Loss-in-Weight Feeders Produce Only Gains - Schenck AccuRate

Case historyLoss-inweightfeedersproduce onlygainsA company installs severalload-cell-based loss-in-weightfeeders to automate itsingredient-feeding processand eliminate problemscaused by manually handlingand feeding the ingredients.PolyOne Corp., headquartered inAvon Lake, Ohio, is a worldwidepolymer services companythat produces and suppliespolymers, elastomers, colorants, andadditives for various products. Thecompany’s plastic compounds andcolors group operates a facility inVonore, Tenn., that produces colorconcentrates used by other industriesto color plastic products. The companyrecently upgraded the Vonoreplant’s processing lines and automatedthe ingredient-feeding processto eliminate problems caused by operatorshaving to manually handleand feed the various ingredients.Making a color concentrateIn the past, to make the various colorconcentrates at the Vonore plant, thecompany operated several processinglines that each used a batch mixer anda continuous single-screw extruder.Many of the ingredients arrived at theplant in bags, which the companystored on the plant’s ground level. Toprepare a batch for one mixer, an operatorhad to manually open the bagsand preweigh and premix the ingredientsin small containers, using a scaleon the ground level. For most ingredients,the operator forklifted the containersup onto a mezzanine builtaround the mixers and manuallydumped the contents into a dedicatedhopper above the mixer’s inlet. Theother ingredients were conveyed intothe hopper.The operator discharged the hopper’scontents into the mixer, which mixedand melted the ingredients. Themolten material discharged from themixer to the extruder and was extrudedas strands. The strands werecooled and cut before being packagedand shipped to customers. The companyoperates the plant’s processinglines 24 hours a day, 7 days a week.Solving an ingredient-feedingproblemThe company experienced severalproblems manually handling the ingredients:It was difficult to maintainthe finished product’s consistency be-The feeder’s controller monitors the hopper’s load cells to ensure a continuousand accurate feedrate to the twin-screw extruder.

cause manually weighing the ingredientswas not 100 percent accurate.This sometimes led to an ingredient’sweighment being outside the acceptableaccuracy range. Also, manuallyopening and emptying ingredientbags and dumping the ingredientsinto the small containers and hopperscreated fugitive dust that decreasedthe plant’s cleanliness. And manuallyhandling the bags and small containerscreated ergonomic issues for theoperators. Additionally, the companyexperienced inefficient productionrates because the dry ingredients inthe hopper couldn’t be discharged tothe mixer until the mixer had completelydischarged the molten materialto the extruder.To maintain its market competitiveness,the company decided to redesignand upgrade the Vonoreplant’s processing lines by eliminatingthe batch mixers and single-screwextruders and installing several continuoustwin-screw extruders, whichmix, melt, and extrude the ingredientsin one continuous process. As part ofthe plant upgrade, the company alsodecided to fully automate the ingredient-feedingprocess to eliminate theproblems caused by manually handlingthe ingredients.During its search for automated feedingequipment, the company contactedseveral feeder suppliers andtraveled to three suppliers’ test labsfor material tests. “We gave each supplierour toughest-flowing materialsfor use in feeder tests that focused ona feeder’s feeding accuracy overtime,” says Dennis Donalson, plantengineer at the Vonore plant. “To helpus nail down the accuracy of eachfeeder, the tests were computerized,and all of the test data was collectedso we could do statistical process controltesting and charting.”Of the three suppliers, two manufacturedfeeders that were able to feedthe material at the accuracies the companyrequired. Because of this, Donalsonsays, “We decided to evaluatethe feeders on other issues, such as thefeeder’s overall design and how theoperators and maintenance crewwould interface with them. We alsolooked at the components of eachTo prepare a batch for one mixer,an operator had to manually openthe bags and preweigh and premixthe ingredients in small containers,using a scale on the ground level.The feeder is connected to a graphical interface and recipe managementsystem that allows an operator to set the feeder parameters and monitorits operation from one central location.

