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Conveyor Design

Specifying the Right Belt Choice

Duncan Gornall, Fenner Drives

As seen in Power In Motion magazine, April 2007

There are many factors and many choices for designers, production managers, and maintenance engineers to consider when designing a conveying system; not least what type of belt will best suit the application.

Chain, timing belts, polyurethane belts, polyester reinforced belts, flat belts, detachable belts and table top modular chain are all widely used on conveying systems around the world. Each has distinct features and distinct characteristics. With such a range of choices, how can the Equipment Designer or Maintenance Engineer be sure he is specifying the optimum? Simply replacing the failed belt with a like or similar solution may not solve the problem long term; it may be time to look at alternatives.

When designing a conveyor system there are many factors to consider such as the item being conveyed, its weight, dimensions and material properties, the length of the conveyor span, the operating conditions, whether the conveyor has to be synchronized to another process and whether it requires accumulation or high grip. Once these questions have been considered and specification found it is time to assess which type of belt is best for the application.

Metal chain Metal chain is one of the most common methods of conveying in the world today on such things as pallet conveyors, lumber processing and heavy duty warehousing systems. The main attraction of chain is its strength being able to convey very large or heavy items up to several thousand kilograms. In general, standard chain is relatively inexpensive, although certain specialist chains with attachments or special toppings can be expensive. While chain works well in many applications, there are inherent problems. Chain can be noisy in operation, a major health and safety consideration. Chain also requires a significant amount of maintenance such as lubrication and tensioning.

There is a risk of damage to the product being conveyed either due to the hard irregular surface or from contamination or staining from oil which makes it unsuitable for certain applications such as food or finished consumer goods like furniture or white goods. Chain is also prone to buildups of dirt and debris which can cause premature corrosion or hygiene issues.

Timing belts For applications where accurate positioning or synchronization is required, such as packaging lines and printing machines, timing belts provide a good solution. With toothed profile, timing belts provide perfect positioning between operations. Timing belts are also widely used on general conveying applications, having many of the advantages of chain such as high strength and positive drive but being cleaner and quieter.

Timing belts do have disadvantages; they have very little elasticity and cannot be joined easily on site. This means that they can be a problem to replace. It is often necessary to dismantle parts on a conveyor to fit news belts which results in costly process down time. Availability is sometimes a problem—many timing belts used in conveying applications, particularly longer lengths and those with special toppings or attachments are non-standard and replacement lead times can be several weeks. Due to their precision design, timing belts do not perform well in non-perfect conditions such as pulley misalignments, side loads from merging conveyors, abrasive, dirty or aggressive conditions.

Detachable belts
Detachable belts are a relatively new concept but now widely used across Europe for many applications. A detachable belt is composed of a series of individual links joined together to make a belt of any length.

This has dual benefits. Belts can be replaced very quickly and easily. No joining tools are required and there is no need to dismantle equipment to fit new belts. They are simply linked together by hand around the shafts and rolled onto the pulleys. It also means that there is no lead time for replacement belts and no need to carry a large stock of different lengths.

Detachable belts are a low maintenance option, no lubrication is required, and they run in standard vee or round pulleys, require minimal retensioning and require no tensioning devices. Generally they are highly durable, performing well in hostile environments. They are generally quieter in operation and cleaner than chain. Common applications include conveying of wood and furniture, glass, car body parts, pallets, building products and general warehousing.

As with all the options, detachable belts have limitations. The belts are not positively driven unlike chain or timing belts and so are not synchronized, the surface is broken rather than smooth and therefore unsuitable for direct food conveying.

Another criticism is that the initial cost is higher in comparison to low grade chain, rubber, or standard polyurethane belts. However, when the true life costs including, belt life, maintenance and downtime are examined, link belt is often shown to be the most cost effective solution.

Flat conveyor belts
Flat conveyor belts are, of course, widely used for bulk conveying; however, they are also used for unit handling either in the form of one wide belt or multi flat tapes. Flat belts are seen as a clean option, offering no places for dirt to accumulate and so are often used for food conveying. A wide variety of surface finishes and materials are available on flat belts, making them one of the most versatile conveying media on the market.

A relatively low cost per meter is also an advantage of flat belts. However, this can be misleading as there can be significant hidden costs and drawbacks. Fitting of flat belts can often be a costly and time consuming process. Often expensive welding tools and specialist knowledge are required and it is common for external belt service companies to be involved.

There are other problems associated with flat belts such as tracking, particularly when side loads from in-feed or out-feed conveyors are involved. Achieving and keeping the correct belt tension and traction are also common problems and tensioning devices are often required, adding to the overall cost.

Extruded polyurethane belting Among the most cost effective conveying solutions is extruded polyurethane belting. These belts are ideal for light or medium duty conveying and are widely used in industries such as food processing, ceramic tiles, roof tiles and flat wood. Extruded PU cords are available in a wide variety of profiles, and in a variety of materials, with different toppings available and some being available with woven reinforcing cords to add strength. Food quality materials are widely available.

One of their main advantages is cost in comparison to other belting options. The cost per meter is relatively low and they can be joined relatively cheaply on site using a simple kit. Tensioning devices are not usually a requirement for non-reinforced extruded PU belting as they are elastic and are fitted in tension. Reinforced belts have far less elasticity and so tensioners may be required. Standard extruded polyurethane belts are prone to stretching and limited in tensile strength, so they are unsuitable for conveying very heavy items. Reinforced belting has a significantly higher load capacity.

Table top chain
Table top chain is used in many applications. Plastic and stainless steel options are available, and it has many of the advantages of chain, being modular and thus joinable to any length. It is strong and positively driven, so synchronizing is possible and is generally cleaner and quieter than roller chain. One significant advantage is its ability to go around corners. Common applications include packaging and filling machinery, woodworking machinery, and general warehousing operations.

In general, the modular chain is relatively expensive in comparison to some alternatives. Additional costs may also include special sprockets, guide track, tensioners and other non-industry standard ancillaries. Generally, this is not a compact solution. Minimum sprocket diameters tend to be larger than for other types of chain or belt and the system can become quite bulky. Although table top chain works well in wash-down situations and can present a smoother surface than roller chain or link belt, there are still many places for dirt to accumulate. This type of system can also be susceptible to damage from abrasive dust.

As the article shows, there are lots of factors and options to consider when specifying or fitting a new or replacement conveyor belt. The conveying system is a vital element for factory efficiency; getting the belt choice right can be crucial. It is important to consider the total costs, including the hidden costs such as maintenance time, ancillary equipment, belt life and downtime.

For more information on how to select the right belting solution for your application, or to learn more about our products, contact us.

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