If the Belt is on Fire

Belt Conveyor Safety

If the Belt is on Fire

A Guide to fire-retardant Conveyor Belts
Playing with fire!? - Belt conveyors are sophisticated equipment widely used in the transportation business. Most often, nevertheless, their function is of paramount importance for the plants they serve: If the belt conveyors fail, the plant (or port) might be paralysed, so their weaknesses should always be kept in mind.
(ed. WoMaMarcel - 27/7/2015)
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ATEX regulations apply to industrial environments where there is a risk of explosion because dust or gas is present in the atmosphere. For those organizations that are buying conveyor belts for use in ATEX regulated areas it is very important to ask potential suppliers for a copy of a certificate provided by an appropriate independent testing authority such as Dekra Exam in Germany.

Interestingly, a belt that has good anti-static properties is also a good indication of the quality of the rubber used on the belt. All (black) rubber belts contain carbon black, which is an ingredient in the rubber compound needed to achieve good mechanical properties. The higher the quality of carbon black used to produce the rubber compound then the better anti-static properties it will have. 

Above-ground and general Service Applications

Because fire safety is such an important issue there are numerous safety classifications and international standards for which there are many different tests used to measure the self-extinguishing properties of conveyor belts. Rubber belts reinforced by layers of textile fabrics (multi-ply) or steelcord reinforcement are the most commonly used type for transhipment and in general service applications. The basis of most tests for belting used in normal industrial applications is EN/ISO 340. This standard makes the distinction between fire resistance with covers (K) and fire resistance with and without covers (S).

The relevance of “with and without covers” is that as belt covers wear during their operational life the amount of fire resistant rubber protecting the flammable carcass reduces. The best way to decide between ‘K’ and ‘S‘ grades is to consider the material being carried. For moderately abrasive materials such as grain, biomass for example then ‘K’ grade is usually perfectly adequate. This also applies to elevator belts. However, if the material is abrasive and tends to wear the top cover quite rapidly then the safest option is be to choose the ‘S‘ (Class 2B) grade.

In both ‘K’ and ‘S’ grades, the rubber skim that bonds the fabric layers of the carcass together should also be fire resistant. In the case of ‘S’ grade (fire resistant without covers), the rubber skim should be thicker than the skim used for ‘K’ grade. The easiest way to tell if a ‘K’ grade belt has the required thicker rubber skims is to obtain technical datasheets from the manufacturer for both ‘S’ grade and ‘K’ grades and compare the carcass thickness figures. 

Another important reason why buyers should always request technical datasheets before placing an order is that they include information on the level of abrasion (wear) resistance. The ingredients used to create a fire resistant rubber compound generally have an adverse effect on its wear resistant properties. Consequently, fire resistant belts tend to wear faster and as the thickness of the rubber reduces so does the level of protection given to the inflammable carcass. To avoid premature wear, in the case of purely fire resistance belting, buyers should always demand an average abrasion resistance level of no more than150mm³.

Dunlop BV XS conveyor on the left stopped the spread of fire.

Thankfully, at Dunlop our rubber compound technicians have proved that it is possible to have the best of both worlds by developing a fire resistant rubber that also has good resistance to abrasion. In fact our technicians have created a compound that has 50% better wear resistance than the DIN Y standard for abrasion resistant rubber. This means that the belt retains its resistance to fire for much longer and at the same time extends the operational lifetime by the same proportion. However, laboratory tests have revealed that this is very much an exception to the rule within the conveyor belt industry.

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