How does EPDM Rubber Channel Strip achieve high-quality molding through precise extrusion process? ​

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1. Preliminary fine processing of rubber compound: the key role of open mixer ​
As the initial raw material of EPDM rubber channel Strip, the rubber compound needs to be deeply processed by the open mixer before entering the extruder to adjust its plasticity and fluidity, laying the foundation for subsequent extrusion molding. The open mixer is mainly composed of two relatively rotating rollers. When the rubber compound is placed between them, the friction and shear force of the rollers work together to make it undergo repeated stretching, folding and extrusion. In this process, the originally disordered macromolecular segments inside the rubber compound are gradually rearranged and oriented, and the originally tight structure becomes loose, and the intermolecular interaction is weakened, thereby greatly improving the plasticity and effectively improving the fluidity. The rubber compound with a tight structure and poor fluidity becomes soft and easy to flow after being processed by the open mixer, which can better adapt to the processing needs of the subsequent extruder. ​
During the open mixing process, the operator can flexibly adjust multiple key parameters according to actual production needs. Roller spacing is one of the important factors affecting the processing effect of rubber compound. Reducing the roller spacing increases the shear force on the rubber compound and improves the plasticity more significantly. On the contrary, increasing the roller spacing reduces the shear force, which can appropriately reduce the mixing strength and avoid excessive processing that may damage the rubber properties. Roller speed is also critical. Increasing the speed can speed up production, but care should be taken to avoid excessive speed causing the temperature of the rubber compound to be too high, which will lead to the degradation of rubber molecules and affect product quality. In addition, the mixing time must also be precisely controlled. If the time is too short, the additives and the rubber matrix will not mix evenly, affecting product performance; if the time is too long, it may cause energy waste and rubber performance degradation. By comprehensively considering and accurately adjusting these parameters, the rubber compound can achieve the best plasticity and fluidity state to meet the production requirements of different EPDM rubber channel strip products. ​
II. Core molding process in the extruder​
(I) Precise temperature control​
When the rubber compound enters the extruder in the best state, the critical molding journey begins. The extruder pushes the rubber compound forward by rotating the screw. During this process, the external heating device of the barrel heats the rubber compound to a suitable processing temperature. It is not easy to determine this temperature range, and multiple factors need to be considered comprehensively. Different types of rubber materials require different processing temperatures due to their differences in chemical structure and physical properties. For example, the common natural rubber and synthetic rubber, such as styrene-butadiene rubber, have significantly different processing temperature ranges. In addition, various compounding agents added to the rubber compound, such as fillers and plasticizers, will also affect the processing temperature. When the filler content is high, in order to ensure that the rubber compound flows smoothly and is extruded evenly, the temperature may need to be appropriately increased; when the amount of plasticizer added is large, the fluidity of the rubber compound is relatively good, and the processing temperature can be appropriately reduced. Accurately controlling the extrusion temperature can ensure that the rubber compound is in a good molten state and can be smoothly passed through the mold to achieve precise molding, which is one of the core elements to ensure product quality. ​
(II) Strict control of pressure​
In the process of the extruder pushing the rubber compound forward, pressure control is crucial. The screw rotates to generate thrust, which causes the rubber compound to form a certain pressure in the barrel. This pressure must be maintained within an appropriate range. If the pressure is too low, the rubber compound cannot fully fill the mold cavity, and the extruded rubber channel strip blank is prone to defects such as lack of rubber and bubbles, which seriously affects the product quality; if the pressure is too high, it will not only produce excessive impact on the mold, shorten the mold life, and may even cause mold damage, but also cause excessive shearing and heat generation in the barrel of the rubber compound, causing rubber molecule degradation, which also has a negative impact on product performance. In order to achieve precise pressure control, modern extruders are usually equipped with advanced pressure sensors and control systems. The pressure sensor monitors the pressure changes of the rubber compound in the barrel in real time and feeds the data back to the control system. The control system automatically adjusts the screw speed, feed rate and other parameters according to the preset pressure value to ensure that the pressure in the barrel is always stable in the appropriate range, thereby ensuring stable product quality. ​
(III) Key influence of the mold ​
As the core component that determines the final shape of the EPDM rubber channel strip blank, the design and manufacturing accuracy of the mold are directly related to product quality. The internal structure of the mold is carefully designed according to the cross-sectional shape required by the rubber channel strip, and every detail has been repeatedly considered and optimized. Taking the common door and window sealing rubber channel strip as an example, its cross-sectional shape is complex and may include a variety of geometric shapes, and some parts are equipped with special lip edges, grooves and other structures to achieve better sealing effects. To manufacture such a precision mold, advanced processing technology and manufacturing technology are required. High-precision CNC processing equipment performs operations such as cutting, drilling, and grinding on the mold material according to the design drawings to ensure that the mold dimensional accuracy and surface roughness meet extremely high standards. After the mold is manufactured, it must also undergo strict quality inspection, and the key dimensions must be measured by professional equipment such as a three-dimensional measuring instrument, and compared with the design drawings to ensure that the error is within the allowable range. Only molds that have passed strict inspection can be installed on the extruder and put into use to ensure that the extruded rubber channel strip blank has an accurate cross-sectional shape and dimensional accuracy. ​
(IV) Reasonable control of extrusion speed​
The extrusion speed is another important parameter that needs to be strictly controlled in the extrusion process. If the extrusion speed is too fast, the rubber mix will stay in the mold for too short a time, and it cannot be fully plasticized and formed, resulting in rough surface and large dimensional deviation of the rubber channel strip blank; if the extrusion speed is too slow, it will reduce production efficiency and increase production costs. Therefore, the extrusion speed needs to be reasonably determined according to the characteristics of the rubber mix, the mold structure and the product quality requirements. For rubber channel strip products with simple structure and relatively low dimensional accuracy requirements, the extrusion speed can be appropriately increased; for products with complex structure and extremely high dimensional accuracy requirements, such as rubber channel strips for high-end automobile doors and windows, the extrusion speed needs to be reduced to ensure product quality. In order to achieve precise control of the extrusion speed, the extruder is usually equipped with a variable frequency speed regulation device. The operator can input the required extrusion speed through the control panel according to the actual production situation, and the variable frequency speed regulation device automatically adjusts the motor speed, thereby accurately controlling the screw speed and stably controlling the extrusion speed. ​
Three, common problems and solutions in the extrusion process​
During the extrusion process of EPDM rubber channel strips, some common problems may be encountered, which require timely handling and adjustment by the operator. When the extruded rubber channel strip blank has surface scratches, it may be that the mold surface is damaged or there are foreign objects attached. At this time, it is necessary to stop the machine in time, check and clean the mold, and repair the damaged parts. If the rubber channel strip blank is twisted and deformed, it may be that the gap between the extruder screw and the barrel is uneven, or the mold flow channel design is unreasonable, resulting in uneven force during the extrusion of the mixed rubber. It is necessary to inspect the screw and barrel, adjust the gap, and optimize the mold flow channel design. By discovering and solving these problems in a timely manner, the extrusion quality and production stability of the rubber channel strip blank can be effectively guaranteed.