Multi-layer co-extrusion pipe die head with pre-diverter

Abstract

The invention relates to the technical field of die heads for extrusion molding of plastic pipelines, in particular to a multi-layer co-extrusion pipe die head with a pre-diverter. In order to solve the problems that a traditional co-extrusion pipe die head shunting structure is integrated on a spiral body, melt retention and uneven distribution are easily caused due to limited runners and steep steering, and then deviation of the wall thickness of a pipe is caused, the scheme is provided with a die body, the spiral body containing three layers of spiral distribution runners, and a first pre-shunting device and a second pre-shunting device which are sequentially arranged in the axial direction; the first pre-diverter diverts an outer-layer melt to an outer-layer spiral distribution runner through a first annular gap runner, and the second pre-diverter diverts an inner-layer melt to an inner-layer spiral distribution runner through a second annular gap runner, and is matched with a plurality of groups of feeding channels, a diversion cone, a closed-loop heating temperature control system and a layered and integrally combined wall thickness adjusting structure; and precise shunting and stable conveying of the melt are achieved. According to the scheme, the melt retention risk is eliminated, the distribution uniformity is improved, the pipe forming quality is guaranteed, and the device is suitable for multi-specification production and convenient to maintain.

Description

Technical Field

[0001] This application relates to the field of die heads for plastic pipe extrusion molding, and more particularly to a multi-layer co-extrusion pipe die head with a pre-diverter. Background Technology

[0002] Multilayer co-extrusion technology is a key process in the production of composite pipes in the field of polymer material processing. It precisely combines and synergistically extrudes melts with different properties within a die, enabling the one-time molding of multilayer composite pipes. In typical multilayer composite pipes (such as three-layer composite pipes), the middle layer is usually the main layer that bears the structural strength, while the inner and outer layers are mostly functional layers with protection, corrosion resistance, or aging resistance. This technology can combine the advantages of each layer's materials to meet complex application requirements. Therefore, this type of composite pipe is widely used in municipal water supply and drainage, chemical media transportation, and building pipe networks.

[0003] Currently, conventional multi-layer co-extrusion dies (including three-layer co-extrusion dies) in the industry rely on spirals (such as inner spirals, outer spirals, and intermediate spirals) corresponding to each melt layer to distribute the melt and ensure the formation of multi-layer composite pipes. However, due to the axial dimension design of the spiral itself, the arc-shaped flow channel area on its outer surface used for melt pre-diversion is often compressed. This not only limits the number of pre-diversion stages but also makes the flow channel turning angle at the end of each arc-shaped flow channel steep, making it difficult to achieve a smooth transition of the melt.

[0004] This pre-diversion structure integrated into the spiral has inherent technical defects: on the one hand, the steep, almost right-angled change in flow direction will seriously hinder the smoothness of melt flow, and easily form flow dead zones and melt stagnation zones in the flow channel. Especially for high-viscosity or shear-sensitive melts with poor flowability, it is very easy to cause melt thermal degradation and retention problems; on the other hand, the unsmooth pre-diversion process will lead to uneven melt flow rate entering each spiral flow channel, which will greatly weaken the spiral's uniform distribution effect on the melt, and thus cause uneven thickness and unstable interlayer interfaces in the corresponding layers of the extruded composite pipe, ultimately affecting the overall performance and quality consistency of the product.

[0005] Therefore, how to effectively solve the problems of poor flow and uneven distribution caused by the integrated pre-diversion structure in existing multi-layer co-extrusion dies has become a technical challenge that urgently needs to be overcome by those skilled in the art. Summary of the Invention

[0006] This application provides a multilayer co-extrusion die with a pre-splitter, comprising: phantom, An outer spiral, a middle spiral, and an inner spiral are coaxially sleeved within the mold body. The outer circumferential surfaces of the outer spiral, the middle spiral, and the inner spiral are respectively formed with an outer spiral distribution channel, a middle spiral distribution channel, and an inner spiral distribution channel. A first pre-divider has a first annular void channel formed thereon. An outer melt inlet is formed at the inlet of the first annular void channel. The outlet of the first annular void channel is connected to the inlet of the outer spiral distribution channel. This pre-divider uniformly pre-divides a single stream of outer melt flowing in through the outer melt inlet into multiple streams of melt, and then conveys them to the outer spiral distribution channel. The second pre-divider has a second annular void channel formed on it. An inner layer melt inlet is formed at the inlet of the second annular void channel. The outlet of the second annular void channel is connected to the inlet of the inner layer spiral distribution channel. It is used to uniformly pre-divide a single inner layer melt flowing in through the inner layer melt inlet into multiple melt streams and transport them to the inner layer spiral distribution channel. The first pre-splitter and the second pre-splitter are arranged sequentially upstream of the melt flow direction along the axial direction of the multilayer co-extrusion die and are assembled with the die body to form an integral unit.

[0007] According to the multi-layer co-extrusion die with pre-splitter provided in this application, the first annular gap flow channel and the second annular gap flow channel are constructed as a multi-stage flow splitting structure, which includes at least two sequentially connected arc-shaped flow channels. The first-stage arc-shaped flow channel is connected to the corresponding outer melt inlet or inner melt inlet in the middle; the last-stage arc-shaped flow channel is connected to the corresponding outer spiral distribution channel or inner spiral distribution channel at both ends; and each arc-shaped flow channel is configured to evenly divide the melt flowing into it into two streams and flow out from its two outlets. The first annular gap flow channel and / or the second annular gap flow channel form a continuous annular path in the radial plane, and the flow channel wall of its diversion region has a smooth transition and a constant or gradually changing radius of curvature.

[0008] According to the multi-layer co-extrusion die with a pre-diverter provided in this application, an outer secondary diverter channel is further provided on the outer circumferential surface of the outer spiral body. The inlet of the outer secondary diverter channel is connected to the outlet of the first pre-diverter, and the outlet of the outer secondary diverter channel is connected to the inlet of the outer spiral distribution channel; and / or, The outer circumferential surface of the inner spiral body is also provided with an inner secondary diversion channel. The inlet of the inner secondary diversion channel is connected to the outlet of the second pre-diverter, and the outlet of the inner secondary diversion channel is connected to the inlet of the inner spiral distribution channel. The outer secondary diversion channel and / or the inner secondary diversion channel are constructed as a multi-stage bow-shaped diversion structure. The multi-stage bow-shaped diversion structure includes at least two sequentially connected bow-shaped channels. Each bow-shaped channel is configured to uniformly divide the melt flowing into it into two streams, which flow from its two outlets to the next bow-shaped channel or the corresponding spiral distribution channel.

[0009] The multi-layer co-extrusion die head with a pre-diverter provided in this application also includes an outer layer feeding channel, a middle layer feeding channel and an inner layer feeding channel; One end of the outer feeding channel is connected to the outlet end of the first annular gap channel of the first pre-diverter, and the other end is connected to the inlet of the spiral distribution channel of the outer spiral body. One end of the intermediate layer feeding channel is used to connect to the intermediate layer melt conveyed by the external intermediate layer extrusion equipment, and the other end is connected to the spiral distribution channel inlet of the intermediate layer spiral body. One end of the inner layer feeding channel is connected to the outlet end of the second annular gap flow channel of the second pre-diverter, and the other end is connected to the inlet of the spiral distribution flow channel of the inner layer spiral.

[0010] The multilayer co-extrusion die head with a pre-diverter provided in this application further includes a diverter cone. The diverter cone extends axially along the multilayer co-extrusion die head and is disposed at the center of the first pre-diverter, and is located in the intermediate layer feeding channel. It is used to guide the intermediate layer melt flowing in through the intermediate layer feeding channel into an annular melt and transport it to the spiral distribution channel of the intermediate layer spiral.

[0011] According to the multi-layer co-extrusion die head with pre-splitter provided in this application, the outlet end of the die body is provided with an outer layer wall thickness adjusting screw and an outer layer wall thickness adjusting ring. The outer layer wall thickness adjusting ring is located inside the outlet end of the die body. The outer layer wall thickness adjusting screw is threadedly engaged with the die body and is used to adjust the circumferential distribution of the outer layer melt extruded by the outer layer spiral.

[0012] According to the multi-layer co-extrusion die head with pre-splitter provided in this application, the outlet end of the die body is also provided with a centering die and a connecting die in sequence, and the outlet end of the centering die is provided with an overall wall thickness adjusting screw for adjusting the overall wall thickness of the composite melt.

[0013] The multilayer co-extrusion die head with a pre-diverter provided in this application further includes at least one set of heating devices. The heating devices are disposed at at least one of the following locations: the outer ring of the die body, the outer ring of the first pre-diverter, the outer ring of the second pre-diverter, the inner side of the inner spiral, the outer side of the die core at the outlet end of the inner spiral, the outer ring of the flange adapter, the outer ring of the centering die, and the outer ring of the connecting die, for heating the melt inside the multilayer co-extrusion die head.

[0014] The multilayer co-extrusion die head with a pre-divider provided in this application further includes at least one temperature detection device, which is disposed at at least one position among the die body, the first pre-divider, the second pre-divider, and the inner spiral body.

[0015] The multilayer co-extrusion die head with a pre-diverter provided in this application further includes a transition die core, a connecting die core, and a connecting plate; the transition die core is installed at the outlet end of the inner spiral body, the connecting die core is installed at the end of the transition die core away from the inner spiral body, and the connecting plate is disposed inside the outlet end of the connecting die core and is fixedly connected to the connecting die core.

