Automatic trace injection method of low-boiling-point foaming agent

Abstract

The invention relates to the technical field of foaming agent injection, in particular to a low-boiling-point foaming agent automatic trace injection method which comprises the following steps: S1, inputting a low-boiling-point medium pressurized to a critical state or above into a V-1012 container, and placing the V-1012 container in an MRU-1002 low-temperature freezer for refrigeration and heat preservation; s2, the low-boiling-point medium in the V-1012 container is subjected to two-stage pressurization through a P-1011 plunger metering pump, and the low-boiling-point medium subjected to two-stage pressurization through plunger metering penetrates through a V-1026 back pressure valve and is shunted to a backflow channel and an outflow channel which are connected in parallel; s3, a low-boiling-point medium flows to the V-1012 container through the backflow channel; the low-boiling-point medium passes through the outflow channel to flow to the next process; therefore, a low-boiling-point medium which is easy for two-phase conversion can be accurately controlled; the problems that low-boiling-point foaming agents are prone to two-phase transformation and injection precision is difficult to control are solved.

Description

Technical Field

[0001] The invention relates to the technical field of foaming agent injection, and in particular to an automatic micro-injection method for a low-boiling-point foaming agent. Background Art

[0002] Low-boiling-point foaming agents can vaporize at relatively low temperatures to produce gas to foam the material. However, due to the characteristic that low-boiling-point foaming agents can vaporize at relatively low temperatures, the molecules of low-boiling-point foaming agents can easily change from liquid to gas even at normal room temperature, or produce a form in which gas and liquid coexist. The transition between the gas and liquid phases makes it difficult to accurately control the injection of low-boiling-point foaming agents in actual injection.

[0003] Therefore, the present invention provides a method for automatically injecting a low-boiling-point foaming agent in a small amount to solve the above-mentioned problems. Summary of the invention

[0004] The technical problem to be solved by the present invention is that low-boiling-point foaming agents are prone to two-phase transition and it is difficult to control the injection accuracy.

[0005] The present invention provides the following technical solution: a method for automatically injecting a low-boiling-point foaming agent in a small amount, comprising the following steps: A method for automatically injecting a low-boiling-point foaming agent in a micro-amount is characterized by comprising the following steps: S1, input the low boiling point medium pressurized to above the critical state into the V-1012 container, and the V-1012 container is placed in the MRU-1002 low temperature freezer for refrigeration and heat preservation; S2, the low boiling point medium in the V-1012 container is pressurized by the P-1011 plunger metering pump for secondary boosting, and the low boiling point medium pressurized by the P-1011 plunger metering pump passes through the V-1026 back pressure valve and is divided into a parallel reflux channel and an outflow channel, wherein the reflux channel is filled with recycled low boiling point medium, and the outflow channel is filled with low boiling point medium flowing to the next process; S3, the low boiling point medium flows to the V-1012 container through the reflux channel; the outflow channel includes parallel flow channel 1 and flow channel 2, the low boiling point medium is switched in the outflow channel through flow channel 1 and flow channel 2 and input into the FT-1002 precision mass flowmeter, the low boiling point medium is input into the V-1033 back pressure valve through the FT-1002 precision mass flowmeter and then flows to the next process.

[0006] The reflux channel is installed with a V-1028 back pressure valve, and a V-1033 back pressure valve is installed behind the outflow channel. The pressure of the P-1011 plunger metering pump after pressurization is greater than that of the V-1026 back pressure valve, the back pressure value of the V-1026 back pressure valve is greater than that of the V-1028 back pressure valve, and the back pressure value of the V-1028 back pressure valve is greater than that of the V-1033 back pressure valve.

[0007] A FT-1002 precision mass flow meter is installed behind the outflow channel.

[0008] A first pressure difference is formed between the V-1026 back pressure valve and the V-1028 back pressure valve, and a second pressure difference is formed between the V-1026 back pressure valve and the V-1033 back pressure valve. The first pressure difference is greater than the second pressure difference to form a third pressure difference.

[0009] The outflow channel includes a parallel flow channel 1 and a flow channel 2, wherein the flow channel 1 is installed with a control valve V-1029 and a manual precision regulating valve V-1031 for controlling the opening and closing of the flow channel 1, and the flow channel 2 is installed with a control valve V-1030 and a pneumatic flow ratio regulating valve V-1032 for controlling the opening and closing of the flow channel 2.

