CN111283947A - Micro-foaming injection molding supercritical fluid gas injection system and method - Google Patents
Micro-foaming injection molding supercritical fluid gas injection system and method Download PDFInfo
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- CN111283947A CN111283947A CN202010081098.3A CN202010081098A CN111283947A CN 111283947 A CN111283947 A CN 111283947A CN 202010081098 A CN202010081098 A CN 202010081098A CN 111283947 A CN111283947 A CN 111283947A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
- B29C44/34—Auxiliary operations
- B29C44/3442—Mixing, kneading or conveying the foamable material
- B29C44/3446—Feeding the blowing agent
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
- B29C44/34—Auxiliary operations
- B29C44/60—Measuring, controlling or regulating
Abstract
The invention discloses a micro-foaming injection molding supercritical fluid gas injection system and a micro-foaming injection molding supercritical fluid gas injection method, wherein the system comprises a gas source, a main path unit, a branch path unit, a gas injector, a main path quick break valve, a branch path quick break valve and a gas injection control device, wherein the gas source, the main path unit, the main path quick break valve and the gas injector are sequentially connected in series, the branch path quick break valve and the branch path unit are arranged between an outlet of the main path quick break valve and an inlet of the gas injector in series, and the gas injection control device is used for controlling the opening and closing of the main path quick break valve and the branch path quick break valve so that the branch path quick break valve is closed when the main path quick break valve is opened; and when the main circuit quick-break valve is closed, the branch circuit quick-break valve is opened. The technical scheme of the invention can eliminate the phenomenon of gas surge in the supercritical fluid intermittent gas injection process of the micro-foaming injection molding process.
Description
Technical Field
The invention relates to the field of micro-foaming injection molding processes, in particular to a micro-foaming injection molding supercritical fluid gas injection system and a micro-foaming injection molding supercritical fluid gas injection method.
Background
The micro-foaming injection molding is a product processing technology combining a micro-foaming technology and an injection molding technology: in the plasticizing stage of the injection molding process, supercritical gas is injected into a machine barrel of an injection molding machine, a foaming agent and polymer melt are fully mixed under the actions of shearing mixing of a screw and high temperature and high pressure in the machine barrel to form single-phase melt, the single-phase melt is injected into a mold cavity in the injection stage, gas in the single-phase melt can be separated out due to rapid change of pressure conditions to form foam holes, and finally, the single-phase melt is cooled according to the shape of the mold cavity to form a product with compact foam holes.
In the micro-foaming injection molding, a screw of an injection molding machine rotates and moves backwards in a plasticizing stage, and simultaneously plasticizes and mixes materials, but the mixing capability of the screw is weak, the plasticizing time of the screw is short, usually within 30s, even within 10s, so that the mixing effect of the screw on gas and polymer melt is limited, if good single-phase melt is formed, the accurate control of gas injection amount and gas injection time is very important, the gas injection amount in the micro-foaming injection molding is usually kept below 0.5%, and meanwhile, a gas injection system can repeatedly inject gas with high precision. The gas usually in a supercritical state used in micro-foaming injection molding is very difficult to control and accurately meter, so a supercritical fluid gas injection system of a micro-foaming injection molding process needs to be reasonably designed, in order to smoothly convey the supercritical fluid into a polymer melt, the pressure of the supercritical fluid needs to be higher than the pressure of the melt, the intermittent characteristic of the injection molding process and the limitation of the structure of the gas injection system ensure that high-pressure gas gathered in a gas pipeline is quickly released into the melt when gas injection is started, the excessive gas is difficult to be uniformly mixed under the shearing action of a screw rod, so the excessive gas can be stored in the melt in a bubble form, after the melt enters a mold, the pressure of the melt is reduced, and small bubbles stored in the melt can grow to form large bubbles. These large bubbles destroy the mechanical structure of the product, and in extreme cases, they burst, so that the whole product is scrapped, and at the same time, the presence of excessive gas makes the local gas concentration too high to be completely dissolved in the melt, resulting in the viscosity change of the high molecular material in the injection molding machine, which may cause problems for production stability and product quality assurance. This phenomenon of rapid release of gas is called gas surge, and the basic conditions for its generation are: the pressure difference between the gas and the melt is large enough and the gas release line is not restricted.