[0016] The above-mentioned one or more technical solutions provided in this application include at least the following technical effects: The multi-layer co-extrusion die with pre-diverters provided in this application fundamentally solves the problems of poor flow and uneven distribution caused by the integration of the pre-diverting structure into the spiral in traditional multi-layer co-extrusion dies. This is achieved by setting up a first pre-diverter and a second pre-diverter, independent of the spiral body. In traditional dies, the pre-diverting arc-shaped flow channel of the spiral body is limited by its axial dimensions, resulting in steep channel turns that easily create dead zones, leading to melt retention and thermal degradation. Furthermore, the direct entry of a single melt stream into the spiral body causes excessive distribution pressure, ultimately resulting in pipe wall thickness deviations. In contrast, the first annular gap flow channel of the first pre-diverter and the second annular gap flow channel of the second pre-diverter adopt a continuous and smooth annular path design. The flow channel walls have a smooth transition and no abrupt turning structures, enabling the uniform pre-diversion of the inner and outer layers of melt into multiple streams, effectively eliminating the risk of melt retention.

[0017] Meanwhile, this solution utilizes an independently designed pre-diverter to handle the main melt diversion task, fundamentally freeing up the axial space of the spiral. This allows the spiral to possess one of two design advantages: firstly, completely eliminating the diversion structure on the spiral significantly increases the effective length of the spiral distribution channel, greatly enhancing the uniformity of the circumferential melt distribution; secondly, a specialized secondary diversion channel is set on the spiral. This channel is optimized based on ample space, featuring a smooth flow path and a diversion stage that can be flexibly set as needed. It can further correct and refine the flow deviation of the pre-diverted melt, achieving a two-stage optimized distribution mode of 'pre-diversion + fine diversion', thereby obtaining superior distribution accuracy compared to the traditional single structure.

[0018] In addition, the first and second pre-splitters can independently adjust the flow channel parameters for melts with different characteristics in the inner and outer layers, adapting to the flow characteristics of different melts, avoiding the defects of traditional one-size-fits-all design, and the two can be disassembled and debugged separately without disassembling the entire spiral assembly, greatly shortening maintenance downtime and reducing production losses.

[0019] During melt delivery and forming, the die head further ensures the forming quality and production adaptability of multi-layer composite pipes through the collaborative work of multiple components. The outer, middle, and inner feeding channels adopt a multi-component, precisely connected structure with open holes. The inner walls of the channels are smooth and the cross-sectional dimensions are matched, ensuring that the melt after pre-diversion enters the corresponding spiral distribution channel in a stable flow state, avoiding pressure fluctuations caused by abrupt changes in cross-section. The diversion cone guides the middle layer melt from a columnar shape to an annular shape, which, together with the coaxial design of the middle layer feeding channel, lays the foundation for the concentric superposition of the three layers of melt at the die head outlet. In terms of temperature control, a multi-zone heating device and a temperature detection device form a closed-loop temperature control system, providing targeted heating for key areas such as the pre-diverter, spiral, centering die, and connecting die. This effectively compensates for temperature losses during melt flow, avoids changes in melt viscosity or thermal degradation due to temperature fluctuations, and ensures stable melt flow throughout the process.

[0020] In the wall thickness control stage, this die head adopts a combined layered and overall adjustment mechanism. The outer layer wall thickness adjustment component achieves local wall thickness calibration of the outer melt through independent multi-point circumferential adjustment, while the overall wall thickness adjustment component achieves overall wall thickness control of the three-layer composite melt by synchronously adjusting the position of the connecting die. The synergistic effect of these two components can control the local wall thickness deviation of the outer layer and the overall wall thickness deviation of the pipe to a very small range, significantly better than the wall thickness control accuracy of traditional die heads. Simultaneously, the integrated assembly design of the die body fixing component and all parts ensures the accuracy of the flow channel connection and structural stability, further reducing the risk of melt leakage and improving the long-term reliability of the die head. In summary, this technical solution, by optimizing the structure and control mechanism of the entire process of melt diversion, transportation, distribution, and forming, comprehensively improves the forming quality, dimensional consistency, and production adaptability of multi-layer composite pipes, making it suitable for high-requirement applications such as municipal water supply and drainage and chemical transportation. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a cross-sectional view of a multilayer co-extrusion die with a pre-splitter provided in some embodiments of this application; Figure 2 This is a schematic diagram of the structure of the first pre-divider of the multilayer co-extrusion die with a pre-divider provided in some embodiments of this application; Figure 3 This is a schematic diagram of the structure of the second pre-divider in a multilayer co-extrusion die with a pre-divider provided in some embodiments of this application; Figure 4 This is a right view of a multilayer co-extrusion die with a pre-splitter provided in some embodiments of this application; Figure 5 This is a left view of a multilayer co-extrusion die with a pre-splitter provided in some embodiments of this application; Figure 6 yes Figure 5 A cross-sectional view along the CC line; Figure 7 yes Figure 4 Sectional view along the DD line; Figure 8 yes Figure 5 A sectional view along the EE line; Figure 9 This is a schematic diagram of the outer spiral of a multilayer co-extrusion die with a pre-diverter provided in some embodiments of this application; Figure 10 This is a schematic diagram of the inner spiral of a multilayer co-extrusion die with a pre-splitter provided in some embodiments of this application.

[0023] Figure label: 110. Mold body; 111. Mold body fixing assembly; 114. Mold body heating coil; 115. Thermocouple; 120. Centering mold; 121. First centering mold heating coil; 122. Second centering mold heating coil; 123. Centering mold-mold body connecting screw; 130. Connecting mold; 131. Connecting mold heating coil; 132. Clamping flange; 133. Clamping flange - connecting mold fixing screws; 140. Outer wall thickness adjusting screw; 141. Outer wall thickness adjusting ring; 150. Overall wall thickness adjustment screw; 210. Outer spiral body; 211. Outer spiral distribution channel; 212. Outer secondary distribution channel; 213. Outer spiral body central hole; 214. Outer spiral body inner hole; 215. Outer feeding channel; 216. Outer spiral body fixing screw; 220. Intermediate layer spiral; 221. Intermediate layer spiral distribution channel; 222. Intermediate layer feeding channel; 223. Inner layer hole of intermediate layer spiral; 224. Connecting screw between intermediate layer spiral and outer layer spiral; 230. Inner spiral body; 231. Inner spiral distribution channel; 232. Inner secondary distribution channel; 233. Inner feeding channel; 234. Inner spiral heating coil; 236. Inner spiral body-intermediate spiral body connecting screw; 310. First pre-diverter; 311. First annular void channel; 312. Outer melt inlet; 313. Outer hole of the first pre-diverter; 314. Middle hole of the first pre-diverter; 317. Connecting screw between the first and second pre-diverters; 320. Second pre-diverter; 321. Second annular void channel; 322. Inner layer melt inlet; 323. Outer layer hole of the second pre-diverter; 324. Middle hole of the second pre-diverter; 325. Inner layer hole of the second pre-diverter; 330. Pre-diverter heating coil; 440. Flange adapter; 441. Flange adapter heating coil; 442. Flange adapter fasteners; 443. Flange adapter fixing screws; 450. Flow divider cone; 451. Flow divider cone tie rod; 452. Flow divider cone support pad; 453. Flow divider cone lock nut; 510. Transition mold core; 511. Transition mold core - inner layer spiral fixing screw; 520. Connecting mold core; 521. Mold core heating coil; 522. Connecting mold core tie rod; 523. Connecting mold core nut; 530. Connecting plate; 531. Connecting plate fasteners. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0026] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0027] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0028] The following is combined Figures 1-10 This application describes a multilayer co-extrusion die with a pre-splitter.

[0029] like Figure 1 As shown, this application provides a multi-layer co-extrusion die with a pre-diverter, which is mainly used to produce multi-layer composite plastic pipes. The core is to solve the problem of uneven distribution of inner and outer melt layers in traditional multi-layer co-extrusion dies by optimizing the melt diversion and distribution structure, thereby improving the molding quality and performance stability of multi-layer composite pipes.

[0030] The multi-layer co-extrusion die head includes a die body 110. The die body 110 serves as the basic load-bearing structure of the entire die head, providing installation space and positioning reference for various internal functional components. At the same time, it can provide a certain degree of heat preservation and protection for the internal flowing plastic melt, ensuring that the die head is structurally stable and not easily affected by external environmental interference during operation.

[0031] A spiral structure is provided inside the mold body 110, specifically comprising an outer spiral 210, a middle spiral 220, and an inner spiral 230. These three spirals are coaxially arranged and nested along the axial direction of the mold head. Spiral distribution channels are formed on the outer circumferential surfaces of the outer spiral 210, middle spiral 220, and inner spiral 230, respectively. Specifically, the outer spiral distribution channel 211 of the outer spiral 210 further uniformly distributes the subsequently delivered outer layer of molten plastic. The middle spiral distribution channel 221 of the middle spiral 220 handles the middle layer of molten plastic, and the inner spiral distribution channel 231 of the inner spiral 230 targets the inner layer of molten plastic. This spiral structure design allows the melt to gradually achieve uniform circumferential and axial distribution as it flows along the channel, laying the foundation for the concentric stacking of each layer of melt at the mold head exit.

[0032] To achieve uniform pre-diversion of the inner and outer melt layers before they enter the spiral, the die head is also equipped with a first pre-diverter 310 and a second pre-diverter 320. Both the first pre-diverter 310 and the second pre-diverter 320 are disc-shaped. The first pre-divider 310 has a first annular void channel 311 and an outer melt inlet 312 formed on it. The outlet end of the first annular void channel 311 is connected to the inlet end of the outer spiral distribution channel 211 of the outer spiral body 210. The working process is as follows: the outer plastic melt conveyed by the external outer extrusion equipment enters the first annular void channel 311 through the outer melt inlet 312 of the first pre-divider 310. The first annular void channel 311 can evenly divide the outer melt that originally flowed in as a single stream into multiple melt streams along its annular path. Then, these multiple melt streams are smoothly conveyed to the outer spiral distribution channel 211 of the outer spiral body 210 through the outlet end of the first annular void channel 311.

