Better belts for driving and timing

Paul Boughton
Power transmission systems often use belt drives of the V, multiple-V or synchronous type, and the technology is generally thought of as mature. Paul Stevens examines the incremental improvements being introduced.

V-belts, multiple V-belts and synchronous (toothed) belts have been available for decades, with hundreds of products available from manufacturers around the world. While the technology appears to be mature, that does not mean that there are no incremental improvements being made to enhance performance. Manufactures periodically launch new products or variants of existing products with higher power ratings, longer life expectancy, enhanced wear resistance and, more recently, improved efficiency to reduce the energy consumption of the machines on which they are installed.

For example, in November 2011 the Contitech Power Transmission Group launched two new V-belts specially designed for the extreme demands of agricultural engineering. Unveiled at the Agritechnica exhibition in Hanover, the Conti-V Multibelt high-performance composite V-belt is for use as a clutch belt in agricultural equipment (Fig.1). Thanks to its low-friction surface, the high-performance multiple V-belt ensures gentle and silent clutching. Also launched at the same event, the high-performance Conti-V Varispeed wide V-belt has been developed for the types of variator and variomatic drives that are often used in agricultural implements. In order to transmit high power safely, the EPDM-based belt has a low-stretch aramid tensile member. The belt also benefits form being maintenance-free and remains stable in operating temperatures from -30 to 140°C.[Page Break]

Earlier in 2011, at the IFPE (International Fluid Power Exposition) in the USA, the Contitech Power Transmission Group exhibited an expanded range of heavy-duty Conti Synchrochain timing belts. These belts are now available in 55 different sizes are suitable for extremely tough operating conditions and applications for which chain drives would have been the used traditionally, including bottling and textile machines, cylinder changing mechanisms in newspaper printing machines, and even in go-karts (Fig.2). One feature in particular that helps these belts to handle extreme starting torques, shock loads and highly dynamic loads, is reinforcement of the teeth on the pulley side.

Another company offering a timing belt alternative to chain drives is the Gates Corporation, which introduced its Poly Chain GT Carbon Extended Length Synchronous Belts just over a year ago. These belts are suitable for drives requiring longer centre distances and high load-carrying capacities. Typical applications will be found in food processing, HVAC&R (heating, ventilation, air conditioning and refrigeration), oilfield, pulp and paper, mining and water treatment. According to the company, the belts offer a number of advantages including a life expectancy three times longer than chains, and pulleys that last ten times longer than sprockets. To help further in reducing the cost of ownership, the belts do not stretch, do not require retensioning and do not need lubricating.[Page Break]

Quietly efficient

Design engineers seeking low-noise, high-efficiency power transmission belts could consider the Eagle NRG introduced by Goodyear Engineered Products in 2010. The Eagle NRG is described as an innovative upgrade to the Eagle Pd power transmission drive, rated for up to 25 per cent more power, while achieving an impressive efficiency of 98 per cent. Additionally, the new belt design is rated for continuous service at 93°C (200°F) and is also static-conductive.

Operating up to 19decibels quieter than straight-toothed synchronous belts, Eagle NRG's Heletical Offset Tooth (HOT) design merges belt and sprocket into what is claimed to be the quietest, smoothest and one of the most compact synchronous drive packages available (Fig.3). The result is a continuous rolling tooth engagement that reduces vibration and improves the overall efficiency of the drive system. Tom Burgett, power transmission products manager for Veyance Technologies, the exclusive manufacturer of Goodyear Engineered Products, states: "Eagle NRG's 98 per cent energy efficiency rating is at least fivepercent higher than typical V-belt drives, which translates to immediate energy savings. Savings really add up when Eagle NRG is applied to high-energy-consuming drives that operate almost continuously year-round."

V-belt variants

So far we have focused on developments in synchronous belts but there are also evolutions in V-belts. Enhanced energy efficiency and sustainability are two themes adopted by manufactures of this type of belt as well. One example of this is the Blueconcept label from Contitech, with the Conti-V Pioneer being the first wrapped V-belt so designated. This belt is manufactured using vegetable oils, mineral fillers, chalk and cotton yarn, and completely dispenses with the carbon black (Fig.4). Nevertheless, the Conti-V Pioneer is still conductive to ISO 1813 (Belt drives - V-ribbed belts, joined V-belts and V-belts including wide section belts and hexagonal belts - Electrical conductivity of antistatic belts: Characteristics and methods of test). The Conti-V Pioneer is also said to be characterised by high strength and stability, minimal elongation and a long service life.

In 2011, Fenner introduced a new range of ultra-high-strength wedge belts for tough applications. Prior to launch, the Fenner Ultra Plus 140 belts were subjected to field tests in tough mining applications in Australia.

Fenner is offering the Ultra Plus 140 in two cross-section sizes, namely the SPB (16 x 13mm) and the SPC (22 x 18mm), and in lengths from 2.8 to 10m. Both belt sections employ the very latest in materials and construction technology, bringing what is essentially a 60-year-old design up-to-date. The belts are named after their enhanced transmission capacity, having 140 per cent of the power rating of regular Fenner Power Plus PB wedge belts. The inner load-bearing cords are made from aramid fibre, which is the same material used in Kevlar. The aramid cords are surrounded by chloroprene rubber (CR) to provide greater wear life than regular compounds, and this rubber is said to be more resistant to heat, oils and chemical exposure, as well as providing improved electrostatic conductivity performance (Fig.5). Similar to other belt drive systems, the CR affords a degree of protection against shock loads.

The Ultra Plus 140 belts are double-wrapped in a hard-wearing woven polyester-cotton fabric that is impregnated with CR. The fabric has been woven at a specially developed angle of warp versus weft, rather than the traditional 90-degree weave.[Page Break]

Cutting costs

Ultra Plus 140 wedge belts are designed to be used in three-, four-, five-, six- or eight-groove pulley drives, either in new installations or to upgrade existing equipment. In new installations the belts can contribute to reduced drive costs, as their higher power rating permits the use of fewer belts without compromising the drive life. For existing drives, fewer belts need to be purchased and fitted to existing pulleys. Either way, there is a significant cost saving.

These larger-section Fenner wrapped wedge belts are designed to drive large rotating plant such as pumps, conveyors, fans, crushers and separators typically used in quarrying, mining, processing, aggregates, the power industry and waste recycling sectors. Individual Fenner Ultra Plus 140 belts are rated at 22kW and above but, in multiples, they can transmit up to 900kW.

The Industrial Power Transmission unit of Gates Corporation recently added more industrial moulded notch V-belts to its range, with the new products benefiting from the use of EPDM (ethylene propylene diene monomer) rubber to give a longer operating life at extreme temperatures, greater efficiency and smoother running.

When the new belts were launched, Gates said it was the first manufacturer to incorporate EPDM in industrial V-belts. The belts' bandless, moulded notch construction provides an improvement in energy efficiency of up to three per cent, and the belts are also better at tolerating misalignment for smoother running. The operating temperature range is also said to be 70 per cent broader.

When customised belts are required, specialist companies can modify standard products to order. One such company is Transmission Developments (Transdev), which is a UK-based distributor for manufacturers such as Continental Contitech, F&F, Gates, Max Schlatterer and PTS Strongbelt, providing its customers with access to brands including Esband, Werner Graf, Breco, Brecoflex, Conti Synchroflex and Conti Synchrochain. Customer-specified modifications and finishes range from machined or bonded features, through to ground surfaces, special facing materials, anti-static coatings, and perforations for vacuum or air blowing processes. In addition, backings can be specified with specific properties such as high or low coefficients of friction, and soft, hard or compressible surfaces.