Plastic parts can not be directly put into use after molding and demoulding, and some treatment is needed. Because this treatment is carried out after molding and demoulding, it is called post-processing. It is described as follows:
- Trimming
After demoulding, the plastic parts always have some excess materials, such as gate flying edge, which bring disadvantage to the appearance and use of the plastic parts, so it needs to be removed. This kind of removal is relatively simple, and can be removed by manual operation of some simple tools.
- Heat treatment
1) the purpose of heat treatment
Because of the different cooling speed of physiology in the uneven plasticizing fire cavity in the barrel, the internal stress often occurs in the plastic parts. The existence of this internal stress brings great harm to the
quality of the plastic parts. The common way to eliminate this internal stress is to heat-treat the plastic parts.
2) the mechanism of heat treatment to eliminate internal stress.
The mechanism of heat treatment can eliminate internal stress.
(1) By heating, the forced frozen macromolecular bonds are relaxed and the solidified macromolecular bonds turn to random positions, thus eliminating this part of the internal stress.
(2) Increasing the crystallinity and stabilizing the crystalline structure, so as to improve the physical properties and reduce the internal stress of crystalline plastic products.
(3)heat treatment methods
The plastic parts are placed in a certain temperature liquid medium (water, mineral oil, glycerin, ethylene glycol, etc.) or hot air circulation oven, after a period of heating, then take out slowly cooling to room temperature.
Heat treatment temperature
Generally, the heat treatment temperature should be controlled at 10-20 C higher than the service temperature of the plastic parts or 10-20 C lower than the hot deformation temperature of the plastic parts. Too high temperature will cause warpage or deformation of the plastic parts. The temperature is too low and the internal stress can not be eliminated.
Heat treatment time
The heat treatment time depends on the plastic variety, the shape of the plastic parts and the molding process conditions. Generally, the greater the rigidity of the molecular bond, the thicker the wall is, the longer the heat treatment time is. In order to eliminate the internal stress of plastic
parts.
- Humidity control
1) The purpose of moisture control treatment is to insulate the plastic parts from air, prevent oxidation, speed up moisture absorption balance and make the size stable.
2) the humidity control time depends on the shape, thickness and crystallinity of the plastic parts, usually in a few hours.
3) the temperature of humidity control. Moisture control treatment is to just demoulded plastic parts into hot water treatment, hot water temperature is generally 80-100 degrees Celsius, hot deformation temperature is high value, low value.
In the humidity control process, when the required temperature and time are reached, it must be slowly cooled to room temperature, if the speed is too fast it will produce new internal stress.
- surface printing, electroplating, ultrasonic welding and so on.
Ultrasonic plastic welding is a very frequently used process for post-processing of plastic products.
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