[0010] An F-1020 precision high-pressure pipeline filter is installed in front of the V-1012 container, and an F-1021 precision high-pressure pipeline filter is installed between the P-1011 plunger metering pump and the V-1026 back pressure valve.

[0011] The P-1011 plunger metering pump adopts open loop control.

[0012] The V-1012 container is provided with a pressure sensor and a front-end booster pump closed-loop control.

[0013] The back pressure value of the V-1033 back pressure valve is 3-5 MPa greater than the pressure at the position where the low boiling point foaming agent is injected into the screw.

[0014] The low-boiling-point medium is transported through an insulation pipe, which includes an outer pipe, an inner pipe and a jacket layer. The inner pipe is coaxially fixedly installed in the outer pipe, a jacket layer is fixedly arranged between the outer pipe and the inner pipe, a circulation loop with a spiral structure is fixedly installed in the jacket layer, and the circulation loop is connected to an external constant temperature device.

[0015] The circulation loops are arranged in a plurality, a circulation loop is fixedly installed between back pressure valves with different back pressure values, and each circulation loop is individually connected to a constant temperature device, and a pressure detector and a temperature detector are fixedly installed in the inner tube.

[0016] The beneficial effects of the present invention are as follows: 1. The present invention uses the pressure difference between the V-1026 back pressure valve and the V-1033 back pressure valve to micro-control the low-boiling point medium through the pressure difference, so that the low-boiling point medium can be accurately injected regardless of whether it is liquid, gaseous, or a combination of gas and liquid; and, through the cooperation of the V-1028 back pressure valve, the low-boiling point medium is stably discharged to the downward process, and the overflowed low-boiling point medium is returned to the container for recycling, thereby avoiding waste during the injection process; at the same time, the pressure difference can also enable the low-boiling point medium of gas and / or liquid to circulate stably, which is beneficial to improving the applicability of the low-boiling point medium during injection.

[0017] 2. The present invention can switch between manual control and automatic control of the flow of low-boiling-point media through the parallel reflux channel and outflow channel, and can further achieve precise and trace control of the flow of low-boiling-point media in conjunction with the FT-1002 precision mass flow meter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a schematic diagram of the overall process of the present invention; Figure 2 This is a schematic diagram of the process of the P-1011 plunger metering pump after secondary pressurization of the present invention; Figure 3 This is a schematic diagram of the structure of the thermal insulation pipe in the second embodiment of the present invention; Figure 4 Schematic diagram of the internal structure of the thermal insulation pipe in the second embodiment of the present invention.

[0020] In the figure: 1. V-1020 back pressure valve; 11. F-1020 precision high pressure pipeline filter; 2. V-1012 container; 3. MRU-1002 low temperature freezer; 4. P-1011 plunger metering pump; 41. F-1021 precision high pressure pipeline filter; 5. V-1026 back pressure valve; 6. Reflux channel; 61. V-1028 back pressure valve; 7. Outflow channel; 71. Flow channel 1; 7 11. V-1029 control valve; 712. V-1031 manual precision regulating valve; 72. Flow channel two; 721. V-1030 control valve; 722. V-1032 pneumatic flow ratio regulating valve; 8. FT-1002 precision mass flow meter; 9. V-1033 back pressure valve; 10. Insulation pipe; 101. Outer pipe; 102. Inner pipe; 103. Jacket layer; 1031. Circulation loop. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents some embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0023] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "back" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use. Such terms are only used to facilitate the description of the present invention and simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0024] It should also be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] The disclosed embodiments are intended to solve the problem that the existing low-boiling point foaming agent is prone to two-phase transition and is difficult to control injection accuracy.

[0026] Embodiment 1: The present disclosure provides a method for automatically injecting a low-boiling-point foaming agent in a small amount, comprising the following steps: S1, input the low boiling point medium pressurized to above the critical state into the V-1012 container 2, and the V-1012 container 2 is placed in the MRU-1002 low temperature freezer 3 for refrigeration and heat preservation; S2, the low boiling point medium in the V-1012 container 2 is pressurized by the P-1011 plunger metering pump 4 for secondary boosting, and the low boiling point medium pressurized by the plunger metering P-1011 secondary boosting passes through the V-1026 back pressure valve 5 and is divided into a parallel reflux channel and an outflow channel, wherein the reflux channel is filled with recycled low boiling point medium, and the outflow channel is filled with low boiling point medium flowing to the next process; S3, the low boiling point medium flows to the V-1012 container 2 through the reflux channel; the outflow channel includes parallel flow channel 1 and flow channel 2, and the low boiling point medium is switched in the outflow channel through flow channel 1 and flow channel 2 and input into the FT-1002 precision mass flowmeter 8, and the low boiling point medium is input into the V-1033 back pressure valve 9 through the FT-1002 precision mass flowmeter 8 and then flows to the next process.

