Low-thermal-conductivity constant-temperature composite runner for valve oil seal injection mold, temperature control system and method

Abstract

The application discloses a low-thermal-conductivity constant-temperature composite runner of an injection mold for a valve oil seal, a temperature control system and a method, and belongs to the technical field of rubber injection molding. The composite runner adopts a function-structure separation design and comprises a low-thermal-conductivity PEEK injection core and a high-strength metal shell. The injection core is responsible for heat insulation and rubber material guiding, and the metal shell bears mechanical load and is integrated with a cylinder-encircling temperature control runner. The temperature control method is based on a first-order inertia plus pure lag mathematical model, adopts a composite control strategy combining a Smith predictor and a PID, and introduces feedforward control to cope with periodic injection heat shock, so that high-precision constant-temperature control of ± 2 DEG C of the injection area is realized. The application effectively solves the problem of premature vulcanization of rubber materials caused by uneven temperature in precise rubber injection, the material utilization rate is increased to more than 95%, and the unitized design is convenient for maintenance and updating.

Description

Technical Field

[0001] This invention relates to the field of rubber injection molding technology, and in particular to a low thermal conductivity constant temperature composite runner, temperature control system and method for valve stem seal injection molds. Specifically, it relates to a modular runner with low thermal conductivity, high strength, and a high-precision constant temperature control method that can overcome temperature measurement lag through the Smith-PID temperature control method. Background Technology

[0002] In the production of precision rubber products such as valve oil seals, the traditional transfer molding process suffers from the problem that the remaining material in the cavity and runner is easily vulcanized by heat and scrapped, resulting in low material utilization (usually only 60%-70%). To address this, the industry has shifted to injection molding and combined it with various measures such as runner insulation and low thermal conductivity injection nozzles, aiming to keep the rubber material in a plasticized but not vulcanized state before entering the high-temperature cavity. However, existing solutions still have shortcomings: First, the metal cooling channel solution uses cooling water channels inside the metal template and external heat insulation plates for cooling. Due to the high thermal conductivity and large heat capacity of the metal body, the temperature in the injection core area is uneven, making it difficult to stably maintain the rubber material within a narrow process window such as 80±2℃. The heat insulation relies on external heat insulation plates, which have limited effectiveness. Second, the low thermal conductivity injection nozzle solution uses materials such as stainless steel to slow down heat transfer. This solution cannot achieve uniform active temperature control of the entire injection core area. In addition, when pursuing high-precision temperature control, the measurement lag of temperature sensors is often overlooked, resulting in a delayed response of traditional PID control, which is prone to overshoot and oscillation, making it difficult to achieve stable control within ±2℃.

[0003] Therefore, existing technologies cannot solve the multiple contradictions of efficient heat insulation, uniform temperature control, and hysteresis compensation in a coordinated manner, and an innovative system solution is urgently needed.

[0004] The specific patent comparison documents are as follows: 1) "Modular Easy-to-Assemble and Disassemble Hot Runner Component and Mold", Patent No. CN205905337U. This utility model relates to a mold component that encapsulates the hot runner system and component body into an integrated module, enabling quick assembly and disassembly with the mold template via connecting bolts. This design facilitates mold maintenance and replacement, improving assembly and disassembly efficiency, and, like this invention, adopts a modular design concept. However, its modular purpose is only to simplify the mechanical assembly process, without considering the heat insulation and temperature control design of the hot runner for the rubber vulcanization process, and therefore lacks the active heat insulation and high-precision temperature control functions to inhibit premature vulcanization of the rubber compound during injection.

[0005] 2) "A Standardized Modular Structure for Hot Runner System of Injection Molds", Patent No. CN212241952U. This utility model discloses a standardized hot runner modular structure for injection molds. Like this invention, it adopts a modular design concept, designing the main runner nozzle, branch runner nozzles, and connecting components as modular components to achieve the reuse and rapid combination of hot runner systems between different molds, aiming to reduce mold development costs and shorten manufacturing cycles. However, the core of this solution lies in improving the versatility and assembly flexibility of the hot runner system. It uses traditional electric heating coils and heating blocks for temperature maintenance, without addressing the design of low thermal conductivity materials for rubber vulcanization processes, and lacks high-precision, anti-hysteresis dynamic constant temperature control capabilities. It cannot solve problems such as premature vulcanization of rubber due to temperature fluctuations in valve stem seal injection.

[0006] 3) "A mold temperature control system and method based on precision injection molding", patent number CN118849365B. This invention discloses a mold temperature control method for precision injection molding. It obtains the heating and cooling rates of the mold during the current operating stage (such as mold closing, filling, holding pressure, and cooling stages), and calculates a compensation heating and cooling rate based on the temperature change rate caused by the environment and the melt. Then, based on the compensation rate, corresponding heating or cooling operations are performed to ultimately bring the mold temperature close to the target temperature for each stage. This method uses a PID controller to adjust the temperature difference between the stationary and moving molds, achieving staged and refined adjustment of the mold temperature. However, this scheme, based on conventional PID and stage rate compensation, lacks the ability to compensate for Smith prediction of sensor measurement lag and cannot achieve high-precision dynamic constant temperature control such as ±2℃. Therefore, it cannot solve the problem of premature vulcanization of the rubber compound caused by uneven temperature in the injection core area during valve stem seal injection.

[0007] 4) "A Temperature Control Method for Injection Molds in the Production of Automotive Parts," Patent No. CN120773296B. This invention discloses a temperature control method for injection molds used in the production of automotive parts. It obtains the temperature values ​​of the cavity and core, and adjusts the temperature of the cavity and core independently in two stages. The first adjustment uses a fuzzy control algorithm to regulate the coolant temperature or flow rate based on the probability of temperature adjustment in the cavity and core. After adjustment, the temperature and coolant flow rate at each monitoring point are further obtained to calculate the consistency of local temperature differences in the cavity and core, and a second temperature adjustment is performed accordingly. The advantage of this method is that it can handle the zoned temperature control requirements of complex deep-cavity parts and identify and handle local temperature differences caused by different reasons. However, this control strategy is based on fuzzy control and local temperature difference consistency analysis using multi-monitoring point data. It lacks the ability to model mathematical lag in temperature sensor measurements and to compensate for Smith predictions, thus failing to achieve high-precision dynamic constant temperature control for preventing vulcanization of the rubber compound in the injection core area.

