Tightening the belt on energy costs
Your belt drives are not the first place you might think to look when you are aiming to increase the energy efficiency of your plant. But when you consider that the right specification can deliver an efficiency gain equivalent to upgrading from an EFF2 electric motor to an EFF1, then you can see how your belt drives can drive energy savings just as effectively as they drive your fans and pumps.
Around a third of applications driven by electric motors in the industrial and commercial sectors are belt-driven. Belt drives are the most common means of driving the fans, pumps, blowers and conveyors that are found in most process industries. Even the growth in availability and affordability of variable speed inverter controls has failed to make an impact in these applications, where the belt drive offers a number of real advantages over a variable speed inverter. Most importantly, the speed ratio capability of a belt drive allows the electric motor to operate at or near its most efficient speed, but belt drives also offer low lifetime costs, and are versatile and easy to maintain.
So the preponderance of belt drives in these applications means that even in an ideal world – where the drives are flawlessly designed, effectively installed and perfectly maintained – they would still represent a large proportion of a plant’s energy use and cost. However, the real, commercial world is far from ideal, and the truth is that belt drives are often poorly designed, badly installed and insufficiently or ineffectively maintained, and therefore operate at far less than their optimum efficiency. This in turn means that they consume – and waste – a disproportionately large amount of energy.
For example, a single 55kW electric motor, running on full load for 24 hours a day, with power costs at £0.07/KW-h, will consume £34,000 of electricity a year. Yet it would take only relatively easily achievable improvements in belt drive efficiency to save as much as 5% of this energy – equal to almost £1,700 a year.
Achieving these savings can be as simple as installing a different type of belt at the next belt change, or fitting a new set of pulleys of the right size. And once that is done, you can expect 25,000 hours of service (three years’ continuous or five years’ normal use) with a power transmission efficiency of more than 95%, before you need to replace the belts again.
Of course, the key is in identifying the right ‘different type’ of belt or the correct ‘new set’ of pulleys, as a wrongly specified system may not appear to have anything wrong but can in fact be running at as low as 80% efficiency. So whereas efficiency improvements can lead to savings of just under £2,000 a year, an inefficient system running just one fan, for example, can cost you around half as much again per annum.
Most of the installed base of belt drives utilises ‘V’ belts, or their derivative: the wedge belt. The wedge belt has a deeper trapezoidal cross-section than a V-belt of the same top width, which provides greater power transmission capability, though at some expense in terms of efficiency. Conventionally these belts are wrapped in a fabric jacket, though the Cogged Raw Edge (CRE) wedge belt is not covered on its working flanks (the ‘raw edge’) and has moulded corrugations (‘cogs’) in the belt base. Together these dramatically reduce bending stiffness of any section of the belt compared with the wrapped version. CRE belts also transmit more power than their conventional counterparts, because of greater tensile strength, lower mass/unit length, and greater bending and fatigue resistance – of which the last two also contribute to increased drive efficiency.
But where do inefficiencies creep in?
Firstly, through creep: the creeping of the belt surface over the pulley as a result of the change in length between the tight and slack sides of the belt, created by the redistribution of the installed tension to achieve torque transmission when the drive is set in motion. The net result is speed loss at the driven pulley, which translates into a loss of power transmitted. With an optimum design this can be as little as 0.5% but is more likely to be 1.0% in commercial installations.
The second source of inefficiency is hysteresis and friction energy loss, which takes place wherever belt bending and belt entry to, or exit from, pulley grooves occur. Because the materials the belts are made from have a finite damping energy ratio, hysteresis energy is converted into heat as the belt bends and straightens in use. Through hysteresis and friction, as much as 10% of energy can be lost, and pulley misalignment, worn pulleys or incorrect belt tension can push the figure even higher. Of course, in an optimum drive design with correct installation and proper maintenance at all times, these losses can be as low as 3.0%, but in most commercial installations they are more likely to be in the region of 4-10%.
Since wrapped wedge belts have higher friction and hysteresis losses than CRE belts, and are also likely to use more belts on similar diameter pulleys – because of their smaller power capacity – you can expect an average loss of an additional 1.5% in any given driven conditions compared with wrapped belts.
Taking all these factors into account, the difference between common practice and best practice in the design and application of belt drives can be measured in thousands of pounds of lost energy costs. Vet an optimised belt drive system can be a long-lasting, efficient, cost-effective solution for typical applications. Where a V-belt drive has a peak efficiency of 95-96% at installation, that can deteriorate by as much as 5% over time, through slippage. CRE belts, on the other hand, which can be used with the same pulleys as equivalently-rated V-belts, are around 2% more efficient.
