AUTOMATIC FILLING OF BULK TRANSPORTERS
By S. HANDEL, A.M.I.E.E. Issued by British Information Services – The Certificated Engineer November 1965.
The cement industry is one of the largest users of bulk transporters for dry products as cement carried in vehicles of this type is much easier to load and unload. No bagging is necessary and there is a complete absence of dust in transit. At the Rochester, Kent, works of one of the largest suppliers of bulk cement in Britain an automatic loading plant for speedy and efficient dispatch of the bulk transporters has been developed and installed.
The transporter fleet consists of eight-ton and 15-ton vehicles. which carry the cement under a pressure of about eight pounds per square inch, designed to facilitate unloading ill conjunction with a blower. To get the best use from this type of transport suitable loading plant is essentials and must work on a 24-hour-day basis. The plant is particularly busy in the early hours as many contractors need deliveries of cement at the start of the working day. At the new loading plant, the tare weight of the transporter lorries is determined and they are then automatically filled to a pre-determined set weight.
The loading plant consists of four silos each containing 250 tons of four different grades of cement, fed by pipeline direct from the processing works. Beneath the silos are two 32-foot long weighbridges both of which have a capacity of 30 tons, and each of the weighbridges is served by two silos. All the weighing equipment and its control gear were built and supplied by another company, and the design and construction of the silos were undertaken by a London company.
When a bulk transporter drives on to the weighbridge a weight card is printed in the unit mounted at the side of the indicating head, the weight printed being the tare weight of the vehicle. At this stage, the weighbridge attendant sends an electric signal to the operator in charge of the silo valves to tell him from which of the four silos the bulk transporter is to be loaded. Once the signal has been sent it automatically blocks the other three silos to prevent any possibility of the wrong cement being loaded. The lorry driver then attaches flexible trunking to the bulk transporter ready for filling.
Meanwhile, the weighbridge attendant has set the indicator on the weighing machine to deliver the required gross weight (that is, tare weight of vehicles plus the weight of cement). When the correct weight has been delivered the valve closes automatically. Cut-off of the cement at the predetermined weight is controlled by an electronic switch, fitted to the scale, which stops the feed of material. During the filling operation, the valve operator on the silos can, if desired, exercise manual control over the flow of cement within the limit set by the weighbridge attendant.
About the same time is needed to fill either an eightton or a 15-ton transporter - approximately eight minutes - as there are problems in displacing the air from the vehicle during loading. The cement itself is fluidised with air so that it flows easily. On completion of loading, the weighbridge attendant again presses the handle of the printing unit, which then records the gross weight of the bulk transporter. As well as printing tare and gross weights on this card, the machine also prints internally on paper tape to produce another permanent record. At busy periods, when queues of transporters are waiting, the plant can dispense between 200 and 250 tons of cement per hour, with both weighbridges in operation.