Vacuum cross screw glue injection process

Abstract

The invention discloses a vacuum cross screw rod glue injection process, which comprises the following steps of: preliminarily mixing rubber raw materials according to a ratio, inputting the rubber raw materials into a cross screw rod inlet of a glue injection device, and carrying out rolling type mixing and conveying on the rubber materials through a pair of cross screw rods with inconsistent screw pitches and different rotating speeds, in the process that the rubber material flows into a rubber injection runner from an outlet of the crossed screw rod, when the flowing direction or stress state of the rubber material is detected to change, the vacuum control mold is started, gas entrained in the rubber material is exhausted in a flowing stress direction change area of the rubber material, and the rubber material is fully compressed and uniformly mixed in the axial conveying process. And during vacuum defoaming, a variable-speed glue injection strategy is adopted, and the glue injection flow speed is controlled to be matched with the vacuum efficiency. Therefore, the problems of insufficient mixing, low defoaming efficiency, aging bubble removal, asynchronous glue injection process and the like in the traditional process are solved, and the compactness, the consistency and the production efficiency of the rubber product are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of screw glue injection, in particular to a vacuum cross-screw glue injection process. Background Art

[0002] In the manufacturing process of rubber products, the injection process is a key step in the rubber material's journey from mixing to mold filling and vulcanization. It has a decisive impact on the final product's density, surface quality, and internal structural integrity. Traditional injection equipment mostly uses a single-screw linear conveying structure. The rotating screw pushes the rubber material into the mold cavity, and vulcanization and shaping are completed at preset temperature conditions. Some equipment is equipped with a basic vacuum device to evacuate the mold cavity before or during the initial injection process to reduce air entrainment. However, due to its limited conveying and mixing capabilities, and the fact that vacuuming is usually disconnected from the injection process, the degassing effect is not ideal, and the subsequent aging process still needs to be relied upon to eliminate residual bubbles.

[0003] However, in actual production, closed bubbles are easily formed during the flow of rubber materials, especially at the point where the flow force direction changes, where bubbles are more likely to aggregate. Traditional equipment is difficult to implement effective degassing at such key points, resulting in a certain proportion of bubbles remaining after the product is vulcanized. Therefore, additional processes such as aging and bubble removal are required within 3 to 12 days. This not only prolongs the production cycle and increases energy consumption and costs, but also poses the risk of product performance degradation due to incomplete removal of bubbles. In addition, the single-pitch conveying method lacks the ability to continuously crush and mix the rubber material, which can easily cause uneven rubber mixing and further affect the quality of the finished product. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0005] To this end, the purpose of the present invention is to propose a vacuum cross-screw glue injection process, which uses a cross-screw with inconsistent pitch and adjustable speed to fully mix and crush the rubber material for transportation, thereby achieving improved uniformity of the rubber during the transportation process, and automatically triggering vacuum extraction at the critical moment when the force direction of the rubber flow changes, effectively removing bubbles entrained in the flow. Through the linkage control of the glue injection process and vacuum extraction, the additional time-consuming bubble removal step required in the traditional process is avoided, thereby improving the density of the product and production efficiency.

[0006] To achieve the above object, the present invention proposes a vacuum cross-screw glue injection process, comprising the following steps:

[0007] S1. Rubber material pretreatment and feeding: the rubber raw materials are preliminarily mixed according to the ratio and then input into the cross-screw inlet of the injection device;

[0008] S2. Cross-screw mixing and conveying: A pair of cross-screws with different pitches and speeds are used to mix and convey the rubber material in a rolling manner, so that the rubber material is fully compressed and evenly mixed during the axial conveying process;

[0009] S3. Dynamically identify changes in flow state. When a change in flow direction or force state is detected during the flow of the rubber material from the cross-screw outlet into the injection channel, the vacuum control module is activated.

[0010] S4. Timely vacuum degassing: In the area where the force direction of the rubber material changes, vacuum degassing is performed to remove the gas trapped in the rubber material, thereby enhancing the rubber's density and flow stability;

[0011] S5. Coordinate the injection control. During vacuum degassing, adopt a variable speed injection strategy to control the injection flow rate to match the vacuum efficiency, prevent gas entrapment and flow channel disturbance, and ensure stable filling of the rubber material into the mold.

