Injection molding method and system for polyurethane sheath

Abstract

The invention discloses an injection molding method and system for a polyurethane sheath, and the method comprises the following steps: mixing a polyurethane matrix with a nano reinforcing material and an interface modifier, preparing modified polyurethane master batches through vacuum banburying, and dividing the modified polyurethane master batches into inner-layer master batches and outer-layer master batches; injecting the inner-layer master batch into an injection mold to form an inner-layer sheath semi-finished product; the outer surface of the inner layer sheath semi-finished product is switched to the outer layer master batch, a composite sheath with a gradient transition layer structure is formed, staged dynamic cooling is carried out, and interlayer internal stress is eliminated; surface and internal defects of the cooled composite sheath are detected through optical detection equipment, and detection data are fed back to an injection molding control system; the interlayer bonding strength of the sheath and the internal structure of the optical cable is remarkably improved through gradient injection molding, and meanwhile, the pressure resistance and impact resistance are enhanced through the microporous buffer layer; the staged dynamic cooling technology effectively eliminates internal stress, avoids cracking or deformation of the sheath, and provides the sheath with high weather resistance and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of injection molding processes, and particularly to an injection molding method and system for a polyurethane sheath. Background Art

[0002] As a key protective component between connectors and cables / optical fibers, polyurethane sheaths are widely used in fields such as communication base stations, industrial equipment, and consumer electronics. They need to perform functions such as mechanical buffering, environmental sealing, and anti-bending protection under complex working conditions. Especially with the increasing demand for miniaturization and high-density wiring of connectors in 5G high-frequency transmission scenarios, the sheath needs to achieve high compressive strength and flexibility simultaneously in a limited space. Traditional sheaths generally face problems such as interlayer peeling caused by outdoor temperature differences and stress cracking caused by frequent plugging and unplugging, and it is difficult to meet the requirements of long life and high reliability of the connector protection structure for intelligent terminal devices.

[0003] Traditional processing of polyurethane sheaths mostly uses single-layer injection molding or co-extrusion molding technology. The mechanical properties are improved by adding fillers or foaming agents, and a uniform microporous structure is formed by premixing the foaming agent to enhance the buffering performance. However, the single material system results in a small difference in modulus between the inner and outer layers of the sheath, and interlayer peeling is likely to occur under dynamic loads; or a double-layer co-extrusion process is used, but due to the mismatch of the thermal shrinkage rates of the inner and outer layer materials and the rough cooling process, the interfacial bonding strength is insufficient, and cracks are likely to be caused by the accumulation of thermal stress after long-term use. Existing technologies generally focus on optimizing single performance, lacking a systematic design for interlayer cooperative strengthening and stress regulation. Especially in the aspects of gradient structure forming and residual stress elimination, there are technical blind spots, resulting in a significant risk of interfacial failure of the sheath in scenarios of alternating temperature differences or high-frequency vibrations, restricting the improvement of its reliability in harsh environments.

[0004] In view of this, it is necessary to improve the sheath processing and forming technology in the existing technology to solve the technical problems of insufficient interlayer bonding force and poor environmental adaptability of the process. Summary of the Invention

[0005] The purpose of the present invention is to provide an injection molding method and system for a polyurethane sheath to solve the above technical problems.

[0006] To achieve this purpose, the present invention adopts the following technical solutions: An injection molding method for a polyurethane sheath, comprising the following steps: S1, mixing a polyurethane matrix with a nano-enhancing material and an interfacial modifier, and preparing a modified polyurethane masterbatch through vacuum kneading, and dividing it into an inner-layer masterbatch and an outer-layer masterbatch; S2, injecting the inner-layer masterbatch into an injection mold with a microporous structure, and forming an inner-layer sheath semi-finished product with a honeycomb-like microporous buffer layer through high-temperature and high-pressure injection; S3. Switch to the outer masterbatch on the outer surface of the semi-finished inner sheath, and cover a low-modulus polyurethane layer by low-temperature and low-pressure injection molding to form a composite sheath with a gradient transition layer structure; S4. Carry out staged dynamic cooling on the composite sheath, first cool down to the intermediate temperature at the first rate, and then cool down to room temperature at the second rate to eliminate the internal stress between layers; S5. Detect the surface and internal defects of the cooled composite sheath through an optical detection device, and feed the detection data back to the injection molding control system to dynamically correct the injection molding process parameters.

[0007] Optionally, the nano-enhanced material is selected from at least one of nano-silica, organic montmorillonite or carbon nanotubes; The interface modifier is selected from at least one of silane coupling agent, titanate coupling agent or epoxy resin modifier; The mass ratio of the polyurethane matrix, nano-enhanced material and interface modifier is 85-97:2-10:0.5-5.

[0008] Optionally, the step S1 specifically includes the following steps: S11. Place the nano-enhanced material in an ethanol solution and ultrasonically disperse it for 30-60 minutes, and then add the interface modifier for surface coating treatment to form a modified nano-enhanced material; S12. Put the polyurethane matrix particles into a vacuum internal mixer, heat to 80-100 °C and stir until it becomes a molten state to form a matrix molten liquid; S13. Add the modified nano-enhanced material to the matrix molten liquid evenly in three times to form a mixed material. After each addition, mix it at a low speed of 50-80 rpm for 5-10 minutes, and then switch to a high-speed shear dispersion at 150-200 rpm for 10-15 minutes; S14. Under the condition that the vacuum degree ≤ -0.08 MPa, carry out degassing treatment on the mixed material for 20-30 minutes to eliminate bubbles and undispersed aggregates; S15. Melt and extrude the degassed mixed material through a twin-screw extruder, control the extrusion temperature at 120-140 °C, and obtain modified polyurethane masterbatch after water-cooling pelletization; S16. Sort the modified polyurethane masterbatch into inner masterbatch and outer masterbatch according to the modulus difference, wherein the nano-enhanced material content of the inner masterbatch is 4-10 wt%, and the nano-enhanced material content of the outer masterbatch is 1-3 wt%.

