Rail transit communication cable skin bubble skin co-extrusion water capacity control process

Abstract

This application discloses a water capacitance control process for co-extrusion of the outer sheath of rail transit communication cables, relating to the field of wire and cable manufacturing technology. The process involves: measuring the matrix dielectric constant of the current batch of halogen-free flame-retardant polyolefin material and calculating the target foaming ratio; conducting calibration tests by changing nitrogen injection pressure, mold temperature, and linear velocity; establishing a response surface model and outputting partial sensitivity; determining initial process parameters based on the response surface model to start the production line; measuring the water capacitance online at the cooling water tank outlet and triggering adaptive adjustment through moving average filtering; adjusting the pressure and linear velocity in conjunction when the cumulative adjustment exceeds the limit; synchronously compensating for the outer sheath extrusion rate to maintain compliant sheath thickness; and determining the core's qualification based on the overall water capacitance deviation and sheath thickness. This application solves the problems of long batch change trial cycles, high scrap rates, and uncontrolled sheathing by measuring the matrix dielectric constant and establishing a response surface model to form a quantitative design path.

Description

Technical Field

[0001] This application relates to the field of wire and cable manufacturing technology, specifically a process for controlling the co-extrusion of water capacitors in the blister pack of rail transit communication cables. Background Technology

[0002] Rail transit communication cables, such as Multifunction Vehicle Bus (MVB) cables and Wire Train Bus (WTB) cables, have strict requirements for the consistency of water capacitance of the insulated cores. The EN50306-2 standard specifies a typical water capacitance of 52 pF / m, with an allowable deviation of only ±2 pF / m. To reduce the equivalent dielectric constant of the insulation layer to meet the water capacitance requirements, the industry commonly uses a three-layer co-extrusion process. This involves introducing a physical foaming layer (using high-pressure nitrogen as the foaming medium) into the insulation layer, utilizing the pore structure to reduce the equivalent dielectric constant, thereby controlling the water capacitance value. The foaming ratio (the ratio of pore volume to the total volume of the foaming layer) is the core control variable of this process, influenced by the coupling effect of nitrogen injection pressure, mold temperature, and linear velocity.

[0003] However, existing foam-co-extrusion processes have significant shortcomings in controlling water capacitance. Specifically, they lack a systematic method for quantitatively calculating the foaming ratio from the target water capacitance and then reverse-engineering the process parameters. This is particularly true for halogen-free flame-retardant (HFFR) materials containing a high proportion of magnesium hydroxide inorganic filler, which are essential for rail transit cables. These materials have high melt viscosity, difficulty in bubble nucleation, and significant variations in the dielectric constant due to batch fluctuations in filler. The process parameter system established for ordinary polyethylene cannot be directly transferred, resulting in long parameter exploration cycles and high start-up scrap rates when changing specifications or batches. Furthermore, existing technologies rely solely on offline sampling to detect water capacitance deviations. The time delay from problem occurrence to deviation detection typically exceeds 30 minutes, and the accumulated length of defective products can reach hundreds of meters. Moreover, when correcting foaming ratio deviations by adjusting gas pressure, there is a lack of a coordinated control mechanism to constrain the outer sheath thickness, posing a risk that the outer sheath thickness may fall below the minimum value specified in EN 50306. Summary of the Invention

[0004] The purpose of this application is to provide a control process for co-extrusion of water capacitors in rail transit communication cable blister packs to solve the problems mentioned in the background art.

[0005] In one aspect, an embodiment of this application provides a water capacitance control process for co-extrusion of foam cores for rail transit communication cables. This process includes: measuring the matrix dielectric constant of the current batch of halogen-free flame-retardant polyolefin material; calculating the target foaming ratio that satisfies the target water capacitance value based on the target equivalent dielectric constant corresponding to the target water capacitance value, combined with the volume-average mixing law; using the target foaming ratio as the design target and the halogen-free flame-retardant polyolefin material as the test object, conducting calibration tests by changing the nitrogen injection pressure, mold temperature, and linear velocity; recording the measured foaming ratio under each parameter combination; and establishing a response surface model of the foaming ratio with respect to the three parameters: nitrogen injection pressure, mold temperature, and linear velocity; the response surface model supports forward querying and backward solving, and outputs the partial sensitivity of the foaming ratio to each parameter at the current working point; based on the response surface model, in the parameter solution set that satisfies the target foaming ratio, considering both bubble uniformity and the bonding strength of the skin layer interface, determining the initial nitrogen injection pressure, initial mold temperature, and initial linear velocity for production start-up; and starting the three-layer co-extrusion production line with the initial parameters. After the process stabilizes, online testing begins. Continuous online water capacitance measurement is performed on the insulated core at the outlet of the cooling water tank after extrusion. The obtained water capacitance deviation along the line is filtered using a moving average to obtain the filtered water capacitance deviation. Adjustment is triggered based on the comparison between the filtered water capacitance deviation and a preset threshold. Using partial sensitivity as a basis, adaptive step-size adjustment of the nitrogen injection pressure, proportional to the deviation magnitude, is prioritized. If the filtered water capacitance deviation still does not converge after the cumulative adjustment of the nitrogen injection pressure exceeds the preset upper limit, the inverse solution function of the response surface model is invoked. The nitrogen injection pressure and linear velocity are then adjusted in a dual-variable linkage manner using the minimum adjustment amount as the criterion. Simultaneously with the nitrogen injection pressure adjustment, the volumetric extrusion rate of the outer sheath extruder is compensated synchronously according to a pre-calibrated compensation coefficient to maintain the outer sheath thickness at no less than the specified minimum value. When the linear velocity is adjusted in linkage, the corresponding outer sheath extrusion rate compensation is simultaneously superimposed. Based on the original online water capacitance deviation data and outer sheath thickness detection data throughout the process, the overall cable core is assessed for compliance.

[0006] In conjunction with the first aspect, in certain implementations of the first aspect, the matrix dielectric constant of the current batch of halogen-free flame-retardant polyolefin material is measured. Based on the target equivalent dielectric constant corresponding to the target water capacitance value, and combined with the volume-average mixing law, the target foaming ratio that satisfies the target water capacitance value is calculated in reverse. This includes: measuring the dielectric constant of the current batch of halogen-free flame-retardant polyolefin material using the planar capacitance method at a preset measurement frequency to obtain the matrix dielectric constant of the current batch; determining the target equivalent dielectric constant required for the insulating layer based on the coaxial capacitance relationship according to the target water capacitance value; using the pore dielectric constant and the current batch matrix dielectric constant as known quantities, and based on the volume-average mixing law, calculating the target foaming ratio in reverse from the target equivalent dielectric constant; and re-performing the above measurement and calculation for each new batch of material to eliminate systematic water capacitance deviations caused by material batch fluctuations.

[0007] In conjunction with the first aspect, in some implementations of the first aspect, with the target foaming ratio as the design objective and halogen-free flame-retardant polyolefin material as the test object, calibration tests are conducted by changing the nitrogen injection pressure, mold temperature, and linear velocity. The measured foaming ratio under each parameter combination is recorded, and a response surface model of the foaming ratio with respect to the three parameters of nitrogen injection pressure, mold temperature, and linear velocity is established. This includes: conducting calibration tests on a three-layer co-extrusion mold; taking multiple levels of nitrogen injection pressure, mold temperature, and linear velocity within a preset range for combined tests; recording the corresponding measured foaming ratio under each parameter combination; and simultaneously recording the average bubble diameter, etc. A database of process parameters is formed by considering the standard deviation of bubble size, the bonding strength of the skin interface, and the surface roughness of the insulation layer. Based on this database, a quadratic polynomial response surface model is used to fit the measured foaming ratio, resulting in a response surface model with nitrogen injection pressure, mold temperature, and linear velocity as independent variables. The model is then cross-validated using the hold-out method, requiring that the root mean square error between the predicted and measured values ​​not exceed two percentage points. At the current operating point, the partial sensitivity of the foaming ratio to nitrogen injection pressure, mold temperature, and linear velocity in the response surface model is calculated, and the priority of subsequent parameter adjustments is determined by the magnitude of the partial sensitivity.

