IV-type gas cylinder rotational molding method and IV-type gas cylinder

Abstract

The invention discloses an IV-type gas cylinder rotational molding method and an IV-type gas cylinder, and relates to the technical field of rotational molding. The IV-type gas cylinder rotational molding method comprises the following steps that a steel valve seat is installed in a cavity of a rotational molding mold, plastic powder is added into the rotational molding mold, and the steel valve seat is fed into a rotational molding machine after the mold is closed; and the steel valve seat is subjected to air blowing and heat supplementing from the initial heating stage to the time before the plastic reaches the sintering stage, and air blowing and heat supplementing are stopped after the plastic reaches the sintering stage. Plastic can be fully spread and wrapped, and the interface forming defect is avoided.

Description

Technical Field

[0001] This invention relates to the field of rotational molding technology, and in particular to a rotational molding method for a Type IV gas cylinder and the Type IV gas cylinder itself. Background Technology

[0002] Type IV gas cylinders are widely used in high-pressure gas storage and transportation due to their excellent lightweight and fatigue resistance. With the development of market demand, gas cylinders are evolving towards larger volumes.

[0003] To meet the rigidity requirements of system integration, large-capacity gas cylinders generally adopt a fixed-neck design. In this design, the valve seat at the cylinder neck not only serves as a medium passage but also becomes a critical mechanical fixing point that bears complex stresses such as vehicle vibration and inertial loads. This places far more stringent requirements on the strength, rigidity, and creep resistance of the valve seat material than on conventional gas cylinders. Under these conditions, the safety margin of traditional aluminum valve seats faces severe challenges and potential risks.

[0004] Therefore, the industry urgently needs to adopt high-strength steel valve seats in large-capacity Type IV gas cylinders to significantly improve the structural integrity and safety margin of the cylinder neck area. However, the rotational molding process of integrating steel valve seats into plastic inner liners presents the problem of interface forming defects. Due to the difference in specific heat capacity and thermal conductivity between steel and aluminum, under the same rotational molding heating environment, the heating rate of the steel valve seat lags significantly behind that of the mold and plastic powder. When the molten plastic comes into contact with the relatively cool surface of the steel valve seat, it is very easy for the plastic to fail to spread and encapsulate fully, resulting in defects such as bubbles and shrinkage cavities at the interface, which seriously compromises the sealing performance.

[0005] In view of the problems of the prior art, those skilled in the art urgently need a rotational molding method for Type IV gas cylinders and a Type IV gas cylinder. Summary of the Invention

[0006] The purpose of this invention is to provide a rotational molding method for Type IV gas cylinders and a Type IV gas cylinder, so as to solve the problems existing in the prior art, enabling the plastic to be fully spread and wrapped, and avoiding interface molding defects.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a rotational molding method for Type IV gas cylinders, comprising the following steps: installing a steel valve seat in the cavity of a rotational molding mold, adding plastic powder to the rotational molding mold, closing the mold, and feeding it into a rotational molding machine; during the initial heating stage until the plastic reaches the melting stage, blowing air to reheat the steel valve seat; and stopping the blowing air to reheat after the plastic reaches the melting stage.

[0008] In some embodiments, the method further includes: performing multi-stage heating during the heating phase, including a first heating phase, a holding phase, and a second heating phase performed sequentially; in the first heating phase, during the initial heating stage until the plastic reaches the melting stage, the steel valve seat is heated by blowing air, and after the plastic reaches the melting stage, the air blowing is stopped.

[0009] In some embodiments, the method further includes: performing multi-stage cooling during the cooling phase, including a first cooling phase, a second cooling phase, and a third cooling phase performed sequentially; in the second cooling phase, blowing air to cool the steel valve seat and the surrounding plastic, and after the second cooling phase ends, removing the components on the rotational molding mold used to fix the steel valve seat; in the third cooling phase, controlling the boom of the rotational molding machine to stop its revolution and controlling the spindle of the rotational molding machine to maintain its rotation.