[0009] Optionally, the injection mold includes a split upper mold and a lower mold, and a honeycomb-shaped micropore generation module is arranged on the inner wall of the lower mold; wherein, the micropore generation module is composed of a uniformly distributed array of conical protrusions; The upper mold is provided with a high-pressure injection molding runner, and the end of the high-pressure injection molding runner is connected to a micro-hole filling cavity, and the surface of the micro-hole filling cavity is plated with a titanium nitride wear-resistant layer; The lower mold internally integrates a multi-stage exhaust channel, and the exhaust hole is located at the root of the conical protrusion, and one end of the exhaust hole is connected to a vacuum pump.

[0010] Optionally, the injection mold is further provided with a gradient temperature control system, and the gradient temperature control system includes a first temperature zone for the inner layer injection molding stage and a second temperature zone for the outer layer injection molding stage, and the first temperature zone and the second temperature zone are isolated by a heat-insulating ceramic layer.

[0011] Optionally, step S3 specifically includes the following steps: S31, switch the injection molding runner to the outer layer masterbatch, control the melt temperature at 160 - 170 °C and the injection pressure at 30 - 50 MPa, and cover the bonding interface of the inner layer sheath semi-finished product with the outer layer masterbatch melt by means of pulse pressure injection; S32, during the injection molding process, stepwise increase the mold clamping pressure of the injection mold three times: 10 MPa → 20 MPa → 30 MPa, and keep the pressure for 3 - 5 minutes each time, so as to promote the outer layer masterbatch melt to penetrate into the inner layer micro-holes to form a mechanical interlocking structure; S33, keep the mold in a semi-open state, cool it at a rate of 5 - 8 °C / min to 100 - 110 °C, so as to form a gradient transition layer at the interface between the outer layer polyurethane layer and the inner layer sheath, and obtain a composite sheath.

[0012] Optionally, step S4 specifically includes the following steps: S41, transfer the composite sheath together with the injection mold as a whole to a cooling chamber, and a dual-channel system of air cooling and liquid cooling is preset in the cooling chamber; S42, start the air cooling channel, and perform forced convection cooling on the outer surface of the composite sheath at a first rate of 10 - 15 °C / min for 8 - 12 minutes to reduce the temperature to 80 - 90 °C; S43, switch to the liquid cooling channel, circulate and inject a liquid cooling cooling medium into the mold interior, control the medium flow rate, and cool down at a rate of 5 - 8 °C / min to 50 - 60 °C to preliminarily cool the composite sheath.

[0013] Optionally, after step S43, it further includes: S44, demold the preliminarily cooled composite sheath from the injection mold and transfer it to a constant temperature stress relaxation chamber, keep it at a constant temperature of 40 - 50 °C for 20 - 30 minutes, and simultaneously apply an axial tensile load; S45, start a slow cooling program, cool the sheath from 50 °C to 25 °C at a second rate of 2 - 3 °C / min, and simultaneously apply an external pressure constraint of 0.5 - 1 MPa evenly along the circumferential direction of the sheath to eliminate the internal stress between layers and obtain a cooled composite sheath.

[0014] Optionally, step S5 specifically includes the following steps: S51. Place the cooled composite sheath on the rotary detection platform, and synchronously scan the surface topography along the axial and circumferential directions of the sheath through a laser scanner to generate three-dimensional point cloud data; S52. Start the ultrasonic detector to perform tomographic imaging on the internal microporous buffer layer and the gradient transition layer of the sheath, detect the pore size distribution, the defects of the interlayer bonding interface and the porosity deviation, and obtain ultrasonic imaging data; S53. Input the three-dimensional point cloud data and the ultrasonic imaging data into the deep learning model to identify the types and positions of cracks, bubbles, and delamination defects, and mark the defect levels to generate a defect analysis result; S54. Based on the defect analysis result, generate dynamic correction values of the injection pressure, temperature, and cooling rate through a parameter compensation algorithm, correct them into the injection process parameters, and associate them with the production instructions of the next batch; S55. Import the corrected injection process parameters into the injection control system in real time, synchronously update the injection process curves of the inner masterbatch and the outer masterbatch, and complete the closed-loop process optimization.

[0015] The present invention also provides an injection molding system for a polyurethane sheath, which is used to implement the injection molding method of the polyurethane sheath as described above. The injection molding system specifically includes: A material pretreatment module, including a vacuum internal mixer, a twin-screw extruder, and a masterbatch sorting device, which is used to prepare modified polyurethane masterbatches and separate the inner masterbatch and the outer masterbatch; An injection mold, which is used to realize the sequential injection molding of the composite sheath and integrate an inner microporous buffer layer and an outer gradient transition layer on the composite sheath; A dynamic cooling module, including a cooling chamber, a constant temperature stress relaxation chamber, and an external pressure constraint device, which supports staged gradient cooling and stress directional release; An optical detection device, which is used to detect the surface and internal defects of the cooled composite sheath; An injection control system, which is used to control the injection process and dynamically correct the injection process parameters according to the detection data of the optical detection device.

