Abnormal pressure in the inner cavity of double-wall products causes deformation

During the rotational molding production process, the product exhibits the quality defect of 「Abnormal pressure in the inner cavity of double-wall products causes deformation」. The specific manifestation is that pressure changes in the inner cavity of double-wall products cause wall deformation. This defect is relatively common when processing materials such as powders such as LLDPE, HDPE, PVC, PA, and its occurrence conditions are usually related to unreasonable settings of heating temperature and time, rotation speed ratio, cooling rate, mold wall thickness. When the Abnormal pressure in the inner cavity of double-wall products causes deformation situation is severe, it causes a series of cascading quality defects in the product in terms of appearance, dimensional accuracy, mechanical properties, and other aspects, not only reducing the product's functionality and safety in use, but also directly increasing the scrap rate and production costs. Therefore, this problem requires systematic diagnosis and optimization from multiple dimensions, including material selection, rotational molding machine, heating oven, rotating arm, cooling station condition, and heating temperature and time, rotation speed ratio, cooling rate, mold wall thickness.

1. Vent hole blockage. Mold venting is a basic condition for ensuring smooth melt filling. When venting is poor, air in the mold cavity is compressed to form a high-pressure air cushion, hindering melt flow and causing problems such as insufficient filling, burning, and weld lines. A reasonable venting design should consider vent positions and vent gaps to ensure air is discharged in time. 2. Gas in the inner cavity shrinks during cooling, generating negative pressure. Cooling conditions determine the shaping process and final internal structure of the product. Uneven cooling causes shrinkage differences and residual stress, leading to warpage and dimensional deviation; insufficient cooling makes the product not rigid enough during demolding; excessively rapid cooling generates large internal stress. The cooling system design should ensure uniform and efficient heat dissipation in all parts. In addition, the insufficient overall coordination between powder melting uniformity and product wall thickness 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 parameter may aggravate the degree of Abnormal pressure in the inner cavity of double-wall products causes deformation through chain effects. In terms of equipment maintenance, the regular overhaul and precision confirmation of the rotational molding machine, heating oven, rotating arm, and cooling station are not in place, causing the actual operating parameters of the equipment to deviate from process requirements, which can also become a potential inducement of the Abnormal pressure in the inner cavity of double-wall products causes deformation problem.

1. Ensure the vent holes are unobstructed. Before implementing this measure, fully evaluate its feasibility and expected effect, communicate with relevant technical personnel to confirm the details of the plan, closely monitor changes in key quality indicators during implementation, record and feedback the adjustment effect in time, and form reusable process experience. 2. Control the cooling speed. The key to process parameter control lies in establishing a reliable closed-loop feedback adjustment mechanism. Through online real-time detection and SPC statistical process monitoring, deviation trends are discovered in time, and automatic control systems or manual intervention are used to maintain key parameters within the set window, achieving a fundamental shift from post-event remediation to pre-event prevention. 3. Supplement inert gas if necessary. Before implementing this measure, fully evaluate its feasibility and expected effect, communicate with relevant technical personnel to confirm the details of the plan, closely monitor changes in key quality indicators during implementation, record and feedback the adjustment effect in time, and form reusable process experience. 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 powders such as LLDPE, HDPE, PVC, PA should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the 「Abnormal pressure in the inner cavity of double-wall products causes deformation」 problem can be attributed to the combined action of multiple factors such as vent hole blockage and gas in the inner cavity shrinking during cooling to generate negative pressure. Solving this problem requires starting from aspects such as ensuring the vent holes are unobstructed and controlling the cooling speed, 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 powder melting uniformity and product wall thickness control.