The Ultimate Buyer's Guide for Purchasing Burning Resistant Conveyor Belt

Fire is one of the most destructive and dangerous forces known to man, destroying everything in its path. Insurance companies are becoming increasingly alarmed about conveyor fires. Anecdotal, as well as factual evidence gained from numerous laboratory tests, certainly indicates that even some of Europe’s biggest users of conveyors, are using belts that do not meet the claims of the supplier. Here, Rob van Oijen, one of Europe’s top application engineers, provides an essential guide to choosing fire resistant conveyor belts. 

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Combustible environments

In environments where potentially combustible materials such as coal dust, fertilizer, grain or biomass are present, it is essential that the conveyor belt cannot create static electricity that could ignite the atmosphere. Belts need to be able to allow static electricity to pass through the metal frame of the conveyor structure down to earth rather than allow static to build up. The safest approach is for all belts to meet EN Category 1, which demands that the belt is anti-static and conforms to EN ISO 284 international standards. This means that they meet the primary requirement for use in ATEX 114 (Directive /34/EU) classified zones if necessary. 

Basic grades of fire-resistance

The basis of most tests for belting fire resistance is EN ISO 340* and is included within the classifications of EN on electrical and flammability safety requirements for general purpose conveyors used above ground. These standards make the distinction between fire resistance with covers, which is Class 2A (or often referred to as K grade) and fire resistance with and without covers, which is Class 2B (or often referred to as S grade). The relevance of “with and without covers” is primarily because the rubber skim layers between the synthetic plies protect what is essentially the most flammable part in the construction and which can actually be the path for flames to propagate. The rubber skim material therefore needs to be as equally fire resistant as the outer covers. Worryingly, manufacturers who want to minimise costs to achieve a more competitive price often use rubber skims that have insufficient resistance to fire.

For the majority of ‘open air’ applications, EN Class 2A (K grade) or Class 2B (S grade) levels of fire resistance should be perfectly adequate. The best way to decide between Class 2A and Class 2B is to consider the material being carried. For moderately abrasive materials, then Class 2A is usually suitable. However, if the material is more abrasive then the safest option is to choose Class 2B.

*EN/ISO 340 tests involve exposing six individual samples of belt to a naked flame causing them to burn. The source of the flame is then removed and the combustion time (duration of flame) of the test piece is recorded.  A current of air is then applied to the test piece for a specified time after the removal of the flame. The flame should not re-ignite. 

The time it takes for the belt sample to self-extinguish after the flame has been removed is then measured. The duration of continued burning (visible flame) should be less than 15 seconds for each sample with a maximum cumulative duration of 45 seconds for each group of six tests. This means that the average allowable time per sample is 7.5 seconds. This factor is of paramount importance because it determines the distance that the fire can be effectively carried by a moving belt. 

Even if a manufacturer states that their belt has passed the ISO 340 test, caution should still be exercised. A typical conveyor belt can easily travel more than 40 meters within the 15 seconds that is allowable for a belt sample to pass the test, which is a potentially very dangerous distance. For this reason, Fenner Dunlop in The Netherlands strive for an average maximum time limit of less than one second, which is more than six times faster than the required standard. 

Conveying biomass

A higher level of fire resistance for conveyors handling biomass is necessary. One of the biggest dangers is dust emission. In the production process of biomass wood pellets, wood chip and similar renewable resources, the materials are continually broken down. This results in high levels of combustible dust that can be easily ignited by static electricity. Biomass dust can also be highly prone to self-ignition, especially if it becomes damp. A chemical reaction can take place that causes self-heating and what is referred to as “off-gassing” (carbon dioxide, carbon monoxide and methane emissions). 

Because of the increased risk of self-ignition, the use of covered conveyors is becoming increasingly commonplace. In enclosed environments the risk of human life is heightened because burning rubber and other synthetic materials such as polyester and nylon release thick toxic smoke that contains cyanide, carbon monoxide, sulfur dioxide, and products of butadiene and styrene. For this reason, EN  Class 4A is usually the best choice for conveyors operating in closed or covered conditions because it involves a more severe fire test according to EN-1 method A, C or D in addition to EN/ISO 340 testing. 

Rubber compounds that have a combined resistance to both fire and oil are available for materials that contain oil. This is an important consideration, so it is necessary to be very specific when requesting quotations from manufacturers and suppliers. If you are still unsure of what grade you need then do not hesitate to seek expert advice. 

For the majority of manufacturers, the chemical ingredients used to create fire-resistant rubber have an adverse effect on its wear resistant properties so fire resistant belts tend to wear faster. As the thickness of the rubber reduces so does the level of protection given to the inflammable carcass so always look at the manufacturer’s technical datasheet to check that the abrasion figure is no higher than 160 mm³.