In order to keep the accuracy and stability of the gas injection process in the prior art, one method is to install the on-off valve of the main pipeline of the gas injection system near the gas injection port at a distance less than 1cm, or to make the volume of the gas pipeline between the gas injection port and the on-off valve less than 7.35ml, even less than 0.735 ml. The second method is to reduce the pressure difference between the gas injection system and the melt at the gas injection section of the cylinder of the injection molding machine as much as possible to prevent the generation of gas surge, the pressure difference is usually set to be less than 0.7Mpa, but the rotation backward movement of the screw rod in the plasticizing stage can cause the fluctuation of the melt pressure in the cylinder, the melt pressure at the gas injection section of the cylinder can possibly rise to exceed the pressure of the gas injection system, so that the gas injection is difficult, finally, the gas content in the single-phase melt is too low or the gas injection process is unstable, if the pressure setting mode is used in the production, in order to ensure the normal operation of the gas injection process, the injection molding machine with higher precision is used, but the cost can. CN101830049A discloses a patent technology, named "supercritical fluid foaming agent metering system", which achieves the purpose of accurately controlling the amount of injected gas by using an accumulator with a certain volume to store the foaming agent and simultaneously controlling the gas pressure in the accumulator at the beginning and at the end of the gas injection, but neglects the stability of the gas injection process, and because of the existence of the gas surge phenomenon, the amount of injected gas is very large at the beginning of each gas injection and is small at the end of the gas injection, so that the quality of the formed single-phase melt is not uniform. CN10165397 discloses a metering device for supercritical fluid foaming agent, which is characterized in that two stop valves connected in series are added behind a controllable throttle valve and in front of a gas injection port, when gas injection is finished, the two stop valves are closed simultaneously to store the pressure state at the position of the gas injection end, and the space between the adjustable throttle valve and the first stop valve is structurally reduced as much as possible, so as to reduce the impact of gas on a downstream gas path when the next stop valve is opened. US6926507B2 "Blowing AgentDelivery System") adds a branch capable of being opened and closed on a foaming agent delivery System, and realizes the change of the flow direction of the foaming agent by matching the opening and closing of a valve between a main path and an air injection port, so that the continuous foaming agent delivery System can match the intermittent operation of an injection molding machine, but the branch in the patent technology is limited to only adjust the foaming agent from a supply source, and the air injection port can generate air surge due to the pressure difference between gas and melt at the beginning of air injection, so that the violent fluctuation of the flow of the foaming agent is caused, and the quality of the generated single-phase melt is influenced.
Disclosure of Invention
The invention aims to solve the technical problems of eliminating the gas surge phenomenon in the intermittent gas injection process of the supercritical fluid in the micro-foaming injection molding process and accurately controlling the gas injection flow rate and the gas injection quantity of the supercritical fluid, thereby improving various properties of a micro-foaming product.
In order to solve the technical problems, the technical scheme of the invention is as follows:
according to one aspect of the invention, a micro-foaming injection molding supercritical fluid gas injection system is provided, which comprises a gas source, a main path unit, a branch path unit, a gas injector, a main path quick-break valve, a branch path quick-break valve and a gas injection control device, wherein the gas source, the main path unit, the main path quick-break valve and the gas injector are sequentially connected in series, the branch path quick-break valve and the branch path unit are arranged in series between an outlet of the main path quick-break valve and an inlet of the gas injector, and the gas injection control device is used for controlling the opening and closing of the main path quick-break valve and the branch path quick-break valve, so that when the main path quick-break valve is opened, the branch path quick-break valve is closed; and when the main circuit quick-break valve is closed, the branch circuit quick-break valve is opened.
Optionally, the injection molding machine further comprises a first gas pressure sensor, a second gas pressure sensor and a melt pressure sensor which are connected with the gas injection control system, wherein the first gas pressure sensor is arranged on the inlet side of the main circuit-speed breaking valve, the second gas pressure sensor is arranged on the inlet side of the branch circuit-speed breaking valve, and the melt pressure sensor is arranged on a barrel of the injection molding machine.
Optionally, the main circuit unit comprises a pressure boosting device and a high pressure air reservoir.
