Multiple Parting Lines
conventionally pinch welding the flashed
plastic on all sides of the bar. The part is
blow molded. Part ejection is achieved by
pulling the separator off the third member
or by retracting the third member out of the
part undercut prior to mold opening.
Reciprocating the third member is an option
which would be desirable to form
deep undercut parts. This was evaluated and
found unnecessary for this particular
part.
Production rates are the same as with any
other part that is prepinched and preblown.
Rates depend on wall thickness, part
geometry, surface appearance, flatness, etc.—all
the same factors that control cycle times for
any large blow molded part.
Because of the greater amount of pinch
welding in this technology, greater press
clamping force than usual would be helpful.
The amount of flash trimming is
proportionally increased by the amount of
pinch blade length. Good pinch blade
quality is important to this methodology.
Preblowing parisons between split mold
sections results in parts that inherently have
more trimmed offal to be granulated. There is
an added cost for the extra regrinding;
however, this is not a high cost if normal
blow molding temperatures are used, the
trimmed offal is kept clean and handled
efficiently.
Orienting 3D Parison
Blow mould and nonaxisymmetric blow mould. In
conventional, the parison
enters the mold vertically rather in a
straight tube. In 3D blow mould, the parison is oriented
in the open or closed mold. It is manipulated
in the tool cavity, providing complex
geometric products that can have uniform or
nonuniform wall thicknesses, corrugated
and noncorrugated sections, and so on. It
provides a means to significantly reduce
scrap=flash (etc.) waste and quality.
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