[0008] In conjunction with the first aspect, in some implementations of the first aspect, based on the response surface model, within the parameter solution set that satisfies the target foaming ratio, the initial nitrogen injection pressure, initial die temperature, and initial linear velocity for production startup are determined by considering both bubble uniformity and skin-interface bonding strength. The three-layer co-extrusion production line is started with these initial parameters, and online detection begins after the process stabilizes. This includes: in the parameter solution set that satisfies the target foaming ratio output by the response surface model, selecting the parameter region with the smallest bubble size standard deviation and satisfactory skin-interface bonding strength; within the parameter region, selecting the parameter combination where the die temperature is within a preset thermal equilibrium stable range as the initial nitrogen injection pressure, initial die temperature, and initial linear velocity; starting the three-layer co-extrusion production line with the initial nitrogen injection pressure, initial die temperature, and initial linear velocity; marking the product length corresponding to the process parameters stabilizing from the start-up time as the startup transition section; products within the startup transition section are not included in the water capacitance qualification range; and online detection begins after the startup transition section ends.

[0009] In conjunction with the first aspect, in certain implementations of the first aspect, continuous online water capacitance measurement is performed on the insulated wire core at the outlet of the cooling water tank after extrusion. The obtained water capacitance deviation along the line is then filtered by a moving average to obtain the filtered water capacitance deviation. This includes: at the outlet of the cooling water tank after insulation extrusion and before the cabling process, continuous online water capacitance measurement is performed on the insulated wire core using the water immersion contact method. Deionized water is used as the outer electrode and the conductor as the inner electrode. The water capacitance value per unit length of the insulated wire core is continuously measured at a preset measurement frequency. The sampling interval along the length of the wire core does not exceed two meters, resulting in a sequence of water capacitance measurement values ​​along the line. Using the target water capacitance value as a benchmark, the water capacitance deviation is calculated for each sampling point in the sequence of water capacitance measurement values ​​along the line, forming a sequence of water capacitance deviations along the line. The sequence of water capacitance deviations along the line is then filtered by a moving average. The average value of the continuous sampling points is calculated using a preset length as the sliding window, resulting in the filtered water capacitance deviation. The filtered water capacitance deviation is used as the criterion for triggering adjustment, and the original value of the sequence of water capacitance deviations along the line is used as the basis for qualification judgment.

[0010] In conjunction with the first aspect, in certain implementations of the first aspect, adjustment is triggered based on the comparison result of the filtered water capacitor deviation and a preset threshold. Based on partial sensitivity, adaptive step-size adjustment of the nitrogen injection pressure, proportional to the magnitude of the deviation, is prioritized. This includes: setting a first threshold and a second threshold, where the second threshold is greater than the first threshold; maintaining the current process parameters and continuing production when the absolute value of the filtered water capacitor deviation does not exceed the first threshold; triggering nitrogen injection pressure adjustment and sending an alert to the operator when the absolute value of the filtered water capacitor deviation exceeds the first threshold but does not exceed the second threshold; and triggering nitrogen injection pressure adjustment and sending an alert to the operator when the absolute value of the filtered water capacitor deviation exceeds the second threshold. When the threshold is reached, nitrogen injection pressure adjustment is triggered and an out-of-tolerance alarm is pushed to the operator; the direction of foaming ratio offset is determined based on the polarity of the filtered water capacitor deviation, and the adjustment direction of nitrogen injection pressure is determined; based on the partial sensitivity of foaming ratio to nitrogen injection pressure, the step size of each nitrogen injection pressure adjustment is determined to be an adaptive step size proportional to the current filtered water capacitor deviation, and an adaptive gain coefficient is introduced to retain adjustment margin and prevent overshoot; after each nitrogen injection pressure adjustment is executed, a time delay corresponding to the preset product length is waited, the filtered water capacitor deviation is reread, and it is determined whether the filtered water capacitor deviation has converged to within the first threshold.

[0011] In conjunction with the first aspect, in some implementations of the first aspect, when the cumulative adjustment of the nitrogen injection pressure exceeds the preset upper limit and the filtered water capacitance deviation still has not converged, the inverse solution function of the response surface model is invoked to perform bivariate linkage adjustment of the nitrogen injection pressure and linear velocity based on the minimum adjustment amount. This includes: when the absolute value of the cumulative adjustment of the nitrogen injection pressure exceeds the preset upper limit and the filtered water capacitance deviation still has not converged to within the first threshold, the inverse solution function of the response surface model is invoked to output the parameter solution set of nitrogen injection pressure and linear velocity that meet the target foaming ratio under the condition of fixing the current mold temperature; in the parameter solution set, the nitrogen injection pressure is used as the criterion for bivariate linkage adjustment of nitrogen injection pressure and linear velocity. The optimization criterion is to minimize the weighted sum of squares of the normalized force adjustment and linear velocity adjustment. A new combination of nitrogen injection pressure and linear velocity is then calculated, and the new nitrogen injection pressure and linear velocity are simultaneously applied to the nitrogen injection control loop and traction speed control loop of the foaming layer. The adjustment step size of the new linear velocity relative to the current linear velocity does not exceed the preset maximum step size to prevent tension fluctuations caused by sudden changes in linear velocity. After the dual-variable linkage adjustment is executed, a time delay corresponding to the preset product length is waited, and the filtered water capacitance deviation is reread. If the filtered water capacitance deviation still does not converge, the dual-variable linkage adjustment is repeated, and a continuous alarm is sent to the operator.

[0012] In conjunction with the first aspect, in certain implementations of the first aspect, while adjusting the nitrogen injection pressure, the volumetric extrusion rate of the outer skin extruder is simultaneously compensated according to a pre-calibrated compensation coefficient to maintain the outer skin thickness not lower than a specified minimum value. This includes: measuring the actual change in outer skin thickness under different nitrogen injection pressure variations through a prior calibration test; determining the pressure compensation coefficient between the nitrogen injection pressure adjustment and the outer skin extrusion rate compensation through linear regression, based on the calibration relationship of the outer skin extrusion rate; the pressure compensation coefficient varies with the halogen-free flame retardant... The polyolefin outer skin material is recalibrated when the batch is changed; each time the nitrogen injection pressure is adjusted, the nitrogen injection pressure adjustment amount is linearly converted into the outer skin extrusion rate compensation amount according to the pressure compensation coefficient. The control command corresponding to the outer skin extrusion rate compensation amount is preset for a duration longer than the nitrogen injection pressure adjustment command to compensate for the mechanical inertia delay of the outer skin extrusion rate response; after the outer skin extrusion rate compensation amount is executed, it is confirmed that the outer skin thickness is not lower than the specified minimum value; if the outer skin thickness is lower than the specified minimum value, an alarm is triggered and the automatic linkage adjustment is suspended, waiting for manual intervention.

[0013] In conjunction with the first aspect, in certain implementations of the first aspect, when the linear velocity is adjusted in a coordinated manner, the corresponding outer skin extrusion rate compensation amount is simultaneously superimposed, including: determining the linear velocity compensation coefficient between the linear velocity change and the outer skin extrusion rate compensation amount through a calibration test in advance; when performing bivariate coordinated adjustment, converting the linear velocity adjustment amount into the outer skin extrusion rate compensation amount corresponding to the linear velocity based on the linear velocity compensation coefficient, superimposing the outer skin extrusion rate compensation amount corresponding to the linear velocity with the outer skin extrusion rate compensation amount corresponding to the nitrogen injection pressure to obtain the total outer skin extrusion rate compensation amount, which is then executed synchronously; after the total outer skin extrusion rate compensation amount is executed, confirming that the outer skin thickness is not lower than the specified minimum value.

