A roll-blow molding equipment and process for a hydrogen storage cylinder plastic inner liner

Abstract

This invention proposes a roll-blow molding equipment and process for plastic liners of hydrogen storage cylinders. The equipment includes an inner liner mold driving device, a rotational molding mold system, a pneumatic control system, and an in-mold gas temperature regulation system. The rotational molding mold includes an inner mold, a heating module, an insulation layer, and an outer mold. The process includes a roll-blow combined process of early-stage high-temperature low-pressure molding, mid-stage high-temperature high-pressure molding, and late-stage low-temperature high-pressure molding. This invention controls the in-mold gas pressure through the pneumatic control system to solve the bubble problem and improve the mechanical properties of the inner liner, thereby increasing processing efficiency and molding accuracy. It innovatively designs a multi-layer mold to improve temperature control efficiency and pressure resistance, and develops a molding equipment with lightweight moving parts. This invention controls the in-mold temperature during the inner liner molding process through the in-mold gas temperature regulation system to solve the temperature imbalance problem during in-mold gas pressure regulation. Furthermore, it designs different temperature gas replacement methods to achieve independent and rapid control of the in-mold gas temperature.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing and molding, specifically to a rapid roll blow molding equipment and process for hollow products such as plastic liners for hydrogen storage bottles. Background Technology

[0002] Large, hollow polymer or polymer composite products are typically molded using methods such as rotational molding, blow molding, injection welding, winding, or transfer molding. As a typical hollow product, the plastic liner of a hydrogen storage cylinder requires high molding precision and efficiency. The most common molding methods are rotational molding, blow molding, and injection welding. Furthermore, commonly used liner materials are high-density polyethylene (HDPE) and nylon. HDPE is suitable for various molding methods due to its good moldability. Nylon, especially nylon 6, which possesses higher barrier properties and creep resistance, is prone to sag during extrusion and welding due to its high processing temperature, narrow processing window, and low viscosity, leading to molding failure. Compared to the other two molding methods, rotational molding offers numerous advantages, including strong dimensional flexibility, easier wall thickness adjustment, stress-free molded products, and low equipment costs, making it suitable for the development of experimental liners and mass production. More importantly, rotational molding uses mold rotation to move the material and adhere it to the mold's inner wall, reducing the impact of gravity on the melt. However, rotational molding also has many problems such as low molding efficiency, low dimensional accuracy, and low material density of the finished product.

[0003] Rotational molding is a pressureless, unconstrained molding process using powder materials, which is prone to various defects such as air bubbles and uneven wall thickness during the molding process. Previous studies have shown that continuous low or high pressure within the mold during the powder melting process of rotational molding can reduce air bubbles in the material (the high pressure refers to the absolute pressure within the mold, approximately 0.1–0.6 MPa; the low pressure refers to the absolute pressure within the mold, approximately 0–0.1 MPa), achieving some success. However, continuous low pressure can easily lead to reduced heat transfer efficiency of the air within the mold and the emergence of temperature dead zones in the mold. Continuous high pressure can reduce air bubbles by accelerating the dissolution of air bubbles in the free volume formed after polymer unentanglement, but during the later atmospheric pressure cooling process, it may cause a further decrease in material density, affecting the barrier performance of key structures such as the inner liner of hydrogen storage cylinders. In addition, the internal pressure that can be applied is currently limited, and before the inner liner reaches the crystallization temperature, higher internal pressure can improve the density and toughness of the material. However, simply increasing the wall thickness of existing molds to withstand internal pressure will cause heating and cooling problems. Furthermore, existing gas pressure adjustment does not consider the impact of gas temperature on the internal temperature during the adjustment process. Furthermore, during the cooling process, the lack of an inner mold to restrict shrinkage makes the outer dimensions and coaxiality of the inner liner prone to significant deviations due to various key factors such as material batch, cooling rate, and structural thickness. Patent 201010582896.0 proposes a device for maintaining the shape of the product by inflating it after demolding. However, according to the PVT curve of plastics, significant shape changes typically occur between the melting point and crystallization temperature. The method proposed in this patent is insufficient to suppress large deformations in the outer dimensions of the product and is unsuitable for manufacturing precision products such as hydrogen storage cylinder liners. In addition, existing patents do not consider gas temperature control, making them highly susceptible to excessive internal stress due to rapid cooling rates. Moreover, for products like inner liners with large dissimilar material inserts, asynchronous cooling may cause the base material to crack due to internal stress. Summary of the Invention

[0004] To address the challenges of residual air bubbles on the product wall during rotational molding, the difficulty in controlling the external dimensional accuracy of the product, and internal stress defects in the hydrogen storage bottle liner caused by different cooling rates of metal-plastic inserts, this invention proposes a rotational-blow molding equipment and process for hydrogen storage bottle plastic liners. The system controls the in-mold pressure through a pneumatic control system, solving the problem of air bubbles failing to escape from the liner wall in a timely manner, increasing the mechanical properties of the liner material after molding, and reducing the hydrogen permeability coefficient. Furthermore, the pneumatic control system can provide sufficient in-mold pressure during the liner cooling process to maintain the external dimensions of the liner within the mold's constraints, improving the molding accuracy of the liner. This invention also utilizes an in-mold gas temperature regulation system to control the in-mold temperature during the liner molding process, solving the temperature imbalance problem during in-mold pressure regulation. Moreover, a gas temperature displacement method can quickly adjust the in-mold gas temperature and achieve independent control of the in-mold gas temperature from the mold. In terms of equipment, this invention designs an easily heated and high-pressure resistant mold and develops a set of molding equipment with lighter moving parts, resolving the contradiction between the heating and cooling efficiency and pressure bearing capacity of existing molds, and saving energy. In terms of process, this invention proposes a roll-blowing synergistic process of early high-temperature low-pressure molding, mid-stage high-temperature high-pressure molding, and late-stage low-temperature high-pressure molding, combined with roll-blowing molding equipment, to solve the problems of low processing efficiency caused by long thermal circulation time during inner liner molding and uncontrollable outer dimensions of the inner liner due to inner liner shrinkage.