[0033] The second pre-divider 320 has a similar structure and function to the first pre-divider 310. It has a second annular void channel 321 and an inner melt inlet 322 formed on it. The outlet end of the second annular void channel 321 is connected to the inlet end of the inner spiral distribution channel 231 of the inner spiral body 230. The inner layer plastic melt conveyed by the external inner layer extrusion equipment enters the second annular void channel 321 through the inner melt inlet 322. It is then evenly divided into multiple streams by the second annular void channel 321 and conveyed from the outlet end of the second annular void channel 321 to the inner spiral distribution channel 231 of the inner spiral body 230. This achieves uniform pre-dividering of the inner layer melt before it enters the spiral body, ensuring accurate distribution of the inner layer melt subsequently.

[0034] From the perspective of positional layout, both the first pre-diverter 310 and the second pre-diverter 320 are located in the upstream region of the melt flow direction and are arranged sequentially along the axial direction of the multi-layer co-extrusion die. This layout allows the inner and outer layers of melt to undergo pre-diversion before entering their respective spirals, preventing undiverted single-strand melt from directly entering the spiral and causing excessive distribution pressure, which in turn affects the uniformity of distribution. At the same time, both the first pre-diverter 310 and the second pre-diverter 320 are assembled with the die body 110 to form an integral unit. This integrated assembly method ensures that the pre-diverters will not loosen or shift during the operation of the die, avoiding the risk of melt leakage due to gaps between components and ensuring precise flow channel docking between the pre-diverters and the spirals. This further improves the stability of melt delivery and distribution, ultimately providing a basic support for the uniform forming of multi-layer composite pipes.

[0035] This application, by separately setting up the first pre-divider 310 and the second pre-divider 320, significantly optimizes melt distribution and die performance compared to the traditional multi-layer co-extrusion die design that integrates the pre-divider structure into the spiral body. Firstly, it breaks through the spatial limitations of traditional integrated pre-dividers, eliminating the dimensional constraints of the outer spiral body 210 and the inner spiral body 230. The first annular gap channel 311 and the second annular gap channel 321 can be designed as continuous, smooth curved surfaces, eliminating protrusions, depressions, and steep corners within the channels. This fundamentally avoids the risks of melt stagnation and thermal degradation, ensuring that a single melt stream is uniformly divided into multiple streams, laying the foundation for precise distribution in the subsequent spiral distribution channels. Simultaneously, the two devices can independently adjust the channel parameters for plastic melts with different characteristics (e.g., corrosion resistance in the inner layer and aging resistance in the outer layer), achieving optimized flow distribution adaptability and avoiding the defects of traditional "one-size-fits-all" designs, further reducing the wall thickness deviation between the inner and outer layers of the extruded pipe. Furthermore, since the flow-dividing functions of the outer and inner spirals have been completed by their respective independent pre-dividers, the traditional pre-dividing bow-shaped flow channels that occupy a large amount of axial dimensions and have limited flow-dividing effects are no longer provided on their outer circumferential surfaces. Instead, there are optional secondary flow channels for fine secondary distribution of the melt after pre-dividing, or the entire outer circumferential surface can be used to arrange spiral distribution channels.

[0036] On the other hand, the first pre-diverter 310 and the second pre-diverter 320 are arranged sequentially along the die head axis to form independent diversion and conveying paths for the inner and outer melt layers, effectively isolating the flow interference between the two melts. Even with dynamic adjustment of flow rate and pressure, they can maintain stable diversion and reduce problems such as instability of the pipe layer interface and bubbles. In addition, the two can be disassembled and debugged separately without disassembling the entire spiral assembly. This not only significantly shortens maintenance downtime and reduces production losses, but also allows for the replacement of the appropriate pre-diverter according to different pipe specifications, significantly improving the die head's adaptability to the production of multi-variety, multi-specification, multi-layer composite pipes.

[0037] In some embodiments, see Figure 2 and Figure 3 The first annular gap channel 311 of the first pre-diverter 310 and the second annular gap channel 321 of the second pre-diverter 320 both adopt a nested structure of multi-stage arc-shaped channels to further improve the uniformity of melt diversion.

[0038] Specifically, taking the first annular void channel 311 as an example, it is arranged along the circumference of the first pre-divider 310, forming a closed annular void structure. Internally, it is divided into a primary arc-shaped channel and a secondary arc-shaped channel. The primary arc-shaped channel is the initial diversion section of the channel, and its arc length is adapted to the circumferential radius of the first pre-divider 310. The outer melt inlet 312 of the first pre-divider 310 is located in the middle of the primary arc-shaped channel. The single stream of outer melt conveyed by the outer extrusion equipment directly enters the primary arc-shaped channel through the outer melt inlet 312. In the middle of the flow channel, the flow proceeds synchronously along the two extension directions of the primary arc-shaped flow channel, completing the first uniform flow division. The secondary arc-shaped flow channel is the secondary flow division section of the flow channel, and its number matches the flow division direction of the primary arc-shaped flow channel (i.e., one secondary arc-shaped flow channel is set at each of the two extension ends of the primary arc-shaped flow channel). The middle of each secondary arc-shaped flow channel is smoothly connected to the corresponding end of the primary arc-shaped flow channel. The melt flowing out from both ends of the primary arc-shaped flow channel enters the middle of the two secondary arc-shaped flow channels respectively, and then continues to flow along the two extension directions of each secondary arc-shaped flow channel, completing the second uniform flow division.

[0039] Ultimately, both ends of each secondary arc-shaped flow channel are connected to the inlet end of the outer spiral distribution flow channel 211. After two-stage diversion, the multiple streams of outer melt smoothly enter the outer spiral distribution flow channel 211 through the outlet end of the secondary arc-shaped flow channel. Similarly, the structure of the second annular gap flow channel 321 is the same as that of the first annular gap flow channel 311. The middle of its primary arc-shaped flow channel is connected to the inner melt inlet 322 of the second pre-diverter 320, and both ends of the secondary arc-shaped flow channel are connected to the inner spiral distribution flow channel 231 of the inner spiral body 230, realizing two-stage uniform diversion of the inner melt.

[0040] It should be noted that the number of multi-stage arc-shaped flow channels in the annular gap flow channel can be adjusted according to actual production needs. For example, for the production of large-diameter multi-layer composite pipes, a third-stage arc-shaped flow channel can be added on the basis of a two-stage arc-shaped flow channel. Each stage of the arc-shaped flow channel still follows the core logic of "feeding in the middle and splitting at both ends" to ensure that the melt can be further uniformly diffused along the circumference after each stage of splitting. When the multi-stage arc-shaped flow channel includes three or more stages of arc-shaped flow channels, the middle of the first-stage arc-shaped flow channel is connected to the corresponding outer melt inlet 312 or inner melt inlet 322; the two ends of the last-stage arc-shaped flow channel are connected to the corresponding outer spiral distribution channel 211 or inner spiral distribution channel 231. This application does not limit the specific number of stages of the multi-stage arc-shaped flow channel, as long as the functional requirement of "a single melt stream can form multiple melt streams uniformly distributed along the circumference after multi-stage splitting" is met.

[0041] In some embodiments, see Figure 2 and Figure 3 To further ensure the precise flow division effect of the melt by the first pre-diverter 310 and the second pre-diverter 320, the first annular gap channel 311 on the first pre-diverter 310 and the second annular gap channel 321 on the second pre-diverter 320 both adopt targeted structural designs. Specifically, the first annular gap channel 311 and the second annular gap channel 321 form a continuous, streamlined annular path in the radial plane. The channel wall transition in their diversion area is smooth, with a constant or gradually changing radius of curvature, and there are no sharp turning corner structures. Furthermore, the inner wall of the channel is entirely flat, without any protrusions, depressions, or steps that may interfere with the melt flow. This structurally eliminates the stagnation zone that is easily formed when the melt flows in the channel. This allows a single melt to be divided into multiple branch melts of equal volume or flow rate. The advantages of this structural design are twofold. First, it significantly reduces the flow resistance of the melt within the flow channel. Even for high-viscosity, shear-sensitive plastic melts (such as corrosion-resistant PVC melts used for the inner layer of pipes and aging-resistant PE melts used for the outer layer), it can prevent the melt from accumulating locally due to flow obstruction, thereby reducing the risk of thermal degradation caused by prolonged melt retention and ensuring the material stability of the final extruded pipe. Second, the smooth and undisturbed inner wall of the flow channel ensures that the flow velocity of the melt along the circumference of the flow channel remains uniform. This allows the single strand of outer layer melt entering the first annular void flow channel 311 from the outer layer melt inlet 312 and the single strand of inner layer melt entering the second annular void flow channel 321 from the inner layer melt inlet 322 to be divided into multiple branch melts with equal volume or flow rate, and the flow rate deviation of each branch melt is controlled within a very small range. Meanwhile, the inlet end of the first annular void channel 311 and the outer melt inlet 312 of the first pre-diverter 310, and the inlet end of the second annular void channel 321 and the inner melt inlet 322 of the second pre-diverter 320, all adopt a gradual smooth transition structure, which can avoid pressure fluctuations caused by abrupt changes in cross-section when the melt enters the channel from the inlet. The outlet ends of the first annular void channel 311 and the second annular void channel 321 are designed with interface forms adapted to the subsequent melt conveying channels, creating conditions for the melt after diversion to smoothly enter the spiral distribution channel of the corresponding spiral body.

[0042] In some embodiments, see Figure 1 and Figure 6 To further optimize the independence of the inner and outer melt flow and conveying paths and clarify the spatial relationship between the second pre-divider 320 and surrounding components, the second pre-divider 320 is positioned between the first pre-divider 310 and the outer spiral 210, and is arranged coaxially with both along the axial direction of the multi-layer co-extrusion die. This layout is designed so that the first pre-divider 310 (processing the outer melt), the second pre-divider 320 (processing the inner melt), and the outer spiral 210 (receiving the outer melt) are arranged sequentially along the axial direction, forming two parallel melt processing paths. One path corresponds to the outer melt, with the outer melt first undergoing diversion, then conveying, and finally entering the distribution stage; the other path corresponds to the inner melt, with the inner melt first undergoing diversion, then conveying, and finally entering the distribution stage. These two paths are spatially staggered, further reducing heat exchange and flow interference between the inner and outer melts during the conveying stage. Especially when the temperature sensitivity of the inner and outer melts differs significantly, such as when the outer layer uses a low-temperature tough material and the inner layer uses a high-temperature heat-resistant material, this parallel path can effectively maintain the temperature stability of the two melts, avoid affecting the viscosity of the melt due to temperature fluctuations, and thus prevent the melt distribution effect from being disturbed.