[0014] In conjunction with the first aspect, in certain implementations of the first aspect, the overall cable core is assessed for conformity based on the original data of water capacitance deviation and outer sheath thickness detection data collected online throughout the entire process. This includes: using the original values ​​of the water capacitance deviation sequence collected online throughout the entire process as a basis, determining whether the absolute value of the original value does not exceed the conformity assessment threshold throughout the entire process, and whether the continuous length of the deviation points does not exceed the preset maximum continuous deviation length; sampling along the line at preset intervals, and confirming through cross-sectional measurement that the outer sheath thickness is not lower than the specified minimum value; when both the water capacitance deviation and the outer sheath thickness meet the requirements, the entire cable core is determined to be a qualified product, and the online water capacitance curve is output as a quality certificate accompanying the reel; if the cumulative length of the water capacitance deviation segment exceeds the preset proportion of the total length of the reel, the entire cable core is determined to be a non-conforming product and isolated; if the continuous length of the deviation segment exceeds the preset maximum continuous deviation length but the cumulative length does not exceed the preset proportion, the deviation segment is marked and cut, and the qualified segment continues to be used.

[0015] Compared with the prior art, the beneficial effects of this application are:

[0016] 1. This application measures the matrix dielectric constant of each batch of halogen-free flame-retardant polyolefin material, calculates the target foaming ratio in reverse using the volume-average mixing law, and establishes a response surface model with nitrogen injection pressure, mold temperature, and linear velocity as independent variables. This forms a quantitative design path for the target water capacitance, target equivalent dielectric constant, target foaming ratio, and initial process parameters, solving the problem that existing technologies lack a method for systematically calculating process parameters from the target water capacitance, resulting in long parameter exploration cycles and high start-up scrap rates when changing batches or specifications.

[0017] 2. This application achieves adaptive adjustment by continuously measuring the online water capacitance of the insulated wire core at the outlet of the cooling water tank and using a sliding average filtering and graded threshold triggering mechanism. While adjusting the nitrogen injection pressure or linear velocity, it also performs coordinated compensation for the outer sheath extrusion rate based on the pre-calibrated compensation coefficient. This solves the problems of existing technologies that rely solely on offline sampling inspection, resulting in a deviation response lag of more than 30 minutes and an accumulated length of hundreds of meters of defective products. It also addresses the lack of a coordinated control mechanism for the outer sheath thickness during the adjustment process, which poses a risk that the sheath thickness may fall below the minimum value specified in EN50306. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart illustrating the control process of co-extrusion water capacitor for the blister sheath of a rail transit communication cable according to an embodiment of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Figure 1 This is a schematic flow diagram illustrating the control process of co-extrusion water capacitors for the blister pack of a rail transit communication cable according to an embodiment of this application. Figure 1 As shown in the figure, the co-extrusion water capacitor control process for rail transit communication cable foam provided in one embodiment of this application includes the following steps: Step 101: The matrix dielectric constant of the current batch of halogen-free flame-retardant polyolefin material is measured. Based on the target equivalent dielectric constant corresponding to the target water capacitance value, and combined with the volume-average mixing law, the target foaming ratio that satisfies the target water capacitance value is calculated in reverse.

[0021] It should be understood that halogen-free flame-retardant polyolefin materials refer to insulating materials that do not contain halogen flame-retardant elements, use polyolefin as the matrix resin and add inorganic flame-retardant fillers, and are used in the inner skin layer, foam layer and outer skin layer of a three-layer co-extruded structure.

[0022] The matrix dielectric constant refers to the intrinsic dielectric constant of halogen-free flame-retardant polyolefin materials in their unfoamed state, reflecting the inherent capacitance characteristics of the material. It varies depending on the batch of filler.

[0023] Water capacitance refers to the capacitance per unit length of an insulated wire core measured with water as the outer electrode and the conductor as the inner electrode. It is a key quality parameter that characterizes the equivalent dielectric constant of the insulation layer and thus reflects the signal transmission characteristics.

[0024] The target equivalent dielectric constant refers to the overall equivalent dielectric constant that the insulation layer needs to achieve in order to meet the target water capacitance value requirement.

[0025] The volume-average mixing law is a rule for calculating the equivalent dielectric constant of a composite material obtained by mixing two media in a volume ratio. It is used to establish a quantitative relationship between the volume fraction of pores in the foam layer and the equivalent dielectric constant.

[0026] The target foaming ratio refers to the ratio of the volume of air pores in the foamed layer to the total volume of the foamed layer in order to make the equivalent dielectric constant of the insulation layer meet the target water capacitance value requirement. It is the core control target of this process.

[0027] Step 102: Using the target foaming ratio as the design objective and halogen-free flame-retardant polyolefin material as the test object, calibration tests are conducted by changing the nitrogen injection pressure, mold temperature, and linear velocity. The measured foaming ratio under each parameter combination is recorded, and a response surface model of the foaming ratio with respect to the three parameters of nitrogen injection pressure, mold temperature, and linear velocity is established. The response surface model supports forward query and backward solution, and outputs the partial sensitivity of the foaming ratio to each parameter at the current working point.

[0028] It should be understood that nitrogen injection pressure refers to the pressure applied to inject high-pressure nitrogen into the foaming layer melt. It is the most sensitive process parameter for controlling bubble nucleation and growth, and thus adjusting the foaming ratio.

[0029] Die temperature refers to the set temperature of the three-layer co-extrusion die, which affects the rheological properties of halogen-free flame-retardant polyolefin melt and the conditions for bubble nucleation.

[0030] Linear velocity refers to the traction speed of the insulated wire core, which determines the residence time of the melt in the mold, and thus affects the gas dissolution and bubble expansion process.

[0031] Calibration testing refers to the experimental process of systematically changing the combination of process parameters and recording the corresponding measured foaming ratio on a three-layer co-extrusion die to provide basic data for the establishment of response surface model.

[0032] The response surface model is a quadratic polynomial fitting model with nitrogen injection pressure, mold temperature and linear velocity as independent variables and foaming ratio as dependent variable. It supports two query modes: forward prediction and backward solving.

[0033] Partial sensitivity refers to the partial derivative of the foaming ratio with respect to a certain process parameter at the current operating point. It quantitatively characterizes the unit control efficiency of the parameter on the foaming ratio and is used to determine the control priority.

[0034] Step 103: Based on the response surface model, in the parameter solution set that satisfies the target foaming ratio, the initial nitrogen injection pressure, initial mold temperature and initial linear velocity for production start-up are determined by taking into account the bubble uniformity and the skin interface bonding strength. The three-layer co-extrusion production line is started with the initial parameters, and online detection is carried out after the process stabilizes.

[0035] It should be understood that the parameter solution set refers to the set of all nitrogen injection pressure, mold temperature, and linear velocity parameter combinations that satisfy the target foaming ratio constraint in the response surface model.

[0036] Bubble uniformity refers to the consistency of bubble size distribution in the foamed layer, characterized by the standard deviation of bubble size. The more uniform the bubbles, the better the consistency of the equivalent dielectric constant of the insulation layer along the length of the wire core.

[0037] The interfacial bonding strength refers to the peel strength of the interface between the inner skin layer and the foam layer, and between the foam layer and the outer skin layer, reflecting the interlayer bonding quality of the three-layer co-extruded structure.

[0038] A three-layer co-extrusion production line refers to a production equipment consisting of an inner skin layer extruder, a foam layer extruder (equipped with a nitrogen injection system), and an outer skin layer extruder, which synchronously extrudes a three-layer insulation structure of skin, foam, and rubber through the same die.

[0039] The start-up transition section refers to the length of the product from the moment the production line starts until the mold thermal balance is established and the back pressure of each extruder screw is stable. The process state of this section of the product is not yet stable and is not included in the water capacitor qualification judgment range.

[0040] Step 104: Continuously measure the online water capacitance of the insulated wire core at the outlet of the cooling water tank after extrusion, and perform a moving average filter on the obtained water capacitance deviation along the line to obtain the filtered water capacitance deviation.

[0041] It should be understood that insulated wire core refers to the semi-finished wire core after the three-layer co-extrusion insulation has been extruded and cooled and shaped, and before entering the cabling process.

