This manual is compiled by the After-sales Service Department of Ningbo Kelonge Machinery. It aims to provide customers with professional and practical guidance on troubleshooting and resolving bubble defects in injection-molded products, helping customers efficiently solve bubble problems during production, improve product qualification rate, fully utilize the performance of Kelonge injection molding machines, and ensure smooth production.

      1. Definition of Bubble Defects

      A. During the plastic injection molding process, if air inside the mold cavity or moisture vapor from raw materials cannot be smoothly discharged and gets trapped inside the mold, hollow bubbles, voids, or air holes will form on the surface or inside the product after cooling.

      B. In the after-sales technical guidance of Kelonge Machinery, such injection molding defects are collectively referred to as bubbles, which are common quality issues in injection production. They can be effectively solved through standardized operation, parameter adjustment, and equipment optimization.

     2. Main Causes of Bubble Defects

     Combined with the equipment characteristics of Kelonge injection molding machines and years of after-sales service experience, the core causes of bubble defects are summarized into five categories: raw materials, process parameters, mold structure, product design, and equipment & screw.

   2.1 Raw Material and Moisture Issues

       Raw materials are the basic cause of bubbles and the <strong>first inspection item</strong> for Ningbo Kelonge Machinery after-sales troubleshooting:

• Raw materials are not fully dried according to standards, resulting in excessive moisture content. Moisture evaporates into vapor when heated, enters the cavity with molten material, and cannot be discharged, forming bubbles after cooling.
• The shrinkage rate of raw materials is too high, which is incompatible with the injection parameters of Kelonge injection molding machines, leading to uneven shrinkage during cooling and easy formation of internal voids.
• Raw materials stay in the barrel for too long, overheat and decompose under the continuous heating system of Kelonge injection molding machines, generating gas that mixes into the melt and forms bubbles.

       2.2 Improper Process Parameters Kelonge injection molding machines are equipped with precise parameter adjustment functions. Improper settings directly cause bubbles. Common unreasonable parameters are as follows:

• Holding pressure is too low: The molten material in the cavity cannot be fully compacted, forming gaps after cooling shrinkage, which appear as bubbles.
• Holding time is too short: Pressure stops before the product is fully compensated, especially for thick-walled products, where unfilled areas easily form bubbles.
• Injection pressure is too low: Slow and insufficient filling, so air inside the cavity cannot be effectively squeezed out and trapped in the melt.
• Barrel temperature is too high: Exceeds the suitable range for raw materials, causing material decomposition and gas generation, while accelerating moisture evaporation and increasing bubble probability.
• Improper back pressure and screw speed: Excessively high back pressure and screw speed cause excessive air entrainment in the barrel, which enters the cavity and forms bubbles.

       2.3 Mold and Gate Design Issues Reasonable mold and gate design directly affect melt flow and venting. Combined with the injection characteristics of Kelonge injection molding machines, common problems include:

• Mold temperature is too low: Poor matching with melt temperature, melt cools rapidly when contacting the mold wall, sealing internal gas and forming bubbles.
• Gate size is too small: High flow resistance and uneven filling, so gas is easily trapped; improper gate position (not avoiding thin-wall areas) causes thick sections to fill last and become gas traps.
• Dead corners and excessive material accumulation in the mold: Accumulated material decomposes under heat and blocks gas discharge.
• Improper or blocked vent grooves: Insufficient quantity, shallow depth, or blockage by oil/ residue are the most common mold-related causes in Kelonge after-sales troubleshooting.

      2.4 Product Structure Issues

       Incompatibility between product structure and the injection capacity of Kelonge injection molding machines easily causes bubbles:

      Excessive difference in product wall thickness. Thick sections cool slowly and cannot be fully compensated during shrinkage, easily forming internal bubbles and voids, especially in large and special-shaped products.

     2.5 Equipment and Screw Issues Related to the structure of Kelonge injection molding machines:

• Nozzle orifice is too small: Poor feeding, easy air entrainment, increased flow resistance, and trapped gas.
• Barrel diameter is too large: Mismatched with required melt volume, leading to long residence time, overheating, and gas generation.
• Unreasonable screw compression ratio: Poor compatibility with raw materials and machine parameters, resulting in weak venting and failure to remove air and vapor effectively.

      3. Corresponding Solutions for Bubble Defects

         (Recommended by Ningbo Konger Machinery After-sales Service)

         Prioritize simple and effective measures, then optimize step by step:

       3.1 Raw Material Handling (First and Most Effective)

• Strictly dry raw materials according to standards and Konger’s guidance: extend drying time and properly increase temperature (avoid material deterioration) to ensure qualified moisture content.
• Use modified materials with lower shrinkage and higher stability to improve compatibility with Konger machines and reduce bubbles caused by uneven shrinkage.
• Control feeding volume reasonably to shorten residence time in the barrel and avoid overheating decomposition, with real-time temperature monitoring via Konger’s barrel control system.

       3.2 Process Parameter Adjustment (Based on Precise Control of Kelonge Machines)

• Increase holding pressure (adjust gradually according to wall thickness and material to avoid deformation) to fully compact melt and compensate for shrinkage gaps.
• Extend holding time, especially for thick-walled products, referring to Konger’s recommended parameters.
• Properly increase injection pressure to accelerate filling and squeeze out air.
• Lower barrel temperature to the suitable range to reduce decomposition and evaporation.
• Optimize back pressure and screw speed: reduce appropriately to minimize air entrainment, with on-site guidance from Konger technicians.

        3.3 Mold Structure Optimization (Matching Kelonge Injection Characteristics)

• Raise mold temperature via Konger’s temperature control system to match melt temperature, slow cooling, and improve venting.
• Enlarge gate size to reduce resistance; relocate the gate to thick-wall areas and avoid thin-wall zones as advised by Konger.
• Clean accumulated material and dead corners; perform regular mold maintenance to prevent gas from decomposed residues.
• Replace with a smaller-diameter barrel to match melt volume and shorten residence time.
• Use a screw with suitable compression ratio to improve venting; contact Konger for screw selection support.

        3.4 Mold and Product Design Modification

• Increase the number and depth of mold vent grooves, or clean blocked vents regularly to ensure smooth air discharge.
• Optimize product design for uniform wall thickness to reduce thickness difference. If structure cannot be revised, adjust Konger machine parameters to compensate for insufficient feeding in thick sections.

      4. After-sales Support from Ningbo Konger Machinery

       If bubble defects persist after following the above instructions, please contact Ningbo Konger Machinery After-sales Service Department.

       We will arrange professional technicians to provide on-site troubleshooting, parameter debugging, and technical guidance based on your Konger machine model, raw materials, and product specifications, fully assisting you in solving production problems and ensuring efficient and stable operation.

      Konger Machinery always focuses on customer needs, relying on professional equipment technology and comprehensive after-sales service to provide customers with full-range injection molding solutions.