Final ReportSummary - FIRE SHIELD (An Innovative Soft Skinned Fire Resistant Cable for Fire Safety Applications Manufactured Using Integrated Cold Gas Dynamic Spraying and Polymer Extrusion Technologi
The main objective of the FIRESHIELD project is to develop a high performance, fire retardant mains cable that will exceed the current fire resistance and fire reaction performance of current soft skinned cables (as defined by EN50200, EN50266, EN50265 and EN50268). However, as a secondary application the project will also address the development of a fire retardant network data cable which is not currently available. The cables will be produced by using a pre-production prototype manufacturing process combining extrusion of a high-hardness fire resistant silicone or elastomeric rubber compound and in-line cold gas dynamic spraying system to deposit solid metallic shields directly onto the moving extruded cables. Cold gas dynamic spraying has been selected as the method to apply a conductive copper coating onto the elastomeric cable compound, replacing the need for a copper foil shield. To achieve the cold gas coating it is necessary to accelerate the metallic particles to embed and deform onto the sheathing compound.
Powder accelerator converging-diverging nozzle designs have been generated and analysed by computational fluid dynamics (CFD). To validate the performance against the theoretical models flat plate and circular nozzles were fabricated and Laser Doppler anemometry (LDA) was selected as the most suitable method for measurement of the air and particle velocities through the nozzle.
To develop a high-hardness elastomer, postulated to be more suitable for cold gas dynamic deposition, commercial grades of silicone rubber were compounded with fillers such as calcium carbonate, boehmite, mica and kaolin. The fire resistance properties of the developed compounds were measured by cone calorimetry at an irradiation of 50 kW/m2. The heat release rate (HRR) of the filled silicone rubber gave interesting fire retardant properties compared to the pure silicone. The presence of fillers decreased the maximum peak and flattened the curve of the HRR which is a required condition for a flame retardant system. Fillers in the form of platelets (mica, kaolin and glass flakes) clearly created a barrier effect that decreased the HRR, and an intumescent behaviour was observed. Cold gas dynamic spraying trials showed copper deposition was achievable onto all the silicone compounds but insufficient deformation occurred to form electrically conductive coatings. Softer metal powders, silver and tin showed increased particle deformation on impact, but only the costly silver coating conveyed electrical conductivity by cold gas dynamic spraying. The consortium then agreed the main focus of the project should be the production of a fire resistant compound having superior char strength to avoid crack formation during the BS EN 50200:2006 standard test, with the advanced feature of the BS 8434-2:2003 test. The best filled silicone formulations were those comprising 10 % of MicroMica W1 with either 10 % of CaCO3 Omyalite 90 or CaCO3 Snowcal. The mica is a lamellar aluminosilicate that may migrate to the surface during fire or appears at the surface of materials when it ablates due to thermal decomposition, and forms a gas barrier layer that limits the combustion. The calcium carbonate reacts with SiO2 forming wollastonite that acts as flame retardant by barrier effect. However, during the 830 °C test cracks formed in the silicone at various points along the conductor. These were attributed to poor dispersion of fillers during the compounding stage. To avoid cracks during the burn test the residue should present the lowest volume variation compared to the unburned sample and the residue must be cohesive. Hg displacement method and compression tests were performed to evaluate those two objectives respectively. Further research work showed that adding boehmite (AlO(OH)), precipitated calcium carbonate (PCC) and glass flake together gave very interesting results. Boehmite releases water around 350 °C then increases the volume, PCC decreases the volume and glass flake forms a glassy phase that increases the cohesion of the residue. Research will continue at l'Ecole des Mines d'Alès, France after the duration of the FIRESHIELD project to optimise the proportion of each filler to give the lowest volume variation with the highest maximum compression force.
Project context and objectives:
The particular aim of the FIRESHIELD project is to develop a soft skinned fire resistant cable that will be able to exceed the current fire resistance and fire reaction performance of current soft skinned cables (as defined by EN50200, EN50266, EN50265 and EN50268). The cables will be produced by using a pre-production prototype manufacturing process combining extrusion of a high-hardness fire resistant silicone or elastomeric rubber compound and in-line cold gas dynamic spraying system to deposit solid metallic shields directly onto the moving extruded cables.