[0042] Online continuous water capacitance measurement refers to a detection method that uses water immersion contact to continuously measure the water capacitance value of the insulated wire core along its length during the production process. Compared with offline sampling inspection, it can reduce the deviation detection time to the second level.

[0043] Water capacitance deviation along the line refers to the difference between the measured water capacitance value at each sampling point and the target water capacitance value. It is continuously recorded along the length of the core to form a deviation sequence that reflects the distribution of water capacitance along the line.

[0044] Moving average filtering refers to averaging the water capacitance deviation of continuous sampling points using a sliding window of fixed length, which is used to eliminate high-frequency measurement noise caused by mechanical disturbances such as wire core jitter.

[0045] The filtered water capacitance deviation refers to the water capacitance deviation after being processed by the moving average filter. It is used to trigger adjustment judgment to improve the stability of control.

[0046] Step 105: Based on the comparison result between the filtered water capacitor deviation and the preset threshold, the adjustment is triggered. Based on the partial sensitivity, the nitrogen injection pressure is preferentially adjusted with an adaptive step size proportional to the deviation. When the cumulative adjustment of the nitrogen injection pressure exceeds the preset upper limit and the filtered water capacitor deviation still does not converge, the inverse solution function of the response surface model is called to perform bivariate linkage adjustment of the nitrogen injection pressure and linear velocity with the minimum adjustment amount as the criterion.

[0047] It should be understood that the preset threshold refers to the absolute value limit of the filtered water capacitor deviation set for triggering adjustment or alarm, and is divided into two levels: the first threshold (adjustment trigger threshold) and the second threshold (over-tolerance alarm threshold).

[0048] Adaptive step size adjustment refers to an adjustment method in which the step size of each nitrogen injection pressure adjustment is designed to be proportional to the current deviation of the filtered water capacitor, and a gain coefficient is introduced to limit the amplitude. When the deviation is large, the step size is automatically increased to speed up convergence, and when the deviation is small, the step size is automatically decreased to prevent overshoot.

[0049] The cumulative adjustment amount refers to the algebraic cumulative value of the nitrogen injection pressure adjustment step size during a single convergence process, which is used to determine whether the single-variable adjustment has reached its upper limit of adjustment capability.

[0050] The preset upper limit refers to the absolute value limit of the cumulative adjustment of nitrogen injection pressure. If the water capacitance deviation still does not converge after exceeding this limit, it is determined that the single-variable adjustment capability is insufficient, triggering the dual-variable linkage adjustment.

[0051] Bivariate linkage regulation refers to a regulation method that, under the condition of fixed mold temperature, uses the minimum normalized weighted adjustment amount as the optimization criterion to simultaneously solve and issue a new combination of nitrogen injection pressure and linear velocity.

[0052] Step 106: While adjusting the nitrogen injection pressure, the volumetric extrusion rate of the outer skin extruder is simultaneously compensated according to the pre-calibrated compensation coefficient to maintain the outer skin thickness at no less than the specified minimum value; when adjusting the linear speed in a coordinated manner, the corresponding outer skin extrusion rate compensation amount is simultaneously superimposed.

[0053] It should be understood that volumetric extrusion rate refers to the volume of halogen-free flame-retardant polyolefin melt extruded per unit time by the outer skin extruder, which is controlled by adjusting the screw speed.

[0054] Synergistic compensation refers to simultaneously adjusting the volumetric extrusion rate of the outer skin extruder according to a pre-calibrated compensation coefficient while performing nitrogen injection pressure or linear speed adjustment, in order to offset the effect of foam layer expansion or linear speed changes on the outer skin thickness.

[0055] The pressure compensation coefficient refers to the compensation amount of the outer skin extrusion rate corresponding to the unit adjustment amount of nitrogen injection pressure determined by linear regression through calibration tests, reflecting the quantitative linkage between the two.

[0056] The linear velocity compensation coefficient refers to the amount of compensation for the extrusion rate of the outer skin layer corresponding to the unit change in linear velocity determined through calibration tests.

[0057] The total compensation amount of the outer skin extrusion rate refers to the total adjustment amount of the outer skin extrusion rate obtained by superimposing the compensation amount of nitrogen injection pressure and the compensation amount of linear velocity when the two variables are linked for regulation.

[0058] The specified minimum value refers to the lower limit of the outer sheath thickness specified by the EN 50306-2 standard for thin-walled insulated cables for rail transit. The goal of the coordinated compensation is to ensure that the outer sheath thickness is always not lower than this value.

[0059] Step 107: Based on the original data of water capacitance deviation and the outer sheath thickness detection data throughout the entire process, the overall cable core is qualified.

[0060] It should be understood that the original data of water capacitance deviation throughout the entire process refers to the original value of the water capacitance deviation sequence continuously collected along the entire length of the core in step 104. It has not been processed by moving average filtering and is used to capture local peak deviations that may be smoothed by filtering. It is the first basis for qualification judgment.

[0061] The outer skin thickness test data refers to the outer skin thickness data obtained by sampling along the line at preset intervals and directly measuring it using a cross-sectional microscope. It is the second basis for determining the pass / fail status.

[0062] The qualification determination refers to the comprehensive judgment process that determines whether the original value of the water capacitance deviation does not exceed the qualification judgment threshold, whether the continuous deviation length does not exceed the preset maximum continuous deviation length, and whether the outer sheath thickness is not lower than the specified minimum value, and makes a conclusion of qualified, marked cutting, or unqualified isolation treatment for the entire cable core.

[0063] A complete reel of cable cores refers to cable core products that are continuously extruded and wound onto the same reel in the same production process, and whose qualification is judged on a reel-by-reel basis.

[0064] The water capacitance control process for co-extrusion of insulation cores in rail transit communication cables provided in this embodiment establishes a full-link quantitative design method. This method starts from the target water capacitance value, uses the measured dielectric constant of the matrix in batches as input, reversely calculates the target foaming ratio using the volume average mixing law, and then determines the initial process parameters through forward and reverse solutions using a response surface model. Combined with an adaptive step-size single-variable and dual-variable linkage adjustment mechanism driven by online continuous water capacitance measurement and filtered deviation, and synchronous collaborative compensation control of the extrusion rate of the outer sheath during nitrogen injection pressure and linear speed adjustment, this process achieves batch-adaptive, real-time closed-loop, and multi-constraint collaborative control of water capacitance deviation in co-extruded insulation cores of rail transit communication cables. This effectively eliminates systematic water capacitance deviation caused by material batch fluctuations and maintains the outer sheath thickness at least as high as the minimum value specified in EN50306-2 during the adjustment process. This shortens the batch parameter exploration cycle, reduces the start-up scrap rate, and ensures the dual qualification of water capacitance consistency and outer sheath thickness for the entire cable reel.

[0065] Furthermore, the dielectric constant of the current batch of halogen-free flame-retardant polyolefin material was measured using the parallel plate capacitance method at a preset measurement frequency to obtain the matrix dielectric constant of the current batch. The preset measurement frequency was 1 kHz. Because halogen-free flame-retardant polyolefin materials contain a large amount of inorganic flame-retardant fillers, their matrix dielectric constant is significantly higher than that of the matrix resin, with measured values ​​of approximately 2.3–2.5. This value fluctuates depending on the filler batch and formulation; therefore, each batch of material must be measured individually, and data from previous batches cannot be reused.

[0066] Based on the target water capacitance value, the required target equivalent dielectric constant of the insulation layer is determined using the coaxial capacitance relationship. Specifically, the relationship between the water capacitance value and the equivalent dielectric constant of the insulation layer is determined by the coaxial capacitance formula. By substituting the target water capacitance value into the coaxial capacitance formula, the required target equivalent dielectric constant of the insulation layer can be calculated. .

