Although not an actual cover grade in its own right, in environments where dust created by the conveying of coal, grain, biomass, fertilizer or other potentially combustible elements is present, the anti-static (electrostatic dischargeability) properties of a conveyor belt are a major safety consideration. Strict conformity to Directive 2014/34/EU (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive’) is applicable to potentially explosive atmospheres of zones 20, 21 and 22 where combustible dust is present. Despite the claims of some manufacturers, not all rubber belts are sufficiently anti-static. However, a major advantage of Dunlop “Made in Holland” belts is that they are all anti-static (ATEX 2014/34/EU) according to EN/ISO 284 international test methods. This means that they can be used in ATEX classified areas. Please be aware that ATEX risk assessments may require additional safety measures.
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ATEX certification: It is important to note that it is not possible to obtain an ATEX certificate for a conveyor belt because belts are classified as a component. ATEX certification only applies to the whole conveyor. When sourcing conveyor belts for use in ATEX regulated areas it is very important to ask for a copy of a certificate provided by an appropriate independent testing authority such as the German Institute Dekra Exam GmBH.
The ATEX standard is designed to help prevent dust or gas explosions in industrial environments, including conveyor systems carrying cargo such as coal, grain, and fertilizers. Health and safety experts determine if there are areas or ‘zones’ in industrial locations where there may be a risk of explosions. These are then classified depending on the severity of the risk. As a result, all equipment installed in these zones is legally required to comply with international ATEX safety standards. Conveyor belts must be conductive and therefore comply with the EN/ISO 284 international standard for electrostatic properties. EN/ISO 284 demands that the surface of the belt must be electro-statically dischargeable to enable the belt to conduct an electrical load. When the conveyor complies with the ATEX requirements the conveyor components will conduct the electrical load to earth via the metal framework of the conveyor. This prevents sparks that could cause an explosion.
The ISO 284 test is intended to ensure that the belt is sufficiently conductive to avoid the accumulation of electrical static charge which can be developed during its service use. The principle of the test is that the electric current of specified voltage is passed via electrodes through a suitably prepared test piece taken from the belt. The test prescribes the use of a contact agent (fluid) to ensure proper contact between the electrodes and the belt surface. The electrical resistance of the conveyor belt, when tested in accordance with this method, should not exceed the maximum resistance value of 300 MΩ.
Belts that may have fabric surfaces that are not covered by rubber such as slider belts and those for certain applications such as sawmills, for example, require even greater consideration than conventional belting. As previously explained, the ISO 284 test allows for the use of a contact fluid on the belt surface. However, when the test is carried out on the fabric (slider) surface, the fluid is partly absorbed by the fabric, which lowers the resistance of the fabric. For most applications, this degree of humidity is highly unlikely to occur so in the majority of cases the measured resistance according to the standard does not reflect normal operating conditions. This means that even though Dunlop Saw Mill and Slider belts fulfill the test criterion of the EN/ISO 284 standard on both belt sides, in an ATEX environment it will be necessary to enable the electrostatic charge on the belt to be conducted to earth via the rubber cover. Dunlop Saw Mill and Slider belts that have a rubber top cover have sufficient conductibility properties through the belt (tested according to EN 1637). This means that any electrostatic charge within the belt can be led to earth provided that the cover is connected to the earth.
IMPORTANT SAFETY ADVICE: Belts that have no rubber cover on either side (double-sided slider belts) will not be sufficiently conductive to meet the EN/ISO 284 standard in dry conditions and therefore should not be used in ATEX classified zones.
Posted on 2/17/2023
AS, ESD and HC. Just throwing around letters? No. Those are all electrical abbreviations that apply to conveyor belting and in some cases to the conveyor as a whole. Let’s look into these terms, and the conveying applications where they may be used.
If you haven’t already guessed it, AS stands for anti-static. So, what does anti-static (or antistatic) mean? According to the Oxford dictionary it is an adjective meaning: preventing the buildup of static electricity or reducing its effects. In the case of antistatic conveyor belts, they are designed to provide electrical resistance to that buildup of static electricity.
Different belt manufacturers make their belts differently, this is also true for anti-static belts. However, the most common way to construct these belts requires that an electrically conductive antistatic agent be imbedded into the belt. Some manufacturers may choose to coat their belt with this agent, however, in order to ensure long and reliable belt life mk North America typically does not use these belts on their antistatic conveyors. For added confidence in the belts antistatic capabilities be sure to ask what the belt’s antistatic resistivity is. Some of mk’s belt suppliers have belts that measure at less than 1010 ohms/squared (1010 Ω/sq.) while others are measured to different standards (ISO 21178) lengthways is parallel to the surface of the belt RDi < 3 x 108 Ω.
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But how can a conveyor have a build up of static electricity? Static electricity is generated in a conveyor between the underside of the conveyor belt and the dead plate on the conveyor due to the constant motion of the belt on the plate – very similar to rubbing a balloon on your hair and watching you hair stand on end. These belts can also be used to address the issue of static discharge between the product and the top surface of the belt. Static discharge can also attract dust and other minute particles, it can ignite flammable items, it can destroy sensitive electrical components and in some cases even disturb the line operators.
Industries that Are Concerned About Static Electricity in Conveyor Belting
Some of the industries that are concerned about the static electricity build up on a conveyor can seem obvious based on what we discussed in the paragraph before.
It seems like there is a lot an AS belt can do, so why do we also need ESD belts? Simply put, ESD belts offer more static discharge capabilities than an anti-static belt. Similar to the different ohm rating we saw with antistatic belts, ESD belts from different manufacturers will have different ohm ratings as well.
Some conveyor belt manufacturers, such as Forbo-Siegling, even offer a Highly Conductive (HC) belt which is one of the highest rated electrostatic dissipative belts on the market.
In the end, the question of “why do we also need ESD belts” comes down to the application requirements. And working with a conveyor company, such as mk North America, who has relationships with a variety of belt manufacturers can help ensure the belt selected for your application is the belt needed for your application.
Many applications also require the conveyor to also be grounded, in order to give the static electricity some place to go. Conveyor can be equipped with devices that provide an “outlet” for the static electricity, but the location in which the conveyor is going also needs to be prepped to provide the grounding mate or anchor. For operators that work on conveyor lines in sensitive areas they may be required to wear grounding wrist bands and/or have workstations that are equipped with anti-static mats that are also grounded.
mk’s line of belt conveyors, particularly the GUF-P 2000 and GUF-P 2041, can easily be outfitted is AS, ESD or HC belts and grounding devices. Our chain conveyors, which feature steel chains, can be built using anti-static wear strips (the channel in which the chain rides). Timing belt conveyors can be built using similar antistatic wear strips, and the timing belts themselves can be coated (topside, tooth side, or both) in an antistatic coating. If you are ready to learn more or want to get started on a project fill out the form below or call us at (860) 769-5500 and we will be happy to assist you.
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