[0012] S6. Rubber vulcanization molding: After the glue injection is completed, the rubber material is hot-vulcanized and shaped in the mold. No further aging and bubble removal treatment is required, and a rubber product with a dense structure and no residual bubbles can be obtained.

[0013] The present invention discloses a vacuum cross-screw glue injection process. By collaboratively designing a cross-screw with inconsistent pitch and adjustable speed difference and a vacuum degassing system, and combining dynamic flow monitoring with multi-stage glue injection control, the process realizes closed-loop linkage of rubber materials in the mixing, conveying, degassing and glue injection processes. The process can draw a vacuum in real time at key nodes where the rubber flow force changes, effectively remove bubbles, and simultaneously maintain appropriate fluidity and stability of the rubber material through temperature regulation and flow channel optimization, ensuring uniform filling of the mold cavity and rapid vulcanization molding, thereby completely solving the problems of insufficient mixing, low degassing efficiency, time-consuming degassing and asynchronous glue injection processes in traditional processes, and significantly improving the density, consistency and production efficiency of rubber products.

[0014] Specifically, the start timing of the vacuum pumping operation is determined by monitoring the flow state of the rubber material. When it is detected that the force direction of the rubber material changes or the pressure fluctuation reaches a preset threshold, the vacuum pumping is triggered to accurately control the degassing timing.

[0015] Specifically, the injection speed regulating device is used to control the speed at which the rubber material is injected into the mold cavity, so that the injection speed is coordinated with the vacuum pumping process to avoid violent fluctuations in the flow of the rubber material and ensure uniform injection.

[0016] Specifically, temperature control is implemented during the mixing, conveying and injection process of the rubber material. By heating or cooling the rubber material and the screw mechanism, the rubber material maintains appropriate viscosity and fluidity, promotes the escape of bubbles and improves the degassing effect.

[0017] Specifically, the flow channel for rubber injection is optimized and a channel or buffer structure for guiding the escape of bubbles is set in the flow channel, so that bubbles can be discharged along the channel when the rubber material flows through the flow channel, thereby further improving the degassing effect.

[0018] Specifically, the vacuum degree and duration of the vacuum pumping operation are adjustable. A higher vacuum degree is applied at the initial stage when the force direction of the rubber material changes to quickly expel bubbles, and then an appropriate vacuum degree is maintained until the injection is completed to ensure that the bubbles are completely expelled.

[0019] Specifically, the pitch difference and speed difference of the cross screws are adjusted according to the viscosity and mixing requirements of the rubber material, and the best mixing and degassing effects are achieved by changing the screw speed ratio or pitch configuration.

[0020] Specifically, a centralized control system is used to coordinate the screw rotation, vacuum extraction and glue injection processes. The mixing, vacuum extraction and glue injection operations are performed sequentially or synchronously through preset programs to ensure close coordination of each link and further improve the glue injection quality and degassing efficiency.

[0021] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a schematic diagram of the vacuum cross-screw glue injection process of the present invention. DETAILED DESCRIPTION

[0024] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention and are not to be construed as limiting the present invention. On the contrary, the embodiments of the present invention include all variations, modifications, and equivalents that fall within the spirit and scope of the appended claims.

[0025] The following describes the vacuum cross-screw glue injection process according to an embodiment of the present invention with reference to the accompanying drawings.

[0026] like Figure 1 As shown, the vacuum cross-screw glue injection process of the embodiment of the present invention may include the following steps:

[0027] S1. Rubber material pretreatment and feeding: the rubber raw materials are preliminarily mixed according to the ratio and then input into the cross-screw inlet of the injection device;

[0028] It should be noted that the rubber material pretreatment process described in this embodiment may include preliminary homogenization methods such as mechanical kneading, internal mixing or open mixing, and adjust the raw material ratio, plasticizing time and temperature according to the process requirements of different rubber formulations, so that the rubber material entering the cross screw has basic uniformity and appropriate viscosity, ensuring subsequent mixing and conveying efficiency.

