Preparation method of high-torsion-resistance special cable

Abstract

The invention relates to the technical field of cable manufacturing, and discloses a preparation method of a high-torsion-resistance special cable, which comprises the following steps of: when a cable insulating layer is in a critical plastic state, synchronously applying a circumferential shear force field and cooling through a dynamic unit so as to construct and lock a macromolecular chain microstructure oriented along the circumferential direction on line, and simultaneously forming a high-torsion-resistance special cable. A dynamic unit is used as a sensor to monitor the dielectric property in the phase change process of the insulating layer in real time, and process parameters are adjusted in a closed-loop feedback mode on the basis of the monitoring result, the micromorphology of the insulating layer is actively reconstructed on line, and a molecular chain disordered freezing structure caused by traditional rapid cooling is changed into an unordered freezing structure. According to the invention, the tensile strength of the cable is changed into an ordered toughness system which is arranged along the circumferential direction and can dissipate stress energy through internal slippage, so that the torsional fatigue resistance mechanism of the cable is qualitatively changed, and the closed-loop regulation and control of the microstructure forming process ensure the production consistency of the high performance of the product under different batches of raw materials.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-torsion-resistant special cable, belonging to the field of cable manufacturing technology. Background Technology

[0002] Currently, in the industrial production of insulated cables, the continuous cooling process after melt extrusion is the foundation for ensuring high-efficiency and large-scale manufacturing. By precisely controlling the extrusion molding and rapid cooling of molten polymer materials, it achieves high-speed coating of the conductor and is a commonly used process in current cable manufacturing. From the perspective of polymer physics, when long polymer chains in a molten disordered state are rapidly cooled to below their glass transition temperature, the molecular chains do not have enough time to rearrange and relax. Their microstructure will be frozen in a state of high-energy random entanglement. This phenomenon is an unavoidable physical result inherent in the aforementioned efficient production process.

[0003] However, when these cables are used in demanding applications such as robotic joint automation equipment that require long-term, high-frequency, and large-angle torsion, a hidden cost of the manufacturing process becomes apparent: the disordered molecular chain network frozen inside the insulation material lacks effective internal slippage and cooperative motion capabilities to dissipate stress energy under repeated torsional stress. Stress concentrates at microscopic defects, leading to the initiation of microcracks and ultimately causing fatigue failure of the cable. This failure mechanism originates from the microscopic physical structure of the material and is a long-term reliability risk that is difficult to detect in advance through conventional quality inspection. It directly restricts the service life and safety of special cables in high-end applications.

[0004] To address this challenge, the industry has attempted improvements in two main directions. One approach involves using insulation materials with higher mechanical strength through cross-linking or modification, but this typically comes at the cost of sacrificing the cable's necessary flexibility, contradicting the actual needs of high-torsion applications. The other approach is to reduce production line speed and extend cooling time to promote molecular chain relaxation, but this directly undermines production efficiency, a core advantage of the process, making it economically unfeasible. Analysis reveals an inherent contradiction in existing technologies: the rapid cooling process upon which high-speed production relies is precisely the root cause of the insulation layer's microstructure fragility, creating an engineering dilemma where both aspects are difficult to reconcile. Specifically, existing technologies suffer from the following shortcomings: 1. The microstructure of the insulation layer is a product of passive, random cooling, and its morphology cannot be actively controlled or optimized to adapt to specific mechanical stresses; 2. There is a direct and irreconcilable conflict between the cable's long-term torsional reliability and the economic efficiency of the production process; 3. Conventional material reinforcement or process speed reduction approaches introduce new performance or cost shortcomings that are unacceptable in practical applications. Therefore, the technical problem to be solved by this invention is how to actively intervene and guide the molecular chain behavior of the insulating layer during the cooling and solidification process without sacrificing the economic efficiency of the existing high-speed continuous extrusion process, and construct an ordered microstructure that can effectively resist torsional fatigue online. Summary of the Invention

[0005] This invention provides a method for preparing a high-torsion-resistant special cable. Its main purpose is to solve the problem of improving the long-term torsional reliability of the cable by actively controlling the microscopic molecular structure of the insulation layer online while maintaining high-speed continuous production efficiency.

[0006] To achieve the above objectives, the present invention provides a method for preparing a high-torsion-resistant special cable, comprising the following steps:

[0007] Step a: Extrude and coat a layer of molten polymer insulating material onto the conductor to form a cable core with an insulating layer;

[0008] Step b: Guide the cable core into a channel defined by at least two relatively rotatable cooling surfaces;

[0009] Step c: Control the temperature of the insulating layer when it enters the channel, so that it is within the range of 5 to 15 degrees Celsius above the crystallization temperature of the polymer insulating material, and obtain the critical plasticity state of the molecular chain.

[0010] Step d: By rotating the cooling surface relative to each other, a lamina shear force field is formed in the circumference of the insulating layer which is in a critical plastic state. At the same time as the shear force field is formed, the insulating layer is cooled by the cooling surface, so that the polymer chains in the insulating layer are cooled to below the crystallization temperature and solidified and locked in the circumferential orientation structure at the moment when the polymer chains in the insulating layer complete the orientation arrangement in the circumferential direction.

[0011] Step e involves using at least two relatively rotatable cooling surfaces as electrodes to monitor the dielectric properties of the insulating layer in real time during the circumferential orientation and curing locking process.

[0012] Step f, and based on the real-time monitoring results of the dielectric property parameters, adjust at least one of the relative rotational speed difference of the cooling surface and the flow rate of the cooling medium inside the cooling surface.

