Down-blow film blowing apparatus, its cooling mechanism and cooling method

Abstract

The application discloses a kind of down-blowing film blowing device and its cooling mechanism and cooling method, belong to plastic film blow molding technical field.Cooling mechanism is set below die head and is located above the bottom end of guide herringbone plate, including built-in cooling water ring, planer assembly and air pipe.Built-in cooling water ring is set inside bubble, and the outer wall and bubble inner wall form cooling water film between them, the water film is sealed in bubble above built-in cooling water ring while cooling bubble inner wall, so that bubble inside is separated into two independent cavities.The planer assembly is opened along the longitudinal direction and forms the planing opening of the lower bubble wall, and the cooling water flows out from the planing opening.The air pipe is connected to the inside of bubble, so that the bubble after being opened keeps expanding and unfolding state.The application realizes the cooperation and unity of cooling water film in cooling and sealing two functions, cooperates with planing drainage and active air inflation, and can effectively solve the problem of uneven cooling and film wrinkle in thick film production.

Description

Technical Field

[0001] This invention relates to the field of plastic film blow molding technology, specifically to a downblown film blowing device and its cooling mechanism and cooling method, which is particularly suitable for the downblown water-cooled production of thick films such as geomembranes. Background Technology

[0002] Blown film is one of the most widely used forming methods for producing plastic films. Depending on the direction of the film bubble traction, it can be divided into top-blowing and bottom-blowing methods. Top-blowing, because the traction direction is the same as the heat flow direction, suffers from low heat exchange efficiency and poor cooling effect. Furthermore, when the frame is high, the film tube is prone to stretching or even breaking due to its own weight. Therefore, bottom-blowing water-cooling has been proposed and applied in production practice, especially for the production of large-diameter ultra-wide films and thick-film products such as geomembranes, where bottom-blowing water-cooling has significant advantages.

[0003] The core of the downblown water-cooling method lies in the design of the cooling mechanism. Existing downblown water-cooled blown film devices mainly employ the following technical approaches for their cooling mechanisms: (a) Immersion Cooling For example, Chinese patent CN209937692U discloses a bottom-blowing water-cooled blown film device, in which the cooling mechanism is a constant-temperature water tank located below the ground. The blown film bubble directly enters the water tank for immersion and cooling. Although this solution is simple in structure and suitable for the production of large-diameter films, it has obvious technical defects: cooling is only performed once through the water tank, and the cooling process lacks gradient control. The film bubble suddenly enters the cold water from the molten state, which can easily lead to increased internal stress and significant thickness deviation in the film due to uneven cooling. More importantly, after the cutting blade cuts the film bubble, although cooling water can enter the inside of the film bubble to balance the pressure, there is no independent air pressure control system inside the film bubble. After the film is folded and guided by the herringbone plate, the film bubbles near the two ends of the traction roller lack the power to actively expand and unfold, and the film is prone to wrinkles after passing through the traction roller. Wrinkles are one of the most serious quality defects in film products, which can lead to serious quality accidents such as stress concentration and increased leakage risk during the laying and use of geomembranes. Obvious wrinkles are not allowed in any grade of geomembrane products.

[0004] Secondly, to achieve stable production, this scheme requires water tanks at a depth of over 7 meters for wide-width, thick films. This ensures the membrane bubble is cooled before contacting the herringbone slab; otherwise, continuous production would cause the slab to stick to the bubble as the membrane bubble heats up, halting further production. Water tanks over 7 meters deep can contain hundreds of tons of water, requiring high tank strength, and the water depth greatly complicates the membrane insertion process and poses significant safety risks. This scheme is not practically feasible for wide-width film production.

[0005] (ii) Water-cooling device inside the membrane bubble To address the internal cooling problem of the membrane bubble, Chinese patent CN103624970A proposed a circulating water cooling device for the membrane tube of a blown film machine. A cooling mandrel is installed inside the membrane tube, and cooling water flows out from the water flow channel, forming a water film along the membrane tube wall for cooling. The water inside the membrane tube is then removed by vacuum suction. While this solution achieves direct water cooling of the membrane bubble's inner wall, its vacuum suction system faces a dilemma: excessive suction creates excessive negative pressure on the inner wall of the membrane bubble, causing it to be drawn down and resulting in localized depressions or deformations, affecting the bubble's roundness and thickness uniformity; insufficient suction fails to completely remove the cooling water from the inner wall, leading to the accumulation of residual water and hindering water circulation, thus disrupting continuous production.

[0006] (iii) Combined internal and external water cooling device Chinese patent CN201128228Y discloses a film cooling and forming device for a blown film machine, which combines an inner cooling water tank and an outer cooling water ring. The inner and outer cooling water simultaneously contact the film preform tube for cooling, and drainage and drying are achieved through a scraper and a water-absorbing sponge. While this scheme achieves simultaneous internal and external cooling, the small gap between the inner and outer cooling water rings makes film threading and guiding operations extremely difficult. During production, changes in the diameter of the film bubble can easily cause it to become stuck between the inner and outer water rings, resulting in production stoppages. This scheme uses a scraper, water-absorbing sponge, air intake, and suction pipe to draw cooling water; however, if the scraper is too close to the film bubble, it will rupture the bubble; if it is too far away, the cooling water will seep through the gap between the scraper and the bubble to the water-absorbing sponge. The water-absorbing sponge has limited absorption capacity and cannot absorb and intercept large amounts of water into the suction tank; ultimately, the cooling water extraction effect is poor, and cooling water continuously accumulates inside the film bubble.

[0007] (iv) Common technical defects in existing technologies In summary, the existing down-blowing water-cooled blown film devices and their cooling mechanisms still have the following technical problems that urgently need to be solved: Firstly, the number of cooling stages is insufficient or the cooling parameters cannot be independently adjusted. In existing solutions, the water tank immersion type only has one cooling stage, and the water cooling device inside the membrane bubble and the combined internal and external water cooling device form a single cooling path. This makes it impossible to control and adjust the cooling intensity in stages according to different formation stages of the membrane bubble, which affects the crystallization quality and thickness uniformity of the film.

[0008] Secondly, water tank immersion cooling involves cutting open the membrane bubble and immersing it completely in cooling water, resulting in high cooling efficiency. However, after the membrane bubble is cut open, it is difficult to maintain the internal air pressure, especially for the membrane below the water level. Because the water pressure inside and outside the membrane bubble is the same, it loses the expansion power and cannot unfold, resulting in wrinkles after traction.

[0009] Third, the cooling water drainage method of the internal water cooling device and the combined internal and external water cooling device of the membrane bubble is complicated, energy consumption is high, and operation is poor. It cannot completely drain the cooling water inside the membrane bubble, which leads to the continuous accumulation of cooling water inside the membrane bubble, making it difficult to sustain production.

[0010] To address the aforementioned technical problems, this invention proposes a downblown film blowing device and its cooling mechanism and cooling method. Summary of the Invention

[0011] (a) Technical problems to be solved This invention addresses the technical problems of existing downblown water-cooled blown film devices, such as insufficient cooling stages, inability to independently control cooling parameters, difficulty in maintaining internal air pressure in the film bubble leading to film wrinkling, and complex and ineffective cooling water drainage methods. It provides a downblown blown film device, its cooling mechanism, and a cooling method.

[0012] (II) Technical Solution 1. Cooling Mechanism Technical Solution To achieve the above objectives, the present invention provides a cooling mechanism for a down-blown film extrusion device. The down-blown film extrusion device includes an extruder, a die, a guide herringbone plate, and a traction roller. The cooling mechanism is disposed below the die and above the bottom end of the guide herringbone plate. A film bubble is formed below the die by blowing. The cooling mechanism includes: An internal cooling water ring is disposed inside the membrane bubble; a cooling water film is formed between the outer wall of the internal cooling water ring and the inner wall of the membrane bubble. The cooling water film cools the inner wall of the membrane bubble while sealing the blown air inside the membrane bubble above the internal cooling water ring, thus dividing the interior of the membrane bubble into a first cavity located above the internal cooling water ring and a second cavity located below the internal cooling water ring; the water in the cooling water film falls into the second cavity; It should be noted that the state in which the membrane bubble is divided into a first cavity and a second cavity is the normal operating state formed after the bottom of the membrane bubble is sealed and the inflation pressure is established inside the membrane bubble. During the membrane insertion stage, before the bottom of the membrane bubble enters the traction roller and before the membrane bubble is sealed, the inside of the membrane bubble is open to the atmosphere, and the water film sealing function is unstable. Only after the membrane enters the traction roller and the membrane bubble is sealed will the water film gradually stabilize and become flat, and play the role of uniformly cooling and sealing the upper membrane bubble.