[0067] Using the pore dielectric constant and the dielectric constant of the current batch matrix as known quantities, the target foaming ratio is calculated inversely from the target equivalent dielectric constant according to the volume-average mixing law. For foam-insulation structures, the equivalent dielectric constant of the foam layer is given by the volume-average mixing law: ; in, The foaming ratio is the ratio of the pore volume to the total volume of the foamed layer. , where is the dielectric constant of nitrogen at the preset measurement frequency; The matrix dielectric constant of the current batch of halogen-free flame-retardant polyolefin materials is taken from the measured value of the above-mentioned parallel plate capacitance method. and Given a known quantity, the target equivalent dielectric constant is... Substituting into the above formula, the target foaming ratio that satisfies the target water capacitance value can be obtained by solving in reverse. : ; Target foaming ratio obtained As a quantitative design objective for subsequent calibration experiments and response surface model establishment, it is passed on to subsequent steps.

[0068] Furthermore, calibration tests were conducted on a three-layer co-extrusion die. Multiple combinations of nitrogen injection pressure, die temperature, and linear speed were tested within preset ranges. The measured foaming ratio for each parameter combination was recorded, along with the average bubble diameter, bubble size standard deviation, skin-layer interfacial bonding strength, and insulation layer surface roughness, forming a process parameter database. Specifically, the preset range for die temperature was 180℃~220℃; the preset range for nitrogen injection pressure was 0.5~2.0MPa; and the linear speed was set to at least four levels based on the actual production line capacity. All recorded data were organized and stored in the process parameter database, indexed by the three parameters: nitrogen injection pressure, die temperature, and linear speed.

[0069] Based on the process parameter database, a quadratic polynomial response surface model was used to fit the measured foaming ratio, resulting in a response surface model with nitrogen injection pressure, mold temperature, and linear velocity as independent variables. The model was then cross-validated using the hold-out method, requiring the root mean square error between the predicted and measured values ​​to not exceed two percentage points. Specifically, the quadratic polynomial response surface model of the following form was used: ; in, Pressurize the nitrogen gas. For mold temperature, For linear velocity, the coefficients are... The parameters were determined by least squares regression using calibration data from the process parameter database. After model establishment, at least 10% of the calibration data points were retained for cross-validation using the hold-out method, requiring the root mean square error (RMSE) to meet the following requirements: ; At the current operating point, the partial sensitivity of the foaming ratio to nitrogen injection pressure, mold temperature, and linear velocity in the response surface model is calculated respectively. The magnitude of the partial sensitivity determines the priority of subsequent parameter adjustments. Specifically, at the current operating point... At each point, calculate the partial derivatives of the foaming ratio with respect to each parameter: ; For halogen-free flame-retardant polyolefin materials, there are typically [specific parameters] within the operating range. In other words, nitrogen injection pressure has the highest efficiency in controlling the foaming ratio, followed by linear velocity, and mold temperature has the lowest efficiency. The results of the partial sensitivity calculation serve as a quantitative basis for determining the subsequent adjustment priorities and are passed on to subsequent adjustment steps.

[0070] Furthermore, in the parameter solution set output by the response surface model that satisfies the target foaming ratio, the parameter region with the smallest bubble size standard deviation and satisfactory skin-layer interface bonding strength is selected. Specifically, the parameters corresponding to the bubble size standard deviation in the process parameter database are... Minimum and cortical interfacial bonding strength The parameter range that meets the specified requirements, and the target foaming ratio output by the response surface model. The intersection of the parameter solution sets yields candidate parameter regions that simultaneously satisfy the three constraints: target foaming ratio, bubble uniformity, and skin-interface bonding strength. The smaller the value, the more uniform the bubble distribution, which is beneficial to the consistency of the equivalent dielectric constant of the insulation layer along the length of the wire core; The specified minimum values ​​must be met to ensure that the interfacial bonding between the inner sheath and the foam layer, and between the foam layer and the outer sheath, meets the mechanical performance requirements of the cable.

[0071] Within the parameter range, a combination of parameters is selected where the mold temperature falls within a preset thermal equilibrium stability range, serving as the initial nitrogen injection pressure, initial mold temperature, and initial linear velocity. Specifically, the preset thermal equilibrium stability range is 180℃~200℃. Within this range, the halogen-free flame-retardant polyolefin material melt exhibits stable plasticization, and the mold thermal equilibrium establishment time is minimized, which is beneficial for shortening the start-up transition period and improving process stability during the start-up phase. The initial nitrogen injection pressure is determined from the intersection of the candidate parameter range and the preset thermal equilibrium stability range. Initial mold temperature and initial linear velocity and will , , The corresponding partial sensitivity , This information is passed on to subsequent adjustment steps as a basis for designing the adjustment step size.

[0072] The three-layer co-extrusion production line is started with initial nitrogen injection pressure, initial mold temperature, and initial linear velocity. The product length from the start-up moment until the process parameters stabilize is marked as the start-up transition section. Products within the start-up transition section are not included in the water capacitance qualification range. After the start-up transition section ends, online inspection begins. Specifically, the total wall thickness of the insulation layer of the three-layer co-extrusion production line meets the following requirements: ; in, The thickness of the endothelial layer. The thickness of the foam layer, The thickness is the outer skin layer. The inner skin layer extruder, foam layer extruder, and outer skin layer extruder are controlled independently. , , Production begins. From the start-up moment, the previous product segment corresponds to the transition section required for mold thermal balance establishment and stable back pressure of each extruder screw. The length of this product segment is marked as the start-up transition segment; the length of the start-up transition segment... Based on the calibration test, the time required for halogen-free flame-retardant polyolefin materials to reach extrusion stability under various parameter combinations is determined. With linear velocity The measured maximum value of the product, plus a safety margin. Sure: ; Products produced during the initial transition period are not included in the qualification criteria for water capacitors. After the process parameters stabilize, the online testing phase begins.

[0073] Furthermore, at the outlet of the cooling water tank after insulation extrusion and before cabling, the insulated wire core is continuously measured online using the water immersion contact method. Deionized water is used as the outer electrode and the conductor as the inner electrode. The water capacitance value per unit length of the insulated wire core is continuously measured at a preset measurement frequency. The sampling interval along the length of the wire core does not exceed two meters, resulting in a sequence of water capacitance measurements along the wire. The preset measurement frequency is 1 kHz; the sampling interval along the length of the wire core is... m, ensuring that deviations in the water capacitor along its length can be captured at high resolution. Compared to existing technologies that rely on offline sampling and have a time delay of more than 30 minutes from the occurrence of a problem to the detection of the deviation, this step compresses the detection time of water capacitor deviation to the second level, allowing adjustments to be made in time before local out-of-tolerance sections spread.

[0074] Using the target water capacitance value as a benchmark, the water capacitance deviation is calculated for each sampling point in the water capacitance measurement sequence along the route, forming a water capacitance deviation sequence along the route. Specifically, using the target water capacitance value... Based on this, the measured water capacitance at each sampling point was... Calculate the water capacitance deviation: ; Based on production length Using the horizontal axis as the data point, continuous recording forms a sequence of water capacitance deviations along the line. The original values ​​of this sequence are used for subsequent qualification determination.

[0075] A moving average filter is applied to the water capacitance deviation sequence along the route. The average value is calculated over consecutive sampling points with a preset sliding window length to obtain the filtered water capacitance deviation. Specifically, the preset sliding window length is 10m, meaning the average water capacitance deviation is calculated over 5 consecutive sampling points to obtain the filtered water capacitance deviation. : ; in, This represents the number of sampling points within the sliding window. Sampling interval. Water capacitance deviation after filtering. It is used to eliminate high-frequency measurement noise caused by mechanical disturbances such as wire core vibration, and improve the stability of trigger adjustment judgment.

[0076] The filtered water capacitance deviation is used as the trigger criterion for adjustment, and the original values ​​of the water capacitance deviation sequence along the line are used as the basis for qualification judgment. Specifically, Used for continuous judgment and adjustment triggering of water capacitance deviation; The original value is used to determine the pass / fail status of the entire cable core, in order to capture local spike deviations that may be smoothed out by the moving average filter, and to ensure the strictness of the pass / fail status determination.