[0013] Preferably, the step of adjusting based on the real-time monitoring results of dielectric property parameters specifically includes: calculating the time change rate of the dielectric constant of the dielectric property parameter in real time; comparing the real-time value of the time change rate with the target change rate curve obtained by performing the same preparation steps on a standard sample to obtain a deviation signal; and performing calculations based on the deviation signal using a proportional-integral-derivative controller to determine the adjustment amount of at least one of the relative rotational speed difference and the flow rate of the cooling medium.

[0014] Preferably, after the polymer chains in the insulation layer are solidified and locked to form the circumferential orientation structure, and before the insulation layer is completely cooled and solidified, the method further includes applying an axial tensile force to the cable core wire. The axial tensile force is generated by passing the cable core wire sequentially through a pair of traction rollers with a speed difference, so as to superimpose the axial molecular chain orientation on the basis of the formed circumferential orientation structure.

[0015] Preferably, real-time monitoring further includes monitoring the dielectric dissipation factor of the insulating layer; and the adjustment step further includes: when it is determined that a parasitic crystal form is being generated in the insulating layer, superimposing torsional micro-vibrations with a frequency of 100 Hz to 500 Hz during the relative rotation of at least two cooling surfaces.

[0016] Preferably, the step of determining that a parasitic crystal form is being generated in the insulating layer specifically includes: calculating the normalized process of the insulating layer crystallization process based on the real-time monitoring value of the dielectric constant; calculating a dynamic threshold proportional to the remaining process of the crystallization process based on the normalized process; and determining that a parasitic crystal form is being generated when the real-time monitoring value of the dielectric dissipation factor is less than the dynamic threshold.

[0017] Preferably, the step of using at least two cooling surfaces as electrodes specifically involves: dividing at least one of the cooling surfaces into multiple independent sector electrodes evenly distributed in the circumferential direction; monitoring the dielectric property parameters between each independent sector electrode and the other cooling surface to obtain a set of parameters characterizing the circumferential distribution of the insulating layer wall thickness; and superimposing torsional micro-vibrations specifically involves: applying torsional micro-vibrations of different amplitudes to different positions in the circumferential direction of the insulating layer by controlling piezoelectric ceramic actuators mounted on the back of the independent sector electrodes, based on the set of parameters.

[0018] Preferably, the step of applying torsional micro-vibrations of different amplitudes to the insulating layer at different positions in the circumferential direction specifically involves: applying a first vibration with a relatively large amplitude to the independent sector electrode corresponding to the thinnest wall position indicated by a set of parameters; and applying a second vibration with a smaller amplitude to the independent sector electrode corresponding to the thickest wall position indicated by a set of parameters.

[0019] Preferably, the polymer insulating material is a polyolefin material containing polypropylene or polyethylene.

[0020] Preferably, the circumferential orientation structure is a tandem crystal structure arranged regularly along the circumferential direction.

[0021] Preferably, the shear force field is a laminar flow field generated inside the insulation layer through the Coulter flow principle.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. During the cooling and solidification process after the cable insulation layer is extruded, a set of relatively rotatable cooling surfaces couples the application of the circumferential shear force field with the cooling process of the insulation layer in time and space. This process allows the orientation and alignment of the molecular chains of the polymer melt to occur synchronously with the solidification and locking behavior of the structure within a specific window close to the crystallization temperature. This results in the formation of an ordered structure arranged circumferentially within the insulation layer, which facilitates the dissipation of torsional stress through microscopic slip. Compared to the physical reality of disordered freezing of molecular chains due to rapid cooling in traditional high-speed production, this invention establishes a method for online reconstruction of the microstructure of the insulation layer. This makes the long-term torsional fatigue reliability of the cable no longer solely dependent on the chemical bond strength of the material itself, but rather on a actively constructed physical structural system.

[0024] 2. This invention further reuses a pair of rotating surfaces that provide shearing and cooling functions as two electrodes of a coaxial capacitor for real-time monitoring of the dielectric properties of the insulating layer during the phase transition process. The evolution of the material's microstructure is transformed into a continuous and measurable electrical signal, which is used to adjust the rotational speed difference or the flow rate of the cooling medium. This establishes a closed-loop tuning path from the actual microstructure formation state to the macroscopic process control parameters, enabling the preparation process to autonomously cope with changes in the process window caused by the melt index or crystallization point drift of different batches of raw materials. This avoids microstructure inconsistencies or performance discounts caused by material state mismatch under fixed parameters, allowing the preparation process to compensate for the characteristic differences of different batches of raw materials and control the performance fluctuations of the final product within a specific range.

[0025] 3. After completing the circumferential molecular chain orientation and before the insulation layer has completely cooled and solidified, a small axial stretch is applied to the cable core wire. This adds axial orientation to the already formed circumferential ordered structure, creating a multi-axial reinforced micro-network similar to an oblique mesh to cope with the combined stress scenarios of torsion and bending. Simultaneously, throughout the process, the generation of non-ideal parasitic crystal forms is identified by monitoring the characteristic changes of the dielectric dissipation factor. After identification, high-frequency micro-vibrations are superimposed on the smooth movement of the rotating surface to quench the fragile crystal forms that are still unstable in the newly formed structure. This eliminates microscopic brittle defects in the material that may lead to stress concentration and crack initiation without disturbing the overall orientation structure, thus achieving online assurance of the correctness of the final product's microstructure. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process flow for online construction of microstructures according to the present invention;

[0027] Figure 2 This is a graph showing the change in dielectric parameters for online determination of parasitic crystal form in this invention.

