Abstract
Dry Silane XLM51 (DS...XL PEarl 51 from Brugg Kabel AG)is delivered in form of solid, free flowing pellets containing liquid XLP 51, a Silane based, 1 step cross-linking agent for unstabilised LDPE and LLDPE, designed for copper/aluminium conductor LV & MV power cables. Our special carrier technology has made it possible to successfully manufacture this highly concentrated batch.
Features:
His gives the user the following advantages:
Easy dosing into the mixer
A hazardous, highly reactive liquid, supplied in the form of dry, free flowing granules.
Safe and accurate dosing and dispersion in continuous compounding operations without the need
Of expensive injection Pumps. Easy dosing into the mixer
Higher onset temperature of the grafting agent provides higher thermal stability during the grafting and extrusion process giving less or no plate out on the screw and hence higher grafting efficiency.
Special stabilisers prevent premature polymerisation of the grafting agent and provide excellent ageing properties of crosslinked polyethylene.
Processing of Dry-Silane
for Low voltage Power Cable applications
Introduction
A typical Dry-Silane processing unit for the low voltage power cable production consists of the following units:
Raw materials
Base polymer:
The Dry-Silane technology can be used for a wide range of LDPE and LLDPE grades ensuring optimized cost effectiveness.
Dry-silane masterbatch:
Dry-silane masterbatches are delivered in the form of solid free flowing pellets.
The dry-silane masterbatches are available with different silane loadings (concentrations).
Depending on the different carrier resins and formula, the silane loading can be in the range of 40% up to 70%.
Antioxidant masterbatch:
In case unstabilized base materials are used an antioxidant masterbatch must be used.
Color masterbatch:
It is used for color identification purposes.
Usually color masterbatches are fed manually to the dosing system.
UV - stabilizator:
Aerial cables require the application of a UV stabilizator which is handled similar as a color masterbatch.
Raw material preparation
Dry-silane masterbatches are sensitive towards humidity; dry components have to be used.
Predrying of the base polymer to water contents below 300 ppm is required. The polymer transport from the dryer to the dosing station has to be carried out utilizing desiccant air coming from the drying system.
Never dry the dry-silane masterbatch!
In extrusion lines special care is taken that dry-silane masterbatches are in contact with silane resistant materials only.
Handling the dry-silane masterbatch
The shelf life time of the dry-silane masterbatch is apx.6 month. Once when the original packing is opened the dry silane masterbatch should be used up immediately.
Storing of the dry silane has to take place in cool and dry conditions.
Transport respectively storage temperatures above 55°C have to be avoided.
Dosing system
A gravimetric dosing system is absolutely necessary for dry-silane masterbatches with a high silane loading.
For masterbatches with a low silane loading, a volumetric system could be used, but we strongly recommend also for these masterbatches a gravimetric system.
Extruder
For applications, in which Dry-Silane as well as PVC compounds have to be processed, electrically heated/air cooled 24 D extruders are recommended.
Typical output figures of a 120 mm 24D machine are 270 kg/h XLPE, respectively 800 kg/h PVC (with individual screws)
For applications, in which Dry-Silane only has to be processed, 30 D machines are a good choice.
The XLPE output of a 120 mm 30 D extruder is apx. 300 kg/h.
In general we use for Dry-Silane applications shallow grooved feeding zones in combinations with barrier type screws.
Separate screws for PVC and dry-silane are provided. For PVC, standard nitrited screws are used; dry-silane XLPE requires screws with a special surface treatment.
Screw heating/cooling
A high performance screw cooling system is essential. Typically cooling capacities of apx. 50 kW is used for a 120 mm main extruder.
We use water based units because of the higher operational dynamic compared to oil based units.
Crosshead
For insulation applications on smaller cross sections usually fixed centered crossheads are used. Compression tooling is used for round conductors.
It is important that the parallel zone on the extrusion tools is kept short.
Best results have been achieved with max. 4mm parallel length.
Manually centered crossheads are commonly used for insulation applications on larger cross sections.
Sector shaped conductors are processed by means of tubing tools.
Die heating system
For improving the surface quality and to reduce the die drewal effect, a powerful die heating system is provided.
The die heating temperature has to be in the range of 300 ~ 320°C, therefore commonly burners (open flames) are used for this application.
Cooling trough
The use of a hot water section after the crosshead is essential. The cooling water temperature in this section is in the range of 60~80°C.
Crosslinking
For an estimation of the crosslinking time the following formula can be used:
|
T=Crosslinking time in hours
X=Insulation wall thickness in
mm
RH=Relative air humidity in %
K(T)=temperature factor
K(95°C)=1,2.10-4 K(90°C)=1,0.10-4
K(75°C)=0,8. 10-4 K(20°C)=0,1.10-4 |
Hot set test
The achievable hot set values depend on the absolute silane dosing rate.
The following chart shows the relation between hot set values, absolute silane concentration and line speed.
The data shown have been collected on the basis of a 1,5mm² insulated conductor.
Summary
The Dry-Silane process offers significant advantages compared to the other crosslinking methods for low voltage cables.
The Dry-Silane Technology can be considered as state of the art for this specific cable types in the meantime.
Cable manufacturers can utilize their well established Monosil or even normal Sioplas extruder to use dry silane.
For any additional information please do not hesitat
| |
Carrier type |
Active Silane contents, % |
Granule size, mm |
Bulk density, kg/liter |
| XLM50-EVA |
EVA |
40 |
4.5 x 2 x 3 |
230 ± 10 |
| XLM50-LD |
LDPE |
37 |
3 x 3 x 2.5 |
195 ± 10 |
| XLM50-LL |
LLDPE |
37 |
3 x 3 x 2.5 |
360 ± 10 |
| XLM50-HD |
HDPE |
31 |
3 x 2 x 3 |
250 ± 10 |
Audited Supplier 
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