In the injection molding production process, product burning is a common and impactful appearance defect, characterized by silver streaks, light brown dark streaks, or black stains on the product surface. It not only severely impairs the product’s aesthetic quality and structural performance but also leads to higher rejection rates, raw material waste, reduced production efficiency, unnecessary cost losses for enterprises, and even damages customer trust and cooperation. As a high-tech enterprise deeply engaged in the R&D and manufacturing of injection molding equipment, Kelongge leverages over 20 years of technical accumulation and advantages in its full range of injection molding equipment, combined with extensive industry application cases, to provide end-to-end solutions for burn defects for injection molding enterprises. These solutions eliminate problems at their root, helping enterprises reduce costs, improve efficiency, and enhance product competitiveness.

       I. Core Manifestations of Burn Defects in Injection Molded Products

      Typical features of burn defects in injection molded products are distinct abnormal marks on the product surface, mainly divided into three categories:

• Silver or light brown dark streaks, mostly distributed along the melt flow path;
• Irregular black stains, often appearing near gates, flow ends, or dead corners of molds;
• Local carbonized spots, which in severe cases are accompanied by product embrittlement and peculiar odors, directly resulting in product scrappage.   

        Such defects commonly occur in the production of various injection molded products, including automotive parts, toys, daily necessities, electronics, and medical devices, and may arise in single-color, two-color, or multi-color injection molding scenarios. Essentially, they are carbonization caused by local overheating of molten plastic, gas compression combustion, or material contamination.

     II. In-Depth Analysis of Core Causes of Burn Defects

     Burn defects in injection molded products stem not from a single factor but from an imbalance across multiple links, including raw materials, processes, equipment, and molds. Drawing on Kelongge’s years of on-site technical service experience, we have summarized the following core causes for enterprises to conduct precise troubleshooting:

   (I) Issues in Raw Material and Material

    Management Raw material quality is the foundation of injection molding production; substandard raw materials or improper management are highly likely to trigger burn defects. Common scenarios include:

• Impurities mixed in raw materials or excessive powder in granular materials, which tend to carbonize during high-temperature melting and adhere to the product surface;
• Excessive residence time of raw materials in the barrel leading to thermal degradation and carbonization, especially for hygroscopic raw materials—insufficient drying causes water vaporization and expansion to form high-temperature bubbles, which in turn burn surrounding raw materials;
• Incomplete purging of machines before mixing different raw materials, resulting in reactions between residual materials and the formation of carbonized impurities.

     (II) Unreasonable Injection Molding Process Parameters

      Process parameter settings are critical to the state of molten plastic and the most common cause of burning. Through extensive mold testing and verification, Kelongge’s technical team has identified the following abnormal parameters that easily cause problems:

• Excessively high screw speed and melt back pressure leading to shear overheating of the melt and raw material carbonization;
• Excessively high barrel temperature and mold hot runner temperature exceeding the raw material’s heat resistance, causing thermal decomposition;
• Excessively high injection speed and pressure—when molten plastic is injected into the mold at high speed, internal air is rapidly compressed, producing the \"Diesel effect\" that ignites plastic instantaneously and forms burn marks;
• Excessively long downtime, leaving residual melt in the barrel under high temperatures for a long time and causing carbonization and deterioration.

       (III) Improper Equipment Condition and Maintenance

       The condition of injection molding equipment directly determines production stability, and inadequate equipment maintenance creates hidden dangers of burning. Examples include:

• Unremoved residual burnt material in the barrel, screw, and nozzle, which continuously contaminates new molten material;
• Excessively large screw compression ratio and barrel length-to-diameter ratio leading to prolonged melt residence time and excessive shear force, causing overheating and carbonization;
• Excessively high clamping force making the mold fit too tightly, aggravating gas retention and indirectly causing burning;
• Wear of core equipment components (e.g., screw and check ring) resulting in uneven shearing and local overheating.

      (IV) Mold Design and Usage Issues

     Unreasonable mold structure design or improper use and maintenance prevents smooth gas discharge and triggers burning. Common problems include:

• Improper gate and runner design (e.g., undersized dimensions) leading to excessively fast melt flow, shear overheating, and obstructed gas exhaust;
• Poor mold cavity smoothness increasing material flow resistance and local overheating carbonization;
• Poor mold venting, especially at dead corners such as flow ends and enclosed structures (e.g., screw pillars, ribs), where trapped air is compressed and combusts;
• Improper use of mold release agents (e.g., unclean agents or excessive dosage) that decompose at high temperatures to produce stains resembling burn marks.

       III. Kelongge’s End-to-End Solutions for Burn Defects

       Targeting the above causes, Kelongge combines its advantages in injection molding equipment R&D with the customized service concept of \"tailored solutions\" to launch end-to-end solutions that balance universality and specificity. We provide professional support covering raw material management, process adjustment, equipment optimization, and mold improvement, helping enterprises quickly resolve burning issues and reduce rejection rates.

