Raised tubular protrusions on the product at mold vent holes

In the rotational molding production process, the product exhibits the quality defect of "Raised tubular protrusions on the product at mold vent holes".The specific manifestation is Tubular material is extruded at the vent holes.This defect is more common when processing materials such as LLDPE, HDPE, PVC and PA powders, and its occurrence is usually related to unreasonable settings of heating temperature and time, rotation speed ratio, cooling rate and mold wall thickness.When the Raised tubular protrusions on the product at mold vent holes situation is severe, it will cause a series of chain quality defects in the product's appearance, dimensional accuracy, mechanical properties and other aspects, which not only reduces the product's functionality and safety 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 rotational molding machine, heating oven, rotating arm and cooling station, and heating temperature and time, rotation speed ratio, cooling rate and mold wall thickness.

1. Vent holes too large.Mold venting is a basic condition for ensuring smooth melt filling.When venting is poor, the air in the cavity is compressed to form a high-pressure air cushion, hindering melt flow and causing problems such as short shots, burning and weld lines.Reasonable venting design should consider vent positions and vent clearances to ensure air is discharged in time. 2. Excessive internal pressure extrudes the material out.Pressure directly determines the filling capacity of the melt and the mold-contacting effect during the forming process.Insufficient pressure results in incomplete filling and poor replication accuracy; excessive pressure may cause secondary defects such as flash and excessive internal stress.The pressure setting should comprehensively consider factors such as material viscosity, product size and mold structure. In addition, the insufficient overall coordination of 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 Raised tubular protrusions on the product at mold vent holes through chain effects. In terms of equipment maintenance, the regular overhaul and accuracy 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 will also become a potential inducement of the Raised tubular protrusions on the product at mold vent holes problem.

1. Reduce the vent hole size.Adjustments should follow the principle of gradual progress; each adjustment should not be too large, and a decrement of 5%~15% of the current value is recommended.After each adjustment, stably observe the product quality changes for at least 5~10 mold cycles, and continue adjusting only after confirming the improvement direction is correct; never make excessive one-step adjustments. 2. Use sintered metal plugs.Before introducing new tools, new materials or new methods, sufficient applicability evaluation and small-batch verification should be carried out.It is recommended to first conduct offline tests or simulation analyses outside production conditions, and introduce them into the formal production line only after confirming effectiveness and safety.Keep proper change management records to facilitate subsequent traceability and experience accumulation. 3. Optimize the heating process.Optimization work must be based on accurate diagnosis of the root cause of the problem; blind attempts must be avoided.It is recommended to first determine the key influencing factors and their interactions through process DOE test methods 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 testing of work-in-progress should be strengthened, and key performance indicators of LLDPE, HDPE, PVC and PA powders should be strictly controlled to ensure the stability of forming quality from the source.

In summary, the causes of the "Raised tubular protrusions on the product at mold vent holes" problem can be attributed to the combined action of multiple factors such as Vent holes too large, Excessive internal pressure extrudes the material out.To solve this problem, it is necessary to start from aspects such as Reduce the vent hole size, Use sintered metal plugs and take 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 powder melting uniformity and product wall thickness control.