Surface weld line (pinch-off seam)

During the extrusion '2079851475616104457 production process, the product exhibits the quality defect of "Surface weld line (pinch-off seam)". Specifically manifested as obvious weld lines or pinch-off marks appearing at the mold closing area at the bottom of the product. This defect is relatively common when processing materials such as HDPE, PP, PVC, and PC, and its occurrence conditions are usually related to unreasonable settings of melt temperature, extrusion speed, blowing air pressure, and mold temperature. When the Surface weld line (pinch-off seam) situation is severe, it will cause a series of chain-reaction quality defects in the product in terms of appearance, dimensional accuracy, mechanical properties, etc., which not only reduces the usability and safety of the product, but also directly increases the scrap rate and production cost. Therefore, this problem requires systematic diagnosis and optimization from multiple dimensions, including material selection, the condition of the extruder, die head, die, mold clamping mechanism, and blowing system, as well as melt temperature, extrusion speed, blowing air pressure, and mold temperature.

1. Uneven mold parting surface. The mold is the core tool that imparts shape and surface quality to the product. Unreasonable mold design, such as improper runner/gate dimensions, insufficient venting, inadequate draft angle, etc., will directly cause molding defects. The machining accuracy, surface treatment quality, and daily maintenance condition of the mold also directly affect product quality. 2. Improper flash groove design. Unreasonable structural design or process layout is often the systemic root of the problem. Runner design defects causing uneven flow, unreasonable cooling water channel layout causing temperature differences, insufficient venting structures causing air entrapment, etc., are all fundamental problems that need to be solved with emphasis during the design and development stage. 3. Insufficient melt reflow after the parison is pinched. This factor leading to the problem reflects that certain process conditions or material properties in extrusion blow '2079851475616104453ing have not met the optimal molding requirements. Such problems often have cumulative and hidden characteristics, and should be investigated and verified as key focus items during process debugging and finalization to ensure that hidden dangers are eliminated from the source. In terms of equipment maintenance, inadequate regular overhaul and accuracy confirmation of the extruder, die head, die, mold clamping mechanism, and blowing system cause the actual operating parameters of the equipment to deviate from the process requirements, which can also become a potential inducement of the Surface weld line (pinch-off seam) problem.

1. Repair and finish the mold parting surface. The polishing operation should proceed step by step from coarse to fine; each time a finer abrasive is used, the polishing direction should be changed to eliminate the texture marks of the previous step. The final surface roughness should be tested with a roughness meter to confirm that it meets the standard. After polishing is completed, it should be thoroughly cleaned to remove residues of abrasives and grinding agents to prevent them from entering the melt and contaminating the product. 2. Optimize the flash groove dimensions. Optimization work must be based on an accurate diagnosis of the root cause of the problem, and blind attempts must be avoided. It is recommended to first determine the key influencing factors and their interactions through the process DOE test method or historical production data analysis, and then carry out targeted parameter optimization and structural improvement to achieve twice the result with half the effort. 3. Adjust the pinch-off design. Optimization work must be based on an accurate diagnosis of the root cause of the problem, and blind attempts must be avoided. It is recommended to first determine the key influencing factors and their interactions through the process DOE test method or historical production data analysis, and then carry out targeted parameter optimization and structural improvement to achieve twice the result with half the effort. In terms of material management, incoming inspection of raw materials and in-process inspection of work-in-progress should be strengthened, and the key performance indicators of HDPE, PP, PVC, and PC should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the "Surface weld line (pinch-off seam)" problem can be attributed to the combined action of multiple factors such as uneven mold parting surface and improper flash groove design. Solving this problem requires starting from aspects such as repair and finish the mold parting surface and optimize the flash groove dimensions, and adopting systematic governance measures. In actual production, it is recommended to establish a prevention and rapid response mechanism for this problem, achieving stable production and continuous improvement through parison wall thickness control and parison temperature uniformity.