Optionally, the gas injector comprises an on-off valve and a non-return valve, and the on-off valve can be switched on and off by receiving a control system signal from the gas injection control device.
Optionally, the bypass unit comprises a back pressure valve connected to an outlet of the bypass quick-disconnect valve, the back pressure valve outlet opening into an inlet of a pressure boosting device connected directly to atmosphere or to the main unit.
Optionally, an adjustable needle valve is arranged between the branch quick-break valve and the back pressure valve.
Optionally, the gas injector further comprises a flow restriction element disposed on an inlet side of the gas injector.
According to a second aspect of the present invention, the present invention provides a gas injection method of a micro-foaming injection molding supercritical fluid gas injection system, comprising:
the opening and closing of a main circuit quick-break valve and a branch circuit quick-break valve are controlled by a gas injection control device, so that the micro-foaming injection molding supercritical fluid gas injection system is switched between the following two states:
(1) in a first state, the main circuit quick-break valve is opened, the branch circuit quick-break valve is closed, so that the gas injector is communicated with the main circuit unit, and the gas injector is closed with the branch circuit unit, so that the gas pressure in a pipeline between the main circuit quick-break valve and the gas injector reaches a first pressure P1;
(2) in a second state, the main circuit quick-break valve is closed, the branch circuit quick-break valve is opened, so that the gas injector and the main circuit unit are closed, the gas injector and the branch circuit unit are communicated, and the gas pressure in a pipeline between the main circuit quick-break valve and the gas injector is equal to or less than a set second pressure P2;
wherein the first pressure P1 is greater than the second pressure P2.
Optionally, the second pressure is a melt back pressure of a gas injection section within a barrel of the injection molding machine.
Optionally, the bypass unit vents at least a portion of the gas in the conduit between the main circuit quick disconnect valve outlet and the gas injector to atmosphere or to an inlet of a pressurising device of the main circuit unit.
The invention has the beneficial technical effects that: in the intermittent gas injection process, a branch unit of the micro-foaming injection molding supercritical fluid gas injection system can reduce the pressure of gas in a gas injection pipeline before the beginning of each gas injection, so that the pressure difference between the gas pressure in an upstream pipeline of a gas injector and the melt pressure in a machine barrel is ensured to be small at the moment of the beginning of the gas injection, the gas surging phenomenon is eliminated, the gas enters the melt at a stable flow rate in the whole gas injection process, the mixing effect of a single-phase melt is optimized, the quality of a finished product is improved, and the gas injection system and the method can be used for occasions with very high requirements on the stability of the intermittent gas injection process of the supercritical fluid, such as micro-foaming injection molding.
Drawings
In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below.
FIG. 1 is a schematic structural diagram of a micro-foaming injection molding supercritical fluid gas injection system according to the present invention.
Fig. 2 is a schematic structural diagram of example 1 of the micro-foaming injection molding supercritical fluid gas injection system of the present invention.
FIG. 3 is a schematic structural diagram of example 2 of the injection molding supercritical fluid injection system according to the present invention.
Fig. 4 is a schematic structural diagram of example 3 of the micro-foaming injection molding supercritical fluid gas injection system of the present invention.
FIG. 5 is a schematic structural diagram of example 4 of the injection molding supercritical fluid injection system according to the present invention.
FIG. 6 is a schematic structural diagram of example 5 of the injection molding supercritical fluid injection system according to the present invention.
FIG. 7 is a schematic structural diagram of example 6 of the injection molding supercritical fluid injection system according to the present invention.
FIG. 8 is a schematic structural diagram of example 7 of a micro-foaming injection molding supercritical fluid gas injection system according to the present invention.
FIG. 9 is a schematic structural diagram of example 8 of the injection molding supercritical fluid injection system according to the present invention.
FIG. 10 is a schematic structural diagram of example 9 of a micro-foaming injection molding supercritical fluid gas injection system according to the present invention.
FIG. 11 is a schematic structural diagram of a microcellular injection molding supercritical fluid gas injection system according to a comparative example.
