Reasons for welding marks of products during injection molding
In the process of injection molding, when the molten plastic meets in the form of multiple strands in the mold cavity due to the holes in the insert, the areas with discontinuous flow rate and the areas with interrupted flow of the filling material, the linear fusion seam is generated due to incomplete fusion. In addition, the main channel injection molding will also produce fusion joints, which have poor strength. The main reasons are as follows:
1. Treatment:
(1) The injection pressure and speed are too low, the barrel temperature and mold temperature are too low, resulting in premature cooling of the molten material entering the mold and the appearance of fusion seams.
(2) When the injection pressure and speed are too high, injection and fusion joints will occur.
(3) The rotational speed and back pressure should be increased to reduce the viscosity and increase the density of plastics.
(4) The plastic should be dry well, and the recycled material should be used less. Too much release agent or poor quality will lead to fusion joints.
(5) Reduce clamping force and facilitate exhaust.
2. Mold:
(1) If there are too many gates in the same cavity, they should be set symmetrically or as close to the fusion joint as possible.
(2) For poor exhaust at the fusion joint, an exhaust system shall be set.
(3) If the runner is too large and the size of the gating system is inappropriate, the opening of the gate should try to avoid the melt flowing around the insert hole, or use the insert as little as possible.
(4) If the wall thickness changes too much or too thin, the wall thickness of the part should be uniform.
(5) If necessary, open the fusion well at the fusion joint to separate the fusion joint from the part.
3. Plastic:
(1) Lubricants and stabilizers should be properly added to plastics with poor fluidity or heat sensitivity.
(2) Plastics contain many impurities. If necessary, replace it with high-quality plastic.
