Dust-Free Piston Package
Durable and Economical Hot-Runner Components for PET Preforms
High material throughput, uniform filling and rapid cooling: high-performance molds with up to 192 cavities, like those used for PET preforms, place severe demands on the hot-runner. MHT Mold & Hotrunner Technology AG, Hochheim/Main, Germany, has revamped its hot-runner components, and, with the new Vulcan II series, now claims to offer three advantages: longer lifetimes and faster maintenance, with lower energy consumption. For this purpose, the development team completely redesigned the piston package.
To increase the stability, the respective structures of the piston and piston housing have now been swapped. The piston itself now consists of two components (previously it was one-part), while the piston housing is now a single piece (previously it was two-part). Another main concern in the redesign was the leak-tightness. While the contact pressure between the piston package and mold plate, which is only generated at the processing temperature, formerly created a metallic seal, this function is now performed by an elastic O-ring. It closes the piston package already while cold, and prevents compressed air from escaping.
A special focus in the development is the insensitivity to PET dust. For this purpose, the valve guide of the diverting plug is significantly longer than before. That prevents PET dust entering the piston package, where its abrasive effect would impair the precise operation of the piston. Nevertheless, just in case, there is an emergency reservoir in the piston housing that would temporarily stow the PET dust. All the measures together have the effect of prolonging the maintenance intervals to up to 6 million cycles. Any refurbishment can be performed quickly, since the piston packages are readily accessible.
Modifications like those to the piston package had already been made to the Vulcan I at the nozzle tip – now these have been further improved. The nozzle tip has been screwed in the nozzle base by means of an internal screw thread, so that it is direct contact with the heater tape. This makes the heat transfer better and more efficient.
To separate the two temperature zones of nozzle and cavity even better, the insulation effect has been increased with a titanium ring. This reduces the energy requirement. In a comparison between molds that are identical except for the hot runner, the power consumption of the Vulcan model is two-digit percentage lower, according to MHT. Another energy saving in comparison to the standard construction can be achieved by the use of an HP base insert, which directs the cooling onto the cavity contour and prevents unnecessary heat removal from the hot-runner nozzle. This provides a double saving for the processor, since less heating power is required at the nozzle tip, and less cooling performance is required in the cooling water system. In addition, the thermal separation has a positive effect on the cycle time, output and preform quality.
MHT Mold & Hot Runner Technology AG
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