[0005] This invention discloses a roll-blow molding equipment for plastic liners of hydrogen storage cylinders, comprising a liner mold driving device, a rotational molding mold system, a pneumatic control system, and an in-mold gas temperature regulation system. This invention uses a swing-type IV hydrogen storage cylinder plastic liner rotational molding machine as an example, but is not limited to rotational molding equipment for swing-type hydrogen storage cylinder liners. The liner mold driving device includes a frame, motor, conductive slip ring, gear roller, smooth roller, axial limiting roller, and reducer, etc. The rotational molding mold system includes a rotational molding mold, mold frame, and heating copper ring. The rotational molding mold includes an inner mold, heating module, insulation layer, and outer mold. The pneumatic control system includes a data acquisition system, shut-off valve, overflow valve, vacuum pressure sensor, in-mold gas pressure sensor, air compressor, quick-connect coupling, pressure and speed regulating valve, rotary joint, gas guide pipe, baffle, vacuum pump, and gas cooling device, etc. The in-mold gas temperature regulation system includes a gas heating device, a gas static mixer, and a temperature sensor, etc.

[0006] The specific connection method of the rotational molding equipment for a hydrogen storage bottle plastic inner liner according to the present invention is as follows: The rotational molding mold of the present invention consists of an inner mold, a heating module, an insulation layer, and an outer mold from the inside out. The positions of each component of the rotational molding mold are relatively fixed during use. The rotational molding mold of the present invention is fixedly connected to a mold frame, which supports the rotational molding mold and prevents it from deforming. It is also used to install structural components or control components that need to move with the rotational molding mold. The mold frame is fixedly connected to a rotating frame by bolts. Gear rollers, axial limiting rollers, and smooth rollers are welded or fastened to the rotating frame by bolts. The gear rollers are connected to a reducer fixed on a special-shaped support frame by gear meshing and are driven to rotate by a motor. The smooth rollers are able to roll relative to the rollers fixed on the special-shaped support frame, serving to cooperate with the gear rollers to support the rotating frame. The axial limiting rollers are connected to a limiting rod fixed on a rocking frame through a limiting groove and a bearing mounted on the limiting rod. The radial separation prevention function of the limit rod and axial limit roller is achieved by a limit block connected to the limit rod via a threaded connection. The electrical input and output of the electrical components on the rotating frame are achieved through conductive slip rings. The irregular support frame is welded to the rocking frame. The rocking frame is connected to the fixed frame on the ground via a rocking bearing and is driven by a motor mounted on the fixed frame. The insert of the hydrogen storage tank's plastic inner liner is fixed to the rotational molding mold by a heating copper ring via a threaded connection. The gas conduit is fixed to the heating copper ring and arranged coaxially. The gas conduit is divided into an inlet conduit and an exhaust conduit. A baffle is installed at the head of the inlet conduit. Both the inlet and exhaust conduits are fixed to the external pipelines via coaxial nuts; if necessary, the threads are designed as sealing threads. The external pipeline connected to the inlet conduit is sequentially connected to an in-mold pressure sensor, an overflow valve, a gas heating device, an inlet shut-off valve, and an inlet rotary joint; all related components are connected via metal pipes. The gas heating device is fixed to the mold frame and moves together with the mold frame. After the air inlet rotary joint, relevant components can be selectively connected using plastic hoses or metal pipes. Following the air inlet rotary joint, it connects to a high-pressure air source via a pressure regulating and speed regulating valve. The high-pressure air source includes a centralized air source provided in the work area / workshop and an air source provided by a specially configured air compressor. The centralized air source in the work area / workshop can be directly connected to the system described in this invention using quick-connect couplings. Depending on the specific requirements of material molding, the air source provided by the air compressor can draw gas directly from the air or nitrogen or inert gas from a storage tank. An external pipeline connected to the exhaust duct is sequentially connected to a vacuum pump shut-off valve, an exhaust rotary joint, a vacuum pressure sensor, a gas cooling device, and a vacuum pump. Gas cooled by the gas cooling device and extracted by the vacuum pump can be either directly discharged into the air via the vent shut-off valve or enter the gas recovery tank via the recovery tank shut-off valve, depending on the specific contents. The gas cooling device and vacuum pump are both mounted on the ground and do not move with the mold.

[0007] The baffle described in this invention is mainly used to solve the problem of poor uniformity of gas temperature distribution within the rotational molding mold due to excessively high gas flow velocity. Preferably, the baffle has a built-in rotor, allowing the gas entering the mold to rotate and constantly change the airflow direction, resulting in better uniformity of gas temperature distribution at various locations. Alternatively, a mesh structure can be used instead, causing the gas to be scattered in different directions after passing through the baffle. Alternatively, the baffle may have an external mesh cylindrical structure with a built-in rotor. The baffle is preferably made of metal. The baffle is coaxially mounted with the air inlet duct, and its outer diameter is preferably smaller than that of the air inlet duct.

[0008] The gear rings and smooth rings described in this invention should be installed on both sides of the central cross-section of the rotational molding die, and the design should consider maintaining balance after the rotational molding die is installed. For shorter rotational molding dies, one gear ring and one smooth ring are preferred; as the die length increases, the number of rings can be appropriately increased to maintain sufficient support capacity. Alternatively, both support rings on the rotational molding die can be gear rings. Alternatively, a gear ring can be installed in the middle of the rotational molding die, with an equal number of smooth rings distributed on both sides of the gear ring.

[0009] The axial limiting roller ring described in this invention is mainly used to prevent the gear roller ring and smooth roller ring from sliding axially away from the reducer gear or roller when the mold is driven to swing by the swinging frame. Alternatively, the reducer gear or roller can also provide axial limiting for both the gear roller ring and the smooth roller ring. This is achieved by having bosses on both sides of the reducer gear or roller that are higher than the contact surface of the roller ring. As a roller ring connection structure that can be used on a 360° rotating swinging frame, the irregular support frame described in this invention can be symmetrically positioned relative to the plane of the swinging frame; in this case, the total number of gears or rollers on a single annular surface should be at least three. Alternatively, the roller surface can be designed with a layer of elastomer or other cushioning material to reduce vibration during equipment operation.

