Why does injection molding burn

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Embark on a journey into the labyrinthine universe of injection molding, a linchpin in the tapestry of contemporary fabrication. This procedure not only facilitates the voluminous production of components but also guarantees uniformity and intricacy in their design.

Yet, the path of injection molding is not devoid of obstacles. Manufacturers often grapple with the emergence of burn marks on the injection-molded articles. These blemishes transcend mere visual flaws; they are harbingers of deeper malfunctions within the fabrication process, potentially undermining the structural soundness of the item.

Grasping the fundamental causes of these burn marks is of paramount importance.Accompany us as we demystify the enigma of burn marks in injection molding, an expedition that promises to not only augment manufacturing efficacy but also to raise the bar of quality for plastic commodities in our quotidian lives.

Strategies to Prevent Burn Marks

In the realm of injection molding, preventing burn marks is not just about rectifying problems but proactively setting up processes and systems to avoid them. Let’s explore some effective strategies that can be employed.

A. Optimizing Molding Conditions

The conditions under which molding takes place have a direct impact on the quality of the final product, especially in preventing burn marks.

Adjusting Melt Relaxation Time: This involves controlling the time it takes for the molten plastic to settle and cool in the mold. Proper management of this time helps in reducing internal stress and heat buildup, which are common causes of burn marks.

Controlling High Resin Temperature: Keeping the resin temperature in check is crucial. Excessively high temperatures can lead to degradation of the plastic, increasing the likelihood of burn marks.

Importance of Anti-Reverse Ring: The anti-reverse ring in the injection molding machine ensures that the molten material flows in one direction and at a controlled rate. This is vital for ensuring proper mold filling and preventing the backflow of molten plastic, which can create uneven temperatures and lead to burning.

B. Design and Maintenance of Molds

The design of the mold and its maintenance are key factors in preventing burn marks.

Significance of Mold Properties: The design elements of the mold, such as the transition cavity and the runner system, play a critical role. A well-designed mold ensures even flow and distribution of the molten plastic, reducing the risk of localized overheating.

Maintenance to Prevent Mold Failure: Regular maintenance of the mold is essential to ensure its proper functioning. This includes checking for and addressing any issues that could lead to improper mold venting or, air trapping, or uneven heat distribution.

C. Material Handling and Pre-treatment

The way materials are handled before the plastic injection speed and molding process can also influence the outcome.

Pre-drying Methods for Materials: Some plastics absorb moisture, which can vaporize during molding and create pressure pockets that lead to burn marks. Pre-drying the material effectively removes this moisture.

Purging Techniques: Regularly purging the injection molding machine with the appropriate cleaning material ensures that any degraded material that could cause burning is removed.

Ensuring Optimal Injection Temperature and Speed: It is crucial to maintain the optimal temperature and speed of injection for the specific type of plastic being used. This helps in achieving a uniform, high melt temperature and reduces the chances of overheating and burning.

Strategies to Prevent Burn Marks

To effectively prevent burn marks in injection molding, a comprehensive approach encompassing molding conditions, mold design and maintenance, and material handling and pre-treatment is essential. Here’s a detailed look at each of these strategies:

A. Optimizing Molding Conditions

1.Adjusting Melt Relaxation Time:

Objective: To manage the settling and cooling time of molten material in the first molding cycle.

Benefit: Optimizing this time reduces internal stress and heat build-up, thereby lowering the risk of burn marks.

2.Controlling High Resin Temperature:

Goal: To keep material temperature and the resin temperature within an optimal range.

Reason: High temperatures can degrade the resin, leading to burn marks.

3.Importance of Anti-Reverse Ring:

Function: Ensures consistent mold filling by preventing the backflow of molten material.

Impact: Helps maintain even temperatures, reducing the potential for burning.

B. Design and Maintenance of Molds

1.Significance of Mold Properties:

Key Aspects: Includes elements like the transition cavity and the runner system.

Effect: A well-designed injection mold that promotes even distribution of plastic, reducing overheating and burn marks.

2.Maintenance to Prevent Mold Failure:

Importance: Regular maintenance ensures proper functioning and identifies issues like improper venting or heat distribution.

Outcome: This helps avoid conditions that can lead to burn marks.

C. Material Handling and Pre-treatment

1.Pre-drying Methods for Materials:

Necessity: Some plastics absorb moisture, which can vaporize and create pressure pockets during molding.

2.Purging Techniques:

Purpose: To clear the injection molding machine of residual or degraded material.

Result: Prevents burning caused by such materials.

3.Ensuring Optimal Injection Temperature and Speed:

Goal: To maintain correct temperature and speed for each type of plastic.

Advantage: Ensures a uniform melt and minimizes the risk of overheating and burn marks.

Implementing these strategies can significantly reduce the occurrence of burn marks, leading to higher quality and more consistent injection molded parts.


In our exhaustive disquisition on the manifestation of burn marks in the domain of injection molding, we have delved into the critical elements that precipitate this prevalent dilemma and perused a spectrum of methodologies to ameliorate it. Grasping the complex equilibrium between melt temperature and injection velocity, alongside the intricate crafting and upkeep of molds, is paramount in determining the caliber of the ultimate injection molded components.

The imperative of confronting burn marks in this sphere is paramount. These blemishes are not mere surface irregularities; rather, they denote more profound process inefficiencies or mishaps in material handling. By identifying and correcting these root causes, manufacturers not only augment the visual allure of their output but also bolster its structural robustness and functional prowess.

Looking ahead, it becomes evident that unceasing enhancement and vigilance in the plastic injection molding process are integral to securing and upholding superior quality outcomes. This necessitates a commitment to exacting control over procedural parameters, routine maintenance of apparatus, and an extensive comprehension of material characteristics. As advancements in materials and technologies continue to revolutionize this field, remaining informed and adaptable is imperative for manufacturers striving to produce transcendent plastic injection molded parts.

To conclude, navigating the path to eradicate burn marks in injection molding is both arduous and fulfilling. It demands a confluence of technical acumen, scrupulous focus on detail, and an unwavering dedication to excellence. For those resolved to conquer this craft, the benefits are unmistakable: impeccable, top-tier plastic components that satisfy the stringent demands of an ever-exacting marketplace.

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