[0008] As can be seen from the comparative documents, none of them proposed a systematic integrated structural and control solution for the special process challenge of premature vulcanization of the rubber compound in the injection core area during rubber injection molding.

[0009] The existing flow channel system in the injection molding process for valve stem seals has the following technical problems: 1. Structural design limitations: Existing runner structures mostly adopt a metal integral type or simple heat insulation design, which makes it difficult to maintain a stable and uniform temperature in the injection core area. It cannot effectively isolate the heat transfer from the high temperature mold (about 160°C) to the plasticized rubber material (about 80°C), resulting in premature vulcanization of the rubber material in the runner.

[0010] 2. Lack of control strategy: Existing temperature control methods mostly focus on the temperature uniformity of the mold as a whole or in different areas. They usually use conventional PID or fuzzy control algorithms, without fully considering the pure lag in the system caused by temperature sensor measurement lag and heat conduction lag. This results in slow control response, easy overshoot and oscillation, and difficulty in achieving high-precision, fast-response constant temperature control in the injection core area.

[0011] The aforementioned problems not only lead to low material utilization and reduced product yield during injection molding, but also reduce production efficiency and increase equipment downtime due to runner blockage and frequent cleaning and maintenance, which seriously restricts the high-quality and efficient production of precision rubber products such as valve oil seals. Summary of the Invention

[0012] To address the aforementioned technical problems, the present invention aims to provide a flow channel, temperature control system, and method that can meet the requirements of low thermal conductivity and overcome sensor hysteresis to achieve high-precision dynamic constant temperature control. Through the synergy of a composite flow channel unit design with "functional-structural separation" and a Smith-PID hysteresis compensation control strategy, high-precision constant temperature control of the injection core area is achieved.

[0013] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Low thermal conductivity constant temperature composite runner for valve stem seal injection mold, including: The injection core is a hollow shaft structure that runs through the axis, forming an injection cavity inside for conveying plasticized rubber material. The injection core is made of a polymer material with a thermal conductivity of less than 0.5 W / (m·K). The metal outer shell is a cylindrical shape with a flange, and has a hollow cylindrical cavity and an annular sealed cavity inside. The annular sealed cavity surrounds the hollow cylindrical cavity. An injection core is coaxially sleeved inside the hollow cylindrical cavity, and the injection core and the hollow cylindrical cavity are transitionally fitted to form a composite structure. A flow channel nozzle, mounted on the metal casing and connected to the annular sealed cavity, is used for the introduction and export of constant temperature circulating fluid. A sealing assembly includes a sealing ring and a sealing cap. The sealing ring is disposed between the mating surfaces of the metal housing and the sealing cap, and the sealing cap is used to seal the axial end of the annular sealed cavity.

[0014] Furthermore, the injection core serves as a functional body for heat insulation and guiding the adhesive, while the metal shell is a structural body that bears mechanical loads. The lower end face of the metal shell forms a sealing mating surface and integrates a temperature control flow channel inside, forming a composite structure of heat insulation for the injection core and load-bearing capacity for the metal shell. The polymer material is selected from polyetheretherketone or polyphenylene sulfide with a thermal conductivity of 0.25-0.35 W / (m·K); A temperature sensor is embedded in the outer wall of the injection core for real-time monitoring of the injection core temperature; the outer diameter of the injection core is Φ25-40mm and the wall thickness is 8-12mm. The annular sealed cavity maintains a distance of 2-4 mm from the outer wall of the hollow cylindrical cavity; The flange of the metal casing is machined with countersunk holes for connecting the metal casing to the mold.

[0015] Furthermore, the metal casing is made of H13 or SKD61 hot work die steel with a hardness of HRC 48-52, and the outer diameter of the metal casing is Φ50-80mm. The width of the annular sealed cavity is 5-8 mm.

[0016] The temperature control system for the low thermal conductivity constant temperature composite runner of the valve stem seal injection mold includes: A composite flow channel unit, including at least one low thermal conductivity constant temperature composite flow channel, is installed in the template of a valve oil seal injection mold; The circulating execution unit includes a liquid storage tank, a circulating pump, a mold temperature controller, and a flow regulating mechanism connected in sequence through pipelines, and is connected to the composite flow channel unit through pipe joints to form a closed fluid circulation path; The temperature detection unit includes a temperature sensor embedded in the core wall of each composite flow channel unit, as well as a corresponding signal conditioning and acquisition module; The control unit includes a processor and a memory; the memory stores a control program, parameters of the heat conduction control differential equation, and a Smith-PID control algorithm for hysteresis compensation; the processor executes the control program, receives signals from the temperature detection unit, runs the Smith-PID control algorithm to calculate control commands for the flow regulating mechanism, and sends control commands to the flow regulating mechanism, thereby realizing closed-loop control of the injection core temperature.

[0017] Furthermore, the flow regulation mechanism includes an electric regulating valve and a flow monitoring unit. The electric regulating valve is installed on the water inlet pipe and is a V-type regulating ball valve with a regulation accuracy of ±1% FS and a response time of ≤3s. The flow monitoring unit uses an electromagnetic flow meter with an accuracy of ±0.5% FS, which is used to monitor the cooling medium flow in real time and feed it back to the control unit. The control unit uses a programmable logic controller as the processing module and is equipped with an analog input module and an analog output module. The analog input module is used to collect temperature and flow signals, which are then processed by the PLC and output as control commands by the analog output module.

[0018] Furthermore, the Smith-PID control algorithm includes: A composite flow channel isothermal circulation system was established, and the heat conduction control differential equation of the system was constructed. The dynamic law of temperature change in the injection core region was fitted by the heat conduction control differential equation. The parameters of the heat conduction control differential equation include thermal inertia time constant, process gain, and total lag time of the composite flow channel isothermal circulation system. A Smith predictor is constructed to compensate for the pure time delay characteristics of the composite flow channel isothermal circulation system. Configure a PID feedback controller to generate feedback control quantities based on temperature deviation; Configure a feedforward controller to generate feedforward compensation control quantities for periodic thermal shock disturbances; The feedforward compensation control quantity and the feedback control quantity are superimposed to synthesize the total circulating fluid flow control command.