[0010] The rotational molding die of this invention comprises an inner mold, a heating module, an insulation layer, and an outer mold. In the equipment described in this invention, the rotational molding die can be used in the following ways: First, the inner mold can be used alone for heating methods such as oven-type or flame-type heating. Second, the inner mold and heating module, or the inner mold, heating module, and insulation layer can be used in combination for heating methods such as electric heating or infrared heating, but the pressure that can be filled into the mold is relatively low and should be controlled within the range of 0–0.4 MPa; alternatively, the inner mold wall thickness can be increased, and the pressure range can be adjusted according to the specific pressure bearing capacity, but this significantly affects processing efficiency and increases energy consumption. Third, the inner mold, heating module, insulation layer, and outer mold can be used in combination for heating methods such as electric heating, and can be applied to higher in-mold pressures. The inner mold is preferably designed with a relatively thin thickness to improve heating and cooling efficiency while ensuring structural rigidity. The heating module is embedded in or covers the inner mold. The insulation layer is preferably made of materials such as fiber felt with low thermal conductivity, and the thickness is preferably 5-10 mm. The outer mold is designed based on the maximum pressure inside the mold and is mainly used to prevent large deformation of the inner mold. The outer mold described in this invention can be made of metal materials or fiber-reinforced thermosetting composite materials. As an alternative, when the outer mold is formed using high-temperature resistant, low-thermal-conductivity, and high-strength materials such as glass fiber, an insulation layer may not be used.

[0011] The gas heating device of this invention is preferably fixed to the mold frame via a bracket, and does not directly contact the rotational molding mold. The exhaust port of the gas heating device is connected to the inlet of the air inlet duct via a metal bend, and the gas flow distance of the bend should be designed to be short.

[0012] The in-mold pressure sensor of this invention is installed near the inlet of the air intake duct. Preferably, a gas cooling structure is installed between the in-mold pressure sensor and the main air intake path to prevent high-temperature gas from affecting the measurement accuracy of the in-mold pressure sensor.

[0013] In this invention, all pipelines of the air heating section in the roll-blow molding equipment for the plastic inner liner of a hydrogen storage bottle are preferably externally covered with insulation materials such as asbestos insulation felt or insulation tape.

[0014] In the roll-blow molding equipment for the plastic inner liner of a hydrogen storage bottle of the present invention, the pipes, rotary joints and other connecting pipes that come into contact with hot air are all made of metal materials, preferably stainless steel.

[0015] The air intake duct and the air exhaust duct of the present invention are preferably coaxially fixed together to facilitate the installation of the gas duct and the removal of the gas duct after the inner liner is formed.

[0016] The gas conduit and the heating copper ring of this invention are coaxially fixed together, and the fixed position should have good airtightness after fixing. Furthermore, the interior of the fixed position between the heating copper ring and the gas conduit should be rounded and free of foreign objects. Preferably, the gas inlet conduit of this invention is coaxially mounted with the mold to facilitate demolding.

[0017] The gas heating device of the present invention preferably uses high-frequency electromagnetic heating, and the gas flow channel of the gas heating device is preferably designed as a labyrinth structure to facilitate gas heating. Preferably, a static gas mixer is installed in the gas flow channel of the gas heating device, and the static gas mixer should be made of metal material.

[0018] The gas cooling device described in this invention is mainly used to cool the gas entering the vacuum pump, preventing prolonged high temperatures from affecting the pump's performance. The cooling method of the gas cooling device can be liquid refrigeration or compressor refrigeration; preferably, fins are used in the gas cooling device to accelerate the cooling effect.

[0019] The connecting surfaces between the segments of the rotational molding die described in this invention should be equipped with guide structures, adjacent mold segments should fit together, and the connection points of the rotational molding die should be designed with external reinforcing structures. The parting line of the rotational molding die described in this invention should be designed with a structure that provides a low-pressure sealing effect, and the sealing direction should prevent gas from outside the rotational molding die from entering its interior. Preferably, the rotational molding dies described in this invention are sealed using sealing rings, and the sealing rings should be made of metal. Alternatively, the sealing ring cross-section is designed as a U-shape, with the opening of the U-shaped sealing ring facing outwards from the mold.

[0020] The specific molding process of the roll-blow molding equipment for the plastic inner liner of a hydrogen storage bottle according to the present invention is as follows:

[0021] First, before starting work, check the equipment and confirm that the equipment is sealed properly. Close all shut-off valves, set the safety air pressure of the overflow valve, add the material, and close the mold. The rotational molding mold is preheated according to the melting temperature of the material being processed. The motor drives the swing frame and the rotating frame to move so that the material inside the rotational molding mold can contact the inner wall of the mold in a predetermined manner. The air pressure inside the mold is set to low pressure. The rotational molding mold is heated according to the normal operation so that the internal material melts and adheres to the inner wall of the mold. When the material is powder or powder / melt multiphase, the low pressure inside the mold is maintained so that the material can expel air bubbles during the melting process.

[0022] The second step is to introduce high-pressure gas with the same temperature as the original gas in the mold into the mold when all the material is adhered to the inner wall of the mold and has become melt. This keeps the mold under high pressure while the material is in the molten state, so that the density of the melt can be further increased. At the same time, it promotes the filling of the groove structure of the insert to a certain extent.

[0023] The third step involves maintaining a high-pressure state of the gas inside the mold while rapidly reducing the temperature of the gas inside the mold through the aforementioned gas replacement method, thereby helping to lower the temperature of the mold and allowing the molded product to gradually cool down.

[0024] This invention discloses a roll-blow molding process for a hydrogen storage bottle plastic inner liner. When it is necessary to increase the gas pressure inside the mold, the inlet shut-off valve is opened. The high-pressure gas supplied by the gas source enters the gas heating device through the gas heating device inlet after the pressure and flow rate are adjusted by the pressure regulating and speed regulating valve. The gas comes into full contact with the gas static mixer to increase the temperature. The temperature of the gas flowing out of the gas heating device exhaust port is adjusted according to the needs inside the mold. The pressure inside the mold is monitored by the inside mold pressure sensor.