[0028] Figure 3 This is a schematic diagram of the closed-loop feedback control system architecture of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] This invention provides a method for preparing a high-torsion-resistant special cable. The process mainly consists of steps including conductor insulation coating and critical state pretreatment, dynamic shear cooling and orientation structure construction, and online monitoring and closed-loop feedback control. In the conductor insulation coating and critical state pretreatment step, an insulating material layer at a specific melting temperature range is formed on the outside of the conductor through an extrusion process. Subsequently, in the dynamic shear cooling and orientation structure construction step, the cable core with the insulating layer is introduced into a processing unit. This unit simultaneously applies a circumferential shear force field and cooling to induce the polymer chains inside the insulation layer to form an ordered circumferential arrangement and solidify instantaneously. Finally, in the online monitoring and closed-loop feedback control step, the preparation system utilizes the structure of the processing unit as a sensor to monitor the physical property parameters of the insulation layer during the phase transition process in real time. The monitoring results are used to adjust the aforementioned key process parameters of shearing and cooling to maintain the stability of the orientation structure forming process.

[0031] In applications requiring high-frequency, large-angle torsion, the disordered entanglement of molecular chains within the insulation layer due to conventional rapid cooling makes it prone to microcrack initiation under repeated stress, leading to fatigue failure. To improve the torsional fatigue resistance of the insulation layer, the preparation steps of this method are as follows: First, step a is performed, where a layer of molten polymer insulation material is extruded and coated onto the conductor using a cable extruder to form the cable core. The polymer insulation material can be a polyolefin material containing polypropylene or polyethylene. Then, step b is performed, where the cable core is inserted into a container consisting of at least two... In the channel defined by the relatively rotating cooling surface, the channel can be composed of two coaxially arranged rings with highly polished metal inner walls and a cooling medium circulation channel. The cable core passes through its axis. This design, based on the Cuyet flow principle, generates a laminar shear force field inside the insulation layer in subsequent steps. To ensure that the applied shear force field effectively induces molecular chain orientation, operation needs to be performed within a temperature window where the molecular chains have sufficient mobility but are about to begin crystallization; this state is called the critical plasticity state. For this purpose, this method performs step c, adjusting the distance between the extruder head and the channel inlet. The distance or auxiliary temperature control device is used to control the temperature of the insulating layer when it enters the channel, keeping it within the range of 5 to 15 degrees Celsius above the crystallization temperature of the polymer insulating material. This temperature range is chosen because if the temperature is above the upper limit, the molecular chains undergo intense thermal motion, and the shear field is insufficient to overcome their disordered tendency. Conversely, if the temperature is below the lower limit, the material has already begun rapid crystallization, its fluidity decreases, and applying shear will destroy the already formed crystalline structure. Therefore, 5 to 15 degrees Celsius is a working window that ensures the molecular chains can respond to the shear force field while facilitating rapid structural locking. In step d, the system controls the relative rotation of the cooling surfaces, for example, the outer ring rotates at a speed of 10 rpm and the inner ring rotates at a slower speed of 9.5 rpm in the opposite or same direction. A lamina shear force field is formed in the circumferential direction of the insulating layer, which is in a critical plastic state. At the same time as the shear force field is formed, the insulating layer is cooled by the cooling medium inside the cooling surface. After the polymer chains in the insulating layer complete the orientation and alignment along the circumferential direction, their temperature drops below the crystallization temperature, thereby solidifying and locking the circumferential orientation structure. In terms of morphology, this structure can be a circumferentially regularly arranged tandem crystal structure.

[0032] In continuous production, the melt index or crystallization point of different batches of raw materials may vary. Using fixed process parameters would cause deviations from the temperature window of the critical plastic state. To address material parameter variations and ensure consistent product performance, this method further executes step e, utilizing a pair of rotating surfaces providing shearing and cooling functions as the two electrodes of a coaxial capacitor to monitor the dielectric properties of the insulating layer during orientation and curing in real time. Then, the system executes step f, adjusting at least one of the relative rotational speed difference of the cooling surfaces and the flow rate of the cooling medium inside the cooling surfaces based on the real-time monitoring results of the dielectric properties. The specific procedure for ring adjustment is as follows: calculate the time change rate of dielectric constant dC / dt in real time; compare the real-time value of this time change rate with a target change rate curve obtained by performing the same preparation steps on a standard sample to obtain a deviation signal; and based on the deviation signal, perform calculations through a proportional-integral-derivative controller to determine the adjustment amount of at least one of the relative rotation speed difference and the cooling medium flow rate. For example, when the real-time value of dC / dt is detected to be higher than the target curve, it indicates that the crystallization rate is too fast. The controller outputs a signal to slightly increase the relative rotation speed difference or decrease the cooling medium flow rate until the real-time value of dC / dt returns to the target curve.

