This was written for Waste industry weighbridges in the UK but it is true for all weighbridges - Scaletec.
In today’s era of landfill charges and LATs reporting, the weighbridge is at the heart of a waste organisation’s data collection. Downtime can bring an operation to a halt so an effective preventative maintenance programme is vital says Chris Thorpe, service manager for Avery WeighTronix UK.
Weighbridges are precision weighing instruments designed to meet stringent weights and measures regulations while operating in extremely harsh environments.
Collecting and reporting waste data is essential for waste disposal authorities, transfer stations and landfill operators. In modern waste management the weighbridge is like a cash register for an organisation. Landfill charges, waste sorting & recycling transactions and landfill taxes all need accurate data.
Indeed, with charges set to increase by 100% over the next three years for active waste going to landfill, it pays to recycle and importantly measure or weigh the different categories of waste. With the weighbridge and its software at the heart of this reporting regime, it is essential that it remains operational and also reports weight data accurately.
Having the right service and maintenance agreement in place is essential, but there is much that weighbridge operators can do to ensure that equipment stays reliable. Perhaps the first thing is to be aware of the most common causes of damage or failure.
For example, if the load cell or weighbar is left in water or even in very damp conditions it can fail prematurely. This is one of the most common causes of inaccurate weighing and leads to rejection by trading standards officers or AP’s.
Second, “shock loading” can cause excessive movement of the weighbridge platform damaging the structure. This can be due to the heavy braking of a vehicle, impact damage caused by a loading shovel or by heavy loads dropped directly onto the weighbridge or into a vehicle positioned on it.
Another common problem is electrical disruption, including mains borne interference through the weighbridge indicator supply or a lightning strike, either directly or via dissipation when the surrounding ground becomes electrically charged. Modern weighbridge designs generally incorporate protection against lightning, but it is important to check the weighbridge for damage after any thunderstorm.
So, assuming you already have a maintenance contract in place, what else can an operator do to help keep the weighbridge operational and legally compliant?
The answer lies in housekeeping and good practice, with daily, weekly, monthly and twice yearly tasks. These simple tasks are important as accumulation of dirt, debris, water or slurry will affect the integrity of the weighbridge. In the short term this will lead to inaccurate weighing and, if allowed to continue, the load cells or weigh bars will fail, making the weighbridge unusable.
On a daily basis, for example, it is best practice to visually inspect the platform to ensure it is free from debris. Check that the side and end frames are not fouled. Next ensure that the digital display reads zero before the vehicle drives onto the platform.
Make sure that vehicles approach the platform slowly and avoid sudden braking and for an accurate weight reading ensure that all of its wheels are on the weighbridge.
For pit-mounted installations where T section rubber is fitted, check it is located correctly and that any pit drainage system and/or automatic pumps are working correctly. For surface mounted weighbridges make sure there is clearance between the superstructure and the ground.
Weekly tasks involve carefully checking the load cell assemblies for debris build up, which should be removed carefully without damaging the load cell cables.
You should also carry out a weekly weigh check using a loaded vehicle. Compare the vehicle’s weight when it is weighed at each end of the weighbridge and in the centre of the platform. If discrepancies of ± 2 indicated divisions are found then it should be reported.
In the example below, the weight is displayed in 20kg increments. At 25980Kg the weight is acceptable at -1 indicated division, but at 26060kg at the front end of the platform it is unacceptable with +3 indicated divisions.
For a pit-mounted weighbridge, check the pit monthly for possible “ponding” of water, debris build up or other damage to the leading edge of foundations, and the side and end frames of the platform. If the platform has moved excessively since the last inspection, then report it to your maintenance service provider.
You should also repeat the end-middle-end test as detailed in the weekly tasks and record the readings. After doing this jet wash the weighbridge to remove any loose debris and any material beneath the platform, taking care to avoid the load cells or weighbars. Rebalance, or zero, the weighbridge and repeat the end-middle-end test noting the readings. Compare these before and after results and report any discrepancies.
Finally, once every six months you should check the weighbridge for any signs of structural damage. For example, inspect the foundations for any significant movement or cracks and report any signs to your maintenance service provider. For surface mounted weighbridges visually check the load cell cables and again report any damage.
Never electrically weld on the weighbridge structure without consulting your service provider as this can seriously damage your loadcells or weighbars.
Also if the weighbridge needs cleaning out then you must take into account that waste can produce methane and other dangerous gases. For pit mounted weighbridges, you must ensure that suitably certified gas detectors are used in compliance with the Confined Space, Health and Safety legislation, both before and during such work.
With proper care your weighbridge will give longer trouble free operation in between planned maintenance visits. But remember not to get carried away by ‘DIY service’. Do not attempt to carry out detailed repair or maintenance work as this may affect its operation and contravene Weights and Measures regulations.
This is where a planned maintenance contract is essential, taking into account the way a weighbridge is used and its frequency of use, as this will vary from one organization to another. Maintenance contracts can be flexible to meet your needs. Often you will find that a basic package is fine for a new weighbridge in its first year, with extra cover added progressively as the equipment ages.
A basic package will typically only include a scheduled preventative maintenance visit or visits – ranging from monthly to annual visits. Additional features can include emergency cover for breakdowns, labour costs for repairs, parts and even replacement of load cells or weighbars.
If replacement parts are fitted, you may need to get the weighbridge re-verified to ensure it meets weights and measures legislation – check whether your service supplier can do this for you as not all service and repair companies have the necessary skills, tools and experience.
To meet your due diligence obligations you should also have your weighbridge calibrated regularly – at least once a year. Again your maintenance service provider should be trained and qualified to offer this service.
If the worst should happen you should also check your contract for response times. Even in the remotest regions of the UK, an eight hour response time is achievable and much shorter response times are available for critical operations.
In summary your weighbridge is one of the most important elements of your business. Without it operating properly, you risk mis-measurement. Even worse, if the problems build up and the weighbridge becomes inoperable it could slow or even close down your operation.
Finally there is the nightmare scenario, of non-compliance with Weights & Measures and the risk of legal action by Trading Standards with all the damage to your reputation, to say nothing of the direct financial losses.
Even though your weighbridge looks a simple, robust, heavy duty piece of kit that can ‘look after itself’, a few minutes spent on basic housekeeping each day, an hour each week and a couple of hours each month, will make all the difference to its reliable, trouble free operation. |
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