[0025] This invention relates to a roll-blow molding process for a hydrogen storage bottle plastic inner liner. When it is necessary to reduce the gas pressure inside the rotational molding mold, the inlet shut-off valve is closed, and the vacuum pump shut-off valve and vacuum pump are opened. The gas inside the rotational molding mold flows out from the exhaust pipe and enters the gas cooling device for cooling before entering the vacuum pump. The pressure inside the mold can be monitored by an in-mold gas pressure sensor or a vacuum pressure sensor.

[0026] This invention relates to a roll-blow molding process for a plastic inner liner of a hydrogen storage bottle. When the gas inside the mold needs to be recovered, the shut-off valve of the recovery tank is opened in advance to allow the gas to enter the recovery tank.

[0027] This invention discloses a roll-blow molding process for a plastic inner liner of a hydrogen storage bottle. The high pressure is the absolute pressure inside the mold, which is 0.1 to 0.6 MPa; the low pressure is the absolute pressure inside the mold, which is 0 to 0.1 MPa.

[0028] This invention discloses a roll-blow molding process for a hydrogen storage bottle plastic inner liner. By using the aforementioned method of different temperature gases, the temperature of the gas inside the mold is rapidly increased under low pressure, and the material is preheated, which helps to increase the mold temperature and improve processing efficiency.

[0029] This invention discloses a roll-blow molding process for a plastic inner liner of a hydrogen storage bottle. During the material melting process, a high-pressure-low-pressure circulation method is used to promote the discharge of air bubbles during the powder melting process and to promote the melt to enter the groove structure set in the insert.

[0030] This invention discloses a roll-blow molding process for a plastic inner liner of a hydrogen storage bottle. During the product cooling process, the gas pressure inside the mold is gradually reduced according to the material's PVT characteristic curve to obtain a better product structure and reduce internal stress.

[0031] This invention discloses a roll-blow molding equipment and process for a hydrogen storage bottle plastic liner. It shortens the rotational molding cycle time and increases the material density of the product by periodically varying the in-mold pressure, thereby improving barrier properties and mechanical properties. Furthermore, this invention designs a combined roll-blow molding process with early-stage high-temperature, low-pressure molding, mid-stage high-temperature, high-pressure molding, and late-stage low-temperature, high-pressure molding, which improves the molding precision of the liner. An innovative multi-layer mold design improves molding efficiency and in-mold pressurization capacity while reducing energy consumption. A gas heating device is designed to maintain the in-mold gas temperature as needed, reducing internal stress in the product. A gas cooling device is designed to extend the equipment's service life. The device utilizes a steel frame structure with an added irregular support frame to provide sufficient rotational space for the rolling ring. The shape of the irregular support frame can be adjusted according to the mold's usage requirements. This invention removes unnecessary steel from both ends of the frame using a swing frame and innovates an irregular support frame structure, reducing equipment weight. Compared to traditional molding equipment, it has the advantages of simple structure, strong adaptability, and low equipment cost. Attached Figure Description

[0032] Figure 1 The diagram shown is an overall structural schematic of a roll-blow molding equipment for a hydrogen storage bottle plastic inner liner according to the present invention.

[0033] Figure 2 The diagram shown is a mold schematic of a roll-blow molding equipment for a hydrogen storage bottle plastic inner liner according to the present invention.

[0034] Figure 3 The diagram shows the connection between the limiting rod and the axial limiting roller ring in a roll-blow molding equipment for a hydrogen storage bottle plastic liner according to the present invention.

[0035] Figure 4 The diagram shows the connection between the gas conduit and the heating copper ring in a roll-blow molding apparatus for a hydrogen storage bottle plastic liner according to the present invention.

[0036] Figure 5 The diagram shown is a schematic diagram of the gas heating element structure of a roll-blow molding equipment for a hydrogen storage bottle plastic inner liner according to the present invention.

[0037] Figure 6 The diagram shown is a schematic diagram of the gas cooling device structure of a roll-blow molding equipment for a hydrogen storage bottle plastic inner liner according to the present invention.

[0038] Figure 7 The diagram shows the connection position of the rotational molding mold in a rotational blow molding equipment for a hydrogen storage bottle plastic inner liner according to the present invention.

[0039] In the diagram: 101-Inner mold; 102-Heating module; 103-Insulation layer; 104-Outer mold; 105-Mold frame; 201-Rotating frame; 202-Gear rolling ring; 203-Smooth rolling ring; 204-Axial limiting rolling ring; 301-Fixed frame; 302-Rocking bearing; 303-Rocking frame; 304-Irregular support frame; 305-Reducer gear; 306-Roller; 307-Limiting rod; 308-Limiting block; 309-Bearing; 4-Vacuum shut-off valve; 5-Recovery tank shut-off valve; 6-Vacuum pump; 7-Gas cooling device; 701-Gas cooling device chamber; 702-Cooling source; 8-Vacuum pressure sensor; 9-Gas recovery tank; 10-Gas storage tank; 11-Gas storage tank; 12-Vacuum pump shut-off valve; 13-Exhaust rotary joint; 14-In-mold pressure sensor; 15-Gas cooling structure; 16-Overflow valve; 17-Gas heating device; 18-Gas heating device inlet; 19-Gas heating device exhaust port; 10-High frequency electromagnetic heating ring; 11-Gas static mixer; 12-Pressure regulating and speed regulating valve; 13-Inlet rotary joint; 14-Inlet shut-off valve; 25-Air compressor; 26-Air tank shut-off valve; 27-Exhaust duct; 28-Inlet duct; 29-Nut; 30-Blowout device; 31-Sealing ring. Detailed Implementation