FIG. 12 is a gas injection flow-time curve for the gas injection system in example 1 of the present invention and for the gas injection system of the comparative example.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 shows a schematic structural diagram of a micro-foaming injection molding supercritical fluid gas injection system of the present invention, which includes a gas source 1, a main path unit a, a branch path unit B, a gas injector 10, a main path quick-break valve 5, a branch path quick-break valve 7, and a gas injection control device 11, wherein the gas source 1, the main path unit a, the main path quick-break valve 5, and the gas injector 10 are connected in series in sequence, and the branch path quick-break valve 7 is connected in series with the branch path unit B and is disposed between an outlet of the main path quick-break valve and the gas injector 10. The gas injection control device 11 is used for controlling the switching of the opening and closing of the main circuit quick-break valve 5 and the branch circuit quick-break valve 7, so that the branch circuit quick-break valve 7 is closed when the main circuit quick-break valve 5 is opened; when the main quick-break valve 5 is closed, the branch quick-break valve 7 is opened. When the main circuit quick-break valve 5 is opened and the branch circuit quick-break valve 7 is closed, the gas injector 10 is communicated with the main circuit unit A, and the gas injector 10 is closed with the branch circuit unit B; when the main path on-off valve is closed and the branch path quick-off valve 7 is opened, the gas injector 10 and the main path unit A are closed, and the gas injector 10 is communicated with the branch path unit B.
According to the technical scheme of the invention, the gas in the pipeline between the main path on-off valve and the gas injector 10 can be switched between the main path unit and the branch path unit by controlling the main path on-off valve 5 and the branch path on-off valve 7: after each gas injection, the main path quick break valve 5 is closed, the branch path quick break valve 7 is opened, the gas injector 10 is isolated from the main path unit A, and the branch path unit B plays a role in discharging a part of gas accumulated in a pipeline between the main path quick break valve 5 and the gas injector 10, so that the gas pressure is reduced to be in a range similar to the melt pressure of a gas injection section in a machine barrel of the injection molding machine 15; when gas injection is started each time, the branch quick-break valve 7 is closed, the main path quick-break valve 5 is opened, the gas injector 10 is opened at the moment, the pressure difference between the gas pressure in the gas injector 10 and the melt in the machine barrel is small, and the gas surge generating condition is not provided, so that the gas surge is prevented, meanwhile, the gas injector 10 is isolated from the branch unit B, the main path unit A plays a role, the gas from the main path unit A can enable the pressure in the gas injector 10 to rise, and the gas starts to be stably injected into the melt in the machine barrel of the injection molding machine 15.
Example 1
Fig. 2 is a schematic structural diagram of example 1 of a micro-foaming injection molding supercritical fluid gas injection system according to the present invention, as shown in fig. 2, the gas injection system includes: the device comprises a gas source 1, a supercharging device 2, a high-pressure gas storage tank 3, a first gas pressure sensor 4, a main path quick-break valve 5, a second gas pressure sensor 6, a branch path quick-break valve 7, a flow limiting element 9, a gas injector 10, a backpressure valve 8, a gas injection control device 11 and a melt pressure sensor 12.
According to an alternative embodiment of the invention, the first pressure sensor 4 is arranged on the inlet side of the main shut-off valve 5, the second pressure sensor 6 is arranged on the inlet side of the branch shut-off valve 7, and the melt pressure sensor 12 is arranged on the barrel of the injection molding machine 14.
According to an alternative embodiment of the present invention, the main circuit unit a may include a pressure boosting device 2 and a high pressure air tank 3. The pressurizing device 2 is capable of pressurizing and stabilizing the gas from the gas source 1 (typically a gas cylinder) at a certain output pressure. When the supercritical fluid is injected into the cylinder of the injection molding machine, the gas pressure in the supercritical fluid pipeline is reduced along with the gas entering the cylinder of the injection molding machine, so that a high-pressure gas storage tank 3 is added to the main path unit, and the gas pressure fluctuation of the whole supercritical fluid injection system is reduced in the working process.
As shown in the partially enlarged view (circled portion) of fig. 2, the gas injector 10 may include an on-off valve and a check valve according to an alternative embodiment of the present invention. When the injection pressure is higher than the melt pressure, the on-off valve is opened, and the gas enters the machine barrel of the injection molding machine. The function of the non-return valve is to prevent the melt from entering the gas line.