[0019] A temperature control method for a low thermal conductivity constant-temperature composite runner in a valve stem seal injection mold, implemented using the aforementioned temperature control system, includes the following steps: Step S1: Install the composite flow channel unit into the template of the valve oil seal injection mold, connect the cycle execution unit, temperature detection unit and control unit to construct a composite flow channel constant temperature circulation system; Step S2: Establish the heat conduction control differential equation characterizing the temperature dynamics of the injection core region, and determine the parameters of the heat conduction control differential equation through system identification; Step S3: Configure the PID feedback controller and generate feedback control quantity based on temperature deviation; Step S4: Construct a Smith predictor, perform hysteresis compensation on the pure hysteresis characteristics of the composite flow channel isothermal circulation system based on the heat conduction control differential equation, and combine it with the PID feedback controller to form a Smith-PID composite control structure. Step S5: Configure the feedforward controller to generate feedforward compensation control quantities for periodic thermal shock disturbances; Step S6: Superimpose the feedforward compensation control quantity and the feedback control quantity to generate a total circulating fluid flow control command. Adjust the opening of the electric regulating valve according to the total circulating fluid flow control command to control the circulating fluid flow through the composite flow channel unit.

[0020] Further, step S2 includes: The dynamic behavior of the injection core temperature is modeled using first-order inertial and pure time-delay differential equations, and the heat conduction control differential equations of the composite flow channel isothermal circulation system are established:

[0021] in, This refers to the actual temperature of the injection core. To control the flow rate of the circulating fluid in real time. The thermal inertia time constant, For process gain, The total lag time of the composite flow channel isothermal circulation system. Q ( t τ d (Lag) The flow signal subsequently applied to the composite flow channel constant temperature circulation system, where t is a time variable; The model parameters , , The parameters are obtained through system identification: a step flow excitation signal is applied to the composite flow channel isothermal circulation system, the temperature step response curve of the injection core is collected simultaneously, and the first-order inertial pure hysteresis differential equation is identified offline based on the least squares method.

[0022] Furthermore, in step S3, the expression for the PID controller output feedback control quantity is:

[0023] In the formula, e p (t) The temperature deviation signal is the integral variable. , , These are the proportional, integral, and differential gain coefficients, respectively, which are tuned using the Ziegler-Nichols method or the critical proportional gain method.

[0024] Further, step S4 includes: Building the internal model of the Smith predictor:

[0025] The Gm (s) For the controlled object model without lag elements, s is the complex variable obtained after Laplace transform; The Smith predictor receives the circulating fluid flow control command output from the PID controller. Q c (s) And calculate the predicted temperature output of the controlled object model without hysteresis. T p (s) :

[0026] The feedback deviation ep(s) after compensation by the Smith predictor is calculated and used as the input to the PID controller:

[0027] In the formula, T set Set the temperature for the composite flow channel constant temperature circulation system. T set This is the Laplace transform of the temperature sensor's measured values. For output of the model with hysteresis, The transfer function is for a pure time-delay element.

[0028] Further, step S5 includes: according to the real-time injection cycle of the valve stem seal injection machine. t cycle Calculate the average heat load disturbance per unit time. P dict Construct feedforward compensation control quantity u ff (t) :

[0029] In the formula, Φ is the estimated heat transferred from the high-temperature mold cavity to the injection core area during a single injection process, which is calculated based on the mold cavity temperature, the thermophysical parameters of the injection core material, and the contact area. K ff The feedforward gain coefficient is based on the process gain. K p Calibration is performed to match the feedforward compensation amount with the actual heat exchange capacity of the composite flow channel isothermal circulation system.

[0030] Furthermore, in step S6, the feedforward control quantity is... u ff ( t ) and PID feedback control quantity u PID ( tThe total circulating fluid flow control command is obtained by superimposing and synthesizing the commands. Q c ( t ):

[0031] In each control cycle, the control unit performs the following actions: reads the measured temperature Tact(k) from the temperature sensor; calls the Smith predictor algorithm to calculate the hysteresis-compensated deviation signal ep(k); obtains the flow control command Qc(k) based on the PID algorithm and feedforward calculation, and converts the flow control command into an electric regulating valve opening signal; adjusts the flow rate of the circulating liquid flowing through the composite flow channel unit according to the electric regulating valve opening signal, so that the temperature of the injection core is stabilized within ±2°C of the target temperature TsetTset. The control cycle is set to 100-500ms; the opening signal of the electric regulating valve adopts a 4-20mA standard current signal; the target temperature T set The setting is based on the plasticizing temperature of the valve stem seal rubber material, where, for fluororubber materials, T set The temperature is set to 80-100°C for acrylic rubber materials. T set Set to 100-120°C.

[0032] Furthermore, the proportional gain coefficient of the controller Integral gain coefficient Differential gain coefficient Tuning using the Ziegler-Nichols method: First, use proportional control, gradually increasing the proportional gain until the composite flow channel isothermal circulation system produces constant amplitude oscillations. Record the critical gain Ku and the oscillation period Tu. Then, calculate the PID parameters using the following formula:

[0033]

[0034]

[0035] The feedforward gain coefficient K ff The calibration method is as follows:

[0036] Where 'a' is the heat exchange efficiency coefficient, which ranges from 0.8 to 1.2 and is determined based on the actual heat exchange efficiency between the circulating fluid and the injection core.

[0037] Compared with the prior art, one or more embodiments of the present invention may have the following advantages: 1) Integrative Structure-Function Innovation: A composite flow channel unit with "separated function and structure" is proposed. A low-thermal-conductivity PEEK injection core serves as both insulation and adhesive guiding, embedded within a high-strength metal shell to form a standardized, replaceable unit. The metal shell integrates an active, cylindrical, temperature-controlled flow channel. This design fundamentally combines efficient insulation with uniform, active temperature control, completely solving the problems of uneven temperature in traditional metal flow channels and the inability of insulated injection nozzles to actively control temperature.