[0013] It should be noted that the air pressure within the first cavity, under normal operating conditions, will not cause the inner wall of the membrane bubble to detach from the outer wall of the built-in cooling water ring. The mechanism is as follows: if the inner diameter of the membrane bubble is larger than the outer diameter of the built-in cooling water ring, meaning there is a large gap between the inner wall of the membrane bubble and the outer wall of the built-in cooling water ring, the compressed air inside the membrane bubble will naturally enter the lower part of the built-in cooling water ring through this gap, causing the membrane bubble diameter to gradually decrease until the inner wall of the membrane bubble approaches the outer wall of the built-in cooling water ring and is sealed by the water film. The built-in cooling water ring continuously sprays water onto the inner wall of the membrane bubble, forming a continuously flowing cooling water film within the annular gap. This water film simultaneously serves as a liquid sealing medium, filling the entire annular gap between the outer wall of the built-in cooling water ring and the inner wall of the membrane bubble. When the air pressure within the first cavity increases, causing the membrane bubble to expand slightly radially, the annular gap increases accordingly. However, the continuous water supply from the built-in cooling water ring causes the water film thickness to adaptively increase to fill the increased gap, always maintaining the liquid-sealed state of the annular gap. Meanwhile, the circumferential stress of the membrane bubble material itself, the atmospheric pressure outside the membrane bubble, and the longitudinal tension applied by the traction roller together constrain the radial displacement of the membrane bubble, limiting it to the adjustment range of the cooling water ring outlet gap; therefore, within the normal working air pressure range of 0.15 to 0.2 MPa in the first cavity, the water film seal remains reliable and effective. A planer assembly, disposed between the guide herringbone plate and the traction roller, is used to longitudinally plan the membrane bubble wall of the second cavity to form a planing kerf; cooling water flows out from the planing kerf; A vent pipe, one end of which is located at the planing kerf or extends into the planing kerf, and the other end is connected to a compressed air source for introducing compressed air into the second cavity to keep the membrane bubble in the second cavity in an expanded state. It is understood that the compressed air source is not limited to supplying air to the second cavity from the planing kerf. As another embodiment, compressed air can also be introduced through a vent pipe located inside the die head, which passes downwards through the internal channel or side wall of the built-in cooling water ring and connects to the second cavity. The two air intake methods can be used individually or in combination depending on the operating conditions.

[0014] As a further preferred technical solution of the present invention, the built-in cooling water ring is connected to a water source; the built-in cooling water ring is provided with two independent annular water outlets distributed circumferentially, namely a first-stage water outlet and a second-stage water outlet, the first-stage water outlet and the second-stage water outlet are respectively connected to independent water supply pipelines, and the cooling water flow rate, flow velocity and water temperature of each stage water outlet can be independently adjusted.

[0015] As a further preferred technical solution of the present invention, the built-in cooling water ring includes an upper conical guide portion and a lower cylindrical portion. The first-stage water outlet is located 100-150mm below the bottom of the conical guide portion, and the second-stage water outlet is located 300-400mm below the first-stage water outlet. The height of the cylindrical portion is 800-1200mm, and the cylindrical portion has a diameter tapering taper of 3-5mm from top to bottom.

[0016] As a further preferred technical solution of the present invention, the cutting opening is located below the cooling water level line in the second cavity, and a water level control device is provided on one side of the cutting opening; the water level control device includes a baffle plate disposed on one side of the cutting opening, and the gap between the baffle plate and the membrane bubble wall is adjustable. By adjusting the gap, the discharge speed of cooling water from the cutting opening is controlled so as to maintain a constant water level in the second cavity.

[0017] As a further preferred technical solution of the present invention, the water level control device further includes a water level sensor disposed inside or outside the second cavity and an automatic position adjustment device that is drivenly connected to the baffle plate. The automatic position adjustment device automatically adjusts the gap between the baffle plate and the membrane bubble wall according to the water level signal detected by the water level sensor.

[0018] As a further preferred technical solution of the present invention, the vent pipe is provided with a vent pipe valve, and the second cavity is provided with a pressure sensor. The vent pipe valve automatically opens or closes according to the pressure signal detected by the pressure sensor to adjust the air pressure in the second cavity and maintain the air pressure in the second cavity at 0.12 to 0.15 MPa.

[0019] As a further preferred technical solution of the present invention, the cooling mechanism further includes an external cooling water ring connected to a water source. The external cooling water ring is disposed on the outer periphery of the internal cooling water ring. The inner diameter of the external cooling water ring is more than 100 mm larger than the diameter of the membrane bubble. The external cooling water ring is provided with an annular flexible water conveying plate for forming a cooling water film on the outer wall of the membrane bubble.

[0020] 2. Technical solution for downblown film blowing device The present invention also provides a downblown film blowing device, including an extruder, a die, a guide herringbone plate and a traction roller, and a cooling mechanism as described above; the cooling mechanism is disposed below the die and above the bottom end of the guide herringbone plate; the extruder is connected to the die, and a film bubble is formed by blowing below the die, and the traction roller is disposed below the guide herringbone plate.

[0021] Preferably, the extruder is a single-screw extruder or a twin-screw extruder, used to melt and plasticize the plastic raw material and convey it to the die head; the die head is an annular die, used to extrude the molten material to form a cylindrical film preform; the guide herringbone plate is used to gradually gather and fold the cylindrical film bubble into a flat sheet film; the traction roller is used to pull the folded film downwards.

[0022] 3. Cooling Method Technical Solution The present invention also provides a method for cooling using the cooling mechanism of the above-described downblown film device, comprising the following steps: S1: Molten material is extruded downward from the die head and blown to form a cylindrical film bubble, which descends along the outer wall of the built-in cooling water ring disposed inside it; S2: Cooling water is introduced into the built-in cooling water ring, so that the cooling water forms a cooling water film between the outer wall of the built-in cooling water ring and the inner wall of the membrane bubble. The water film is used to cool the inner wall of the membrane bubble, and at the same time, the sealing effect of the cooling water film is used to lock the blown air into the membrane bubble above the built-in cooling water ring; the water in the cooling water film falls into the membrane bubble below the cooling water ring, i.e., the second cavity. S3: When the membrane bubble descends to the bottom of the guide plate, the membrane bubble wall is longitudinally cut open by a planer, so that the cooling water inside the membrane bubble flows out from the planing opening; S4: Introduce compressed air into the second cavity; the compressed air can be introduced from the planing opening, or it can be introduced into the second cavity through the air pipe set inside the die head after passing through the built-in cooling water ring; so that the planed membrane bubble is kept in an expanded state, and after being folded and flattened by the guide herringbone plate, it is pulled out by the traction roller.

[0023] As a further preferred technical solution of the method of the present invention, in step S2, the built-in cooling water ring is provided with two independent annular outlets. The first outlet supplies water to the inner wall of the membrane bubble for pre-cooling at a first flow rate and a first flow velocity; the second outlet supplies water to the inner wall of the membrane bubble for deep cooling at a second flow rate and a second flow velocity; the first flow rate, the first flow velocity, the second flow rate, and the second flow velocity are adjusted independently; the cooling water in the second cavity further cools the inner wall of the membrane bubble; and a cooling water film is formed on the outer wall of the membrane bubble by an external cooling water ring disposed on the outer periphery of the built-in cooling water ring for cooling.

[0024] As a further preferred technical solution of the method of the present invention, in step S3, the drainage speed of the cut is adjusted by the baffle plate set on one side of the cut to maintain a constant water level inside the membrane bubble; in step S4, the air pressure inside the membrane bubble is adjusted by controlling the on / off state and flow rate of the compressed air to maintain the air pressure at 0.12-0.15 MPa, and the membrane bubble is fully expanded and deployed at the guide plate by the coordinated control of the air pressure and the water level inside the membrane bubble.

[0025] (III) Beneficial Effects Compared with the prior art, the present invention has the following advantages: 1. Multi-stage gradient cooling significantly improves cooling quality. This invention achieves graded gradient cooling of the membrane bubble's inner wall through a two-stage independent outlet design with an internal cooling water ring. The first-stage outlet performs pre-cooling and shaping, the second-stage outlet performs deep cooling, and after the membrane bubble enters the second cavity, the cooling water accumulated in the second cavity further immerses and cools the inner wall of the membrane bubble. Depending on the configuration of the cooling structure, three-stage gradient cooling (internal two-stage water ring cooling + second cavity immersion cooling) can be achieved, or a fourth-stage gradient cooling can be achieved by adding an external cooling water ring (internal two-stage water ring cooling + second cavity immersion cooling + external water ring outer wall cooling), realizing multi-stage gradient cooling from the melt expansion stage → pre-cooling and shaping stage → deep cooling stage. Compared with the single cooling path of existing technologies such as water tank immersion single cooling, membrane bubble internal water cooling device, and internal and external combined water cooling device, this invention can implement precise gradient cooling according to the differentiated thermodynamic requirements of the membrane bubble at different forming stages, effectively reducing film internal stress and improving properties such as thickness uniformity and crystal quality. This invention allows for precise control of the membrane's crystallinity, maintaining it within the optimal range of 60-70%. This significantly improves key performance indicators such as the membrane's mechanical properties, aging resistance, and chemical corrosion resistance. Example data shows that, using this invention, the thickness deviation of the finished geomembrane can be controlled within ≤±3%, and overall energy consumption is reduced by 43%–48%.