[0043] Meanwhile, to ensure the stability of the mold body 110 as a load-bearing structure and to prevent it from shifting due to vibration or melt pressure during the operation of the mold head, thereby affecting the flow channel docking accuracy of the components, a mold body fixing assembly 111 is also provided inside the mold head. This assembly specifically includes a mold body fixing tie rod, a mold body fixing gasket, and a mold body fixing nut. The die fixing tie rods are high-strength rigid rods, evenly distributed radially along the multi-layer co-extrusion die head. One end of each set of die fixing tie rods passes through the side wall through hole of the die 110 and the die fixing gasket, and is threadedly connected to the side wall threaded hole of the outer spiral 210. The die fixing gasket is an annular metal gasket, sandwiched between the mating surfaces of the die 110 and the outer spiral 210. It can fill the tiny gaps between the mating surfaces, enhance the sealing effect, and disperse the local pressure generated when the die fixing tie rods are tightened, preventing deformation of the die 110 or the outer spiral 210 due to stress concentration. The die fixing nut is threaded to the end of the die fixing tie rod that extends out of the die 110. By tightening the die fixing nut, the die 110 can be tightly fixed to the outside of the outer spiral 210, ensuring that the two always maintain a relatively fixed positional relationship.

[0044] The advantages of this fixing method are as follows: First, the mold 110 can be fixed from multiple points around the circumference by the radially evenly distributed mold fixing rods, preventing the mold 110 from tilting due to uneven force on one side and ensuring the installation accuracy of the internal components of the mold 110. Second, the detachable design of the mold fixing assembly facilitates subsequent maintenance or replacement of the internal components of the mold head. When it is necessary to inspect the first pre-diverter 310 or the second pre-diverter 320, simply loosen the mold fixing nut and remove the mold fixing rod to separate the mold 110 from the outer spiral 210 without disassembling the entire spiral assembly, greatly improving the convenience of maintenance. Third, the mold fixing gasket effectively isolates the direct rigid contact between the mold 110 and the outer spiral 210, reducing frictional losses caused by vibration during equipment operation, extending the service life of the components, and further eliminating the risk of melt leakage from the contact surface between the mold 110 and the outer spiral 210, ensuring the overall safety and stability of the mold head operation.

[0045] In some embodiments, see Figure 1 , Figure 6 and Figure 7 To ensure stable delivery of the melt after pre-diverting to the corresponding auger and to ensure that the melt maintains a uniform flow state after diversion and before auger distribution, the feeding channel in the die head adopts a multi-part open-hole docking structure, specifically including an outer feeding channel 215, an intermediate feeding channel 222 and an inner feeding channel 233. All three extend along the axial direction of the multi-layer co-extrusion die head and are precisely docked by special channels opened on the corresponding pre-diverter and auger, ensuring that the melt flow path is continuous and uninterrupted.

[0046] The outer layer feeding channel 215 is composed of two coaxially connected channels. One part is the outer layer hole 313 of the first pre-diverter 310, which connects to the outlet end of the first annular gap channel 311. The other part is the outer layer hole 323 of the second pre-diverter 320, which is opened axially. The multiple streams of outer layer melt after being diverted by the first annular gap channel 311 first flow out through the outer layer hole 313 of the first pre-diverter, and then simultaneously enter the outer layer hole 323 of the second pre-diverter. The diameters of the two channels are exactly the same, and the inner walls of the channels maintain a continuous and smooth transition without steps or abrupt changes in cross-section. The outlet end of the outer layer hole 323 of the second pre-diverter is directly connected to the inlet end of the outer spiral distribution channel 211 of the outer spiral body 210, forming a complete outer layer feeding channel 215. The inner wall of the channel is polished to form a continuous and smooth curved surface without any protrusions, depressions or abrupt changes in cross-section. The cross-sectional dimensions of the channel match the outlet cross-section of the first annular gap flow channel 311 and the inlet cross-section of the outer spiral distribution flow channel 211. This avoids pressure fluctuations caused by abrupt changes in cross-section when the melt enters the channel, and ensures that the multiple outer melt streams after being diverted by the first annular gap flow channel 311 maintain their original flow uniformity during transportation. The flow rate will not be affected by differences in flow resistance, and the melt will eventually enter the outer spiral distribution flow channel 211 in a stable flow state.

[0047] The intermediate layer feeding channel 222 is formed by three sets of channels connected sequentially, covering the entire path of the melt entering the intermediate layer spiral 220 from the external equipment. The first set is the first pre-divider intermediate hole 314 opened axially in the central region of the first pre-divider 310, whose inlet end is connected to the outlet end of the external intermediate layer extrusion equipment, used to receive the intermediate layer melt. The second set is the second pre-divider intermediate hole 324 opened axially in the central region of the second pre-divider 320, which is coaxially aligned with the first pre-divider intermediate hole 314 and has the same diameter, used to receive the intermediate layer melt flowing from the first pre-divider 310. The third set is the outer spiral intermediate hole 213 opened on the end panel of the outer spiral 210 near the second pre-divider 320, whose inlet end is connected to the outlet end of the second pre-divider intermediate hole 324, and whose outlet end extends to the inner side of the outer spiral 210, connected to the inlet end of the intermediate layer spiral distribution channel 221 of the intermediate layer spiral 220. The axes of the three sets of channels are completely coincident, and the inner walls of the channels are designed to be smooth, ensuring that the intermediate layer melt forms a uniform annular flow trend during the conveying process. To ensure that the intermediate layer melt and the inner and outer layer melts subsequently overlap concentrically at the die outlet, the axis of the intermediate layer feeding channel 222 is kept coaxial with the axes of the outer layer feeding channel 215 and the inner layer feeding channel 233, creating favorable conditions for the subsequent circumferential distribution of the melt by the intermediate layer spiral distribution channel 221.

[0048] The inner feeding channel 233 consists of three sets of channels connected sequentially to accommodate its path requirements through the second pre-diverter 320, the outer spiral 210, and the intermediate spiral 220. The first set is the inner layer hole 325 of the second pre-diverter 320, which connects to the outlet end of the second annular gap channel 321 and is used to output the inner layer melt after being diverted by the second annular gap channel 321. The second set is the inner layer hole 214 of the outer spiral 210, which is evenly distributed around the intermediate hole 213 of the outer spiral on the end panel of the outer spiral. The number of these channels corresponds one-to-one with the number of inner holes 325 of the second pre-diverter, and the hole diameters are matched. The inlet end is connected to the inner hole 325 of the second pre-diverter to ensure that the melt does not cause flow interference when flowing through the outer spiral. The third group consists of intermediate spiral inner layer holes 223 on the end panel of the intermediate spiral 220, corresponding to the inner layer holes 214 of the outer spiral. These holes extend axially along the intermediate spiral 220, with the inlet end connecting to the outlet end of the inner layer hole 214 of the outer spiral, and the outlet end connecting to the inlet end of the inner spiral distribution channel 231 of the inner spiral 230. The axes of the three groups of holes remain coaxial, and their inner walls are polished to form a continuous, smooth curved surface without protrusions, depressions, or abrupt changes in cross-section. The length of the holes is adaptively designed according to the axial spacing of the corresponding components, extending in a straight line to reduce flow resistance. For high-viscosity, corrosion-resistant inner layer melts, this structure with precise connection of multiple groups of holes effectively reduces frictional loss between the melt and the hole walls, avoids melt performance degradation caused by localized heating, and ensures that multiple streams of inner layer melt, after being diverted by the second annular void channel 321, smoothly enter the inner spiral distribution channel 231.

[0049] In addition, all the connection points of the channels are sealed, and with the axial clamping force between the components, it is ensured that there is no melt leakage at the connection points between each feeding channel and the pre-diverter and the spiral body, which further ensures the stability and safety of the overall melt flow of the die head.

[0050] In some embodiments, see Figure 1To ensure a stable connection between the external intermediate layer extrusion equipment and the internal intermediate layer feeding channel 222 of the die head, and to guarantee that the intermediate layer melt enters the die head without leakage or pressure loss from the external equipment, the die head is also equipped with a flange adapter 440 and matching flange adapter fasteners 442. The flange adapter 440 is a cylindrical transition piece. Its inlet end inner diameter matches the outlet outer diameter of the external intermediate layer extrusion equipment, while its outlet end inner diameter matches the inner diameter of the first pre-diverter intermediate hole 314 of the first pre-diverter 310. This first pre-diverter intermediate hole 314 is the starting section of the intermediate layer feeding channel 222. The outlet end of the flange adapter 440 is fixedly connected to the end of the first pre-diverter 310 furthest from the second pre-diverter 320 via flange adapter fixing screws 443, ensuring precise alignment between the transition channel of the flange adapter 440 and the first pre-diverter intermediate hole 314, forming a complete transitional conveying path for the intermediate layer melt from the external equipment to the intermediate layer feeding channel 222.

[0051] The flange adapter fastener 442 is specifically a combination of bolts, gaskets, and nuts. The bolts are evenly distributed circumferentially along the inlet end of the flange adapter 440, with one end passing through the flange hole of the flange adapter 440 and engaging with the flange thread hole of the external intermediate layer extrusion equipment; the gasket is sandwiched between the flange adapter 440 and the flange of the external equipment to fill the tiny gaps between the mating surfaces; the nut is tightened onto the protruding end of the bolt, and the axial clamping force of the fasteners achieves a sealed connection between the two, preventing the molten material from leaking from the flange joint.