[0033] Before mass production, an offline calibration procedure for the control system parameters must be performed. This procedure first establishes electrical and thermal references, that is, with no cable cores passing through, the cooling medium is circulated until the cooling surface temperature stabilizes within ±0.1 degrees Celsius of the process set value, and the reference capacitance value C under no-load is recorded at this time. base This is used to offset the dielectric constant measurement value in subsequent production; subsequently, a specific batch of standard polymer insulating material is selected, and a complete dynamic shear cooling and orientation structure construction process is performed on the experimental platform. Dielectric constant data C(t) from the initial molten state to complete solidification is continuously collected at a sampling rate of no less than 100 Hz. By numerically differentiating this standard C(t) curve, a standard dielectric constant time-varying curve dC / dt| is obtained. standard This curve is embedded in the central integrated control system and serves as the target setpoint curve tracked by the PID controller in subsequent production. The proportional, integral, and derivative gain parameters of the PID controller are tuned by performing a step response test on this experimental platform. That is, during the closed-loop operation of the control system, a step input signal is given to the cooling medium flow rate or relative speed difference, and the three gain parameters are repeatedly adjusted until the overshoot of the real-time value of dC / dt output by the system to the target setpoint curve is less than 5% and there is no steady-state error. The key parameters in the additional steps such as parasitic crystal form determination and multi-axis enhancement are also determined through a set of standardized experimental procedures. Among them, the dynamic threshold formula T used to determine the parasitic crystal form is... δThe coefficient k in =k(1-α(t)) is calibrated as follows: During the stable processing of standard samples using a tuned PID controller, a pulse disturbance with an amplitude of 20% and a duration of 1 second is applied to the cooling medium flow rate in the middle of the crystallization process. The dielectric dissipation factor tanδ(t) and dielectric constant C(t) during this period are recorded simultaneously. After the experiment, a cable sample is taken at the disturbance time point, and the precise time t at which the parasitic crystal form begins to form is determined by polarized light microscopy analysis. fault Using the measured data at that moment, namely the dielectric dissipation factor tanδ(t) fault ) and based on the synchronously measured C(t) fault The normalized process α(t) calculated fault ), through k = tanδ(t) fault ) / (1-α(t fault The value of coefficient k is calculated from the relationship between the axial tension step and the speed ratio of the outlet and inlet traction rollers. Multiple sets of samples with different speed ratios are prepared and tested on a composite fatigue testing machine that can simultaneously apply torsion and bending. The average failure cycle number of each set of samples is recorded and compared, and the ratio that results in the highest failure cycle number is selected as the production process parameter.

[0034] In scenarios where the cable is subjected to both torsional and bending stresses, to disperse the axial tensile stress caused by bending, this method, after the polymer chains within the insulation layer are solidified and locked to form a circumferential orientation structure, and before the insulation layer has completely cooled and solidified, further includes applying an axial tensile force to the cable core. This axial tensile force is generated by sequentially passing the cable core through a pair of traction rollers with a speed difference. For example, the speed of the inlet traction roller is V1, and the speed of the outlet traction roller is V2, where V2 is set to be 1.005 to 1.02 times V1. This operation superimposes an axial molecular chain orientation onto the already formed circumferential orientation structure. During crystallization, in addition to the desired orientation structure, parasitic crystal forms such as brittle spherulites may also be generated. To suppress the formation of such structures online, the real-time monitoring of this method also includes monitoring the dielectric dissipation factor of the insulation layer and setting a parasitic crystal form determination step. The procedure is as follows: based on the real-time monitoring value of the dielectric constant, the normalized process α(t) of the crystallization process is calculated; then, based on this normalized process, a dynamic threshold T is calculated. δ= k(1-α(t)), where k is a coefficient calibrated by standard sample experiments; when the real-time monitoring value of the dielectric dissipation factor is less than the dynamic threshold, it is determined that a parasitic crystal form is being generated; once the parasitic crystal form is determined to be generated, the adjustment steps further include: in the relative rotation of at least two cooling surfaces, a torsional micro-vibration with a frequency of 100 Hz to 500 Hz is superimposed by a servo motor, which is used to destroy the crystal nuclei of the still unstable parasitic crystal form; considering that conductor eccentricity may occur in the extrusion process, resulting in uneven insulation layer wall thickness, so that a uniform process field acts on an uneven object, this method also provides an alternative implementation method; in this method, the step of using at least two cooling surfaces as electrodes specifically involves: dividing at least one of the cooling surfaces into multiple independent sector electrodes evenly distributed in the circumferential direction; respectively The dielectric properties between each independent sector electrode and another cooling surface are monitored to obtain a set of parameters characterizing the circumferential distribution of the insulating layer wall thickness. The superimposed torsional micro-vibration step is adjusted accordingly: based on these parameters, piezoelectric ceramic actuators mounted on the back of each independent sector electrode are controlled to apply torsional micro-vibrations of different amplitudes to different positions of the insulating layer in the circumferential direction. The compensation logic is as follows: a first vibration with a relatively large amplitude is applied to the independent sector electrode corresponding to the thinnest position indicated by the parameters; simultaneously, a second vibration with a smaller amplitude than the first vibration is applied to the independent sector electrode corresponding to the thickest position indicated by the parameters. Through this differentiated vibration application, the molecular chain orientation state of the local area is adjusted to counteract the influence of uneven wall thickness on the uniformity of the final product performance.