[0016] Compared with the prior art, the present invention has the following beneficial effects: First, a modified masterbatch is prepared by mixing a polyurethane matrix, nano-enhancing materials, and an interfacial modifier through vacuum internal mixing and the inner and outer layer masterbatches are separately set; Subsequently, the inner layer masterbatch is injected into a microporous mold to form a semi-finished inner sheath with a honeycomb microporous buffer layer under high temperature and high pressure; Then, the outer layer masterbatch is injection-molded on its outer surface at low temperature and low pressure to cover a low-modulus polyurethane layer, forming a composite sheath with a gradient transition structure; Then, the internal stress between layers is eliminated through staged dynamic cooling (cooling at a decreasing rate, fast first and then slow); Then, an optical detection device is used to scan for sheath defects and the data is fed back to the control system to dynamically correct the subsequent injection molding parameters, realizing closed-loop optimization; This process significantly improves the interfacial bonding strength between the sheath and the internal structure of the optical cable through gradient injection molding, while the microporous buffer layer enhances the compressive and impact resistance; The staged dynamic cooling technology effectively eliminates the internal stress, avoids sheath cracking or deformation, and provides a sheath with high weather resistance and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] The structures, proportions, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0019] Figure 1 is one of the flow schematic diagrams of the injection molding method of the polyurethane sheath in the first embodiment; Figure 2 is the second of the flow schematic diagrams of the injection molding method of the polyurethane sheath in the first embodiment; Figure 3 is the cross-sectional structure schematic diagram of the injection mold in the first embodiment; Figure 4 is for the injection mold in the first embodiment Figure 3 is the partial enlarged structure schematic diagram at position A. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] In order to make the object, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be an intermediate component present at the same time.

[0022] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and through specific embodiments.

[0023] Embodiment 1: Combined Figures 1 to 4 As shown, the embodiment of the present invention provides an injection molding method for a polyurethane sheath, including the following steps: S1, mixing a polyurethane matrix with a nano-enhancing material and an interfacial modifier, and preparing a modified polyurethane masterbatch through vacuum internal mixing, and dividing it into an inner masterbatch and an outer masterbatch; In this step, by mixing the polyurethane matrix with the nano-enhancing material and the interfacial modifier, combined with the vacuum internal mixing process, the uniform dispersion of the nano-fillers and the optimization of the interfacial bonding are realized. Vacuum internal mixing can effectively eliminate air bubbles and prevent filler agglomeration, and the division of the inner masterbatch (high nano-content) and the outer masterbatch (low nano-content) provides a material basis for the subsequent formation of a gradient structure, ensuring the differential performance requirements of the inner and outer layers.

[0024] S2, injecting the inner masterbatch into an injection mold with a microporous structure, and forming an inner sheath semi-finished product with a honeycomb-like microporous buffer layer through high-temperature and high-pressure injection molding; By injecting the inner masterbatch into a mold with a microporous structure through the high-temperature and high-pressure injection molding process, the high temperature ensures that the polyurethane melt fully flows and fills the micropores of the mold, and the high pressure promotes the tight combination of the melt and the microporous structure. The formation of the honeycomb-like microporous buffer layer significantly improves the compressive performance and energy absorption capacity of the sheath, providing structural adaptability for the deep-sea high-pressure environment.

[0025] S3. Switch to the outer masterbatch on the outer surface of the inner sheath semi-finished product, and cover a low-modulus polyurethane layer by low-temperature and low-pressure injection molding to form a composite sheath with a gradient transition layer structure; Switch to the outer masterbatch on the surface of the formed inner sheath, and cover the low-modulus polyurethane layer by using the low-temperature and low-pressure injection molding process. The low temperature avoids thermal damage to the inner structure, and the low pressure reduces the melt flow stress, finally forming a gradient transition layer with a gradually changing modulus. This structure enhances the interfacial bonding force through chemical bonding and mechanical interlocking, and at the same time disperses the external load stress.

[0026] S4. Carry out staged dynamic cooling on the composite sheath. First, cool down to an intermediate temperature at a first rate, and then cool down to room temperature at a second rate to eliminate the internal stress between layers; The staged dynamic cooling is controlled by a cooling rate that is fast first and then slow. The overall structure of the sheath is initially quickly cooled and shaped, and then slowly cooled to release the internal residual stress. The gradient cooling strategy effectively reduces the uneven shrinkage and microcracks caused by the temperature difference, and improves the dimensional stability and environmental durability of the sheath.

[0027] S5. Use an optical detection device to detect the surface and internal defects of the cooled composite sheath, and feed the detection data back to the injection molding control system to dynamically correct the injection molding process parameters.

[0028] An optical detection device combined with a data feedback system is used to conduct multi-dimensional analysis of the surface and internal defects of the sheath (such as cracks, pores, delamination). The detection data is transmitted to the control system in real time, and the injection molding temperature, pressure and cooling parameters are dynamically corrected through algorithms to form a closed-loop process optimization, improving the production consistency and product yield.

