Floater applied to liquid level induction of electric water boiler of passenger train

Abstract

The invention discloses a floater applied to liquid level induction of an electric heating water boiler of a passenger train. The floater is composed of a floater body and a magnet embedded in the floater body. The floater main body is obtained by injection molding of a foamed polypropylene material which can resist high temperature of more than or equal to 120 DEG C and has the density of less than or equal to 0.5 g / cm < 3 >, and the foamed polypropylene material comprises the following components in percentage by mass: 75-85wt% of a high-melt-strength PP base material, 10-15wt% of an SEBS elastomer, 3-8wt% of a heat-resistant modifier, 0.5-1.2 wt% of a foaming nucleating agent and 0.3-0.8 wt% of an antioxidant. The floater applied to the liquid level induction of the electric heating water boiler of the passenger train solves the problems that an existing floater made of PP materials is short in service life in the working process of the water boiler, the dead weight is prone to being increased, and the floating requirement cannot be met, and meanwhile the floater is simple in structure, convenient to produce and suitable for popularization and application. And high production yield can be ensured.

Description

Technical Field

[0001] This invention relates to the field of float technology, and specifically to a float for level sensing in electric water heaters for railway passenger cars. Background Technology

[0002] Currently, there are significant quality issues with magnetron level gauges, particularly with their internal floats, according to production and after-sales feedback. These floats are typically made of general-purpose PP material. However, water heaters often operate at temperatures exceeding 95℃, and under these conditions, the lifespan of these general-purpose PP floats is generally less than 12 months. The high temperatures in water heaters easily cause the molecular chains of the PP material to break down rapidly, leading to significant embrittlement, surface cracking, and water ingress. This increases the float's weight, making it unable to meet the floating requirements and resulting in various product malfunctions.

[0003] Meanwhile, existing magnetron level gauge floats (such as...) Figures 1-4 (As shown) These are generally manufactured using multi-part, modular ultrasonic welding, which results in complex processes and low production yield. The volume and density parameters of existing magnetron level gauge floats are generally as follows: volume v is approximately 4.9 cm³. 3 (Measured with a measuring cup), the mass m is approximately 3.6g (average of multiple weighings), therefore its density ρ is calculated to be approximately 0.75g / cm³. 3 (ρ=m / v=3.6g / 4.9cm 3 =0.735g / cm 3 ). Summary of the Invention

[0004] The purpose of this invention is to provide a float for level sensing in electric water heaters for railway passenger cars. It aims to solve the problems of existing PP material floats having a short service life and easily increasing weight during the operation of the water heater, thus failing to meet the floating requirements. At the same time, the float of this invention has a simple structure, is easy to produce, and can ensure a high production yield.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] The present invention provides a float for liquid level sensing in an electric water heater for railway passenger cars. The float is composed of a float body and a magnet embedded inside the float body.

[0007] The float body is made of material resistant to high temperatures ≥120℃ and with a density ≤0.5g / cm³. 3 The foamed polypropylene material is obtained by injection molding, and the foamed polypropylene material comprises the following components by mass fraction:

[0008] The composition includes 75-85 wt% high melt strength PP substrate, 10-15 wt% SEBS elastomer, 3-8 wt% heat-resistant modifier, 0.5-1.2 wt% foaming nucleating agent, and 0.3-0.8 wt% antioxidant.

[0009] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the main body of the float is a cylindrical structure with a diameter of 10.5 mm and a height of 50.0 mm, and the magnet is a cylindrical structure with a diameter of 8.0 mm and a height of 4.0 mm.

[0010] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the high melt strength PP substrate provides the foaming skeleton and thermal stability, and it is made of HMSPP resin with isotacticity >95%, such as Borclean. TM HMSPP resin.

[0011] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the SEBS elastomer is used to improve the toughness and cell uniformity of the foamed polypropylene material, and hydrogenated SEBS, such as Kraton G1651, is selected.

[0012] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the heat-resistant modifier is used to increase the heat distortion temperature (HDT) of the foamed polypropylene material, and is selected from one or more of maleic anhydride-grafted polypropylene (MAH-g-PP), nano clay, and silicon carbide whiskers.

