Plastic annealing and Moisture conditioning process for plastic product

Plastic annealing process

Plastic annealing process

The purpose of plastic annealing is to eliminate internal stress. For example, in the area where the thin and thick parts meet, the cooling of the thick part is slower than that of the thin part, causing the joint to shrink unevenly. As a result, there is stress concentration in the area. This phenomenon is more obvious around metal inserts. If annealing is not performed, cracking or even deformation may occur in the stress concentration area after a period of time. Annealing method: Usually, the product is immersed in hot oil, hot water, or cycling hot air. The annealing temperature is adjusted according to the type of the plastic, but usually, it is 10-20°C lower than the product’s thermal deformation temperature, or the product will deform. However, the temperature should not be too low either, or the desired effect will not be achieved.

Annealing conditions for several common plastics are shown in the table below:

Plastic Agent Temperature (°C) Product Thickness (mm) Time
Nylon Oil 130 12 15
ABS   80-100   16-20
PC Air 125-130 1 30-40
PE Water 100 >6 60
PP Air 150 <6 15-30
PS Air or Water 60-70 <6 30-60
PSU Air or Water 160 <6 60-180

Moisture Conditioning of Plastic Products

Moisture conditioning of plastic products is mainly for polyamide (nylon) products. After storage for a period of time, products made from this raw material will deform and expand due to absorption of moisture in the air, thus resulting in size change. Therefore, after a nylon product is molded, it should first be immersed in 100-120°C water or potassium acetate solution, to keep it isolated from the air. The immersion time is determined according to the wall thickness and the shape of the product. Then, take the product out after the temperature is slowly lowered to the room temperature.