[0029] S2. Cross-screw mixing and conveying: A pair of cross-screws with different pitches and speeds are used to mix and convey the rubber material in a rolling manner, so that the rubber material is fully compressed and evenly mixed during the axial conveying process;

[0030] It should be noted that the cross-screw described in this embodiment can form multi-stage shear zones and compression zones through a segmented pitch arrangement, and generate a cross-mixing flow field under the action of the speed difference, thereby enhancing the internal dispersion and plasticizing effect of the rubber material, and is particularly suitable for dynamic mixing and conveying of highly filled, high-viscosity or multi-phase system rubber materials.

[0031] S3. Dynamically identify changes in flow state. When a change in flow direction or force state is detected during the flow of the rubber material from the cross-screw outlet into the injection channel, the vacuum control module is activated.

[0032] It should be noted that the state change identification described in this embodiment can be achieved by setting up a pressure sensor, a stress detection device or a flow rate change analysis module, and performing real-time monitoring of the rubber material at key locations such as flow bending, diameter change, and turning, to ensure that the vacuum pumping operation is accurately activated at the location and time where bubbles are most likely to accumulate, thereby improving the timeliness and pertinence of the degassing response.

[0033] S4. Timely vacuum degassing: In the area where the force direction of the rubber material changes, vacuum degassing is performed to remove the gas trapped in the rubber material, thereby enhancing the rubber's density and flow stability;

[0034] It should be noted that the vacuum pumping operation described in this embodiment can achieve switching of different vacuum degrees through a multi-stage pumping system, and form a local low-pressure environment in the degassing area, so that bubbles can expand and escape rapidly. Combined with the slow flow structure, the residence time of the rubber material in this area is further extended, which significantly improves the bubble discharge efficiency and the density of the rubber material.

[0035] S5. Coordinate the injection control. During vacuum degassing, adopt a variable speed injection strategy to control the injection flow rate to match the vacuum efficiency, prevent gas entrapment and flow channel disturbance, and ensure stable filling of the rubber material into the mold.

[0036] It should be noted that the variable speed injection control described in this embodiment adopts a staged flow regulation system. The initial injection stage maintains a low speed to cooperate with the degassing operation, and switches to a high-efficiency filling mode in the middle and late stages. Differentiated injection programs can be set according to the mold cavity structure to avoid vortexes or air entrapment caused by sudden changes in flow rate, thereby achieving high-quality mold filling.

[0037] S6. Rubber vulcanization molding: After the glue injection is completed, the rubber material is hot-vulcanized and shaped in the mold. No further aging and bubble removal treatment is required, and a rubber product with a dense structure and no residual bubbles can be obtained.

[0038] It should be noted that the vulcanization molding process described in this embodiment is combined with efficient front-end degassing measures, which can greatly shorten the vulcanization cycle. Moreover, since the internal bubbles have been basically eliminated before the rubber material enters the mold cavity, the product does not require additional heat treatment or secondary aging and degassing operations after vulcanization, which helps to improve production cycle, reduce energy consumption, and ensure that the performance of the product is stable and reliable during its service life.

[0039] Specifically, first, the rubber raw materials are preliminarily mixed according to a predetermined formula, and the raw materials are preliminarily homogenized through internal mixing or open mixing equipment to control the viscosity and fluidity, making them suitable for entering the injection system. Subsequently, the rubber material is fed into a cross-screw mechanism and axially conveyed by a pair of screws with inconsistent pitches and adjustable speed differences. Multiple shear zones and compression zones are formed within the screw structure, and dynamic rolling is used to achieve re-mixing and uniform dispersion of the rubber material. Before the rubber material is continuously conveyed to the screw outlet and enters the injection flow channel, the pressure or flow rate sensor installed in the system monitors its flow state in real time. Once a change in the force direction is detected (such as a change in the flow channel structure from a straight line to a bend, from wide to narrow, etc.), the vacuum control system is immediately triggered to perform a vacuum pumping operation at the turning point to quickly remove entrained gas from the rubber material and prevent the formation of sealed bubbles. In order to ensure that the vacuuming process does not interfere with the injection rhythm, the system adopts a segmented injection strategy. During the degassing stage, the rubber material is injected at a low and stable speed. After the vacuum is completed, it switches to high-speed injection mode for rapid mold filling. At the same time, different injection speed curves can be set according to the mold cavity shape and flow path. After the injection is completed, the rubber material immediately enters the hot vulcanization stage in the mold. With the help of the previous efficient mixing and thorough degassing, there is no need for subsequent 3-12 days of aging and degassing treatment to obtain high-quality rubber products with dense structure and no pores. This process solves the problems of residual bubbles and additional aging treatment caused by insufficient mixing of a single screw, no effective degassing measures at the flow inflection point, and the inability to synchronize vacuum extraction and injection in traditional technologies, thereby achieving a comprehensive improvement in degassing efficiency, injection quality and production efficiency.