[0035] A method for preparing a high-torsion-resistant special cable, wherein the polymer insulation material is a polyolefin composite material, and the components and their weight percentage contents are as follows: highly crystalline polypropylene: 60%-80%; polyolefin elastomer: 15%-35%; maleic anhydride-grafted polypropylene: 3%-8%; composite antioxidant: 0.3%-0.7%. Highly crystalline polypropylene, as the continuous phase matrix of the composite material, provides the necessary rigidity, heat resistance, and dimensional stability for the insulation layer. The string-crystal structure formed in the subsequent dynamic shear cooling step forms the skeleton of the circumferentially oriented ordered toughness system. When its content is less than 60%, the overall modulus and heat resistance of the composite material are insufficient. It is difficult to maintain a stable geometry during extrusion and subsequent processing; when its content is higher than 80%, the brittleness of the material increases significantly, and the flexibility decreases. Under repeated torsional stress, the initiation and propagation rate of internal microcracks accelerates. Polyolefin elastomers, as dispersed or cocontinuous phases, form micro-regions in the polypropylene matrix to absorb and dissipate externally applied torsional stress energy, and are the core functional components for improving the toughness and fatigue resistance of the material. When its content is lower than 15%, the size or quantity of the dispersed phase is too small, which cannot effectively prevent crack propagation, and the improvement in the impact and torsional resistance of the material is not significant. When its content is higher than 35%, the overall strength of the composite material is affected. Excessive decrease in hardness can lead to permanent deformation of the insulation layer in practical applications, and reduced melt strength may cause instability in the extrusion process. Maleic anhydride-grafted polypropylene, as a compatibilizer, exhibits physical compatibility between the polypropylene segments in its molecular chain and the matrix, while the maleic anhydride functional groups interact with the polyolefin elastomer molecules, forming an effective bond at the interface between the matrix and elastomer phases, reducing interfacial tension. When its content is below 3%, the interfacial bonding is weak, and the interface is prone to debonding under stress, leading to deterioration of the material's mechanical properties. When its content is above 8%, the compatibilization effect is saturated, and excessive compatibilizer will form its own agglomerates, becoming internal defects in the material. Furthermore, it does not unnecessarily increase material costs. The composite antioxidant, composed of hindered phenolic primary antioxidants and phosphite auxiliary antioxidants, is used to capture free radicals generated during the melt processing and long-term use of polymer materials, inhibiting the thermo-oxidative aging and degradation of the materials. Using the aforementioned polyolefin composite material and the above preparation method, in the dynamic shear cooling and orientation structure construction steps, the compatibilizer allows the polyolefin elastomer phase to be stretched and refined into circumferentially arranged microfibers or lamellar structures under a high shear field, interpenetrating with the simultaneously formed polypropylene string crystal skeleton. After curing, a two-phase co-continuous interpenetrating network structure with high circumferential orientation is formed. This structure unifies stress dispersion capability and load-bearing stiffness, providing the microstructural basis for the high torsional fatigue life of the final cable product.

[0036] Example 1: In an automated cleanroom environment for high-precision wafer handling, the wrist cable of a six-axis industrial robot needs to perform large-angle torsional and bending composite movements of more than 50 times per minute (±180 degrees) within a confined space. Cables manufactured using conventional processes on the production line experience fatigue cracking of their insulation layers after a certain service life, leading to signal interruptions and production stoppages. This is especially true after replacing the polyolefin insulation material with a new batch, resulting in significant and irregular fluctuations in the cable's service life. To address this situation, a high-torsion-resistant special cable is prepared using the method disclosed in the aforementioned specific embodiment. During production, polyethylene insulation material from a new batch is extruded and coated onto the conductor. Before the formed cable core enters a channel defined by two relatively rotatable cooling surfaces, its surface temperature is controlled to be 10 degrees Celsius above the material's crystallization temperature. When the cable core passes through this channel... The online monitoring and closed-loop feedback control steps are activated. By using the cooling surface as an electrode to monitor the dielectric constant of the insulating layer in real time, the control system calculates the real-time value of the dielectric constant change rate dC / dt and detects a deviation between this value and the target change rate curve established from the historical data of the standard sample. This indicates that the crystallization kinetics of the current batch of materials has drifted. Based on this deviation signal, the proportional-integral-derivative controller immediately adjusts the relative rotational speed difference of the cooling surface from 5.0 rpm to 5.2 rpm, and simultaneously reduces the flow rate of the cooling medium by 3%. This allows the circumferential shear force field and cooling rate in the dynamic shear cooling step to be rematched, thereby ensuring that even if the raw material properties fluctuate, the orientation induction and solidification locking of the molecular chains can still occur within the critical plasticity window corresponding to this batch of materials. Ultimately, a circumferentially regular chain crystal structure is formed in the insulating layer.

[0037] This preparation process does not reduce the operating speed of the production line. By simultaneously performing shear induction and cooling solidification, this method constructs an ordered molecular arrangement structure while maintaining high-speed production, thus addressing the technical constraint that high-speed production usually leads to a decrease in product durability. The online monitoring and closed-loop feedback control steps provide real-time process parameter benchmarks for the execution of the dynamic shear cooling structure construction step, while the execution of the dynamic shear cooling step provides the monitoring system with analyzable phase transition signals. The synergistic effect of these two steps transforms an open-loop production process dependent on the stability of raw materials into a closed-loop manufacturing method that can be adjusted according to the real-time state of the material. When the cable prepared by this method is installed on the wrist of a six-axis industrial robot and its continuous operation at high frequency and large angles is restored, the electrical performance and mechanical integrity of the cable remain stable after a long period of continuous operation. Its cumulative torsion count exceeds that of previously used conventional cables by several times. Furthermore, when subsequent cables of the same specification produced from different batches of raw materials are used, their service life shows a high degree of consistency, and the number of unplanned downtimes on the production line is correspondingly reduced.

[0038] Example 2: To objectively verify the influence of the preparation method of the present invention on the torsional fatigue resistance of the cable, and to confirm the effectiveness of the critical plastic state temperature range when the insulation layer enters the channel, the following comparative test was conducted. The test used a dynamic shear cooling experimental platform with independent temperature control and speed adjustment functions. This platform was connected in series after the standard cable extrusion production line. Its core components are two coaxial cooling rings that can rotate relative to each other, and it integrates electrodes and a data acquisition system for real-time monitoring of dielectric properties. The prepared cable samples were uniformly tested using a torsional fatigue testing machine. This testing machine can apply ±180 degrees of torsion to the sample at a frequency of 1 Hz, and automatically record the cumulative number of torsions when the sample experiences electrical failure.

