.