Removal of internal stresses by annealing

Plastic molded parts may undergo significant deformation or develop cracks in certain areas due to internal stresses. In such cases, these stresses are removed through annealing.

The method involves placing the moulded part on a conveyor or trolley and passing it through a high-temperature furnace (40°C to 120°C). When only stress in a specific part of the moulded part needs to be removed, instead of heating the entire part, a method exists where far-infrared radiation or similar is applied directly to the stress-generating area for treatment.

Figure 1 below shows the distortion removal effect of annealing in a cross-flow fan.

(Note) Causes of distortion in moulded parts and the effect of annealing

　(1) Distortion arising from molecular orientation, caused by the moulded part's shape, cannot be removed by annealing.

(2) Thermal distortion occurring during cooling and mechanical distortion caused by machining can be removed by annealing.

(3) Distortion arising from bolting, interlocking, or crimping can be somewhat alleviated by annealing, but there is a risk of weakening the resin's bonding strength.

Figure 1. Effect of annealing on distortion removal relative to the imbalance quantity of a cross-flow fan