When melted plastic meets multiple strands in the cavity due to the presence of insert holes, areas where the flow velocity is not continuous, and areas where the filling flow is interrupted, a linear weld seam is generated because it cannot be completely fused. In addition, weld splices can also be generated during gate injection molding, and the strength at the weld joint is poor. The main reasons are as follows:
1. Processing:
(1) injection pressure, speed is too low, cylinder temperature, mold temperature is too low, resulting in molten material entering the mold premature cooling and weld joints.
(2) When the injection pressure or velocity is too high, spray occurs and the weld seam appears.
(3) The rotational speed should be increased, and the pressure of the back pressure should be increased so that the viscosity of the plastic will decrease and the density will increase.
(4) Plastics should be dried well. Recycled materials should be used sparingly. Excessive amount of mold release agent or poor quality can also cause weld seams.
(5) Reduce the clamping force to facilitate exhaust.
2. Mold aspect:
(1) Too many gates in the same cavity should be reduced in gate or symmetrical setting, or set as close to the weld joint as possible.
(2) Exhaust is not good at the weld seam. An exhaust system should be opened.
(3) The runner is too large, the size of the gating system is improper, and the gate opening is designed to avoid the flow of melt around the insert hole, or to minimize the use of inserts.
(4) If the wall thickness changes too much, or if the wall thickness is too thin, the wall thickness of the part shall be uniform.
(5) If necessary, a fusion well should be set up at the weld joint to make the weld joint separate from the workpiece.
3. Plastics:
(1) Lubricants and stabilizers should be properly added to poorly fluid or heat-sensitive plastics.
(2) The plastic contains many impurities. If necessary, replace the plastic with good quality.
1. Processing:
(1) injection pressure, speed is too low, cylinder temperature, mold temperature is too low, resulting in molten material entering the mold premature cooling and weld joints.
(2) When the injection pressure or velocity is too high, spray occurs and the weld seam appears.
(3) The rotational speed should be increased, and the pressure of the back pressure should be increased so that the viscosity of the plastic will decrease and the density will increase.
(4) Plastics should be dried well. Recycled materials should be used sparingly. Excessive amount of mold release agent or poor quality can also cause weld seams.
(5) Reduce the clamping force to facilitate exhaust.
2. Mold aspect:
(1) Too many gates in the same cavity should be reduced in gate or symmetrical setting, or set as close to the weld joint as possible.
(2) Exhaust is not good at the weld seam. An exhaust system should be opened.
(3) The runner is too large, the size of the gating system is improper, and the gate opening is designed to avoid the flow of melt around the insert hole, or to minimize the use of inserts.
(4) If the wall thickness changes too much, or if the wall thickness is too thin, the wall thickness of the part shall be uniform.
(5) If necessary, a fusion well should be set up at the weld joint to make the weld joint separate from the workpiece.
3. Plastics:
(1) Lubricants and stabilizers should be properly added to poorly fluid or heat-sensitive plastics.
(2) The plastic contains many impurities. If necessary, replace the plastic with good quality.
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