[0026] 2. Water film sealing and zoned pressure control completely solves the wrinkling problem. This invention is the first to propose using the cooling water film between the outer wall of the built-in cooling water ring and the inner wall of the membrane bubble as both a cooling medium and a gas sealing medium. The sealing effect of the water film locks the inflated air within the membrane bubble above the built-in cooling water ring, dividing the inside of the membrane bubble into two independent chambers, each with independently controllable air pressure. Unlike existing water tank immersion solutions, where the membrane below the planer loses its outward expansion force after the membrane bubble is cut open, and the membrane accumulates towards the center of the traction roller when it flattens from a circular bubble over the herringbone plate, resulting in wrinkles, this invention introduces compressed air into the second chamber through a vent pipe, actively inflating the lower membrane bubble to its maximum expansion state. Even when the membrane is cut open under the planer blade, it will bulge outwards and expand because the internal cooling water is higher than the planer blade. This causes the membrane bubble to push the membrane at both ends of the traction roller outwards after entering the herringbone plate, thus keeping it fully unfolded. Combined with the water pressure inside the membrane bubble and the guiding and squeezing action of the herringbone plate, the membrane is fully flattened, eliminating wrinkle defects at the source.

[0027] 3. The planer-type free drainage method features a simple structure, is located outside the membrane bubble, is easy to operate, and ensures stable production. This invention eliminates the complex internal operation methods of existing vacuum suction drainage (CN103624970A) and scraper sponge drainage (CN201128228Y). By longitudinally planing the membrane bubble with a planer, cooling water flows freely from the planed opening under gravity to an external storage tank for recycling. Compared to the dilemma of excessive suction leading to membrane bubble deformation and insufficient suction leading to water accumulation, and the technical defects of the scraper sponge method such as limited water absorption capacity and the scraper disc easily damaging the membrane bubble, the planer-type free drainage method of this invention has a simple structure, high reliability, strong adaptability, and convenient operation. It can continuously and stably drain the cooling water from the membrane bubble, ensuring long-term continuous and stable production.

[0028] 4. Synergistic automatic control of water level and air pressure ensures high process stability. This invention achieves real-time monitoring and automatic adjustment of water level and air pressure within the second chamber through the coordinated action of a water level control device (baffle plate + water level sensor + automatic position adjustment device) and a pressure control device (vent valve + pressure sensor). When the water level deviates from the set value, the drainage speed is adaptively adjusted by changing the gap of the baffle plate; when the air pressure deviates from the set range, automatic compensation is achieved by controlling the opening and closing of the vent valve. The coordinated control of water level and air pressure ensures the stability of the membrane bubble's shape and its full expansion under different operating conditions, significantly improving process adaptability and product consistency.

[0029] 5. Internal and external cooling can be combined and configured to adapt to different production needs. This invention allows for the selective configuration of an external cooling water ring according to production requirements. This ring, in conjunction with the internal cooling water ring, achieves simultaneous water film cooling of the inner and outer walls of the membrane bubble, further improving cooling efficiency. The inner diameter of the external cooling water ring is more than 100mm larger than the membrane bubble diameter and employs a ring-shaped flexible water delivery plate design. Compared to existing technologies with small gaps between internal and external cooling structures, which are prone to jamming (CN201128228Y), this invention provides ample space between the external cooling water ring and the membrane bubble, facilitating membrane insertion and guiding operations. It also prevents jamming when the membrane bubble diameter changes during production, effectively ensuring production continuity. Furthermore, the external cooling water ring can be selectively opened or closed according to product specifications and production modes (e.g., closing the external water ring in Example 3 achieves low-energy, economical mass production), offering high process flexibility.

[0030] 6. The device features a compact structure, with all components working in tandem to achieve efficient and stable production. This invention integrates a built-in cooling water ring, planer assembly, air pipe, water level control device, and pressure control device into a downblown film extrusion device. The cooling mechanism works in conjunction with the extruder, die head, guide herringbone plate, and traction roller to form a complete production chain from melt extrusion, film bubble cooling, air pressure control, water level control to planing and leveling. The spatial layout of each component is reasonable. The cooling mechanism is located below the die head and above the bottom of the guide herringbone plate, making full use of the downward stroke of the film bubble for graded cooling and stable control. The planer assembly is located between the guide herringbone plate and the traction roller, promptly planing and draining the film bubble after it has cooled and shaped, and then expanding it through air blowing to ensure that the film enters the traction roller in a flat state. The overall device has a compact structure and stable operation, making it suitable for large-scale continuous production of thick films such as geomembranes. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of the cooling mechanism of the blown film device of the present invention; Figure 2 This is a schematic cross-sectional view of the built-in cooling water ring of the present invention; Figure 3 This is a schematic diagram of the bubbling state of the planer assembly of the present invention; Figure 4 This is a schematic diagram of the working state of the baffle plate and the vent pipe device of the present invention (the vent pipe is set at the planing opening); Figure 5 This is a schematic diagram of another embodiment of the vent pipe of the present invention (the vent pipe is disposed inside the mold head).

[0032] The labels in the attached figures are explained as follows: 1—Extruder; 2—Die head; 201—Air blowing pipe; 202—Cooling water ring water supply pipe; 3—Membrane bubble; 31—First cavity; 32—Second cavity; 4—Built-in cooling water ring; 41—Conical guide section; 42—Cylindrical section; 43—First stage water outlet; 44—Second stage water outlet; 5—Cooling water film; 6—Guide herringbone plate; 7—Traction roller; 8—Planer assembly; 81—Planer blade; 82—Planer kerf; 83—Planer blade connecting rod; 84—Planer blade fixing seat; 9—Air pipe; 91—Air pipe valve; 10—Baffle plate; 11—Water level sensor; 12—Pressure sensor; 13—External cooling water ring; 131—Flexible water supply plate; 14—Water storage tank; 15—Water level line. 16. Automatic adjustment device for baffle position; 1601. Servo motor; 1602. Adjustment device mounting base; 1603. Slide rail; 1604. Slider; 1605. Baffle connecting rod; 1606. Nut; 1607. Screw. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. In the following embodiments, unless specific process parameters are specified, conventional extrusion blow molding process conditions in the art are used.

[0034] I. Specific Implementation Method of Cooling Mechanism 1. Basic Structure See Figures 1-4 The cooling mechanism of the downblown film device of the present invention is located below the die head 2 and above the bottom end of the guide herringbone plate 6. The die head 2 is connected to the extruder 1, and the film bubble 3 is formed by blowing below the die head 2. The cooling mechanism mainly includes a built-in cooling water ring 4, a planer assembly 8, and a vent pipe 9. The extruder 1 adds additives to plastic raw materials (such as HDPE, LLDPE, or their blends) and melts and plasticizes them before conveying them to the die head 2. The die head 2 adopts an annular die structure to extrude the molten material to form a cylindrical film preform, which is then blown to form the film bubble 3. The film bubble 3 moves downward under the action of gravity and traction. The die head 2 is provided with an air blowing pipe 201 for blowing air to the upper part of the film bubble 3 and a cooling water ring water supply pipe 202 for supplying cooling water to the cooling water ring 4.

[0035] An internal cooling water ring 4 is positioned inside the membrane bubble 3 (the internal cooling water ring 4 is fixed to the die head 2 via a connecting frame). Before extrusion, the internal cooling water ring 4 is pre-installed at a predetermined position below the die head 2 and connected to a water source (such as a water storage tank, cooling water circulation pump, and temperature control system). After the membrane bubble 3 is extruded from the die head 2, it covers the outer wall of the internal cooling water ring 4 and descends. Cooling water is supplied into the internal cooling water ring 4 through a water supply pipeline and sprayed out from its outer wall. During operation, a continuous and uniform cooling water film 5 is formed between the outer wall of the internal cooling water ring 4 and the inner wall of the membrane bubble 3. The thickness of the cooling water film 5 is controlled by the cooling water supply flow rate and the outlet gap, typically within the range of 0.5–3 mm, preferably 1–2 mm. The cooling water film 5 is in direct contact with the inner wall of the high-temperature membrane bubble, rapidly carrying away the heat of the membrane bubble through heat exchange, achieving efficient cooling. Meanwhile, the cooling water film 5 also serves as a gas seal—because the water film fills the annular gap between the outer wall of the built-in cooling water ring 4 and the inner wall of the bubble 3, the blown air cannot leak downwards through this gap, thus locking the blown air within the bubble region above the built-in cooling water ring 4. Therefore, the bubble 3 is divided into a first cavity 31 located above the built-in cooling water ring 4 and a second cavity 32 located below the built-in cooling water ring 4. The blown air pressure in the first cavity 31 is independently controlled, and the air pressure and liquid level in the second cavity 32 are independently controlled.