[0052] The advantages of this design are as follows: First, the inner wall of the transition channel of the flange adapter 440 is polished and maintains a smooth transition with the inner wall of the intermediate hole 314 of the first pre-diverter, ensuring smooth flow of the intermediate layer melt and avoiding melt stagnation due to rough channels or abrupt changes in cross-section. Second, the detachable flange connection facilitates subsequent maintenance and replacement of the flange adapter 440 or the first pre-diverter 310 without disassembling external equipment, reducing maintenance costs. Third, the gasket buffers the vibration transmission between external equipment and the die head, preventing vibration from interfering with the stable delivery of the intermediate layer melt, while further enhancing the sealing effect and completely eliminating the risk of melt leakage. Through the precise docking of the flange adapter 440 and the intermediate hole 314 of the first pre-diverter, a seamless connection of "external input - internal delivery" of the intermediate layer melt is achieved, laying the foundation for the stable delivery of the subsequent intermediate layer feeding channel 222.

[0053] In some embodiments, see Figure 1To ensure that the intermediate layer melt can quickly form a uniform annular flow state after flowing out of the flange adapter 440, and to adapt to the conveying requirements of the intermediate hole 314 of the first pre-diverter, the intermediate hole 324 of the second pre-diverter and the intermediate hole 213 of the outer spiral body, and to match the distribution logic of the intermediate layer spiral distribution channel 221, a flow divider cone 450 is also provided in the die head, and an assembly component for fixing the flow divider cone 450 is designed to ensure its positional stability under the impact of the melt.

[0054] The flow divider cone 450 extends axially along the multi-layer co-extrusion die head, with its installation position precisely corresponding to the area between the outlet end of the flange adapter 440 and the inlet end of the intermediate hole 314 of the first pre-divider, and its head extending directly into the outlet end of the flange adapter 440. Specifically, the tail of the flow divider cone 450 is fixed to the central area of ​​the first pre-divider 310 (coaxial with the intermediate hole 314 of the first pre-divider but not occupying the flow channel space), while the head extends towards the outlet end of the flange adapter 440, partially penetrating into the outlet end of the flange adapter 440, and the head has a smooth transition structure in the shape of a cone or frustum, with no protrusions or sharp edges on the surface.

[0055] The core purpose of this structural design is to pre-guide the intermediate layer melt flowing out of the flange adapter 440: when the melt conveyed by the external intermediate layer extrusion equipment flows out through the transition channel of the flange adapter 440, it will directly contact the smooth surface of the head of the flow divider cone 450. The columnar melt that originally flowed axially is uniformly guided to the periphery by the conical surface of the flow divider cone 450. The guided annular melt then smoothly enters the first pre-divider intermediate hole 314 of the first pre-divider 310, avoiding the accumulation of melt in the central area of ​​the first pre-divider intermediate hole 314 to form a "dead zone", or uneven flow caused by excessively fast flow velocity in the center and too slow flow velocity at the edge. The subsequent annular melt flows sequentially through the second pre-divider intermediate hole 324 of the second pre-divider 320 and the outer spiral intermediate hole 213 of the outer spiral 210, always maintaining an annular flow pattern, creating favorable conditions for the circumferential uniform distribution of the melt by the intermediate layer spiral distribution channel 221.

[0056] To prevent the flow divider cone 450 from shifting under the impact of high-velocity melt, its assembly includes a flow divider cone tie rod 451, a flow divider cone support pad 452, and a flow divider cone locking nut 453. The flow divider cone tie rod 451 is a rigid rod, arranged axially along the die head. One end is fixedly connected to the center of the tail of the flow divider cone 450 (e.g., by threaded connection), and the other end passes through the flow divider cone support pad 452 and the tie rod mounting hole of the first pre-divider 310 (this hole is coaxial with but independent of the intermediate hole 314 of the first pre-divider, and does not affect the melt flow). The flow divider cone support pad 452 is an annular structure, fitted to the inner wall of the first pre-divider 310, which can both radially position the flow divider cone tie rod 451 and prevent the tie rod from shifting. The tilting action causes the flow divider cone 450 to deflect, which also buffers the impact force transmitted from the flow divider cone 450 to the first pre-diverter 310, preventing excessive local stress from damaging the components. The end of the flow divider cone pull rod 451 extending out of the first pre-diverter 310 is threadedly engaged with the flow divider cone locking nut 453. By tightening the flow divider cone locking nut 453, the flow divider cone pull rod 451, the flow divider cone 450 and the first pre-diverter 310 can form a stable integral structure, ensuring that the flow divider cone 450 always remains coaxial with the middle hole 314 of the first pre-diverter during the long-term operation of the die head, and will not shift its position due to melt pressure fluctuations or equipment vibration, further ensuring the stable flow guiding effect of the intermediate layer melt.

[0057] Furthermore, the cone angle and length of the diverting cone 450 can be adjusted according to the characteristics of the intermediate layer melt (such as viscosity and flowability) and the inner diameter of the intermediate hole 314 of the first pre-diverter. For example, for intermediate layer melts with high viscosity and poor flowability, the cone angle of the diverting cone 450 can be appropriately reduced to extend the contact and guiding distance between the melt and the cone surface, allowing the melt more time to complete the transformation from a columnar to annular shape. For the intermediate hole 314 of the first pre-diverter with a larger inner diameter, the length of the diverting cone 450 can be increased accordingly to ensure that its head can extend to the core flow area of ​​the channel, achieving uniform guidance of the melt within the entire channel cross-section. This adjustability further enhances the die head's adaptability to intermediate layer melts of different specifications and materials. Combined with the connection function of the flange adapter 440 and the conveying function of the intermediate layer feeding channel 222, a more complete intermediate layer melt "input-guidance-conveying" processing system is formed.

[0058] In some embodiments, see Figure 9 and Figure 10 To further refine the distribution accuracy of the melt and make the pre-diverted melt better suited to the circumferential distribution requirements of the spiral distribution channel, the outer spiral 210 and the inner spiral 230 can be respectively equipped with secondary diversion structures. Through the synergistic effect of the primary diversion of the pre-diverter and the secondary diversion of the spiral, the flow deviation of each melt stream can be further reduced. Specifically, this includes the outer secondary diversion channel 212 and the inner secondary diversion channel 232, which can be set individually or simultaneously.

[0059] The outer spiral body 210 has an outer secondary diversion channel 212 on its outer circumferential surface, and its inlet end is connected to the diversion outlet of the first pre-diverter 310. The diversion outlet needs to be connected through the outer feeding channel 215. That is, the outer melt after being diverted by the first pre-diverter 310 is first transported to the outer hole 323 of the second pre-diverter through the outer feeding channel 215, and then flows into the outer secondary diversion channel 212 from the outlet end of the outer hole 323 of the second pre-diverter. The outlet end of the outer secondary diversion channel 212 is directly connected to the inlet end of the outer spiral distribution channel 211 of the outer spiral body 210, forming a complete outer melt distribution link. That is, the melt is diverted by the first pre-diverter, transported by the outer feeding channel, refined and distributed by the outer secondary diversion channel, and finally enters the outer spiral distribution channel.

[0060] An inner secondary diversion channel 232 is formed on the outer circumferential surface of the inner spiral body 230, and its inlet end is connected to the diversion outlet of the second pre-diverter 320. The diversion outlet needs to be connected through the inner feeding channel 233. That is, the inner melt after being diverted by the second pre-diverter 320 is first transported to the inner hole 223 of the middle spiral body through the inner feeding channel 233, and then flows into the inner secondary diversion channel 232 from the outlet end of the inner hole 223 of the middle spiral body. The outlet end of the inner secondary diversion channel 232 is connected to the inlet end of the inner spiral distribution channel 231 of the inner spiral body 230, forming a complete inner melt distribution link. That is, the melt is diverted by the second pre-diverter, transported by the inner feeding channel, refined and distributed by the inner secondary diversion channel, and finally enters the inner spiral distribution channel.

[0061] Both the outer secondary flow channel 212 and the inner secondary flow channel 232 adopt a multi-stage bow-shaped flow structure, and their structural designs are completely identical. The core is to achieve the gradual and uniform division of the melt through at least two sequentially connected bow-shaped flow channels. The specific diversion process is as follows: The inlet of the first-stage bow-shaped flow channel receives a single stream of melt from the feeding channel. Inside the flow channel, the single stream of melt is evenly divided into two streams by an arc-shaped guide structure. The two streams of melt flow out from the two outlets of the first-stage bow-shaped flow channel respectively. Each outlet corresponds to the inlet of the next-stage bow-shaped flow channel. The second-stage bow-shaped flow channel continues the "single stream in, double stream out" diversion logic, further dividing the two streams of melt from the previous stage into four streams. If the actual requirement is to set up three or more bow-shaped flow channels, the division continues step by step according to this logic until the number of melt streams completely matches the number of inlets of the subsequent spiral distribution flow channels. Finally, the outlet of the last-stage bow-shaped flow channel is directly connected to the inlet of the corresponding outer spiral distribution flow channel 211 or inner spiral distribution flow channel 231. After completing the secondary diversion, the melt enters the spiral flow channel for subsequent circumferential distribution.

[0062] This synergistic structure, combining the initial flow division of the pre-diverter with the secondary flow division of the spiral, offers several advantages: the pre-diverter achieves initial uniform division of the melt through an annular gap channel, resolving the distribution difficulties caused by excessive flow rates of a single melt stream; the secondary flow channel further reduces the flow rate deviation of each melt stream through progressively increasing refinement, avoiding uneven circumferential distribution caused by differences in the flow paths of individual melt streams within the spiral distribution channel. Especially in large-diameter pipe production scenarios requiring coverage of a wider circumference, the secondary flow division ensures that the melt forms a sufficient number of balanced streams before entering the spiral distribution channel. Combined with the circumferential extension of the spiral channel, this significantly improves the circumferential distribution accuracy of the outer and inner melt layers, reduces pipe wall thickness deviation, and results in tighter interlayer bonding and a more stable structure in multi-layer composite pipes.