As shown in fig. 2, according to an alternative implementation of the embodiment of the present invention, the bypass unit B may include a back pressure valve 8 connected to an outlet of the bypass quick-break valve 7, the outlet of the back pressure valve 8 being open to be directly connected to the atmosphere.
The gas injection control system 11 is composed of a controller with a certain data acquisition function and a control signal output function and auxiliary systems thereof, so that data of gas pressure sensors (the first gas pressure sensor 4 and the second gas pressure sensor 6) in a supercritical fluid pipeline, data of a melt pressure sensor 12 on the injection molding machine 15, and related signals (such as plasticizing signals and the like) of the injection molding machine 15 are sent to the gas injection control system 11 through communication wires; meanwhile, the gas injection control system 11 processes the obtained signals, judges the operating state by a program, and controls the signal output to realize the operations (e.g., opening and closing) of the main and branch quick- break valves 5 and 7 in the supercritical fluid line and the operation of the gas injector 10.
In the intermittent gas injection process, when gas injection is started each time, the branch quick-break valve 7 is closed, the main path quick-break valve 5 and the on-off valve of the gas injector 10 are opened, the gas injector 10 is opened for gas injection, the pressure in the gas injector 10 rises, and the gas starts to be stably injectedInto the melt in the barrel; the gas injection control system device 11 sends out signals to close the on-off valves of the main circuit quick-break valve 5 and the gas injector 10, gas injection is stopped, the branch circuit quick-break valve 7 is opened after the gas injection is finished, the backpressure valve 8 discharges a part of gas in the pipeline from the main circuit quick-break valve 5 to the gas injector 10, and the gas pressure in the pipeline is reduced to be equal to or less than the melt backpressure of the gas injection section in the cylinder of the injection molding machine, and optionally equal to the melt backpressure of the gas injection section in the cylinder of the injection molding machine. At the beginning of the next gas injection period, the branch quick-break valve 7 is closed, the pressure difference between the gas pressure in the main path quick-break valve 5 and the pipeline of the gas injector 10 and the melt in the machine barrel is small, and the gas surge generating condition is not met, so that the gas surge is prevented. The injected gas, i.e., blowing agent, may include, but is not limited to, N2。
When injecting gas into the barrel of an injection molding machine, the injected gas flow is limited by adding a flow restriction element 9 upstream of the inlet of the gas injector 10, because the difference between the gas injection system and the melt pressure is large, which would allow a large amount of gas to be injected into the melt, far in excess of the process requirements, if the pipe diameter is not limited. The flow-limiting element 9 can be a flow-limiting orifice plate with 10-100 μm small holes processed on special materials with certain size and thickness, the size and thickness are determined according to the pipeline connection requirements, and the flow-limiting orifice plate is combined with a special polytetrafluoroethylene support. For example, a restriction orifice plate having 10-100 μm small holes is laser machined in a 4mm diameter, approximately 0.45mm thick, circular sheet of synthetic sapphire.
The pressure of the back pressure valve 8 is set as melt backpressure of a gas injection section on the cylinder during plasticization, and after the branch quick-break valve 7 is opened, high-pressure gas stored in the supercritical gas pipeline is released in a controlled manner, so that the gas pressure in a pipeline of a gas injection unit is reduced, the gas surge phenomenon in the gas injection process is eliminated, and the flow rate of a foaming agent injected into the melt is uniform and stable. The outlet of the backpressure valve 8 is directly connected with the atmosphere, a part of gas is released into the atmosphere, and the gas pressure of the branch unit B is adjusted to a set value, such as a melt backpressure value.
The gas source 1 is usually a gas cylinder, in which the pressure is reduced as the gas content in the cylinder is reduced, and the gas in the cylinder is reduced to 2Mpa and then introduced into the pressurizing device 2 in order to stably supply gas to the gas injection system.
Example 2
As shown in fig. 3, the structure of the injection system of a supercritical fluid for microcellular injection molding is similar to that of example 1, except that the bypass unit B does not include a back pressure valve, and the gas in the bypass unit B is directly discharged to the atmosphere.