[0036] Below the built-in cooling water ring 4 is a planer assembly 8, which is located at the bottom of the guide herringbone plate 6. The planer assembly 8 includes a planer blade 81 and a drive mechanism (such as a cylinder, hydraulic cylinder, or servo motor drive). The drive mechanism drives the planer blade 81 to longitudinally plan open the membrane bubble wall of the second cavity 32, forming a slit 82. The length and position of the slit 82 can be adjusted according to the membrane bubble diameter and production speed (e.g., the position of the slit 82 is selected at a height of 200-400mm from the center of the traction roller). Water from the cooling water film 5 continuously falls downward into the second cavity 32, forming a certain water level at the bottom of the second cavity 32, and then flows out from the slit 82.

[0037] One end of the vent pipe 9 extends into the gouge 82, and the other end is connected to a compressed air source (such as an air compressor or factory compressed air network). Preferably, the outlet of the vent pipe 9 is higher than the water level inside the membrane bubble 3. A vent pipe valve 91 is provided on the vent pipe 9 (see...). Figure 4 The compressed air is used to control the on / off state and flow rate of compressed air. Compressed air enters the second cavity 32 from the cutout 82 and applies outward expansion pressure to the membrane bubble 3, keeping the cut membrane bubble 3 in an expanded and bulging state.

[0038] like Figure 5 As shown, as another optional implementation, the compressed air for the second cavity 32 can also be introduced through a vent pipe 9 located inside the die head 2. This vent pipe 9 passes from top to bottom through the internal channel or side wall of the built-in cooling water ring 4, with its lower outlet extending into or connecting to the second cavity 32, and its upper end connected to a compressed air source. This method, due to its shorter gas flow path, lower pressure loss, and insensitivity to kerf opening and water level fluctuations, is particularly suitable for production conditions requiring more precise control of the second cavity's air pressure. The above two air supply methods (kerf air supply and die head built-in air supply) can be used individually or in combination depending on the actual working conditions.

[0039] It is understandable that when a built-in vent pipe is used in the mold head, the vent pipe valve 91 can be set on the air inlet pipe of the vent pipe 9 above the mold head 2, and the pressure sensor 12 is still set inside the second cavity 32. Its control logic is the same as the air supply method of the planing hole - the vent pipe valve 91 automatically opens or closes according to the pressure signal detected by the pressure sensor 12 to regulate the air pressure in the second cavity 32.

[0040] An external cooling water ring 13 can be selectively disposed on the outer periphery of the internal cooling water ring 4, and its inner diameter is more than 100 mm larger than the diameter of the membrane bubble. The external cooling water ring 13 is provided with an annular flexible water delivery plate 131 (such as a silicone plate, rubber plate, etc.) for forming a cooling water film on the outer wall of the membrane bubble. The external cooling water ring 13 is connected to an independent water source and water supply pipeline, and can be turned on or off according to production needs.

[0041] 2. Specific structure of the built-in cooling water ring See Figure 2 The built-in cooling water ring 4 includes an upper conical guide portion 41 and a lower cylindrical portion 42. The conical guide portion 41 has a conical structure that is smaller at the top and larger at the bottom, and its bottom smoothly transitions to the upper end of the cylindrical portion 42. The outer wall of the conical guide portion 41 is a smooth curved surface, and the cone angle (i.e., the angle between the outer wall and the vertical axis) is 30° to 45°, preferably 35° to 40°. During the membrane penetration operation, the membrane bubble 3 slides smoothly down the outer wall of the conical guide portion 41 without getting stuck or damaged due to abrupt structural changes. The outer wall of the cylindrical portion 42 is a cylindrical surface, and its diameter is determined according to the diameter of the target membrane bubble. The height of the cylindrical portion 42 is 800 to 1200 mm, preferably 900 to 1100 mm. The cylindrical portion 42 has a diameter taper of 3 to 5 mm from top to bottom, that is, the diameter of the top of the cylindrical portion 42 is 3 to 5 mm larger than that of the bottom, and the taper value is preferably 4 mm. This micro-tapered design is based on the following considerations: As the temperature of the membrane bubble 3 gradually decreases during the cooling process, the diameter of the membrane bubble will gradually shrink due to the thermal expansion and contraction effect. The tapered design ensures that the gap between the outer wall of the built-in cooling water ring 4 and the inner wall of the membrane bubble 3 remains relatively constant or slightly expands during the downward movement of the membrane bubble, which is conducive to the stability of the water film thickness and the uniformity of the cooling effect. At the same time, the operation of the membrane bubble is also smoother.

[0042] The cylindrical portion 42 is provided with two independent annular water outlets distributed circumferentially: a first-stage water outlet 43 and a second-stage water outlet 44. The first-stage water outlet 43 is located 100-150 mm below the bottom of the conical guide portion 41, preferably 120-130 mm. The first-stage water outlet 43 is an annular slit or multiple water outlet holes evenly distributed along the circumference, with a water outlet gap of 2-5 mm, preferably 3-4 mm. This position corresponds to the stage when the membrane bubble 3 has just been extruded from the die head 2 and is in a highly elastic state and has not yet been fully shaped. After the cooling water is sprayed out here, it forms an initial water film on the inner wall of the membrane bubble. Since this area is close to the bottom of the conical guide portion 41, the cooling water will stay in this area briefly due to the inability to flow downward in time, forming a pre-cooling zone to pre-cool and shape the membrane bubble. The second-stage water outlet 44 is located 300-400 mm below the first-stage water outlet 43, preferably 340-360 mm. The second-stage outlet 44 is also an annular slit or multiple outlet holes evenly distributed along the circumference, with an outlet gap of 3–6 mm, preferably 4–5 mm. This position corresponds to the deep cooling stage after the membrane bubble 3 has undergone pre-cooling. The large flow rate of cooling water from the second-stage outlet 44 deeply cools and shapes the membrane bubble. The first-stage outlet 43 and the second-stage outlet 44 are connected to independent water supply pipelines. Each water supply pipeline is equipped with an independent flow regulating valve and flow rate regulating device (such as a variable frequency pump or throttle valve). The cooling water flow rate, flow rate, and water temperature of each outlet can be independently adjusted. The cooling water flow rate of the first-stage outlet 43 is usually controlled at 5–14 m³ / h, and the cooling water flow rate of the second-stage outlet 44 is usually controlled at 6–16 m³ / h. The specific values ​​are determined comprehensively based on factors such as membrane bubble diameter, membrane thickness, production speed, and cooling water temperature.

[0043] The first chamber 31 is equipped with an independent inflation pipeline and pressure control device, which is used to fill the first chamber 31 with inflation air and maintain the air pressure at 0.15-0.2 MPa. The air pressure in the first chamber 31 is mainly used to inflate the membrane bubble 3 to the target diameter and to maintain the stability of the membrane bubble diameter during the production process.

[0044] 3. Specific structure of the planer assembly and water level control device See Figure 3 The planer assembly 8 is located at the bottom of the guide herringbone plate 6. The planer assembly 8 includes planer blades 81 and a drive mechanism (not shown in the figure). The planer blades 81 can be arranged on one side or symmetrically on both sides. In the case of a single-side arrangement, only one planer blade 81 is provided on one side of the membrane bubble; in the case of a symmetrical arrangement on both sides, one planer blade 81 is provided on each side of the membrane bubble. The symmetrical arrangement on both sides is beneficial for uniform stress on the membrane bubble and a smooth planing edge, and is suitable for the production of large-diameter membrane bubbles.

[0045] The planer blade 81 is fixedly connected to one end of the planer blade connecting rod 83. The planer blade connecting rod 83 is hinged to the planer blade fixing seat 84 and can rotate to adjust the angle between the planer blade and the membrane bubble wall, which is beneficial for planing the membrane bubble. After the angle is adjusted, the planer blade can be fixed. The other end of the planer blade fixing seat 84 is connected to the drive mechanism; the drive mechanism can drive the planer blade fixing seat 84, the planer blade connecting rod 83 and the planer blade 81 to move back and forth to adapt to the size of the membrane bubble.

[0046] The cutting edge of the planer 81 faces the bubble wall. The drive mechanism moves the planer 81 along the longitudinal direction perpendicular to the bubble (i.e., the downward direction of the bubble), longitudinally planing open the bubble wall of the second cavity 32 to form a slit 82. The length of the slit 82 is generally 200-400 mm, preferably 300 mm, and the specific length is determined according to the bubble diameter, cooling water volume, and production speed. The cutting depth of the planer 81 should be controlled to just penetrate the bubble wall without damaging the venting pipe 9 and other internal components inside the bubble.

[0047] The cutting edge 82 is located below the cooling water level 16 inside the second cavity 32, and the distance between the cutting edge 82 and the water level 16 is greater than 50 mm, preferably 60-100 mm. The purpose of this position design is to ensure that the cutting edge 82 is always below the water surface, so that the cooling water in the second cavity 32 can flow out continuously and stably from the cutting edge 82, without interruption of drainage or gas leakage from the cutting edge due to water level fluctuations.