[0063] In some embodiments, see Figure 1 In order to accurately control the uniformity of wall thickness after extrusion of multi-layer composite melt and solve the problem of pipe wall thickness deviation caused by uneven circumferential distribution of melt in traditional dies, the outlet end of the die body 110 is equipped with a wall thickness adjustment structure that combines layer adjustment and overall adjustment. Specifically, it includes an outer layer wall thickness adjustment component and an overall wall thickness adjustment component. The two work together to ensure the wall thickness accuracy of the final extruded pipe.

[0064] The outer layer wall thickness adjustment assembly consists of an outer layer wall thickness adjustment screw 140 and an outer layer wall thickness adjustment ring 141. The outer layer wall thickness adjustment ring 141 is a ring-shaped metal part, coaxially embedded in the inner step of the outlet end of the mold body 110. Its inner wall and the outer wall of the outlet end of the outer layer spiral 210 form an annular gap, which is the extrusion channel of the outer layer melt. The flatness of the inner wall of the outer layer wall thickness adjustment ring 141 directly affects the circumferential distribution of the outer layer melt during extrusion. The outer layer wall thickness adjustment screw 140 is evenly distributed along the circumference of the outlet end of the mold body 110. Each set of outer layer wall thickness adjustment screws 140 is threaded with the side wall of the mold body 110, and its end passes through the mold body 110 and abuts against the outer wall of the outer layer wall thickness adjustment ring 141. When an excessively thick outer layer melt is detected in a certain circumferential direction, the corresponding outer layer melt thickness adjusting screw 140 can be tightened, pushing the outer layer melt thickness adjusting ring 141 inward to reduce the extrusion channel gap at that location and decrease the melt flow rate. If the wall thickness at a certain location is too thin, the corresponding outer layer melt thickness adjusting screw 140 can be loosened, and the outer layer melt thickness adjusting ring 141 will reset outward under the action of melt pressure, increasing the channel gap and supplementing the melt flow rate. This method of independent adjustment at multiple points in the circumferential direction can control the circumferential wall thickness deviation of the outer layer melt to a very small range, avoiding the defect of traditional die heads where "overall adjustment cannot take into account local deviations".

[0065] The overall wall thickness adjustment assembly is used to calibrate the overall wall thickness of the inner, middle, and outer three-layer composite melt. Its core components include a centering mold 120, a connecting mold 130, and an overall wall thickness adjustment screw 150. The centering mold 120 is a tapered transition piece, coaxially mounted on the outer side of the mold body 110 outlet end. Its inner channel smoothly connects with the extrusion channel at the mold body 110 outlet end, guiding the three-layer composite melt from the mold body 110 outlet to the connecting mold 130, preventing eddies from forming in the transition area. The connecting mold 150... Mold 130 is a cylindrical structure, coaxially assembled at the end of centering mold 120 away from mold body 110. Its inner channel is the final forming channel for the multi-layer composite pipe, and the inner diameter of the channel matches the outer diameter of the target pipe. The overall wall thickness adjusting screws 150 are evenly distributed around the circumference of centering mold 120 (usually the same number as the outer wall thickness adjusting screws 140). Each set of overall wall thickness adjusting screws 150 is threaded into the side wall of centering mold 120, and the end abuts against the outer wall of connecting mold 130. When it is necessary to adjust the overall wall thickness of the three-layer composite pipe, all overall wall thickness adjusting screws 150 can be tightened or loosened simultaneously: when tightened simultaneously, connecting mold 130 moves inward to centering mold 120, shortening the channel connection length between centering mold 120 and connecting mold 130, fine-tuning the residence time and pressure of the melt in the forming channel, thereby reducing the overall wall thickness; when loosened simultaneously, connecting mold 130 returns to its original position, extending the connection length and increasing the overall wall thickness. This overall adjustment method can precisely control the overall thickness of the pipe without compromising the accuracy of the local wall thickness of the outer layer, thus adapting to the production needs of pipes of different specifications.

[0066] In addition, to ensure that the connecting mold 130 does not loosen or shift during long-term operation, the mold head is also equipped with a clamping flange 132. The clamping flange 132 is a ring structure, coaxially sleeved on the outside of the connecting mold 130. One end of it is fixedly connected to the end of the centering mold 120 away from the mold body 110 by bolts, and the other end is clamped to the outer wall step of the connecting mold 130 by the end face. The function of the clamping flange 132 is: first, to firmly limit the connecting mold 130 to the centering mold 120 by axial clamping force, to prevent the connecting mold 130 from axial displacement under the impact of melt pressure, and to ensure the positional stability of the forming channel; second, to fill the fitting gap between the centering mold 120 and the connecting mold 130, to enhance the sealing of the joint between the two, and to prevent the composite melt from leaking from the gap; and third, to provide circumferential positioning for the connecting mold 130, to prevent it from rotating radially, and to ensure that the adjustment effect of the overall wall thickness adjusting screw 150 always corresponds to the preset circumferential position, further ensuring the adjustment accuracy and consistency of the pipe wall thickness.

[0067] By coordinating local and overall adjustments of the outer layer, and with the fixing guarantee of the clamping flange 132, the outer layer wall thickness deviation and overall wall thickness deviation of the multi-layer composite pipe can be significantly reduced, which is significantly better than the wall thickness control accuracy of traditional die heads. At the same time, it greatly improves the adaptability of the die head to pipes with different wall thickness specifications, and reduces the debugging time and material loss when switching specifications.

[0068] In some embodiments, see Figure 1 To ensure that the inner layer melt can form a regular inner layer tube structure after being extruded from the inner layer spiral 230, and to avoid uneven inner layer forming due to changes in melt flow state, an inner layer melt forming auxiliary component is also provided in the die head. This component specifically includes a transition die core 510, a connecting die core 520 and a connecting plate 530, and is equipped with fasteners for fixing these components to ensure structural stability during the forming process.

[0069] The transition core 510 is a cylindrical or frustum-shaped structure, coaxially mounted at the outlet end of the inner spiral 230. One end is fixedly connected to the outlet end of the inner spiral 230 via a threaded or interference fit, while the other end extends outward. The outer wall of the transition core 510 smoothly connects to the outlet end of the inner spiral distribution channel 231 of the inner spiral 230. The core function of the transition core 510 is "flow guidance": after the inner melt is evenly distributed circumferentially through the inner spiral distribution channel 231, it flows along the outer wall of the transition core 510. The smooth outer wall of the transition core 510 guides the melt to smoothly transition from "spiral flow" to "axial straight flow," preventing the melt from generating eddies or accumulating at the outlet end due to abrupt changes in flow direction. At the same time, its outer wall diameter is designed according to the target inner diameter of the inner tube, providing a preliminary forming reference for the inner melt.

[0070] The connecting mold core 520 is a long cylindrical structure, coaxially assembled at the end of the transition mold core 510 away from the inner spiral body 230. Its outer wall has the same diameter as the outer wall of the transition mold core 510, ensuring that there are no steps to obstruct the flow of the inner melt along the outer walls of both. The length of the connecting mold core 520 is designed according to the cooling and forming requirements of the inner melt, and usually extends into the forming channel of the connecting mold 130, so that the inner melt can be simultaneously superimposed and initially cooled with the outer and intermediate melts under the guidance of the connecting mold core 520, avoiding the inner melt from deviating from the forming reference in advance and causing inner diameter deviation. To secure the connecting mold core 520, the mold head is also equipped with a connecting mold core fastener. Specifically, the fastener is a combination of a connecting mold core pull rod 522 and a connecting mold core nut 523. The connecting mold core pull rod 522 passes axially through the central through hole of the transition mold core 510 and the connecting mold core 520. One end is fixed inside the inner spiral body 230, and the other end extends out of the connecting mold core 520 and is tightened with the connecting mold core nut 523 to securely connect the transition mold core 510 and the connecting mold core 520 into one unit, preventing axial displacement of the two under the impact of the melt.

[0071] The connecting plate 530 is an annular metal plate, coaxially positioned inside the outlet end of the connecting mold core 520. Its inner diameter matches the outer diameter of the connecting mold core 520, while its outer diameter matches the inner diameter of the forming channel of the connecting mold 130. The connecting plate 530 is fixed to the outlet end face of the connecting mold core 520 by connecting plate fasteners 531 (specifically screws). Its main functions are twofold: first, to "limit" the inner layer melt at the outlet end of the connecting mold core 520, preventing excessive diffusion of the melt at the outlet end and ensuring the flatness of the inner layer tube end face; second, to assist in the interface bonding between the inner layer melt and the intermediate layer melt. The end face of the connecting plate 530 is designed with a slightly rough surface, which can enhance the adhesion between the inner and intermediate layer melts at the interface and reduce the risk of interlayer peeling.

[0072] In some embodiments, see Figure 1 , Figure 7 and Figure 8 The core components of the multi-layer co-extrusion die head with pre-diverter provided in this application are precisely assembled and securely connected using dedicated fasteners. The specific assembly relationship is as follows: The outer spiral 210 is fixedly connected to the second pre-divider 320, the first pre-divider 310, and the flange adapter 440 in sequence by the outer spiral fixing screw 216, ensuring a tight fit between the four and precise flow channel docking to avoid melt leakage. The second pre-divider 320 is fixed to the first pre-divider 310 by the first pre-divider-second pre-divider connecting screw 317. The screw 317 extends along the axial direction of the first pre-divider 310, with one end engaging with the threaded hole of the first pre-divider 310 and the other end fastened to the end face mounting hole of the second pre-divider 320, realizing the coaxial positioning of the two pre-dividers along the die head axial direction and ensuring the independence of the inner and outer melt flow paths.

