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How to Solve Poor Plasticization in the Injection Molding Process？

2025/12/15 By le zhan

Injection Molding Process 1-2(1)

Poor plasticization in the injection molding process can lead to bubbles, uneven surfaces, or brittle edges on parts, making them unsuitable for quality inspection. This not only wastes raw materials but also consumes time and increases labor costs. The main problem lies in poor management during the pre-plasticization stage; unstable pressure or temperature can cause insufficient melting or excessive degradation of the plastic resin. Topstar’s proportional back pressure control technology effectively solves this problem, improving both product quality and efficiency.

The Root Causes of Poor Plasticization in the Injection Molding Process

Before addressing poor plasticization in the injection molding process, engineers must first diagnose its root cause. Plasticization is the process of melting a solid resin into a uniform flow state, which depends on three interrelated factors: temperature, pressure, and screw motion. Problems arise when any of these factors become unbalanced. Common causes include insufficient barrel temperature, excessive screw speed, or unstable back pressure. Material-related issues also play a role: damp resin absorbs moisture, which evaporates during molding, forming bubbles; contaminated particles can lead to uneven melting. Even minor changes, such as a 5°C drop in barrel feed zone temperature or a 10% fluctuation in back pressure, can disrupt the entire injection molding process. And 68% of plasticizing failures stem from controllable pre-plasticizing variables, not material defects or machine wear.

Proportional Back Pressure Control: Topstar’s Core Solution to Plasticizing Problems in the Injection Molding Process

Topstar’s technological advantage lies in its pre-plasticizing stage, which directly targets the root causes of pressure-related plasticizing defects during injection molding. Traditional injection molding machines use a fixed back pressure setting—the same value for all materials and batches—a method suitable for simple processing but inadequate for complex resins such as PC or glass fiber-reinforced nylon. Topstar’s proportional back-pressure control addresses this, enabling multi-stage pressure adjustment during pre-plasticizing to adapt to the resin’s unique needs at each melting stage. Its working principle is as follows: as the screw retracts and feeds resin into the barrel, the injection molding machine automatically adjusts the back pressure according to preset parameters—using lower pressure during the initial feeding stage and higher pressure during the melting stage.

On the user interface, operators input the material type via a touchscreen, and the injection molding machine loads an optimized pressure profile, eliminating the need for repeated manual trials. Whether processing PE for packaging or rigid ABS for electronics, Topstar injection molding machines use proportional back-pressure control to adjust pressure in real time, ensuring consistent melt flow.

Proportional Back Pressure Control

Optimizing Temperature Parameters for Enhanced Plasticization in Injection Molding

Combining proportional back-pressure control with precise temperature management yields optimal results and is key to resolving poor plasticization in injection molding.

We need to adhere to the temperature range recommended by the resin manufacturer: ABS requires 230–250°C to fully melt without scorching, while PE requires 180–220°C. A common mistake operators make is setting a single temperature for the entire barrel, neglecting the different roles of each zone. Topstar injection molding machines address this issue with zone-specific temperature control, calibrated to ±1°C—a precision that eliminates “cold spots” where the resin remains solid. For example, the feed zone should be cooler to prevent particle clumping, while the metering zone requires the highest temperature to ensure uniformity. Combined with proportional back pressure control, this temperature strategy effectively addresses poor plasticization.

Adjusting screw speed and rotation angle improves plasticization efficiency

Screw motion is the third key factor for effective plasticization in injection molding, and improper screw speed adjustment is a common cause of poor melt flow. Excessive screw speed generates excessive frictional heat, which can degrade sensitive resins such as PVC or TPU. Conversely, excessively slow screw speed prolongs resin residence time in the barrel, leading to uneven melting and carbonization. Topstar injection molding machines synchronize screw speed with back pressure and temperature settings. Sensors monitor melt viscosity and adjust screw speed in real time, reducing speed for high-viscosity materials like acrylic and increasing speed for low-viscosity materials like PP.

This is particularly important for batch production of blended materials. For example, if you switch from processing high-density HDPE to processing VPE and VPE blends, the injection molding machine automatically adjusts the screw speed to prevent fiber breakage and ensure uniform melt flow. By combining this with pressure and temperature control, Topstar injection molding machines transform the injection molding process into a dynamic, self-correcting system.

Topstar injection molding machines

Pre-treatment of materials further avoids poor plasticization

Moisture is the biggest problem with injection molding materials, such as PET. This moisture turns into water vapor during melting, creating bubbles or voids in the final molded part. Contamination is another issue; dust, oil, or residual resin from the previous production process can interfere with the melting process, leading to streaks or weak points. The solution is rigorous pre-treatment. Topstar’s injection molding machines can be used with dehumidifying dryers to reduce the resin’s moisture content to below 0.02%, the threshold for bubble-free plasticization, thus providing a complete integrated injection molding process solution.
Furthermore, these machines are even equipped with a “material ready” sensor: if the dryer doesn’t process the resin long enough, the injection molding machine pauses pre-plasticization to avoid waste. Simultaneously, to prevent contamination, Topstar’s feeding system is equipped with a magnetic separator and mesh filter to remove metal fragments and impurities before the resin enters the barrel. By connecting the machine control system to the pre-treatment tools, Topstar ensures that every resin particle entering the barrel is fully prepared for plasticization.

Injection molding materials

Utilizing Proportional Back Pressure for a Stable Injection Molding Process

Poor plasticization may seem daunting, but its root lies in controllable variables: pressure, temperature, screw motion, and material pretreatment. Topstar’s proportional back pressure control is at the heart of this solution, offering flexibility for any resin while simplifying operations for the team. Combined with precise temperature zoning, variable screw speed, and integrated material pretreatment, this technology reduces scrap rates, shortens production cycles, and ensures consistent product quality.

 

 

 

 

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