How to deal with weld lines during injection molding? The main reasons for weld lines are: when molten plastics meet inserts, holes, areas with inconsistent flow rate or areas with interrupted filling material flow in the cavity, multiple strands of melt converge; In case of gate injection mold filling, the material cannot be completely started from --. Next, we will share the specific causes of weld lines and corresponding solutions.
Low temperature molten materials have poor shunt and convergence performance, and are easy to form weld lines. If the internal and external surfaces of the plastic parts have weld lines at the same position, it is often due to poor welding caused by low material temperature. In this regard, the temperature of the barrel and nozzle can be properly increased or the injection cycle can be extended to promote the rise of the material temperature. At the same time, the amount of cooling water passing through the mold should be controlled, and the mold temperature should be properly increased
Generally, the strength at the weld line of plastic parts is poor. If local heating is applied to the corresponding part of the mold where the weld line occurs to increase the local temperature at the weld line of molded parts, the strength at the weld line of plastic parts can often be improved.
If the low-temperature molding process is required due to special needs, the injection speed can be properly increased to increase the injection pressure, so as to improve the fusion performance of the melt. A small amount of intercalary slip agent can also be added to the raw material formula to improve the fluidity of the melt. The structural parameters of the mold gating system have a great impact on the fusion of the molten materials, because the poor fusion is mainly caused by the shunt and convergence of the molten materials. Therefore, try to adopt the gate form with less diversion and reasonably select the gate position to avoid inconsistent filling rate and interruption of filling material flow. If possible, one point gate should be selected, because this gate does not produce multiple streams of material flow, and molten materials will not converge from two directions, which is easy to avoid weld lines.
If there are too many or too small gates in the pouring system of the mold, the multi gate positioning is incorrect or the distance between the gate and the flow fusion is too large, and the flow channel section of the main channel inlet and the shunt channel of the pouring system is too small, the material flow resistance is too large, which will lead to poor start fusion, resulting in obvious weld lines on the surface of the plastic parts. Therefore, the number of gates shall be reduced as far as possible, the gate position shall be set reasonably, the gate section shall be increased, the auxiliary runner shall be set, and the diameter of the main runner and the shunt runner shall be expanded.
The above is an introduction to how to deal with weld lines in the injection molding process. If you want to know more professional knowledge, you can consult professional books!