[0077] Furthermore, a first threshold and a second threshold are set, with the second threshold being greater than the first threshold. Specifically, the first threshold... Second threshold ,and .

[0078] When the absolute value of the water capacitance deviation after filtering does not exceed the first threshold, production continues while maintaining the current process parameters. Specifically, when If the current water capacitor is determined to be in a controlled range, the current process parameters are maintained to continue production, and the process returns to the online water capacitor continuous measurement step to continue data acquisition.

[0079] When the absolute value of the filtered water capacitance deviation exceeds the first threshold but does not exceed the second threshold, nitrogen injection pressure regulation is triggered and an alarm is sent to the operator. Specifically, when At this time, the nitrogen injection pressure is adjusted first, and a warning signal is pushed to the operator interface.

[0080] When the absolute value of the deviation of the filtered water capacitance exceeds the second threshold, nitrogen injection pressure regulation is triggered and an out-of-tolerance alarm is sent to the operator. Specifically, when At the same time, while prioritizing the adjustment of nitrogen injection pressure, an out-of-tolerance alarm signal is pushed to the operator interface.

[0081] The direction of the foaming ratio shift is determined by the polarity of the water capacitance deviation after filtering, thus determining the direction of nitrogen injection pressure adjustment. Specifically, if... This indicates that the actual equivalent dielectric constant is too large and the foaming ratio is insufficient. The nitrogen injection pressure needs to be increased, and the adjustment direction is as follows: ;like This indicates over-foaming ( The nitrogen injection pressure needs to be reduced, and the adjustment direction is as follows: .

[0082] Based on the partial sensitivity of the foaming ratio to the nitrogen injection pressure, the adjustment step size for each nitrogen injection pressure is determined to be an adaptive step size proportional to the current deviation of the filtered water capacitance. An adaptive gain coefficient is introduced to retain adjustment margin and prevent overshoot. Specifically, the adjustment step size for each nitrogen injection pressure... Calculate using the following formula: ; in, The adaptive gain coefficients are used to absorb 50% of the current estimation deviation in each adjustment, leaving an adjustment margin to prevent overshoot; each transfer coefficient is calculated from the target foaming ratio inverse calculation step and the model parameters of the response surface model.

[0083] After each nitrogen injection pressure adjustment, a time delay corresponding to the preset product length is waited before the filtered water capacitance deviation is reread to determine if it has converged to within the first threshold. Specifically, after a 4m product length passes the measurement point, the deviation is reread. ,judge Check if the condition is met; if converged, update the current nitrogen injection pressure. And return to the online water capacitance continuous measurement step; if the cumulative adjustment of nitrogen injection pressure meets the requirements... However, if convergence has not yet occurred, then priority adjustment of nitrogen injection pressure will continue; if If convergence is still not achieved, then bivariate linkage regulation will be initiated.

[0084] Furthermore, when the absolute value of the cumulative adjustment of the nitrogen injection pressure exceeds the preset upper limit and the water capacitance deviation after filtering still has not converged to within the first threshold, the inverse solution function of the response surface model is invoked. Under the condition of fixing the current mold temperature, the parameter solution set of nitrogen injection pressure and linear velocity that satisfies the target foaming ratio is output. Specifically, when and At the same time, with the current mold temperature fixed. Under the given conditions, find the parameter set for nitrogen injection pressure and linear velocity that satisfy the following equation: ; In the parameter solution set, the optimization criterion is to minimize the weighted sum of squares of the normalized nitrogen injection pressure adjustment and the linear velocity adjustment. A new combination of nitrogen injection pressure and linear velocity is then solved, and the new nitrogen injection pressure and linear velocity are synchronously applied to the nitrogen injection control loop and the traction speed control loop of the foaming layer. Specifically, the optimization problem is formulated as follows: ; ; Wherein, the weight coefficient is taken , ; , , , These are the upper and lower limits of the equipment's permissible range for nitrogen injection pressure and linear velocity, respectively. , Given the current nitrogen injection pressure and current linear velocity, and since the response surface model is a quadratic polynomial, the above constrained optimization problem can be solved analytically to obtain the new nitrogen injection pressure. With the new linear velocity ,Will and Simultaneously, the nitrogen injection control circuit for the foaming layer and the traction speed control circuit are activated.

[0085] The new linear velocity, relative to the current linear velocity, should not exceed a preset maximum step size in each adjustment step to prevent tension fluctuations caused by sudden changes in linear velocity. Specifically, the requirements are: m / min; After the dual-variable linkage adjustment is executed, a time delay corresponding to the preset product length is waited, and the filtered water capacitance deviation is reread. If the filtered water capacitance deviation still has not converged, the dual-variable linkage adjustment is repeated, and a continuous alarm is pushed to the operator. Specifically, after a time delay of 6 meters (6m product length), the deviation is reread. ,like The dual-variable linkage adjustment will be repeatedly executed, and a continuous alarm will be pushed to the operator, indicating that there may be equipment abnormality or material batch problem, which requires manual intervention for verification.

[0086] Furthermore, prior calibration experiments were conducted to measure the actual changes in the outer skin layer thickness under different nitrogen injection pressure variations. Combined with the calibration relationship of the outer skin layer extrusion rate, a pressure compensation coefficient between the nitrogen injection pressure adjustment and the outer skin layer extrusion rate compensation was determined through linear regression. Specifically, increasing the nitrogen injection pressure will lead to an increase in the pore volume of the foamed layer, which is related to the total wall thickness of the insulation layer. Under certain conditions, if the extrusion rate of the outer skin layer remains constant, then the thickness of the outer skin layer... The foam layer will be compressed due to its expansion, and thus exist. The risk. The pressure compensation coefficient was determined through linear regression. (unit: ), so that: ; The pressure compensation coefficient is recalibrated with each batch change of the halogen-free flame-retardant polyolefin outer skin material. Specifically, Related to the rheological properties of the halogen-free flame-retardant polyolefin outer skin material at operating temperature, calibration tests must be repeated and the material updated each time the outer skin material batch is changed. The calibration values ​​from the previous batch must not be used.

[0087] Each time nitrogen injection pressure adjustment is performed, the nitrogen injection pressure adjustment amount is linearly converted into an outer skin extrusion rate compensation amount based on the pressure compensation coefficient. The control command corresponding to the outer skin extrusion rate compensation amount is preset for a duration longer than the nitrogen injection pressure adjustment command to compensate for the mechanical inertia delay in the outer skin extrusion rate response. Specifically, the step size for each nitrogen injection pressure adjustment is... At that time, the compensation amount for the extrusion rate of the outer skin layer is calculated: ; The corresponding outer skin extruder screw speed control command has a pre-set duration. When the nitrogen injection pressure adjustment command is issued, it ensures that the outer skin thickness compensation is reflected synchronously at the same mold position where the nitrogen injection pressure change takes effect, avoiding the generation of localized excessively thin outer skin sections due to compensation lag.

[0088] After the outer skin extrusion rate compensation is applied, confirm that the outer skin thickness is not less than the specified minimum value, i.e., confirm that: ; If the outer skin thickness is below the specified minimum, an alarm will be triggered and automatic adjustment will be paused, awaiting manual intervention. Specifically, if If an alarm signal is triggered, an alarm signal will be sent to the operator interface, pausing automatic linkage adjustment. Automatic linkage adjustment can only be resumed after the operator has manually checked and confirmed the alarm.

[0089] Furthermore, a linear velocity compensation coefficient is determined beforehand through calibration tests, relating the linear velocity variation to the outer skin extrusion rate compensation. Specifically, the linear velocity compensation coefficient is determined through calibration tests. This makes the compensation amount for the outer skin extrusion rate corresponding to the linear velocity as follows: ; When performing bivariate linkage regulation, the linear velocity adjustment is converted into the corresponding outer skin extrusion rate compensation based on the linear velocity compensation coefficient. This outer skin extrusion rate compensation is then superimposed with the outer skin extrusion rate compensation corresponding to the nitrogen injection pressure to obtain the total outer skin extrusion rate compensation. This total outer skin extrusion rate compensation is executed synchronously. Specifically, the total outer skin extrusion rate compensation is: ; Will The corresponding screw speed control command for the outer skin extruder is executed synchronously with the nitrogen injection pressure adjustment command and the linear speed adjustment command.