[0010] In some embodiments, after the boom of the rotational molding machine stops rotating, the boom is adjusted to a horizontal position.

[0011] In some embodiments, during the first heating stage, the temperature inside the rotational molding die is raised to an activation temperature range that allows the plastic to fully melt; during the heat preservation stage, the temperature inside the rotational molding die is kept constant at the activation temperature range that allows the plastic to fully melt for a certain period of time, so that the molten plastic fully encapsulates the steel valve seat; during the second heating stage, the temperature inside the rotational molding die is raised to a peak value that allows the plastic to completely melt.

[0012] In some embodiments, during the first cooling stage, natural cooling is used to reduce the temperature inside the mold to a first preset cooling temperature; during the second cooling stage, air blowing is used to reduce the temperature inside the mold to a second preset cooling temperature. At the second preset cooling temperature, the plastic around the steel valve seat is cured and can support and fix the steel valve seat.

[0013] In some embodiments, the method further includes: after the cooling stage, opening the mold to remove the finished inner liner of the strip valve seat; winding continuous fibers around the outer wall of the finished inner liner of the strip valve seat; and placing the wound part in a curing oven for curing to form a Type IV gas cylinder.

[0014] In some embodiments, the step of "winding continuous fibers around the finished inner liner of the strip valve seat" involves: impregnating the continuous fibers with resin before winding; and winding according to a preset layup design and tension.

[0015] In some embodiments, before inserting the steel valve seat into the cavity of the rotational molding mold, the method further includes cleaning the steel valve seat with an organic solvent and ensuring that the steel valve seat is completely dry.

[0016] The present invention also provides a Type IV gas cylinder, which is prepared by the above-mentioned rotational molding method for Type IV gas cylinders.

[0017] The present invention achieves the following technical effects compared to the prior art: The rotational molding method for Type IV gas cylinders and the Type IV gas cylinder of the present invention involve blowing air to reheat the steel valve seat during the initial heating stage until the plastic reaches the melting stage. This ensures that the temperature of the steel valve seat can keep up with the heating of the rotational molding mold, avoiding incomplete plastic molten encapsulation due to a "cold core". After the plastic reaches the melting stage, the blowing air is stopped to prevent the gas that is continuously blown in from being blocked at the interface due to the difference in thermal expansion between steel and plastic, forming bubble defects. Thus, the present invention enables the plastic to spread out fully for encapsulation, avoiding interface forming defects.

[0018] Furthermore, the present invention employs a multi-stage heating strategy during the heating phase. By setting up a heat preservation phase, the constant temperature environment helps the internal temperature field of the mold and valve seat to tend to be balanced, reducing thermal stress concentration and thus improving fatigue resistance.

[0019] Furthermore, this invention employs a multi-stage cooling strategy during the cooling phase. In the second cooling phase, air blowing is used to cool the steel valve seat and its surrounding plastic, which accelerates the cooling and solidification of the steel valve seat and its surrounding plastic. This aims to quickly achieve sufficient mechanical strength by allowing the plastic to pass through its viscoelastic state, effectively preventing the risk of displacement or falling of the steel valve seat due to its high temperature and soft surrounding materials. Simultaneously, after removing the inserts used to fix the steel valve seat, the main arm is controlled to stop its revolution and the main shaft is controlled to maintain its rotation. The rotation ensures the uniformity of circumferential cooling of the inner liner, prevents deformation, and avoids the centrifugal force generated by the revolution from applying complex stress to the shrinking interface, which is conducive to the uniform release of stress and thus improves fatigue resistance. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. 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.