[0013] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the foaming nucleating agent is used to control the size and density distribution of the bubbles, and it is selected from talc powder or organic nucleating agents with a particle size of less than 5.0 μm.

[0014] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the antioxidant is used to inhibit high-temperature oxidation of foamed polypropylene material, and it adopts a composite system composed of primary antioxidant 1010 and secondary antioxidant 168.

[0015] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the preparation process of the foamed polypropylene material includes the following steps:

[0016] S1. The high melt strength PP substrate, SEBS elastomer, heat-resistant modifier, foaming nucleating agent and antioxidant are mixed in proportion to form a uniform material;

[0017] S2. Put the above materials into a high-pressure reactor and introduce supercritical CO2 into the reactor to mix the materials thoroughly.

[0018] S3. Maintain a temperature of 155–160℃ and a pressure of 14–18 MPa for 25–45 minutes to allow the supercritical CO2 to fully dissolve and reach saturation. Then, slowly depressurize the material at a rate not exceeding 1.0 MPa / s to 60–80% of the original pressure, causing the supercritical CO2 to expand and form bubbles. Next, rapidly depressurize the material to atmospheric pressure within 10 seconds, causing the CO2 to rapidly expand and form pores. Finally, rapidly cool and solidify the foamed material to obtain a density of 0.25–0.45 g / cm³. 3 Foamed polypropylene material.

[0019] Specifically, the density of foamed polypropylene material can be controlled between 0.25 and 0.45 g / cm³ by adjusting the temperature and pressure. 3 Requirements between them.

[0020] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the forming process of the float body is as follows: the foamed polypropylene material is filled into an injection mold preheated to 165-170°C, steam is then introduced into the injection mold, and then it is rapidly cooled to obtain the float body; the steam permeation pressure is 0.8-1.2 MPa, and the cooling rate is >15°C / min.

[0021] Furthermore, a float for level sensing in an electric water heater for railway passenger cars: the magnet is a ferrite magnet or a neodymium iron boron magnet.

[0022] The beneficial effects of this invention are:

[0023] This invention improves the formulation of foamed polypropylene material, enabling the floats made from it to maintain structural stability at long-term operating temperatures above 120℃. This solves the problem of short service life of existing PP material floats during water heater operation, and also addresses the issue that PP material floats are prone to accelerated molecular chain breakage due to high temperatures during water heater operation, resulting in float embrittlement, surface cracking, water ingress, increased float weight, and failure to meet floating requirements. The floats of this invention can be used normally for more than 3 years.

[0024] Meanwhile, this invention, through the optimization of the foaming formula, not only achieves the characteristic of easy injection molding (good processing fluidity) of the foamed polypropylene material, but also ensures that the float made of this foamed polypropylene material does not affect water quality during long-term use in water dispensers, i.e., it will not release harmful substances (such as formaldehyde, heavy metal ions), meeting drinking water and food contact standards. Furthermore, thanks to the optimization of the foaming formula and foaming process of this invention, the resulting foamed polypropylene material can achieve a low density (0.25~0.45g / cm³). 3The density of polypropylene foam is significantly lower than that of water (less than 50%), making it more suitable as a float material compared to traditional PP materials. Furthermore, this invention incorporates steam with a permeation pressure of 0.8–1.2 MPa during injection molding, which further ensures the uniformity of the foamed polypropylene material's cell structure during the molding process.

[0025] The float provided by this invention, which is used for liquid level sensing in electric water heaters for railway passenger cars, consists of only a cylindrical float body and a magnet embedded in the float body. Its structure is simple, easy to manufacture, and can ensure a high production yield. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of an existing float;

[0028] Figure 2 A front view of the existing float;

[0029] Figure 3 This is a cross-sectional view of an existing float, which is... Figure 2 Cross-sectional view along the AA direction;

[0030] Figure 4 A schematic diagram of an explosion of an existing float;

[0031] Figure 5 This is a schematic diagram of the structure of the float for liquid level sensing in an electric water heater for railway passenger cars, provided in Embodiment 1 of the present invention.

[0032] Figure 6 for Figure 5 Cross-sectional view along the AA direction.