[0040] In one embodiment of the present invention, Figure 1As shown, the start timing of the vacuum pumping operation is determined by monitoring the flow state of the rubber material. When it is detected that the force direction of the rubber material changes or the pressure fluctuation reaches a preset threshold, the vacuum pumping is triggered to accurately control the degassing timing.

[0041] It should be noted that the flow state monitoring described in this embodiment can be based on multi-point data collection by pressure sensors, flow rate sensors or stress probes installed at key nodes of the flow channel, and combined with preset threshold judgment logic and time delay algorithm, dynamic comparison is performed through the control system. When the system determines that the rubber material may be prone to bubbles due to direction change, speed mutation or compression recovery, it can issue a vacuum command to ensure that the vacuum operation responds in a timely manner, the degassing is highly targeted, and the process is controlled and stable.

[0042] In one embodiment of the present invention, Figure 1 As shown, the injection speed regulating device is used to control the speed of the rubber material injected into the mold cavity, so that the injection speed is coordinated with the vacuum pumping process to avoid violent fluctuations in the flow of the rubber material and ensure uniform injection.

[0043] It should be noted that the injection speed adjustment device described in this embodiment can adopt a servo-controlled pump, a stepping screw or a frequency-controlled injection mechanism. Through data interconnection with the vacuum control module, the injection speed can be dynamically adjusted in real time according to the current vacuuming status. In the initial stage of vacuuming, low-speed injection is maintained to keep the negative pressure stable. After degassing is completed, the rubber material is accelerated to fill the mold cavity, thereby ensuring the degassing quality while improving the overall molding efficiency and avoiding the occurrence of air pockets or incomplete filling in the mold cavity.

[0044] In one embodiment of the present invention, Figure 1 As shown, temperature control is implemented during the mixing, conveying and injection process of the rubber material. By heating or cooling the rubber material and the screw mechanism, the rubber material maintains appropriate viscosity and fluidity, promotes the escape of bubbles and improves the degassing effect.

[0045] It should be noted that the temperature control system described in this embodiment can be divided into zones to set different temperature control parameters for key areas such as the screw barrel, feed section, compression section, injection section and mold cavity inlet. The mixing section maintains the medium and high temperature required for high shear, the injection section is appropriately cooled to control the viscosity and stabilize the flow rate, and the mold cavity area maintains the vulcanization temperature to ensure product performance. At the same time, the temperature sensor provides real-time feedback and dynamic correction to the adjustment system to ensure that the rubber material is always in the optimal viscosity range throughout the entire process, which is conducive to mixing, conveying and bubble escape.

[0046] In one embodiment of the present invention, Figure 1As shown, the flow channel for rubber injection is optimized and a channel or buffer structure for guiding the escape of bubbles is set in the flow channel, so that bubbles can be discharged along the channel when the rubber material flows through the flow channel, thereby further improving the degassing effect.

[0047] It should be noted that the flow channel optimization design described in this embodiment adopts a structure that adds a degassing cavity, a back-pressure expansion zone or an arc-shaped buffer section, and provides a local volume expansion zone in the flow channel before the rubber material enters the mold cavity from the screw. The expansion cross-section and deceleration effect of this area are used to cause bubbles to float up and escape under low-pressure slow flow conditions, and are discharged through a special guide tube or vacuum port. At the same time, this design minimizes interference with the mainstream path, can effectively improve the efficiency of bubble aggregation and release, and avoid bubbles being retained in the molded product.