[0021] Figure 1 This is a flowchart of the steps of the rotational molding method for Type IV gas cylinders in some embodiments of the present invention; Figure 2 This is a schematic diagram illustrating the installation of the rotational molding machine and the rotational molding die in some embodiments of the present invention; 1-Rotational molding mold; 2-Rotational molding machine; 21-Main boom. Detailed Implementation

[0022] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The purpose of this invention is to provide a rotational molding method for Type IV gas cylinders and a Type IV gas cylinder, so as to solve the problems existing in the prior art, enabling the plastic to be fully spread and wrapped, and avoiding interface molding defects.

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Example 1 This embodiment provides a rotational molding method for Type IV gas cylinders, such as... Figure 1 As shown, it includes the following steps: Step S1: Install the steel valve seat into the cavity of the rotational molding mold 1, add plastic powder into the rotational molding mold 1, close the mold and send it into the rotational molding machine 2; Step S2: In the initial stage of heating until the plastic reaches the melting stage, the steel valve seat is heated by blowing air. After the plastic reaches the melting stage, the air blowing is stopped.

[0026] It should be noted that in step S1 above, the pre-treated steel valve seat is installed in the cavity of the rotational molding mold 1 using a high-precision positioning fixture; in the initial stage of heating, before the plastic reaches the first preset heating temperature, the steel valve seat is blown with air, and the first preset heating temperature corresponds to the plastic reaching the melting stage, which is the stage where the plastic begins to form layer by layer on the inner surface of the mold.

[0027] In some embodiments, step S2 further includes: The heating stage involves multiple stages of heating, including a first heating stage, a heat preservation stage, and a second heating stage performed sequentially. During the first heating stage, the steel valve seat is heated by blowing air during the initial heating phase until the plastic reaches the melting stage. After the plastic reaches the melting stage, the air blowing is stopped.

[0028] In some embodiments, the method further includes: Step S3: In the cooling stage, multi-stage cooling is performed, including a first cooling stage, a second cooling stage, and a third cooling stage performed sequentially; in the second cooling stage, the steel valve seat and its surrounding plastic are cooled by blowing air, and after the second cooling stage, the inserts used to fix the steel valve seat on the rotational molding mold 1 are removed; in the third cooling stage, the main arm 21 of the rotational molding machine 2 is controlled to stop its revolution and the main shaft of the rotational molding machine 2 is controlled to maintain its rotation.

[0029] It should be noted that, as Figure 2 As shown, the large arm 21 of the rotational molding machine 2 of the present invention can drive the rotational molding mold 1 to revolve, and the main shaft of the rotational molding machine 2 can drive the rotational molding mold 1 to rotate, and the rotation axes of the revolve and the rotation are perpendicular to each other.

[0030] In some embodiments, in step S3 above, after the boom 21 of the rotational molding machine 2 stops rotating, the boom 21 is adjusted to a horizontal position.

[0031] It should be noted that when the boom 21 is in a horizontal position, the rotational molding mold 1 is in a horizontal posture, the steel valve seat and the plastic inner liner are in a horizontal position, and the axis of the plastic inner liner is in a horizontal position. After the steel valve seat is released from the constraint, because the boom 21 is horizontal and does not rotate, its own weight is always vertically downward, and it will not swing and impact repeatedly in the mold, thus completely avoiding the risk of the steel valve seat damaging the precision mold cavity.

[0032] In some embodiments, in step S2 above, during the first heating stage, the temperature inside the rotational molding mold 1 is raised to the activation temperature range that allows the plastic to fully melt; during the heat preservation stage, the temperature inside the rotational molding mold 1 is kept constant at the activation temperature range that allows the plastic to fully melt for a certain period of time, so that the plastic melt fully covers the steel valve seat; during the second heating stage, the temperature inside the rotational molding mold 1 is raised to the peak value that allows the plastic to completely melt.

[0033] It should be noted that, in the first heating stage, the temperature is raised to a second preset heating temperature, which corresponds to the activation temperature range where the plastic reaches full melting. In the heat preservation stage, the temperature is maintained at the second preset heating temperature. In the second heating stage, the temperature is raised to a third preset heating temperature, which corresponds to the peak value where the plastic reaches complete melting. The third preset heating temperature is greater than the second preset heating temperature, which is greater than the first preset heating temperature.