[0040] like Figure 1 As shown, the present invention provides a rotational-blow molding equipment for a hydrogen storage bottle plastic liner, comprising an inner liner mold driving device, a rotational molding mold system, a pneumatic control system, and an in-mold gas temperature regulation system. This invention uses a swing-type IV hydrogen storage bottle plastic inner liner rotational molding machine as an example, but is not limited to rotational molding equipment for swing-type hydrogen storage bottle inner liners. The inner liner mold driving device of the present invention includes a frame, a motor, a conductive slip ring, a gear rolling ring 202, a smooth rolling ring 203, an axial limiting rolling ring 204, a reducer, etc. The rotational molding mold system of the present invention includes a rotational molding mold, a mold frame 105, and a heating copper ring 25. Figure 2 As shown, the rotational molding mold includes an inner mold 101, a heating module 102, an insulation layer 103, and an outer mold 104. The pneumatic control system of this invention includes a data acquisition system, a shut-off valve, an overflow valve 15, a vacuum pressure sensor 8, an in-mold pneumatic pressure sensor 13, an air compressor 20, a quick-connect coupling 24, a pressure and speed regulating valve 17, a rotary joint, a gas guide pipe, a vacuum pump 6, and a gas cooling device 7, etc. The in-mold gas temperature regulation system includes a gas heating device 16, a gas static mixer 1604, and a temperature sensor, etc.

[0041] The specific connection method of the roll-blow molding equipment for the plastic inner liner of a hydrogen storage bottle according to the present invention is as follows: Figure 2As shown, the rotational molding mold of the present invention consists of an inner mold 101, a heating module 102, a heat insulation layer 103, and an outer mold 104 from the inside out. The positions of each component of the rotational molding mold are relatively fixed during use. Figure 1 As shown, the rotational molding mold of the present invention is fixedly connected to the mold frame 105. The mold frame 105 is used to support the rotational molding mold and prevent its deformation, and also to install structural components or control components that need to move with the rotational molding mold. The mold frame 105 is fixedly connected to the rotating frame 201 by bolts. A gear ring 202, an axial limiting ring 204, and a smooth ring 203 are welded or bolted onto the rotating frame 201. The gear ring 202 is connected to a reducer fixed on the irregular support frame 304 via gear meshing and is driven to rotate by a motor. The smooth ring 203 is rollably connected to a roller 306 fixed on the irregular support frame 304, serving to support the rotating frame 201 in conjunction with the gear ring 202. Figure 3 As shown, the axial limiting roller ring 204 is connected to the limiting rod 307, which is fixed to the rocker frame 303, via a limiting groove and a bearing 309 mounted on the limiting rod 307. The radial separation prevention function between the limiting rod 307 and the axial limiting roller ring 204 is achieved by a limiting block 308 threadedly connected to the limiting rod 307. Figure 1As shown, the electrical input and output of the electrical components on the rotating frame 201 are achieved through conductive slip rings. The irregular support frame 304 is welded to the swing frame 303. The swing frame 303 is connected to the fixed frame 301, which is fixed to the ground, via a swing bearing 302 and is driven by a motor mounted on the fixed frame 301. The insert 26 of the hydrogen storage tank's plastic inner liner is fixed to the rotational molding mold by a heating copper ring 25 via a threaded connection. The gas conduit is fixed to the heating copper ring 25 and arranged coaxially. The gas conduit is divided into an inlet conduit 28 and an exhaust conduit 27. A baffle 30 is installed at the head of the inlet conduit 28. Both the inlet conduit 28 and the exhaust conduit 27 are fixed to external pipelines via coaxial nuts 29; if necessary, the connecting threads are designed as sealing threads. An internal pressure sensor 13, an overflow valve 15, a gas heating device 16, an intake shut-off valve 19, and an intake rotary joint 18 are sequentially connected to the external pipeline connected to the intake duct 28. All components are connected via metal pipes. The gas heating device 16 is fixed to the mold frame 105 and moves together with it. After the intake rotary joint 18, either a plastic hose or a metal pipe can be selectively used to connect to related components. After the intake rotary joint 18, it is connected to a high-pressure gas source via a pressure regulating and speed regulating valve 17. The high-pressure gas source includes a centralized gas source provided in the work area / workshop and a gas source provided by a specially configured air compressor 20. The centralized gas source in the work area / workshop can be directly connected to the system described in this invention using a quick-connect coupling 24. The gas source provided by the air compressor 20 can be directly drawn from the air or from the gas storage tank 10, depending on the specific requirements of material molding. The external pipeline connected to the exhaust duct 27 is sequentially connected to a vacuum pump shut-off valve 11, an exhaust rotary joint 12, a vacuum pressure sensor 8, a gas cooling device 7, and a vacuum pump 6. The gas cooled by the gas cooling device 7 and extracted by the vacuum pump 6 can be either directly discharged into the air through the vent shut-off valve 4 or enter the gas recovery tank 9 through the recovery tank shut-off valve 5, depending on the specific contents. The gas cooling device 7 and the vacuum pump 6 are both installed on the ground and do not move with the mold.

[0042] The baffle 30 of this invention preferably has a built-in rotor, allowing the gas injected into the mold to rotate and constantly change the airflow direction. Alternatively, the baffle 30 can use a mesh structure, scattering the gas in different directions after passing through it. Alternatively, the baffle 30 can have a mesh cylindrical structure on its exterior, with a built-in rotor. The baffle 30 of this invention is preferably made of metal. The baffle is coaxially mounted with the air inlet duct 28, and its outer diameter is preferably smaller than that of the air inlet duct 28. The baffle 30 extends into the middle of the mold or its head extends into two-thirds of the mold's length. The mesh openings of the mesh structure gradually increase in size along the axial direction from the air inlet to the air outlet, increasing the flow area for gas entering the mold and allowing the gas temperature inside the mold to become uniform more quickly.

[0043] The gear roller 202 and smooth roller 203 described in this invention should be installed on both sides of the central cross-section of the mold, and the design should consider maintaining balance after the rotational molding mold is installed. For shorter rotational molding molds, one gear roller 202 and one smooth roller 203 are preferred; as the length of the rotational molding mold increases, the number of rollers can be appropriately increased to maintain sufficient support capacity. Alternatively, both support rollers on the rotational molding mold can be gear rollers. Alternatively, a gear roller is installed in the middle of the rotational molding mold, and an equal number of smooth rollers are distributed on both sides of the gear roller.

