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EuroWire – September 2009
78
technical article
A newmethod for
cable gel filling
By Zhenfu Zhou, Zhuang Xiong, Zhongping Luo, Yangtze Optical Fibre and Cable Co Ltd
Abstract
In this paper, a new cable gel filling
method is proposed for optical fibre cables
with metal tape armour; the fundamentals
as well as the implementation of the
method are described in detail.
In addition, the optimum gel parameters
in production are obtained by the water
penetration test, which is also performed
after the temperature cycling test and the
mechanical performance test of the cable.
The test results exhibit that this new
method is quite reliable and easy for
operation. Moreover, it can effectively
reduce production cost.
1 Introduction
Generally, good water-blocking perfor-
mance is a prerequisite for the required life
expectancy and high-quality transmission
characteristics of optical fibre cables. Thus,
water penetration test is an indispensable
item in international standards for cable
performance tests
[1]
.
In China, the water blocking performance
of optical fibre cables is usually achieved
by the following two methods (for cables
with metal tape armour):
The interstices in the cable core
•
are filled with ordinary gel, and a
water-blocking tape is wrapped around
the cable core. If corrugated steel tape is
adopted, a layer of hot melt compound
or water-swellable filling compound is
added continuously at the overlap of
the tape but, in some cases, nothing is
added. If aluminium tape is employed,
the melted PE coating on the tape often
conglutinates the overlap
The interstices in the cable core are
•
filled with water or heat-swellable
filling compound. If corrugated steel
tape is adopted, a layer of hot melt
compound or water-swellable filling
compound is added continuously at
the tape overlap. If aluminium tape is
employed the water or heat-swellable
filling compound is squeezed into the
overlap, or the overlap is conglutinated
by the melted PE coating on the tape
In some countries, semi-dry cable structure
is often used in which water-blocking yarns
are stranded over the non-metallic central
strength member and a water-blocking
tape is wrapped around the cable core.
If water penetrates into the cable, the
water-blocking yarns or tape will swell
immediately to block the water. For those
cables with metal tape armour the overlap
is sealed, mainly, by the melting of PE
coating on the tape. However, this method
is not reliable in practical production,
especially for those cables with corrugated
steel tape armour.
From the above descriptions, we can
conclude that the water blocking measures
for the cable core are quite effective
but the water blocking performance at
the overlap of the metal tape cannot be
guaranteed. For cables with aluminium
tape armour the overlap should be sealed
by the melting of the PE coating on the
tape, so production speed should be
relatively low to allow the coating to melt.
On the other hand, if the cable sheath wall
thickness is rather small, the same problem
will occur due to the insufficient heat
during the production. For those cables
with steel tape armour, even if the hot
melt compound or water-swellable filling
compound is employed, the quantity and
the position of the compound cannot be
controlled to get the best result.
In practical production, the quantity of the
compound should be increased in order
to ensure the good sealing at the overlap,
leading to the overflow of the compound
into or out of the steel tape armour.
For hot melt compound, if it overflows
into the steel tape armour, it will crush
the cable core (loose tubes) since the
compound will harden after it cools
down. If it overflows out of the armour, it
will contaminate the forming dies for the
tape. In the case of water-swellable filling
compound, if it overflows out of the steel
tape armour, it will reduce the adhesion
strength between the cable sheath and
the steel tape, sometimes resulting in
defects on the surface of the cable sheath,
eg lumps and neck downs.
In order to solve the above-mentioned
problems, a new method for cable gel
filling is proposed in this paper.
2 Fundamentals and
characteristics
of method
The new method is suitable for cables with
metal tape armour and it is implemented
layer by layer. The procedures of the
method are illustrated as follows:
First, the interstices between the
•
central strength member and loose
tubes are filled with ordinary gel
during the stranding process
The cable core goes through a
•
compound filling pump during the
sheathing process when the interstices
in the cable core are also filled with
ordinary gel, and superfluous gel is
wiped away by an eraser with the inner
diameter almost the same as the outer
diameter of the cable core
Figure 1
▼
▼
: Sketch map of water-swellable gel spread intermittently on metal tape
Water swellable gel
Metal tape