The injection molding reset rod reset mechanism is a key device to ensure that the mold ejection system can accurately return to its initial position after mold opening. Its core function is to push the ejector plate to reset during the mold closing process to prepare for the next injection molding. The reset rod is usually rigidly connected to the ejector plate. When the movable mold and the fixed mold are closed, the top of the reset rod first contacts the fixed mold plate. As the mold closing action continues, the reset rod drives the ejector plate to gradually return to its original position, ensuring that the ejector, ejector plate and other ejection components are completely out of the cavity area. The number of reset rods needs to be determined according to the size and weight of the ejector plate. Small and medium-sized molds are generally equipped with 4 reset rods, evenly distributed at the four corners of the ejector plate; large molds need to be increased to 6-8 reset rods, and an auxiliary reset rod is added in the center area of the ejector plate to ensure that the ejector plate is evenly stressed and avoid tilting during the reset process. For example, in a car dashboard mold, the ejector plate has a size of 1500mm×1000mm and is equipped with six reset rods with a diameter of 20mm, four of which are located at the four corners and two at the midpoint of the long side to ensure that the flatness error of the ejector plate does not exceed 0.05mm during reset.
The structural design of the reset lever mechanism in injection molding must ensure smooth and accurate reset action. The precise fit between the reset lever and the reset hole is crucial. The reset lever diameter typically ranges from 12-25mm, depending on mold size. The clearance between the reset lever and the reset hole should be 0.05-0.1mm. Excessive clearance can cause the reset lever to wobble, affecting reset accuracy; too little clearance can lead to jamming and improper reset. The tip of the reset lever should be chamfered at an angle of 30°-45° and a height of 2-5mm to facilitate smooth insertion into the reset hole during mold closing and prevent collision with the fixed platen. The reset lever length must be precisely calculated to ensure that the tip of the ejector pin is flush with the cavity surface (within a tolerance of no more than 0.02mm) after the ejector plate is reset. For example, if the distance from the cavity surface to the ejector plate is 200mm and the ejector pin is 180mm long, the effective length of the reset lever should ensure that the tip of the ejector pin is flush with the cavity surface after the ejector plate is retracted. In addition, the reset rod must be made of high-strength steel (such as 45# steel quenched to HRC40-45) to ensure that it is not easily deformed under long-term mold clamping impact and its service life reaches more than 500,000 mold times.
The reset force of the injection molding reset lever mechanism must be properly designed to overcome the resistance of the ejector system while avoiding damage to mold components caused by excessive force. The magnitude of the reset force is related to factors such as the weight of the ejector system, the friction between the ejector pin and the ejector hole, and the spring preload. The calculation formula is: Reset force (N) = (Ejector system weight × Gravity acceleration + Total friction) × Safety factor (1.2-1.5). For example, if the ejector system weighs 50 kg and the total friction is 1000 N, the required reset force = (50 × 9.8 + 1000) × 1.3 ≈ (490 + 1000) × 1.3 ≈ 1937 N. To ensure sufficient reset force, auxiliary reset springs can be installed near the reset lever. The spring force should be selected based on the required reset force. For example, if each spring has a force of 500 N, four springs can provide an auxiliary force of 2000 N, which works in conjunction with the push of the reset lever to complete the reset. The compression of the spring needs to be controlled within 30%-50% of the free length to avoid elastic fatigue caused by excessive compression. For example, for a spring with a free length of 100mm, the working length after compression should be 60-70mm to ensure stable elastic force.
The limit and guide design of the reset lever mechanism for injection molding is crucial for ensuring reset accuracy. Clear limit devices and guide structures are essential. A limit block should be placed at the reset endpoint of the ejector plate. The block’s height must be precisely machined to ensure a clearance of 0.01-0.03mm between the ejector plate and the movable platen after reset. For example, if the limit block is 10mm high, the clearance between the ejector plate and the movable platen after reset should be strictly controlled to 0.02mm by the limit block. The reset lever and the ejector plate should be rigidly secured, such as with a nut or interference fit, to prevent loosening and displacement of the lever during reset. A reset guide post should be placed between the ejector plate and the movable platen. The guide post’s diameter should be the same as the reset lever’s, with a clearance of 0.03-0.05mm. This ensures that the ejector plate moves linearly and without deflection during reset. For example, two reset guide posts with a diameter of 20mm should be placed in the center of the ejector plate. These guide posts mate with guide sleeves on the movable platen to maintain the ejector plate’s motion accuracy within 0.03mm, ensuring synchronous reset of all ejectors.
Common issues and solutions for injection molding reset lever mechanisms are crucial aspects of mold maintenance. Countermeasures must be developed for issues such as improper reset, bent reset levers, and ejector pin interference with the cavity. If improper reset occurs, inspect the reset lever for wear, the reset hole for foreign matter, and the spring tension for attenuation. For example, if the tip of the reset lever is worn more than 0.5mm, it should be replaced; if the spring tension drops by more than 15%, it should be replaced. Bent reset levers are typically caused by uneven force distribution or excessive mold closing speeds. Repositioning the reset lever to ensure balanced force distribution and reducing the mold closing speed to 30-50mm/s are essential. If the ejector pin interferes with the cavity, it may be due to insufficient reset lever length or worn stoppers. Remeasure and adjust the reset lever length, replace worn stoppers, and ensure complete ejector retraction. Additionally, lubricate the reset mechanism regularly. Apply grease to the mating surface between the reset lever and the reset hole every 2,000 molds to reduce friction, effectively preventing reset failures and improving mechanism reliability.