[0044] The axial limiting roller ring 204 described in this invention is mainly used to prevent the gear roller ring 202 and the smooth roller ring 203 from sliding axially away from the reducer gear 305 or roller 306 when the rotational molding mold is driven to swing by the swing frame 303. Alternatively, the reducer gear 305 or roller 306 can also provide axial limiting for both the gear roller ring 202 and the smooth roller ring 203. This is achieved by having bosses on both sides of the reducer gear 305 or roller 306 that are higher than the contact surface of the roller rings. As a roller ring connection structure that can be used on the swing frame 303 that can rotate 360°, the irregular support frame 304 described in this invention can be set with another set of the same irregular support frame at a plane symmetrical to the plane on which the swing frame 303 is located; in this case, the total number of gears 305 or rollers 306 on a single annular surface should be designed to be at least 3. Alternatively, the surface of the roller 306 can be designed with a layer of elastomer or other cushioning material.

[0045] like Figure 2As shown, the rotational molding mold of the present invention includes an inner mold 101, a heating module 102, a heat insulation layer 103, and an outer mold 104. In the equipment of the present invention, the mold can be used in the following ways: First, the inner mold 101 can be used alone for heating methods such as oven-type or flame-type heating. Second, the inner mold 101 and heating module 102, or the inner mold 101, heating module 102, and heat insulation layer 103 can be used in combination for heating methods such as electric heating or infrared heating, but the pressure that can be filled into the mold is relatively low and should be controlled within the range of 0-0.4 MPa; alternatively, the inner mold wall thickness can be increased, and the pressure range can be adjusted according to the specific pressure bearing capacity, but this significantly affects processing efficiency and increases energy consumption. Third, the inner mold 101, heating module 102, heat insulation layer 103, and outer mold 104 can be used in combination for heating methods such as electric heating, and can be used for higher internal mold pressures. The inner mold 101 is preferably designed with a relatively thin thickness to improve heating and cooling efficiency while ensuring structural rigidity. The heating module 102 is embedded in or covers the inner mold 101. The insulation layer 103 is preferably made of a material with low thermal conductivity, such as fiber felt, and its thickness is preferably 5-10 mm. The outer mold 104 is designed according to the maximum pressure inside the mold and is mainly used to prevent large deformation of the inner mold 101. The outer mold 104 of the present invention can be made of metal materials or fiber-reinforced thermosetting composite materials. As an alternative, when the outer mold 104 is formed using a material with high temperature resistance, low thermal conductivity, and high strength, such as glass fiber, the insulation layer 103 may not be used.

[0046] The gas heating device 16 of the present invention is preferably fixed to the mold frame 105 via a bracket, and does not directly contact the rotational molding mold. For example... Figure 4 As shown, the exhaust port 1602 of the gas heating device is connected to the inlet of the air inlet duct 28 by a metal bend, and the gas flow distance of the bend should be designed to be short.

[0047] The in-mold pressure sensor 13 of this invention is installed near the inlet of the air intake duct 28. For example... Figure 4 As shown, a gas cooling structure 14 is preferably installed between the in-mold pressure sensor 13 and the main air intake path to prevent high-temperature gas from affecting the measurement accuracy of the in-mold pressure sensor 13.

[0048] In this invention, all pipelines of the air heating section in the roll-blow molding equipment for the plastic inner liner of a hydrogen storage bottle are preferably externally covered with insulation materials such as asbestos insulation felt or insulation tape.

[0049] In the roll-blow molding equipment for the plastic inner liner of a hydrogen storage bottle of the present invention, the pipes, rotary joints and other connecting pipes that come into contact with hot air are all made of metal materials, preferably stainless steel.

[0050] like Figure 4As shown, the intake duct 28 and exhaust duct 27 of the present invention are preferably coaxially fixed together to facilitate the installation of the gas duct and the removal of the gas duct after the inner liner is formed.

[0051] like Figure 4 As shown, the gas conduit and the heating copper ring 25 are coaxially fixed together, and the fixed position should have good airtightness after fixing; in addition, the interior of the fixed position between the heating copper ring 25 and the gas conduit should be rounded and free of foreign objects. Figure 1 As shown, the air intake duct of the present invention is preferably installed coaxially with the mold to facilitate demolding. A silencer plug is preferably installed at the gas outlet end of the air intake duct 28. The silencer plug is made of copper mesh to prevent the gas flow rate entering the mold from being too fast and affecting the local temperature distribution inside the mold.

[0052] like Figure 5 As shown, the gas heating device 16 of the present invention preferably uses high-frequency electromagnetic heating, and the gas heating device 16 preferably has a labyrinth structure for the gas flow channel to facilitate gas heating. Preferably, a static gas mixer 1604 is installed in the gas flow channel of the gas heating device 16, and the static gas mixer 1604 should be made of metal material.

[0053] like Figure 1 As shown, the gas cooling device 7 of this invention is mainly used to cool the gas entering the vacuum pump 6, preventing long-term high temperatures from affecting the performance of the vacuum pump 6. Figure 6 As shown, the gas cooling device 7 of the present invention can be cooled by liquid refrigeration or by compressor refrigeration. It is preferred to use fins in the gas cooling device 7 to accelerate the cooling effect.

[0054] like Figure 7 As shown, the connecting surfaces between the segments of the rotational molding die of the present invention should be provided with guide structures, adjacent rotational molding die segments should be interlocked, and the connection positions of the rotational molding die should be designed with external reinforcing structures. The parting line position of the rotational molding die of the present invention should be designed with a structure that has a low-pressure sealing effect, and the sealing direction is to prevent gas outside the rotational molding die from entering the interior of the rotational molding die. Preferably, the rotational molding dies of the present invention are sealed with sealing rings 31, and the sealing rings 31 should be made of metal. Alternatively, the sealing rings 31 are designed with a U-shaped cross-section, and the opening of the U-shaped sealing rings 31 faces outward.