[0034] In some embodiments, in step S3 above, in the first cooling stage, the temperature inside the mold is reduced to a first preset cooling temperature by natural cooling to release thermal stress; in the second cooling stage, the temperature inside the mold is reduced to a second preset cooling temperature by air blowing; at the second preset cooling temperature, the plastic around the steel valve seat is cured and can support and fix the steel valve seat; and the second preset cooling temperature is lower than the first preset cooling temperature.

[0035] In some embodiments, the method further includes: Step S4: After the cooling stage is completed, open the mold and remove the finished inner liner of the strip valve seat; Step S5: Continuous fibers are wound around the outer wall of the finished inner liner of the steel valve seat; Step S6: Place the wound part in a curing oven for curing to form a Type IV gas cylinder.

[0036] In some implementations, in step S5 above: Before winding, the continuous fibers are impregnated with resin; Winding is performed according to the preset layup design and tension.

[0037] In some embodiments, the method further includes, before inserting the steel valve seat into the cavity of the rotational molding die 1: Step S7: Clean the steel valve seat with an organic solvent and then allow it to dry completely to ensure the cleanliness of the mating surface of the steel valve seat, providing a good foundation for subsequent processes. Before use, thoroughly clean the surface of the steel valve seat with organic solvents such as acetone or alcohol to remove grease and residual abrasives, and ensure that it is completely dry.

[0038] In some embodiments, the ratio of the rotational speed at which the spindle drives the rotational molding mold 1 to rotate to the rotational speed at which the boom 21 drives the rotational molding mold 1 to revolve is 20:1 to 4:1, to ensure uniform material distribution and consistent inner wall thickness.

[0039] In some embodiments, a controllable air blowing system is integrated on the area of ​​the rotational molding die 1 corresponding to the steel valve seat; the controllable air blowing system is used to blow hot air to the steel valve seat for heat replenishment, or the controllable air blowing system is used to blow room temperature or low temperature air to the steel valve seat and its surrounding plastic for cooling.

[0040] The rotational molding method for Type IV gas cylinders of the present invention can effectively solve problems such as thermal mismatch, interface bubbles and cooling process in the rotational molding of steel valve seats, and achieve a permanent bond with high strength, high sealing performance and high reliability between the steel valve seat and the plastic inner liner.

[0041] The specific process steps of the rotational molding method for Type IV gas cylinders of the present invention are as follows: First, this invention employs a blowing heating strategy during the heating phase, including a heating period and a stop period. Heating period: In the initial heating stage until the plastic reaches the melting stage, the blowing system is activated to provide additional heat to the steel valve seat, ensuring its temperature keeps pace with the heating of the rotational molding mold 1. This prevents the plastic melt from being poorly encapsulated due to a "cold core," thus avoiding material shortage defects. Stop period: When the plastic reaches the melting stage, for example, approximately 100°C, the blowing heating is stopped. After this stage, the plastic powder begins to form layer by layer on the inner surface of the rotational molding mold 1, preventing the continued blowing of gas from being blocked at the interface due to the thermal expansion difference between steel and plastic, thus avoiding bubble defects.