[0038] 2) High-precision hysteresis-compensated temperature control: A differential equation for heat conduction control of the composite flow channel isothermal circulation system is constructed, and a feedforward-feedback composite control strategy combining a Smith predictor and PID is adopted. This algorithm can accurately compensate for the measurement hysteresis of the temperature sensor and the heat conduction hysteresis of the composite flow channel isothermal circulation system, significantly improving the response speed and control stability, achieving uniform isothermal temperature in the injection area, and fundamentally preventing premature vulcanization of the rubber compound caused by temperature fluctuations.

[0039] 3) Improve production efficiency and product quality: By achieving uniform and constant temperature in the flow channel, the rubber material is kept in a plasticized state before entering the high-temperature cavity, which basically eliminates the phenomenon of premature vulcanization and scrapping of the rubber material in the flow channel. The material utilization rate is greatly improved, the product consistency and yield are significantly improved, and the downtime cleaning time caused by flow channel blockage is reduced.

[0040] 4) Easy to maintain and promote in engineering: The standardized unit design makes disassembly, replacement and maintenance extremely simple, without the need for professional electric heating personnel or disassembling the entire mold, which reduces maintenance costs and technical thresholds, and facilitates the transformation and upgrading of existing production lines, with good practicality and economy. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a composite flow channel unit structure with "functional-structural separation"; where a is the composite assembly section of the injection core and the metal shell, b is the composite assembly structure of the injection core and the metal shell, and c is the flow channel nozzle structure. Figure 2 This is a schematic diagram of the temperature control system for a low thermal conductivity constant temperature composite flow channel unit; Figure 3 This is a flowchart of the temperature control method for the low thermal conductivity constant temperature composite runner of valve oil seal injection mold; Figure 4 This is a schematic diagram of the Smith-PID circulating flow channel temperature control principle. Figure 5 This is a comparison of temperature change curves between a traditional metal cooling channel and the composite channel unit of the present invention; where a is the temperature change curve of the traditional metal cooling channel and b is the temperature change curve of the composite channel unit of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in further detail below with reference to the embodiments and accompanying drawings.

[0043] like Figure 1 The diagram shows a low thermal conductivity constant temperature composite flow channel for a valve stem seal injection mold. A represents the cross-section of the injection core and metal shell assembly, b represents the assembly structure of the injection core and metal shell, and c represents the flow channel nozzle structure. The composite flow channel includes: an injection core 1, a metal shell 2, a flow channel nozzle 3, and a sealing assembly. The injection core is an axially continuous hollow shaft structure with an internal injection cavity for guiding the flow of plasticized material. The metal shell is a flanged cylinder assembled with the injection core. An annular sealed cavity 4 is machined inside the metal shell, tightly surrounding the outer circumference of the injection core to form a cylindrical temperature-controlled flow channel. The flow channel nozzle is located on the metal shell and communicates with the annular sealed cavity for the inflow and outflow of circulating fluid within the low thermal conductivity constant temperature composite flow channel. The sealing assembly includes a sealing ring 6 and a sealing cap 7. The sealing ring is located between the mating surfaces of the metal shell and the sealing cap, and the sealing cap seals the annular sealed cavity.

[0044] The injection core, as a functional component, is responsible for heat insulation and guiding the adhesive, while the metal shell, as a structural component, bears the mechanical load. The lower end face of the metal shell forms a sealing mating surface and integrates an active temperature control channel inside, forming a composite structure with functional and structural separation. The injection core is made of a high-temperature resistant polymer material with a thermal conductivity of less than 0.5 W / (m·K). It has a hollow shaft structure that runs through the axis and forms two opposite and connected inverted conical injection cavities with a cone angle of 15°-25° to guide the plasticized material. A temperature sensor mounting groove 5 is provided on the outer circumference of the injection core, through which a temperature sensor is installed for real-time monitoring of the injection core temperature. A countersunk hole 8 is machined on the flange for threaded connection between the metal shell and the mold.

[0045] The injection core material is selected from polyetheretherketone (PEEK) or polyphenylene sulfide (PPS), with a thermal conductivity of 0.25-0.35 W / (m·K) and a temperature resistance of ≥250°C. The outer diameter of the injection core is Φ25-40mm, and the wall thickness is 8-12mm. The temperature sensor is embedded in the middle of the injection core wall. The metal shell material is made of H13 or SKD61 hot work die steel with a hardness of HRC 48-52. The width of the annular sealed cavity is 5-8mm, and the distance between the annular sealed cavity and the outer wall of the injection core is 2-4mm. The outer diameter of its metal shell is Φ50-80mm.

[0046] like Figure 2 As shown, this embodiment also provides a temperature control system for a low thermal conductivity constant temperature composite runner in a valve stem seal injection mold, comprising: A composite runner unit, comprising at least one low thermal conductivity constant temperature composite runner, is installed in the template of a valve oil seal injection mold; The circulation execution unit includes a liquid storage tank, a circulation pump, a mold temperature controller, and a flow regulation mechanism connected sequentially via pipelines, and is connected to the composite flow channel unit via quick-connect couplings to form a closed fluid circulation path; the flow channel working pressure is 0.3-0.5MPa, and the flow rate range is 5-50L / min; the high-precision mold temperature controller has a temperature control accuracy of not less than ±0.5℃; the flow regulation mechanism includes an electric regulating valve and a flow monitoring unit. The electric regulating valve is installed on the water inlet pipeline, wherein the electric regulating valve is a V-type ball valve with an adjustment accuracy of ±1% and a response time ≤3s; the flow monitoring unit uses an electromagnetic flow meter with an accuracy of ±0.5%FS, used to monitor the cooling medium flow rate in real time and feed it back to the control unit; The temperature detection unit includes a PT100 temperature sensor (measurement accuracy ±0.5℃) embedded in the core wall of each composite flow channel unit, and a corresponding signal conditioning and acquisition circuit. The control unit includes a processor and a memory. The memory stores a control program, parameters of the thermal conduction control differential equation of the composite flow channel isothermal circulation system, and a Smith-PID control algorithm for hysteresis compensation. The control unit uses a programmable logic controller as a processing module. It acquires temperature and flow signals through an analog input module, processes them, and outputs control commands via an analog output module, providing 4-20mA control commands. The memory stores the control program, parameters of the thermal conduction control differential equation of the composite flow channel isothermal circulation system, and the Smith-PID control algorithm. The processor is configured to execute the control program, receive signals from the temperature detection unit, run the Smith-PID control algorithm to calculate control commands for the flow regulation mechanism, and send control commands to the flow regulation mechanism to achieve closed-loop control of the injection core temperature.

