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There are many factors and choices to consider when designing a conveying system; not least what type of belt will best suit the application. In this article Duncan Gornall (Sales Director, Fenner Drives, UK) examines the popular belt alternatives available - assessing strengths,weaknesses and giving an insight into typical applications.
Factors to consider when specifying conveyor belts include: the item being conveyed, its weight, dimensions and material properties, the length of the conveyor span, the operating conditions, does the conveyor have to be synchronized to another process, does it require accumulationor 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 is one of the most common methods of conveying on such things as pallet conveyors, lumber processing and heavyduty warehousing systems. The main attraction is its strength, beingable to convey very large or heavy items. Standard chain is relativelyinexpensive, although certain specialist chains with attachments or special toppings can be expensive.
Whilst chain works well in many applications, there are inherent problems. Chain can be noisy in operation and requires a significant amount of maintenance such as lubrication and tensioning. There is a risk of damage to the product beingconveyed 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. Chain is also prone to build ups of dirt and debris which can cause premature corrosion or hygiene issues.
Timing Belts with their toothed profile provide agood solution for applications where accurate positioning or synchronization is required, such as packaging lines and printing machines. Timing belts are also widely used on general conveying applications, having many of the advantages of chain such as high strength and positivedrive but being cleaner and quieter.
Timing belts do have disadvantages; they have very little elasticity and cannot be joined easily on site. It is often necessary to dismantle parts on a conveyor tofit new belts which results in costly process down time. Many timing belts are not standard and replacement lead times can be several weeks.Due to their precision design, they do not perform well in non-perfect conditions such as pulley misalignments, side loads from merging conveyors, and abrasive, dirty or aggressive conditions.
Detachable Belts are composed of a series of individual links joined together to make a belt of any length. Belts can be replaced very quickly and easily. No joining tools are required and there is no need to dismantleequipment to fit new belts. 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, 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.
As with all the options, Detachable Belts have limitations, the belts are not positively driven so they are not synchronized; the surface is broken 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 PU belts; however when the true life costs, including belt life, maintenance and down time, are examined link belt is often shown to be the most cost effective solution.
Flat conveyor Belts are widelyused for bulk conveying; however they are also used for unit handling. 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 varietyof surface finishes and materials are available on flat belts making them one of the most versatile conveying media on the market.
The relatively low cost per metre can be misleading as there can be significant hidden costs and drawbacks. Fitting of flat belts can often bea costly and time consuming process. There are other problems such astracking – particularly when side loads from in-feed or out-feed conveyors are involved. Achieving and keeping the correct belt tension andtraction are also common problems and tensioning devices are often required.
Extruded Polyurethane Cords are among the most cost effective conveying solutions. These belts are ideal for light or mediumduty conveying and are widely used in industries such as food processing, ceramic tiles. They are available in a wide variety of profiles, and materials, with different toppings, some being available with wovenreinforcing cords to add strength. Food quality materials are widelyavailable.
The cost per metre is relatively low and they can bejoined relatively cheaply on site using a simple kit. Tensioning devices are not usually a requirement for unreinforced extruded PU beltingas they are elastic and are fitted in tension. Reinforced belts havefar less elasticity and so tensioners may be required.
Standardextruded polyurethane belts are prone to stretching and limited in tensile strength so are unsuitable for conveying very heavy items. Reinforced belting has a significantly higher load capacity.
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 so joinable to any length. It is strong and positively driven sosynchronizing 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.
In comparison, the modular chain is relatively expensive, additional costs may include special sprockets, guide track and tensioners. 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 orreplacement conveyor belt. The conveying system is a vital element forfactory efficiency, getting the belt choice right can be crucial. Itis important to consider the total costs including the hidden costs, such as maintenance time, ancillary equipment, belt life and downtime.Fortunately there are several alternatives available so virtually every application has a solution.
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