[0048] In one embodiment of the present invention, Figure 1 As shown, the vacuum degree and duration of the vacuum pumping operation are adjustable. A higher vacuum degree is applied at the initial stage when the force direction of the rubber material changes to quickly expel bubbles, and then an appropriate vacuum degree is maintained until the injection is completed to ensure that the bubbles are completely expelled.

[0049] It should be noted that the vacuum exhaust control system described in this embodiment realizes the dynamic setting of the vacuum degree through a multi-stage vacuum pump group or a variable frequency exhaust device, and combines the exhaust time controller and the sensor feedback closed loop to adjust the exhaust process. In the initial stage, a high negative pressure environment is quickly established to allow the tiny bubbles in the rubber material to expand and escape. In the later stage, a medium negative pressure is maintained to ensure continuous degassing without interfering with subsequent glue injection. At the same time, the entire exhaust process can be set and monitored in real time through the HMI human-machine interface to ensure the stability and traceability of the production process.

[0050] In one embodiment of the present invention, Figure 1 As shown, the pitch difference and speed difference of the cross screw are adjusted according to the viscosity and mixing requirements of the rubber material, and the best mixing and degassing effect is achieved by changing the screw speed ratio or pitch configuration.

[0051] It should be noted that the adjustment of the pitch difference and the speed difference described in this embodiment can be based on the rheological properties and mixing requirements of different rubber systems (such as NR, EPDM, silicone, etc.), and the independent speed adjustment of the two cross screws can be achieved through an electronically controlled servo motor. A replaceable modular thread segment configuration is adopted in the screw design. The pitch difference and speed ratio are increased in the low-viscosity and high-shear system, and a small differential pitch and close-speed rotation strategy is adopted in high-viscosity materials, thereby achieving a comprehensive effect of strong material adaptability, uniform mixing, and sufficient primary degassing.

[0052] In one embodiment of the present invention, Figure 1As shown, a centralized control system is used to coordinate the screw rotation, vacuum extraction and injection processes. The mixing, vacuum extraction and injection operations are performed sequentially or synchronously through preset programs to ensure close coordination of each link and further improve the injection quality and degassing efficiency.

[0053] It should be noted that the centralized control system described in this embodiment uses a PLC or an industrial-grade embedded controller as the core control unit, which links the drive motor, vacuum pump group and injection device. By setting the logic flow chart and process parameter library, it automatically executes the start-up, transition and termination operations between each process. At the same time, it supports users to set process curves, fault alarms and historical data backtracking through the touch interface or remote monitoring platform, ensuring that the entire injection process is automated, standardized and highly repeatable, and achieving optimal coordination between degassing and mold filling from the system level.

[0054] Example 1:

[0055] Vacuum injection and degassing process of EPDM rubber automobile sealing strips

[0056] This embodiment provides a vacuum cross-screw glue injection and degassing process for EPDM rubber sealing strips for automobiles. First, the rubber raw materials are pretreated to ensure that the rubber is dry and pure. After the EPDM raw rubber and compounding agents are fully mixed, they are preheated in an oven at 6080°C for 12 hours to remove moisture and low-molecular volatiles. At the same time, a vacuum mixer is used to degas the rubber and expel the air entrained during the mixing process. When storing the pretreated rubber, pay attention to sealing and moisture-proofing to ensure that no new bubble sources are generated in subsequent processes.

[0057] Next, the processed rubber compound is placed into the hopper of the cross-twin screw injection machine. A cross-screw extruder is a pair of interlocking, intersecting screw elements that rotate in opposite directions, effectively mixing and conveying the EPDM rubber compound. The screw is designed with a gradual thread structure and self-exhausting. A vacuum exhaust port is located in the middle of the screw and connected to a vacuum pump. The screw speed is controlled at a moderate level (e.g., 50 rpm), causing the rubber compound to undergo continuous shear mixing and cyclic tumbling within the screw channel. Through a combination of thin-layer mixing and vacuum extraction, residual bubbles in the barrel are continuously carried to the surface of the material flow and exposed to the vacuum environment, achieving sufficient degassing. To prevent excessive suction of the rubber compound during vacuuming, the vacuum section of the screw is designed with a reverse conveying element to reduce the local screw channel pressure and control the vacuum level to approximately 1×10^3 Pa, rather than an infinitely close vacuum. The entire mixing and conveying process is carried out in a closed state to prevent external air from re-entering the barrel.