[0055] The specific process for adjusting the in-mold gas pressure and temperature in the roll-blow molding equipment and process for a hydrogen storage bottle plastic inner liner of the present invention is as follows:

[0056] Before starting work, inspect the equipment and confirm that the equipment is sealed properly. Close all shut-off valves and set the safety air pressure of the overflow valve 15. The motor drives the swing frame 303 and the rotating frame 201 to move so that the material in the rotational molding die can contact the inner wall of the rotational molding die in a predetermined manner. The rotational molding die is heated according to the normal operation so that the internal material melts and adheres to the inner wall of the rotational molding die.

[0057] When it is necessary to increase the in-mold air pressure, the inlet shut-off valve 19 is opened. The high-pressure gas supplied by the air source enters the gas heating device 16 through the inlet 1601 after the pressure and flow rate are adjusted by the pressure regulating and speed regulating valve 17. The gas fully contacts the gas static mixer 1604 to increase the temperature. The temperature of the gas flowing out of the gas heating device exhaust port 1602 is adjusted according to the needs of the mold. At this time, the walls of the gas static mixer 1604 and the gas heating device 16 are heated by eddy currents generated by the high-frequency electromagnetic heating ring 1603. The heating temperature is controlled by controlling the power of the high-frequency electromagnetic heating ring 1603. The in-mold air pressure is monitored by the in-mold air pressure sensor 13. The high-pressure gas includes high-pressure gas centrally supplied in the work area / workshop or high-pressure gas supplied by a specially configured air compressor 20. If the air source centrally supplied in the work area / workshop is used, the quick connector 24 is connected to the pipeline in the work area / workshop, and the external air source shut-off valve 22 is opened. If the air compressor 20 is used to provide high-pressure gas, and the gas is to be obtained directly from the air, the air shut-off valve 23 is opened; if nitrogen or inert gas is to be used, the gas tank shut-off valve 21 is opened to obtain gas from the gas tank 10. Alternatively, when the gas tank 10 is used as the gas source, the pressure inside the gas tank 10 is sufficient for the system, so the gas tank 10 can also be directly connected to the quick connector 24.

[0058] When it is necessary to reduce the gas pressure inside the rotational molding mold, close the inlet shut-off valve 19 and open the vacuum pump shut-off valve 11 and vacuum pump 6. The gas inside the rotational molding mold flows out through the exhaust pipe 27 and enters the gas cooling device 7 for cooling before entering the vacuum pump 6. The mold pressure can be monitored by the mold pressure sensor 13 or the vacuum pressure sensor 8. When the gas inside the mold needs to be recovered, open the recovery tank shut-off valve 5 in advance to allow the gas to enter the recovery tank 9. When the gas inside the mold does not need to be recovered, open the vent shut-off valve 4 in advance to allow the gas to be directly discharged into the air.

[0059] When it is necessary to quickly adjust the gas temperature inside the mold or to make the gas temperature inside the mold higher than that of the mold, this can be achieved by gas temperature displacement. That is, high-pressure gas is used to enter the mold after the temperature is adjusted by the gas heating device 16, while the vacuum pump 6 is used to remove the excess gas inside the mold. During the process, the pressure inside the mold can be kept stable by the cooperation of the pressure regulating and speed regulating valve 17, the gas inlet shut-off valve 19, and the vacuum pump shut-off valve 11.

[0060] This invention relates to a roll-blow molding equipment and process for a hydrogen storage bottle plastic inner liner. It proposes a roll-blow synergistic process involving early-stage high-temperature low-pressure molding, mid-stage high-temperature high-pressure molding, and late-stage low-temperature high-pressure molding. The high pressure is the absolute pressure inside the mold, approximately 0.1–0.6 MPa; the low pressure is the absolute pressure inside the mold, approximately 0–0.1 MPa. An innovative multi-layer mold is designed to improve molding efficiency and in-mold pressurization capacity.

[0061] The high-temperature, low-pressure molding described in this invention refers to maintaining low pressure within the mold when the material is in the form of powder or a powder / melt multiphase state, so as to facilitate the expulsion of air bubbles during the melting process. Preferably, the aforementioned method of using gases at different temperatures can be used to rapidly increase the temperature of the gas inside the mold under low pressure and preheat the material, thereby helping to increase the mold temperature and improve processing efficiency. Alternatively, during the material melting process, a high-pressure-low-pressure cycle can be used to promote the expulsion of air bubbles during the powder melting process and to promote the melt to enter the groove structure provided in the insert 26.

[0062] The intermediate high temperature and high pressure molding of the present invention refers to the process where, when all the material adheres to the inner wall of the mold and becomes a melt, a high pressure gas with the same temperature as the original gas in the mold is introduced into the mold, so that the material is kept in a high pressure state in the mold while it is in a molten state, so as to further increase the density of the melt and at the same time promote the filling of the groove structure of the insert 26 to a certain extent.

[0063] The low-temperature high-pressure molding described in this invention maintains a high-pressure state for the gas inside the mold while rapidly reducing the temperature of the gas inside the mold through the aforementioned gas replacement method, thus assisting in lowering the temperature of the mold 10. Maintaining high pressure in the later stage prevents the inner liner from shrinking due to the characteristics of PVT. Preferably, during the cooling process of the inner liner, the gas pressure inside the mold can be appropriately adjusted to obtain a better inner liner structure.

[0064] The above examples are illustrative only and not restrictive of the present invention. Equivalent modifications and variations made without departing from the spirit and scope defined by the claims shall fall within the protection scope of the present invention.

