The traditional cure for an inefficient belt drive has been to simply replace the worn belt with a new one. However, Mark Maher, Technical Manager at ERIKS UK, argues that the replacement of a pulley is actually the far more effective way to resolve the problem.
Looking beneath the surface
Belt drives, which operate through friction between belts and pulleys, are commonplace in many industrial applications, ranging from fans, pumps and compressors, to conveyors, mills and crushers.
However, when a belt drive either appears tobe operating well below its intended efficiency, or fails completely, more often than not the belt is simply replaced whilst the pulley condition is overlooked. Remarkably, as many as fifty per cent of new belts are actually fitted to worn pulleys.
A pulley is just as susceptible to wear and tear as it goes through the rigours of everyday life, yet in many cases its condition passes a maintenance manager by. However, determining a pulley’s condition is not a difficult task, nor does it require any expensive machinery or tools to undertake.
More often than not, a simple tool to measure the groove gauge such as the Fenner Pulley Groove Gauge – which can fit on a key ring – is enough to determine whether a pulley needs to be replaced.
Simple pulley inspection
Simply clean off a section of the pulley and insert the appropriate width gauge profile into the groove and if there is more than five percent wear on the pulley’s pitch-line then it needs to be replaced. Another good rule of thumb to bear in mind is that when the gauge is inserted, there should be no visible gap on either side.
In addition, if there are any gaps or movement either side of the gauge it indicates that the belt is not sitting flush with the pulley and therefore unable to produce the optimum amount of friction to operate the drive as efficiently as possible.
Improving drive efficiency
In reality, actually replacing a worn belt and then ignoring the condition of the pulley will not only do little to improve the efficiency of a drive, but it will actually reduce the life of the new belt as one of the most noticeable effects of pulley groove wear is rapid belt deterioration.
From a financial perspective, poor drive efficiency will undoubtedly impact on both overall plant production and energy bills. To put it into context, a 37kW electric motor running continuously at an average electricity tariff of £0.08 kWh could cost £28,500 per year to run if fully loaded. Poor pulley groove condition can easily waste ten per cent of the energy input into the unit, amounting to £2,800 per annum of the energy being absorbed by the worn belt drive, rather than being transmitted to the load. However, in this context, replacement pulleys for this system would have a payback period of less than two months.
Prevention rather than cure
Whilst it is inevitable that pulley damage will occur, there are a number of actions a maintenance manager can investigate to increase a pulley’s operation life. Correct installation is key as seventy per cent of belt friction drives are actually incorrectly fitted. Given the wide variety of industrial applications which employ such technology, this figure is quite astounding.
In the first instance, the maintenance manager must ensure that the most appropriate drive has been chosen. A correctly selected drive uses the fewest number of belts or the minimum belt width required. Doing so will reduce loading on machine bearings which in turn will increase the system’s lifespan and reduce the potential for both machine downtime and mechanical failure. Selecting the correct drive will also keep noise levels to a minimum and reduce the amount of raw materials used.
Once the correct drive has been chosen, it then must be installed effectively. Alignment is key and there are various ways of testing this, from simply holding a taught length of string across the pulley faces in different positions, to probably the most effective way – a laser alignment gauge. Similarly, a belt tension indicator can be used to monitor accurate belt tension, which can reduce pulley groove wear and prevent belt slippage.
By making use of the correct tools available, the drive is far more likely to deliver its maximum rated power at its premium efficiency.
As well as correctly choosing and installing the most appropriate drive for your application, I would highly advise conducting regular equipment health inspections. These are neither difficult nor time-consuming, and can either be undertaken though a professional belt efficiency audit and assessment, or independently by a maintenance manager. If you are looking to conduct regular audits independently, the one-off cost to purchase the correct monitoring equipment can easily be offset by the costs of not having to undertake further serious remedial works which are often linked to irregularly checked equipment.
I would recommend storing a full belt efficiency kit on site, such as one from Fenner, which includes a belt tension indicator, a drive alignment laser and a pulley groove gauge. Keeping up to speed with the condition of your drives and including them within any planned maintenance schedule will ensure process up-time is at a maximum, whilst extending both machine and bearing life. Overall, this will lead to improved system efficiency and a reduction in both monthly energy bills and ongoing maintenance costs.
Best practice maintenance for ongoing efficiency
Given the frequency of belt drives in industrial applications, it is vitally important that maintenance managers are aware of the need to monitor both belt and pulley condition. All too often an underperforming drive is ‘cured’ with a new belt. However, ignoring the pulley component will not only shorten the operational life of a new belt, but will continue to affect a system’s operational efficiency and a plants annual energy bills. Attention must be paid equally to the pulley and the belt, right the way through from initial installation - particularly with regard to drive choice and belt alignment – through to regular planned maintenance checks. Only then will you truly be able to reap the rewards of an optimised and highly efficient belt drive system.
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