[0029] The working principle of the present invention is as follows: First, a modified masterbatch is prepared by mixing a polyurethane matrix, a nano-enhancing material and an interfacial modifier through vacuum mixing and kneading, and the inner and outer masterbatches are separately set; then the inner masterbatch is injected into a microporous mold and formed into an inner sheath semi-finished product with a honeycomb-like microporous buffer layer at high temperature and high pressure; then switch to the outer masterbatch on its outer surface and cover a low-modulus polyurethane layer by low-temperature and low-pressure injection molding to form a composite sheath with a gradient transition structure; then eliminate the internal stress between layers through staged dynamic cooling (cooling at a fast rate first and then a slow rate); then use an optical detection device to scan the sheath defects and feed the data back to the control system to dynamically correct the subsequent injection molding parameters to achieve closed-loop optimization; this process significantly improves the interfacial bonding strength between the sheath and the internal structure of the optical cable through gradient injection molding, and at the same time the microporous buffer layer enhances the compressive and impact resistance; the staged dynamic cooling technology effectively eliminates the internal stress, avoids the cracking or deformation of the sheath, and provides a sheath with high weather resistance and mechanical properties.

[0030] In this embodiment, the nano-enhancing material is selected from at least one of nano-silica, organic montmorillonite or carbon nanotubes; the interfacial modifier is selected from at least one of silane coupling agent, titanate coupling agent or epoxy resin modifier. Among them, the mass ratio of the polyurethane matrix, nano-enhancing material and interfacial modifier is 85-97:2-10:0.5-5. The nano-material improves the compressive and hydrolysis resistance of the sheath, and the modifier enhances the chemical bonding between the filler and the matrix. The ratio control balances the mechanical properties and processing fluidity. By defining the selection range of the nano-enhancing material and the interfacial modifier and combining the mass ratio, the efficient dispersion and interfacial compatibility of the nano-filler are ensured.

[0031] In this embodiment, specifically, step S1 specifically includes the following steps: S11, Place the nano-enhancing material in an ethanol solution and ultrasonically disperse it for 30-60 minutes, then add the interfacial modifier for surface coating treatment to form a modified nano-enhancing material; Place the nano-enhancing material in an ethanol solution and ultrasonically disperse it for 30-60 minutes. Utilize the ultrasonic cavitation effect to break the agglomeration of nano-particles and form a uniform dispersion system; then add the interfacial modifier for surface coating to form a coating layer on the surface of the nano-particles through chemical bonding or physical adsorption, enhancing its compatibility with the polyurethane matrix. The ethanol solution serves as a dispersion medium to avoid organic solvent pollution. The duration of 30-60 minutes balances the dispersion efficiency and energy consumption, ensuring that the active surface of the nano-material is fully exposed.

[0032] S12, Put the polyurethane matrix particles into a vacuum internal mixer, heat to 80-100 °C and stir until in a molten state to form a matrix melt; Heat the polyurethane matrix in a vacuum internal mixer to 80-100 °C. This temperature range can not only achieve complete melting of the matrix but also avoid high-temperature thermal degradation; the vacuum environment can prevent air bubbles from mixing in during the melting process and simultaneously inhibit the oxidation side reaction of polyurethane, ensuring the purity and processing stability of the matrix melt.

[0033] S13, Add the modified nano-enhancing material to the matrix melt evenly in three portions to form a mixed material. After each addition, mix at a low speed of 50-80 rpm for 5-10 minutes, and then switch to a high-speed shear dispersion of 150-200 rpm for 10-15 minutes; Add the modified nano-material in three portions, with a low-speed mixing (50-80 rpm) for 5-10 minutes at intervals each time to avoid local overload caused by concentrated feeding of the filler; then switch to high-speed shear (150-200 rpm) dispersion for 10-15 minutes to peel off the incompletely dispersed nano-agglomerates through high shear force. The staged process takes into account both the dispersion uniformity and energy consumption control, ensuring that the nano-filler is evenly distributed in the matrix and the interfacial bonding is tight.

[0034] S14. Under the condition that the vacuum degree is ≤ -0.08 MPa, degas the mixed material for 20 - 30 minutes to eliminate bubbles and undispersed aggregates. Degas for 20 - 30 minutes under a vacuum degree of ≤ -0.08 MPa, and remove the residual bubbles and undispersed fine aggregates in the mixed material through negative pressure suction. The continuous degassing time ensures that the gas inside the material escapes fully, reduces the formation of micropores or interfacial weaknesses in subsequent injection molding, and improves the compactness and mechanical property consistency of the masterbatch.

[0035] S15. Extrude the degassed mixed material through a twin - screw extruder, control the extrusion temperature at 120 - 140 °C, and obtain the modified polyurethane masterbatch after water - cooled pelletizing. Use a twin - screw extruder to melt - extrude at 120 - 140 °C. The temperature is set below the thermal decomposition threshold of polyurethane to ensure melt fluidity while avoiding molecular chain breakage; water - cooled pelletizing enables the masterbatch to be quickly shaped, prevents secondary aggregation of nano - fillers at high temperatures, and ensures the uniformity of particle size, providing a stable raw material for subsequent injection molding.

[0036] S16. Sort the modified polyurethane masterbatch into an inner - layer masterbatch and an outer - layer masterbatch according to the modulus difference. The content of the nano - reinforcing material in the inner - layer masterbatch is 4 - 10 wt%, and the content of the nano - reinforcing material in the outer - layer masterbatch is 1 - 3 wt%.

[0037] After that, store the sorted inner - layer masterbatch and outer - layer masterbatch separately in a storage box, controlling the humidity ≤ 10% and the temperature at 25 - 30 °C.