[0027] It should be noted that in S1, the low boiling point medium is increased to a critical state by the electric or pneumatic means of the previous stage; the V-1012 container 2 can also be refrigerated, and the cooling capacity can also reach -18°C, thereby forming a double-layer refrigeration effect. In addition, the refrigeration temperature of the V-1012 container 2 can be selected to be lower than that of the MRU-1002 low-temperature freezer 3, and the refrigeration temperature of the V-1012 container 2 can also be selected to be higher than that of the MRU-1002 low-temperature freezer 3. The pressure in the V-1012 container 2 is 600 bar.

[0028] In S2, the reflux channel is installed with a V-1028 back pressure valve 61, and the outflow channel is installed with a V-1033 back pressure valve 9. The pressure of the P-1011 plunger metering pump 4 after pressurization is greater than that of the V-1026 back pressure valve 5. The back pressure value of the V-1026 back pressure valve 5 is greater than that of the V-1028 back pressure valve 61. The back pressure value of the V-1028 back pressure valve 61 is greater than that of the V-1033 back pressure valve 9, thereby forming a stable pressure difference among the P-1011 plunger metering pump 4, the V-1026 back pressure valve 5, the V-1028 back pressure valve 61 and the V-1033 back pressure valve 9. Among them, a first pressure difference is formed between the V-1026 back pressure valve 5 and the V-1028 back pressure valve 61, and a second pressure difference is formed between the V-1026 back pressure valve 5 and the V-1033 back pressure valve 9. The first pressure difference is greater than the second pressure difference to form a third pressure difference.

[0029] Through the first pressure difference, the second pressure difference and the third pressure difference formed between the V-1026 back pressure valve 5, the V-1028 back pressure valve 61 and the V-1033 back pressure valve 9, the low boiling point medium can be injected by micro-controlling through the pressure difference, thereby improving the accuracy of the injection of the low boiling point medium. In addition, both the gaseous medium and the liquid medium can be micro-controlled through the pressure difference, which is conducive to improving the applicability of the injection of the low boiling point medium.

[0030] The pressure of the P-1011 plunger metering pump 4 after boosting can reach 45MPa, the pressure inside the plunger metering P-1011 is 50Mpa, and the internal flow rate is 3.2L / H. The back pressure value of the V-1026 back pressure valve 5 is set at 38 MPa, the set pressure inside the V-1026 back pressure valve 5 is 300bar, and the cv value of the V-1026 back pressure valve 5 is 0.14, that is, when the valve is fully open and the pressure difference is 1psi, the water flow rate passing through per minute is 0.14 US gallons, so that the flow rate of low boiling point media can be finely controlled. The back pressure value of the V-1028 back pressure valve 61 is set at 35 MPa.

[0031] In the S2, by setting the pressure difference of the back pressure values ​​among the V-1026 back pressure valve 5, the V-1028 back pressure valve 61 and the V-1033 back pressure valve 9, and coordinating the first pressure difference, the second pressure difference and the third pressure difference, the low-boiling-point medium can be diverted to the parallel reflux channel and the outflow channel due to the pressure difference, forming a recycled low-boiling-point medium and a low-boiling-point medium flowing to the next process. The recycled low-boiling-point medium can be discharged back to the V-1012 container 2 through the V-1028 back pressure valve 61 for recovery and cooling and reuse.