Synchronous belt drives (also known as timing, positive-drive or high-torque drive belts) are even more efficient, at approximately 98% efficiency maintained over a wide load range. These belts do require installation of mating toothed drive pulleys, but once installed and in use they need less maintenance and retensioning, operate efficiently even in wet or oily environments, and run slip-free. There is a small price premium for new installations, but this is balanced to a certain extent by the avoidance of conventional pulley costs.
A synchronous drive belt such as the Fenner Torque Plus 3 (TDP3) delivers highly desirable 98% efficiency, running on your existing HTD pulleys. However, if you have a particularly high-power requirement, the Synchrochain synchronous drive belt will provide a more effective solution, transmitting even more power at the same high level of efficiency.
This high-performance drive belt has high tooth shear resistance combined with exceptional tensile strength, enabling it to deliver robust, reliable power transmission at high speeds and under high dynamic stressing up to 40m/sec. It also allows reverse flexing in multi-pulley drives – the first belt to do so in this high performance class – making it the ideal alternative to chain drives. The belt is finished with a smooth, low-friction PE foil tooth surface and has a smooth side which suits the use of back pulleys for belt tensioning. Highly resistant to chemicals, fuels, oil, grease, cleaning agents, UV and ozone, it also has an operating temperature range of –40°C to +100°C.
The belt has a specially developed modified involute tooth profile, which ensures faultless meshing and smooth running even at high speeds, as well as preventing cogging at high torques. It features S and Z wound aramid cord tension members, and an advanced moulded polyurethane/ polyamide fabric construction, for maximum resistance to belt elongation. This also means that Synchrochain requires no lubrication and effectively no maintenance. In a high-throughput application such as manufacturing, processing equipment, heavy engineering or the automotive sector, that can represent another valuable cost and efficiency gain through reduced or eliminated downtime. The robustness of the belt also makes it ideal for the tough conditions found in quarrying and mining, materials handling applications, and on construction sites. In fact, Synchrochain can be recommended for any application where ultra-high forces need to be transmitted effectively in an adverse environment.
However, the world of drive belts is not all grit and grime – there’s also glamour. Synchrochain even plays its part in Formula 1 racing, on the machines used to make pistons for F1 engines. It is also already standard equipment on go-karts from a number of manufacturers and – less racy but equally importantly – the belt is increasingly the choice for bottle filling machines, textile machinery for embroidery work, and printing roll changers for newspaper printing machines.
In addition to its efficiency advantages, when correctly installed Synchrochain runs more quietly than other solutions, and is less aggressive on pulleys. The new material mix of the belt also helps it to overcome issues which sometimes arise with toothed or synchronous belt drives, which may have deterred specifiers from choosing this option in the past.
Synchrochain comes in a choice of over 55 different belt lengths, from 640-4480mm, and in 8M and 14M pitch versions. Changing to the high-performance belt should be a fairly simple decision to make in most cases and for most high-performance applications. However, you may feel that an expert assessment of the kind offered by ERIKS will provide the facts and figures you need to clarify the energy savings and cost savings achievable, and therefore the need for change.
ERIKS will survey the five main belt drives on your site. These will be selected according to their importance to the process, historical cost, or the power they transmit. They may be the largest drives in terms of power transmission, but the list may also include smaller drives. These could be drives which have proved unreliable, drives which have used many sets of belts in a short space of time, or which are crucial to the operation and have high downtime costs.
Once the five drives to be surveyed have been established, an analysis of the effectiveness of the individual drives will be carried out, and the increase in efficiency achievable through the use of new belts or a new drive will be identified. From this, it will be possible to estimate the cash savings from reduced energy and belt use. Adding this to the downtime savings associated with more reliable running and fewer belt changes will then give you a clear and accurate figure on which you can base your decision.
With higher energy costs now a fact of life, and the growing need to find cost savings anywhere and everywhere, maximising energy efficiency is a relatively painless route to lower costs. It also has the added benefit of reducing your carbon footprint, which already holds the risk of financial penalties, and will be increasingly targeted by governments in search of carbon emission reductions and tax revenue.
No doubt you have already considered then savings which can be made in the areas of inverter drives and motors. However, as shown above, belt drives can either maximise or wipe out the efficiency gains made in other areas – and the relatively low cost of maximising their energy-saving potential makes them an important area to consider when belt-tightening is on the agenda.