[0038] Sort the masterbatch according to the nano - content (4 - 10 wt% for the inner layer and 1 - 3 wt% for the outer layer). The high filler content in the inner layer improves the compressive and hydrolysis - resistant properties, and the low content in the outer layer maintains flexibility to meet the deformation requirements. The sorting process realizes precise grading through density or spectral detection, ensuring that the properties of the inner - layer and outer - layer masterbatches are adapted to the gradient structure design and avoiding stress concentration caused by sudden changes in inter - layer modulus.

[0039] In this embodiment, combined with Figure 3 and Figure 4 shown, specifically, among them, Figure 3 is a schematic cross - sectional structure diagram of an injection mold. In the figure, there is a molding cavity with multiple composite sheaths arranged in parallel. Figure 4 is Figure 3 The partial enlarged structure diagram at A in shows the distribution of the micropore generation module 21 and the exhaust channel 50. The injection mold includes a split upper mold 10 and a lower mold 20. The inner wall of the lower mold 20 is provided with a honeycomb - shaped micropore generation module 21; among them, the micropore generation module 21 is composed of an array of uniformly distributed conical protrusions; the height of a single protrusion is 50 - 100 μm, the bottom diameter is 80 - 150 μm, and the distance between adjacent protrusions is 200 - 300 μm.

[0040] The upper mold 10 is provided with a high-pressure injection molding runner 30, and the end of the high-pressure injection molding runner 30 is connected to a micro-hole filling cavity 40. The surface of the micro-hole filling cavity 40 is plated with a titanium nitride wear-resistant layer; the lower mold 20 internally integrates a multi-stage exhaust channel 50. The exhaust holes are located at the roots of the conical protrusions, and one end of the exhaust hole position is connected to a vacuum pump.

[0041] When the injection mold operates, the inner-layer masterbatch is injected into the micro-hole filling cavity 40 through the high-pressure injection molding runner 30 of the upper mold 10. Under high temperature and high pressure, the melt wraps the conical protrusion array of the lower mold 20 to form honeycomb-shaped micro-holes; the vacuum pump exhausts gas through the root exhaust holes to avoid micro-hole collapse or air-gap defects; the titanium nitride coating reduces melt adhesion and ensures continuous demolding.

[0042] This mold significantly improves the uniformity and compressive strength of the micro-holes in the sheath through the precise forming of the micro-hole structure and the coordinated control of exhaust, while reducing the risk of demolding damage.

[0043] In this embodiment, further description is that the injection mold is also provided with a gradient temperature control system. The gradient temperature control system includes a first temperature zone for the inner-layer injection molding stage and a second temperature zone for the outer-layer injection molding stage. The first temperature zone and the second temperature zone are isolated by a heat-insulating ceramic layer. Among them, the temperature of the first temperature zone is set to 180 - 200 °C, and the temperature of the second temperature zone is set to 160 - 180 °C.

[0044] The gradient temperature control system separates the high-temperature zone (180 - 200 °C) of the inner-layer injection molding from the low-temperature zone (160 - 180 °C) of the outer-layer injection molding through the heat-insulating ceramic layer, ensuring that the inner and outer layer melts are independently formed at different temperatures: the high temperature of the inner layer guarantees the integrity of micro-hole filling, and the low temperature of the outer layer prevents the thermal deformation of the already formed inner layer. The independent regulation of different temperature zones avoids process interference and realizes the high-precision forming of the gradient structure and the interface stability.

[0045] In this embodiment, specifically, step S3 specifically includes the following steps: S31, switch the injection molding runner to the outer-layer masterbatch, control the melt temperature to be 160 - 170 °C, the injection pressure to be 30 - 50 MPa, and cover the bonding interface of the inner-layer sheath semi-finished product with the outer-layer masterbatch melt through the pulse pressure injection method; Controlling the melt temperature to be 160 - 170 °C not only guarantees the low-temperature fluidity of the outer-layer masterbatch to completely cover the inner-layer interface but also avoids the thermal deformation of the inner-layer sheath caused by high temperature; the injection pressure is set to 30 - 50 MPa, providing sufficient power to evenly fill the interface gap with the melt, while reducing the risk of micro-cracks caused by flow stress. The pulse pressure injection method (such as intermittent pressurization) is adopted, and the pressure fluctuation promotes the penetration of the melt into the interface micro-holes, enhancing the wettability of the melt and the inner-layer structure, thereby improving the interface bonding strength and uniformity.

[0046] S32. During the injection molding process, the clamping pressure of the injection mold is increased step by step in three stages: 10 MPa → 20 MPa → 30 MPa, and each time the pressure is maintained for 3 - 5 minutes to promote the infiltration of the outer masterbatch melt into the inner micropores to form a mechanical interlock structure; The clamping pressure is increased step by step in three stages (10 MPa → 20 MPa → 30 MPa). By applying pressure gradually, it is possible to avoid the collapse of the inner micropore structure caused by the instantaneous high - pressure impact of the outer melt. Each time the pressure is maintained for 3 - 5 minutes, which not only ensures that the melt fully infiltrates into the inner micropores to form an anchoring effect but also reserves the solidification time of the melt to stabilize the interlock structure. This strategy significantly enhances the anti - peeling ability of the interface between the inner and outer layers through the synergistic effect of mechanical interlock and melt penetration.

[0047] S33. Keep the mold in a semi - open state and cool it at a rate of 5 - 8 °C / min to 100 - 110 °C to form a gradient transition layer at the interface between the outer polyurethane layer and the inner sheath, so as to obtain a composite sheath.