[0032] In S3, the outflow channel includes a flow channel 1 and a flow channel 2 in parallel, and the flow channel 1 is installed with a V-1029 control valve 711 and a V-1031 manual precision regulating valve 712 for controlling the opening and closing of the flow channel 1, and the flow channel 2 is installed with a V-1030 control valve 721 and a V-1032 pneumatic flow ratio regulating valve 722 for controlling the opening and closing of the flow channel 2. By switching the opening and closing of the valve V-1029 and the valve V-1030, the flow of the flow channel 1 and the flow channel 2 is switched and controlled, and the V-1031 manual precision regulating valve 712 and the V-1032 pneumatic flow ratio regulating valve 722 are connected in parallel. The back pressure valve V-1031 is a manually controlled precision regulating valve, and the back pressure valve V-1032 is a pneumatic flow proportional regulating valve and can be automatically controlled, so that the V-1031 manual precision regulating valve 712 and the V-1032 pneumatic flow proportional regulating valve 722 can be set between the stable pressure differences of the first pressure difference, the second pressure difference and the third pressure difference to facilitate switching between manual or automatic flow control.

[0033] It should be noted that only one of the parallel flow channel 1 and flow channel 2 can be kept open to circulate the low boiling point medium at the same time. In the injection system, either manual or automatic control mode can be selected separately. That is, by closing valve V-1030, the flow rate can be manually controlled by using the V-1031 manual precision regulating valve 712 circuit alone, or by closing valve V-1029, the flow rate can be automatically controlled by using the V-1032 pneumatic flow ratio regulating valve 722 circuit alone.

[0034] In S3, the V-1031 manual precision regulating valve 712 and / or the V-1032 pneumatic flow ratio regulating valve 722 are followed by an FT-1002 precision mass flow meter 8, and the FT-1002 precision mass flow meter 8 and the V-1032 pneumatic flow ratio regulating valve 722 form a closed-loop control, thereby enabling the V-1032 pneumatic flow ratio regulating valve 722 to achieve precise automatic control. The V-1031 manual precision regulating valve 712 is a multi-turn precision regulating valve, thereby enabling the flow and / or pressure of the low-boiling-point medium to be more precisely regulated.

[0035] In S1 and S2, an F-1020 precision high-pressure pipeline filter 11 is installed in front of the V-1012 container 2, and an F-1021 precision high-pressure pipeline filter 41 is installed between the P-1011 plunger metering pump 4 and the V-1026 back pressure valve 5. The F-1020 precision high-pressure pipeline filter 11 and the F-1021 precision high-pressure pipeline filter 41 can ensure that the low-boiling point medium remains clean when entering the V-1012 container 2, and ensure that the low-boiling point medium remains clean when it is discharged back to the V-1012 container 2 through the V-1028 back pressure valve 61 for recycling.

[0036] In S2, the P-1011 plunger metering pump 4 adopts open-loop control, thereby ensuring that the pressure value is stably within the set range.

[0037] In the S1, a pressure sensor is provided on the V-1012 container 2 and connected to the booster pump at the front end to realize closed-loop control of the pressure, so that the pressure of the V-1012 container 2 itself is stably maintained at the set pressure value.

[0038] The back pressure value of the V-1033 back pressure valve 9 is usually set at 32MPa. The back pressure value of the V-1033 back pressure valve 9 is 3-5MPa greater than the pressure at the low boiling point foaming agent injection screw position. The set pressure of the V-1033 back pressure valve 9 is 240bar, and the cv value is 0.14.

[0039] The low-boiling-point medium is pressurized to above the critical state and then filtered through the F-1020 precision high-pressure pipeline filter 11. After filtration, it enters the V-1012 container 2 through the V-1020 back pressure valve 1 for refrigeration and insulation. Then the low-boiling-point medium in the V-1012 container 2 passes through the P-1011 plunger metering pump 4 and then is pressurized to 45 MPa in the second stage. The low-boiling-point medium after the second stage of pressurization is filtered again through the F-1021 precision high-pressure pipeline filter 41 and maintained at a pressure of 38 MPa through the V-1026 back pressure valve 5.

[0040] After the low boiling point medium passes through the V-1026 back pressure valve 5, open either the control valve V-1029 or the control valve V-1030. When the control valve V-1029 is opened, the low boiling point medium passes through the V-1031 manual precision regulating valve 712, thereby manually controlling the flow of the low boiling point medium; when the control valve V-1030 is opened, the low boiling point medium passes through the V-1032 pneumatic flow ratio regulating valve 722 for automatic control flow.

[0041] After the low-boiling-point medium passes through the V-1031 manual precision regulating valve 712 or the V-1032 pneumatic flow ratio regulating valve 722, it enters the FT-1002 precision mass flowmeter 8 to further control the injection amount of the low-boiling-point medium in a small and precise manner. After passing through the FT-1002 precision mass flowmeter 8, it is discharged through the V-1033 back pressure valve 9 with a pressure 3-5MPa greater than the low-boiling-point foaming agent injection screw position for injection, thereby completing the injection of the low-boiling-point medium.