[0033] The markings in the image are as follows:

[0034] 1-Float body, 2-Magnet. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] like Figures 5-6 As shown, this embodiment 1 provides a float for level sensing in an electric water heater used in railway passenger cars. The float consists of a float body 1 and a magnet 2 embedded inside the float body 1. The float body 1 is cylindrical with a diameter of 10.5 mm and a height of 50.0 mm. The magnet 2 is also cylindrical with a diameter of 8.0 mm and a height of 4.0 mm. The magnet 2 has a density of approximately 7.4 g / cm³. 3 High-performance neodymium iron boron magnets;

[0038] The float body 1 is made of material with a high temperature resistance of ≥120℃ and a density of ≤0.5g / cm³. 3 The foamed polypropylene material (EPP) is obtained by injection molding, wherein the foamed polypropylene material (EPP) comprises the following components by mass fraction:

[0039] The composition includes 82.5 wt% high melt strength PP substrate, 12.0 wt% SEBS elastomer, 4.0 wt% heat-resistant modifier, 0.8 wt% foaming nucleating agent, and 0.7 wt% antioxidant.

[0040] The high melt strength PP substrate is used to provide the foaming skeleton and thermal stability, and it is selected from HMSPP resin (Borclean) with an isotacticity >95%. TM HMSPP resin); the SEBS elastomer is used to improve the toughness and cell uniformity of the foamed polypropylene material, and hydrogenated grade SEBS (Kerteng G1651) is selected; the heat-resistant modifier is used to increase the heat distortion temperature (HDT) of the foamed polypropylene material, and maleic anhydride grafted polypropylene (MAH-g-PP) is selected; the foaming nucleating agent is used to control the cell size and density distribution, and talc powder with a particle size of less than 5.0 μm is selected; the antioxidant is used to inhibit the high-temperature oxidation of the foamed polypropylene material, and it adopts a composite system composed of primary antioxidant 1010 and secondary antioxidant 168 (the ratio of the two is 1:1).

[0041] The preparation process of the foamed polypropylene material includes the following steps:

[0042] S1. The high melt strength PP substrate, SEBS elastomer, heat-resistant modifier, foaming nucleating agent and antioxidant are mixed in proportion to form a uniform material;

[0043] S2. Put the above materials into a high-pressure reactor and introduce supercritical CO2 into the reactor to mix the materials thoroughly.

[0044] S3. Maintain a temperature of 156℃ and a pressure of 15.0 MPa for 30 minutes to allow the supercritical CO2 to fully dissolve and reach saturation. Then, slowly depressurize to 70% of the original pressure at a rate not exceeding 1.0 MPa / s, causing the supercritical CO2 to expand and form bubbles. Next, rapidly depressurize to atmospheric pressure within 10 seconds, causing the CO2 to rapidly expand and form pores. Finally, rapidly cool and solidify the foamed material to obtain a density of 0.35 g / cm³. 3 Foamed polypropylene material;

[0045] The forming process of the float body 1 is as follows: the obtained foamed polypropylene material is filled into an injection mold preheated to 168°C, steam (steam permeation pressure of 1.0MPa) is introduced into the injection mold, and then the material is rapidly cooled at a rate of >15°C / min to obtain the float body 1.

[0046] Example 2

[0047] The difference between Example 2 and Example 1 is that the magnet 2 in Example 2 has a density of approximately 5.0 g / cm³. 3 The ferrite magnet is the same as in Example 1.

[0048] Example 3

[0049] Example 3 also provides a float for level sensing in an electric water heater for railway passenger cars. This float consists of a float body 1 and a magnet 2 embedded inside the float body 1. The float body 1 is a cylindrical structure with a diameter of 10.5 mm and a height of 50.0 mm. The magnet 2 is also a cylindrical structure with a diameter of 8.0 mm and a height of 4.0 mm. The magnet 2 has a density of approximately 5.0 g / cm³. 3 Ferrite magnets;

[0050] The float body 1 is made of material with a high temperature resistance of ≥120℃ and a density of ≤0.5g / cm³. 3 The foamed polypropylene material (EPP) is obtained by injection molding, wherein the foamed polypropylene material comprises the following components by mass fraction:

[0051] The composition includes 81.0 wt% high melt strength PP substrate, 10.0 wt% SEBS elastomer, 8.0 wt% heat-resistant modifier, 0.5 wt% foaming nucleating agent, and 0.5 wt% antioxidant.