[0042] Furthermore, this invention employs a multi-stage rotational molding temperature curve, comprising three stages. The first stage is a slow heating period, for example, the temperature rises from the initial temperature to a first preset heating temperature, such as 150°C, taking 10-30 minutes. The core of this stage is uniform preheating, controlling a low heating rate so that all parts of the rotational molding mold 1, the plastic powder, and the steel valve seat can absorb heat uniformly and synchronously. This avoids premature melting, clumping, or degradation of the plastic due to local overheating, ensuring uniform distribution of the powder within the rotational molding mold 1 and the uniformity of subsequent melting, laying the foundation for forming an inner liner with uniform wall thickness. The second stage: interface activation and heat preservation period, for example, maintaining the temperature at 150℃ ± 5℃ for 5-15 minutes; this stage is the key preparation period for interface bonding. 150℃ is the melting starting point of typical rotational molding plastics such as HDPE and the activation temperature of high-performance hot melt adhesives. Heat preservation at this temperature can achieve three important goals: full melting of plastic: allowing most of the plastic powder to fully melt at this constant temperature to form a melt with consistent fluidity; full wetting of the interface: giving the plastic melt enough time to fully flow, spread and wet the surface of the steel valve seat in a low viscosity state, achieving initial tight wrapping; initial stress relaxation: the constant temperature environment helps the temperature field inside the rotational molding mold 1 and the steel valve seat to tend to be uniform, reducing thermal stress concentration. The third stage: the fusion and curing stage, for example, the temperature rises from 150℃ to the peak value of 200~230℃, taking 5~15 minutes; this stage aims to achieve final cross-linking and curing, further raising the temperature to the peak value of complete melting of the plastic, allowing the plastic molecular chains to obtain sufficient energy for full diffusion and entanglement, achieving the best plasticizing effect and mechanical properties. At the same time, it ensures that any incompletely melted crystalline areas are melted, thereby obtaining a dense, stress-free final product structure. The multi-stage rotational molding temperature curve of this invention includes a specific holding stage at around 150℃ and a process window for controlling the peak temperature and the duration of high temperature, slowly heating from the initial temperature to 150℃, holding at 150℃, and rapidly heating from 150℃ to the peak temperature.

[0043] Then, the present invention adopts a segmented cooling strategy in the cooling stage, including a natural cooling period, a forced cooling period, and a horizontal rotation cooling period. Natural cooling period: In the early stage of cooling, the air blowing system is turned off, allowing the mold and inner liner to cool naturally and slowly to release interfacial thermal stress. Forced cooling period: When the temperature inside the rotational molding mold 1 is detected by the temperature monitoring system to drop to the first preset cooling temperature, such as below 150°C, the air blowing system is restarted; at this time, the gas blown in can be room temperature or low temperature air, used to accelerate the cooling and solidification of the steel valve seat and its surrounding plastic; to quickly pass through the viscoelastic state of the plastic, so that it can reach sufficient mechanical strength as soon as possible; and to ensure that when the valve seat fixing parts on the rotational molding mold 1 are removed, the plastic around the steel valve seat has sufficient strength and rigidity, effectively preventing the risk of displacement or falling of the steel valve seat due to the high temperature of the steel valve seat itself and the softness of the surrounding material. When the temperature inside the rotational molding mold 1 drops below 120℃, remove the steel valve seat fixing insert. That is, under the premise that the plastic inner liner has been initially shaped, safely remove the insert used to fix the steel valve seat on the rotational molding mold 1; immediately stop the revolution of the main arm of the rotational molding machine 2, and precisely adjust the main arm 21 to a horizontal position, while keeping the main shaft rotating. Horizontal rotation cooling period: With the main arm 21 stopped and in a horizontal position and the main shaft continuing to rotate, continue to complete the subsequent cooling process; thus, the rotation ensures the uniformity of circumferential cooling of the inner liner and prevents deformation; avoids the centrifugal force generated by the revolution from applying complex stress to the shrinking joint interface, which is conducive to the uniform release of stress; after the steel valve seat is released from the constraint, because the main arm 21 is horizontal and has no revolution, its own weight is always vertically downward, and it will not swing and impact repeatedly inside the rotational molding mold 1, completely avoiding the risk of the steel valve seat damaging the precision mold cavity.