Choosing the right supplier

Deciding on the correct grade of fire-resistant belt is much easier than deciding who should supply that belt. Always select a supplier that has a reputation for quality, who will be easy to reach and communicate with and who will provide a high standard of professional technical support. Most importantly of all, always select belts based on their safety and longevity (whole life cost) rather than for short-term ‘economic’ or budgetary motives. Experience categorically shows that the price of the belt will invariably be reflected in its overall quality and its ability to self-extinguish fire in good time. 

The biggest source of low-price, low-grade belting is Southeast Asia, primarily China. Their low prices are usually attributed to much lower labour costs, but this is a fallacy because labour accounts for as little as 5% of the total production cost. The real reason for the difference in price is that raw materials, including the expensive chemicals needed to create rubber that has a good standard of resistance to fire, ozone & ultraviolet, oil and wear, represent up to 70% of the cost of producing a conveyor belt. Consequently, the only way to manufacture a low-price belt is to use low-price (low grade), raw materials and/or minimise or omit the use of key ingredients. This is confirmed by extensive laboratory testing that shows that some so-called ‘fire-resistant’ belts actually burn like paper and up to 90% of all belts sold in Europe are not even resistant to the damaging effects of ground-level ozone and ultraviolet light.

Of equal concern is that manufacturers located outside of the Europe are not subject to REACH (Registration, Evaluation and Authorisation of Chemical substances) and POP’s (Persistent Organic Pollutants) regulations. This provides them with an open door because they are free to use unregulated chemicals, which cost much less compared to their regulated counterparts, even though they may be entirely prohibited or at least have strict usage limitations within Europe. 

Always check the provenance 

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Even if the manufacturer is based in Europe, always ensure that you are totally confident of the true provenance (origin) of what you are being quoted for by asking for certified confirmation of the actual place of manufacture rather than where the belt will be shipped from. This is important because, with the exception of Fenner Dunlop in The Netherlands and North America, virtually all manufacturers supplement their production with imported belting. 

Conveyor belt specialist Jeremy Clark shares his essential dos and don’ts when buying industrial conveyor belts.

Conveyors are indispensable but expensive pieces of equipment. With operating budgets under continuous scrutiny from senior management, it is all too easy to make a costly mistake when buying conveyor belts. Here, conveyor belt specialist Jeremy Clark shares what he considers to be the most important dos and don’ts when buying industrial conveyor belts.

Check the specifications

Never assume that the specifications of your conveyor belts are correct. Most conveyors have been in operation for a number of years. During their lifetime they are likely to have been operated by several different managers and maintenance personnel. It never fails to surprise me to find that mistakes have been made by the original builders of the conveyor when calculating the belt specification best suited to the conveyor. Likewise, subsequent attempts to solve problems such as rapid wear and ripping and tearing, may have resulted in the wrong specification of belt being fitted. The same applies if the material mix or volumes have changed significantly. It is imperative that the belt specification always matches the conveyor design and the materials being conveyed. 

For example, belts that are too thick for the design of the application can cause problems such as excessive rigidity (lack of troughability) and steering and handling difficulties. The same applies to tensile strengths that are too high. It is important to remember that for every step increase in tensile strength, the pulley and drum diameters need to be increased by 25%. The belt carcass may fail due to dynamic stress if this action is not taken. Quality belt manufacturers and their service partners who supply and fit their belts, will have experienced engineers. When provided with sufficient information, they can verify the belt selection.

Select belts based on durability

Always select belts based on their durability, suitability and longevity (whole life cost) rather than for short-term ‘economic’ or budgetary motives. Experience shows, without doubt, that the price of the belt will invariably be reflected in both its quality of performance and the length of its working life. I regularly see cases where a good quality belt can produce a working life of more than five years compared to low-grade belts that have been purchased on the basis of their low price but need regular repairs and then have to be replaced after only a year or two, often less.

The biggest source of low-price, low-grade belting is, of course, the Far East, primarily China. Their prices may be very tempting, but it is important to understand how those prices are achieved. The ‘lower labour costs’ argument is a fallacy because the labour element accounts for as little as 5% of the production cost. The true reason for the difference in price is that raw materials make up to 70% of the cost of producing a conveyor belt. Consequently, the only way to manufacture a low-price belt is to use low-price (low grade), unregulated raw materials. There simply is no other way. Cost-cutting practices include using cheap, low-grade carbon black made by burning old car tyres, the use of ‘bulking fillers’ such as clay instead of good quality polymers and using low-grade inner synthetic plies. The two best indicators of poor quality rubber are its low price and its pungent smell. Good quality rubber rarely has any smell at all. As the old saying goes, price is what you pay but cost is what you spend.

Choose belts in the standard stock range

Always (unless significant quantities are involved), choose belts from within the manufacturers standard stock range whenever possible Any deviation from the standard specification of a belt held in stock means that the belt would have to be made to special order, invoking higher production costs and potential minimum length order quantities. It also increases the delivery lead time, which can be especially bad newsif a belt needs to be replaced inan emergency.