To enable this, the specific technological objectives of our work were to:
- develop a high-hardness extrudable silicone or elastomeric rubber compound that will have a surface hardness of 80 Shore A;
- develop a cold gas dynamic spraying process for the deposition of copper powders of particle diameter 20 - 50 mm directly on to the extruded high-hardness silicone or elastomeric rubber annulus (whose diameter is down to 5 mm) at a speed of 3 m/sec;
- develop an integrated extrusion and cold gas dynamic spraying pre-production system for the production of the soft skinned fire resistant cable for the manufacture of FIRESHIELD cable of diameter 10 - 20 mm at an output speed of 3 m/s;
- develop a metal powder recovery and recycling system for the integrated extrusion / cold gas dynamic spraying pre-production system.
Project results:
The technical work programme over the period 1 October 2008 to 30 September 2010 has involved the following work packages (WPs):
WP1: Modelling of impact behaviour and fluid flow
WP2: Polymer compound developments
WP3: Cold gas dynamic spraying equipment development
WP4: Cold gas dynamic spraying onto polymer samples
WP5: Extrusion development
WP6: System integration and validation.
Cold gas dynamic spraying has been selected as the method to apply a conductive copper coating onto the elastomeric cable compound, replacing the need for a copper foil shield. To achieve the cold gas coating it is necessary to accelerate the metallic particles to embed and deform onto the sheathing compound. Previous research in the field of cold gas dynamic spraying has shown that to achieve sufficient energy the copper particles need to be travelling at supersonic speeds in the region of 300 - 400m/s and upwards.
Powder accelerator converging-diverging nozzle designs have been generated and analysed by CFD. The effects of air temperature, air pressure, nozzle length and rectangular or circular nozzle profile were all modelled to investigate the influence on the air velocity exiting the nozzle.
To validate the performance against the theoretical models flat plate and circular nozzles were fabricated and laser doppler anemometry (LDA) was selected as the most suitable method for measurement of the air and particle velocities through the nozzle.
The air speed was measured by passing a very fine seeding powder of aluminium oxide through the nozzle and making LDA measurements on the particles. As the 1µm aluminium oxide particles have a very small mass they are rapidly accelerated up to the air speed. The speed of the particles exiting the nozzle is therefore directly related to the speed of the air.
Spherical particles are aerodynamically favoured for cold gas dynamic spraying in order to achieve the required velocities for high-rate deposition. Irregular shaped particles suffer from drag in the air stream and are prone to friction through the de Laval nozzle. Speed measurements of spherical copper powders were carried out at a series of points across the X-Y direction of the flow and at various points along the Z axis to build up a picture of the distribution of the copper on the flow. In all cases, the highest velocities occurred in the centre of the air jet with the smaller particles showing the highest velocities typically 425 m/s for the circular profiled nozzle. Trial spraying onto a ceramic substrate produced a conductive track which showed that particles were achieving the required speed to deform on impact.
From a manufacturing point of view a rectangular nozzle offers the best solution as it can be machined fairly simply using conventional machine tools. However, the CFD work showed that the sharp corners of a rectangular nozzle create turbulent flow and form a series of shock waves which decelerate the copper particles. A circular profile was therefore selected and to ensure that the internal surfaces were smooth with no joint lines the nozzle was machined from a single piece of steel. The throat and the convergent-divergent profile were machined using electrical discharge machining (EDM) to ensure accuracy and to achieve a good surface finish.
Cold gas dynamic spraying normally involves the delivery of metallic powder into the nozzle before the throat. However, this is where pressures are at a maximum and therefore require the use of expensive high pressure powder delivery equipment. By feeding the powder into the low pressure side of the nozzle, that is, below the throat, reduces the complexity and cost of the powder feed process.
To determine the velocities and conditions required to deposit metal powders onto elastomers the impact behaviour and particle-to-substrate interactions were investigated experimentally by cold spray trials. Using CFD, it was possible to calculate the maximum outlet air velocity under different air temperature and pressure conditions. The influence of these conditions on the nature of the deposited coatings and the deposition efficiency of the process were assessed visually and scanning electron microscopy was employed to analyse the surface coating and depth of particle penetration. In general, penetration depth and size of the penetrating copper particle were found to increase with air velocity (a function of temperature and pressure) and air pressure.
