Needle Valve System with 5.8 mm Nozzle Spacing
Narrow-Track Production of Tube Strips
Heitec Heisskanaltechnik GmbH, Burgwald Bottendorf, Germany, has created a new, miniature hot-runner system with valve gate for gating tube strips used in medical technology. The system is based on 61.041 flat-line nozzles and allows distances between gates of just 5.8 mm. Aside from the need for ever smaller distances between individual tubes, absolutely uniform cavity filling is essential for warpage-free and optically perfect parts. Close collaboration with a maker of medical products has now yielded a one-cavity mold for a 10-strip tube made from PMMA. The mold dimensions are 196 x 296 mm, with an installation height on the nozzle side of 240 mm.
The stringent requirements imposed on warpage, concentricity, and optical properties of the tube strips require that needle-valve gating be employed, with the gate centrally located at the bottom of the tube. Unlike side gating of the article, this arrangement avoids deflection of the mold core. Homogeneous melt flow is possible because the plastic melt does not first have to flow around the core and can rise evenly into the cavity. Thus, core misalignment and weld lines can be avoided in the tube. Gating through the bottom of the vessel permits venting of the cavities via the mold parting line. The use of core vents is unnecessary.
Each nozzle in the row of ten has its own heater and thermocouple, and can thus be controlled independently. This allows the temperature in each cavity to be adjusted individually, and also helps the various tubes to be filled uniformly. The flow channel layout ensures that the system is evenly balanced.
The shut-off needles are actuated by means of the syncro-valve system with fitted servo motor, which ensures simultaneous opening and closing of all needles. In contrast to traditional needle actuators with lifting plate, in which the mold structure must be weakened extensively, mold stability with syncro-valve is comparable to that of a mold that does not employ a needle-valve system. The use of central lubrication eliminates virtually all wear or maintenance. As the mold is used in an all-electric injection molding machine under cleanroom conditions, a visio drive serves as the actuator for the electric motor. Needles whose positions can be varied to the nearest 0.01 mm, and whose every movement is monitored and readjusted as needed; traverse speeds of up to 255 mm/s; and opening and closing times adjustable to the nearest 0.01 s all serve to underscore the system’s performance.
Heitec Heisskanaltechnik GmbH
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