Patent Application
20050255187
The present invention relates to methods and devices for use with apparatus for processing molten materials, and in particular to a self-regulating valve for regulating the melt pressure of a melt at the outlet of the valve.
Apparatus for processing molten materials, such as injection molding, extrusion, and blow molding apparatus, are highly efficient techniques for plasticizing and pressurizing a melt for subsequent forming through a mold or die. Such processes, however, are governed by the flow of a heated melt into a mold or die, and thus the quality of the molded products is related to the pressure of the melt. In conventional feed systems, the volumetric flow rate and pressure of the melt is determined by the design of the feed system. Once machined, conventional feed systems are unable to significantly change the behavior of flow entering a die or cavity at one location without similarly affecting the flow of plastic at other locations or retooling the feed system. As such, these forming processes may not achieve the desired quality or economic performance in a given application.
Several techniques have therefore been developed to regulate the melt pressure. Such techniques include, for example, the use of dynamically actuated pins to modify the flow resistance in a feedback control loop that compares the observed downstream pressure to the desired downstream pressure. Alternatively, the use of gear pumps rotating at a constant speed has been used to supply melt pressure at a desired level. Both of these solutions are limited in their performance and cost. Specifically, these systems are relatively large and require costly control systems. Furthermore, the reaction time of these systems is limited by their design.
Accordingly, there remains a need for improved methods and devices for controlling the pressure of a melt in an apparatus for processing molten materials that does not require pressure transducers, control systems, or large actuation forces.
The present invention provides methods and devices for controlling the pressure of a melt in an apparatus for processing molten materials. In one exemplary embodiment, a self-regulating valve is provided and it is effective to receive a dynamic force that is proportional to a pressure of a melt flowing through a flow channel in a body, and to move in response to changes in the dynamic force applied thereto so as to regulate a melt pressure of the melt at the outlet of the flow channel. In use, by way of non-limiting example, the self-regulating valve can be part of a machine nozzle, an injection mold, or an extrusion die.
While the valve can have a variety of configurations, in one embodiment the valve includes a body having an inlet and an outlet with a flow channel extending therebetween for receiving a melt therethrough, and a valve pin having a distal end that is adapted to communicate with the flow channel to control the melt therethrough. The distal end can be adapted to receive a proximally-directed dynamic force that is proportional to a pressure of the melt at the outlet of the flow channel, and the valve pin can be adapted to receive a distally-directed control force that is effective to move the valve pin in response to changes in the dynamic force thereby regulating a melt pressure if the melt through the channel. In one exemplary embodiment, the proximally-directed dynamic force can be adapted to move the valve pin toward a closed proximal position, in which melt flowing through the outlet of the flow channel is substantially prevented, and the distally-directed control force can be adapted to move the valve pin toward an open distal position, in which melt flowing through the outlet is allowed.
A variety of techniques can be used to provide a control force to the valve pin, however in one exemplary embodiment the valve pin is coupled to an actuator for applying a control force to the valve pin to move the valve pin in response to imbalances between the control and dynamic forces. The actuator can be adapted to move the valve pin toward an open position, in which the valve pin allows melt flow through the flow channel, in response to an undesired decrease in the dynamic force. The actuator can also be adapted to move the valve pin toward a closed position, in which the valve pin substantially limits the melt flowing through the channel to avoid an undesired increase in the dynamic force. In certain exemplary embodiments, the control force applied by the actuator can be adapted to be adjusted as a function of time. In other embodiments, the control force applied by the actuator can be adapted to be adjusted in response to a melt pressure sensed at a location remote to the valve pin. Exemplary actuators include, for example, hydraulic cylinders, pneumatic actuators, pre-loaded springs, solenoids, and electric motors. The actuator can be adjustable to allow adjustment of the control force applied by the actuator to the valve pin.
The configuration of the valve pin can also vary, but in one exemplary embodiment the valve pin can have an aperture formed therein and in communication with the inlet in the flow channel of the body, and a distal head positioned distal of the aperture and adapted to control melt pressure at the outlet. In one exemplary embodiment, the valve pin can have a cylindrical shape with an outer diameter that is about 5 mm, and the aperture can be in the form of an annular grove or annulus having a diameter about one-half the outer diameter. One skilled in the art will appreciate that the size of the valve can be modified to accommodate varying applications.