Only buy belts when you are totally confident of their provenance (manufacturer’s origin) and where the manufacturer clearly states the level of anticipated performance rather than simply claiming to have been tested to a certain standard. Unfortunately, in today’s market, with the exception of Fenner Dunlop in The Netherlands and North America, nearly all manufacturers now supplement their production with imported belting, mostly from the Far East. My advice is to always ask for certified confirmation of the actual place of manufacture.

Consider the belt edge

Avoid over-specifying the type of belt edge. This may surprise you, but it can have a very significant impact on belt costs, repairs, maintenance, lost production and lead times. Many years ago, moulded edges (fully covered in rubber) were the standard because cotton was used as the reinforcing fabric in multi-ply belts. A moulded edge was therefore essential to prevent moisture penetrating the cotton fabric and causing it to rot. Since the introduction of synthetic ply fabrics using polyester and polyamide, this problem effectively no longer exists. Despite this, many conveyor operators and their buying departments continue to specify moulded edges, even though they do not provide any structural or performance advantage and can actually be susceptible to damage if the belt wanders off-track.

Nowadays, the most commonly used type of belt edge is the ‘cut & sealed edge’ or simply ‘sealed edge’, which is sufficient to prevent moisture being drawn into the carcass from the edge by capillary forces. Although the synthetic fibre plies are barely affected, moisture can ultimately cause vulcanising problems when making splice joints. A sealed edge also enables a belt to be used in very wet conditions and makes it better suited to long-term storage outdoors.

The reason why it is important not to over-specify the type of belt edge is that manufacturers need to manufacture belts at the optimum width and length for cost and production efficiency. Consequently, standard width stock belts are usually made as wide as the manufacturing machinery will allow, creating huge rolls known as ‘slabs’. These are then cut and sealed to create a range of narrower widths. For example, using metric measurements in this case, 400 meters of 2,200mm wide belt ‘slab’ would be manufactured and then be slit (cut) to produce 400m of 1,000mm wide belt and 400m of 1,200mm wide. This is why the vast majority of rubber multi-ply belting held in stock by manufacturers, distributors and traders has sealed edges. Moulded edges can only be created when a belt is manufactured in isolation and to an exact width. Consequently, the manufacturer is unable to achieve optimum production line efficiency, the cost of which has to be reflected in the selling price.

Ensure the belt is UV and Ozone resistant

Never order a conveyor belt without first obtaining written confirmation from the supplier/manufacturer that the belt being supplied is fully resistant to ozone and UV. As every manufacturer of rubber products will know only too well, at high altitude ozone (O3) acts as a protective shield by absorbing harmful ultraviolet rays but at low altitude, it becomes a pollutant that attacks the molecular structure of rubber. Ground level ozone increases the acidity of carbon black surfaces with natural rubber, polybutadiene, styrene-butadiene rubber and nitrile rubber being the most sensitive to degradation. The reaction that occurs is known as ozonolysis.

The first visible sign is when cracks start to appear in the surface of the rubber. Further attacks then occur inside the freshly exposed cracks, which continue to grow steadily until they complete a ‘circuit’ and the product separates or fails.

Ultraviolet light from sunlight and fluorescent lighting also has a seriously detrimental effect on rubber because it accelerates rubber deterioration by producing photochemical reactions that promote the oxidation of the rubber surface resulting in a loss in mechanical strength and wear resistance. This is known as ‘UV degradation’. The combination of ozone and UV has a seriously limiting effect on the operational lifetime of a rubber belt, regardless of geography or type of climate.

Fortunately, ozone and ultraviolet damage is easy to prevent. Unfortunately, laboratory testing consistently reveals that some 90% of belts tested according to EN ISO /1 procedure B static ozone resistance test are not resistant. In fact, the vast majority typically start to crack within the first 6 to 8 hours of the 96-hour test duration. This is because the anti-ozonants needed to protect the rubber have been omitted from the rubber compound mix because of cost so always insist on ozone & UV resistance when selecting any rubber conveyor belt.

Choose specifically engineered belts

Choose belts that are specifically engineered for the conditions they are required to cope with. This is especially important on sites where rip, tear and impact damage problems occur. Attempting to solve the problem by fitting belts with thicker covers and heavier carcasses is invariably a mistake. Simply using more of the same material will not provide the solution. As mentioned earlier, thicker, heavier belts can also cause other problems including lack of troughability, steering and handling problems and dynamic stress due to the pulleys and drums now being
too small.

The most economical solution is to fit a conveyor belt that has been specially designed for the purpose, such as Fenner Dunlop’s UsFlex, Nova X and Ultra X range belts that are proven to last up to four or five times longer than conventional multi-ply conveyor belts.  The initial buying price might be appreciably higher, but the cost will be substantially less over the working life of the belt, with the added benefits of far less repairs, change-out costs and disruption to output.

Choose the right belt supplier

Always choose a belt supplier who you can rely on to be accountable in the event of a problem. It is important to have a supplier that will readily provide a high standard of professional technical support and who has a good reputation for quality. This, I feel, should always be an essential part of the criteria when choosing a supplier. A tall order perhaps, but they do exist.

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