date：2019-01-03view：1104
hot runner mold injection molding has significant advantages. its main value is that it saves raw materials without the flow system condensate. the hot runner system is essentially an extension of the machine nozzle, through which the plastic melt directly enters the cavity. for plastic parts with the same weight, the amount of plasticized plastic is less than that of the cold runner mold, because the cold runner mold also needs to fill the amount of plastic required for the runner system. the required pre-forming time is short, so the total molding cycle time is correspondingly shortened resulting in an increase in machine productivity. hot runner molds are particularly suitable for multi-cavity molds, molds for small plastic parts, and molds that can withstand high loads of high-quality plastic without re-pulverizing the flow-through aggregate. the hot runner mold forming process and economic advantages are often obtained by modifying the cold runner mold, even though the entire runner system cannot be eliminated due to mold design reasons. however, in general, a lot of time and raw materials can still be saved. the hot runner mold is a mold that uses a heating device to keep the melt in the flow passage from solidifying at all times. because it is shorter than the traditional mold forming cycle and saves raw materials, hot runner molds are widely used in various industrialized countries and regions in the world today.
while these advantages are well illustrated for the use of hot runner molds, the use of hot runner molds often encounters certain difficulties and problems. moreover, the use of hot runner molds requires additional temperature controllers and heating systems. some general rules for properly designing hot runner molds are discussed below. thermal balance considerations hot runner molds - not paying attention to the hot runner system used - are the most common problems encountered due to improper heat balance. this deficiency may be the result of many different factors.
for example, the problem with externally heated hot runner nozzles with wound heating elements may be that the heat transfer surface is too small to cause a complete failure of the hot runner system. when using a tubular heater, the same problem may occur if there is no suitable support. in this case, the thermal insulation of the air gap between the tubular heater and the hole of the tubular heater may cause heat accumulation in the tubular heater on the one hand, and cause at least partial unreasonable heating on the other hand, even if the heating power has been correctly determined. the accumulation of heat in the tubular heater usually causes premature failure of the tubular heater, which shortens the service life of the tubular heater. it has been demonstrated that the tubular heating element is embedded in the thermally conductive adhesive placed in the roughened passageway. because of the arrangement of the hot runner plates, these tubular heating elements can be adapted to local heating requirements, respectively, and in many cases they can help improve heat balance. when a reasonable process procedure is adopted, namely: avoiding entrainment of air in the heat transfer adhesive, the entire surface of the tubular heating element and the passage of the heating element of the mounting tube is coated with a heat transfer drying agent, for handling the heat transfer adhesive, follow the manufacturer's operating procedures so that the service life of the tubular heating element is extended and the sensitivity to failure is reduced. heat transfer bonding
depending on the principle of heat transfer, it is best to use a bright cold-rolled aluminum plate or polished aluminum plate to fix it on the hot runner plate. the requirement for uniform heat balance on the hot runner plate mainly consists of as little as possible local temperature difference, because when the probe (torpedo body) is heated indirectly by the hot runner system, the same temperature is necessary at the tip of the probe. the hot runner must have no temperature fluctuations as much as possible: most of the spacers should be as high as possible, heat loss should be as small as possible, and the temperature should be controllable.
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