[0090] After the total compensation for the outer skin extrusion rate is applied, confirm that the outer skin thickness is not lower than the specified minimum value, i.e., confirm that: ; If the outer skin thickness is lower than the specified minimum value, an alarm will be triggered and automatic linkage adjustment will be suspended, awaiting manual intervention.

[0091] Furthermore, based on the original values ​​of the water capacitance deviation sequence collected online throughout the entire process, it is determined whether the absolute value of the original value does not exceed the pass / fail threshold throughout the entire process, and whether the continuous length of the out-of-tolerance points does not exceed the preset maximum continuous out-of-tolerance length. Specifically, the pass / fail threshold is set as follows: The preset maximum continuous deviation length is set to The requirement is that all sampling points throughout the entire process must meet the following conditions: ; And the length of any consecutive out-of-tolerance segments satisfy: ; Sampling was conducted along the route at predetermined intervals, and cross-sectional measurements were performed to confirm that the outer skin thickness was not lower than the specified minimum value. Specifically, one cross-sectional sample was taken every 100m along the route, and the outer skin thickness was directly measured using a cross-sectional microscope to confirm: ; When both water capacitance deviation and outer sheath thickness meet the requirements, the entire reel of cable cores is deemed a qualified product, and a full-process online water capacitance curve is output as a quality certificate accompanying the reel. Specifically, when both of the above criteria are met, the reel of cable cores is deemed a qualified product, and a curve based on the production length is output. The horizontal axis represents the water capacitance value, and the vertical axis represents the target water capacitance value. and the upper and lower limits of the qualified range The marked online water-capacity curve is used as a quality certificate for the tray and enters the cabling process.

[0092] If the cumulative length of the out-of-tolerance section of the water capacitor exceeds a preset proportion of the total cable length, the entire cable core is deemed defective and isolated. Specifically, let the total length of the cable core be... The preset ratio is %, if the cumulative length of the out-of-tolerance paragraphs satisfy: ; If the cable core is found to be defective, it must be isolated and disposed of, and it must not be allowed to enter the cabling process.

[0093] If the continuous length of a segment exceeding the preset maximum continuous deviation length but the cumulative length does not exceed a preset proportion, the segment exceeding the deviation length is marked and cut, while the acceptable segment continues to be used. Specifically, if there is a continuous length... There are m out-of-tolerance paragraphs, but the cumulative length of the out-of-tolerance paragraphs meets the following requirements: ; The out-of-tolerance sections are then precisely located and marked, cut off, and the remaining qualified sections are used in the cabling process.

[0094] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A process for controlling the co-extrusion of water-capacitor capacitors in the blister pack of rail transit communication cables, characterized in that, include: The matrix dielectric constant of the current batch of halogen-free flame-retardant polyolefin materials was measured. Based on the target equivalent dielectric constant corresponding to the target water capacitance value, and combined with the volume-average mixing law, the target foaming ratio that satisfies the target water capacitance value was calculated in reverse. Using the target foaming ratio as the design objective and halogen-free flame-retardant polyolefin material as the test object, calibration tests were conducted by changing the nitrogen injection pressure, mold temperature, and linear velocity. The measured foaming ratio under each parameter combination was recorded, and a response surface model of the foaming ratio with respect to the three parameters of nitrogen injection pressure, mold temperature, and linear velocity was established. The response surface model supports forward query and backward solution, and outputs the partial sensitivity of the foaming ratio to each parameter at the current operating point. Based on the response surface model, in the parameter solution set that satisfies the target foaming ratio, the initial nitrogen injection pressure, initial mold temperature and initial linear velocity for production start-up are determined by taking into account the bubble uniformity and the skin interface bonding strength. The three-layer co-extrusion production line is started with the initial parameters and enters online detection after the process stabilizes. The insulated wire core was continuously measured online at the outlet of the cooling water tank after extrusion. The obtained water capacitance deviation along the line was filtered by moving average to obtain the filtered water capacitance deviation. The adjustment is triggered based on the comparison result between the filtered water capacitor deviation and the preset threshold. Based on the partial sensitivity, the nitrogen injection pressure is preferentially adjusted with an adaptive step size proportional to the deviation. When the cumulative adjustment of the nitrogen injection pressure exceeds the preset upper limit and the filtered water capacitor deviation still has not converged, the inverse solution function of the response surface model is called to perform bivariate linkage adjustment of the nitrogen injection pressure and linear velocity with the minimum adjustment amount as the criterion. While adjusting the nitrogen injection pressure, the volumetric extrusion rate of the outer skin extruder is simultaneously compensated according to the pre-calibrated compensation coefficient to maintain the outer skin thickness at no less than the specified minimum value; when adjusting the linear speed in a coordinated manner, the corresponding outer skin extrusion rate compensation amount is simultaneously superimposed. Based on the original data of water capacitance deviation and the outer sheath thickness test data throughout the entire process, the qualification of the entire cable core is determined.

2. The process according to claim 1, characterized in that, The method involves measuring the matrix dielectric constant of the current batch of halogen-free flame-retardant polyolefin materials, and, based on the target equivalent dielectric constant corresponding to the target water capacitance value, calculating the target foaming ratio that satisfies the target water capacitance value using the volume-average mixing law. This includes: The dielectric constant of the current batch of halogen-free flame-retardant polyolefin materials was measured by the parallel plate capacitance method at a preset measurement frequency, and the dielectric constant of the matrix of the current batch was obtained. Based on the target water capacitance value, the target equivalent dielectric constant required for the insulating layer is determined by the coaxial capacitance relationship. Using the pore dielectric constant and the dielectric constant of the current batch matrix as known quantities, the target foaming ratio is calculated in reverse from the target equivalent dielectric constant according to the volume-average mixing law; For each new batch of materials, the above measurements and calculations are repeated to eliminate systematic water capacitance deviations caused by material batch fluctuations.

3. The process according to claim 1, characterized in that, The process involves using the target foaming ratio as the design objective, halogen-free flame-retardant polyolefin material as the test object, and conducting calibration tests by changing nitrogen injection pressure, mold temperature, and linear velocity. The measured foaming ratio under each parameter combination is recorded, and a response surface model of the foaming ratio with respect to the three parameters of nitrogen injection pressure, mold temperature, and linear velocity is established, including: Calibration tests were conducted on a three-layer co-extrusion die. Within a preset range, multiple levels of nitrogen injection pressure, die temperature and linear velocity were combined to conduct tests. The measured foaming ratio corresponding to each parameter combination was recorded. At the same time, the average bubble diameter, bubble size standard deviation, skin layer interface bonding strength and insulation layer surface roughness were recorded to form a process parameter database. Based on the process parameter database, a quadratic polynomial response surface model is used to fit the measured foaming ratio to obtain a response surface model with nitrogen injection pressure, mold temperature and linear velocity as independent variables. The response surface model is then cross-validated using the hold-out method, requiring that the root mean square error between the predicted value and the measured value does not exceed two percentage points. At the current operating point, the partial sensitivity of the foaming ratio to nitrogen injection pressure, mold temperature and linear velocity in the response surface model is calculated respectively, and the priority of subsequent adjustment parameters is determined by the magnitude of the partial sensitivity.

4. The process according to claim 3, characterized in that, Based on the response surface model, within the parameter solution set that satisfies the target foaming ratio, and considering both bubble uniformity and skin-interface bonding strength, the initial nitrogen injection pressure, initial mold temperature, and initial linear velocity for production startup are determined. The three-layer co-extrusion production line is then started with these initial parameters. After the process stabilizes, online monitoring begins, including: In the parameter solution set that satisfies the target foaming ratio output by the response surface model, the parameter region with the smallest standard deviation of bubble size and the required skin-interface bonding strength is selected. Within the parameter range, a combination of parameters is selected where the mold temperature is within a preset thermal equilibrium stable range, which serves as the initial nitrogen injection pressure, initial mold temperature, and initial linear velocity. The three-layer co-extrusion production line is started with the initial nitrogen injection pressure, the initial mold temperature and the initial linear speed. The length of the product from the start time to the stable process parameters is marked as the start-up transition section. The product within the start-up transition section is not included in the water capacitor qualification judgment range. After the start-up transition section ends, online detection begins.