[0058] During the injection molding stage, a segmented injection filling strategy is adopted to further avoid bubble defects. The vacuum system is started immediately after the mold is closed to evacuate the mold cavity. When the vacuum degree of the mold cavity reaches about -0.09MPa (equivalent to an absolute pressure of nearly 1 millibar), injection begins. The initial injection is carried out at a lower speed (for example, the first 50% volume fraction of the rubber is injected at a steady low speed), and the air at the front is extracted in time by vacuum. Then the screw advance speed is increased in the middle section to quickly fill the remaining cavity, and the speed is slowed down when it is close to filling to prevent overshoot and ensure a smooth pressure transition. The vacuum is maintained continuously throughout the injection process until the mold filling is completed and the pressure is stopped for a few seconds, and then the vacuum valve is closed to prevent the rubber from being over-extracted or sucked back. At the same time, during the injection of the rubber, the mold exhaust groove and vacuum pipeline remain unobstructed to ensure that any residual tiny bubbles can escape the mold cavity.

[0059] In terms of temperature control, the barrel and screw sections of the glue injection machine adopt low-temperature temperature control (for example, kept at around 70°C) to prevent the EPDM rubber from vulcanizing prematurely during transportation. The mold is heated to the vulcanization temperature of EPDM, which is about 160°C. After the rubber is injected into the mold cavity, the mold temperature is maintained and the mold closing pressure is maintained at about 1020MP for vulcanization. The vulcanization time depends on the size and thickness of the product, generally about 23 minutes, and the complete cross-linking of the rubber can be further ensured by staged pressurization. During the vulcanization process, the vacuum environment prevents the gas generated by the heat of the rubber from accumulating in the product. After vulcanization is completed, the mold is opened and the finished product is taken out. The surface of the sealing strip is smooth and there are no bubbles or pores inside, achieving high density.

[0060] Through the above process, this embodiment significantly improves the density and mechanical properties of EPDM sealing strip products. Vacuum degassing eliminates bubble defects inside the product, and the rubber material is fully vulcanized and tightly fills the cavity, thereby improving the product's resistance to permanent compression deformation and aging resistance. Compared with the traditional non-vacuum injection process, the airtightness and watertightness of the product are greatly improved. At the same time, since rework caused by poor exhaust and prolonged vulcanization waiting time are eliminated, the production cycle is significantly shortened, and the vulcanization cycle of a single product can be reduced by about 15-20%, thereby improving production efficiency. In short, this embodiment achieves rapid molding of EPDM automotive sealing strips without bubbles and high-quality one-time molding through continuous mixing and conveying by a vacuum cross-screw and optimized injection strategy.

[0061] Example 2:

[0062] Clean injection molding process for transparent liquid silicone rubber medical catheters

[0063] This embodiment is aimed at the molding of transparent liquid silicone rubber (LSR) catheters for medical use, and adopts a clean molding process of vacuum cross-screw injection to ensure high transparency and consistency of the product. First, a two-component low-viscosity liquid silicone rubber raw material (component A and component B) is used, and a precision metering pump is used to deliver equal proportions of A and B silicone rubber. The two components are filtered through a 0.1μm filter before entering the injection system to ensure that the raw materials are free of impurity particles. Then low-speed shear mixing is carried out in the mixing unit: the cross-screw (or static mixer) mixes the A and B components thoroughly and evenly at a relatively mild shear rate. The multi-stage spiral element of the static mixer ensures that the silicone rubber is repeatedly divided and re-converged at a lower flow rate, thereby achieving uniform mixing without introducing excess bubbles. For colored catheter products, medical color paste is also accurately metered in simultaneously to control the color paste ratio and ensure consistent color.

