Barrel Heaters - Hasmak.com.tr

<strong>Barrel</strong> <strong>Heaters</strong>Case HistoriesMI Band <strong>Heaters</strong> AllowTighter Temperature ControlThan Ceramic Knuckle Band<strong>Heaters</strong>Problem:A plastics processor was usingceramic knuckle heaters on aKrauss-Maffei plastic extruder tomake profile shapes with PVC andTFE <strong>com</strong>pounds. Both resins requireoperating temperatures in excess of370°C (700°F), During operation,temperature swings in excess of±24°C (±75°F) were experienced.The PVC and TFE extrusionsresponded poorly to these widetemperature variations and productquality suffered.Solution:Initial attention focused on the temperaturecontroller to see if it wascausing the wide temperature fluctuations.Further investigation revealedthat construction characteristicsinherent to the ceramic knuckleheaters were the true source of theproblem. The ceramic knuckle’spoor thermal conductivity wasunable to conduct heat away fromthe resistance element fast enough,causing it to operate in excess of760°C (1400°F). When the powerwas shut off upon reaching the370°C (700°F) set point, the 760°C(1400°F) heat stored in the ceramicknuckles’ mass continued to be conductedinto the barrel.This over-heating problem was<strong>com</strong>pounded by the additional heatgenerated by friction in the processitself and the ceramic fiber insulationthat trapped the <strong>com</strong>bined heatagainst the barrel, raising theprocess/extrusion temperaturebeyond acceptable limits.The initial customer was advised byhis Watlow representative to replaceall ceramic knuckle heaters on oneof his extruders with a <strong>com</strong>plete setof MI bands. Although more narrowin width, the MI band heaters coveredthe same amount of barrel surfacearea. The same day the MIband heaters were installed, theresults were in, the over-temperatureproblem was gone. The lower mass,faster response and superiorthermal conductivity of the MI bandheaters kept the extruder operatingwith a ±3°C (±5°F) of set point. Italso came up to operating temperaturefaster with MI band heaters.As a result, all 35 extruders in theshop were converted from ceramicknuckle heaters to Watlow MI bandheaters.Cast-In Heat/Cool Bands ForPlastic Extrusion MachinesProblem:Plastic extrusion machines producepolymer films, sheets, pipe, rods,filaments and other profiles eitherindependently or as coatings onwire, paper, metal, etc.Extrusion machines differ from injectionmolding machines (which primarilyuse mica heaters) in that theyoften require heating and cooling.Cooling is required on extruderbarrels to offset heat generated byfrictional shear as the screw pumppushes plastic melt through thebarrel and die head.Solution:Watlow’s UL ® <strong>com</strong>ponent recognizedcast-in aluminum heat/coolbands provide a solution for theextrusion application. Cast-inheat/cool bands are designed tomatch the heating and coolingneeds of extruders by:1. Offering longer heater life thanany other band heaterconstruction2. Utilizing aluminum, an excellentheat conductor, to deliver avery uniform heat pattern onthe barrel3. Providing rugged construction4. Offering a 12.7 mm (0.5 in.) O.D.tubing cast in for maximum coolingcapacity216