Example 3
As shown in fig. 4, the structure of the micro-foaming injection molding supercritical fluid gas injection system is similar to that of example 1, except that a flow restriction element 9 is provided on the pipeline between the outlet of the main path quick-break valve 5 and the inlet of the branch path quick-break valve 7.
Example 4
As shown in fig. 5, the structure of the injection system of micro-foaming injection molding supercritical fluid is similar to that of example 1, except that the flow restriction element 9 is disposed on the pipeline between the outlet of the main path quick-break valve 5 and the inlet of the branch path quick-break valve 7, and the branch path unit B does not include a back pressure valve, and the gas in the branch path unit B is directly discharged to the atmosphere.
Example 5
As shown in fig. 6, the structure of the injection system of micro-foaming injection molding supercritical fluid is similar to that of example 1, except that the outlet of the back pressure valve 8 is connected to the inlet of the pressurizing device 2, so that the gas released by the back pressure valve 8 can be recycled, the gas utilization efficiency can be increased, the gas loss can be reduced, and the inlet of the pressurizing device 2 is provided with the check valve 13 to prevent the gas in the pressurizing device 2 from entering the back pressure valve 8.
Example 6
As shown in fig. 7, the structure of the supercritical fluid injection system for microcell injection molding is similar to that of example 1, except that the branching unit B (branching speed cut-off valve 7) does not include a back pressure valve, the branching unit B (branching speed cut-off valve 7) is connected to the inlet of the pressurizing means 2, and a check valve 13 is provided near the inlet of the pressurizing means 2.
Example 7
As shown in fig. 8, the structure of the injection system of a supercritical fluid for microcellular injection molding is similar to that of example 1, except that a flow restriction element 9 is provided on a pipeline between the outlet of the main path quick-break valve 5 and the inlet of the branch path quick-break valve 7, the outlet of the back pressure valve 8 is connected to the inlet of the pressurizing device 2, and a check valve 13 is provided near the inlet of the pressurizing device 2.
Example 8
As shown in fig. 9, the structure of the injection system of a supercritical fluid for microcell injection molding is similar to that of example 1, except that a flow restriction element 9 is provided on a pipeline between the outlet of the main path quick break valve 5 and the inlet of the branch path quick break valve 7, and the branch path unit B (the branch path quick break valve 7) does not include a back pressure valve, the branch path unit B (the branch path quick break valve 7) is connected to the inlet of the pressurizing device 2, and a check valve 13 is provided near the inlet of the pressurizing device 2.
Example 9
As shown in fig. 10, the structure of the supercritical fluid injection system for microcellular injection molding is similar to that of example 1, except that an adjustable needle valve 14 is provided at an inlet of a back pressure valve 8. By adjusting the opening of the needle valve 14, the impact of high-pressure gas stored in the pipeline at the moment when the branch on-off valve 7 is opened on the back pressure valve 8 can be reduced, and the influence of long-time gas impact on the service life of the back pressure valve 8 is prevented. In the gas injection system of the present invention, the needle valve 14 is not limited to being mounted to the embodiment 9 shown in fig. 9, and a needle valve may be mounted in other embodiments including the back pressure valve 8.
Comparative example
The gas injection system of the comparative example is shown in fig. 11, and does not include a branch unit and a branch quick-break valve 7, and the high-pressure closed system, the data acquisition system and the gas injection control system of the comparative example have the same structure as the micro-foaming injection molding supercritical fluid gas injection system of the present invention, and the gas injection process is also similar.
According to another aspect of the present invention, there is provided a method for injecting gas into a micro-foaming injection molding supercritical fluid system, comprising:
the gas injection control device 11 is adopted to control the opening and closing of the main circuit quick-break valve 5 and the branch circuit quick-break valve 7, so that the micro-foaming injection molding supercritical fluid gas injection system is switched between the following two states:
(1) in the first state, the main path quick-break valve 5 is opened, the branch path quick-break valve 7 is closed, so that the gas injector 10 is communicated with the main path unit a, and the gas injector 10 is closed with the branch path unit 7, so that the gas pressure in the pipeline between the main path quick-break valve 5 and the gas injector 10 reaches a first pressure P1;
(2) in the second state, the main path quick-break valve 5 is closed, the branch path quick-break valve 7 is opened, so that the gas injector 10 and the main path unit a are closed, the gas injector 10 and the branch path unit 7 are communicated, and the gas pressure in the pipeline between the main path quick-break valve 5 and the gas injector 10 is equal to or less than the set second pressure P2;
wherein the first pressure P1 is greater than the second pressure P2.