    (I) Raw Material and Material Control Solutions

1. Raw Material Selection: Enterprises are advised to use qualified raw materials, sieve granular materials to remove powder and impurities, and use magnetic frames to adsorb metal impurities to avoid contamination at the source. Hygroscopic raw materials must be fully dried in accordance with standards to prevent burning caused by water vaporization.
2. Material Management: Establish raw material usage records to avoid mixing different materials; conduct thorough machine purging before material switching. Shorten downtime and inject residual melt from the barrel before shutdown to prevent long-term high-temperature retention of residual materials. Regularly inspect raw material conditions and prohibit the use of expired or deteriorated materials.

     (II) Process Parameter Optimization Solutions

      Konger’s full range of injection molding equipment (including the K-TEC Servo Energy-Saving Series, CMS Two-Color Multi-Color Series, PET Preform Special Series, etc.) supports precise parameter control, paired with guidance from our professional technical team to optimize process parameters:

1. Temperature Control: Lower segmented barrel temperatures (recommended: rear section > middle section > front section) and mold hot runner temperature within the raw material’s heat resistance range to avoid thermal decomposition.
2. Speed and Pressure Control: Reduce screw speed and melt back pressure to minimize shear overheating; lower injection speed and pressure, or adopt multi-stage injection (slow front stage, fast middle stage, slow rear stage) to allow sufficient time for gas exhaust and prevent air compression combustion.
3. Residual Material Control: Shorten the residence time of residual materials in the barrel, regularly empty the barrel, and clean residual melt to avoid carbonized contamination.

     (III) Equipment Maintenance and Optimization Solutions

1. Equipment Cleaning: Regularly clean the barrel, screw, and nozzle to completely remove burnt material and carbon deposits; disassemble and clean the screw when necessary to ensure internal cleanliness. Kelongge’s injection molding equipment features an easy-to-clean structure that greatly improves purging efficiency and reduces downtime.
2. Equipment Parameter Adjustment: Adjust the screw compression ratio according to production needs, and replace small length-to-diameter ratio barrels if necessary to reduce melt residence time and shear force. Properly reduce clamping force to avoid gas retention caused by overly tight mold fitting. Replace worn components in a timely manner to ensure stable equipment operation.
3. Customized Equipment Adaptation: For different industries and product requirements, Kelongge provides customized injection molding equipment (e.g., CMS two-color injection molding machines, high-speed PET preform special machines). Precise temperature and speed control designs avoid burn defects at the equipment level while achieving energy conservation and consumption reduction.

     (IV) Mold Optimization and Maintenance Solutions

1. Mold Design Optimization: Kelongge’s technical team provides mold flow analysis services to predict gas retention locations in advance, optimize gate and runner dimensions, increase runner cross-sectional area, and reduce shear overheating. Add venting grooves at mold flow ends and dead corners, and deepen and widen venting channels to improve exhaust efficiency and eliminate gas compression combustion at the source.
2. Mold Maintenance: Regularly repair and polish molds to improve cavity smoothness and reduce material flow resistance. Standardize mold release agent usage by selecting high-quality, clean agents and controlling dosage to avoid stains from agent decomposition. Regularly inspect mold hot runner conditions to ensure uniform temperature and prevent local overheating.

      IV. Konger’s Core Strengths: Empowering Enterprises Holistically from Equipment to Service

      As a high-tech enterprise rooted in Ningbo, the \"Capital of China’s Plastic Machinery\", Kelongge focuses on the injection molding equipment segment and has built a full product matrix covering general and special applications. Backed by 19 patented technologies and a comprehensive service system, we provide solid support for enterprises in solving various defects in injection molding production:  

• Technical Strengths: With a professional R&D team and over 20 years of deep cultivation in injection molding technology, Kelongge’s products are equipped with imported core components for precise temperature and speed control, effectively avoiding shear overheating, gas retention, and other issues to reduce burn defect rates at the equipment source. Its two-color sandwich injection molding technology also helps enterprises cut raw material costs by 15%–25% without compromising product quality.
• Service Strengths: Kelongge has established a \"one-stop after-sales service\" system with offices in more than 20 cities across China and distributors in countries and regions such as India and Vietnam. We provide 24/7 online technical support, equipment commissioning, maintenance guidance, and other services. For production defects like burning, we quickly dispatch technicians for on-site troubleshooting and customized solutions.
• Industry Adaptability Strengths: Kelongge’s injection molding equipment is widely used in automotive parts, toys, daily necessities, electronics, medical devices, packaging, and other fields, with extensive industry application cases. We provide suitable equipment and technical solutions for single-color, two-color, and multi-color injection molding, as well as small precision parts, large fruit crates, and preforms, helping enterprises address production pain points.

       V. Conclusion

       Although burn defects in injection molded products seem complex, they can be effectively avoided through standardized raw material management, optimized process parameters, and proper equipment and mold maintenance. Upholding the philosophy of \"Empowering the Transformation and Upgrading of Global Manufacturing\", Konger provides end-to-end burn defect solutions for injection molding enterprises with high-quality equipment, professional technical support, and comprehensive after-sales service, helping them reduce rejection rates, improve production efficiency, and control production costs.

      If your enterprise is facing issues such as burned injection molded products and high rejection rates, please contact Kelongge. We will provide tailored customized solutions based on your production scenarios, equipment models, and product requirements, making injection molding production more efficient and stable, and helping you gain a competitive edge in the industry!