Thread automatic demoulding mechanism
The threaded automatic demolding mechanism is a core component in the automated production of threaded plastic parts. It automatically rotates the threaded core or cavity and ejects the plastic part during the mold opening process, eliminating the need for manual intervention. This significantly improves production efficiency and reduces labor costs. This mechanism is widely used in the mass production of threaded plastic parts, such as plastic bottle caps, pipe fittings, and threaded connectors. Its design directly impacts the production cycle and the stability of part quality. Compared to manual or semi-automatic demolding, the threaded automatic demolding mechanism offers advantages such as consistent operation, high repeatability (typically up to ±0.02mm), and adaptability to continuous production. It is an indispensable key technology in modern injection molding production.
Threaded automatic demolding mechanisms are primarily powered by hydraulic motors, servo motors, and mold opening force transmission, each with its own application scenarios. Hydraulic motor-driven automatic demolding mechanisms, powered by a hydraulic system, offer high torque output and convenient speed regulation, making them suitable for large threaded plastic parts (such as pipe fittings with a diameter ≥ 100mm). Their speed can be infinitely adjusted via a flow valve to meet the demolding requirements of parts with varying thread pitches. Servo motor-driven mechanisms offer high control precision and fast response speed. They can precisely control the core’s rotation angle (within 0.5°) using an encoder, making them particularly suitable for demolding precision threaded plastic parts (such as those with thread tolerances ≤ 6g). They can also be integrated with the injection molding machine’s control system, facilitating intelligent production. Mold opening force transmission (e.g., converting the mechanical motion of the mold opening into rotational force via gears and racks) offers a simple structure and low cost, but limited power output, making them suitable only for small threaded plastic parts (such as bottle caps with a diameter ≤ 30mm).
The transmission system of a threaded automatic demolding mechanism is crucial for ensuring rotational accuracy and power transmission. It typically consists of a driving element, a driven element, and a transmission medium. Gear transmission systems are widely used due to their high transmission efficiency (over 95%) and compact structure. A driving gear is connected to the power source, while a driven gear is coaxially fixed to the threaded core. The meshing of the two transmits power to the core. To ensure smooth transmission, the gear module is typically 2-5mm, and the number of teeth is determined by the transmission ratio. Hardened gears (surface hardness ≥ HRC50) are required to improve wear resistance and service life. For applications requiring silent operation, synchronous belt drives can be used. They offer excellent transmission stability and low noise (≤65dB). However, tensile deformation of the synchronous belt can affect transmission accuracy, making them suitable for plastic parts with less demanding rotation angles. Worm and worm gear drives offer a self-locking feature, preventing the core from reversing due to external forces during mold closing. They are suitable for vertical thread demolding, but their transmission efficiency is lower (approximately 70-80%) and require a higher-power power source.
The control system for the threaded automatic demolding mechanism must precisely coordinate the rotation and ejection actions to ensure an orderly demolding process. The control system typically consists of sensors (such as position sensors and pressure sensors), a controller (PLC or dedicated control module), and actuators (solenoid valves or servo drives). During the initial mold opening, when the position sensor detects that the mold has opened to a set distance (usually 1/3 of the maximum mold opening), the controller sends a signal to activate the rotary power source, driving the threaded core. When the rotation angle reaches the set value (calculated based on the thread pitch and thread length, for example, 180° for a 2mm pitch and 10mm thread length), the pressure sensor detects a decrease in the core’s rotational resistance (indicating complete thread disengagement), triggering the controller to initiate an ejection signal, causing the ejection mechanism to eject the part from the core. Once ejection is complete, the controller controls the rotary power source to reverse and reset, preparing for the next injection cycle. The entire process is timed to within 0.1 seconds, ensuring compatibility with the injection molding machine’s production cycle (typically 10-30 seconds per mold).
The design of a threaded automatic demolding mechanism must consider safety, maintainability, and cost-effectiveness. For safety, an overload protection device (such as a relief valve in the hydraulic system or an overload relay in the motor drive) should be installed. This automatically shuts down the machine when the demolding resistance exceeds a set value (typically 1.2 times the rated torque) to prevent damage. For maintainability, transmission components should be designed for easy assembly and disassembly (e.g., gears using keyed or expansion sleeve connections), and rotating bearings should be lubricated (e.g., deep-groove ball bearings with grease fittings) to facilitate routine maintenance. For cost-effectiveness, the appropriate power source and transmission method should be selected based on the production batch size and part precision requirements. For example, a simple mechanism using mold opening force transmission can be used for small-batch production, while a high-precision mechanism driven by a servo motor is required for large-scale, precision production. Furthermore, the mechanism’s dimensions must be compatible with the injection molding machine’s installation space to avoid interference with components such as tie rods and ejector cylinders, ensuring smooth installation and commissioning.