5. The process according to claim 1, characterized in that, The continuous online water capacitance measurement of the insulated wire core at the outlet of the cooling water tank after extrusion, and the resulting water capacitance deviation along the line are filtered by moving average to obtain the filtered water capacitance deviation, including: At the outlet of the cooling water tank after insulation extrusion and before cabling, the water capacitance of the insulated wire core is continuously measured online using the water immersion contact method. Deionized water is used as the outer electrode and the conductor is used as the inner electrode. The water capacitance value per unit length of the insulated wire core is continuously measured at a preset measurement frequency. The sampling interval along the length of the wire core does not exceed two meters, and a sequence of water capacitance measurement values ​​along the line is obtained. Based on the target water capacitance value, the water capacitance deviation is calculated for each sampling point in the water capacitance measurement value sequence along the line to form a water capacitance deviation sequence along the line. The water capacitor deviation sequence along the line is filtered by moving average filtering. The mean value of continuous sampling points is calculated with a preset length as the sliding window to obtain the filtered water capacitor deviation. The filtered water capacitance deviation is used as the criterion for triggering adjustment, and the original value of the water capacitance deviation sequence along the line is used as the basis for qualification judgment.

6. The process according to claim 3 or 5, characterized in that, The adjustment is triggered based on the comparison result between the filtered water capacitance deviation and a preset threshold. Using the bias sensitivity as a basis, an adaptive step size adjustment proportional to the deviation magnitude is preferentially applied to the nitrogen injection pressure, including: Set a first threshold and a second threshold, wherein the second threshold is greater than the first threshold; When the absolute value of the filtered water capacitor deviation does not exceed the first threshold, production continues while maintaining the current process parameters; When the absolute value of the filtered water capacitance deviation exceeds the first threshold but does not exceed the second threshold, nitrogen injection pressure adjustment is triggered and an early warning is sent to the operator. When the absolute value of the deviation of the filtered water capacitor exceeds the second threshold, the nitrogen injection pressure is adjusted and an out-of-tolerance alarm is sent to the operator. The direction of foaming ratio offset is determined based on the polarity of the filtered water capacitance deviation, and the direction of nitrogen injection pressure adjustment is determined accordingly. Based on the partial sensitivity of the foaming ratio to the nitrogen injection pressure, the step size of each nitrogen injection pressure adjustment is determined to be an adaptive step size that is proportional to the current deviation of the filtered water capacitor, and an adaptive gain coefficient is introduced to retain adjustment margin and prevent overshoot. After each nitrogen injection pressure adjustment is executed, wait for the corresponding preset product length time delay, reread the filtered water capacitor deviation, and determine whether the filtered water capacitor deviation has converged to within the first threshold.

7. The process according to claim 6, characterized in that, When the cumulative adjustment of the nitrogen injection pressure exceeds the preset upper limit and the filtered water capacitance deviation still fails to converge, the inverse solution function of the response surface model is invoked to perform bivariate linkage adjustment of the nitrogen injection pressure and linear velocity based on the minimum adjustment amount, including: When the absolute value of the cumulative adjustment of nitrogen injection pressure exceeds the preset upper limit and the filtered water capacitor deviation still does not converge to within the first threshold, the inverse solution function of the response surface model is called to output the parameter solution set of nitrogen injection pressure and linear velocity that meet the target foaming ratio under the condition of fixed current mold temperature. In the parameter solution set, the optimization criterion is to minimize the weighted sum of squares of the normalized nitrogen injection pressure adjustment amount and the linear velocity adjustment amount. The new nitrogen injection pressure and linear velocity combination is then solved, and the new nitrogen injection pressure and the new linear velocity are synchronously applied to the foaming layer nitrogen injection control loop and the traction speed control loop. The adjustment step size of the new linear velocity relative to the current linear velocity does not exceed the preset maximum step size to prevent tension fluctuations caused by sudden changes in linear velocity; After the dual-variable linkage adjustment is executed, wait for the time delay corresponding to the preset product length, and reread the filtered water capacitor deviation. If the filtered water capacitor deviation still does not converge, repeat the dual-variable linkage adjustment and push a continuous alarm to the operator.

8. The process according to claim 6, characterized in that, The process of simultaneously adjusting the nitrogen injection pressure and coordinating the volumetric extrusion rate of the outer skin extruder according to a pre-calibrated compensation coefficient to maintain the outer skin thickness at a specified minimum value includes: Beforehand, calibration tests were conducted to measure the actual change in the thickness of the outer skin layer under different nitrogen injection pressure variations. Combined with the calibration relationship of the outer skin layer extrusion rate, the pressure compensation coefficient between the nitrogen injection pressure adjustment and the outer skin layer extrusion rate compensation was determined by linear regression. The pressure compensation coefficient is recalibrated as the batch of halogen-free flame-retardant polyolefin outer skin material is changed; Each time the nitrogen injection pressure is adjusted, the nitrogen injection pressure adjustment amount is linearly converted into the outer skin extrusion rate compensation amount according to the pressure compensation coefficient. The control command corresponding to the outer skin extrusion rate compensation amount is preset to a duration longer than the nitrogen injection pressure adjustment command, so as to compensate for the mechanical inertia delay of the outer skin extrusion rate response. After the outer skin extrusion rate compensation is applied, it is confirmed that the outer skin thickness is not lower than the specified minimum value. If the thickness of the outer skin layer is lower than the specified minimum value, an alarm will be triggered and automatic linkage adjustment will be suspended, awaiting manual intervention.

9. The process according to claim 7 or 8, characterized in that, The simultaneous superposition of the corresponding outer skin extrusion rate compensation amount during the linkage adjustment of the linear speed includes: The linear velocity compensation coefficient between the linear velocity change and the outer skin extrusion rate compensation is determined in advance through calibration tests; When performing bivariate linkage regulation, the linear speed regulation amount is converted into the outer skin extrusion rate compensation amount corresponding to the linear speed according to the linear speed compensation coefficient. The outer skin extrusion rate compensation amount corresponding to the linear speed is superimposed with the outer skin extrusion rate compensation amount corresponding to the nitrogen injection pressure to obtain the total outer skin extrusion rate compensation amount. The total outer skin extrusion rate compensation amount is executed synchronously. After the total compensation for the extrusion rate of the outer skin layer is applied, it is confirmed that the thickness of the outer skin layer is not lower than the specified minimum value.

10. The process according to claim 5, characterized in that, The qualification assessment of the entire cable core is based on the original data of water capacitance deviation and the outer sheath thickness detection data throughout the entire process, including: Based on the original values ​​of the water capacitance deviation sequence along the entire line collected online, it is determined whether the absolute value of the original value does not exceed the qualified judgment threshold throughout the entire process, and whether the continuous length of the out-of-tolerance point does not exceed the preset maximum continuous out-of-tolerance length. Samples were taken along the line at preset intervals, and cross-sectional measurements were used to confirm that the outer skin layer thickness was not lower than the specified minimum value. When both the water capacitance deviation and the outer sheath thickness meet the requirements, the entire cable core is determined to be a qualified product, and a full-process online water capacitance curve is output as a quality certificate document accompanying the reel. If the cumulative length of the out-of-tolerance section of the water capacitor exceeds a preset proportion of the total length of the reel, the entire reel of cable cores is determined to be a defective product and isolated for disposal. If the continuous length of the out-of-tolerance paragraph exceeds the preset maximum continuous out-of-tolerance length but the cumulative length does not exceed the preset proportion, then the out-of-tolerance paragraph is marked and cut, and the qualified paragraph continues to be used.

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