[0048] Cooling the mold in a semi - open state at a rate of 5 - 8 °C / min to 100 - 110 °C can reduce the interfacial stress concentration caused by the difference in thermal shrinkage between the inner and outer layers by delaying the cooling rate. The semi - open state allows the sheath to balance between constrained and free shrinkage, promoting the orderly arrangement of the outer polyurethane molecular chains and the inner interface, and finally forming a gradient transition layer with continuously varying modulus. This gradient structure can effectively disperse the external load stress and improve the durability of the sheath in an alternating pressure environment.

[0049] In this embodiment, specifically, step S4 specifically includes the following steps: S41. Transfer the composite sheath together with the injection mold as a whole to a cooling chamber, and a dual - channel system of air cooling and liquid cooling is pre - installed in the cooling chamber; Transfer the composite sheath and the mold as a whole to an air - liquid dual - channel cooling chamber, and adapt to the different thermal characteristics of the inner and outer layers of the sheath through a staged cooling strategy. Air cooling quickly reduces the surface temperature of the sheath to shape the macroscopic structure, and liquid cooling precisely controls the internal temperature gradient, avoiding uneven shrinkage or stress concentration caused by a single cooling medium, and taking into account both the cooling efficiency and the integrity of the sheath.

[0050] S42. Start the air - cooling channel and perform forced - convection cooling on the outer surface of the composite sheath at a first rate of 10 - 15 °C / min for 8 - 12 minutes to reduce the temperature to 80 - 90 °C; Cooling down to 80 - 90 °C at a rate of 10 - 15 °C / min by forced air cooling quickly shapes the outer layer of the sheath and prevents surface shrinkage deformation caused by rapid temperature drop. The 8 - 12 - minute air - cooling time ensures the initial solidification of the outer layer while retaining a certain degree of thermoplasticity in the inner layer to adapt to the subsequent liquid - cooling stage and reduce the inter - layer thermal stress difference.

[0051] S43. Switch to the liquid cooling channel, circulate and inject the liquid cooling medium into the mold interior, control the medium flow rate, and cool down to 50 - 60°C at a rate of 5 - 8°C / min to preliminarily cool the composite sheath.

[0052] After switching to liquid cooling, cool down to 50 - 60°C at a rate of 5 - 8°C / min by circulating the cooling medium (such as silicone oil). The high heat capacity characteristic of liquid cooling enables uniform heat dissipation inside the sheath. Controlling the medium flow rate (such as 2 - 5 L / min) can adjust the cooling intensity, avoid microcracks or abnormal porosity caused by local overcooling, and ensure the structural stability of the microporous buffer layer.

[0053] S44. After demolding the preliminarily cooled composite sheath from the injection mold, transfer it to a constant - temperature stress relaxation chamber, keep it at a constant temperature of 40 - 50°C for 20 - 30 minutes, and simultaneously apply an axial tensile load. Keep it at a constant temperature of 40 - 50°C in the constant - temperature stress relaxation chamber for 20 - 30 minutes. Utilize the synergistic effect of the temperature field and the axial tensile load (strain rate 0.1 - 0.3%) to promote the directional relaxation of polyurethane molecular chains and release the residual stress. The axial tensile load can offset the radial stress during the cooling and contraction of the sheath, improving the axial dimension consistency of the sheath.

[0054] S45. Start the slow - cooling program, cool the sheath from 50°C to 25°C at a second rate of 2 - 3°C / min, and simultaneously apply an external pressure constraint of 0.5 - 1 MPa uniformly along the circumferential direction of the sheath to eliminate the interlayer internal stress and obtain the cooled composite sheath.

[0055] Slow - cool to room temperature at a rate of 2 - 3°C / min, combined with the circumferentially uniform external pressure constraint (0.5 - 1 MPa), to inhibit the interlayer misalignment or warping deformation caused by the free contraction of the sheath. The external pressure constraint mechanically compensates for the thermal shrinkage difference, ensuring the geometric accuracy and interface bonding strength of the sheath, and avoiding the long - term performance degradation caused by residual stress.

[0056] In this embodiment, specifically, step S5 specifically includes the following steps: S51. Place the cooled composite sheath on the rotating detection platform, and synchronously scan the surface topography along the axial and circumferential directions of the sheath through a laser scanner to generate three - dimensional point cloud data. Drive the composite sheath to rotate axially and circumferentially synchronously through the rotating detection platform, combine with the laser scanner for non - contact surface topography scanning, and generate high - precision three - dimensional point cloud data. The rotational motion ensures full - coverage detection of the sheath surface and eliminates the detection blind area; laser scanning can identify surface cracks, depressions or protrusion defects at the micron level, and the three - dimensional point cloud data provides spatial topological information for subsequent defect analysis, improving the defect location accuracy and detection efficiency.

[0057] S52. Start the ultrasonic detector to perform tomographic imaging on the microporous buffer layer and the gradient transition layer inside the sheath, detect the pore size distribution, the defects of the interlayer bonding interface, and the porosity deviation, and obtain ultrasonic imaging data; The ultrasonic detector emits high-frequency sound waves to penetrate the inside of the sheath, and generates tomographic images of the microporous buffer layer and the gradient transition layer based on the sound wave reflection signals. By analyzing the characteristics of sound wave attenuation and reflection, the uniformity of pore size distribution, the integrity of the interlayer bonding interface, and the porosity deviation can be quantified, and hidden defects such as internal bubbles, delamination, or micropore collapse can be accurately detected, making up for the limitations of surface detection.

