Technology

Hot Runner


A hot runner system is an assembly of heated components used in plastic injection molds that inject molten plastic into the cavities of the mold. (The cavities are the part of the mold shaped like the parts to be produced.)

By contrast, a cold runner is simplyachannelformed between the two halves of the mold, for thepurposeofcarrying plastic from the injectionmolding machinenozzle to the cavities. Each timethemold opens to eject the newlyformed plastic parts, the materialinthe runner is ejected aswell, resulting in waste. A hotrunnersystem usually includes aheated manifold and a number ofheatednozzles. The main task ofthe manifold is to distribute theplasticentering the mold to thevarious nozzles which then meteritprecisely to the injectionpoints in thecavities.

Hot runner systems were first developedandcameinto sporadic use in the early 60swithgenerallynegativeresults. Theygained popularity in the 80s and 90s astechnological advantagesallowed improved reliability and theescalation of plasticmaterials prices made hot runner systems moredesirableand cost effective. Hot runners are fairly complicated systems, they have to maintain the plastic materialwithin them heated uniformly,while the rest of the injection mold is being cooled in order tosolidify the product quickly. For this reason they are usuallyassembled from components premanufactured by specialized companies.Two main types of hot runner systems are the externallyheated and internally heated. In the externally heatedtype, molten plastic runs within a solid manifold and within thenozzles. In the internally heated, (now obsolete) the plastic flowsdirectly over slender heaters inside oversized runners. Theoutside boundaries of the runners normally solidify, so the plasticmaterial flows only in proximity of the internal heaters or"torpedoes". A hot runner controller is a temperature controllerused to control the temperature in the hot runner. This helpscreate the most consistent part(s).

Hot runners usually make the moldmoreexpensiveto manufacture and run, but allow savings byreducingplastic wasteand by reducing the cycle time. (do not haveto waituntil theconventional runners freeze).

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