Claims

1. A roll-blow molding process for a hydrogen storage cylinder plastic inner liner, employing a roll-blow molding equipment comprising an inner liner mold driving device, a rotational molding mold system, a pneumatic control system, and an in-mold gas temperature regulation system. The inner liner mold driving device includes a frame, a motor, a conductive slip ring, a gear roller, a smooth roller, an axially limiting roller, and a reducer. The rotational molding mold system includes a rotational molding mold, a mold frame, and a heating copper ring. The rotational molding mold includes an inner mold, a heating module, an insulation layer, and an outer mold. The pneumatic control system includes a data acquisition system, a shut-off valve, an overflow valve, a vacuum pressure sensor, and an in-mold gas temperature regulation system. The system includes a pressure sensor, air compressor, quick-connect coupling, pressure and speed regulating valve, rotary joint, air duct, baffle, vacuum pump, and gas cooling device. The in-mold gas temperature control system includes a gas heating device, a static gas mixer, and a temperature sensor. The various components of the rotational molding mold are relatively fixed in position during use. The rotational molding mold is fixedly connected to a mold frame, which supports the mold and prevents deformation. The mold frame also houses structural components or control devices that need to move with the mold. The mold frame is bolted to a rotating frame, which has gear rings welded or bolted to it, and axial limiters. The rotating frame consists of a smooth rolling ring and a geared rolling ring. The geared rolling ring is connected to a reducer fixed to a shaped support frame via gear meshing and is driven to rotate by a motor. The smooth rolling ring and the rollers fixed to the shaped support frame can roll relative to each other, serving to support the rotating frame in conjunction with the geared rolling ring. The axially limiting rolling ring is connected to a limiting rod fixed to the rocking frame via a limiting groove and a bearing mounted on the limiting rod. The radial separation function between the limiting rod and the axially limiting rolling ring is achieved by a limiting block threadedly connected to the limiting rod. The electrical input and output of the electrical components on the rotating frame are achieved through conductive slip rings. The shaped support frame is welded to the rocking frame, and the rocking frame is connected to... The fixed frame, which is fixed to the ground, is connected by a rocker bearing and driven by a motor mounted on the fixed frame. The insert of the plastic inner liner of the hydrogen storage cylinder is fixed to the rotational molding mold by a heating copper ring through a threaded connection. The gas conduit is fixed to the heating copper ring and arranged coaxially. The gas conduit is divided into an inlet conduit and an outlet conduit. A baffle is installed at the head of the inlet conduit. The inlet conduit and the outlet conduit are fixed to the external pipeline by coaxial nuts. The external pipeline connected to the inlet conduit is connected in sequence to the in-mold pressure sensor, overflow valve, gas heating device, inlet shut-off valve and inlet rotary joint. All related components are connected by metal pipelines.The gas heating device is fixed on the mold frame and moves with the mold frame. After the gas inlet rotary joint, it is connected to the high-pressure gas source through the pressure regulating and speed regulating valve. The external pipeline connected to the exhaust pipe is sequentially connected to the vacuum pump shut-off valve, the exhaust rotary joint, the vacuum pressure sensor, the gas cooling device, and the vacuum pump. The gas cooled by the gas cooling device and extracted by the vacuum pump can be either directly discharged into the air through the vent shut-off valve or enter the gas recovery tank through the recovery tank shut-off valve, depending on the specific contents. The gas cooling device and the vacuum pump are both installed on the ground and do not move with the mold. The molding process is as follows: First, before starting work, check the equipment and confirm that the equipment is sealed properly. Close all shut-off valves, set the safety air pressure of the overflow valve, add the material, and close the mold. The rotational molding mold is preheated according to the melting temperature of the material being processed. The motor drives the swing frame and the rotating frame to move so that the material inside the rotational molding mold can contact the inner wall of the mold in a predetermined manner. The air pressure inside the mold is set to low pressure. The rotational molding mold is heated according to the normal operation so that the internal material melts and adheres to the inner wall of the mold. When the material is powder or powder / melt multiphase, the low pressure inside the mold is maintained so that the material can expel air bubbles during the melting process. The second step is to introduce high-pressure gas with the same temperature as the original gas in the mold into the mold when all the material is adhered to the inner wall of the mold and has become melt. This keeps the mold under high pressure while the material is in the molten state, so that the density of the melt can be further increased. At the same time, it promotes the filling of the groove structure of the insert to a certain extent. The third step involves maintaining a high-pressure state for the gas inside the mold while rapidly reducing the temperature of the gas inside the mold through gas displacement, thereby helping to lower the temperature of the mold and allowing the molded product to cool gradually.

2. The roll-blow molding process for a hydrogen storage cylinder plastic inner liner according to claim 1, characterized in that: In the first step, the temperature of the gas inside the mold is rapidly increased under low pressure to preheat the material and assist in raising the mold temperature. In the second step, during the material melting process, a high-pressure-low-pressure cycle is used to promote the removal of bubbles during the powder melting process and to promote the melt to enter the groove structure set in the insert. In the third step, during the product cooling process, the gas pressure inside the mold is gradually reduced according to the material's PVT characteristic curve to obtain a better product structure and reduce internal stress. High pressure is the absolute pressure inside the mold, which is 0.1~0.6MPa; low pressure is the absolute pressure inside the mold, which is 0~0.1MPa.

3. The roll-blow molding process for a hydrogen storage cylinder plastic inner liner according to claim 2, characterized in that: When it is necessary to increase the gas pressure inside the mold, open the inlet shut-off valve. The high-pressure gas supplied by the gas source enters the gas heating device through the inlet after the pressure and flow rate are adjusted by the pressure regulating and speed regulating valve. The gas comes into full contact with the gas static mixer to increase the temperature. The temperature of the gas flowing out of the exhaust port of the gas heating device is adjusted according to the needs inside the mold. The pressure inside the mold is monitored by the inlet gas pressure sensor. Alternatively, when it is necessary to reduce the gas pressure inside the rotational molding mold, close the inlet shut-off valve and open the vacuum pump shut-off valve and the vacuum pump. The gas inside the rotational molding mold flows out from the exhaust pipe and enters the gas cooling device for cooling before entering the vacuum pump. The pressure inside the mold can be monitored by the inlet gas pressure sensor or the vacuum pressure sensor. Alternatively, when the gas inside the mold needs to be recovered, open the recovery tank shut-off valve in advance to allow the gas to enter the recovery tank.

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