Injection molding rack and pinion horizontal side core pulling mechanism
The horizontal lateral core-pulling mechanism for injection molding utilizes a rack-and-pinion meshing transmission to achieve lateral core pulling. It primarily consists of a rack core, a gear, a transmission rack, and a guide mechanism. It is suitable for molding gear-like plastic parts with horizontal lateral projections or side holes. Its operating principle is to use mold opening force to drive the transmission rack, which in turn rotates the gear, pulling the rack core horizontally and completing the core-pulling action. Compared to other core-pulling mechanisms, this mechanism offers advantages such as high core-pulling precision, smooth movement, and a large core-pulling distance. It is particularly suitable for molding lateral structures with complex tooth shapes, such as lateral axial holes or bosses in plastic gears. For example, when molding plastic gears in automotive seat adjustment mechanisms, which have side bosses for mounting, a rack-and-pinion horizontal core-pulling mechanism can precisely control the core-pulling action, ensuring the dimensional accuracy and surface quality of the bosses to meet assembly requirements.
The structural design of a horizontal lateral core-pulling mechanism for a gear rack in injection molding requires a critical consideration of the meshing accuracy between the gear and rack to ensure accurate and stable core-pulling operation and avoid core-pulling deviation or mechanism damage due to poor meshing. The gear’s module, number of teeth, pressure angle, and other parameters must match those of the rack. Standard gears with a module of 1-3mm and a pressure angle of 20° are typically used to ensure good meshing performance. The lateral structural dimensions of the rack core and the plastic part must be precisely matched, and the rack pitch error should be controlled within ±0.02mm to ensure the tooth profile accuracy of the molded part. The design of the guide mechanism is also crucial. The rack core should be equipped with high-precision guide grooves with a clearance of 0.01-0.03mm and a hardened guide surface (HRC 50-55) to reduce wear and vibration during operation. In addition, the mechanism needs to be equipped with positioning devices, such as limit blocks and spring pins, to ensure that the rack core is accurately reset after the core is pulled into place to avoid collision during mold closing. For example, a limit block can be set at the end of the rack to control the core pulling distance error within ±0.05mm.
There are various power transmission methods for horizontal rack-and-pinion lateral core pulling mechanisms in injection molding. These can be driven directly by mold opening force, or by hydraulic motors or servo motors. Different drive methods are suitable for different production requirements. Mold opening force drive is the most common method. When the movable mold separates from the fixed mold, a transmission rack fixed to the fixed mold rotates the gear, which in turn pulls the rack core. Its simple structure and low cost make it suitable for applications with low core pulling forces and large production batches. For example, a rack-and-pinion mechanism driven by mold opening force can achieve efficient and stable production for lateral core pulling of small toy gears. Hydraulic motor drive uses a hydraulic motor to rotate the gear to achieve core pulling. The core pulling force and speed can be precisely controlled by the hydraulic system. This method is suitable for large plastic parts with high core pulling forces and long core pulling distances, such as plastic gears in automotive transmissions. Core pulling forces can reach 50-100kN and core pulling distances can reach 200-300mm. The servo motor drive has higher control accuracy and can monitor the core pulling position in real time through the encoder to achieve closed-loop control. It is suitable for the molding of high-precision plastic parts. The core pulling position accuracy can reach ±0.01mm, meeting the lateral structural molding requirements of precision gears.
The installation and commissioning of the horizontal lateral core-pulling mechanism for injection molding racks and pinions significantly impacts its performance. The precise installation and coordinated movement of all components must be ensured to avoid problems such as jamming and abnormal noise. During installation, the axial center distance between the pinion and rack must be precisely adjusted to within ±0.01mm, ensuring a meshing side clearance between 0.02-0.05mm. Excessive side clearance can easily cause impact and noise, while too little can lead to jamming. The rack core must be installed with guaranteed relative positioning accuracy to the mold cavity, with the perpendicularity error between its axis and the cavity parting plane no more than 0.02mm/m to prevent positional deviation between the lateral structure and the main body of the molded part. During commissioning, the core-pulling action must be tested step by step. First, manually confirm the absence of interference, then perform a no-load test mold to observe smooth movement, and finally perform a test mold with material to verify the core-pulling effect and dimensional accuracy of the molded part. For example, when debugging the lateral core-pulling mechanism of a certain gear plastic part, the core-pulling action is smooth by adjusting the gap of the guide groove and the meshing side clearance of the gear rack, and the dimensional tolerance of the lateral boss of the plastic part is controlled within ±0.03mm.
Maintenance and upkeep of the horizontal lateral core-pulling mechanism for injection molding pinion and rack systems is crucial to ensuring long-term, stable operation. Regular inspection of all components for wear and timely lubrication and replacement are essential to extend the lifespan of the mechanism. Grease (such as lithium-based grease) should be regularly applied to the meshing surfaces of the pinion and rack, replenished every 1,000 molds, to reduce friction and wear and ensure transmission efficiency. The guide chute should be regularly cleaned to prevent dust and plastic debris from entering the clearance, which could increase movement resistance or scratch the surface. This can be done by blowing it out with compressed air weekly and disassembling and cleaning it monthly. Regular inspection of the pinion and rack tooth surfaces for wear is also crucial. If the tooth thickness wear exceeds 0.1mm, it should be replaced promptly to prevent compromising core-pulling accuracy. Furthermore, the positioning device and stopper should be regularly inspected to ensure they are securely fastened and accurately positioned to prevent loosening that could cause core-pulling errors or damage the mechanism. For example, after 100,000 molds, the pinion and rack core-pulling mechanism on a certain production line showed slight wear on the rack teeth. The rack was promptly replaced and the meshing clearance adjusted to ensure that subsequent production of plastic parts met dimensional accuracy requirements. Through scientific maintenance, the service life of the mechanism can reach more than 500,000 molds, ensuring the continuity and stability of production.