In other aspects, an apparatus is provided for controlling melt pressure, and it includes a body having an inlet and an outlet with a flow channel extending therebetween, a control member movably coupled to the body and adapted to receive a dynamic force proportional to a melt pressure of a melt at the outlet of the flow channel, and an actuator adapted to apply a control force to the control member in response to the dynamic force. In use, differentials between the control force and the dynamic force can cause movement of the control member until the control force and the dynamic force equilibrate, thereby regulating the melt pressure at the outlet of the flow channel. In one exemplary embodiment, the control member can be movable between an open position, in which a melt can flow through the outlet, and a closed position, in which the melt is substantially prevented from flowing through the outlet. The control member can be adapted to move toward the open position in response to an increase in the dynamic force, and the control member can be adapted to move toward the closed position in response to a decrease in the dynamic force.
The control member can have a variety of configurations, for example it can be in the form of a pin member having a proximal portion that is coupled to the actuator and a distal portion that is positioned adjacent to the outlet. The distal portion can include a reduced diameter region disposed within the flow channel to allow a melt to flow through the flow channel in the body, and a head distally adjacent to the reduced diameter region that is configured to regulate melt pressure at the outlet of the flow channel.
Exemplary methods are also provided for controlling a melt pressure of a melt at an outlet port of a melt flow apparatus having an inlet and an outlet port. In one embodiment, the method includes positioning a portion of a self-regulating control member within a melt flow channel such that the control member receives a dynamic force proportional to a melt pressure at the outlet of the flow channel, and applying a control force to the control member in response to deviations in the dynamic force to regulate a melt pressure at the outlet. The control member can be movable between an open position, in which a melt can flow through the outlet of the flow channel, and a closed position, in which the melt is substantially prevented from flowing through the outlet of the flow channel. The dynamic force applied to the control member can move to the control member toward the closed position, and the control force applied to the control member can move the control member toward an open position.
The present invention provides methods and devices for controlling a melt pressure of a melt in an apparatus that processes molten material. In one exemplary embodiment, a self-regulating valve is provided and it has a control member that is effective to receive a dynamic force that is equivalent to a melt pressure of a melt at the outlet, and that is effective to generate a control force for counteracting any changes that occur in the dynamic force. As a result, an equilibrium can be created between the control force and the dynamic force to maintain regulate a melt pressure. The self-regulating valve can be used in virtually any apparatus for processing molten material, hereinafter “melt flow apparatus.” Exemplary apparatus include, by way of non-limiting example, a polymer processing apparatus (e.g., extruder, injection molder, blow molder, or other net shape plastics manufacturing apparatus), or similar metal casting apparatus for manufacturing of net shape products.
The body 12 can have a variety of configurations, shapes, and sizes depending on the intended use. In the illustrated embodiment, the body 12 is in the form of a housing that is configured to be removably or fixedly disposed within a melt flow apparatus. As indicated above, the body 12 includes a flow channel 14 extending therethrough and having an inlet 14a and an outlet 14b. The inlet 14a is configured to couple to the outlet of a melt flow apparatus such that a melt, e.g., a molten polymer or molten metal, flows from the apparatus into the inlet 14a, through the channel 14, and out the outlet 14b which can be coupled to a variety of devices including, for example, a die, cavity, mandrel, cast, etc. The particular shape or path of the melt flow channel 14 can vary depending on the intended use.
In the embodiment shown in
A person having ordinary skill in the art will appreciate that the configuration of the valve body 12, 12′, 12″, as well as the shape and configuration of the flow channel 14, 14′, 14″ can vary depending on the intended use. For manufacturing, assembly, and maintenance reasons it may be desirable to assemble the body from more than one component that can be readily manufactured, assembled, and disassembled.
Referring back to
The head 20b is also preferably adapted to receive a dynamic force from a melt flowing through the channel 14, as will be discussed in more detail below. The shape of the head 20b can thus be streamlined to facilitate proper translation of the dynamic force from the melt to the control member 16. As shown in
A person skilled in the art will appreciate that the control member 16 can have a variety of other configurations and it does not have to be symmetric about the axis, as shown in the accompanying drawings. Many other designs are also feasible. For example, the control member 16 may utilize an annulus that has a rectangular section with rounded corners or an annulus with an elliptical annulus that is shaped like a rain drop. It is also possible to utilize a control member 16 that is non-symmetrical about the axis to control the flow around and along the pin.
