Barrel Heaters - Hasmak.com.tr

W A T L O W<strong>Barrel</strong> <strong>Heaters</strong>Problem SolversWatlow Solutions To Common<strong>Barrel</strong> Heater ProblemsProblemMachine has GFI protection andtrips on machine startup.Controllability of plasticsprocess. Processing temperatureset point continually over shootscausing poor product quality.Part or all of this problem may betraced to heaters used in theprocess.Heater SolutionMany mineral insulated barrel heaters can pick up moisture if they are nottreated with a moisture retardant. This moisture will easily be driven out of anunsealed heater as it heats without causing damage. Check the machine GFIto see if it is adjustable to a higher but safe current leakage value setting tooverride until heaters dry out. This usually takes no more than a few minutes.If you know ahead of time that insulation resistance is low and nuisance GFItripping can occur, heaters may be baked or dried at 121°C (250°F) for twoto three hours.When GFIs are known to be required in advance, specify the Watlow EuroNorm or moisture resistant option at no additional cost. Note that Euro Normconstruction refers to specifications required to pass the European standardEN-60204.First, examine the type of barrel heating present and if the machine hasinsulation applied directly over the heaters to reduce heat loss from themachine. The following points influence temperature control and should beconsidered in barrel heating.• Heavy ceramic knuckle heaters with excessive insulation can lead totemperature control difficulties in some applications. As the barrel be<strong>com</strong>esmore insulated, the control thermocouple can be satisfied by the shearingaction of the screw which will generate sufficient British Thermal Units(BTUs) to melt the plastic resin. In some cases, there is no ability to coolthe process as there typically is in extruder applications and the temperatureof the process can over shoot.• When temperature over shoot is present, consider replacing the ceramicknuckle heater with a thermally efficient MI barrel. The MI has extremelygood heat transfer characteristics and responds quickly to make up heatrequirements.• Consider eliminating insulation that is directly on the heat source. As analternate approach, install insulation inside the machine cover if spacepermits. This will maintain heat without applying insulation directly on theheater bands. If desired, a cover can be made in multiple sections whichcan be vented if over shoot occurs.Injection Molding<strong>Barrel</strong> <strong>Heaters</strong>61