[0073] The intermediate layer spiral 220 is installed inside the outer layer spiral 210 via an intermediate layer spiral-outer layer spiral connecting screw 224. This screw 224 is evenly distributed circumferentially along the end panel of the outer layer spiral 210 near the second pre-diverter 320. One end passes through the mounting hole on the side wall of the outer layer spiral 210 and engages with the threaded hole on the outer wall of the intermediate layer spiral 220. This not only defines the radial position of the intermediate layer spiral 220 but also ensures precise alignment between the intermediate layer spiral distribution channel 221 of the intermediate layer spiral 220 and the intermediate spiral center hole 213 of the outer layer spiral 210, guaranteeing that the intermediate layer melt flows from the outer layer spiral 210... There is no flow channel deviation when conveying to the intermediate layer spiral 220; the inner layer spiral 230 is installed inside the intermediate layer spiral 220 through the inner layer spiral-intermediate layer spiral connecting screw 236. The screw 236 is arranged circumferentially along the end panel of the intermediate layer spiral 220, and one end passes through the side wall hole of the intermediate layer spiral 220 and engages with the threaded hole on the outer wall of the inner layer spiral 230, further defining the radial position of the inner layer spiral 230, ensuring that the inner layer spiral distribution flow channel 231 of the inner layer spiral 230 is precisely connected with the inner layer hole 223 of the intermediate layer spiral 220, and ensuring smooth inner layer melt conveying.

[0074] The centering mold 120 is fixed to the outlet end of the mold body 110 by centering mold-mold body connecting screws 123. The screws 123 are evenly distributed around the circumference of the outlet end of the mold body 110. One end passes through the side wall boss of the mold body 110 and engages with the flange hole of the centering mold 120 by thread, so that the inner channel of the centering mold 120 is smoothly connected with the extrusion channel of the outlet end of the mold body 110, avoiding flow obstruction of the composite melt in the transition area. The clamping flange 132 clamps the connecting mold 130 to the outlet end of the centering mold 120 by clamping flange-connecting mold fixing screws 133. The screws 133 are evenly distributed around the circumference of the clamping flange 132. One end passes through the mounting hole of the clamping flange 132 and engages with the threaded hole of the centering mold 120. The axial clamping force ensures that the forming channel of the connecting mold 130 is coaxial with the transition channel of the centering mold 120, and at the same time enhances the sealing at the connection between the two to prevent leakage of the composite melt.

[0075] The transition mold core 510 is installed at the outlet end of the inner spiral 230 by the transition mold core-inner spiral fixing screw 511. The screw 511 is spaced circumferentially along the end face of the transition mold core 510, with one end passing through the rear of the transition mold core 510 and engaging with the threaded hole at the outlet end of the inner spiral 230. This allows the outer wall of the transition mold core 510 to smoothly transition with the outlet end of the inner spiral distribution channel 231 of the inner spiral 230, guiding the inner melt to smoothly transition from spiral flow to axial flow, and preventing the melt from generating eddies or accumulating at the outlet end.

[0076] In some embodiments, see Figure 1To ensure that the plastic melt in each area of ​​the die head always maintains the temperature that meets the molding requirements and to avoid changes in melt viscosity, decreased fluidity or thermal degradation due to temperature fluctuations, the die head is also equipped with a special heating and temperature control system. This system includes multiple heating devices and several temperature detection devices. The two work together to form a closed-loop temperature control, ensuring the temperature stability of the melt throughout the entire process of diversion, transportation, distribution and molding.

[0077] The heating device specifically refers to heating coils, which are positioned at multiple key locations according to the temperature control requirements of different functional areas of the die head. For example, the outer ring of the flange adapter 440 is equipped with a flange adapter heating coil 441, used to heat the transition channel inside the flange adapter 440. This channel receives the melt transported by the external intermediate layer extrusion equipment. The heating coil compensates for temperature loss during the melt's entry into the die head from the external equipment, preventing the intermediate layer melt from increasing in viscosity due to cooling. This ensures that the melt flows smoothly into the first pre-diverter intermediate hole 314 of the first pre-diverter 310, thereby guaranteeing the continuity of subsequent transport and distribution of the intermediate layer melt.

[0078] The outer ring of the mold body 110 is equipped with a mold body heating coil 114 for heating and heat preservation of the entire mold body 110. As the basic load-bearing structure of the mold head, the mold body 110 houses core components such as the pre-diverter and the spiral body. The mold body heating coil 114 maintains a stable internal temperature of the mold head, which can prevent external temperature changes from interfering with the temperature of each layer of melt and provide a stable temperature environment for melt diversion and conveying.

[0079] The outer rings of the first pre-splitter 310 and the second pre-splitter 320 are equipped with pre-splitter heating coils 330 to heat the melt within the first annular void channel 311 and the second annular void channel 321. Since it takes a certain amount of time for the melt to complete the splitting process within the annular channel, the temperature is prone to drop due to heat loss during the process. The heating coils can compensate for the temperature loss in real time, preventing the melt from increasing in viscosity and flow resistance due to cooling, and ensuring that the flow uniformity of each melt stream is not affected by temperature during the splitting process.

[0080] An inner spiral heating coil 234 is provided on the inner side of the inner spiral 230 to specifically control the temperature of the inner melt entering the inner spiral distribution channel 231. The inner melt is mostly made of corrosion-resistant, high-viscosity material with relatively poor fluidity. Maintaining a suitable temperature for the melt through the inner spiral heating coil 234 can prevent it from stagnating due to excessive viscosity during spiral distribution. A mold core heating coil 521 is also provided on the outer side of the mold core at the outlet end of the inner spiral 230 to perform final temperature calibration on the inner melt that is about to enter the molding stage, ensuring that the temperature of the inner melt matches that of the outer and intermediate melts, and reducing the problem of poor interfacial bonding caused by temperature differences between layers.

[0081] The outer ring of the centering mold 120 is provided with a first centering mold heating ring 121 and a second centering mold heating ring 122, which are arranged at intervals along the axial direction of the centering mold 120 to heat and keep the three-layer composite melt in the transition channel inside the centering mold 120. After the composite melt enters the centering mold 120 from the mold body 110 outlet, it needs to complete the transition of the flow direction from the "post-diversion state" to the "pre-forming state". The heating ring can maintain the stability of the melt temperature, avoid the decrease of melt fluidity due to heat loss during the transition process, prevent the generation of eddies or local accumulation, ensure the flow stability of the composite melt in the transition channel, and lay the temperature foundation for the final forming stage of the connecting mold.

[0082] The outer ring of the connecting mold 130 is equipped with a connecting mold heating ring 131, which is used to heat the composite melt in the forming channel inside the connecting mold 130. This channel is the final forming area of ​​the multi-layer composite pipe, where the melt needs to be shaped. The connecting mold heating ring 131 ensures that the melt maintains a suitable viscosity and fluidity throughout the forming process, which can avoid unevenness of the inner wall of the pipe, wall thickness deviation or surface defects caused by temperature fluctuations, and ensure the forming quality and dimensional accuracy of the final extruded pipe.

[0083] To achieve precise monitoring and regulation of temperature in each area, the temperature detection device is specifically a thermocouple, with each thermocouple corresponding to a specific heating coil. These thermocouples are screwed into pre-set mounting holes on their respective components using a threaded connection, ensuring tight contact between the sensing end and the component body and improving the accuracy of temperature detection. When a thermocouple in a certain area detects a temperature lower than a preset value, it sends a signal to the temperature control system, increasing the power of the corresponding heating coil; if the temperature is higher than the preset value, the heating coil power is reduced, forming a closed-loop temperature control logic of "detection-feedback-regulation".

[0084] The advantages of this heating and temperature control system are as follows: First, it enables targeted temperature control for each functional area of ​​the die head, avoiding the problems of "local overheating" or "local underheating" caused by traditional single heating methods. For example, the pre-diverter area needs to maintain a high temperature to prevent melt stagnation, while the die core area needs to be precisely matched to the molding temperature. Each heating coil can independently adjust its power to meet the differentiated needs of different areas. Second, the real-time detection of multiple thermocouples can quickly respond to temperature changes, especially when the die head is started or stopped or the melt material is changed. It can quickly adjust the temperature of each area to the target range, reducing debugging time and material waste. Third, the coordinated work of the heating coils and thermocouples effectively ensures the temperature stability of the melt throughout the entire flow process, avoiding uneven melt viscosity and changes in flow resistance caused by temperature fluctuations. This further improves the uniformity of the distribution of the inner, middle, and outer three layers of melt, ultimately ensuring that the extruded multilayer composite pipe is free from quality defects such as bubbles, delamination, and excessive wall thickness deviation caused by temperature issues.

[0085] In practical operation, the multi-layer co-extrusion die head with pre-diverter of this application can complete the entire process from input of multi-layer composite plastic melt to extrusion of the final formed pipe through the coordinated cooperation of various components. The specific working process of the multi-layer co-extrusion die head with pre-diverter provided in one embodiment is as follows, further demonstrating the functional synergy of the various structures and the feasibility of the technical solution: The external extrusion equipment synchronously delivers the corresponding melt to the die head, and starts the heating and temperature control system of the die head. The die body heating ring 114 on the outer ring of the die body 110, the flange adapter heating ring 441 on the outer ring of the flange adapter 440, the pre-divider heating ring 330 on the outer ring of the first pre-divider 310 and the second pre-divider 320, the inner spiral heating ring 234 on the inner side of the inner spiral 230, the die core heating ring 521 on the outer side of the die core at the outlet end of the inner spiral 230, the first centering die heating ring 121 and the second centering die heating ring 122 on the outer ring of the centering die 120, and the connecting die heating ring 131 on the outer ring of the connecting die 130 are started synchronously. At the same time, the thermocouples 115 on the die body 110 detect the temperature of the corresponding area in real time, and maintain the melt in each area within the temperature range suitable for molding through closed-loop temperature control.

