Key Components of Extrusion Blow Molding Machines and Their Functions

1. Extrusion System: The "Heart" of Material Melting and Conveying

• Screw: As the "core of the core" of the extrusion system, the screw is made of high-strength alloy steel with wear-resistant and corrosion-resistant properties. Its main functions are: pushing the plastic raw materials forward from the hopper to the die head; generating mechanical shear force through rotation to assist the melting of raw materials; and mixing the molten plastic uniformly to ensure stable plasticizing quality. The key parameters of the screw include length-diameter ratio (L/D), compression ratio and thread structure. For example, a larger length-diameter ratio can improve the plasticizing uniformity of raw materials, which is suitable for processing materials with high viscosity; a reasonable compression ratio can avoid bubbles in the molten plastic.
• Barrel: It is closely matched with the screw and provides a closed space for the melting and conveying of raw materials. The outer wall of the barrel is equipped with a multi-section heater (usually electric heating), which heats the raw materials step by step to avoid local overheating and decomposition. At the same time, the barrel is also equipped with a cooling water channel to adjust the temperature precisely and ensure the stability of the plasticizing process.
• Hopper: It is the feeding device of the extrusion system, used to store plastic granules. The hopper is usually equipped with a level sensor, which can automatically remind when the raw materials are insufficient, ensuring continuous production. Some high-end EBM machines are also equipped with a pre-drying device in the hopper to remove moisture from the raw materials and avoid bubbles in the products.

2. Die Head: The "Mold" of Parison Forming

• Core Functions: The molten plastic from the barrel enters the die head, and is evenly distributed through the flow channel inside the die head, then extruded through the annular gap between the die core and the die sleeve to form a parison. The die head is equipped with a wall thickness adjustment device (manual or automatic), which can adjust the gap between the die core and the die sleeve in real time to correct the uneven wall thickness of the parison. For example, when the wall thickness of one side of the parison is too thin, the adjustment device can expand the local gap to make the wall thickness uniform.
• Die Head Types: Cross-head die heads have a simple structure and are suitable for small and medium-sized EBM machines, mainly used to produce small-batch, multi-specification products; spiral die heads have a more reasonable flow channel design, which can make the molten plastic distribute more evenly, and are suitable for large-scale EBM machines or high-precision product production, such as automotive parts and thick-walled chemical barrels.

3. Clamping System: The "Clamp" for Sealing and Shaping

• Mold: It is the forming tool of the product, usually composed of two halves (male mold and female mold). The inner surface of the mold is processed according to the shape of the final product. The mold is equipped with a cooling water channel, which can rapidly cool the molten plastic attached to the inner wall of the mold to shorten the production cycle. The material of the mold is usually alloy steel, which has high hardness and wear resistance to ensure long-term stable use.
• Clamping Cylinder: It provides power for mold clamping and opening, usually driven by hydraulic pressure or servo motor. The clamping force is an important parameter of the clamping system. If the clamping force is insufficient, the parison may leak air during blowing, resulting in product deformation; if the clamping force is too large, it may damage the mold or increase energy consumption. The clamping force needs to be adjusted according to the size of the mold and the material of the product.
• Guide Rail: It ensures the smooth movement of the mold during clamping and opening, avoids mold deviation, and ensures the accuracy of product forming.

4. Blowing System: The "Power Source" of Parison Expansion

• Air Compressor & Air Storage Tank: The air compressor compresses air to generate high-pressure air, which is stored in the air storage tank. The air storage tank can stabilize the air pressure and avoid pressure fluctuations during the blowing process. At the same time, the air storage tank is equipped with a filter device to remove moisture and impurities in the air, preventing the product from being contaminated or generating bubbles.
• Air Needle: It is inserted into the parison during the clamping process to blow air into the parison. The diameter and position of the air needle need to be matched according to the size of the parison. For large parisons, multiple air needles can be used to ensure uniform air intake.
• Pressure & Flow Control Valve: Precisely control the pressure and flow of compressed air. The air pressure directly affects the expansion effect of the parison: too high air pressure may cause the product to be too thin or even burst; too low air pressure may cause the parison to not fully expand and fit the mold. The air flow affects the expansion speed of the parison, which needs to be adjusted according to the cooling speed of the product.

5. Cooling System: The "Coolant" for Shortening Production Cycles

• Mold Cooling: Cooling water channels are arranged inside the mold, and cooling water flows through the channels to take away the heat of the molten plastic. The temperature and flow of the cooling water need to be controlled precisely: too low temperature may cause the product to be brittle; too high temperature will prolong the cooling time and reduce production efficiency.
• Barrel Cooling: Cooling water channels are also arranged on the barrel, mainly used to control the temperature of the barrel and avoid overheating and decomposition of raw materials. Especially in the feeding section of the barrel, proper cooling can prevent the raw materials from melting in advance and affecting the conveying effect.

6. Control System: The "Brain" of Equipment Operation

• PLC Controller: It is the core of the control system, which processes the signals from various sensors and issues control commands to the actuator (such as heater, motor, cylinder) to realize the automatic control of the production process.
• Touch Screen: It is the human-machine interaction interface, through which operators can set production parameters (such as temperature, screw speed, clamping force, air pressure, etc.), monitor the operation status of the equipment in real time, and view fault prompts.
• Sensor: It is responsible for collecting various parameters during the production process, such as barrel temperature, mold temperature, clamping force, air pressure, etc., and feeding them back to the PLC controller to realize closed-loop control.