[0064] To completely eliminate air entrapment after mixing, a gradual vacuuming strategy is employed to ensure the degassing and cleanliness of the liquid silicone. First, during the feeding and mixing phase, the mixer outlet is connected to a vacuum degassing chamber, where the mixed silicone undergoes a primary vacuum degassing treatment. If the silicone viscosity is low, bubbles will naturally escape during mixing. If the viscosity is high, a vacuum is activated to remove any remaining bubbles. The pressure in the vacuum degassing chamber is slowly reduced to approximately 5 × 10^3 Pa and maintained for several seconds to allow the bubbles to fully rise and burst. Then, pressure is applied to transfer the degassed silicone into the injection cavity. Subsequently, after the mold is closed, a secondary vacuuming process is performed to ensure a good seal between the mold parting surfaces and gradually remove all air from the cavity through the vacuum port. To prevent premature silicone from entering the cavity and hindering the vacuum effect, the cavity vacuum is maintained at approximately -0.08 MPa for several seconds before injection is initiated. Vacuuming continues during injection to ensure that any traces of air are immediately removed as the liquid silicone fills the mold. This phased vacuuming strategy ensures a bubble-free environment from mixing to molding, maximizing the transparency of the finished product.

[0065] The entire injection molding process is rigorously controlled for temperature and cleanliness. Because liquid silicone rubber is an addition-curing system, it has a limited operating time at room temperature but rapidly cures at elevated temperatures. To prevent premature crosslinking and curing of the silicone before entering the mold, the injection machine's barrel and nozzle utilize a water-cooled constant-temperature system, maintaining a low temperature of 20-25°C. The mold is equipped with a heater and preheated to a relatively low temperature (e.g., 70°C) to prevent the silicone from instantly curing upon contact and affecting flow. Once injection is complete and the mold cavity is filled, the mold is rapidly heated to the required temperature of approximately 150°C for vulcanization and maintained for the appropriate time to complete the curing and finalization of the catheter. The mold cavity remains clean and contaminant-free throughout the entire production process. Before each molding cycle, the cavity is wiped with alcohol and vacuum-purged to ensure no residual dust particles. The production environment meets medical cleanliness requirements (Class 10,000 cleanliness level), with operating equipment and piping constructed from food-grade stainless steel to prevent any secondary contamination of the silicone.

[0066] The injection rhythm is meticulously controlled to meet the molding requirements of transparent products. A low initial injection speed ensures that the silicone slowly fills the elongated tube cavity, preventing air vortices and stagnation. As the cavity gradually fills, the injection speed is increased to ensure a smooth flow of silicone throughout its entire length, while continuous vacuum action removes air from the front end. As the cavity nears fullness, the injection speed is reduced until it stops, and pressure is applied and maintained to compensate for the shrinkage volume and prevent the formation of vacuum voids. The entire injection process is precisely controlled by a control system, ensuring uniform and synchronized filling without interruptions or overshoot. With vacuum assistance, silicone can fill complex, long tubular mold cavities at low injection pressures without flash or burrs. The use of vacuum venting also prevents underfilling caused by air blockage, ensuring uniform wall thickness and consistent transparency throughout each tube.

[0067] Through the above process measures, this embodiment achieves excellent degassing and consistent quality for medical catheter products. On the one hand, multi-stage vacuum degassing ensures a bubble-free interior of the liquid silicone rubber, resulting in crystal-clear, transparent finished catheters that meet the stringent visibility and bubble-free requirements of medical devices. On the other hand, low-speed, uniform mixing and low-temperature injection prevent impurities and scorching, resulting in products with no yellowing or black spots, and stable dimensions without shrinkage or deformation. Vacuum-assisted molding also ensures excellent batch consistency, with highly consistent dimensional deviations and mechanical properties across each batch of catheters. Because vacuum molding in the mold cavity allows for more thorough filling, the finished products are free of porosity defects, eliminating the need for scrapping and sorting due to bubbles later, reducing the defect rate. Notably, vacuum clean molding effectively prevents flash, resulting in smooth edges on the finished catheters without the need for additional trimming. In summary, this embodiment, through the combination of two-component, low-speed mixing, gradual vacuuming, and clean molding processes, significantly improves the degassing purity and quality consistency of the finished product, meeting the high transparency and reliability requirements for medical-grade products.