[0047] The Smith-PID control algorithm includes: A composite flow channel isothermal circulation system was constructed, and the heat conduction control differential equation of the system was constructed. The dynamic law of temperature change in the injection core region was fitted by the differential equation. A Smith predictor is constructed to provide feedforward compensation for the pure time delay characteristics of the composite flow channel isothermal circulation system. Configure a feedforward controller to generate feedforward compensation control quantities for periodic thermal shock disturbances; Configure a PID feedback controller to generate feedback control quantities based on temperature deviation; The feedforward compensation control quantity and the feedback control quantity are superimposed to synthesize the total circulating fluid flow control command.

[0048] The parameters of the thermal conduction control differential equation model of the composite flow channel isothermal circulation system include the thermal inertia time constant, process gain, and total lag time of the composite flow channel isothermal circulation system. The parameters of the thermal conduction control differential equation model are obtained through system identification: a step flow excitation signal is applied to the composite flow channel isothermal circulation system, the temperature step response curve of the injection core is collected simultaneously, and the thermal conduction control differential equation is determined by offline fitting based on the least squares method.

[0049] like Figure 3 As shown, this embodiment also provides a temperature control method for a low thermal conductivity constant temperature composite runner in a valve stem seal injection mold, including the following steps: Step S1: Install the composite flow channel unit into the template of the valve oil seal injection mold, connect the cycle execution unit, temperature detection unit and control unit to construct a composite flow channel constant temperature circulation system; Step S2: Establish the heat conduction control differential equation characterizing the temperature dynamics of the injection core region, and determine the parameters of the heat conduction control differential equation through system identification; Step S3: Configure the PID feedback controller and generate feedback control quantity based on temperature deviation; Step S4: Construct a Smith predictor, based on the heat conduction control differential equation, to perform hysteresis compensation on the pure hysteresis characteristics of the composite flow channel isothermal circulation system, and combine it with the PID feedback controller to form a Smith-PID composite control structure. Step S5: Configure the feedforward controller to generate feedforward compensation control quantities for periodic thermal shock disturbances; Step S6: Superimpose the feedforward compensation control quantity and the feedback control quantity to generate a total circulating fluid flow control command. Adjust the opening of the electric regulating valve according to the total circulating fluid flow control command to control the circulating fluid flow through the composite flow channel unit.

[0050] Step S1 includes: installing at least one composite flow channel, consisting of an injection core, a metal shell, a flow channel nozzle, and a sealing assembly, into the template of the valve oil seal injection mold; connecting the flow channel nozzle to an external circulation pipeline; the external circulation pipeline is sequentially connected to a circulation pump, a heating / cooling device, a liquid storage tank, and a flow regulating mechanism to form a closed circulation loop.

[0051] Step S2 includes: During the valve stem seal injection molding process, a dynamic mathematical model of the temperature of the composite flow channel constant temperature circulation system is established, and the actual temperature of the injection core of the composite flow channel unit is collected in real time through the temperature sensor thermistor. T act (t) The target control temperature required for valve stem seal injection process T set(Set at 80±2℃) For comparison, the temperature control error e(t) is defined as:

[0052] Considering the significant thermal inertia and temperature transfer hysteresis in the heat exchange process between the injection core (PEEK material) and the circulating fluid inside the metal shell, a first-order inertial and pure hysteresis differential equation is used to model the dynamic temperature behavior of the flow channel core, establishing the heat conduction control differential equation of the composite flow channel isothermal circulation system:

[0053] in, This refers to the actual temperature of the injection core. To control the flow rate of the circulating fluid in real time. This is the thermal inertia time constant. It is related to the equivalent heat capacity of the injection core, the heat capacity of the metal shell, and the thermal resistance between the two; Q(t) τd) is the flow signal acting on the composite flow channel isothermal circulation system after hysteresis, and t is the time variable; The process gain represents the coefficient of influence of the circulating fluid flow rate on the core temperature, which is related to the specific heat capacity of the circulating fluid, the thermal conductivity area of ​​the core, and the convective heat transfer coefficient. The total lag time of the composite flow channel constant temperature circulation system includes the measurement response lag of the temperature sensor thermistor, the transmission lag of the circulating fluid from the mold temperature controller to the unit, and the lag of heat conduction inside the injection core; , , The parameters are obtained through system identification: During the equipment commissioning phase, a step flow excitation signal is applied to the composite flow channel constant temperature circulation system, and the temperature step response curve of the injection core is collected simultaneously. The first-order inertial pure lag differential equation is identified offline based on the least squares method, thereby determining the parameter values ​​that are suitable for the current specific equipment and process.

[0054] In step S3, the expression for the PID controller's output feedback control quantity is:

[0055] In the formula, ep(t) is the temperature deviation signal. For integration variables, For proportional gain coefficient, For integral gain coefficient, The differential gain coefficient is tuned using the Ziegler-Nichols method or the critical proportionality method. The proportional, integral, and derivative gain coefficients of the controller , , Tuning using the Ziegler-Nichols method: First, proportional control is used, and the proportional gain is gradually increased until the composite flow channel isothermal circulation system produces constant amplitude oscillations. The critical gain Ku and the oscillation period Tu are recorded. Then, the PID parameters are calculated according to the Ziegler-Nichols tuning formula.

