Injection molding push rod, flat push rod demoulding matters needing attention
Injection molding push rods and flat push rods are important components in the mold release mechanism, each suitable for demolding plastic parts with different structures. The rationality of their design and use directly affects the demolding effect and surface quality of the plastic part, so many considerations are required during application. Push rods are the most commonly used demolding parts. They are cylindrical and suitable for demolding the interior of the plastic part or on relatively flat surfaces. Flat push rods are flat and have a larger contact area with the plastic part. They are suitable for demolding large, thin-walled, or easily deformed plastic parts, and can reduce ejection marks on the plastic part surface. Whether using a push rod or a flat push rod, uniform demolding force and smooth movement must be ensured during use to avoid defects such as deformation, strain, and whitening of the plastic part.
The design parameters of push rods and flat push rods require strict control to ensure effective demolding. The push rod diameter should be determined based on the weight of the part and the demolding force. A diameter that is too small will result in insufficient push rod strength, leading to bending or breaking during ejection. A diameter that is too large will increase mold processing difficulty and may leave noticeable ejection marks on the part surface. Typically, the push rod diameter should be no less than 3mm. For large parts, the diameter can be increased or the number of push rods can be increased. The width and thickness of the flat push rod should be designed based on the contact area and part structure. The width is generally 10-30mm, and the thickness is no less than 5mm to ensure sufficient rigidity. The length of the push rod and flat push rod should ensure that they do not separate from the guide sleeve during ejection. The top should be flush with the cavity surface or slightly lower by 0.05-0.1mm to avoid forming a protrusion on the part surface. Furthermore, the clearance between the push rod and flat push rod and the mold plate should be appropriate, typically 0.02-0.05mm. Excessive clearance can easily cause melt overflow, while too little clearance can affect movement flexibility.
The installation and debugging of push rods and flat push rods are the key to ensure their normal operation. Before installation, the surface quality of the push rods and flat push rods must be checked to ensure that there are no defects such as burrs and scratches. The top should be polished, and the surface roughness Ra should not be greater than 0.8μm to avoid scratching the surface of the plastic part. During installation, it is necessary to ensure that the push rods and flat push rods are perpendicular to the ejector plate, and the concentricity error does not exceed 0.02mm. Positioning can be achieved through positioning pins or guide sleeves. During debugging, it should be checked whether the movement of the ejection mechanism is smooth, without jamming or abnormal noise. The ejection speed and stroke should meet the design requirements to ensure that the plastic parts can be demolded smoothly and without deformation. For molds with multiple push rods or flat push rods, it is necessary to ensure that each push rod is evenly stressed. This can be adjusted by adjusting the length of the push rod or setting a gasket between the ejector plate and the base plate to avoid tilting or damage to the plastic part due to uneven force.
During the injection molding production process, the push rods and flat push rods need to be maintained and inspected regularly to detect and solve problems in a timely manner. Before production, the surface of the push rods and flat push rods should be cleaned to remove residual plastic debris and oil stains, and high-temperature resistant grease should be applied to reduce movement friction. If defects such as whitening and strain are found on the surface of the plastic part during the production process, it may be due to the small contact area between the push rod or flat push rod and the plastic part, too fast ejection speed or poor lubrication. The ejection parameters should be adjusted or the push rod should be replaced in time. If the push rod is bent or broken, it is necessary to check whether the ejection mechanism is stuck and whether the push rod strength is sufficient. If necessary, replace the push rod with a larger diameter or higher strength. In addition, the wear of the push rods and flat push rods needs to be checked regularly. If the top is worn or deformed, it should be repaired or replaced in time to avoid affecting the demolding effect.
The selection and use of push rods and flat push rods require tailored considerations for different types of plastic parts. For thin-walled parts, flat push rods are preferred to increase contact area, reduce ejection force per unit area, and avoid part deformation. For deep-cavity parts, stepped push rods can be used to enhance rigidity and prevent bending during ejection. For parts requiring high surface quality, the top of the push rod or flat push rod should be nitrided or hard chrome plated to improve surface hardness and wear resistance, thereby minimizing ejection marks. When manufacturing plastics prone to mold sticking (such as PVC and POM), a release agent can be applied to the push rod or flat push rod surface. However, careful attention should be paid to the amount of release agent used to avoid compromising subsequent processing (such as painting and bonding) of the part. Furthermore, for parts with slopes or undercuts, push rods and flat push rods should be used in conjunction with a core-pulling mechanism to ensure that the part is fully free of the undercut before ejection, thus avoiding damage caused by forced ejection. The appropriate selection and proper use of push rods and flat push rods can effectively improve mold release quality and production efficiency.
