Injection molding push tube demoulding mechanism
The injection molding push-tube demolding mechanism is a demolding device suitable for cylindrical, annular, or center-hole plastic parts. It smoothly ejects the plastic part from the core by moving the push tube along the core axis. It offers advantages such as a large ejection area, uniform force distribution, and resistance to deformation. It is widely used in the production of plastic parts such as bottle caps, bearing sleeves, and pen holders. The push-tube demolding mechanism primarily consists of a push tube, core, push-tube retaining plate, and push rod. A clearance fit between the push tube and core ensures smooth sliding along the core while preventing melt from entering the clearance and forming flash. Compared to traditional push-rod demolding, the push-tube demolding mechanism better adapts to plastic parts with center holes, avoids ejection marks from a single push rod on the inner wall of the plastic part, and improves the surface quality and dimensional accuracy of the plastic part.
The structural design of the push tube demoulding mechanism needs to be customized according to the shape and size of the plastic part. The core is to ensure the fitting accuracy and movement coordination between the push tube and the core. The inner diameter of the push tube should be slightly larger than the outer diameter of the core, and the fitting clearance is usually controlled at 0.02-0.04mm, which not only ensures that the push tube can move flexibly, but also effectively prevents the melt from entering the gap. The outer diameter of the push tube needs to be determined according to the inner diameter of the plastic part, and is generally 0.1-0.2mm smaller than the inner diameter of the plastic part to avoid damage caused by friction between the push tube and the inner wall of the plastic part during the ejection process. The length of the push tube should cover the molding length of the plastic part on the core, and leave a certain margin to ensure that the top of the push tube can completely push the plastic part off the core when it is in the maximum ejection position. The push tube fixing plate is used to fix the push tube. Its connection with the push tube must be firm and reliable. Interference fit or screw fastening can be used to prevent the push tube from loosening or offset during the ejection process.
The working principle of the ejector mechanism is based on the transmission and conversion of linear motion. The ejector mechanism of the injection molding machine drives the push rod, which drives the push tube fixing plate and the push tube forward along the axis of the core to achieve demolding of the plastic part. During the injection molding stage, the top of the push tube is flush with the bottom surface of the mold cavity, and together with the core, it forms the molding space for the plastic part. After the plastic part is molded and cooled, the ejector mechanism of the injection molding machine begins to operate. The push rod pushes the push tube fixing plate forward. The push tube moves synchronously with the fixing plate. Its top contacts the end face of the plastic part and applies an ejection force, causing the plastic part to gradually separate from the core along the axis of the core. When the push tube moves to its maximum stroke, the plastic part completely separates from the core and falls due to gravity or the action of the robot. The ejector mechanism then drives the push tube to reset, preparing for the next injection molding cycle. The relative movement of the push tube and the core must be kept smooth to avoid eccentricity or tilting, otherwise it will cause uneven wall thickness or surface scratches in the plastic part.
The push-tube ejection mechanism has a specific application scope, primarily for cylindrical or annular plastic parts with a central hole and a short height. Complex shapes require integration with other ejection mechanisms. Taller parts require increased push-tube length, which reduces rigidity and can easily cause bending and deformation during ejection, affecting demolding effectiveness. In these cases, a guide structure or reinforced push-tube can be incorporated into the push-tube. For cylindrical parts with undercuts, the push-tube ejection mechanism must be integrated with a core-pulling mechanism. The core-pulling mechanism first removes the undercut, and then the push-tube ejects the part, avoiding damage caused by forced ejection. Wear resistance and strength are important considerations when selecting the push-tube material. High-quality carbon tool steel (such as T8A, T10A) or alloy tool steel (such as Cr12, Cr12MoV) is typically used. Both the inner and outer surfaces of the push-tube are hardened to a hardness of HRC 50-55 to extend its service life.
The installation, commissioning and maintenance of the push tube demoulding mechanism must follow strict operating procedures to ensure its long-term stable operation. During the installation process, it is necessary to ensure that the coaxiality error between the push tube and the core does not exceed 0.03mm. The position of the push tube can be corrected by a dial indicator to avoid increased friction between the push tube and the core due to eccentricity. The connection between the push tube and the push tube fixing plate must be firm. After installation, the movement flexibility of the push tube should be checked to ensure that there is no jamming within the full stroke. During debugging, the ejection speed and pressure need to be adjusted step by step, and the demoulding status of the plastic part needs to be observed. If the plastic part is deformed, it may be due to excessive ejection speed or too small a gap between the push tube and the core. The speed needs to be reduced or the gap needs to be repaired. If the push tube movement is not smooth, the mating surface needs to be checked for impurities or wear, and cleaned and repaired. During routine maintenance, the mating surfaces between the push tube and the core must be regularly lubricated with high-temperature resistant grease to reduce friction and wear. The push tube should also be regularly inspected for wear. If the inner diameter of the push tube wear exceeds 0.05mm, the push tube should be replaced promptly to prevent melt overflow due to excessive clearance. Through scientific installation , commissioning, and maintenance, the push tube demolding mechanism can maintain stable demolding performance over long-term production, improving the production efficiency and quality of plastic parts.
