Injection molded push rod plate return spring
The injection molding push rod plate return spring is a key component in the injection mold’s ejection system. Its primary function is to return the push rod plate to its initial position after ejection is complete, preparing for the next injection molding cycle. During the injection molding process, after the product has cooled and formed, the ejector mechanism ejects the product from the mold cavity. The push rod plate drives the push rod forward to complete the ejection, while the return spring provides a restoring force when the ejector mechanism returns to its original position, accurately returning the push rod plate and push rod to their original positions. This prevents collision or interference with other mold components and ensures the mold’s normal cycle operation. Therefore, the performance of the return spring directly affects the mold’s operating efficiency and service life.
The selection of the reset spring requires comprehensive consideration of multiple factors to ensure that it can meet the working requirements of the mold. The first is the elastic force of the spring. Too little elastic force will result in incomplete reset of the push rod plate, affecting the next molding; too much elastic force will increase the opening and closing resistance of the mold, aggravating the wear of the spring and related components. The calculation of the elastic force needs to be determined based on parameters such as the weight of the push rod plate, the friction of the ejection mechanism, and the acceleration required for reset. It can usually be estimated through empirical formulas or finite element analysis software. The second is the size of the spring, including free length, outer diameter, wire diameter, etc. The size of the spring needs to match the installation space of the mold to ensure that it can be smoothly installed between the push rod plate and the mold base or other fixed components. At the same time, it is necessary to ensure that the spring has sufficient travel during compression and extension to meet the reset distance requirements of the push rod plate.
The material of the spring is also an important consideration when selecting a spring. The operating environment of an injection mold typically maintains a certain temperature. Especially for thermoplastic injection molding, mold temperatures can reach tens or even hundreds of degrees Celsius. Therefore, the return spring needs to possess excellent heat resistance and elastic stability. Common spring materials include carbon spring steel and alloy spring steel. Alloy spring steel (such as 60Si2Mn) offers high strength, toughness, and heat resistance, and is less susceptible to elastic failure at high temperatures, making it suitable for most injection mold environments. Surface treatment of the spring is also important, typically undergoing electroplating (such as zinc plating or chromium plating) or phosphating to improve corrosion and wear resistance, thereby extending its service life.
The installation and maintenance of the return spring have a significant impact on its performance and lifespan. During installation, the spring should be installed vertically in the spring hole to ensure uniform force and avoid unbalanced loading, which can cause the spring to flex, deform, or even break. The size of the spring hole should match the outer diameter of the spring. A gap that is too large can easily cause the spring to wobble, while a gap that is too small can increase frictional resistance. At the same time, both ends of the spring should be in close contact with the push rod plate and the fixed plate. If necessary, spring washers can be installed to disperse pressure and prevent localized wear. During routine maintenance, the condition of the spring should be regularly checked for deformation, cracks, rust, and other signs. If the spring force is weakened or damaged, it should be replaced promptly to avoid mold failure due to spring failure. In addition, the spring should be cleaned and lubricated regularly to remove oil and impurities from the spring surface and apply an appropriate amount of grease to reduce friction and wear.
There may be a variety of faults in the return spring during use, and it is necessary to analyze the causes in time and take corresponding solutions. Common faults include spring breakage, insufficient elasticity, lateral bending, etc. Spring breakage is usually caused by excessive elasticity, eccentric installation, material fatigue or inappropriate spring size. Solutions include recalculating the elasticity and replacing the appropriate spring, adjusting the installation position to ensure uniform force, and selecting higher strength materials. Insufficient elasticity may be caused by spring fatigue, improper heat treatment or too long use time. At this time, a new spring should be replaced and the heat treatment process of the spring should be checked to see if it meets the requirements. Spring lateral bending is mostly caused by excessive verticality deviation or insufficient spring hole processing accuracy during installation. The spring hole needs to be reprocessed or the installation position needs to be adjusted to ensure the verticality of the spring. By promptly handling these faults, the normal operation of the return spring can be ensured, and the reliability and production efficiency of the injection mold can be improved.
