Powder self-ignition after being heated in the mold

In the rotational molding production process, the product exhibits the quality defect of "Powder self-ignition after being heated in the mold".The specific manifestation is The powder catches fire during high-temperature heating.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 Powder self-ignition after being heated in the mold 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. Heating temperature far exceeds the resin decomposition temperature.Temperature is the core factor affecting melt fluidity and viscosity.Excessively high temperature settings will cause decreased melt viscosity, insufficient melt strength and even thermal degradation; excessively low temperature results in poor melt fluidity and insufficient plasticization, making smooth filling or forming impossible.A reasonable temperature window should be optimally determined within the recommended range according to the melting characteristics and thermal stability of the material. 2. Flammable gas accumulates in the mold.The mold is the core tool that gives the product its shape and surface quality.Unreasonable mold design, such as improper runner/gate dimensions, insufficient venting and inadequate draft angle, will directly lead to forming defects.The machining accuracy, surface treatment quality and daily maintenance status of the mold also directly affect product quality. 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 Powder self-ignition after being heated in the mold 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 Powder self-ignition after being heated in the mold problem.

1. Install an over-temperature protection device.Installation of equipment or accessories should strictly follow the installation manual; key mating surfaces must be cleaned and checked for damage before installation.Fastening bolts should be tightened evenly according to the specified torque values and diagonal sequence; after installation, use precision measuring tools to verify whether the installation accuracy meets technical requirements. 2. Regularly clean the mold.Cleaning work should be incorporated into the equipment preventive maintenance plan, and the cleaning frequency should be reasonably determined according to the actual conditions of the processed material and operating cycle.Use dedicated cleaning tools and cleaning materials to avoid scratching or electrolytic corrosion of the cavity surface caused by improper operation.After cleaning, re-check and confirm that the key clearances are accurate. 3. Calibrate the temperature control system.Inspection work should establish a standardized checklist, specifying inspection items, technical standards, inspection frequency and responsible persons.Key equipment components should be regularly disassembled to check the condition of hidden parts, and judgment should not be based solely on operating appearance.Inspection results should be recorded in detail and a trend analysis mechanism established to predict potential failures. 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 "Powder self-ignition after being heated in the mold" problem can be attributed to the combined action of multiple factors such as Heating temperature far exceeds the resin decomposition temperature, Flammable gas accumulates in the mold.To solve this problem, it is necessary to start from aspects such as Install an over-temperature protection device, Regularly clean the mold 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.