As indicated above, in use the control member 16 is configured such that a melt pressure of a melt flowing through the channel 14 will act on the head 20b of the control member 16 to generate a force 24, referred to herein as a dynamic force 24. This force is substantially proportional to a melt pressure of the melt. While the application of the force to the head 20b will vary depending on the shape of the head 20b, in the embodiment shown in
As explained in more detail with reference to
A person skilled in the art will appreciate that certain variables present within the system need to be considered and adjusted as necessary in order to regulate the melt pressure at the outlet 14b of the device 10. For example, because melts are viscous in nature, there will be shear stresses which would tend to pull the control member 16 in the direction of flow, as well as a related pressure differential that would tend to push the control member 16 opposite to the direction of flow. Since these forces counteract and are small compared to the control force 26, it is possible to design the control member 16 such that the forces resulting from melt flowing through the valve 10 do not induce significant error in the outlet pressure. One skilled in the art is familiar with viscous flow in such valve geometries and may analyze the shear stresses and pressure drop through the valve using flow equations or numerical simulations. By comparing the forces due to the pressures and shear stresses acting on the control member 16, the control member 16 may be designed to minimize the sensitivity to fluctuations in viscosity and flow rate.
The control force 26 can be generated using a variety of techniques, however in one exemplary embodiment the proximal portion 16a of the control member 16 is coupled to an actuating member, certain exemplary embodiments of which will be described in more detail with respect to
In use, the actuating member is preferably adapted to apply a control force 26 at an amount that is effective to counteract any changes in the dynamic force 24 and to establish an equilibrium. An intensification ratio may be utilized to relate the control force 26 to the melt pressure at the outlet 14b. For example, a valve 10 having a control member 16 with a head 20b having a diameter dh of 5 mm may be utilized with a pneumatic cylinder having a diameter of 50 mm and a pneumatic supply valve that provides 0-1 MPa pneumatic pressure corresponding to a 0 to 10 V control signal. For this case, a 10 V control signal would correspond to a 100 MPa pressure at the valve outlet 14b; other intermediate voltages between 0 and 10 V would proportionally provide between 0 and 100 MPa pressure at the valve outlet 14b. The valve body 12, control member 16, and actuator can thus be design to achieve the desired range of pressures at the valve outlet 14b.
As indicated above,
Referring first to
In the illustrated exemplary embodiment, the machine nozzle 200 generally includes a barrel 215 having a screw 216 that is used to plasticate and force a melt through an outlet 217 of the barrel 215, into the inlet 14a of the valve 10, through the outlet 14b of the valve 10, to the inlet 219 of a nozzle tip 218, and then from an orifice 220 in the nozzle tip 218 to an injection mold. As previously described with respect to
The valve 10 can also be used in a variety of other melt flow apparatus. For example, a self-regulating valve may be provided at the inlet of a runner system or sprue of an injection mold to limit the melt pressure supplied to an injection mold from the injection unit of a plastics molding machine. In other embodiments, the pressure from an extruder may be regulated by placing a self-regulating valve in a plate between an extruder and a die. One skilled in the art would understand that the valve may also be used in many other processing applications.
In the illustrated embodiment, the control force used to regulate the melt pressure through each valve 10, 10′ is provided by a piston 322, 322′ that travels within a housing 323, 323′ of a mold plate 346, 346′. Hydraulic pressure is provided via a push port 324, 324′ and a pull port 325, 325′ that acts on each piston 322, 322′. A pressure control valve 326, 326′ communicates hydraulic fluid at controlled pressures to the push and pull ports 324, 324′, 325, 325′ in response to a control signal provided by an electrical cable 337, 337′. A person skilled in the art will appreciate that many other types of hydraulic valves may be used. Typically, the hydraulic fluid is supplied via a hose 332, 332′ from a hydraulic pump and accumulator. With respect to the selection of the hydraulic valve, a proportional control valve may be utilized to provide hydraulic fluid to the push ports 324, 324′ at a pressure that is proportional to the control signal. As an alternative, a servo-valve may be utilized to provide hydraulic fluid to the push ports 324, 324′ at a pressure that is proportional to the control signal and in response to the measured hydraulic output pressure. When available, feedback signals relating to the measured hydraulic pressure may be fed back to one or more microcontrollers through an appropriate multi-conductor cable 337, 337′. In the embodiment shown in
In the embodiment shown in
While the self-regulating valve does not require a controller to receive any information regarding the melt pressure or control forces, it is possible to utilize such information to control the melt pressure at locations remote to the valve itself. For example, one or more melt pressure transducers may be placed in a mold cavity to measure the melt pressure at one or more locations downstream of one or more self-regulating valves. As another example, one or more thickness gages may be utilized to measure the thickness of one or more extrudates downstream of one or more self-regulating valves. If such information is available, then a closed loop control system may be utilized to adjust the control force and the outlet melt pressure from one or more self-regulating valves to control the measured downstream state. A portion of a control algorithm is shown in Table 1 below for providing control signals to one or more actuators that provide control forces to one or more corresponding control member according to both open and closed loop control algorithms.