To spray around the circumference of the cable a multi-nozzle array comprising of three identical circular nozzles was designed and manufactured, and an overspray vacuum system was developed to enable unused copper powders to be recovered and recycled. To demonstrate the prototype the cold gas dynamic spray system, multi-nozzle array, single powder delivery unit and the developed powder recovery system were integrated with cable feed and haul-off systems. Trials were carried out under various conditions, the main parameters being powder feed rate (100 - 250 rpm), air pressure (2 - 8 Bar), air temperature (50 - 400°C) and nozzle stand-off distance (10 - 70 mm).
To develop a high-hardness elastomer, postulated to be more suitable for cold gas dynamic deposition, commercial grades of silicone rubber were compounded with fillers such as calcium carbonate, boehmite, mica and kaolin. All the samples were press cured into sheets and shore A hardness and microindentation measurements were made; the mica filled compound displaying the highest hardness. Cold gas dynamic spraying trials showed copper deposition was achievable onto all the silicone compounds under all the trial conditions. The coatings were subsequently analysed by scanning electron microscopy, this showing the best coatings to be onto the mica and kaolin filled compounds.
The fire resistance properties of the developed compounds were measured by cone calorimetry at an irradiation of 50 kW/m2. The heat release rate (HRR) of the filled silicone rubber gave interesting fire retardant properties compared to the pure silicone. The presence of fillers decreased the maximum peak and flattened the curve of the HRR which is a required condition for a flame retardant system. Fillers in the form of platelets (mica, kaolin and glass flakes) clearly created a barrier effect that decreased the HRR, and an intumescent behaviour was observed.
A further requirement of the coating is electrical conductivity. This could be achieved onto a hard ceramic but insufficient deformation of the copper particles occurred onto the silicone compounds. Increasing the hardness of the compounds further was not an option as this would deem them unsuitable for extrusion and a flexible cable application.
Softer metal powders, silver and tin were investigated and these showed increased particle deformation on impact, but only the costly silver coating conveyed electrical conductivity by cold gas dynamic spraying. The thermal techniques of flame and arc spraying were examined as these methods apply coatings in the molten state. Both methods successfully deposited conductive copper coatings to cured and uncured silicone compounds.
The substantial cold gas and thermal spray investigations had showed that metallic coatings could be successfully applied to elastomeric compounds; however, the FIRESHIELD consortium concluded that neither process was likely to deposit a coating flexible enough for the shield application, nor produce a strong enough bond to the silicone formulations.
The industrial partners agreed that the project should continue with the polymer compound and extrusion development to produce superior fire resistance properties. The main focus would be the production of a fire resistant compound having superior char strength to avoid crack formation during the BS EN 50200:2006 standard test, with the advanced feature of the BS 8434-2:2003 test.
Ten formulations were upscaled and compounding and extrusion trials were carried out on the main production line at Ventcroft Ltd. Cables were tested to according to BS EN 50200:2006 'Method of test for resistance to fire of unprotected small cables for use in emergency circuits'. The best filled silicone formulations were those comprising 10 % of MicroMica W1 with either 10 % of CaCO3 Omyalite 90 or CaCO3 Snowcal. The mica is a lamellar aluminosilicate that may migrate to the surface during fire or appears at the surface of materials when it ablates due to thermal decomposition, and forms a gas barrier layer that limits the combustion. The calcium carbonate reacts with SiO2 forming wollastonite that acts as flame retardant by barrier effect. However, during the 830 °C test cracks formed in the silicone at various points along the conductor. These were attributed to poor dispersion of fillers during the compounding stage.
To avoid cracks during the burn test the residue should present the lowest volume variation compared to the unburned sample and the residue must be cohesive. Hg displacement method and compression tests were performed to evaluate those two objectives respectively. Further research work showed that adding boehmite (AlO(OH)), precipitated calcium carbonate (PCC) and glass flake together gave very interesting results. Boehmite releases water around 350 °C then increases the volume, PCC decreases the volume and glass flake forms a glassy phase that increases the cohesion of the residue.
Potential impact:
A final dissemination and use plan has been prepared by the consortium and will be submitted as part of the project final report, section 'Use and dissemination of foreground report'.