[0058] S53. Input the three-dimensional point cloud data and the ultrasonic imaging data into the deep learning model to identify the types and locations of cracks, bubbles, and delamination defects, and mark the defect levels to generate defect analysis results; Input the three-dimensional point cloud data (surface defects) and the ultrasonic imaging data (internal defects) into a pre-trained deep learning model (such as a convolutional neural network). Through feature fusion and pattern matching, automatically identify the defect types (cracks, bubbles, delamination) and mark their hazard levels (critical / non-critical). The collaborative analysis of multi-modal data can reduce the misjudgment rate of a single detection method, improve the accuracy of defect classification, and provide a reliable basis for process optimization.

[0059] S54. Based on the defect analysis results, generate dynamic correction values for the injection molding pressure, temperature, and cooling rate through a parameter compensation algorithm, correct them into the injection molding process parameters, and associate them with the production instructions for the next batch; Based on the defect analysis results, the parameter compensation algorithm establishes an association mapping model between the defect types and the injection molding pressure, temperature, and cooling rate, and generates targeted parameter correction values (such as pressure ±5%, temperature ±3°C). The correction values are directly associated with the production instructions for the next batch, and the process parameters corresponding to critical defects are adjusted preferentially to achieve the forward shift of defect prevention and reduce the recurrence rate of the same type of defects.

[0060] S55. Import the corrected injection molding process parameters into the injection molding control system in real time, and synchronously update the injection molding process curves of the inner masterbatch and the outer masterbatch to complete the closed-loop process optimization.

[0061] Import the corrected injection molding parameters into the control system in real time, and synchronously update the injection molding process curves of the inner and outer masterbatches (such as the pressure-time curve, the temperature-time curve). Through the closed-loop feedback mechanism, the system continuously optimizes the process parameter combination, gradually approaches the optimal production state, improves the consistency between batches, and reduces the need for manual intervention.

[0062] Embodiment 2: The present invention also provides an injection molding system for a polyurethane sheath, which is used to implement the injection molding method of the polyurethane sheath as in Embodiment 1. The injection molding system specifically includes: The material pretreatment module, including a vacuum internal mixer, a twin-screw extruder and a masterbatch sorting device, is used to prepare modified polyurethane masterbatch and separate the inner masterbatch and the outer masterbatch.

[0063] The injection mold is used to realize the sequential injection molding of the composite sheath and integrate the inner microporous buffer layer and the outer gradient transition layer on the composite sheath.

[0064] The dynamic cooling module, including a cooling chamber, a constant temperature stress relaxation chamber and an external pressure constraint device, supports staged gradient cooling and stress directional release.

[0065] The optical detection equipment is used to detect the surface and internal defects of the cooled composite sheath.

[0066] The injection control system is used to control the injection process and dynamically correct the injection process parameters according to the detection data of the optical detection equipment.

[0067] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements 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 the present invention.

Claims

1. A method for injection molding a polyurethane sheath, characterized in that: The following steps are involved: S1, mixing a polyurethane matrix with a nano-reinforcement material and an interface modifier, preparing a modified polyurethane masterbatch by vacuum mixing, and dividing the masterbatch into an inner layer masterbatch and an outer layer masterbatch; S2, injecting the inner layer masterbatch into an injection mold with a microporous structure, and forming an inner layer jacket semi-finished product with a honeycomb microporous buffer layer by high temperature and high pressure injection molding; S3, switching the outer surface of the inner layer jacket semi-finished product to the outer layer masterbatch, covering a layer of low modulus polyurethane layer by low temperature and low pressure injection molding, to form a composite jacket with a gradient transition layer structure; S4, dynamically cooling the composite jacket in stages, first cooling it to an intermediate temperature at a first rate, and then cooling it to room temperature at a second rate, to eliminate interlayer internal stress; S5, the surface and internal defects of the cooled composite jacket are inspected by optical inspection equipment, and the inspection data are fed back to the injection molding control system to dynamically correct the injection molding process parameters.

2. The method for injection molding of a polyurethane sheath according to claim 1, characterized in that: The nano-reinforcement material is selected from at least one of nano-silicon dioxide, organic montmorillonite or carbon nanotubes; The interface modifier is selected from at least one of a silane coupling agent, a titanate coupling agent or an epoxy resin modifier; The mass ratio of the polyurethane matrix, the nano-reinforcement material and the interface modifier is 85-97:2-10:0.5-5.

3. The method for injection molding of a polyurethane sheath according to claim 1, characterized in that: The step S1 specifically includes the following steps: S11, placing the nano-reinforced material in an ethanol solution for ultrasonic dispersion for 30-60 minutes, and then adding an interface modifier for surface coating treatment to form a modified nano-reinforced material; S12, putting the polyurethane matrix particles into a vacuum internal mixer, heating to 80-100° C. and stirring until molten, to form a matrix melt; S13, adding the modified nano-reinforced material into the matrix melt evenly three times to form a mixed material, mixing at a low speed of 50-80 rpm for 5-10 minutes after each addition, and then switching to a high-speed shear dispersion of 150-200 rpm for 10-15 minutes; S14, degassing the mixed material under vacuum degree ≤-0.08MPa for 20-30 minutes to eliminate bubbles and undispersed agglomerates; S15, melt-extrude the degassed mixture through a twin-screw extruder, control the extrusion temperature at 120-140° C., and obtain modified polyurethane masterbatch after water cooling and pelletizing; S16, sorting the modified polyurethane masterbatch into an inner layer masterbatch and an outer layer masterbatch according to the difference in modulus, wherein the nano-reinforcement material content of the inner layer masterbatch is 4-10wt%, and the nano-reinforcement material content of the outer layer masterbatch is 1-3wt%.