[0048] A water level control device is provided on one side of the cutout 82. The water level control device includes a baffle plate 10. The baffle plate 10 is an arc-shaped plate or flat plate, located on one side (outer side) of the cutout 82. Its width is greater than the width of the cutout 82, and its length is adapted to the length of the cutout 82. The gap between the baffle plate 10 and the membrane bubble wall is adjustable. The baffle plate 10 can be adjusted manually (e.g., by screw adjustment) or automatically (by a servo motor and transmission mechanism). By adjusting the gap between the baffle plate 10 and the membrane bubble wall, the speed at which cooling water is discharged from the cutout 82 is controlled—when the gap increases, the drainage speed increases, and the water level decreases; when the gap decreases, the drainage speed decreases, and the water level rises. In this way, a constant water level can be maintained in the second cavity 32. In some embodiments, the vent pipe 9 is fixedly connected to the baffle plate 10, and the vent pipe 9 is located at the center of the baffle plate 10.

[0049] See Figure 4As a preferred embodiment of the water level control device, it also includes a water level sensor 11 disposed inside or outside the second cavity 32. The water level sensor 11 may be a float-type liquid level sensor, an ultrasonic liquid level sensor, or a capacitive liquid level sensor, etc., for real-time monitoring of the water level height inside the second cavity 32. The baffle plate 10 is adjusted using an automatic baffle plate position adjustment device 16. The automatic baffle plate position adjustment device 16 includes an adjustment device mounting base 1602, on which a servo motor 1601 and a slide rail 1603 are fixedly connected. A slider 1604 is slidably connected to the slide rail 1603, restricting the slider 1604 to move only along the length of the slide rail and preventing rotation. The slider 1604 is fixedly connected to the baffle plate 10 via a baffle plate connecting rod 1605. A nut 1606 is fixedly connected to the top of the slider 1604, and a screw 1607 is fixedly connected to the output shaft of the servo motor 1601, with the screw 1607 threadedly connected to the nut 1606. The servo motor 1601 drives the baffle plate 10 to move via a screw-slider mechanism. The water level sensor 11 is signal-connected to the servo motor 1601 of the automatic baffle plate position adjustment device 16. The automatic position adjustment device automatically adjusts the gap between the baffle plate 10 and the membrane bubble wall based on the water level signal detected by the water level sensor 11. When the water level is detected to be higher than the set value, the gap of the baffle plate 10 is automatically increased to accelerate drainage; when the water level is detected to be lower than the set value, the gap of the baffle plate 10 is automatically decreased to slow down drainage. Through this closed-loop automatic control, precise and constant water level control is achieved without manual intervention.

[0050] The water level setting is typically 200–400 mm above the center of the traction roller 7, preferably 300–350 mm. Setting the water level too high will result in excessive water pressure at the bottom of the second chamber 32, exerting excessive outward pressure on the membrane bubble 3, affecting the stable operation of the membrane bubble and the normal traction of the traction roller 7. Setting the water level too low will hinder the installation of the planer blade 81 (which needs to be submerged below the water surface) and the arrangement of the baffle plate 10 and the vent pipe 9.

[0051] 4. Specific structure of the pneumatic control device See Figure 4A vent valve 91 is provided on the vent pipe 9. The vent valve 91 can be a solenoid valve, pneumatic valve, or electric regulating valve, used to control the on / off state and flow rate of compressed air. A pressure sensor 12 is provided in the second chamber 32 to monitor the air pressure in the second chamber 32 in real time. The pressure sensor 12 is connected to the vent valve 91. The vent valve 91 automatically opens or closes according to the pressure signal detected by the pressure sensor 12: when the air pressure in the second chamber 32 is detected to be lower than the set value, the vent valve 91 opens to allow compressed air to enter; when the air pressure is detected to be higher than the set value, the vent valve 91 closes or reduces its opening to stop or reduce the entry of compressed air. Through this automatic control, the air pressure in the second chamber 32 is maintained in the range of 0.12 to 0.15 MPa, preferably 0.13 to 0.14 MPa. Maintaining the air pressure inside the second cavity 32 plays the following important roles: First, it ensures that the slit bubble 3 remains fully expanded before entering the guide plate 6, preventing wrinkles caused by the bubble collapsing; Second, in conjunction with the outward pressure exerted on the bubble wall by the cooling water inside the bubble 3, the bubble 3 enters the guide plate 6 at its maximum diameter, and is gradually compressed and folded by the guide plate 6 into a flat film; Third, the air pressure and water level are controlled in tandem. When the air pressure increases, it can help push the cooling water out of the slit 82, and when the air pressure decreases, the drainage speed slows down accordingly. The two work together to achieve stable control of the water level and the shape of the bubble. It should be noted that the air pressure in the second chamber 32 is lower than that in the first chamber 31 (0.15~0.2MPa). This is because the second chamber 32 is a pre-formed membrane bubble, and its internal gas is isolated from the outside. However, the air pressure in the second chamber 32 fluctuates due to drainage from the cut-out 82, requiring air replenishment to maintain the internal pressure and fill the membrane bubble. However, a large air pressure is not necessary. Secondly, if the air pressure in the second chamber is greater than that in the first chamber, it may enter the first chamber, affecting the stability of the membrane bubble in the first chamber. In addition, besides regulating air pressure, the vent pipe 9 also affects the drainage speed when the water level in the second chamber 32 rises or falls for various reasons—when compressed air is introduced, the air pressure pushes the cooling water to be discharged from the cut-out 82 faster, and the water level drops; when compressed air is stopped, the drainage speed slows down, and the water level rises. The vent pipe 9 works in conjunction with the baffle plate 10 to achieve comprehensive control of water level and air pressure.

[0052] In other embodiments, the vent valve 91 can be directly connected to the water level sensor 11. When the water level sensor 11 detects a high water level and controls the baffle plate 10 to move backward to increase the discharge of cold water, the vent valve 91 opens to allow air to fill the air pressure in the second chamber 32. When the water level is detected to be low and the baffle plate 10 moves forward to reduce the discharge of cold water, the vent valve 91 closes and stops allowing air to flow. The air pressure inside the membrane bubble can be maintained by the entry of the upper cooling water into the second chamber 32 and the rise of the water level in the second chamber 32.

[0053] 5. Specific structure of the external cooling water ring See Figure 1 An external cooling water ring 13 is disposed on the outer periphery of the internal cooling water ring 4. The inner diameter of the external cooling water ring 13 is at least 100 mm larger than the diameter of the membrane bubble 3, preferably 150–250 mm. This large gap design ensures that the membrane bubble 3 will not come into contact with the external cooling water ring 13 during membrane insertion and normal operation, avoiding the difficulties in membrane insertion and operational jamming caused by excessively small gaps in the prior art. The external cooling water ring 13 is provided with an annular flexible water delivery plate 131, which can be made of 2–3 mm thick silicone plate, rubber plate, or other flexible material plate. The flexible water delivery plate 131 is annular, and its inner edge is close to the outer wall of the membrane bubble 3 but does not contact the membrane bubble 3 (the gap is 0.5–2 mm). Cooling water is supplied through the water supply pipe of the external cooling water ring 13 and overflows through the outlet to the flexible water conveying plate 131. The flexible water conveying plate 131 evenly distributes the water along the outer wall of the membrane bubble 3, forming an outer wall cooling water film that cools the outer wall of the membrane bubble 3. The flexibility of the flexible water conveying plate 131 allows the membrane bubble 3 to pass smoothly without damage during membrane insertion. Furthermore, the flexible water conveying plate 131 can adaptively adjust its position to ensure the uniformity of the cooling water film even with slight changes in the membrane bubble diameter. The external cooling water ring 13 is connected to an independent water source and water supply pipe, and can be turned on or off according to production needs. In thick film production modes requiring extremely high cooling efficiency (such as in Example 2), the external cooling water ring 13 is turned on to achieve simultaneous internal and external cooling. In ordinary production modes or low-energy-consumption economical production modes (such as in Example 3), the external cooling water ring 13 is turned off, relying solely on the cooling water in the internal cooling water ring 4 and the second cavity 32 for cooling, thus reducing energy consumption.

[0054] 6. Cooling water circulation system See Figure 1 A water storage tank 14 is located below the cutout 82 to receive the cooling water flowing out of the cutout 82. The water storage tank 14 is connected to an external cooling water tank (not shown in the figure) via a cooling water circulation pipeline. The external cooling water tank is equipped with a cooling device (such as a cooling tower, heat exchanger, or chiller unit) to cool the recovered cooling water to a set cooling temperature (usually 20-35°C), and then pumped back to the built-in cooling water ring 4 and the external cooling water ring 13 for reuse by a circulating water pump. The cooling water circulation system is also equipped with a filter to remove impurities and film debris that may be entrained in the cooling water, ensuring the cleanliness of the cooling water.

[0055] II. Specific Implementation Methods of Cooling The cooling method using the cooling mechanism of the aforementioned downblown film blowing device specifically includes the following steps: Step S1: Melt extrusion and membrane bubble formation Plastic raw materials (such as HDPE, LLDPE, or their blends) and additives are added to the hopper of extruder 1. The temperature of each heating zone of extruder 1 is set to 170–210°C (the specific temperature is determined according to the type of raw material and the formulation). After being heated and melted in extruder 1 and plasticized by the screw, the material is conveyed to die 2. The temperature of die 2 is set to 190–205°C. The molten material is extruded from the annular die gap of die 2 to form a cylindrical preform. At the same time, blown air is introduced into the preform to inflate it into a cylindrical preform 3.