A project website was set-up at the beginning of the project to inform other SMEs of the FIRESHIELD objectives: http://FIRESHIELD.uk-matri.org/
Research will continue at l'Ecole des Mines d'Alès, France after the duration of the FIRESHIELD project to optimise the silicone cable compound formulation. This will be reported in research papers and in the Doctor of Philosophy (PhD) thesis by Siska Hamdani. As aspects of the research were carried out within the FIRESHIELD project, knowledgements to the European Commission (EC) and the project will be made. Publications to date include:
1. Siska Hamdani, Claire Longuet, José-Marie Lopez-Cuesta, François Ganachaud
Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices. I. Blend preparation and thermal properties - Polymer Degradation and Stability, Volume 95, Issue 9, September 2010, Pages 1911 - 1919.
2. Siska Hamdani, Claire Longuet, Didier Perrin, José-Marie Lopez-cuesta, François Ganachaud
Flame retardancy of silicone-based materials - Polymer Degradation and Stability, Volume 94, Issue 4, April 2009, Pages 465-495.
3. Siska Hamdani, Claire Longuet, Audrey Pommier, José-Marie Lopez-Cuesta, François Ganachaud
Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices. II. Résidue - Polymer Degradation and Stability, to be submitted.
4. Etienne Delebeck, Siska Hamdani, Julia Raeke, José-Marie Lopez-Cuesta, François Ganachaud
High Residue Contents Indebted by Platinum and Silica Synergistic Action during the Pyrolysis of Silicone Formulations, to be submitted.
Other communications by Siska Hamdani include:
- Eurofillers 2009 (Alessandria), Italy
- European Meeting on Fire Retardant Polymers (FRPM) 2009 (Poznan), Poland
- Les Journées d'Etude sur les Polymères (JEPO) 2009 St Etienne, France
- Groupe Français des Polymères, Méditerranée (GFP Méditerranée) 2010 Montpellier, France
- ISPO (7th International workshop on silicone-based polymers) 2010 (Lodz), Poland.
Further publications and communications will be made as the work progresses.
These developments, aspects of which were conducted within the FIRESHIELD project, will make a significant contribution to fire safety across the EU by enabling safety system manufacturers and installers to be able to access this cutting-edge cable technology. Figures from the World Fire Statistics Organisation has estimated that within the EU there are 2.5 million reported fires p.a. causing 20 - 25 000 deaths and 250 - 500 000 injuries. Maintaining the operational integrity of emergency systems has been identified as a major contributor to personal safety following the 9 - 11 terrorist attacks. Therefore, the introduction of the developed technology can reduce the effects of fire and impact health and safety by significantly increasing fire resistance.
Mr Frank Rotheram
Managing Director
Ventcroft Limited
Goddard Road
Ashmoor Industrial Estate
Runcorn
WA7 1NQ
United Kingdom
Tel. +44-192-8581098
Fax. +44-192-8581099
email: Frank@ventcroft.co.uk
Project website address: http://FIRESHIELD.uk-matri.org/
Powder accelerator converging-diverging nozzle designs have been generated and analysed by computational fluid dynamics (CFD). To validate the performance against the theoretical models flat plate and circular nozzles were fabricated and Laser Doppler anemometry (LDA) was selected as the most suitable method for measurement of the air and particle velocities through the nozzle.
To develop a high-hardness elastomer, postulated to be more suitable for cold gas dynamic deposition, commercial grades of silicone rubber were compounded with fillers such as calcium carbonate, boehmite, mica and kaolin. The fire resistance properties of the developed compounds were measured by cone calorimetry at an irradiation of 50 kW/m2. The heat release rate (HRR) of the filled silicone rubber gave interesting fire retardant properties compared to the pure silicone. The presence of fillers decreased the maximum peak and flattened the curve of the HRR which is a required condition for a flame retardant system. Fillers in the form of platelets (mica, kaolin and glass flakes) clearly created a barrier effect that decreased the HRR, and an intumescent behaviour was observed. Cold gas dynamic spraying trials showed copper deposition was achievable onto all the silicone compounds but insufficient deformation occurred to form electrically conductive coatings. Softer metal powders, silver and tin showed increased particle deformation on impact, but only the costly silver coating conveyed electrical conductivity by cold gas dynamic spraying. The consortium then agreed the main focus of the project should be the production of a fire resistant compound having superior char strength to avoid crack formation during the BS EN 50200:2006 standard test, with the advanced feature of the BS 8434-2:2003 test. The best filled silicone formulations were those comprising 10 % of MicroMica W1 with either 10 % of CaCO3 Omyalite 90 or CaCO3 Snowcal. The mica is a lamellar aluminosilicate that may migrate to the surface during fire or appears at the surface of materials when it ablates due to thermal decomposition, and forms a gas barrier layer that limits the combustion. The calcium carbonate reacts with SiO2 forming wollastonite that acts as flame retardant by barrier effect. However, during the 830 °C test cracks formed in the silicone at various points along the conductor. These were attributed to poor dispersion of fillers during the compounding stage. To avoid cracks during the burn test the residue should present the lowest volume variation compared to the unburned sample and the residue must be cohesive. Hg displacement method and compression tests were performed to evaluate those two objectives respectively. Further research work showed that adding boehmite (AlO(OH)), precipitated calcium carbonate (PCC) and glass flake together gave very interesting results. Boehmite releases water around 350 °C then increases the volume, PCC decreases the volume and glass flake forms a glassy phase that increases the cohesion of the residue. Research will continue at l'Ecole des Mines d'Alès, France after the duration of the FIRESHIELD project to optimise the proportion of each filler to give the lowest volume variation with the highest maximum compression force.