[0068] In summary, the vacuum cross-screw injection process of the embodiment of the present invention realizes the closed-loop linkage of the rubber material in the mixing, conveying, degassing and injection processes by co-designing a cross-screw with inconsistent pitch and adjustable speed difference with a vacuum degassing system, combining dynamic flow monitoring and multi-stage injection control. It can draw vacuum in real time at the key nodes where the rubber flow force changes, effectively remove bubbles, and maintain the appropriate fluidity and stability of the rubber material through temperature regulation and flow channel optimization, ensuring uniform filling of the mold cavity and rapid vulcanization molding, thereby completely solving the problems of insufficient mixing, low degassing efficiency, time-consuming degassing and asynchronous injection process in traditional processes, and significantly improving the density, consistency and production efficiency of rubber products.

[0069] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and deform the above embodiments within the scope of the present invention.

Claims

1. A vacuum cross-screw glue injection process, characterized in that: The following steps are involved: S1. Rubber material pretreatment and feeding: the rubber raw materials are preliminarily mixed according to the ratio and then input into the cross-screw inlet of the injection device; S2. Cross-screw mixing and conveying: A pair of cross-screws with different pitches and speeds are used to mix and convey the rubber material in a rolling manner, so that the rubber material is fully compressed and evenly mixed during the axial conveying process; S3. Dynamically identify changes in flow state. When a change in flow direction or force state is detected during the flow of the rubber material from the cross-screw outlet into the injection channel, the vacuum control module is activated. S4. Timely vacuum degassing: In the area where the force direction of the rubber material changes, vacuum degassing is performed to remove the gas trapped in the rubber material, thereby enhancing the rubber's density and flow stability; S5. Coordinate the injection control. During vacuum degassing, adopt a variable speed injection strategy to control the injection flow rate to match the vacuum efficiency, prevent gas entrapment and flow channel disturbance, and ensure stable filling of the rubber material into the mold. S6. Rubber vulcanization molding: After the glue injection is completed, the rubber material is hot-vulcanized and shaped in the mold. No further aging and bubble removal treatment is required, and a rubber product with a dense structure and no residual bubbles can be obtained.

2. The vacuum cross-screw glue injection process according to claim 1, characterized in that: The start timing of the vacuum pumping operation is determined by monitoring the flow state of the rubber material. When it is detected that the force direction of the rubber material changes or the pressure fluctuation reaches a preset threshold, the vacuum pumping is triggered to accurately control the degassing timing.

3. The vacuum cross-screw glue injection process according to claim 1, characterized in that: The injection speed regulating device is used to control the speed of rubber material injected into the mold cavity, so that the injection speed is coordinated with the vacuum pumping process to avoid violent fluctuations in the flow of rubber material and ensure uniform injection.

4. The vacuum cross-screw glue injection process according to claim 1, characterized in that: Temperature control is implemented during the mixing, conveying and injection process of the rubber material. By heating or cooling the rubber material and the screw mechanism, the rubber material maintains appropriate viscosity and fluidity, promotes the escape of bubbles and improves the degassing effect.

5. The vacuum cross-screw glue injection process according to claim 1, characterized in that: The flow channel for rubber injection is optimized and a channel or buffer structure for guiding the escape of bubbles is set in the flow channel, so that bubbles can be discharged along the channel when the rubber material flows through the flow channel, thereby further improving the degassing effect.

6. The vacuum cross-screw glue injection process according to claim 1, characterized in that: The vacuum degree and duration of the vacuum pumping operation are adjustable. A higher vacuum degree is applied at the initial stage when the force direction of the rubber material changes to quickly expel bubbles. Then, an appropriate vacuum degree is maintained until the injection is completed to ensure that the bubbles are completely expelled.

7. The vacuum cross-screw glue injection process according to claim 1, characterized in that: The pitch difference and speed difference of the cross screws are adjusted according to the viscosity and mixing requirements of the rubber material, and the best mixing and degassing effect is achieved by changing the screw speed ratio or pitch configuration.

8. The vacuum cross-screw glue injection process according to claim 1, characterized in that: A centralized control system is used to coordinate the screw rotation, vacuum extraction and injection processes. Mixing, vacuum extraction and injection operations are performed sequentially or synchronously through preset programs to ensure close coordination of all links and further improve injection quality and degassing efficiency.

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