[0056]

[0057]

[0058] like Figure 4 The schematic diagram of Smith-PID circulating flow channel temperature control is shown. Step S4 includes: Construct a Smith predictor to compensate for the pure time lag τd in a composite flow channel isothermal circulation system: Define the internal model of the Smith predictor:

[0059] The G m (s) The model represents the controlled object without any hysteresis; s is the complex variable obtained after the Laplace transform; the Smith predictor receives the circulating fluid flow control command output by the PID controller. Q c (s) And calculate the predicted temperature output of the controlled object model without hysteresis. T p (s) :

[0060] Calculate the feedback bias after compensation by the Smith predictor. e p (s) As input to the PID controller, thus advancing the response time. τ d The calculation relationship for compensating for temperature changes is as follows:

[0061] In the formula, T set Set the temperature for the composite flow channel constant temperature circulation system. T act (s) This is the Laplace transform of the temperature sensor's measured values. For output of the model with hysteresis, The transfer function is for a pure time-delay element; this structure effectively eliminates pure time delay. τd Negative impact on the stability and dynamic performance of the composite flow channel isothermal circulation system.

[0062] Step S5 includes: introducing feedforward control to cope with the thermal shock caused by periodic injection. According to the real-time injection cycle of the valve stem seal injection machine t cycle Calculate the average heat load disturbance per unit time. P dict Construct feedforward compensation control quantity u ff (t) :

[0063] In the formula, Φ represents the estimated heat transferred from the high-temperature mold cavity to the injection core area during a single injection process. K ff The feedforward gain coefficient is based on the process gain. K p Calibration is performed to match the feedforward compensation amount with the actual heat exchange capacity of the composite flow channel isothermal circulation system; Feedforward gain coefficient K ff The calibration method is as follows:

[0064] in a The heat exchange efficiency coefficient ranges from 0.8 to 1.2 and is determined based on the actual heat exchange efficiency between the circulating fluid and the injection core.

[0065] In step S6, the feedforward control quantity is... u ff ( t ) and PID feedback control quantity u PID ( t The total circulating fluid flow control command is obtained by superimposing and synthesizing the commands. Q c ( t ):

[0066] In each control cycle, the control unit reads the measured temperature from the thermistor of the temperature sensor. T act (k) The Smith predictor algorithm is called to calculate the hysteresis-compensated deviation signal. e p (k) Flow control commands are obtained based on PID algorithm and feedforward calculation. Qc (k) The flow control command is converted into an electric regulating valve opening signal; the flow rate of the circulating liquid flowing through the composite flow channel unit is adjusted according to the electric regulating valve opening signal to stabilize the core temperature at the target temperature. T set Within ±2°C; The control cycle is set to 100-500ms; the opening signal of the electric regulating valve adopts a 4-20mA standard current signal; the target temperature T set The setting is based on the plasticizing temperature of the valve stem seal rubber material, where, for fluororubber materials, T set The temperature is set to 80-100°C for acrylic rubber materials. T set Set to 100-120°C.

[0067] The internal model of the Smith predictor G m (s) The model is a first-order inertial model of the controlled object without hysteresis. The Smith predictor compensates for the difference between the output of the hysteresis-free model and the output of the actual control quantity through the hysteresis element in the feedback loop, thus eliminating the influence of pure hysteresis on the stability of the composite flow channel isothermal circulation system. The internal model of the Smith predictor... G m (s) The parameter (τ) c K p The lag time τd needs to be periodically calibrated online. The calibration method is as follows: during a stable production interval, apply a small-amplitude flow test signal and compare the model. G m (s) The goodness of fit between the predicted temperature curve and the sensor-measured temperature curve is determined by using the recursive least squares method to adjust the model parameters. , , Fine-tuning is performed to adapt to long-term, slow changes in the thermal properties of the injection core (such as aging of PEEK materials) or changes in the heat exchange characteristics of the circulating fluid.

[0068] Implementation of closed-loop control: Smith-PID temperature control includes the following: In each control cycle (sampling period from 100ms to 500ms), the control unit performs the following operations: Read the measured temperature of the thermistor of the temperature sensor. T act (k) k is the current sampling time; The Smith predictor algorithm is called to calculate the hysteresis-compensated deviation signal e. p (k); By executing the PID control algorithm and feedforward calculation, the circulating fluid flow control command at the current moment is obtained. Q c (k) ; Establish flow control command Q c (k) The linear mapping relationship between the electric regulating valve opening θ(k) in the composite flow channel constant temperature circulation system and the following:

[0069] In the formula, K v For valve flow coefficient, θ min To maintain the basic valve opening required for minimum circulation, the calculated valve opening value θ(k) is converted into a 4-20mA standard analog current signal via a digital-to-analog converter. This current drive signal is sent to the actuator of the electric regulating valve, linearly driving the valve core to move and changing the flow rate of the circulating liquid through the annular sealed cavity in the composite flow channel unit. This dynamically adjusts the cooling or heating power of the injection core, thereby controlling the actual temperature of the injection core. T set Rapidly and stably approaching the target control temperature T act (t) It achieves ultra-uniform constant temperature control of ±2℃.

[0070] like Figure 5 The figure shows a comparison of temperature change curves between a traditional metal cooling channel and the composite channel unit of the present invention, where a represents the temperature change curve of the traditional metal cooling channel and b represents the temperature change curve of the composite channel of the present invention. Because the traditional metal cooling channel uses temperature control methods such as PID, it cannot compensate for the interference caused by temperature measurement delay, and it also lacks effective compensation for periodic injection thermal shock, resulting in a long-term periodic oscillation of temperature. In contrast, the present invention uses a composite channel unit combined with Smith-PID and feedforward compensation control methods, which can effectively suppress thermal shock and resist delay interference, resulting in relatively stable temperature changes. As shown in Table 1, the Smith-PID method proposed in this invention performs well in the isostatic control of the injection zone in the valve oil seal injection process, exhibiting good temperature uniformity and settling time. Steady-state temperature error e ssFurthermore, the replacement time of the flow channel unit is superior to that of traditional metal cooling flow channel methods. The temperature difference along the entire length of the injection zone is less than 2℃, the adjustment time is less than 100s, and the temperature fluctuation is within ±1.2℃. This effectively reduces the temperature change range of the injection zone and fully verifies the effectiveness of the present invention in suppressing the effects of injection thermal shock and ensuring uniform temperature in the injection zone.