Project context and objectives:
The particular aim of the FIRESHIELD project is to develop a soft skinned fire resistant cable that will be able to exceed the current fire resistance and fire reaction performance of current soft skinned cables (as defined by EN50200, EN50266, EN50265 and EN50268). The cables will be produced by using a pre-production prototype manufacturing process combining extrusion of a high-hardness fire resistant silicone or elastomeric rubber compound and in-line cold gas dynamic spraying system to deposit solid metallic shields directly onto the moving extruded cables.
To enable this, the specific technological objectives of our work were to:
- develop a high-hardness extrudable silicone or elastomeric rubber compound that will have a surface hardness of 80 Shore A;
- develop a cold gas dynamic spraying process for the deposition of copper powders of particle diameter 20 - 50 mm directly on to the extruded high-hardness silicone or elastomeric rubber annulus (whose diameter is down to 5 mm) at a speed of 3 m/sec;
- develop an integrated extrusion and cold gas dynamic spraying pre-production system for the production of the soft skinned fire resistant cable for the manufacture of FIRESHIELD cable of diameter 10 - 20 mm at an output speed of 3 m/s;
- develop a metal powder recovery and recycling system for the integrated extrusion / cold gas dynamic spraying pre-production system.
Project results:
The technical work programme over the period 1 October 2008 to 30 September 2010 has involved the following work packages (WPs):
WP1: Modelling of impact behaviour and fluid flow
WP2: Polymer compound developments
WP3: Cold gas dynamic spraying equipment development
WP4: Cold gas dynamic spraying onto polymer samples
WP5: Extrusion development
WP6: System integration and validation.
Cold gas dynamic spraying has been selected as the method to apply a conductive copper coating onto the elastomeric cable compound, replacing the need for a copper foil shield. To achieve the cold gas coating it is necessary to accelerate the metallic particles to embed and deform onto the sheathing compound. Previous research in the field of cold gas dynamic spraying has shown that to achieve sufficient energy the copper particles need to be travelling at supersonic speeds in the region of 300 - 400m/s and upwards.
Powder accelerator converging-diverging nozzle designs have been generated and analysed by CFD. The effects of air temperature, air pressure, nozzle length and rectangular or circular nozzle profile were all modelled to investigate the influence on the air velocity exiting the nozzle.
To validate the performance against the theoretical models flat plate and circular nozzles were fabricated and laser doppler anemometry (LDA) was selected as the most suitable method for measurement of the air and particle velocities through the nozzle.
The air speed was measured by passing a very fine seeding powder of aluminium oxide through the nozzle and making LDA measurements on the particles. As the 1µm aluminium oxide particles have a very small mass they are rapidly accelerated up to the air speed. The speed of the particles exiting the nozzle is therefore directly related to the speed of the air.
Spherical particles are aerodynamically favoured for cold gas dynamic spraying in order to achieve the required velocities for high-rate deposition. Irregular shaped particles suffer from drag in the air stream and are prone to friction through the de Laval nozzle. Speed measurements of spherical copper powders were carried out at a series of points across the X-Y direction of the flow and at various points along the Z axis to build up a picture of the distribution of the copper on the flow. In all cases, the highest velocities occurred in the centre of the air jet with the smaller particles showing the highest velocities typically 425 m/s for the circular profiled nozzle. Trial spraying onto a ceramic substrate produced a conductive track which showed that particles were achieving the required speed to deform on impact.