[0039] Polypropylene of grade T30S was selected as the insulating material in the experiment, and its crystallization temperature measured by differential scanning calorimetry was 115℃. One sample group and four control groups were set up. Except for specific process parameters, all other conditions such as extrusion speed and conductor specifications were kept consistent across all sample groups. The preparation of the sample group followed the complete method disclosed in the specific implementation method, namely, dynamic shear cooling with online monitoring and closed-loop feedback control enabled, and the temperature of the insulating layer entering the channel was set to 125℃, which is 10℃ above the crystallization temperature. Control group A differed from the sample group in that it disabled the online monitoring and closed-loop feedback control functions, using a fixed relative speed difference and cooling medium flow rate for open-loop production, with the inlet temperature also set at 125℃. Control group B was prepared using a conventional high-speed extrusion followed by rapid water cooling and shaping process, without applying any circumferential shear force field. Control groups C and D were used to verify the temperature range. The preparation method of the intermediate boundary is basically the same as that of the sample group of the present invention, but the inlet temperature is set to 117°C, which is 2°C above the crystallization temperature, and 135°C, which is 20°C above the crystallization temperature, respectively. The cable samples prepared in the above groups are tested on a torsion fatigue testing machine. Ten samples are taken from each group and their average failure torsion count is recorded. The test results are recorded as follows: the control group B, which uses the conventional rapid cooling process, has an average failure torsion count of 42,000 times; in contrast, the sample group of the present invention, which uses the complete method of the present invention, has an average failure torsion count of 358,000 times; the control group A, which also applies shear cooling but uses open-loop control, has an average failure torsion count of 215,000 times; the control group C, which has an inlet temperature below the lower limit of the defined range, has an average failure torsion count of 151,000 times; and the control group D, which has an inlet temperature above the upper limit of the defined range, has an average failure torsion count of 189,000 times.

[0040] Experimental data show that the torsional life of the sample group of this invention is several times higher than that of the control group B, indicating that the circumferential orientation structure formed by applying a circumferential shear force field and solidifying it is the mechanism for improving the torsional performance of the cable. Simultaneously, the torsional life of the sample group of this invention is also significantly improved compared to the control group A which uses open-loop control, indicating that closed-loop feedback control can compensate for process fluctuations in real time during production, and has a positive effect on forming a more regular and consistent circumferential orientation structure. Furthermore, the performance of control groups C and D is lower than that of the sample group of this invention; the former suffers from excessively low inlet temperature, resulting in poor material orientation. Under sufficient conditions, large-scale crystallization begins. However, due to the excessively high inlet temperature, the thermal motion of the molecular chains weakens the orientation-inducing effect of the shear field. The data from these two sample groups verify the effectiveness of controlling the inlet temperature within the range of 5 to 15 degrees Celsius above the crystallization temperature. The experimental results show that by simultaneously applying a circumferential shear force field and cooling within the critical plasticity temperature range, and supplementing it with online monitoring and closed-loop feedback control, a circumferentially oriented molecular structure can be formed in the insulating layer. Compared with the random structure formed by conventional processes, this structure can withstand a higher number of torsional stresses.

[0041] Example 3: This example combines Figures 1 to 3 The preparation method of a high-torsion-resistant special cable is described, such as... Figure 1 As shown, in this stage, the conductor and polymer insulating material are fed into the extrusion coating and critical state pretreatment unit. A molten insulating layer is formed through precise temperature control, with the temperature controlled within the range of 5°C to 15°C above the crystallization temperature. Subsequently, the cable core enters the dynamic shear cooling and orientation structure construction unit. This unit simultaneously applies circumferential shearing and cooling to construct an ordered micro-chain crystal structure. This core process step is subject to real-time regulation by a closed-loop feedback control module. This control module calculates the time change rate of the dielectric constant based on the dielectric property parameters of the insulating layer collected by an online monitoring module, and adjusts the process parameters through a PID controller. At the same time, the online monitoring module also runs a logic branch in parallel to determine whether parasitic crystal forms are generated. If the determination is yes, a step of superimposed torsional micro-vibration is triggered to quench the fragile crystal forms and remove micro-defects online. After the circumferential structure is constructed, the axial stretching and multiaxial reinforcement steps can be selectively entered. By superimposing axial molecular chain orientation to cope with the composite stress scenario, a high-torsion-resistant special cable product with an ordered toughness system along the circumferential orientation is finally produced.

[0042] like Figure 2 As shown in the figure, the horizontal axis represents the percentage of time progress, the left vertical axis represents the normalized progress, and the right vertical axis represents the dielectric dissipation factor. The three curves in the figure represent the normalized progress α(t), the dielectric dissipation factor tanδ, and the dynamic threshold T, respectively. δAmong them, the normalized process α(t) curve increases linearly from 0 to 1, reflecting the gradual completion of the crystallization process, and the dynamic threshold T δ The curve correspondingly decreases linearly from an initial value to 0, while the dielectric dissipation factor tanδ curve shows a trend of first decreasing and then increasing during the crystallization process. When the real-time monitoring value of tanδ is less than the dynamic threshold T at 44% of the time progress. δ At that time, the system determines that a parasitic crystal form is being generated.