[0056] The membrane bubble 3 descends along the outer wall of the built-in cooling water ring 4 located inside it. In the initial membrane insertion stage, the built-in cooling water ring 4 is first installed at a predetermined position below the die head 2, and the cooling water supply is turned off. The starting end of the membrane bubble 3 is then pulled downward along the outer wall of the conical guide part 41.

[0057] The membrane penetration process is as follows: Before the melt passes through the internal cooling water ring 4 from the die head 2, compressed air is introduced through the air blowing pipe 201 to continuously inflate the membrane bubble 3. At the same time, cooling water is supplied through the cooling water ring water supply pipe 202 with the first-stage outlet 43 and the second-stage outlet 44 slightly open. At this time, due to the unstable air pressure inside the membrane bubble 3, the membrane bubble 3 fluctuates in size, and the membrane bubble 3 will briefly contact the conical guide part 41 of the internal cooling water ring 4. After further inflation and downward movement, the membrane bubble 3 contacts the cylindrical portion 42 of the built-in cooling water ring 4. As the cooling water film 5 is established and the inflated air inside the upper membrane bubble 3 is sealed, if the membrane bubble cooling line (the membrane bubble cooling line refers to the boundary position where the membrane bubble 3 transitions from the conical expansion section to the equal-diameter cylindrical section, that is, the circumferential boundary line where the membrane bubble wall changes from the molten high-elastic state to the cooled and shaped state, specifically, the annular junction area where the funnel-shaped membrane bubble 3 transitions from the conical expansion section to the equal-diameter cylindrical section) approaches the upper part of the cylindrical portion 42, then compressed air continues to be introduced through the air blowing pipe 201 until the membrane bubble cooling line is 100-400mm higher than the upper end of the cylindrical portion 42 of the built-in cooling water ring 4 (this distance can fully adapt to and adjust the situation caused by the fluctuation of the membrane bubble 3 when producing films of different thicknesses). The membrane bubble 3 adheres to and easily passes through the cylindrical portion 42 of the built-in cooling water ring 4, and then the introduction of compressed air can be stopped.

[0058] After the membrane bubble 3 passes smoothly through the built-in cooling water ring 4 and enters the traction roller 7, the traction speed is adjusted to make the membrane bubble 3 run stably from the die head 2 to the traction roller 7.

[0059] After the bottom of the membrane bubble 3 is clamped and sealed by the traction roller 7, and a stable inflation pressure is established inside the membrane bubble 3 to form a complete internal closed space, it can enter the normal operation state and execute the following steps S2 to S4.

[0060] Step S2: Water film formation and sealing cooling Cooling water is introduced into the built-in cooling water ring 4 and sprayed out from the first-stage outlet 43 and the second-stage outlet 44, forming a continuous and uniform cooling water film 5 between the outer wall of the built-in cooling water ring 4 and the inner wall of the membrane bubble 3. The cooling water is in direct contact with the inner wall of the high-temperature membrane bubble, and the heat of the membrane bubble is quickly carried away through heat exchange, achieving efficient cooling. The thickness of the cooling water film is controlled within the range of 0.5 to 3 mm, preferably 1 to 2 mm.

[0061] The cooling water film 5 also serves as a gas seal—because the water film fills the annular gap between the outer wall of the built-in cooling water ring 4 and the inner wall of the bubble 3, the blown air cannot leak downwards through this gap, thus locking the blown air inside the bubble 3 above the built-in cooling water ring 4. The bubble 3 is divided into a first cavity 31 located above the built-in cooling water ring 4 and a second cavity 32 located below the built-in cooling water ring 4.

[0062] Inflated air is introduced into the first chamber 31, and the air pressure inside the first chamber 31 is maintained at 0.15-0.2 MPa by an independent air pressure control system to ensure the stability of the inflation diameter of the membrane bubble 3. The water in the cooling water film 5 continues to flow downwards under gravity and falls into the second chamber 32 below the cooling water ring. The cooling water accumulated in the second chamber 32 continues to contact the inner wall of the membrane bubble, further immersing and cooling the membrane bubble.

[0063] Step S3: Dig open for drainage When the membrane bubble 3 descends to the bottom of the guide plate 6, the planer 81 of the planer assembly 8, driven by the drive mechanism, longitudinally cuts open the membrane bubble wall of the second cavity 32, forming a planing opening 82. The planing opening 82 is located below the cooling water level line 16 in the second cavity 32 (the distance between the planing opening and the water level line is greater than 50mm). The cooling water in the second cavity 32 continuously flows out from the planing opening 82 under the action of gravity and falls into the water storage tank 14.

[0064] The drainage speed of the cutter is adjusted by a baffle plate 10 located on one side of the cutter 82. Increasing the gap between the baffle plate 10 and the membrane bubble wall speeds up the drainage and lowers the water level; decreasing the gap slows down the drainage and raises the water level. The water level sensor 11 monitors the water level in the second chamber 32 in real time. The automatic position adjustment device automatically adjusts the gap of the baffle plate 10 according to the water level signal, so that the water level in the second chamber 32 is maintained within a set range of 200-400mm above the center of the traction roller 7.

[0065] Step S4: Inflating and traction output Compressed air is introduced into the second cavity 32 through the air pipe 9 from the vent 82 (or through the air pipe 9 located inside the die head 2 and passing through the built-in cooling water ring 4) to keep the slit membrane bubble 3 in an expanded state. The pressure sensor 12 monitors the air pressure in the second cavity 32 in real time, and the air pipe valve 91 automatically controls the amount of compressed air introduced according to the pressure signal to maintain the air pressure in the second cavity 32 at 0.12-0.15 MPa. Under the action of compressed air, the slit membrane bubble 3 maintains its full maximum diameter and moves down along the guide herringbone plate 6. The guide herringbone plate 6 gradually gathers and folds the cylindrical membrane bubble into a flat sheet film. Since the membrane bubble 3 has been fully expanded before entering the guide herringbone plate 6, the film after being folded by the guide herringbone plate 6 is flat and wrinkle-free, and is pulled out at a uniform speed by the traction roller 7 to enter the subsequent winding process. In steps S3 and S4, the vent pipe 9 and the baffle plate 10 work together to achieve comprehensive control of air pressure and water level: when the water level in the second cavity 32 is higher than the set value, the baffle plate 10 is moved back to increase the drainage gap, and the airflow of the vent pipe 9 can be opened or increased, using air pressure to accelerate the discharge of cooling water from the cut-out 82; when the water level is lower than the set value, the baffle plate 10 is moved forward to reduce the drainage gap, and the airflow of the vent pipe 9 can be reduced or stopped to slow down the drainage speed. Through this coordinated control of air pressure and water level, it is ensured that the membrane bubble fully expands and unfolds at the guide herringbone plate 6, while the water level in the second cavity 32 remains constant.

[0066] III. Explanation of the Reasons for Selecting Parameters for Each Component 1. Height of the built-in cooling water ring and position of the outlet The height of the cylindrical part of the built-in cooling water ring is 800-1200mm. This height range is determined based on the following considerations: if the height is too low (less than 800mm), the residence time of the membrane bubble in the cooling water ring is too short, the heat exchange between the cooling water and the membrane bubble is insufficient, and the membrane bubble is not fully shaped when it exits the cooling water ring, making it prone to deformation after entering the second cavity; if the height is too high (greater than 1200mm), the support length of the cooling water ring for the membrane bubble is too long, the operating resistance of the membrane bubble increases, and the equipment size is too large, increasing the cost.

[0067] The first-stage outlet is 100-150mm from the bottom of the conical guide section. This position allows the cooling water to begin pre-cooling as soon as the membrane bubble leaves the conical guide section. At this time, the membrane bubble is still in a high-temperature, highly elastic state. Pre-cooling helps the membrane bubble to set its shape earlier, reducing shrinkage and deformation during subsequent cooling. The second-stage outlet is 300-400mm from the first-stage outlet. This distance allows the membrane bubble some time to achieve thermal equilibrium after pre-cooling before deep cooling, achieving gradient cooling.

[0068] 2. Taper of the cylindrical part The cylindrical section has a 3-5mm diameter taper from top to bottom. As the temperature of the membrane bubble gradually decreases from the inner wall to the outer wall during cooling, the bubble diameter gradually decreases due to thermal expansion and contraction (the diameter shrinkage is typically in the range of 2-6mm). The taper design ensures that the gap between the outer wall of the internal cooling water ring and the inner wall of the membrane bubble remains relatively constant as the bubble descends, preventing the gap from widening, the water film from thinning, or even breaking due to bubble contraction, thus ensuring uniform cooling performance.