[0042] Embodiment 2: Based on Embodiment 1, only the differences from Embodiment 1 are described below, and the similarities are not repeated here.

[0043] In this embodiment, a low-boiling-point medium is transported through an insulation pipe 10, and the insulation pipe 10 includes an outer pipe 101 and an inner pipe 102. The inner pipe 102 is coaxially fixedly installed in the outer pipe 101, and the inner pipe 102 is used to transport the low-boiling-point medium. The outer pipe 101 is made of rock wool, glass wool, polyurethane foam or rubber and plastic sponge, so that the outer pipe 101 can insulate the inner pipe 102, thereby avoiding the external temperature from affecting the temperature of the low-boiling-point medium in the inner pipe 102, avoiding the pressure change of the low-boiling-point medium temperature due to the interference of the external temperature, which is conducive to ensuring that the temperature of the low-boiling-point medium remains stable.

[0044] A jacket layer 103 is fixedly arranged between the outer tube 101 and the inner tube 102, and a circulation loop 1031 with a spiral structure is fixedly installed in the jacket layer 103. A constant temperature medium flows in the circulation loop 1031, and the circulation loop 1031 is connected to an external constant temperature device. The constant temperature device allows the constant temperature medium to flow in the circulation loop 1031 and keep the temperature of the inner layer in a stable state or at a preset temperature value, so that when the outdoor temperature is too low or too high, the inner tube 102 can be kept in a constant temperature stable state or at a preset temperature value, and cooperate with the insulation of the outer tube 101 to ensure that the temperature of the low boiling point medium is stable and not affected by the external temperature.

[0045] It should be noted that the constant temperature medium is preferably in liquid state, and can also be in gaseous state. In the embodiment of the present disclosure, water is selected as the constant temperature medium. The constant temperature device adopts a constant temperature bath, a constant temperature water bath, a constant temperature oil bath, or other constant temperature devices composed of a temperature controller and a heating and cooling device in the prior art. Since the constant temperature device adopts a very mature technology in the prior art, the specific structure and principle of the constant temperature device in the embodiment of the present disclosure are not elaborated in detail.

[0046] The circulation loop 1031 is set to be multiple, and a circulation loop 1031 is fixedly installed between back pressure valves with different back pressure values, and each circulation loop 1031 is individually connected to a constant temperature device. A pressure detector and a temperature detector are fixedly installed in the inner tube 102. The pressure and temperature of the low boiling point medium in the inner tube 102 are detected in real time by the pressure detector and the temperature detector, and the temperature of the constant temperature device is controlled in real time according to the temperature detected by the pressure detector and the temperature detector.

[0047] It should be noted that the installation method, structure and principle of the pressure detector and the temperature detector can adopt the standards and methods in the prior art, so they are not described in detail in the embodiments of the present disclosure.

[0048] When the pressure detector and the temperature detector detect that the pressure value and / or the temperature value of the low-boiling-point medium is abnormal, the temperature of the constant temperature medium is changed by changing the temperature of the constant temperature equipment of this section, and then when the constant temperature medium flows in the circulation loop 1031, the inner tube 102 is heated or cooled by the constant temperature medium to fine-tune the abnormal pressure of the low-boiling-point medium, so that the low-boiling-point medium with the abnormal pressure value is adjusted toward the preset pressure value, thereby ensuring that the pressure value of the low-boiling-point medium is stable after passing through the back pressure valves with different back pressure values, thereby stabilizing the pressure difference between the back pressure valves, and thereby ensuring that the low-boiling-point medium is stably and accurately controlled by the stable pressure difference for micro-injection.

[0049] While the constant temperature medium is circulated in the circulation loop 1031 in the interlayer, the outer tube 101 insulates the low boiling point medium in the interlayer and the inner tube 102 through its own insulation material, thereby further avoiding the influence of the external temperature on the low boiling point medium, which is beneficial to ensure the stability of the pressure value of the low boiling point medium, and further ensures that the low boiling point medium is stably and accurately controlled by a stable pressure difference for micro-injection.