From a manufacturing point of view a rectangular nozzle offers the best solution as it can be machined fairly simply using conventional machine tools. However, the CFD work showed that the sharp corners of a rectangular nozzle create turbulent flow and form a series of shock waves which decelerate the copper particles. A circular profile was therefore selected and to ensure that the internal surfaces were smooth with no joint lines the nozzle was machined from a single piece of steel. The throat and the convergent-divergent profile were machined using electrical discharge machining (EDM) to ensure accuracy and to achieve a good surface finish.
Cold gas dynamic spraying normally involves the delivery of metallic powder into the nozzle before the throat. However, this is where pressures are at a maximum and therefore require the use of expensive high pressure powder delivery equipment. By feeding the powder into the low pressure side of the nozzle, that is, below the throat, reduces the complexity and cost of the powder feed process.
To determine the velocities and conditions required to deposit metal powders onto elastomers the impact behaviour and particle-to-substrate interactions were investigated experimentally by cold spray trials. Using CFD, it was possible to calculate the maximum outlet air velocity under different air temperature and pressure conditions. The influence of these conditions on the nature of the deposited coatings and the deposition efficiency of the process were assessed visually and scanning electron microscopy was employed to analyse the surface coating and depth of particle penetration. In general, penetration depth and size of the penetrating copper particle were found to increase with air velocity (a function of temperature and pressure) and air pressure.
To spray around the circumference of the cable a multi-nozzle array comprising of three identical circular nozzles was designed and manufactured, and an overspray vacuum system was developed to enable unused copper powders to be recovered and recycled. To demonstrate the prototype the cold gas dynamic spray system, multi-nozzle array, single powder delivery unit and the developed powder recovery system were integrated with cable feed and haul-off systems. Trials were carried out under various conditions, the main parameters being powder feed rate (100 - 250 rpm), air pressure (2 - 8 Bar), air temperature (50 - 400°C) and nozzle stand-off distance (10 - 70 mm).
To develop a high-hardness elastomer, postulated to be more suitable for cold gas dynamic deposition, commercial grades of silicone rubber were compounded with fillers such as calcium carbonate, boehmite, mica and kaolin. All the samples were press cured into sheets and shore A hardness and microindentation measurements were made; the mica filled compound displaying the highest hardness. Cold gas dynamic spraying trials showed copper deposition was achievable onto all the silicone compounds under all the trial conditions. The coatings were subsequently analysed by scanning electron microscopy, this showing the best coatings to be onto the mica and kaolin filled compounds.
The fire resistance properties of the developed compounds were measured by cone calorimetry at an irradiation of 50 kW/m2. The heat release rate (HRR) of the filled silicone rubber gave interesting fire retardant properties compared to the pure silicone. The presence of fillers decreased the maximum peak and flattened the curve of the HRR which is a required condition for a flame retardant system. Fillers in the form of platelets (mica, kaolin and glass flakes) clearly created a barrier effect that decreased the HRR, and an intumescent behaviour was observed.
A further requirement of the coating is electrical conductivity. This could be achieved onto a hard ceramic but insufficient deformation of the copper particles occurred onto the silicone compounds. Increasing the hardness of the compounds further was not an option as this would deem them unsuitable for extrusion and a flexible cable application.
Softer metal powders, silver and tin were investigated and these showed increased particle deformation on impact, but only the costly silver coating conveyed electrical conductivity by cold gas dynamic spraying. The thermal techniques of flame and arc spraying were examined as these methods apply coatings in the molten state. Both methods successfully deposited conductive copper coatings to cured and uncured silicone compounds.
The substantial cold gas and thermal spray investigations had showed that metallic coatings could be successfully applied to elastomeric compounds; however, the FIRESHIELD consortium concluded that neither process was likely to deposit a coating flexible enough for the shield application, nor produce a strong enough bond to the silicone formulations.
The industrial partners agreed that the project should continue with the polymer compound and extrusion development to produce superior fire resistance properties. The main focus would be the production of a fire resistant compound having superior char strength to avoid crack formation during the BS EN 50200:2006 standard test, with the advanced feature of the BS 8434-2:2003 test.