[0069] 3. Water level in the second chamber The water level is set 200-400mm above the center of the traction roller. If the water level is too high, the water pressure at the bottom of the second chamber will be too high (water pressure = ρgh, approximately 980Pa of pressure is generated per 100mm water column), which will exert excessive outward pressure on the membrane bubble wall, causing the membrane bubble to over-expand before entering the traction roller, affecting the normal clamping and traction of the traction roller; if the water level is too low, it will also be unfavorable for the installation and arrangement of the planer and air pipe.

[0070] 4. Second chamber air pressure The air pressure in the second chamber is maintained at 0.12–0.15 MPa. This pressure range is sufficient to keep the slit membrane bubble fully expanded, but not so high as to cause the membrane bubble to rupture or generate excessive reaction force on the traction roller. The preferred value is 0.13–0.14 MPa.

[0071] IV. Examples The present invention will be further illustrated by specific embodiments below.

[0072] Example 1: High-capacity production mode of conventional geomembrane This embodiment is applicable to high-capacity continuous production of HDPE geomembranes with a thickness of 1.0–2.0 mm. Process parameter settings: Extruder body temperature in each zone: 170–210℃ (increasing progressively from feed to discharge direction); Down-blowing die temperature: 190–205℃. First chamber (above the built-in cooling water ring) pressure: 0.18 MPa; Second chamber (below the built-in cooling water ring) compressed air pressure adjustment: 0.13 MPa. Traction section water level setting: 320 mm (distance from the center of the traction roller); Cutting blade immersion depth: 60 mm. First-stage cooling water inlet flow rate of the built-in cooling water ring: 6–8 m³ / h, water temperature: 15–25℃; Second-stage cooling water inlet flow rate: 9–12 m³ / h, water temperature: 15–25℃. Total flow rate of external cooling water ring: 10-15 m³ / h (external cooling water ring is turned on in this embodiment); circulating water temperature is controlled at 15-25℃. Production line traction speed: 4-8 m / min; planer blades are arranged symmetrically on both sides with longitudinal opening.

[0073] Work process: HDPE raw material is melted and plasticized in an extruder and extruded through a die to form a cylindrical membrane bubble. The membrane bubble descends smoothly along the conical guide section with an internal cooling water ring. The first-stage outlet sprays water onto the inner wall of the membrane bubble at a flow rate of 6–8 m³ / h for pre-cooling, forming an initial water film on the inner wall. After descending approximately 350 mm, the membrane bubble reaches the second-stage outlet, where it undergoes deep cooling at a flow rate of 9–12 m³ / h. The cooling water film seals the inflated air within the first chamber, maintaining the air pressure in the first chamber at 0.18 MPa. The membrane bubble continues its descent into the second chamber, where the cooling water further contacts and immerses the membrane bubble in cooling. When the membrane bubble reaches between the guide plate and the traction roller, a planer cuts the membrane bubble wall longitudinally, allowing cooling water to flow from the planing opening into a water storage tank. Compressed air is introduced into the second chamber through a vent pipe, maintaining the air pressure at 0.13 MPa to keep the membrane bubble fully expanded. The baffle plate automatically adjusts the drainage gap based on the signal from the water level sensor, maintaining the water level at 320mm. After being folded and flattened by the guide plate, the membrane bubble is pulled out by the traction roller at a speed of 4-8m / min.

[0074] Effect: Compared with the traditional air-cooled production line of the same specifications, this embodiment increases the production capacity by 2.5 times, reduces the power consumption per unit product by 43%, reduces the thickness deviation of finished products by ≤±3%, and significantly reduces the range of mechanical property fluctuations.

[0075] Example 2: High-performance production mode of thick geomembrane This embodiment is applicable to the high-performance production of thickened impermeable geomembranes with a thickness >2.0mm, focusing on solving technical problems such as uneven cooling of thick films, high internal stress, warping deformation, and subsequent shrinkage. Process parameter settings: Extruder temperature range: 180~215℃; Die temperature: 195~210℃. First chamber pressure holding pressure: 0.18MPa; Second chamber compressed air pressure adjustment: 0.14MPa (due to the greater expansion force required for thick films). Traction section water level setting: 400mm (distance from the center of the traction roller); Cutting blade immersion depth: 80mm. First-stage cooling water ring outlet inlet flow rate: 10~14m³ / h (high flow rate quickly removes surface melting heat); Second-stage outlet flow rate adjustment: 12~15m³ / h (rapid shaping to ensure uniform crystallinity inside and outside the membrane). The external cooling water ring operates at a low flow rate of 13–16 m³ / h, ensuring that the surface temperature of the outer wall is approximately the same as that of the inner wall. This prevents the thick film from cooling too quickly, which could lead to a large temperature difference between the inside and outside and generate internal stress. The traction line speed is 3–6 m / min (for slow cooling to release internal stress).

[0076] Work process: The method is basically the same as in Example 1, except that: for thick films (>2.0 mm) with high heat and long cooling time, the first-stage outlet uses a larger flow rate (10-14 m³ / h) for high-intensity pre-cooling to quickly remove surface heat and shape the surface of the membrane bubble; the second-stage outlet uses a relatively larger flow rate (12-15 m³ / h) to increase the cooling rate and allow the cooling inside the membrane bubble to be transferred to the outer layer more quickly, avoiding stress concentration caused by inconsistent cooling between the inside and the surface of the membrane.

[0077] The external cooling water ring operates at a high flow rate of 13–16 m³ / h to rapidly cool the outer wall of the membrane bubble, preventing excessive temperature differences between the inner and outer walls of the thick film that could lead to warping and inconsistent crystallization. The traction speed is reduced to 3–6 m / min to ensure that the thick film has sufficient time to release internal stress during the cooling process.

[0078] Effect: This embodiment can effectively avoid problems such as thick film warping, stress concentration, and later shrinkage deformation, reduce overall energy consumption by 45%, and significantly improve the puncture resistance and impermeability of the finished product.

[0079] Example 3: Low-energy, economical mass production mode This embodiment is suitable for the stable and continuous production of cost-sensitive, high-volume, affordable geomembranes, ensuring product performance meets standards without the use of an external cooling water ring. Process parameter settings: The external cooling water ring supply branch is closed, relying solely on the two-stage outlets and the second chamber of the internal cooling water ring for cooling (i.e., a three-stage cooling mode). Flow rate at the first-stage outlet of the internal cooling water ring: 7–10 m³ / h; Flow rate at the second-stage outlet: 5–8 m³ / h. Inlet water temperature: 18–28℃ (a wider temperature range than in embodiments 1 and 2, reducing cooling energy consumption). Traction speed: 6–10 m / min. Working process: Basically the same as in embodiment 1, except that the external cooling water ring is closed, and the membrane bubble is cooled only by the cooling water in the two-stage outlets and the second chamber of the internal cooling water ring. Because the external cooling water ring is not activated, the cooling water volume is reduced, allowing for a slight increase in cooling water temperature (18–28℃), significantly reducing the energy consumption of the refrigeration equipment.

[0080] Effect: Under the premise that all national standards for geomembrane are met, the overall energy consumption of this embodiment is reduced by 48% compared with the traditional air-cooled production line, making it suitable for stable and continuous production of large quantities of affordable geomembrane.

[0081] Example 4: Comparison of the effects of different cooling modes on membrane bubble stability To verify the effect of the cooling mechanism of this invention on improving membrane bubble stability, a comparative production test was conducted using the same specification geomembrane (1.5mm thick HDPE geomembrane) under the following three modes: Mode A (only the first-stage outlet operates): The second-stage outlet and the external cooling water ring are closed, and cooling is achieved solely through the first-stage outlet. After 10 minutes of operation, the membrane bubble diameter fluctuated within ±2mm, and the film thickness deviation was ±6%.

[0082] Mode B (Two-stage outlet operation, external water ring off): The first and second stage outlets operate simultaneously, with the external cooling water ring closed. After 30 minutes of operation, the membrane bubble diameter fluctuation range is ±1.5mm, and the film thickness deviation is ±3%, indicating stable operation.

[0083] Mode C (Two-stage outlet + external water ring operation): The first-stage outlet, the second-stage outlet, and the external cooling water ring operate simultaneously. After 60 minutes of operation, the membrane bubble diameter fluctuation range is ±1mm, the film thickness deviation is ±2.5%, the membrane bubble appearance is round and without vibration, and the product quality is optimal.

[0084] The comparative results show that, compared to operating with only the first-stage outlet (Mode A), the combined operation of the first and second-stage outlets (Mode B) reduced the membrane bubble diameter fluctuation range from ±2mm to ±1mm and the thickness deviation from ±6% to ±3%, fully demonstrating the improving effect of two-stage gradient cooling on membrane bubble stability and film uniformity. Further addition of an external cooling water ring (Mode C) further improved membrane bubble stability. However, in the low-energy-consumption economical production mode of Example 3, the three-stage cooling of Mode B (two-stage water ring + second chamber immersion) already meets the product performance requirements.

