A guide to conveyor belt buying

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 1431/1 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.

More information at Fenner Dunlop.