Injection molding external pull plate fixed distance parting mechanism
The external pull-plate spacing parting mechanism for injection molding is a crucial device for enabling the orderly opening of multiple parting surfaces in molds. It is widely used in molds with side core pulls, complex cavities, or those requiring sequential removal of runner slurry and finished product. Compared to internal pull-plate mechanisms, the external mechanism places core components such as the pull-plate and tie rods on the outside of the mold, offering advantages such as compactness, ease of commissioning, and low maintenance. Its operating principle is to limit the opening distance of each mold parting surface by the length of the pull-plate. During the mold opening process, the injection molding machine’s opening force drives each parting surface to open sequentially in a pre-set sequence, ensuring that runner slurry is released first before the product is removed, thus avoiding part deformation or mold damage caused by a mismatched parting sequence. For example, in a three-plate mold, the external pull-plate spacing parting mechanism precisely controls the parting distances between the fixed mold base plate and the runner plate, and between the runner plate and the moving plate, ensuring smooth runner slurry removal.
The structural design of an external pull-plate fixed-distance parting mechanism requires careful consideration of the pull-plate’s installation position and force balance. Pull-plates are typically symmetrically positioned on either side of the mold, parallel to the mold’s guide posts. This ensures even force distribution during the mold opening process and prevents unbalanced loading of the mold due to unilateral force. The pull-plate length must be precisely calculated based on the desired parting distance. One end is fixed to the fixed mold, while the other is connected to the movable mold via a stopper or nut. When the mold opening distance reaches the set pull-plate length, the pull-plate pulls the corresponding mold plate to stop, achieving fixed-distance parting. For example, if the required parting distance between the runner plate and the fixed mold base plate is 100mm, the pull-plate length should be set to 100mm plus the dimensions of the connecting components to ensure the correct parting distance. Furthermore, the pull-plate connection to the mold plate must be secure and reliable, and can be secured with bolts or pins to prevent loosening or falling off during mold opening.
The material selection and dimensional parameters of the pull plate are crucial to the performance of the mechanism. Since the pull plate needs to withstand large tensile forces during operation, high-strength alloy structural steel, such as 45 steel or 40Cr, must be selected and tempered to a hardness of 28-32HRC to improve wear resistance and fatigue resistance. The cross-sectional shape of the pull plate is usually rectangular or circular. Rectangular pull plates have better guidance, while circular pull plates are easier to process, and the appropriate shape can be selected according to the mold space. The diameter or thickness of the pull plate needs to be calculated and determined based on the tensile force it withstands. For example, for small and medium-sized molds, the pull plate diameter is generally 12-16mm, while large molds need to reach 20-25mm to ensure that it will not bend or break under the maximum mold opening force. In addition, the surface of the pull plate needs to be chrome-plated to improve its surface hardness and smoothness, reduce friction with other components, and extend its service life.
Controlling the fit accuracy of the external pull plate spacing parting mechanism is key to ensuring spacing accuracy. The fit clearance between the pull plate, the limit block, and the template must be strictly controlled. Excessive clearance can easily lead to shaking during the parting process, affecting the spacing accuracy; too small a clearance will increase the resistance to movement and even cause jamming. Usually, the fit clearance should be controlled between 0.05-0.1mm. Precision machining can be used to ensure the straightness and flatness of the pull plate, allowing it to move smoothly and without obstruction. At the same time, the design of the pull plate’s guide device is also very important. Guide sleeves or guide grooves can be provided on the template to constrain the pull plate’s movement trajectory and prevent the pull plate from deflecting when subjected to force. For example, a guide sleeve that matches the pull plate is installed on the movable template. The inner diameter of the guide sleeve is 0.05mm larger than the pull plate diameter, which can not only ensure the free movement of the pull plate, but also play a good guiding role.
The commissioning and maintenance of an external pull-plate spacing parting mechanism must follow a scientific and standardized process. After the mold is installed on the injection molding machine, a trial mold commissioning is required to check whether the opening sequence and distance of each parting surface meet the design requirements. If the parting distance is found to be inaccurate, it can be corrected by adjusting the limit nuts on the pull-plate. If the parting sequence is incorrect, the pull-plate connection method must be checked for correctness and the relevant components must be replaced or adjusted promptly. During routine maintenance, the pull-plate surface must be regularly cleaned of oil and impurities and lubricated to reduce friction and wear. The pull-plate should also be inspected for deformation, cracks, or thread damage, and any problems should be replaced promptly. For molds used over a long period of time, the length and diameter of the pull-plate should be regularly measured to ensure that its dimensions have not changed due to wear or deformation, thereby ensuring the stable performance of the spacing parting mechanism. Through reasonable design, precise processing, and standardized maintenance, the external pull-plate spacing parting mechanism can effectively improve the efficiency and reliability of the mold and meet the production requirements of complex injection molded products.
