Water marks in the sheet (bubbles)

In the '2079851475616104458 (vacuum forming) production process, the product exhibits the quality defect of "Water marks in the sheet (bubbles)". The specific manifestation is that water marks or bubbles appear inside the sheet. This defect is relatively common when processing materials such as PP, PS, PET, PVC, ABS sheets, and its occurrence conditions are usually related to the unreasonable settings of sheet heating temperature, forming pressure/vacuum level, mold temperature, and cooling time. When the "Water marks in the sheet (bubbles)" situation is severe, it will cause a series of chain quality defects in the product in terms of appearance, dimensional accuracy, mechanical properties, etc., which not only reduces the functionality and safety of the product in use, but also directly increases the scrap rate and production cost. Therefore, this problem requires systematic diagnosis and optimization from multiple dimensions such as material selection, the status of the '2079851475616104458 machine, heating oven, mold, and vacuum/air pressure system, and sheet heating temperature, forming pressure/vacuum level, mold temperature, and cooling time.

1. Moisture content of the sheet too high during sheet production. Moisture is one of the variables that need to be focused on and controlled in plastic processing. Moisture in hygroscopic resins evaporates rapidly during high-temperature melting, producing bubbles and silver streaks, and also triggers hydrolysis reactions leading to molecular weight reduction. Adequate drying treatment and strict anti-moisture-regain management are the basic prerequisites for ensuring melt quality. 2. Poor venting during sheet extrusion. Mold venting is a basic condition for ensuring smooth filling of the melt. When venting is poor, the air in the mold cavity is compressed to form a high-pressure air cushion, which hinders melt flow and causes problems such as insufficient filling, burning, and weld lines. A reasonable venting design should consider the venting positions and venting gaps to ensure that air is discharged in time. In addition, the insufficient overall coordination of sheet heating uniformity and stretch ratio control is also a factor that cannot be ignored; there are complex interactions and coupling relationships among the process parameters, and the deviation of any one parameter may aggravate the degree of "Water marks in the sheet (bubbles)" through chain effects. In terms of equipment maintenance, the regular overhaul and precision confirmation of the '2079851475616104458 machine, heating oven, mold, and vacuum/air pressure system are not in place, causing the actual operating parameters of the equipment to deviate from the process requirements, which will also become a potential inducement of the "Water marks in the sheet (bubbles)" problem.

1. Use qualified sheets. Before introducing new tools, new materials, or new methods, a full applicability assessment and small-batch verification should be carried out. It is recommended to first conduct offline tests or simulation analysis outside production conditions, and introduce them into the formal production line only after confirming effectiveness and safety. Keep change management records to facilitate subsequent traceability and experience accumulation. 2. Check the sheet supplier quality. Inspection work should establish a standardized inspection checklist, clarifying inspection items, technical standards, inspection frequency, and responsible persons. Key equipment components should be regularly disassembled to check the status of hidden parts, and judgments should not be made solely based on operating appearance. Inspection results should be recorded in detail and a trend analysis mechanism should be established to predict potential failures. It is recommended to formulate a preventive checklist for the "Water marks in the sheet (bubbles)" problem, incorporate sheet heating uniformity and stretch ratio control into the daily inspection scope, and conduct online monitoring of key parameters through the SPC statistical process control method to achieve early warning and rapid response to the problem. In terms of material management, incoming inspection of raw materials upon arrival and in-process inspection of work-in-progress should be strengthened, and the key performance indicators of PP, PS, PET, PVC, ABS sheets should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the "Water marks in the sheet (bubbles)" problem can be attributed to the combined action of multiple factors such as Moisture content of the sheet too high during sheet production, Poor venting during sheet extrusion. Solving this problem requires starting from aspects such as Use qualified sheets, Check the sheet supplier quality and adopting systematic governance measures. In actual production, it is recommended to establish a prevention and rapid response mechanism for this problem, and achieve stable production and continuous improvement through sheet heating uniformity and stretch ratio control.