[0071] Table 1

[0072] Data shows that the present invention performs well in temperature control of the injection zone. Compared with traditional metal cooling channels, the Smith-PID control method combined with the designed composite flow channel unit improves temperature uniformity by 80% and reduces steady-state error by more than 70%, which fully verifies the effectiveness of the present invention in suppressing the effects of injection thermal shock and ensuring temperature uniformity in the injection zone. In addition, since the composite flow channel unit adopts a quick-release design, its replacement and maintenance time is shorter, which facilitates equipment maintenance, reduces downtime, and improves production efficiency.

[0073] Application Results: After applying this embodiment to a valve stem seal injection molding production equipment, the temperature in the injection zone was controlled within ±2°C. After 8 hours of continuous production, there was no vulcanization or residual material in the injection nozzle channel, and the material utilization rate increased from 65% to 96%. The produced rubber valve stem seals exhibited high integrity and consistency, effectively improving the material utilization rate and product yield of the injection molding process. The product qualification rate also increased from 88% to 99.2%. Experimental data shows that, compared to traditional metal cooling channels, the Smith-PID control method combined with the designed composite flow channel unit reduces the temperature uniformity across the entire length from >10°C to <2°C, an improvement of 80%. The steady-state error decreased from periodic oscillations of ±5.7°C to a stable ±1.2°C, a reduction of over 70%. The unit replacement time decreased from requiring mold disassembly for >2 hours to a quick-change design of <15 minutes. This fully verifies the effectiveness of this invention in suppressing the effects of injection thermal shock and ensuring uniform temperature in the injection zone.

[0074] Other implementation methods: Other filler core materials available include Solvay KetaSpire KT-820 (thermal conductivity 0.28 W / (m·K)), PPS (thermal conductivity 0.35 W / (m·K)), or PI (thermal conductivity 0.35 W / (m·K)), selected based on specific temperature resistance requirements and cost considerations.

[0075] The metal casing material can also be selected from hot work die steels such as SKD61 and 2344, with a hardness range of HRC 48-52.

[0076] For valve stem seals of different specifications, the outer diameter of the injection core can be designed in a series within the range of Φ25-40mm, corresponding to the outer diameter of the metal shell Φ50-80mm, forming a standardized product series.

[0077] In the control algorithm, the PID parameters can be adjusted according to the specific characteristics of the equipment: proportional gain Kpctrl The range is 0.5-2.0, the integration time is 30-120s, and the derivative time is 5-15s.

[0078] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A low thermal conductivity constant temperature composite runner for valve stem seal injection molds, characterized in that, include: The injection core is a hollow shaft structure that runs through the axis, forming an injection cavity inside for conveying plasticized rubber material. The injection core is made of a polymer material with a thermal conductivity of less than 0.5 W / (m·K). The metal outer shell is a cylindrical shape with a flange, and has a hollow cylindrical cavity and an annular sealed cavity inside. The annular sealed cavity surrounds the hollow cylindrical cavity. An injection core is coaxially sleeved inside the hollow cylindrical cavity, and the injection core and the hollow cylindrical cavity are transitionally fitted to form a composite structure. A flow channel nozzle, mounted on the metal casing and connected to the annular sealed cavity, is used for the introduction and export of constant temperature circulating fluid. A sealing assembly includes a sealing ring and a sealing cap, wherein the sealing ring is disposed between the mating surfaces of the metal housing and the sealing cap, and the sealing cap is used to seal the axial end of the annular sealed cavity; The injection core is a heat-insulating and flow-guiding core, and the metal shell is a pressure-bearing shell; the lower end face of the metal shell is a sealing mating surface, and the interior of the metal shell integrates a temperature-controlled flow channel; the injection core and the metal shell are coaxially assembled to form a composite structure of heat insulation and load bearing. The polymer material is selected from polyetheretherketone and polyphenylene sulfide, which have a thermal conductivity of 0.25 to 0.35 W / (m·K). A temperature sensor is embedded in the outer wall of the injection core for real-time monitoring of the injection core temperature; the outer diameter of the injection core is Φ25~40mm and the wall thickness is 8~12mm; The inner wall of the annular sealed cavity maintains a radial distance of 2-4 mm from the outer wall of the hollow cylindrical cavity; The flange of the metal casing is machined with countersunk holes for connecting the metal casing to the mold.

2. The low thermal conductivity constant temperature composite flow channel for valve oil seal injection mold according to claim 1, characterized in that, The metal outer shell is made of H13 or SKD61 hot work die steel with a hardness of HRC 48-52 and an outer diameter of Φ50-80mm. The width of the annular sealed cavity is 5-8 mm.

3. A temperature control system for a low thermal conductivity constant temperature composite runner in a valve stem seal injection mold, characterized in that, include: A composite flow channel unit, including the low thermal conductivity constant temperature composite flow channel of any one of claims 1-2, is installed in the template of the valve oil seal injection mold; The circulating execution unit includes a liquid storage tank, a circulating pump, a mold temperature controller, and a flow regulating mechanism connected in sequence through pipelines; the circulating execution unit is connected to the composite flow channel unit through a pipe joint to form a closed fluid circulation path; The temperature detection unit includes a temperature sensor embedded in the core wall of the composite flow channel unit, and a corresponding signal conditioning and acquisition module; The control unit includes a processor and a memory; the memory stores a control program, parameters of the heat conduction control differential equation, and a Smith-PID control algorithm for hysteresis compensation. The processor executes the control program, receives the signal from the temperature detection unit, runs the Smith-PID control algorithm to calculate the control command for the flow regulating mechanism, and sends the control command to the flow regulating mechanism, thereby realizing closed-loop control of the injection core temperature.

4. The temperature control system for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 3, characterized in that, The flow regulation mechanism includes an electric regulating valve and a flow monitoring unit. The electric regulating valve is installed on the water inlet pipe and is a V-type regulating ball valve with a control accuracy of ±1% FS and a response time of ≤3s. The flow monitoring unit uses an electromagnetic flow meter with an indication error of ±0.5% FS, which is used to monitor the flow of the cooling medium in real time and feed it back to the control unit. The control unit uses a programmable logic controller as the processing module and is equipped with an analog input module and an analog output module. The analog input module is used to collect temperature and flow signals, which are then processed by the PLC and output as control commands by the analog output module.