[0052] The high melt strength PP substrate is used to provide the foaming skeleton and thermal stability, and it is selected from HMSPP resin (Borclean) with an isotacticity >95%. TM HMSPP resin); the SEBS elastomer is used to improve the toughness and cell uniformity of the foamed polypropylene material, and hydrogenated grade SEBS (Kerteng G1651) is selected; the heat-resistant modifier is used to increase the heat distortion temperature (HDT) of the foamed polypropylene material, and nano-clay is selected; the foaming nucleating agent is used to control the cell size and density distribution, and talc powder with a particle size of less than 5.0 μm is selected; the antioxidant is used to inhibit the high-temperature oxidation of the foamed polypropylene material, and it adopts a composite system composed of primary antioxidant 1010 and secondary antioxidant 168 (the ratio of the two is 1:2).

[0053] The preparation process of the foamed polypropylene material includes the following steps:

[0054] S1. The high melt strength PP substrate, SEBS elastomer, heat-resistant modifier, foaming nucleating agent and antioxidant are mixed in proportion to form a uniform material;

[0055] S2. Put the above materials into a high-pressure reactor and introduce supercritical CO2 into the reactor to mix the materials thoroughly.

[0056] S3. Maintain the temperature at 160℃ and the pressure at 14.0MPa for 45 minutes to allow the supercritical CO2 to fully dissolve and reach saturation. Then, slowly depressurize the supercritical CO2 to 60% of the original pressure at a depressurization rate not exceeding 1.0MPa / s to allow the supercritical CO2 to expand and form bubbles. Then, rapidly depressurize the supercritical CO2 to atmospheric pressure within 10 seconds to allow the CO2 to expand rapidly and form pores. Finally, rapidly cool and solidify the foamed material to obtain foamed polypropylene material.

[0057] The forming process of the float body 1 is as follows: the obtained foamed polypropylene material is filled into an injection mold preheated to 165°C, steam (steam permeation pressure of 0.8MPa) is introduced into the injection mold, and then the material is rapidly cooled at a rate of >15°C / min to obtain the float body 1.

[0058] Example 4

[0059] Example 4 also provides a float for level sensing in an electric water heater for railway passenger cars. This float consists of a float body 1 and a magnet 2 embedded inside the float body 1. The float body 1 is a cylindrical structure with a diameter of 10.5 mm and a height of 50.0 mm. The magnet 2 is also a cylindrical structure with a diameter of 8.0 mm and a height of 4.0 mm. The magnet 2 has a density of approximately 7.4 g / cm³. 3 High-performance neodymium iron boron magnets;

[0060] The float body 1 is made of material with a high temperature resistance of ≥120℃ and a density of ≤0.5g / cm³. 3 The foamed polypropylene material (EPP) is obtained by injection molding, wherein the foamed polypropylene material comprises the following components by mass fraction:

[0061] The composition includes 79.0 wt% high melt strength PP substrate, 14.5 wt% SEBS elastomer, 4.5 wt% heat-resistant modifier, 1.2 wt% foaming nucleating agent, and 0.8 wt% antioxidant.

[0062] The high melt strength PP substrate is used to provide the foaming skeleton and thermal stability, and it is selected from HMSPP resin (Borclean) with an isotacticity >95%. TM HMSPP resin); the SEBS elastomer is used to improve the toughness and cell uniformity of the foamed polypropylene material, and hydrogenated grade SEBS (Kerteng G1651) is selected; the heat-resistant modifier is used to increase the heat distortion temperature (HDT) of the foamed polypropylene material, and 4.0 wt% maleic anhydride grafted polypropylene (MAH-g-PP) and 0.5 wt% silicon carbide whiskers are selected; the foaming nucleating agent is used to control the cell size and density distribution, and talc powder with a particle size of less than 5.0 μm is selected; the antioxidant is used to inhibit the high-temperature oxidation of the foamed polypropylene material, and it adopts a composite system composed of primary antioxidant 1010 and secondary antioxidant 168 (the ratio of the two is 1:2).