[0044] The subsequent processing steps of this invention include demolding and post-processing, fiber winding molding, and curing and post-processing. The demolding and post-processing steps include: after cooling to a safe temperature, opening the mold and removing the part; after inspection, a finished inner liner with an integrated steel valve seat, used for manufacturing Type IV gas cylinders, is obtained. The fiber winding molding step includes: on the outside of the obtained finished inner liner with integrated steel valve seat, continuous fibers impregnated with resin, such as carbon fiber or glass fiber, are wound according to a preset layup design and tension. The curing and post-processing steps include: placing the wound shell part in a curing oven and curing it according to the resin system's curing process, so that the fiber winding layer is firmly bonded to the plastic inner liner, forming the final Type IV gas cylinder.

[0045] This invention achieves a dual improvement in product performance and manufacturing efficiency through a complete process control system from inner liner molding to gas cylinder solidification.

[0046] The rotational molding method for Type IV gas cylinders of the present invention has the following beneficial effects: This invention, through precise implementation of staged air blowing control, eradicates interface defects and cooling risks, providing a reliable foundation for manufacturing high-performance gas cylinders. During the heating stage, staged air blowing control, also known as heat replenishment control, employs a scheme of pre-melting heat replenishment and post-melting cessation, ensuring both the steel valve seat temperature and preventing gas blockage, thus increasing the first-pass yield of interface molding to over 98%. During the cooling stage, air blowing control, also known as forced cooling control, introduces secondary air blowing control triggered by a first preset cooling temperature, such as 150°C. Initially, no air blowing is used, achieving slow cooling of the interface and effectively releasing thermal stress, reducing residual stress by over 30%. Air blowing is initiated below the first preset cooling temperature (e.g., 150°C) to provide targeted forced cooling of the steel valve seat area, rapidly solidifying the surrounding plastic. This measure completely eliminates the risk of steel valve seat displacement or falling due to high steel valve seat temperature and soft surrounding plastic during mold positioning fixture removal, ensuring the accuracy of product dimensions and the stability of the production process.

[0047] Furthermore, this invention employs a stepped heating curve, optimizing the physical process of material melting and interfacial bonding, ensuring the core quality of the inner liner, and guaranteeing the final lifespan and safety of the gas cylinder. During the slow heating period, uniform preheating of the material and the rotational molding mold 1 is achieved, laying the foundation for uniform wall thickness and avoiding material degradation caused by thermal shock. During the interfacial activation and heat preservation period, the plastic melt fully encapsulates the steel valve seat at the optimal viscosity, providing the necessary thermodynamic conditions for achieving high-strength mechanical interlocking. The fusion and curing stage ensures complete plasticization and crystallization of the plastic material, enabling the inner liner to achieve optimal mechanical properties. Through a three-stage heating curve, the three key steps of preheating, interfacial preparation, and body curing are decoupled and optimized separately, achieving high-quality molding with uniformity from the interface to the body.

[0048] Furthermore, this invention simultaneously solves the problems of cooling uniformity, stress release, and equipment protection by adjusting the posture of the boom 21 during the cooling stage. After removing the steel valve seat fixing insert, the boom 21's revolution is immediately stopped and adjusted to a horizontal position, with only the spindle rotating to complete the cooling process. Firstly, this ensures uniform cooling; the rotation ensures consistent circumferential cooling of the inner liner, preventing deformation problems such as ellipticity. Secondly, it promotes stress release, eliminating the additional complex stress exerted on sensitive bonding interfaces by the centrifugal force of revolution, allowing the product to shrink freely and uniformly in a static state, significantly reducing residual stress. Thirdly, it protects the mold; the horizontal posture constrains the unconstrained steel valve seat, ensuring its weight remains vertically downward, preventing any lateral swaying or impact within the mold cavity, completely eliminating the risk of the steel valve seat damaging the precision mold cavity, and protecting core assets.

[0049] Furthermore, this invention establishes a logically rigorous and continuous gas cylinder manufacturing process that combines steel valve seat liner molding with fiber winding, improving production efficiency and ensuring consistent quality. The Type IV gas cylinder produced using this process features a plastic liner with a steel valve seat, manufactured through precise process control. The complete gas cylinder, consisting of this liner and the fiber winding layer, possesses extremely high safety margin at the nozzle, excellent fatigue resistance, and overall reliability, meeting the highest requirements for large-capacity, fixed-nozzle gas cylinders and providing strong technical support for the manufacturing of high-performance, large-capacity Type IV gas cylinders.