[0085] Example 5: Comparison of the effects of different slit positions and air pressures on film wrinkling To verify the effect of the air-blowing expansion of the vent pipe in eliminating wrinkles, a comparative production was conducted using the same specification of geomembrane (1.5mm thick HDPE geomembrane) under the following three conditions: Condition A (no compressed air is introduced): After the slit is cut open, compressed air is not introduced into the second cavity through the vent pipe. Obvious longitudinal wrinkles can be observed on the surface of the film output by the traction roller, with a wrinkle width of approximately 3-8mm and a wrinkle spacing of approximately 50-150mm.

[0086] Condition B (Compressed air is introduced, pressure 0.11 MPa): The air pressure in the second chamber is maintained at 0.11 MPa. The wrinkles on the film surface output by the traction roller are significantly reduced, with only slight wrinkles remaining at the edges of the film.

[0087] Condition C (Compressed air is introduced, pressure 0.14 MPa): The air pressure in the second chamber is maintained at 0.14 MPa. The surface of the film output by the traction roller is smooth and wrinkle-free, fully meeting the quality requirements of geomembrane products.

[0088] The comparative results show that: without compressed air (condition A), the membrane bubble quickly deflates after being cut open and cannot fully expand when entering the guide plate, resulting in severe wrinkles in the finished product; with 0.11 MPa compressed air (condition B), the wrinkles are somewhat improved but not completely eliminated; with 0.14 MPa compressed air (condition C), the membrane bubble remains fully expanded, and the wrinkles are completely eliminated. This verifies the key role of the air-blowing expansion technology in eliminating wrinkles, and also indicates that the air pressure in the second chamber needs to be maintained within an appropriate range (preferably 0.12–0.15 MPa) to achieve the ideal flattening effect.

[0089] In summary, this invention effectively solves the technical problems of uneven cooling mechanism, easy wrinkling of membrane bubbles, and difficult drainage in existing downblown water-cooled blown film devices through the synergistic effect of multiple technical means such as two-stage gradient cooling with built-in cooling water ring, water film sealing zone pressure control, open-type free drainage, and air blowing expansion through vent pipe. It is suitable for efficient and high-quality downblown water-cooled production of thick films such as geomembranes.

[0090] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A cooling mechanism for a downblown film blowing device, disposed below the die head (2) of the downblown film blowing device and above the bottom end of the guide plate (6) of the downblown film blowing device; characterized in that, include: An internal cooling water ring (4) is located inside the bubble (3) formed by blowing below the die head (2); The outer wall of the built-in cooling water ring (4) can spray water onto the inner wall of the membrane bubble (3) to form a cooling water film (5) between the two. While cooling the inner wall of the membrane bubble (3), the cooling water film (5) seals the blown air inside the membrane bubble (3) above the built-in cooling water ring (4), so that the interior of the membrane bubble (3) is divided into a first cavity (31) located above the built-in cooling water ring (4) and a second cavity (32) located below the built-in cooling water ring (4); the water in the cooling water film (5) falls into the second cavity (32). A planer assembly (8) is used to longitudinally plan open the membrane bubble wall of the second cavity (32) to form a planer opening (82) for discharging cooling water. Ventilation pipe (9), the outlet of the ventilation pipe (9) is connected to the second cavity (32), and the inlet is connected to the air source for introducing gas into the second cavity (32) so that the membrane bubble (3) in the second cavity (32) remains in an expanded state; the ventilation pipe (9) is located at the planing opening (82) or extends into the planing opening (82), or is located inside the mold head (2) and passes downward through the built-in cooling water ring (4) and is connected to the second cavity (32).

2. The cooling mechanism of the downblown film blowing device according to claim 1, characterized in that, The built-in cooling water ring (4) is connected to a water source; the built-in cooling water ring (4) is provided with two independent annular water outlets distributed in the circumferential direction, namely the first water outlet (43) and the second water outlet (44), and the first water outlet (43) and the second water outlet (44) are respectively connected to independent water supply pipelines.

3. The cooling mechanism of the downblown film blowing device according to claim 2, characterized in that, The built-in cooling water ring (4) includes an upper conical guide section (41) and a lower cylindrical section (42). The first stage water outlet (43) is located 100-150 mm below the bottom of the conical guide section (41), and the second stage water outlet (44) is located 300-400 mm below the first stage water outlet (43). The height of the cylindrical section (42) is 800-1200 mm, and the cylindrical section (42) has a diameter tapering of 3-5 mm from top to bottom.

4. The cooling mechanism of the downblown film blowing device according to claim 1, characterized in that, The cut (82) is located below the cooling water level line (16) in the second cavity (32), and a water level control device is provided on one side of the cut (82). The water level control device includes a baffle plate (10) disposed on one side of the cut (82). The gap between the baffle plate (10) and the membrane bubble wall is adjustable. The discharge speed of cooling water from the cut (82) is controlled by adjusting the gap, so as to maintain a constant water level in the second cavity (32).

5. The cooling mechanism of the downblown film blowing device according to claim 4, characterized in that, The water level control device also includes a water level sensor (11) for detecting the water level in the second cavity (32) and an automatic position adjustment device that is connected to the flow baffle (10) in a transmission manner. The automatic position adjustment device automatically adjusts the gap between the flow baffle (10) and the membrane bubble wall according to the water level signal detected by the water level sensor (11). The ventilation pipe (9) is provided with a ventilation pipe valve (91), and the second cavity (32) is provided with a pressure sensor (12). The ventilation pipe valve (91) automatically opens or closes according to the pressure signal detected by the pressure sensor (12) to adjust the air pressure in the second cavity (32) so that the air pressure in the second cavity (32) is maintained at 0.12 to 0.15 MPa.

6. The cooling mechanism of the downblown film blowing device according to claim 1, characterized in that, The cooling mechanism also includes an external cooling water ring (13) connected to a water source. The external cooling water ring (13) is disposed on the outer periphery of the internal cooling water ring (4). The inner diameter of the external cooling water ring (13) is more than 100 mm larger than the diameter of the membrane bubble (3). The external cooling water ring (13) is provided with a flexible water conveying plate (131) for forming a cooling water film on the outer wall of the membrane bubble (3).

7. A downblown film extrusion device, comprising an extruder (1), a die (2), a guide plate (6), and a traction roller (7), characterized in that, It also includes a cooling mechanism for the downblown film blowing apparatus as described in any one of claims 1 to 6; The cooling mechanism is located below the die head (2) and above the bottom end of the guide herringbone plate (6); the extruder (1) is connected to the die head (2), the die head (2) is blown to form a film bubble (3), and the guide herringbone plate (6) is provided with the traction roller (7).

8. A method for cooling using the cooling mechanism of the downblown film device as described in claim 1, characterized in that, Includes the following steps: S1: The molten material is extruded downward from the die head (2) and blown to form a cylindrical film bubble (3), which descends along the outer wall of the built-in cooling water ring (4) disposed inside it; S2: Cooling water is introduced into the built-in cooling water ring (4) so ​​that a cooling water film (5) is formed between the outer wall of the built-in cooling water ring (4) and the inner wall of the membrane bubble (3). The cooling water film (5) is used to cool the inner wall of the membrane bubble (3). At the same time, the sealing effect of the cooling water film (5) is used to lock the blown air into the membrane bubble (3) above the built-in cooling water ring (4). The water in the cooling water film (5) falls into the membrane bubble (3) below the cooling water ring, i.e., into the second cavity (32). S3: When the membrane bubble (3) descends to the guide plate (6), the membrane bubble wall is longitudinally cut open by the planer (81) so that the cooling water inside the membrane bubble (3) flows out from the planer (82); S4: Compressed air is introduced into the second cavity (32) to keep the slit membrane bubble (3) in an expanded state. After being folded and flattened by the guide plate (6), it is pulled out by the traction roller (7).

9. The method according to claim 8, characterized in that, In step S2, the built-in cooling water ring (4) is provided with two independent annular outlets. The first outlet (43) supplies water to the inner wall of the membrane bubble (3) with a first flow rate and a first flow velocity for pre-cooling. The second outlet (44) supplies water to the inner wall of the membrane bubble (3) with a second flow rate and a second flow velocity for deep cooling. The first flow rate, the first flow velocity, the second flow rate, and the second flow velocity are adjusted independently. The cooling water in the second cavity (32) further cools the inner wall of the membrane bubble (3). A cooling water film is formed on the outer wall of the membrane bubble (3) by an external cooling water ring (13) set on the outer periphery of the built-in cooling water ring (4) for cooling.

10. The method according to claim 8, characterized in that, In step S3, the drainage speed of the cut (82) is adjusted by the baffle plate (10) set on one side of the cut (82) to maintain a constant water level inside the membrane bubble (3); in step S4, the air pressure inside the membrane bubble (3) is adjusted by controlling the on / off and flow rate of the compressed air to maintain the air pressure at 0.12-0.15 MPa. At the same time, the membrane bubble (3) is fully expanded and unfolded at the guide plate (6) by the coordinated control of the air pressure and the water level inside the membrane bubble (3).

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