[0043] like Figure 3 As shown, the architecture is centered around a central integrated control system. The system contains a data processing and analysis core module for executing the core algorithm, which is mainly responsible for calculating the dielectric constant time change rate, a PID controller module for adjusting the speed difference and cooling flow rate based on the aforementioned calculation results, and a parasitic crystal form determination module for monitoring the dielectric dissipation factor. The central system retrieves reference data from a process database storing target curves and process parameters, and performs unified command control and parameter adjustment on the cable extruder as the source equipment, the dynamic shear cooling unit as the core process execution hardware, and the axial traction roller group as the downstream equipment.

[0044] Example 4: Before applying the preparation method of this invention to the mass production of a novel polypropylene insulating material, an offline calibration procedure needs to be performed to determine the core control parameters of its online monitoring and closed-loop feedback control system. This procedure is carried out on an experimental platform consistent with the production line process environment. This platform can accurately control the temperature, rotation speed, and cooling rate, and is equipped with a dielectric property parameter acquisition system with a time resolution of 10 milliseconds. To establish a standard crystallization model of this novel material under specific processing conditions, a standard sample is subjected to a complete dynamic shear cooling process on the experimental platform. The inlet temperature is set to 10°C above the crystallization temperature, and the relative rotation speed difference and cooling medium flow rate are set to initial values ​​suitable for this type of material. During this process, the dielectric constant C(t) data is continuously collected from the initial molten state to the fully solidified state. After the data collection is completed, the dielectric constant C of the material in the initial molten state is determined. min The dielectric constant C of the final cured state max Furthermore, the normalized process α(t) of the crystallization process is calculated using the following relationship: α(t) = (C(t) - C min ) / (C max -C min Subsequently, the standard C(t) curve collected this time was numerically differentiated to obtain a standard dielectric constant time change rate curve, which was set as the target change rate curve tracked by the PID controller during online production.

[0045] To tune the PID controller parameters, the target rate of change curve obtained above was used as the setpoint of the control system. The Ziegler-Nichols tuning method was employed, and step response tests were conducted on an experimental platform to gradually adjust the proportional, integral, and derivative gain parameters until the system output could respond to changes in the setpoint with an overshoot of less than 5%. This set of gain parameters was then fixed into the online control system. To calibrate the dynamic threshold coefficient k used for parasitic crystal form determination, a process disturbance was introduced based on the stable processing using the previously tuned PID controller. Specifically, during the middle stage of the crystallization process, the flow rate of the cooling medium was instantaneously increased by 20% and maintained for 1 second. During this disturbance experiment, the dielectric constant C(t) and dielectric dissipation factor tanδ(t) were recorded simultaneously. After the experiment, a cable sample was taken at this time point, and structural analysis was performed using a polarizing microscope to determine the moment t when the parasitic crystal form began to form. fault Using the measured data at that moment, namely the dielectric dissipation factor tanδ(t) fault ) and based on the synchronously measured C(t) fault The normalized process α(t) calculated fault ), through k = tanδ(t) fault) / (1-α(t fault The relationship between the two is used to calculate the value of coefficient k. By executing the above offline calibration procedure, the target rate of change curve, PID controller gain parameters and parasitic crystal dynamic threshold coefficient k are obtained and then deployed to the control system of the formal production line as process data for subsequent production.

[0046] Example 5: When the cable is used in a composite stress condition that simultaneously withstands high-frequency torsion and large-radius bending, the speed difference of the traction rollers needs to be set. Specifically, while keeping other manufacturing process parameters constant, the speed ratios of the outlet and inlet traction rollers are set to 1.005, 1.010, 1.015, and 1.020, respectively, to prepare four sets of cable samples. Subsequently, these four sets of samples are placed on a composite fatigue testing machine that can simultaneously apply ±180-degree torsion and 90-degree bending for testing. After recording the average failure cycles of each set of samples, it was found that the sample group with a speed ratio of 1.015 had the highest average failure cycles. Therefore, 1.015 was determined as the production process parameter for this application scenario.

[0047] In addition, to compensate for conductor eccentricity during extrusion, the amplitude of torsional micro-vibration applied at different locations needs to be calibrated. After the online monitoring system measures a set of dielectric characteristic parameters indicating a 10% difference in insulation layer wall thickness in the circumferential direction using independent sector electrodes, the calibration procedure is initiated. First, an initial differentiated vibration scheme is set, that is, a vibration with a reference amplitude of 120% is applied to the piezoelectric ceramic actuator corresponding to the thinnest wall thickness position, and a vibration with a reference amplitude of 80% is applied to the thickest wall thickness position. The cable samples prepared with these parameters are subjected to fatigue testing, and their failure locations are observed. If the failure points are still concentrated at the original thinnest wall thickness position, the amplitude difference is gradually increased until the fatigue failure points of the samples in the whole life cycle test are randomly distributed in the circumferential direction. Finally, the differentiated vibration amplitude parameters associated with the 10% wall thickness difference corresponding to this random distribution state are stored in the process database of the production line control system.

[0048] Example 6: To provide an accurate measurement benchmark for the online monitoring and closed-loop feedback control system during continuous production, a baseline model construction and calibration procedure needs to be performed before the task starts. This procedure first establishes a thermal equilibrium state. With no cable core wires passing through, the control system drives the cooling medium to circulate inside at least two relatively rotatable cooling surfaces until the temperature sensor reading installed inside the cooling surface stabilizes within the range of ±0.1°C of the process set value and remains so for more than 1 minute.