Ten formulations were upscaled and compounding and extrusion trials were carried out on the main production line at Ventcroft Ltd. Cables were tested to according to BS EN 50200:2006 'Method of test for resistance to fire of unprotected small cables for use in emergency circuits'. The best filled silicone formulations were those comprising 10 % of MicroMica W1 with either 10 % of CaCO3 Omyalite 90 or CaCO3 Snowcal. The mica is a lamellar aluminosilicate that may migrate to the surface during fire or appears at the surface of materials when it ablates due to thermal decomposition, and forms a gas barrier layer that limits the combustion. The calcium carbonate reacts with SiO2 forming wollastonite that acts as flame retardant by barrier effect. However, during the 830 °C test cracks formed in the silicone at various points along the conductor. These were attributed to poor dispersion of fillers during the compounding stage.
To avoid cracks during the burn test the residue should present the lowest volume variation compared to the unburned sample and the residue must be cohesive. Hg displacement method and compression tests were performed to evaluate those two objectives respectively. Further research work showed that adding boehmite (AlO(OH)), precipitated calcium carbonate (PCC) and glass flake together gave very interesting results. Boehmite releases water around 350 °C then increases the volume, PCC decreases the volume and glass flake forms a glassy phase that increases the cohesion of the residue.
Potential impact:
A final dissemination and use plan has been prepared by the consortium and will be submitted as part of the project final report, section 'Use and dissemination of foreground report'.
A project website was set-up at the beginning of the project to inform other SMEs of the FIRESHIELD objectives: http://FIRESHIELD.uk-matri.org/
Research will continue at l'Ecole des Mines d'Alès, France after the duration of the FIRESHIELD project to optimise the silicone cable compound formulation. This will be reported in research papers and in the Doctor of Philosophy (PhD) thesis by Siska Hamdani. As aspects of the research were carried out within the FIRESHIELD project, knowledgements to the European Commission (EC) and the project will be made. Publications to date include:
1. Siska Hamdani, Claire Longuet, José-Marie Lopez-Cuesta, François Ganachaud
Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices. I. Blend preparation and thermal properties - Polymer Degradation and Stability, Volume 95, Issue 9, September 2010, Pages 1911 - 1919.
2. Siska Hamdani, Claire Longuet, Didier Perrin, José-Marie Lopez-cuesta, François Ganachaud
Flame retardancy of silicone-based materials - Polymer Degradation and Stability, Volume 94, Issue 4, April 2009, Pages 465-495.
3. Siska Hamdani, Claire Longuet, Audrey Pommier, José-Marie Lopez-Cuesta, François Ganachaud
Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices. II. Résidue - Polymer Degradation and Stability, to be submitted.
4. Etienne Delebeck, Siska Hamdani, Julia Raeke, José-Marie Lopez-Cuesta, François Ganachaud
High Residue Contents Indebted by Platinum and Silica Synergistic Action during the Pyrolysis of Silicone Formulations, to be submitted.
Other communications by Siska Hamdani include:
- Eurofillers 2009 (Alessandria), Italy
- European Meeting on Fire Retardant Polymers (FRPM) 2009 (Poznan), Poland
- Les Journées d'Etude sur les Polymères (JEPO) 2009 St Etienne, France
- Groupe Français des Polymères, Méditerranée (GFP Méditerranée) 2010 Montpellier, France
- ISPO (7th International workshop on silicone-based polymers) 2010 (Lodz), Poland.
Further publications and communications will be made as the work progresses.
These developments, aspects of which were conducted within the FIRESHIELD project, will make a significant contribution to fire safety across the EU by enabling safety system manufacturers and installers to be able to access this cutting-edge cable technology. Figures from the World Fire Statistics Organisation has estimated that within the EU there are 2.5 million reported fires p.a. causing 20 - 25 000 deaths and 250 - 500 000 injuries. Maintaining the operational integrity of emergency systems has been identified as a major contributor to personal safety following the 9 - 11 terrorist attacks. Therefore, the introduction of the developed technology can reduce the effects of fire and impact health and safety by significantly increasing fire resistance.
Mr Frank Rotheram
Managing Director
Ventcroft Limited
Goddard Road
Ashmoor Industrial Estate
Runcorn
WA7 1NQ
United Kingdom
Tel. +44-192-8581098
Fax. +44-192-8581099
email: Frank@ventcroft.co.uk
Project website address: http://FIRESHIELD.uk-matri.org/