Fans & thermal comfort Carbon loading


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polypropylene to prevent electrostatic discharge in ATEX environments


In this feature, ATEX fans examines how polypropylene corrosion resistant fans are modifi ed to enhance suitability for potentially explosive environments


T


o avoid electrostatic discharge, plastics used in explosive fume extraction systems that move air, or are situated in an area where


potentially hazardous fumes are present, must be electrically conductive or static dissipative. The most eff ective way of dissipating electrostatic discharge is to add conductive carbon black to the polymer matrix. For the context of this article, we’ll consider


how polypropylene corrosion resistant fans which are the preferred construction material used to handle toxic and hazardous fumes in fume extraction systems, are modifi ed to enhance the ATEX suitability for zone 2 potentially explosive environments. These ATEX certifi ed polypropylene fans are manufactured from polymers that have special branched carbons with a structure that can transport the fl ow of electrons and dissipate electrostatic charge. In potentially explosive environments, if the


conditions call for it, such as the build-up of IIC hydrogen gas in large quantities, the presence of static discharge can be enough to ignite and cause an explosion. The concept of ensuring a product is ATEX certifi ed ensures that the fan component in our case, is not itself, a risk or an ignition source. ATEX fans reduce the risks of creating sparks from friction, static electricity or from arcs in motor malfunctions for example. In ATEX product labelling, Ex h markings signify that the non-electrical fan component (excluding the motor) has been constructed suffi ciently to be used as intended in an explosive environment. In short, precautions during the manufacturing process have reduced this risk. By nature, without additives or fi llers, commercial plastics are electrical insulators. Charges deposited on the polymer surface are living therefore a long time, and the longer the lifetime, the more likely the possibility of an electrostatic discharge event such as static discharge. The rate of charge dissipation is known as the charge decay time, this considers the electric resistivity which tells us how strongly a material opposes the fl ow of electric current, and the dielectric permittivity, which characterises the ability of the material of storing an electrical charge when subjected to an applied voltage. For static dissipation, we must reduce the decay time of the charge, by enhancing conductivity and


10 April 2024


reducing permittivity. The loading of polymers with conducting additives reduces the resistivity of polymers.


Due to the presence of static charges, polymers must be turned into materials capable of draining these charges and protect the devices from static discharges. Therefore be able to conduct electricity to some extent. Commercial polymers are natural electrical insulators, so they need to be engineered to become anti-static dissipative or conductive. This is realised either through chemical treatment or through the addition of conductive agents during the processing.


One of those fi llers is known as carbon black,


a relatively inexpensive and processible fi ller material, formed by burning hydrocarbons in a limited oxygen environment. These are used


extensively in packaging but also used, as shown in our ATEX corrosion resistant range, for CB fi lled high density and low-density polypropylene. Simply put, carbon loading is a process in which


carbon black particles or fi bres are incorporated into the polypropylene during manufacturing. This addition of carbon enhances the conductivity allowing it to dissipate accumulated static charge more eff ectively, minimising the risk of ESD. Where airfl ow passes through fan blades, friction can generate static charges on the fan surfaces, and in environments with combustible materials, static charges can ignite or trigger an explosion So, in a nutshell, that’s how we ensure that our


ATEX polypropylene fans are manufactured in line with the ATEX directive, making them suitable for their intended use.


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