MIXING, WEIGHING & CONVEYING DEALING WITH VARIABLES


A Flexicon batching system is streamlining clay blending operations at Gladding, McBean


G


ladding, McBean manufacturers terra cotta products. The company mines clay from its own reserves and combines traditional methods with modern technology to create roof tiles, floor and paving tiles, clay pipe, ornamental pieces, and architectural elements for buildings. To streamline batching and mixing of


clay blends for different products, the company installed five bulk bag dischargers and five pairs of flexible screw conveyors from Flexicon to automatically deliver weighments of bulk ingredients for blending of clay compounds. The system has cut dispensing and weighing time for each batch by half, and reduced out-of- spec material and scrap by 95 percent. Clay is a natural material that varies in


composition, so the company must determine the ideal ratio of ingredients for various products. “We have to ensure that what we create in the lab will translate to the final material. The only way to accomplish that is to maintain precise control of production,” said Joe Parker, operations manager. The clay is sourced from the company’s


nearby mine, classified, and loaded into bulk bags at the plant. Crushed, recycled ceramic material called grog is the other major component used in the process. To prepare a batch, operators previously


retrieved clays and grogs from bins, weighed them on a scale, and transferred them to the mixer using an open trough conveyor. The new batching system, supplied by


Flexicon, integrates bulk bag dischargers, flexible screw conveyors and a central weigh hopper, all of which are actuated by programmable controls, also from the


supplier. The system enables Gladding, McBean to vary bulk bag discharging, conveying, weighing, and mixing on a batch- by-batch basis according to recipes developed in the lab. A HMI includes options for automatic or hand-mode operation, as well as setpoints, adjustments, status, start/stop, completion and other parameters. Once the recipe is programmed for a batch,


each ingredient is conveyed by a flexible screw conveyor from a bulk bag discharger to a central weigh hopper. Load cells supporting the hopper transmit weight gain amounts to the controller, which steps-down the conveyor's feed rate to a dribble before stopping it once the precise batch weight has been gained. The system weighs up to 30 batches per day, with improved accuracy and reduced labour. The clays and grogs are batched and


blended by five, forklift-loaded BULK-OUT BFF model bulk bag dischargers that stand side by side. An operator attaches a bulk bag to the steel lifting frame by sliding the bag straps into four Z-Clip strap holders. A forklift raises the lifting frame with the 909kg bag of clay or grog intact, into four self-centring cradles atop the discharger frame. With the bag in place, the operator opens a


305mm diameter iris valve, pulls the bag spout through it, and closes the valve before untying the spout. The operator can then open the iris valve gradually to prevent bursts of material into the hopper, and displaced dust from escaping the enclosed system. FLOW-FLEXER massaging devices on each


discharger promote flow by raising and lowering opposite edges of the bag at timed intervals. The clay or grog is transferred to the 1133L


capacity central weigh hopper by flexible screw conveyors in two stages to


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accommodate the plant’s limited floor area and headroom. Each conveyor extends either 4.6 or 6.1 m, depending on the position of the discharger and the need to route the conveyors under the roof trusses or between the truss components. Each conveyor consists of a polymer tube with


an inner flexible screw, which is driven above the discharge point, avoiding material contact with seals. Material moves through the transition discharge adapter of the lower conveyor into the inlet of the upper conveyor. The upper conveyor gravity discharges into the weigh hopper, which is 1.2 m in diameter and suspended 5.7 m above the floor. Most batches of clay mix weigh 454kg or


341kg, Parker says, with a typical loading/ blending cycle requiring 10 to 15 minutes. After blending with water, the batch is delivered to the appropriate process elsewhere in the plant. “The system allows us to blend up to five


different types of clays or grogs,” said Parker. For example, the dischargers might handle bulk bags of two kinds of clay and three grogs, delivering the correct amount of each for a given batch. “The versatility of the system makes it cost


efficient,” said Egidio Modolo, plant manager. He notes that no maintenance was required in the six months since installation, and that throughout discharging, conveying, and mixing the enclosed system prevents dusting. “We can make a small or large batch, and


alter the recipe and raw materials,” said Parker, adding: “Currently we have two different clays and three different grogs. We can change that any time.” “It gives us the ability to be accurate in spite of


clay’s unpredictability,” he said. “Now we have a tool for our team in the lab to create a mix that will allow us to be very precise with our final product specifications.” Microscopically, clay is very abrasive. Parker


said: “It will destroy just about any equipment you use, over time. One of the reasons we chose this system was for simplicity of maintenance due to few moving parts...” Parker says the system, “opens-up possibilities


for other types of products and materials that need the same type of batching accuracy.”


Flexicon (Europe) www.flexicon.co.uk


36 DECEMBER 2020/JANUARY 2021 | PROCESS & CONTROL


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