Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – With internal application of fluid pressure
Reexamination Certificate
1999-08-16
2002-08-13
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
With internal application of fluid pressure
C425S130000, C264S328800
Reexamination Certificate
active
06432352
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the simultaneous or sequential introduction of multiphase matter into a plastic melt through a plasticating screw.
2. Prior Art
Heretofore, plastic in molds or dies have been treated by introduction of matter through the wall of the mold, for cooling or the like, or matter has been added only to the plastic as it is worked between the lasticating screw and the housing in which it is rotatively supported.
BRIEF SUMMARY OF THE INVENTION
The present invention discloses a novel way to introduce high pressure gas, vapors and/or liquids into the process of manufacturing plastic material by a plasticating screw machine. The invention comprises drilling (coring) a hole axially through a plasticating screw of appropriate size to accommodate the introduction of gas, vapors and/or liquids into the melt shot.
A non return shut off valve may be arranged on the tip of that plasticating screw, which valve is made with a drilled hole through it including the tip so that during or after the injection phase (short shot) or in the process of completion the tip opens either due to air pressure, mechanical actuation (spring loaded) etc. to allow the assist gas, vapors or liquids to hollow out the plastic part, where that screw is utilized in an injection molding operation. A finely controlled gas (typically nitrogen) pressure and volume may be applied to the driving (proximal) end of the plasticating screw by means of a rotational collar. The gas will pass through the length of the screw to the non return shut off valve, or tip, where it will enter the molten plastic material. Required gas volume or material viscosity may necessitate fine gas entry apertures such as with a jewelled orifice and/or a gas check valve to prevent material from blocking gas passages. A typical processing sequence will be incorporated to the gas cycle. The part will be a short shot. The screw will remain fully forward through the second stage while gas is applied (no cushion). After this phase, allowances must be made for venting or degassing of the unnecessary gas before the part is ejected, when utilized in an injection molding format. The introduction of gas, vapors, or liquids into the plasticating screw is from the rear of the screw in one embodiment, or from a design mated entry point, such as a radial channel from a collar radially outwardly of the screw and into the core of the reciprocating injection screw ina further embodiment. Assist media is proportionally regulated via the described gas control system to allow for maximum efficiency of profiling.
A description of the mechanical aspects of the invention includes: (a) Injection screw coring for the introduction of gas, vapor, or liquids (fluids); (b) Non return shut off valve threaded onto the delivery end of the plasaticating screw for the purpose of: (1) shuting off the backflow of the molten plastic during an injection, holding and cooling phase of the plastic, (2) Enhancing the mixing of the molten plastic, (3) Allowing for the passage of high pressure gas, vapors or liquids through the center hole drilled (to specific size) through the center of the injection screw tip (aka non return valve), (4) Prevent plastic coming into center core during the screw recovery or plastification phase.
The center bore in the plasatication screw is arranged to accommodate the passage of gas, vapor, liquids through the screw injection tip under certain pressures and temperatures. The center core hole should also be able to accommodate single, double or multiphase coaxial tubes for the passage of multiphase materials with a conveying point in the injection tip. Temperature control is of paramount value for the constituent plastics being worked.
A high pressure rotary union may be arranged at the back end of the screw depending as to whether constituents are introduced axially or radially.
The phase process for injection molding plastics utilizing the center cored screw comprises: (a) Injection phase: control by a control circuit of the melt and high pressure gas, vapor, or liquid and temperature control thereof, (b) Holding and Cooling phase: control of gas, vapor, or liquid pressure and temperature for efficient cooling of the molded parts to control surface finish and part shrinkage. This is accomplished by: (1.) Introduction of gas, vapor, or liquid simultaneously (without a time delay) using control circuit components comprising a further embodiment of the present invention; or (2.) Introduction of gas, vapor, or liquid sequentially (after a preprogrammed time delay) the control circuit components of the present invention; (3.) Temperature control of the gas to provide an optimal “gas bubble”, coring, or tunneling, or thereof into the plastic melt; and (4.) Profiling of gas pressure by use of software with a programmed capability to ramp or step up the gas pressure using a menu driven system allowing various time/pressure durations in the gas injection phase.
A PID (proportional integral derivative) controlled micro-controller, comprises a further embodiment of this invention. This Proportional Controller is a closed loop PID controlled pressure regulating system, having a digital (LCD) display used as an attachment to commercially available gas control systems.
The proportional control is achieved through an electro-pneumatic circuit with a proportional regulator (or valve) pilot operating a booster unit which then pilot operates a high pressure regulator. Low pressure compressed air 0.55-0.70 MPa (typically 80-150 psi) is used as a control pressure which then regulates the pressurized gas to desired levels up to a maximum of 103 MPa (~15,000 psi max.). With this system, as the low pressure signal is boosted to the respective high pressure setting, it “loads” a “dome loaded” high pressure regulator. The proportional regulation is controlled by a Pulse Width Modulating (PWM) controller operating a normally closed on/off three way valve. Upon the completion of the cycle, the line pressure from the gas tubing can be vented through a vent port in the “dome” regulator.
A downstream high pressure transducer attached to the gas line provides feedback to the micro-controller thus adjusting the PWM proportional valve to the set point (closed loop). This closed loop system with a full PID control algorithm and controlled by the micro-controller allows the gas pressure to be controlled via a voltage (or current) profile thus creating an infinite number of pressure versus time settings. An on-board RS232 interface allows the capability to capture the information from the gas pressure transducer before the gas enters the mold and thus may be used as a monitoring and statistical tool. A PC displays a menu system, where pressure can be profiled either up or down as a geometric function.
A digital display is arranged to show the pressure set point and the actual value (during cycle). The micro-controller (PWM) is driven using a separate 0-24 VDC, 4.0 amps max. rated regulated power supply. Ports for the pressure sensor, RS232, allow for data acquisition and valve control signals (#1, #3, #5, #6) allow voltage input into the controller board. Using the up/down keys, the pressure settings are easily adjusted within a pressure sensitivity scale of +−1 psi and can be seen on screen as setpoint vs. actual. Adjustments to the software are made using diagnostics modeand coarse adjust. The response time of the PID controller from the start of the cycle to reaching the setpoint is approximately 50 milliseconds (response time can be adjusted to specific needs).
A prototype of the micro-controller is currently used with the gas control system on for example, a 250 Ton 32 oz. Cincinnati Milacron injection molding machine as an added feature to study the process parameters of the gas-assisted injection molding process.
A Gas-Assist Controller system will be attached to an existing commercial gas unit utilizing the volume controll technique and will be operational as an integrated attachment.
Halgren Don
McDowell Suzanne E.
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