Submerged gate condensate removal mechanism
The latent gate slurry ejection mechanism is a key device used in injection molds to automatically separate slurry from latent gates. Its core function is to mechanically separate and eject the slurry from the gate during mold opening, achieving automated separation of the part and slurry, significantly improving production efficiency. Because latent gates are located inside the part or in hidden locations (such as below the parting surface or at the base of a rib), the bond between the slurry and the part is strong. Traditional manual removal is not only time-consuming and labor-intensive, but can also damage the part surface. A dedicated ejection mechanism, using the coordinated motion of inclined guide pins, push rods, or pull rods, instantly separates and ejects the slurry from the mold opening, making it suitable for mass-produced small plastic parts such as electronic connectors, gears, and toy parts. For example, in the production of mobile phone charging port plastic parts, a latent gate with internal feed combined with a tilted ejection mechanism allows slurry separation within 0.5 seconds after mold opening, increasing the hourly output of a single machine to more than three times that of traditional manual operation.
The basic components of a latent gate solids ejection mechanism include a shearing assembly, an ejection assembly, and a reset assembly, all of which must work precisely together to achieve reliable operation. The shearing assembly is usually a combination of an inclined guide pin and a slider. The inclined guide pin is fixed to the fixed mold, and the slider is installed in the movable mold. When the mold is opened, the inclined guide pin drives the slider to move laterally. The cutting edge on the slider severs the gate solids from the base of the plastic part. For micro-gates with a diameter less than 1mm, a fixed cutting edge design can also be used, utilizing the relative movement during mold opening to naturally cut the solids. The ejection assembly is responsible for pushing the severed solids out of the mold. Common forms include a push rod, push tube, or ejector plate. The front end of the push rod must match the shape of the solids, such as providing a groove to enhance gripping force. The reset assembly returns the moving parts to their initial positions when the mold is closed. It usually uses a reset spring or reset rod to ensure the accuracy of the next molding cycle. For example, the diameter of the latent gate of a gear mold is 1.5mm. Its ejection mechanism uses an inclined guide column to drive the slider to cut off, and cooperates with a Φ3mm push rod to eject the solidified material. The action response time is controlled within 0.3 seconds, and 100,000 molds can be produced continuously without any problems.
Depending on the part structure and gate location, latent gate slurry ejection mechanisms can be divided into several types, each with its own applicable scenarios. The inclined ejector mechanism is suitable for situations where the gate is located on the inner wall of the part. While ejecting the part, the inclined ejector rod’s bevel drives the cutter to move laterally to cut the slurry. This mechanism features a compact structure and good synchronization. For example, when producing plastic boxes with inner buckles, the inclined ejector rod is responsible for both ejecting the box body and cutting off the inner latent gate with the cutting edge at the top. The rocker-type ejector mechanism uses the rotational motion of the rocker rod to cut the slurry. This mechanism is suitable for situations where the gate is located at the end of the part. One end of the rocker rod is connected to the fixed mold guide column. When the mold is opened, it swings with the guide column, and the blade at the other end cuts the slurry. This mechanism has the advantage of high cutting force and is suitable for thicker latent gates (2-3mm in diameter). The push rod cutting type is the simplest structure. It uses the relative movement of the push rod and the fixed mold to directly cut the solidified material. It is suitable for shallow-cavity plastic parts, such as the end face latent gate of a small plastic gear. When the push rod is ejected, the boss on the fixed mold and the push rod form a shear force to cut the solidified material.
The design of the latent gate slurry ejection mechanism must focus on reliable cutting, smooth operation, and mold life. The angle and sharpness of the cutting edge are crucial. Typically, an acute angle of 30°-45° is used, and the surface roughness of the cutting edge should be below Ra0.8μm to reduce friction and part damage during cutting. For tough materials (such as polyethylene), a slight radius (R0.05mm) can be applied to the cutting edge to prevent part tearing. The mechanism’s movement clearance must be strictly controlled. The clearance between the slider and the guide groove should be 0.01-0.02mm, and the clearance between the inclined guide post and the slider hole should not exceed 0.03mm to prevent movement and misalignment of the cutting position. Furthermore, the ejection distance of the slurry must be calculated to ensure that the slurry can be easily dropped or removed by the robot after ejection. The ejection distance is generally 1.5-2 times the slurry length. For example, if the slurry is 10mm long, the ejector stroke should be set to 15-20mm. For example, when designing the latent gate mechanism of a nylon connector, the cutting edge angle is 35°, combined with a movement clearance of 0.015mm, so that the cutting position error is controlled within ±0.1mm, and the gate mark of the plastic part is less than 0.3mm, meeting the appearance requirements.
Common problems and solutions for the latent gate solids ejection mechanism require special attention during mold trials and production. If the solids are not completely cut, it is often due to blade wear or improper angle. In this case, the blade components should be replaced or the angle should be adjusted to a sharper state. If the blade frequently breaks, it may be due to excessive cutting force. The gate diameter can be increased or the mold opening speed can be reduced to reduce the impact load. If the solids are stuck in the mold after ejection, check whether the push rod position is offset or the gripping force is insufficient. Adjust the push rod position to align with the center of the solids, or add a serrated pattern to the tip of the push rod to increase friction. Poor resetting is another common problem, often caused by insufficient spring force or a deformed reset rod. A high-strength spring should be replaced or the reset rod should be straightened to ensure accurate return of the mechanism during mold closing. For example, a company producing plastic toy wheels found that solids were frequently stuck between the push rod and the mold cavity. After inspection, it was found that the tip of the push rod was too smooth. After replacing it with a structure with a 0.5mm deep annular groove, the solids grip was improved and the sticking problem was completely eliminated. Regularly lubricating the moving parts of the mechanism (such as applying high-temperature grease) can reduce wear and extend the service life to more than 500,000 cycles.