[0050] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for automatically injecting a low-boiling-point foaming agent in a small amount, characterized in that The following steps are involved: S1, inputting the low boiling point medium pressurized to above the critical state into the V-1012 container (2), and placing the V-1012 container (2) in the MRU-1002 low temperature freezer (3) for refrigeration and heat preservation; S2, the low boiling point medium in the V-1012 container (2) is subjected to secondary pressurization by the P-1011 plunger metering pump (4), and the low boiling point medium that has been subjected to secondary pressurization by the P-1011 plunger metering pump (4) passes through the V-1026 back pressure valve (5) and is divided into a parallel reflux channel (6) and an outflow channel (7), wherein the reflux channel (6) is filled with a recycled low boiling point medium, and the outflow channel (7) is filled with a low boiling point medium that flows to the next process; S3, the low boiling point medium flows to the V-1012 container (2) through the reflux channel (6); the outflow channel (7) includes a flow channel 1 (71) and a flow channel 2 (72) connected in parallel, and the low boiling point medium is switched in the outflow channel (7) through the flow channel 1 (71) and the flow channel 2 (72) and input into the FT-1002 precision mass flow meter (8), and the low boiling point medium is input into the V-1033 back pressure valve (9) through the FT-1002 precision mass flow meter (8) and then flows to the next process.

2. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 1, characterized in that: The reflux channel (6) is installed with a V-1028 back pressure valve (61), and the outflow channel (7) is followed by a V-1033 back pressure valve (9). The pressure after pressurization by the P-1011 plunger metering pump (4) is greater than that of the V-1026 back pressure valve (5). The back pressure value of the V-1026 back pressure valve (5) is greater than that of the V-1028 back pressure valve (61). The back pressure value of the V-1028 back pressure valve (61) is greater than that of the V-1033 back pressure valve (9).

3. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 2, characterized in that: An FT-1002 precision mass flow meter (8) is installed behind the outflow channel (7).

4. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 3, characterized in that: A first pressure difference is formed between the V-1026 back pressure valve (5) and the V-1028 back pressure valve (61), and a second pressure difference is formed between the V-1026 back pressure valve (5) and the V-1033 back pressure valve (9). The first pressure difference is greater than the second pressure difference to form a third pressure difference.

5. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 4, characterized in that: The outflow channel (7) comprises a flow channel 1 (71) and a flow channel 2 (72) connected in parallel. The flow channel 1 (71) is provided with a valve V-1029 and a manual precision regulating valve V-1031 (712) for controlling the opening and closing of the flow channel 1 (71). The flow channel 2 (72) is provided with a valve V-1030 and a pneumatic flow ratio regulating valve V-1032 (722) for controlling the opening and closing of the flow channel 2 (72).

6. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 5, characterized in that: An F-1020 precision high-pressure pipeline filter (11) is installed in front of the V-1012 container (2), and an F-1021 precision high-pressure pipeline filter (41) is installed between the P-1011 plunger metering pump (4) and the V-1026 back pressure valve (5).

7. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 6, characterized in that: The back pressure value of the V-1033 back pressure valve (9) is 3-5 MPa greater than the pressure at the position where the low boiling point foaming agent is injected into the screw.

8. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 7, characterized in that: The pressure of the P-1011 plunger metering pump (4) after pressurization is 45 MPa, the back pressure value of the V-1026 back pressure valve (5) is set at 38 MPa, the back pressure value of the V-1028 back pressure valve (61) is set at 35 MPa, and the back pressure value of the V-1033 back pressure valve (9) is set at 32 MPa.

9. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 8, characterized in that: The low-boiling-point medium is transported through an insulation pipe (10), the insulation pipe (10) comprising an outer pipe (101), an inner pipe (102) and a jacket layer (103), the inner pipe (102) being coaxially fixedly installed inside the outer pipe (101), the jacket layer (103) being fixedly arranged between the outer pipe (101) and the inner pipe (102), a circulation loop (1031) having a spiral structure being fixedly installed inside the jacket layer (103), and the circulation loop (1031) being connected to an external constant temperature device.

10. The method for automatically injecting a low-boiling-point foaming agent in a micro-amount according to claim 9, characterized in that: The circulation loops (1031) are arranged in a plurality, and a circulation loop (1031) is fixedly installed between back pressure valves with different back pressure values, and each circulation loop (1031) is individually connected to a constant temperature device, and a pressure detector and a temperature detector are fixedly installed in the inner tube (102).

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