According to an alternative embodiment of an embodiment of the present invention, the second pressure is the melt back pressure of a gas injection section in the barrel of the injection molding machine 15.
According to an alternative embodiment of the invention, the by-pass unit B discharges at least a portion of the gas in the line of the gas injector 10 to the atmosphere or to the inlet of the pressurization device 2 of the main unit a.
According to the system and the method for injecting the supercritical fluid for micro-foaming injection molding, the gas main path unit and the gas inlet of the gas injector can be communicated or disconnected in a controlled manner; meanwhile, a branch unit is additionally arranged between the gas inlet of the gas injector and the main path on-off valve, the branch unit can be controlled to be connected with or disconnected from the gas injector, the gas in the pipeline of the gas injector can be decompressed before gas injection at each time, the fact that the gas in the gas injector does not have a large pressure difference with the melt in the machine barrel at the moment of the beginning of gas injection is ensured, the gas surging phenomenon is eliminated, the fact that the gas stably enters the melt in the whole gas injection process is ensured, the mixing effect of single-phase melt is optimized, and the quality of finished products is improved.
The advantageous effects of the examples of the present invention compared with the comparative examples are specifically described below by experiments.
The test was conducted using a gas injection system similar to that shown in FIG. 2; the difference from fig. 2 is that: a visual high-pressure closed system is adopted to replace an injection molding machine system. Therefore, the gas injection process can be observed more clearly, the pressure change in the high-pressure closed system can be collected, and the change rule of the gas injection amount can be simulated and calculated according to the gas equation. The method comprises the following specific steps: the visual high-pressure closed system is provided with a gas injection port, and the gas injector 10 is arranged on the gas injection port; in addition, a pressure sensor is mounted on the high-pressure device. And compiling a matched LABVIEW program, and realizing high-speed data acquisition and gas injection action control by adopting an NI6221 data acquisition card. In the gas injection process, gas is injected into the high-pressure sealing device, the pressure value in the device is increased, pressure data in the device is collected, and the flow rate of the gas injected into the device is calculated by utilizing a van der Waals gas equation. The van der waals equation is represented by formula (1), and Vm is obtained by transforming formula (1) and rewriting it into formula (2) and solving for formula (2). The mass of the gas can be calculated using equation (3). Therefore, the total mass value of the gas in the device at a corresponding moment can be obtained by the pressure value at each moment in the device, and the total mass of the gas obtained at different moments is subjected to difference calculation, so that the mass flow of the gas entering the visualization device is obtained.
The result of the expansion is shown in equation (2):
r-gas universal constant 8.314J. mol-1·K-1
TCCritical temperature of nitrogen 126.1K
PcThe critical pressure of nitrogen gas is 3.4MPa
T-the temperature in the apparatus was about 15 ℃ in the experiment, i.e., 28.15K
P-pressure value in the apparatus obtained in real time during the experiment, in Mpa
Vm-gas molar volume of nitrogen in the apparatus, in L.mol-1
V-gas volume in the apparatus, about 0.135L
M-relative molecular weight of Nitrogen 28.013
The micro-foaming injection molding gas injection system is used for injecting gas into a closed high-pressure device respectively, and the gas is injected for 10s under the conditions that the pressure of the gas injection system is 11Mpa and the initial pressure in the high-pressure device is 6Mpa, so that a gas injection flow-time curve of the micro-foaming injection molding gas injection system is obtained.
The gas injection flow-time curve of the gas injection system of the comparative example was obtained by the same operation. The results of comparing the gas injection flow-time curves of the gas injection systems of the examples of the present invention and the comparative examples are shown in FIG. 12. As can be seen from the graph of fig. 12, the gas is released rapidly at the beginning of the gas injection in the gas injection system of the comparative example, and the gas injection amount suddenly increases to a larger value and then falls back to the required gas injection amount, and the sudden increase of the gas injection amount at the beginning of the gas injection in the gas injection system is likely to cause the gas surging phenomenon. Compared with the prior art, the gas injection system comprising the branch unit can effectively relieve the phenomenon that the gas injection amount of the gas injection system is too high when gas injection is started, and gas stably enters a melt in the gas injection process, so that the gas surge phenomenon is eliminated.