[0086] The outer layer melt conveyed by the outer layer extrusion equipment enters the outer layer melt inlet 312 of the first pre-divider 310, and then flows into the first annular void channel 311 of the first pre-divider 310. The first annular void channel 311 uniformly pre-divides the single outer layer melt into multiple streams. The multiple streams of outer layer melt flow out through the first pre-divider outer layer hole 313 of the first pre-divider 310 and enter the second pre-divider outer layer hole 323 of the second pre-divider 320. The outer layer feeding channel 215 formed by the two flows together smoothly to the outer layer spiral 210. The melt flows first... The outer secondary flow channel 212 of the outer spiral body 210 is further divided into more strands through multi-stage bow-shaped channels, and then enters the outer spiral distribution channel 211 of the outer spiral body 210. The outer spiral distribution channel 211 completes the uniform distribution of the melt along the axial and circumferential directions. The distributed outer melt flows towards the outlet end of the mold body 110 and passes through the outer wall thickness adjustment component at the outlet end of the mold body 110. By adjusting the outer wall thickness adjustment screw 140 at the corresponding position, the outer wall thickness adjustment ring 141 is pushed to optimize the extrusion channel gap to ensure that the outer melt is evenly distributed circumferentially.

[0087] The intermediate layer melt conveyed by the external intermediate layer extrusion equipment enters the die head through the transition channel of the flange adapter 440 and contacts the flow divider cone 450 in the intermediate hole 314 of the first pre-divider. The flow divider cone 450 guides the axially flowing columnar melt evenly to the inner wall of the channel, transforming it into annular melt. The annular melt then flows into the first pre-divider intermediate hole 314 of the first pre-divider 310, continues to flow through the second pre-divider intermediate hole 324 of the second pre-divider 320, and then enters the outer spiral intermediate hole 213 of the outer spiral 210. The intermediate layer feeding channel 222, which is jointly formed by the first pre-divider intermediate hole 314, the second pre-divider intermediate hole 324, and the outer spiral intermediate hole 213, conveys the melt to the intermediate layer spiral distribution channel 221 of the intermediate layer spiral 220, completing the circumferential and axial uniform distribution of the melt.

[0088] The inner layer melt conveyed by the external inner layer extrusion equipment enters the inner layer melt inlet 322 of the second pre-divider 320, and then flows into the second annular void channel 321 of the second pre-divider 320. The second annular void channel 321 uniformly pre-divides the single inner layer melt into multiple streams. The multiple streams of inner layer melt flow out through the second pre-divider inner layer hole 325 of the second pre-divider 320, and flow sequentially through the outer spiral inner layer hole 214 of the outer spiral 210 and the middle spiral inner layer hole 22 of the middle spiral 220. 3. The inner layer feeding channel 233, which is formed by the three components, transports the melt to the inner layer spiral 230. The melt first flows into the inner layer secondary diversion channel 232 of the inner layer spiral 230. After being further evenly divided by the multi-stage bow-shaped channel, it enters the inner layer spiral distribution channel 231 of the inner layer spiral 230. The evenly distributed inner layer melt flows to the outlet end of the inner layer spiral 230. Then, it is guided by the transition mold core 510 to transition from spiral flow to axial flow, and then flows through the connecting mold core 520 to continue to be transported to the mold head outlet end.

[0089] The inner, middle, and outer layers of melt converge at the outlet of the mold 110 and enter the centering mold 120. Guided by the centering mold 120, they smoothly transition to the forming channel of the connecting mold 130. By synchronously adjusting the overall wall thickness adjusting screw 150 on the centering mold 120, the position of the connecting mold 130 is changed to calibrate the overall wall thickness of the three-layer composite melt. The clamping flange 132 ensures the stability and sealing of the position of the connecting mold 130. The composite melt is shaped in the forming channel of the connecting mold 130. Finally, after the connecting plate 530 at the outlet of the connecting mold core 520 assists in optimizing the interlayer interface bonding, it is extruded from the outlet of the connecting mold 130 to form a multi-layer composite pipe.

[0090] Throughout the entire process, the mold fixing group maintains the overall structural stability of the mold head, ensuring that the mold 110 and the outer spiral 210 maintain a relatively fixed positional relationship, and ensuring the connection accuracy of the flow channels of each component and the stability of melt flow.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A multi-layer co-extrusion die with a pre-diverter, characterized in that, include: phantom, An outer spiral, a middle spiral, and an inner spiral are coaxially sleeved within the mold body. The outer circumferential surfaces of the outer spiral, the middle spiral, and the inner spiral are respectively formed with an outer spiral distribution channel, a middle spiral distribution channel, and an inner spiral distribution channel. A first pre-divider has a first annular void channel formed thereon. An outer melt inlet is formed at the inlet of the first annular void channel. The outlet of the first annular void channel is connected to the inlet of the outer spiral distribution channel. This pre-divider uniformly pre-divides a single stream of outer melt flowing in through the outer melt inlet into multiple streams of melt, and then conveys them to the outer spiral distribution channel. The second pre-divider has a second annular void channel formed on it. An inner layer melt inlet is formed at the inlet of the second annular void channel. The outlet of the second annular void channel is connected to the inlet of the inner layer spiral distribution channel. It is used to uniformly pre-divide a single inner layer melt flowing in through the inner layer melt inlet into multiple melt streams and transport them to the inner layer spiral distribution channel. The first pre-splitter and the second pre-splitter are arranged sequentially upstream of the melt flow direction along the axial direction of the multilayer co-extrusion die and are assembled with the die body to form an integral unit.

2. The multi-layer co-extrusion die with a pre-splitter according to claim 1, characterized in that, The first annular gap flow channel and the second annular gap flow channel are constructed as a multi-stage flow splitting structure, which includes at least two sequentially connected arc-shaped flow channels. The first-stage arc-shaped flow channel is connected to the corresponding outer melt inlet or inner melt inlet in the middle; the last-stage arc-shaped flow channel is connected to the corresponding outer spiral distribution channel or inner spiral distribution channel at both ends; and each arc-shaped flow channel is configured to evenly divide the melt flowing into it into two streams and flow out from its two outlets. The first annular gap flow channel and / or the second annular gap flow channel form a continuous annular path in the radial plane, and the flow channel wall of its diversion region has a smooth transition and a constant or gradually changing radius of curvature.

3. The multi-layer co-extrusion die with a pre-diverter according to claim 1, characterized in that, The outer circumferential surface of the outer spiral body is further provided with an outer secondary diversion channel. The inlet of the outer secondary diversion channel is connected to the outlet of the first pre-diverter, and the outlet of the outer secondary diversion channel is connected to the inlet of the outer spiral distribution channel; and / or, The outer circumferential surface of the inner spiral body is also provided with an inner secondary diversion channel. The inlet of the inner secondary diversion channel is connected to the outlet of the second pre-diverter, and the outlet of the inner secondary diversion channel is connected to the inlet of the inner spiral distribution channel. The outer secondary diversion channel and / or the inner secondary diversion channel are constructed as a multi-stage bow-shaped diversion structure. The multi-stage bow-shaped diversion structure includes at least two sequentially connected bow-shaped channels. Each bow-shaped channel is configured to uniformly divide the melt flowing into it into two streams, which flow from its two outlets to the next bow-shaped channel or the corresponding spiral distribution channel.

4. The multi-layer co-extrusion die with a pre-splitter according to claim 1, characterized in that, It also includes an outer layer feeding channel, a middle layer feeding channel, and an inner layer feeding channel; One end of the outer feeding channel is connected to the outlet end of the first annular gap channel of the first pre-diverter, and the other end is connected to the inlet of the spiral distribution channel of the outer spiral body. One end of the intermediate layer feeding channel is used to connect to the intermediate layer melt conveyed by the external intermediate layer extrusion equipment, and the other end is connected to the spiral distribution channel inlet of the intermediate layer spiral body. One end of the inner layer feeding channel is connected to the outlet end of the second annular gap flow channel of the second pre-diverter, and the other end is connected to the inlet of the spiral distribution flow channel of the inner layer spiral.

5. The multilayer co-extrusion die with a pre-splitter according to claim 4, characterized in that, It also includes a flow divider cone, which extends axially along the multi-layer co-extrusion die and is located at the center of the first pre-flow divider and within the intermediate layer feeding channel. The flow divider cone is used to guide the intermediate layer melt flowing in through the intermediate layer feeding channel into annular melt and transport it to the spiral distribution channel of the intermediate layer spiral.

6. The multilayer co-extrusion die with a pre-splitter according to claim 1, characterized in that, The mold body is provided with an outer wall thickness adjusting screw and an outer wall thickness adjusting ring at the outlet end. The outer wall thickness adjusting ring is located inside the outlet end of the mold body. The outer wall thickness adjusting screw is threaded into the mold body and is used to adjust the circumferential distribution of the outer melt extruded by the outer spiral body.

7. The multilayer co-extrusion die with a pre-splitter according to claim 6, characterized in that, The outlet end of the mold body is also provided with a centering mold and a connecting mold in sequence, and the outlet end of the centering mold is provided with an overall wall thickness adjustment screw for adjusting the overall wall thickness of the composite melt.

8. The multilayer co-extrusion die with a pre-splitter according to claim 1, characterized in that, It also includes at least one set of heating devices, which are disposed at at least one of the following locations: the outer ring of the die body, the outer ring of the first pre-diverter, the outer ring of the second pre-diverter, the inner side of the inner spiral, the outer side of the die core at the outlet end of the inner spiral, the outer ring of the flange adapter, the outer ring of the centering die, and the outer ring of the connecting die, for heating the melt inside the multilayer co-extrusion die head.

9. The multilayer co-extrusion die with a pre-splitter according to claim 8, characterized in that, It also includes at least one temperature detection device, which is disposed at at least one of the mold body, the first pre-diverter, the second pre-diverter and the inner spiral body.

10. The multilayer co-extrusion die with a pre-splitter according to claim 1, characterized in that, It also includes a transition mold core, a connecting mold core, and a connecting plate; the transition mold core is installed at the outlet end of the inner spiral body, the connecting mold core is installed at the end of the transition mold core away from the inner spiral body, and the connecting plate is disposed inside the outlet end of the connecting mold core and is fixedly connected to the connecting mold core.

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