[0049] After thermal equilibrium is established, the system immediately constructs and verifies the electrical baseline model; with air as the medium between the cooling surfaces, the reference capacitance value C is measured and recorded at this moment. base And compare it with the reference capacitance value C stored during the initial commissioning of the equipment. ref The system compares the two values; if the difference exceeds a preset threshold of 0.5%, the system stops the production task and prompts for equipment maintenance; if the difference is within the threshold range, the system sets the difference C. offset =C base -C ref As a real-time capacitance bias parameter, this bias value is subtracted from all real-time monitored dielectric constant measurements during subsequent formal production processes to compensate for measurement baseline drift caused by long-term equipment operation or environmental changes.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high-torsion-resistant special cable, characterized in that, Includes the following steps: Step a: Extrude and coat a layer of molten polymer insulating material onto the conductor to form a cable core with an insulating layer; Step b: Guide the cable core into a channel defined by at least two relatively rotatable cooling surfaces; Step c: Control the temperature of the insulating layer when it enters the channel, so that it is within the range of 5 to 15 degrees Celsius above the crystallization temperature of the polymer insulating material, and obtain the critical plasticity state of the molecular chain. Step d: By rotating the cooling surface relative to each other, a lamina shear force field is formed in the circumference of the insulating layer which is in a critical plastic state. At the same time as the shear force field is formed, the insulating layer is cooled by the cooling surface, so that the polymer chains in the insulating layer are cooled to below the crystallization temperature and solidified and locked in the circumferential orientation structure at the moment when the polymer chains in the insulating layer complete the orientation arrangement in the circumferential direction. Step e involves using at least two relatively rotatable cooling surfaces as electrodes to monitor the dielectric properties of the insulating layer in real time during the circumferential orientation and curing locking process. Step f, and based on the real-time monitoring results of the dielectric property parameters, adjust at least one of the relative rotational speed difference of the cooling surface and the flow rate of the cooling medium inside the cooling surface.

2. The method for preparing a high-torsion-resistant special cable according to claim 1, characterized in that, The adjustment steps based on the real-time monitoring results of dielectric property parameters are as follows: the time change rate of the dielectric constant of the dielectric property parameter is calculated in real time; the real-time value of the time change rate is compared with the target change rate curve obtained by performing the same preparation steps on the standard sample to obtain a deviation signal; and based on the deviation signal, a proportional-integral-derivative controller is used to calculate to determine the adjustment amount of at least one of the relative rotational speed difference and the flow rate of the cooling medium.

3. The method for preparing a high-torsion-resistant special cable according to claim 1, characterized in that, After the polymer chains within the insulation layer are solidified and locked to form the circumferential orientation structure, and before the insulation layer is completely cooled and solidified, the process includes applying an axial tensile force to the cable core. The axial tensile force is generated by passing the cable core sequentially through a pair of traction rollers with a speed difference, so as to superimpose the axial molecular chain orientation on the basis of the formed circumferential orientation structure.

4. The method for preparing a high-torsion-resistant special cable according to claim 1, characterized in that, Real-time monitoring also includes monitoring the dielectric dissipation factor of the insulating layer; and the adjustment steps also include: when it is determined that a parasitic crystal form is being generated in the insulating layer, superimposing torsional micro-vibrations with a frequency of 100 Hz to 500 Hz during the relative rotation of at least two cooling surfaces.

5. The method for preparing a high-torsion-resistant special cable according to claim 4, characterized in that, The steps for determining that a parasitic crystal form is being formed in the insulating layer are as follows: based on the real-time monitoring value of the dielectric constant, the normalized process of the insulating layer crystallization process is calculated; based on the normalized process, a dynamic threshold proportional to the remaining process of the crystallization process is calculated. When the real-time monitoring value of the dielectric dissipation factor is less than the dynamic threshold, it is determined that a parasitic crystal form is being generated.

6. The method for preparing a high-torsion-resistant special cable according to claim 4, characterized in that, The step of using at least two cooling surfaces as electrodes specifically involves: dividing at least one of the cooling surfaces into multiple independent sector electrodes evenly distributed in the circumferential direction; monitoring the dielectric property parameters between each independent sector electrode and the other cooling surface to obtain a set of parameters characterizing the circumferential distribution of the insulating layer wall thickness; and superimposing torsional micro-vibrations, specifically involving: applying torsional micro-vibrations of different amplitudes to different positions in the circumferential direction of the insulating layer by controlling piezoelectric ceramic actuators mounted on the back of the independent sector electrodes, based on the set of parameters.

7. The method for preparing a high-torsion-resistant special cable according to claim 6, characterized in that, The steps of applying torsional micro-vibrations of different amplitudes to different positions of the insulating layer in the circumferential direction are as follows: applying a first vibration with a relatively large amplitude to the independent sector electrode corresponding to the thinnest position indicated by a set of parameters; and applying a second vibration with a smaller amplitude to the independent sector electrode corresponding to the thickest position indicated by a set of parameters.

8. The method for preparing a high-torsion-resistant special cable according to claim 1, characterized in that, Polymer insulating materials are polyolefin materials containing polypropylene or polyethylene.

9. The method for preparing a high-torsion-resistant special cable according to claim 1, characterized in that, The circumferential orientation structure is a tandem crystal structure arranged regularly along the circumferential direction.

10. The method for preparing a high-torsion-resistant special cable according to claim 1, characterized in that, The shear force field is a laminar flow field generated inside the insulation layer through the Coulter flow principle.

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