Although the present invention has been described with reference to the specific embodiments, it should be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (10)
1. A micro-foaming injection molding supercritical fluid gas injection system is characterized by comprising a gas source, a main path unit, a branch path unit, a gas injector, a main path quick-break valve, a branch path quick-break valve and a gas injection control device, wherein the gas source, the main path unit, the main path quick-break valve and the gas injector are sequentially connected in series, the branch path quick-break valve and the branch path unit are connected in series and arranged between an outlet of the main path quick-break valve and an inlet of the gas injector, and the gas injection control device is used for controlling the opening and closing of the main path quick-break valve and the branch path quick-break valve so that the branch path quick-break valve is closed when the main path quick-break valve is opened; and when the main circuit quick-break valve is closed, the branch circuit quick-break valve is opened.
2. The micro-foaming injection molding supercritical fluid gas injection system according to claim 1, further comprising a first gas pressure sensor, a second gas pressure sensor and a melt pressure sensor connected to the gas injection control system, wherein the first pressure sensor is disposed on the inlet side of the main shut-off valve, the second pressure sensor is disposed on the inlet side of the branch shut-off valve, and the melt pressure sensor is disposed on the barrel of the injection molding machine.
3. The micro-foaming injection molding supercritical fluid gas injection system according to claim 1, wherein the main path unit comprises a pressurization device and a high-pressure gas storage tank.
4. The system of claim 1, wherein the gas injector comprises an on-off valve and a check valve, and the on-off valve can be turned on and off by a control system signal from the gas injection control device.
5. The micro-foaming injection molding supercritical fluid gas injection system according to claim 1, characterized in that the branch unit comprises a back pressure valve connected to the outlet of the branch quick-break valve, the outlet of the back pressure valve being open to the atmosphere or to the inlet of the pressurization device of the main unit.
6. The system of claim 5, wherein an adjustable needle valve is disposed between the branch quick-break valve and the back pressure valve.
7. The microfoam injection molding supercritical fluid gas injection system of claim 1, wherein the gas injector further comprises a flow restriction element disposed on an inlet side of the gas injector.
8. A gas injection method of the micro-foaming injection molding supercritical fluid gas injection system according to any one of claims 1 to 7, comprising:
the opening and closing of a main circuit quick-break valve and a branch circuit quick-break valve are controlled by a gas injection control device, so that the micro-foaming injection molding supercritical fluid gas injection system is switched between the following two states:
(1) in a first state, the main circuit quick-break valve is opened, the branch circuit quick-break valve is closed, so that the gas injector is communicated with the main circuit unit, and the gas injector is closed with the branch circuit unit, so that the gas pressure in a pipeline between the main circuit quick-break valve and the gas injector reaches a first pressure P1;
(2) in a second state, the main circuit quick-break valve is closed, the branch circuit quick-break valve is opened, so that the gas injector and the main circuit unit are closed, the gas injector and the branch circuit unit are communicated, and the gas pressure in a pipeline between the main circuit quick-break valve and the gas injector is equal to or less than a set second pressure P2;
wherein the first pressure P1 is greater than the second pressure P2.
9. The gas injection method of claim 8, wherein the second pressure is a melt back pressure of a gas injection section within a barrel of an injection molding machine.
10. A gas injection method according to claim 9, wherein the branching unit exhausts at least a portion of the gas in the conduit between the main path quick disconnect valve outlet and the gas injector to atmosphere or to the inlet of the main path unit's pressurization device.
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Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| US20010033040A1 (en) * | 2000-03-07 | 2001-10-25 | Cardona Juan C. | Blowing agent delivery system |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20010033040A1 (en) * | 2000-03-07 | 2001-10-25 | Cardona Juan C. | Blowing agent delivery system |
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| Title |
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| 段涛等: "超临界流体微孔发泡注塑中气涌现象的研究与定量测量", 《中国塑料》 * |
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