INJECTION MOLDING APPARATUS WITH A MELT CHANNEL IN A VALVE PIN
Publication Date: 2005-Aug-29
The IP.com Prior Art Database
An injection molding apparatus includes a manifold with a manifold melt channel, a nozzle with a nozzle channel and a valve pin with an outer surface in proximal to an inner surface of the nozzle channel. A valve pin melt channel is defined by and substantially coaxial to the valve pin. The valve pin melt channel communicates with the manifold melt channel when the valve pin is retracted and is restricted from the manifold melt channel when the valve pin is extended. A mold gate is open when the valve pin is retracted and is closed by a valve pin tip of the valve pin when the valve pin is extended. An outlet extends from a longitudinal portion of the valve pin melt channel to the surface of the valve pin adjacent to the valve pin tip and is in continuous communication with a well adjacent the mold gate.
INJECTION MOLDING APPARATUS WITH A MELT CHANNEL IN VALVE PIN
Inventor: Denis Babin
Field of the Invention
The present invention relates generally to an injection molding apparatus and, in particular to a valve gated nozzle and valve pin arrangement for an injection molding apparatus.
Background of the Invention
In a valve gated injection molding apparatus, a valve pin reciprocates
through a nozzle to open and close a mold gate forming an opening to a mold
cavity. Improper alignment of the valve pin with the mold gate may result in
leaking at the mold gate, which may cause blemishes around the gate area of
the molded part. Further, improper valve pin alignment may result in damage
to or pre-mature wear of the valve pin and/or the mold gate. Such damage
necessitates frequent repair or replacement of the valve pin and/or mold gate
components, which can be costly.
Solutions for improving valve pin alignment have typically included a guide positioned towards the downstream end of the nozzle melt channel to capture and align the free end of the valve pin before it exits the nozzle and enters the mold gate. Because melt is required to flow past the guide when the valve pin is in the open position, a plurality of circumferentially spaced slots are typically provided in either the valve pin or the guide for melt to move around the valve pin and valve guide. A disadvantage of this arrangement is that the melt flow in the nozzle melt channel must separate to pass around the guide means, and subsequently reunite downstream of the guide, which may cause weld lines to appear in the molded product. Furthermore, having a guide in the nozzle melt channel typically causes melt stream color changes in the injection molding apparatus to be less efficient.
- 2 -
Further, many injection molding applications include a plurality of hot
runner nozzles that are arranged closely with one another, i.e., having a tight
pitch. These hot runner nozzles may have melt channels with very small
diameters. Valve pin gating presents several challenges in small diameter hot
runner nozzles. For example, the valve pin diameter must be sized to allow
sufficient space for the melt to flow between the pin and the melt channel. If
the flow restriction is too great, the injection pressure required must be
increased and, as a result, the shear on the melt stream may cause overheating
and degradation of the melt material. However, a valve pin that would not
cause a significant flow restriction would likely be weak and subject to
damage during use due to its extremely small diameter.
Solutions for improving a nozzle channel of a small diameter nozzle include carving a groove into an exterior of the valve pin to create a nozzle melt channel defined between the nozzle channel inner surface and the groove of the valve pin. However, these grooves do not define clear melt channels since the valve pins move with respect to the nozzle c...