4. The method for injection molding of a polyurethane sheath according to claim 1, characterized in that: The injection mold comprises a split upper mold and a lower mold, and the inner wall of the lower mold is provided with a honeycomb-shaped micropore generation module; wherein the micropore generation module is composed of an array of evenly distributed conical protrusions; The upper mold is provided with a high-pressure injection molding flow channel, the end of the high-pressure injection molding flow channel is connected to the microporous filling cavity, and the surface of the microporous filling cavity is plated with a titanium nitride wear-resistant layer; The lower mold is internally integrated with multi-stage exhaust channels, the exhaust hole is located at the root of the conical protrusion, and one end of the exhaust hole is connected to a vacuum pump.

5. The method for injection molding of a polyurethane sheath according to claim 1, characterized in that: The injection mold is also provided with a gradient temperature control system, which includes a first temperature zone in the inner layer injection stage and a second temperature zone in the outer layer injection stage, and the first temperature zone and the second temperature zone are isolated by a heat-insulating ceramic layer.

6. The method for injection molding of a polyurethane sheath according to claim 1, characterized in that: The step S3 specifically comprises the following steps: S31, switching the injection channel to the outer layer masterbatch, controlling the melt temperature to 160-170°C and the injection pressure to 30-50MPa, and covering the outer layer masterbatch melt on the bonding interface of the inner layer sheath semi-finished product by pulse pressure injection; S32, during the injection molding process, the mold clamping pressure of the injection mold is increased three times in a stepwise manner from 10MPa to 20MPa to 30MPa, and the pressure is maintained for 3-5 minutes each time, so as to cause the outer layer masterbatch melt to penetrate into the inner layer micropores to form a mechanical interlocking structure; S33, keeping the mold in a half-open state, cooling to 100-110°C at a rate of 5-8°C / min, so that a gradient transition layer is formed at the interface between the outer polyurethane layer and the inner jacket, so as to obtain a composite jacket.

7. The method for injection molding of a polyurethane sheath according to claim 1, characterized in that: The step S4 specifically comprises the following steps: S41, transferring the composite jacket together with the injection mold as a whole to a cooling chamber, wherein a dual-channel system of air cooling and liquid cooling is pre-installed in the cooling chamber; S42, start the air cooling channel to perform forced convection cooling on the outer surface of the composite jacket at a first rate of 10-15°C / min for 8-12 minutes until the temperature drops to 80-90°C; S43, switch to the liquid cooling channel, circulate and inject liquid cooling medium into the mold, control the medium flow rate, and cool down to 50-60°C at a rate of 5-8°C / min to preliminarily cool the composite jacket.

8. The method for injection molding of a polyurethane sheath according to claim 7, characterized in that: After step S43, the following steps are further included: S44, demolding the composite jacket after preliminary cooling from the injection mold and transferring it to a constant temperature stress relaxation chamber, maintaining the constant temperature at 40-50° C. for 20-30 minutes, and simultaneously applying an axial tensile load; S45, start the slow cooling program, cool the jacket from 50°C to 25°C at a second rate of 2-3°C / min, and at the same time uniformly apply 0.5-1MPa external pressure constraint along the circumference of the jacket to eliminate the internal stress between layers, so as to obtain a cooled composite jacket.

9. The method for injection molding of a polyurethane sheath according to claim 1, characterized in that: The step S5 specifically comprises the following steps: S51, placing the cooled composite jacket on a rotating testing platform, and synchronously scanning the surface topography along the axial and circumferential directions of the jacket by a laser scanner to generate three-dimensional point cloud data; S52, starting the ultrasonic detector to perform tomographic imaging of the microporous buffer layer and the gradient transition layer inside the sheath, detecting the pore size distribution, interlayer bonding interface defects and porosity deviation, and obtaining ultrasonic imaging data; S53, inputting the three-dimensional point cloud data and the ultrasonic imaging data into the deep learning model, identifying the types and locations of cracks, bubbles, and delamination defects, and marking the defect levels to generate defect analysis results; S54, based on the defect analysis result, generating dynamic correction values ​​of injection pressure, temperature and cooling rate through parameter compensation algorithm, so as to correct them into injection process parameters and associate them with the next batch production instruction; S55, import the corrected injection molding process parameters into the injection molding control system in real time, synchronously update the injection molding process curves of the inner layer masterbatch and the outer layer masterbatch, and complete the closed-loop process optimization.

10. An injection molding system for a polyurethane sheath, characterized in that: The method for implementing the injection molding of the polyurethane sheath according to any one of claims 1 to 9, wherein the injection molding system specifically comprises: The material pretreatment module includes a vacuum mixer, a twin-screw extruder and a masterbatch sorting device, which is used to prepare modified polyurethane masterbatch and separate the inner layer masterbatch and the outer layer masterbatch; An injection mold, used for realizing sequential injection molding of the composite sheath, and integrating an inner microporous buffer layer and an outer gradient transition layer on the composite sheath; Dynamic cooling module, including cooling cabin, constant temperature stress relaxation chamber and external pressure restraint device, supports phased gradient cooling and directional stress release; Optical inspection equipment, used to inspect the surface and internal defects of the composite jacket after cooling; The injection molding control system is used to control the injection molding process and dynamically correct the injection molding process parameters according to the detection data of the optical detection device.

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