5. The temperature control system for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 3, characterized in that, The Smith-PID control algorithm includes: A composite flow channel isothermal circulation system was established, and the heat conduction control differential equation for this system was constructed. The dynamic law of temperature change in the injection core region was fitted by the heat conduction control differential equation. The model parameters of the heat conduction control differential equation include the thermal inertia time constant. Process gain Total lag time of composite flow channel constant temperature circulation system ; A Smith predictor is constructed to compensate for the pure time delay characteristics of the composite flow channel isothermal circulation system. Configure a PID feedback controller to generate feedback control quantities based on temperature deviation; Configure a feedforward controller to generate feedforward compensation control quantities for periodic thermal shock disturbances; The feedforward compensation control quantity and the feedback control quantity are superimposed to synthesize the total circulating fluid flow control command.

6. A temperature control method for a low thermal conductivity constant temperature composite runner in a valve stem seal injection mold, implemented using the temperature control system described in any one of claims 3-5, characterized in that... Includes the following steps: Step S1: Install the composite flow channel unit into the template of the valve oil seal injection mold, connect the cycle execution unit, temperature detection unit and control unit to construct a composite flow channel constant temperature circulation system; Step S2: Establish the heat conduction control differential equation characterizing the temperature dynamics of the injection core region, and determine the parameters of the heat conduction control differential equation through system identification; Step S3: Configure the PID feedback controller and generate feedback control quantity based on temperature deviation; Step S4: Construct a Smith predictor, perform hysteresis compensation on the pure hysteresis characteristics of the composite flow channel isothermal circulation system based on the heat conduction control differential equation, and combine it with the PID feedback controller to form a Smith-PID composite control structure. Step S5: Configure the feedforward controller to generate feedforward compensation control quantities for periodic thermal shock disturbances; Step S6: Superimpose the feedforward compensation control quantity and the feedback control quantity to generate a total circulating fluid flow control command. Adjust the opening of the electric regulating valve according to the total circulating fluid flow control command to control the circulating fluid flow through the composite flow channel unit.

7. The temperature control method for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 6, characterized in that, Step S2 includes: The dynamic behavior of the injection core temperature is modeled using first-order inertial and pure time-delay differential equations, and the heat conduction control differential equations of the composite flow channel isothermal circulation system are established: in, This refers to the actual temperature of the injection core. To control the flow rate of the circulating fluid in real time. The time constant is the thermal inertia. For process gain, The total lag time of the composite flow channel isothermal circulation system. Q ( t τ d (Lag) The flow signal subsequently applied to the composite flow channel constant temperature circulation system t It is a time variable; The model parameters , , The system identification process yielded the following results: a step flow excitation signal was applied to the composite flow channel isothermal circulation system, the temperature step response curve of the injection core was simultaneously acquired, and the first-order inertial pure hysteresis differential equation was identified offline based on the least squares method.

8. The temperature control method for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 7, characterized in that, In step S3, the expression for the PID controller output feedback control quantity is: In the formula, e p (t) This is a temperature deviation signal. For integration variables, , , These are the proportional, integral, and differential gain coefficients, respectively, which are tuned using the Ziegler-Nichols method or the critical proportional gain method.

9. The temperature control method for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 8, characterized in that, Step S4 includes: Building the internal model of the Smith predictor: The G m (s) For a controlled object model without any lag elements, s These are the complex variables obtained after the Laplace transform; The Smith predictor receives the circulating fluid flow control command output from the PID controller. Q c (s) And calculate the predicted temperature output of the controlled object model without hysteresis. T p (s) : Calculate the feedback bias after compensation by the Smith predictor. e p (s) As input to the PID controller: In the formula, T set Set the temperature for the composite flow channel constant temperature circulation system. T act (s) This is the Laplace transform of the temperature sensor's measured values. For output of the model with hysteresis, The transfer function is for a pure time-delay element.

10. The temperature control method for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 8, characterized in that, Step S5 includes: according to the real-time injection cycle of the valve stem seal injection machine. t cycle Calculate the average heat load disturbance per unit time. P dict Construct feedforward compensation control quantity u ff (t) : In the formula, Φ is the estimated heat transferred from the high-temperature mold cavity to the injection core area during a single injection process. The estimated heat is calculated based on the mold cavity temperature, the thermophysical parameters of the injection core material, and the contact area. K ff This is the feedforward gain coefficient, which is based on the process gain. K p Calibration is performed to match the feedforward compensation amount with the actual heat exchange capacity of the composite flow channel isothermal circulation system.

11. The temperature control method for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 10, characterized in that, In step S6, the feedforward control quantity is... u ff ( t ) and PID feedback control quantity u PID ( t The total circulating fluid flow control command is obtained by superimposing and synthesizing the commands. Q c ( t ): In each control cycle, the control unit performs the following steps: Read the measured temperature of the temperature sensor T act (k) The Smith predictor algorithm is invoked to calculate the hysteresis-compensated deviation signal. e p (k) Flow control commands are obtained based on PID algorithm and feedforward calculation. Q c (k) The flow control command is converted into an electric regulating valve opening signal; the flow rate of the circulating liquid flowing through the composite flow channel unit is adjusted according to the electric regulating valve opening signal to stabilize the temperature of the injection core at the target temperature. T set Within ±2°C; The control cycle is set to 100–500 ms; the opening signal of the electric regulating valve adopts a 4–20 mA standard current signal; the target temperature T set The setting is based on the plasticizing temperature of the valve stem seal rubber material, where, for fluororubber materials, T set The temperature is set to 80–100°C for acrylic rubber materials. T set Set to 100–120°C.

12. The temperature control method for the low thermal conductivity constant temperature composite flow channel of the valve oil seal injection mold according to claim 10, characterized in that, The proportional gain coefficient of the controller Integral gain coefficient Differential gain coefficient Tuning using the Ziegler-Nichols method: First, use proportional control, gradually increasing the proportional gain until the composite flow channel isothermal circulation system produces constant amplitude oscillations. Record the critical gain Ku and the oscillation period Tu. Then, calculate the PID parameters using the following formula: The feedforward gain coefficient K ff The calibration method is as follows: in, a The heat exchange efficiency coefficient ranges from 0.8 to 1.2 and is determined based on the actual heat exchange efficiency between the circulating fluid and the injection core.

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