Each time step ilter occurs, the control of valve i is considered. If the control type is open loop as specified by iControlType(i) equal to one, then the output voltage sVout at the time step ilter for valve i is set directly to whatever control profile has been specified by the user. The described design and open loop control algorithm was found to provide a stable and rapid response for all process conditions and materials investigated. If the control type is closed loop as specified by iControlType(i) equal to two, then the desired pressure is obtained from the specified profile and placed in dProfilePressures(ilter, i). The proportional error for valve i, dErrPropP(i), is obtained by subtracting the desired pressure from the observed pressure at line 7. The integral error, dErrlntP(i), is then updated at line 8 and the derivative error, dErrDerP(i), is updated at lines 9-13. The output voltage is then calculated by multiplying the proportional, integral, and derivative errors with the proportional, integral, and derivative gains (respectively dkP, dkl, and dkD). Finally, the output voltage is restricted to the limits of 0 to 10 to correspond to the allowable range of input voltages for the actuators. For a design in which the pressure is in the range of 0 to 100 MPa, the control signal is in the range of 0 to 10 V, and the time step dt was 0.005 seconds, the closed loop controller was found to provide a desirable response for a proportional gain between 0.6 and 0.8, an integral gain between 0 and 1, and a derivative gain between 0 and 0.02.
One skilled in the art would appreciate the simplicity of the open loop control, as well as the potential trade-offs associated with closed loop control. In general, closed loop control may provide compensation to external variation, but at the cost of additional transducers, cabling, and controller complexity. As such, an instrumentation strategy and control system design can be configured to provide the desired performance based on the intended application.
As previously indicated with respect to
While not required, the controller can optionally utilize other forms of sensed process information and perform various functions other than those explicitly described herein. For example, in some applications it may be useful to monitor the temperature and pressure of the melt at the inlet of a nozzle, hot runner manifold, an extrusion die, and at other locations. This information may be used by the controller to assess the consistency of the manufacturing process, to diagnose faults in the manufacturing process, to assist the operator in obtaining a desirable process, and to accomplish other process feats.
A person skilled in the art will appreciate that the valve can have a variety of other configurations, and that it can be used with either open or closed loop control system designs. The valve can also be used, for example, to fine-tune and automatically regulate a melt supply to multiple dies from a single extruder, to limit the pressure at the inlet of an injection mold, and to achieve closed loop control of melt pressure at multiple points in an injection mold.
While not a requirement of the design, it is also possible to use process instrumentation such as melt pressure or temperature transducers to provide feedback of the manufacturing process to a process or quality controller. Such feedback may be useful for a quality controller to identify fluctuations in the pressure and/or temperature of the melt being provided to the inlet of the self-regulating valve. As another example, such feedback may be useful by a process controller to identify improper processing conditions (such as inadequate supply pressure to the inlet) and subsequently suggest corrective action to the process operators. In other embodiments, process feedback may be used by a process controller to directly control the melt pressure at locations downstream of the valve by providing closed loop control signals to adjust the control force to the valve pin.
The following non-limiting examples serve to further describe certain exemplary embodiments of the invention.
A control member, i.e., a valve pin, was machined from steel with an outer diameter of 5 mm and an inner annulus or aperture having a diameter of 2.5 mm. With 3 mm travel, the valve was found to provide excellent performance and longevity in an injection molding process for flow rates of 20 cc/sec and pressures of 100 MPa. Flow analysis and experimental validation has shown that this design is suitable for a wide range of materials and processing conditions. Flow analysis was performed with commercially available flow simulations and indicates that much higher rates of flow may be accommodated with a small increase in the size of the aperture.
The performance of the self-regulating is shown in
A person of ordinary skill in the art will appreciate further features and advantages of the invention based on the above-described embodiments Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entity.
This application claims priority to U.S. Provisional Application No. 60/571,103, filed on May 14, 2004 and entitled “Methods and Devices for Pressure Regulation in a Melt Flow Apparatus,” which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60571103 | May 2004 | US |