[0050] Example 2 This embodiment provides a Type IV gas cylinder, which is prepared using the rotational molding method for Type IV gas cylinders described in Embodiment 1.

[0051] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A rotational molding method for Type IV gas cylinders, characterized in that, Includes the following steps: The steel valve seat is installed in the cavity of the rotational molding mold, plastic powder is added to the rotational molding mold, and after the mold is closed, it is sent into the rotational molding machine. During the initial heating phase until the plastic reaches the melting stage, the steel valve seat is heated by blowing air. After the plastic reaches the melting stage, the air blowing is stopped.

2. The rotational molding method for Type IV gas cylinders according to claim 1, characterized in that, The method further includes: The heating stage involves multiple stages of heating, including a first heating stage, a heat preservation stage, and a second heating stage performed sequentially. In the first heating stage, the steel valve seat is heated by blowing air during the initial heating phase until the plastic reaches the melting stage. After the plastic reaches the melting stage, the air blowing is stopped.

3. The rotational molding method for Type IV gas cylinders according to claim 1, characterized in that, The method further includes: The cooling phase involves multiple stages of cooling, including a first cooling stage, a second cooling stage, and a third cooling stage performed sequentially. During the second cooling stage, the steel valve seat and its surrounding plastic are cooled by blowing air, and after the second cooling stage is completed, the components used to fix the steel valve seat on the rotational molding mold are removed. During the third cooling stage, the boom of the rotational molding machine is controlled to stop its revolution and the spindle of the rotational molding machine is controlled to maintain its rotation.

4. The rotational molding method for Type IV gas cylinders according to claim 3, characterized in that, After the boom of the rotational molding machine stops rotating, the boom is adjusted to a horizontal position.

5. The rotational molding method for Type IV gas cylinders according to claim 2, characterized in that, In the first heating stage, the temperature inside the rotational molding die is raised to the activation temperature range that allows the plastic to fully melt; During the heat preservation stage, the temperature inside the rotational molding mold is kept constant within the activation temperature range that allows the plastic to fully melt for a certain period of time, so that the molten plastic fully encapsulates the steel valve seat. In the second heating stage, the temperature inside the rotational molding die is raised to a peak value that allows the plastic to completely melt.

6. The rotational molding method for Type IV gas cylinders according to claim 3, characterized in that, In the first cooling stage, natural cooling is used to reduce the temperature inside the mold to the first preset cooling temperature; In the second cooling stage, the temperature inside the mold is reduced to the second preset cooling temperature by blowing air. At the second preset cooling temperature, the plastic around the steel valve seat is cured and can support and fix the steel valve seat.

7. The rotational molding method for Type IV gas cylinders according to claim 2, characterized in that, The method further includes: After the cooling stage is completed, the mold is opened and the finished inner liner with the steel valve seat is removed; The outer wall of the finished inner liner of the strip valve seat is wound with continuous fibers; The wound part is placed in a curing oven for curing to form a Type IV gas cylinder.

8. The rotational molding method for Type IV gas cylinders according to claim 7, characterized in that, In the step of "winding continuous fibers around the outer surface of the finished inner liner of the steel valve seat": Before winding, the continuous fibers are impregnated with resin; Winding is performed according to the preset layup design and tension.

9. The rotational molding method for Type IV gas cylinders according to claim 1, characterized in that, Before inserting the steel valve seat into the cavity of the rotational molding mold, the method further includes: The steel valve seat is cleaned with an organic solvent and then completely dried.

10. A type IV gas cylinder, characterized in that, It is prepared by the rotational molding method of any one of claims 1-9 for type IV gas cylinders.

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