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How to solve the problem of poor back-pressure control in a plastic molding machine?

2025/11/14 By le zhan

plastic molding machine 7-5

Many manufacturers encounter the issue of poor back-pressure control in plastic molding machine, leading to average scrap rates of 8% to 12% and annual losses of tens of thousands of dollars per machine. Some packaging manufacturers have also scrapped defective bottles worth tens of thousands of dollars due to uneven wall thickness caused by unstable back pressure. Some automotive parts suppliers have experienced a 23% increase in customer returns due to parts deformation caused by unstable back pressure. To address these issues, we utilize control technology, optimize settings, and implement proactive maintenance. Topstar’s TMll series injection molding machines utilize a proportional back pressure system and multi-level settings to provide precision and ease of use, resolving the problem of poor back pressure control.

What is back-pressure control in a plastic molding machine, and why does it fail?

To address the issue of poor back pressure control, it is essential first to understand back pressure and its underlying causes. Back pressure refers to the resistance applied to the screw by the plastic molding machine during the plasticizing process. It ensures uniform resin melting, removes air bubbles, and ensures uniform mixing of additives. Poor back pressure control typically stems from three root causes:

Outdated manual control: Older plastic molding machines utilize manual valves to set back pressure, rendering it impossible to maintain a stable pressure during production. Even minor adjustments can lead to pressure overshoot or drop.

Worn parts, such as leaking hydraulic valves, faulty pressure sensors, or worn screw barrels, can all prevent accurate pressure transmission or detection, resulting in unstable performance.

Improper settings: Operators often set the back pressure too high or too low because they lack data on material requirements or machine capabilities.

back-pressure control in a plastic molding machine

The Cost of Poor Back Pressure Control in Plastic Molding Machine

Poor back pressure control not only causes waste but also affects all aspects of production, damaging profits. When back pressure is poorly controlled, unstable melt quality occurs. Too low or unstable back pressure can lead to bubbles, unmelted resin particles, or uneven color distribution in the melt. This results in shrinkage marks, voids, or streaks in parts, with 90% of parts being unsellable.

Furthermore, excessive back pressure can cause resin scorching. Too high a back pressure generates excessive heat, causing the resin to scorch and form a black, degraded layer that damages the parts. A plastic medical product manufacturer once lost tens of thousands of dollars due to a batch of products contaminated by charred resin, which had contaminated polycarbonate components. Simultaneously, extended cycle times occur, with operators frequently slowing down cycles to compensate for insufficient back pressure, leading to a 10-15% reduction in output. Furthermore, premature wear of the injection molding machine can occur; unstable pressure puts stress on the screw, barrel, and hydraulic system, shortening the lifespan of the plastic molding machine by 20-30%.

The Cost of Poor Back Pressure Control in Plastic Molding Machines

Proportional Back Pressure Control: Topstar’s Solution

The most effective way to solve poor back pressure control is to upgrade to proportional back pressure control, which is precisely the technology used in Topstar’s TMll series injection molding machines. Unlike manual or on/off control, proportional control enables precise, automated pressure regulation.

The TMll injection molding machine utilizes a proportional pressure valve to regulate back pressure in real-time. It responds to changes in resin viscosity, screw speed, and temperature, maintaining pressure within ±0.1 MPa for consistent results. Operators can set the desired back pressure through the TMll’s touchscreen interface, eliminating the need for manual knobs or guesswork. The system can store settings for different materials, so switching from PP to ABS takes only seconds, eliminating the need for hours of adjustment.

Furthermore, the proportional valve is more durable than manual valves, with a lifespan three times longer. TMll’s sealed sensors prevent resin dust and moisture damage, avoiding the drift problems common in older machines. One of our contract molding plants stated, “We used to spend two hours adjusting the back pressure every shift. With the TMll injection molding machine, we only need to set it once, and it remains stable.”

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Multi-stage back pressure settings, precise control, improved plasticizing quality

The TMll plastic molding machine series takes it a step further with multi-stage back pressure settings, allowing you to adjust the pressure at different stages of plasticization. This level of control ensures optimal melt quality even for the most demanding materials:

  • Stage 1: Low back pressure (0.5-1 MPa) prevents resin from burning when the screw begins to retract and draw in raw materials.
  • Stage 2: Medium back pressure (1-3 MPa) Mixes additives and removes air bubbles without generating excessive heat.
  • Stage 3: High back pressure (3-5 MPa) (MPa) homogenizes the melt, ensuring uniform density and flowability, thus guaranteeing consistent part quality.

For example, an injection molding plant producing glass fiber reinforced nylon used TMll’s multi-stage settings to reduce porosity by 92%. Their process engineer explained, “Glass fiber reinforced resin needs gentle melting but also thorough homogenization. TMll’s multi-stage control allows us to achieve both simultaneously, something our previous plastic molding machines couldn’t do.” This precision translates into improved plasticizing quality, resulting in a smoother, bubble-free, and more uniformly mixed melt, which produces parts that meet stringent tolerances and consistently pass quality inspections.

Calibration and Maintenance for Precise Back Pressure Control

Even the best proportional control systems require regular calibration and maintenance to achieve optimal performance. Pressure sensors can be calibrated quarterly, verifying TMll sensor readings using a certified pressure gauge. If deviations occur, adjustments can be made via the TMll’s touchscreen. Additionally, valves should be inspected every 6 months for leaks or wear on the proportional pressure valves.

Topstar’s TMll features easily replaceable valve cores, eliminating the need for costly hydraulic system overhauls. Annual Screw Barrel Cleaning: Worn or fouled screw barrels can affect pressure transmission. The TMll injection molding machine’s screw barrel features an easy-to-remove design, reducing maintenance time compared to comparable products. 50%. Furthermore, when changing resins, please test and store the optimal back pressure setting in the TMll’s memory. This avoids waste caused by repeated trials during changeovers.

Precisely and efficiently solve back-pressure control problems.

If you experience poor back pressure control, don’t worry too much. Topstar’s TMll series injection molding machines offer the simplest and most effective solution to back pressure control problems through their easy-to-use interface, precise proportional control, and multi-level settings.

 

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