The supplier connected the feeders inthe Vonore plant to the DG-2000,which allows the company to set thefeedrate and hopper setpoints, managerecipes, and monitor process trendingfrom one central location. At this time,the control station isn’t programmedto print reports about the feeders’ opfeederand how well they would functionover time in our manufacturingenvironment.”After further evaluation of the twocompeting feeders, the company decidedto purchase 14 MECHATRONcontinuous loss-in-weight (LIW) single-screwfeeders with DISOCONT(LIW) controllers and a DG-2000Group Manager graphical interfaceand recipe management system fromSchenck AccuRate Inc., Whitewater,Wis. The supplier supplies volumetricand gravimetric feeding systems,multiple-ingredient batching systems,weighfeeders, flow meters,bulk bag discharging systems, and vibratoryfeeders.Installing the LIW feedersThe MECHATRON feeder is constructedof Type 304 stainless steeland has a Coni-Flex flexible vinylhopper with an external paddle agitatorthat continuously massages thehopper’s outer wall to promote materialflow. The feeder can gravimetricallyfeed material between 0.117 and330 ft 3 /h and is available with feedscrews in eight different diametersand a range of flight arrangements tosuit customers’ applications. Feedscrew lengths can be customized tomeet specific installation requirements.The feeder is suspended froma set of load cells, which are connectedto the feeder’s controller. Thecontroller is prewired and integratedinto the feeder’s frame.During operation, an operator enters afeedrate setpoint into the controllerand starts the feeder. As the materialdischarges from the feeder, the controllermonitors the load cells and accuratelykeeps track of the weight-lossrate from the feeder. The controllercompares the actual weight-loss rateto the feedrate setpoint and automaticallyadjusts the screw speed.To ensure that there is a sufficientamount of material in the hopper whenthe feeder is operating, the operator entersa low and high refill setpoint intothe controller. When the materialweight reaches the low setpoint, thecontroller signals the material-deliverysystem to discharge material into thefeeder. When the material weightreaches the high setpoint, the controllershuts down the material-delivery system.(The company’s new material-deliverysystem consists of one surgehopper mounted above each feeder; thesurge hoppers are fed ingredients pneumaticallyor directly from bulk bags.)When the feeder goes into refill mode,the controller uses a dynamic refillcompensation algorithm that automaticallyadjusts the screw speed to compensatefor material changes that canoccur during refills. For example, ifduring the refill the material aerates inthe feeder and its density decreases,the algorithm detects this change andthe controller automatically increasesthe screw speed to feed more material.And if the material in the feeder compressesduring the refill, the controllerdecreases the screw speed to feed lessmaterial. This algorithm maintains anaccurate feedrate at all times.The feeder can be completely disassembledin place between productruns and its internal components accessedfrom the non-process side.This allows the operator to simplyand quickly change the feed screw orhopper, clean the feeder, or performany required maintenance. The feedscrew motor is mounted on a pivotand easily swings up and out of theway, allowing access to the internalcomponents. Releasing a 360-degreeband clamp allows the operator toeasily remove the hopper. Additionally,process connections between thefeeder inlet and the material-deliverysystem or between the feeder dischargeand the extruder remain inplace when an operator disassemblesthe feeder.eration. “However, we’re workingwith the supplier to connect the feedersto the central computer interfacewe use for our systems,” says KeithMcCormack, plant manager of theVonore plant. “The feeders have networkingcapabilities, and we’re in theprocess of developing them.”Experiencing the gainsSince upgrading the processing linesand automating the ingredient-feedingprocess with the feeders, the companyhas eliminated all of the problemscaused by manually handling and feedingingredients. “Because the operatorsno longer manually handle the ingredients,we’ve improved the product consistencyand plant cleanliness andeliminated the ergonomic issues,” saysDonalson. “We’ve also increased ourproduction efficiencies, because thefeeders continuously feed ingredientsto the twin-screw extruders — there’sno batching involved anymore.”Since upgrading the processinglines and automating the ingredientfeedingprocess with the feeders,the company has eliminated all ofthe problems caused by manuallyhandling and feeding ingredients.And even though the feeders are all thesame model, Donalson says, “We canuse the same feeder to discharge differentingredients at different rates by insertinga feed screw with a differentdiameter and flight arrangement.”PBENote:To find other articles on this topic,go to www.powderbulk.com, click on“Article Index,” and look under the subjectheading “Feeders,” or see Powderand Bulk Engineering’s comprehensive“Index to Articles” in this issue.Schenck AccuRate,Whitewater, WI877-498-2671www.accuratefeeders.com