[0063] The preparation process of the foamed polypropylene material includes the following steps:

[0064] S1. The high melt strength PP substrate, SEBS elastomer, heat-resistant modifier, foaming nucleating agent and antioxidant are mixed in proportion to form a uniform material;

[0065] S2. Put the above materials into a high-pressure reactor and introduce supercritical CO2 into the reactor to mix the materials thoroughly.

[0066] S3. Maintain the temperature at 158℃ and the pressure at 18.0MPa for 25 minutes to allow the supercritical CO2 to fully dissolve and reach saturation. Then, slowly depressurize the supercritical CO2 to 80% of the original pressure at a depressurization rate not exceeding 1.0MPa / s to allow the supercritical CO2 to expand and form bubbles. Then, rapidly depressurize the supercritical CO2 to atmospheric pressure within 10 seconds to allow the CO2 to expand rapidly and form pores. Finally, rapidly cool and solidify the foamed material to obtain foamed polypropylene material.

[0067] The forming process of the float body 1 is as follows: the obtained foamed polypropylene material is filled into an injection mold preheated to 170°C, steam (steam permeation pressure of 1.2MPa) is introduced into the injection mold, and then the material is rapidly cooled at a rate of >15°C / min to obtain the float body 1.

[0068] The key parameters of the float for liquid level sensing in the electric water heater of railway passenger car provided in the above embodiment 1 are calculated as follows: the volume of the float is denoted as V(total), the actual volume of the float body 1 is denoted as V(EPP), the volume of the magnet 2 is denoted as V(magnet), the mass of the float is denoted as m(total), the actual mass of the float body 1 is denoted as m(EPP), and the mass of the magnet 2 is denoted as m(magnet).

[0069] First, calculate the volume V(total) of the float. Since magnet 2 is embedded in the float body 1, the volume V(total) of the float is equivalent to the volume of the cylindrical float body 1, i.e., Vtotal = πr 2 h = 3.14 × (5.25 mm) 2 ×50mm=4329.8mm 3 =4.330cm 3 ;

[0070] Next, calculate the volume V(magnet) of cylindrical magnet 2, V(magnet) = 3.14 × (4.0 mm) 2 ×4mm=201.0mm 3 =0.201cm 3 ;

[0071] Then, the actual volume of the float body 1 is calculated and denoted as V(EPP). Since the magnet 2 is embedded in the float body 1, the actual volume V(EPP) of the float body 1 is correspondingly the volume of the cylindrical float body 1 minus the volume of the cylindrical magnet 2, V(magnet), that is, V(EPP) = V(total) - V(magnet) = 4.330 cm 3 -0.201cm 3 =4.129cm 3 ;

[0072] Based on this, the actual mass m(EPP) of the float body 1 is calculated, where m(EPP) = ρ(EPP).

[0073] ×V(EPP)=0.35g / cm 3 ×4.129cm 3 =1.445g;

[0074] Calculate the mass m(magnet) of magnet 2: m(magnet) = ρ(magnet) × V(magnet) = 7.4 g / cm³ 3 ×0.201cm 3=1.487g;

[0075] Therefore, the mass of the float, m(total), is m(total) = m(magnet) + m(EPP) = 1.445g + 1.487g = 2.932g. Based on this, the overall density ρ(total) of the float in Example 1 is calculated as ρ(total) = m(total) / V(total) = 2.932g / 4.330cm². 3 =0.677g / cm 3 ;

[0076] It can be seen that the average density of the float provided in Example 1 is significantly lower than that of water, which meets the floating requirements of the float in the water heater. Furthermore, the float in Example 1, through improvements to the foamed polypropylene material formula, has the effect of maintaining a long-term operating temperature above 120°C, solving the problem of short service life of existing PP material floats during water heater operation. Because the foamed polypropylene material of this invention has the effect of long-term resistance to high temperatures above 120°C, it also overcomes the problem that existing PP material floats are prone to accelerated molecular chain breakage due to high temperatures during water heater operation, causing float embrittlement, surface cracking, and water ingress, resulting in increased float weight and failure to meet floating requirements. The float of this invention can be used normally for more than 3 years. In addition, the float of this invention has a simple structure, avoiding the problems of complex production processes and low yield rates associated with existing ultrasonically welded floats.

[0077] The difference between the float of Example 2 and that of Example 1 is that the magnet 2 used in the float of Example 2 is a ferrite magnet. Based on the above calculation process, the overall density ρ of the float of Example 2 is 0.566 g / cm³. 3 .

