Acrylic products generally appear in the processing of injection molding warping, deformation, bubbles, cracks, wrinkles move and Ma face, shrinkage, overflow edge, weld marks, burns, silver lines, jet pattern and other defects. What kind of solution should we adopt when warping?
Cracking is a common plastic defects, the main reason is due to stress and deformation caused by residual stress, external stress and stress caused by the external environment deformation.
Residual stress caused by cracking
Residual stress mainly due to the following three conditions, namely, overfill, release release and metal inserts caused by overfill in the case of cracks, the solution can be mainly in the following aspects:
As the straight sprue pressure loss is minimal, so if the crack occurs mainly in the vicinity of the sprue, you can consider the use of multi-point distribution point gate, side gate and stalk gate way.
Under the premise of ensuring that the resin does not decompose and not deteriorate, appropriately raising the temperature of the resin can reduce the melt viscosity, improve the fluidity, and at the same time, can reduce the injection pressure so as to reduce the stress.
Under normal circumstances, when the mold temperature is lower prone to stress, should be appropriate to increase the temperature, but when the injection speed is high, even if the mold temperature is lower, but also reduce the stress.
Injection and dwell time is too long will produce stress, its appropriate shortening or Th times the packing pressure switching effect is better.
Non-crystalline resins, such as AS resins, ABS resins, and PMMA resins, tend to generate residual stress more easily than crystalline resins such as polyethylene and polyoxymethylene.
Demoulding launch, due to the stripping of small tilt mold die and punch rough, the push out force is too large, resulting in stress, sometimes even in the introduction of bar produce albino or rupture.As long as careful observation of the location of the crack, You can determine the reason.
In injection molding at the same time embedded metal parts, the most prone to stress, but also easy to produce after a period of time cracking, endangering.This is mainly due to the thermal expansion coefficient of metal and resin disparity generate stress, and over time , The stress exceeds the strength of the deteriorated resin material to cause cracks.
In order to prevent the resulting cracking, it has been empirically known that the wall thickness 7 'and the outer diameter of the insert metal-coated polystyrene are substantially unsuitable for the insert and the insert has the least effect on the nylon. Since the glass fiber reinforced The thermal expansion coefficient of the resin material is small, more suitable for embedded parts.In addition, pre-molding the metal insert preheating, but also has good results.
External stress caused by cracking
The external stress here is mainly due to the unreasonable design caused by stress concentration, especially in sharp corners more attention should be taken R / 7 'a 0.5 ~ 0.7.
External environment caused by cracking
Chemicals, water-induced moisture absorption, and excessive use of recycled materials can deteriorate physical properties and cause cracking.