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December 19 2002

Technical Paper - Advanced Valve Gate Technology For Use in Specialty Injection Molding

December 19, 2002
Technical Paper - Advanced Valve Gate Technology For Use in Specialty Injection Molding

Advanced Valve Gate Technology For Use in Specialty Injection Molding
Incoe Corporation
Introduction
The use of valve gate hot runner systems has been generally accepted in our industry as a more precise method of controlling the gate vestige, allowing the user open/close capability. The use of larger orifices would allow for faster fill and part stress reduction. However, due to the complexity, these systems do present areas of concern. Consideration for operating the mechanism either hydraulically or pneumatically must be properly designed to provide reliability. Contamination generated by material passing around the shutoff pin can cause flow lines on the finished part with some resins. Absolute control of the open/close position, which is usually based on time, can present difficulties. Advances in system design, computer technology, materials and manufacturing processes have allowed great improvements in valve gate systems. These advanced systems will be reviewed in the following four sections of this report.

Co-Injection
Co-Injection molding of two similar or dissimilar resins in the same molded part creating a separate skin of one material and a separate core of a second material requires the use of valve gates. Advances valve gate systems are key to successful single cavity, multi-cavity or sequential molding for Co-Injection applications. The special valve gate cylinder provides for three unique positions for resin flow and controls the volume of skin and core material.

Image 1

 

Position one starts the injection of the skin (surface) layer into the cavity. This is followed by the second position which starts the flow core material while continuing the flow of skin material. After the desired amount of core is achieved, the pin moves to the secondary position allowing the skin material to fully encapsulate the core. Finally, pack pressure is applied prior to shutting off both skin and core materials. This unique three-position actuator, along with the shut-off pin and mixing pin on, provide the necessary mechanical flow channels and precise shut-off sequence for the successful con-injection processing. This advanced system is the result of a joint technology between INCOE® Corporation and Bemis Corporation. INCOE®’s patented valve gate technology along with Bemis’s processing “know how”, provide the stimulus for improved Co-Injection technology. This part

Image 2

illustrates a part performance advantage in that it the overall rigidity of the arm rest was improved while allowing the desired cosmetic requirements to be maintained. Various features and benefits can be realized by the co-injection process including improved engineering properties, lower product cost and cycle time reduction.

Gas – Assist Valve Gate
When applying gas-assist technology for applications where gas is introduced in the mold, in either the part or runner system, valve gate technology is, in most cases, required. This process requires a valve gate to allow for proper pack-out and to keep the plastic from flowing back into the manifold. This example

Image 3

Is typical of any gas assist and can be duplicated for multiple cavities or for sequential fill applications. The systems are designed such that all valve gates are closed prior to the gas injection cycle.

Clear-Flo Valve Gate
The development of the Clear-Flo™ valve gate system

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has advanced hot technology by removing the valve gate shut-off pin from the material until the exact point of close. This advanced design concept opens the door to the use of shear/heat sensitive materials in the valve gate applications. The flow channel is increased and flow separation “which is inherent in conventional valve gates” is eliminated. This larger flow channel also minimizes flow induced material stress. The design allows material to maintain a consistent velocity from the manifold entrance to the gate area. These advantages corrected a processing problem shown in this lawn tractor hood application

Image 5

The quality issue was a shadow or streak created by shear sensitive colored resin. The shut off pin separates the material flow creating a difference in velocity which would cause the color concentrate to be somewhat darker, thus, creating an imperfection on the part. The larger flow channel provided a better condition for the engineering resin. The rate of reject was reduced by 100% for this defect. This defect represented 75% of all defects.

Image 6

Color changes are dramatically improved as the absence of the shut-off pin eliminates the flow separation condition as well as creating an area that is not directly removed by the new incorporates several other advantages. First, a straight shut- off pin is used

Image 7

This concept provides positive seal between the shut-off pin and pin channel, which virtually eliminates plastic leaks, as well as providing for an improved gate appearance. Additionally, the actuator provides for improved reliability by reducing the components for 19 to 9 and uses either pneumatic or hydraulic power

Image 8

Sequential Gate Control System
Further, improving the technology available in the area of valve gate pin position control has been achieved using a newly developed Sequential Gate Control System. It is the result of developing and using proprietary software with the latest in Computer technology. Based on Windows Software, this system can be used on any valve gate system and can be interfaced with all injection molding Machines. This Development is especially beneficial for sequential molding, con-injection or the Clear-Flo™ systems since pin position directly influences molded part quality. Sequential Filling can assist the mold in moving weld lines.

Image 9

Image 10

Family Molds

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Clamp Force Resolution Image 12
Back Molding Image 13
The controller provides precise control based on linear movement of the injection screw. The system is designed to allow for two open and closed sequences per valve gate cycle. The sequential valve gate system can be activated by time and/or linear position using either the inch or metric scale. The system includes many unique features such as system ready protection, modem hook-up for trouble shooting or upgrade, mold file storage for quick security code and 24 printable run history.. The system pictured here Can control up to 40 separate valve gates for positive open and close actuation’s. Image 14
Summary
Valve gate systems continue to be very important part of many of today’s molding applications. Valve gates are being used for con-injection both single cavity and multi-cavity molds. Valve gates are, in most cases, mandatory for gas-assisted molding. Valve gates systems are also used for sequential molding, family molds and back molding. The Refinements in Valve gate technology will continue to advance the capabilities of the plastic molding industry.

About INCOE® Corporation
Since 1958, INCOE® has engineered productivity built hot runner systems starting with their original patented design of the first commercial hot runner nozzle. Today, a wide range of nozzles and manifolds, pre-wired unitized systems, complete hot halves and advanced control technologies provide optimized systems suitable for appliances, automotive, electronics, medical disposables, packaging and technical markets. A network of representatives in over 35 countries are supported by INCOE® facilities located in the United States, Germany, Brazil, China, Hong Kong and Singapore. Wherever your molding operation is, INCOE® can support your business with complete hot runner systems engineered for your application. That's
INCOE® Hot Runner Performance.


For more information:

INCOE® CORPORATION
1740 E. Maple Road
Troy, MI 48083
T (248) 616 0220
F (248) 616 0225
e-mail: info@incoe.com

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