Precia-Molen supply weighing system to Lafarge Aggregates

Belt weighers provide efficient and reliable weighing system for Dowlow Quarry

Dowlow Quarry lies in the heart of the Derbyshire Peak district and is owned and operated by Lafarge Aggregates being their second most important site in the UK. Producing over 1.5 million tonnes of limestone a year the site has some considerable history, originally dating back to 1899.

Some months ago Precia-Molen engineers were asked to review an underperforming belt weigher on the aggregate blending line and supply a replacement that would ensure reliability and accuracy of weight measurement.

Consequently, Precia-Molen engineers recommended a FX VA PA 1000 belt weigher. Used in conjunction with the Precia-Molen I400 belt weigher indicator this provides reliable control and an accurate weight of material delivered to a lorry load-out point for volumetrically blended materials.

When a vehicle arrives on site it will visit the weighbridge with the gross weight recorded; the vehicle then proceeds to the load-out point for collection of the material blend to be loaded. As it is illegal for a vehicle to leave the site over their gross laden weight limit the Precia-Molen FX VA PA 1000 belt weigher will prevent the risk of vehicle overloading; thus eliminating additional vehicle movement on site to remove excess weight from the vehicle, which would result in further visits to the weighbridge.

The benefits are clearly defined as accurate and efficient weighing will not only extend the life of the weighbridge, but will reduce the risk of accidents and increase safety on a busy site underlining Lafarge's active approach to safety.

The Precia-Molen FX VA PA 1000 belt weigher provides a reliable and good degree of accuracy of weight measurement processing material ranging in size from 4/6/10/14/20mm to 50mm, providing specific blends of custom-blended material for Lafarge Aggregates' customers. Each blend of material is selected from a customer base recipe and each material selected is delivered from a storage bunker volumetrically, via volumetric extractor and gate on to a conveyor belt. The vehicle to be loaded is then positioned under the outlet of the belt conveyor. Once in position the control room operator selects the weight and blend of material to be delivered to the vehicle and the filling commences.

The control room operator also has the added benefit of observing, via the Precia-Molen I400 controller, the weight of material being delivered by means of a weight pulse count that measures every tonne of material passing over the scale into the vehicle. When filling is near completion, signalled by the pulse count and the total weight indication, a pre-set point triggers the system to stop filling and automatically close the bunker feed gates preventing further material being discharged onto the conveyor belt.

During discharge, the I400 Indicator also provides an indication of the average and total weight that has been delivered. This signal provides the final indication of weight delivered to the vehicle. On completion of all the belt-discharged material into the vehicle the belt scale provides a total weight indication. The control room, once satisfied the weight is within legal limits, then instructs the driver to return to the weighbridge, where they will receive a copy of the tare, gross and net weight.

The installation of the new Precia-Molen FX VA PA 1000 belt weigher and I400 belt weigher has consistently achieved accuracies of 0.7%, confirmed by the use of a known weight of material recorded on the Precia-Molen I400 belt scale indicator and the recorded weighbridge gross weight record.

Richard Scott, quarry manager at Dowlow, commented: ‘The service from Precia Molen has been very comprehensive from initial recommendations right through to installation and commissioning.’