Analysis of weld mark of plastic products
In the cavity of the molten plastic, the linear weld joint is produced because of the inflow of holes, incoherent flow area, and the interruption of the filling material flow in a multi strand form. In addition, there will be a weld seam when the gate jet is filled, and the strength of the weld joint is very poor. The main reasons are as follows:
1. aspects of processing:
(1) the injection pressure and speed are too low, the barrel temperature and the mold temperature are too low, resulting in premature cooling of the melt entering the mold and the weld seam.
(2) when the injection pressure and speed are too high, there will be spray and weld seam.
(3) speed should be increased and back pressure should be increased to reduce viscosity and increase density.
(4) plastic should be dried well, and recycled materials should be used less. If the amount of release agent is too much or the quality is not good, there will be a fusion seam.
(5) reduce the clamping force and facilitate the exhaust.
2. aspects of mold:
(1) if the gate of the same type is too large, gate or symmetrical setting should be reduced, or as close to the weld seam as possible.
(2) exhaust joints at the weld seam are poor, and exhaust system should be set up.
(3) if the runner is too large and the size of the gating system is not proper, the gate should be opened to avoid the flow of the melt around the cavity, or to minimize the use of inserts.
(4) the wall thickness is too large or the wall thickness is too thin, so the wall thickness of the parts should be uniform.
(5) if necessary, a fusion well should be opened at the weld seam to separate the weld seam from the workpiece.
3. plastic aspects:
(1) suitable lubricants and stabilizers should be added to plastics with poor fluidity or heat sensitivity.
(2) plastic contains many impurities, and when necessary, it should be replaced with good quality plastic.