Injection molded connecting rod reset mechanism
The injection molding link pre-reset mechanism is a key device in mold design, ensuring the ejector system resets before mold closing. Its core function is to prevent ejector components such as ejectors and lifters from colliding with the cavity and core, thereby protecting mold precision and extending mold life. In complex molds, when there is motion interference between the ejector mechanism and the side core pulling mechanism, if the ejector components are not reset in time, they are prone to component damage during mold closing. The link pre-reset mechanism, through ingenious mechanical transmission, can drive the ejector system to reset in the early stages of mold closing, clearing the way for subsequent mold closing operations.
The structure of a connecting rod pre-reset mechanism typically includes core components such as a connecting rod, a rocker arm, a slider, and a guide post. The precision of the fit of these components directly affects the reset effect. The connecting rod, a key component for force transmission, is connected to the ejector plate of the movable mold at one end and hinged to the rocker arm via a pin at the other end. The rocker arm is fixed to the guide post of the fixed mold. When the mold begins to close, the fixed mold guide post pushes the rocker arm to rotate around a fixed axis. The rocker arm, through the connecting rod, drives the ejector plate upward, achieving premature reset of the ejector element. The length of the connecting rod must be precisely calculated based on the mold opening stroke and reset distance. For example, when the ejection distance is 50mm, the connecting rod length is typically set to 120-150mm to ensure a reasonable force arm during transmission and avoid jamming. In addition, the clearance between the slider and the guide post must be controlled between 0.02-0.05mm to ensure smooth and smooth rocker movement.
The working principle of this mechanism is based on lever transmission and mechanical linkage, and its reset timing can be precisely controlled by adjusting the structural parameters. At the initial stage of mold closing, when the fixed mold and the movable mold just come into contact, the guide pillar starts to push the rocker arm. At this time, the ejection system starts to reset under the pull of the connecting rod. The reset action precedes the reset of the side core pulling mechanism or the closing of the cavity, thereby completely eliminating the risk of interference. The reset speed is proportional to the mold closing speed, but the acceleration needs to be controlled by adjusting the fulcrum position of the rocker arm to avoid reset too quickly and causing the ejection component to be impacted. For example, when the fulcrum of the rocker arm is set close to the connecting end of the connecting rod, the reset acceleration can be reduced, which is suitable for molds with longer ejection components; when the fulcrum is close to the contact end of the guide pillar, the reset speed is faster, which is suitable for small precision molds.
The design of the connecting rod reset mechanism needs to be personalized according to the specific structure of the mold, and different types of ejection systems require different connecting rod layouts. For molds that use ejector plates for ejection, the connecting rods are usually symmetrically arranged on both sides of the ejector plate to ensure uniform force during reset and prevent the ejector plate from tilting; for inclined ejectors or core-pulling ejection mechanisms, the connecting rods need to match the motion trajectory of the inclined ejectors, and multiple sets of connecting rods can be used to ensure synchronous reset of each inclined ejector. In deep-cavity molds, due to the large ejection distance, guide sleeves need to be added to provide auxiliary support for the connecting rods to prevent the connecting rods from bending and deforming during movement. In addition, the installation position of the mechanism needs to avoid the runner and cavity to avoid affecting the melt flow and plastic part molding.
Daily maintenance and debugging are crucial to ensure the stability of the connecting rod reset mechanism. It is necessary to regularly check whether the hinge between the connecting rod and the rocker arm is loose and whether the pin is worn. If the gap is found to be too large, the pin should be replaced and lubricant should be added in time. Before closing the mold, the reset action needs to be manually tested to observe whether the ejection component can be completely reset to the initial position. After reset, the flushness of the ejector end face and the cavity surface must be controlled within 0.01mm. If the reset is not in place, it can be corrected by adjusting the connecting rod length or the rocker arm fulcrum position. For example, shortening the connecting rod length can increase the reset stroke, and moving the fulcrum can change the reset angle. After long-term use, the connecting rod needs to be strength-checked. If fatigue deformation occurs, the connecting rod should be replaced with a high-strength alloy material in time to ensure that the mechanism can work reliably in a high-pressure mold closing environment.
