Diesel Resistant RTV Silicone Sealant
Modern diesel engines require gaskets to seal a variety of components including fuel systems and control units. RTV silicones have been used with in and around the engine for many years, being chosen for their flexibility and ability to with stand high temperatures. For use within a diesel engine the gasket material must be able to withstand the temperatures generated from the engine but most importantly, must be able to withstand the continual contact with diesel fuel.
In general silicone RTV sealants are prone to attack from mineral oils. To overcome this problem silicone RTV's can be formulated using fluorosilicone polymers, however the dramatic increase in costs usually prohibits their commercial use.
ACC have taken one of their patented acetone cure RTV silicone sealants and carried out extensive testing to prove their suitability for applications involving contact with both conventional and bio-diesel fuels.
Technical Data*
Cure type: Acetone
Colour: Black
Tack free: 4 min
SG: 1.05
Extrusion rate: 169 g/m
Temp range: -50oC to +220oC
Hardness (Duro): 35 shore A
Tensile: 1.81 MPa
Elongation: 353%
Tear: 6.00 kN/m
*for full product data refer to technical data sheet
Additional testing would be required to establish the fuel resistance of the Acetone cure silicone. In addition to testing with standard grade diesel, tests would be carried out using RME (Rapeseed Methyl Ester) Bio-grade diesel.
Testing
As a supplier to the aerospace industry for well over 25 years ACC silicones are well qualified to carry out an extensive rage of material testing within their own facilities. In addition to the standard tests carried out under their own stringent quality control and development procedures, ACC commissioned a specialist outside testing house.
ACC employed MERL (Materials Engineering Research Laboratories) to carry out tests using Liquid F diesel (ISO1817) and RME diesel (DIN EN 14214) at ambient and elevated temperatures relating to common demands of automotive applications. Mechanical stress testing, heat capacity and modulus changes over the working temperature range were all measured to provide comprehensive data on the suitability of AS1810 as a gasket sealer in fuel contact applications.
As a brief summary, the AS1810 showed suitable resistance to both Liquid F Diesel and RME Diesel to remain useful as a gasket, even after 1000 hours at 100°C to simulate long term contact with the test fuels. There was expected loss in physical strength but no chemical breakdown was observed.
DMA analysis at temperature extremes showed minimal changes in the elastic properties of AS1810 from -45°C to 60°C proving the suitability of the material for terrestrial conditions without the influence of heat from the exhaust and engine areas of the vehicle.
Specific heat capacity testing i.e. the amount of energy required to ra ise the temperature of the test material revealed that AS1810 requires substantial energy to raise the temperature by 1°C in comparison to metallic materials. This demonstrates that AS1810 is a good insulator of heat and would also require a longer time period to dissipate the heat and return to ambient conditions. It has been commonly known that silicones need to be filled with conductive materials to change the heat capacity and thermal management properties, ACC also have a range of specific products that are designed to meet these needs.
Summary
Extensive testing proved AS1810 suitable for use with conventional and Bio-diesel when used as a gasket material in conjunction with mechanical fixings.
Sean Stoodley
European Technical Manager