[0078] Water quality safety testing was conducted on the float of Example 1: migration testing was performed in accordance with GB 4806.7-2023 standard. The test results showed that the heavy metal leaching amount of the float of Example 1 was <0.01mg / L, which met the safety standard.

[0079] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A float for level sensing in an electric water heater used in railway passenger cars, characterized in that, The float is composed of a float body (1) and a magnet (2) embedded inside the float body (1); The float body (1) is made of a material resistant to high temperatures ≥120℃ and with a density ≤0.5g / cm³. 3 The foamed polypropylene material is obtained by injection molding, and the foamed polypropylene material comprises the following components by mass fraction: The composition includes 75-85 wt% high melt strength PP substrate, 10-15 wt% SEBS elastomer, 3-8 wt% heat-resistant modifier, 0.5-1.2 wt% foaming nucleating agent, and 0.3-0.8 wt% antioxidant.

2. The float for level sensing in an electric water heater for railway passenger cars according to claim 1, characterized in that, The float body (1) is a cylindrical structure with a diameter of 10.5 mm and a height of 50.0 mm, and the magnet (2) is a cylindrical structure with a diameter of 8.0 mm and a height of 4.0 mm.

3. A float for level sensing in an electric water heater for railway passenger cars according to claim 1, characterized in that, The high melt strength PP substrate is used to provide a foaming skeleton and thermal stability, and it is selected from HMSPP resin with isotacticity > 95%.

4. A float for level sensing in an electric water heater for railway passenger cars according to claim 1, characterized in that, The SEBS elastomer is used to improve the toughness and cell uniformity of foamed polypropylene materials, and hydrogenated SEBS is selected.

5. A float for level sensing in an electric water heater for railway passenger cars according to claim 1, characterized in that, The heat-resistant modifier is used to increase the heat distortion temperature of the foamed polypropylene material, and it is selected from one or more of maleic anhydride-grafted polypropylene, nano clay, and silicon carbide whiskers.

6. A float for level sensing in an electric water heater for railway passenger cars according to claim 1, characterized in that, The foaming nucleating agent is used to control the cell size and density distribution, and it is selected from talc powder or organic nucleating agents with a particle size of less than 5.0 μm.

7. A float for level sensing in an electric water heater for railway passenger cars according to claim 1, characterized in that, The antioxidant is used to inhibit the high-temperature oxidation of foamed polypropylene materials, and it adopts a composite system composed of primary antioxidant 1010 and secondary antioxidant 168.

8. A float for level sensing in an electric water heater for railway passenger cars according to any one of claims 1 to 7, characterized in that, The preparation process of the foamed polypropylene material includes the following steps: S1. The high melt strength PP substrate, SEBS elastomer, heat-resistant modifier, foaming nucleating agent and antioxidant are mixed in proportion to form a uniform material; S2. Put the above materials into a high-pressure reactor and introduce supercritical CO2 into the reactor to mix the materials thoroughly. S3. Maintain a temperature of 155–160℃ and a pressure of 14–18 MPa for 25–45 minutes to allow the supercritical CO2 to fully dissolve and reach saturation. Then, slowly depressurize the material at a rate not exceeding 1.0 MPa / s to 60–80% of the original pressure, causing the supercritical CO2 to expand and form bubbles. Next, rapidly depressurize the material to atmospheric pressure within 10 seconds, causing the CO2 to rapidly expand and form pores. Finally, rapidly cool and solidify the foamed material to obtain a density of 0.25–0.45 g / cm³. 3 Foamed polypropylene material.

9. A float for level sensing in an electric water heater for railway passenger cars according to any one of claims 1 to 7, characterized in that, The forming process of the float body is as follows: The foamed polypropylene material is filled into an injection mold preheated to 165-170°C, steam is then introduced into the injection mold, and then it is rapidly cooled to obtain the float body (1). The vapor permeation pressure is 0.8–1.2 MPa, and the cooling rate is >15 °C / min.

10. A float for level sensing in an electric water heater for railway passenger cars according to claim 1, characterized in that, The magnet (2) is a ferrite magnet or a neodymium iron boron magnet.

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