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What to do if weld marks appear during injection molding?

TIME:2020-12-24 Share

The main reason for the weld marks in the injection molding process is: when the molten plastic encounters inserts, holes, areas with inconsistent flow rates or areas where the filling flow is interrupted in the cavity of the injection molding machine, the convergence of multiple melts occurs; When the gate is injected into the mold, the materials cannot be completely together. Below, we will share with you the specific causes of weld marks and corresponding solutions.

The shunting and confluence performance of low-temperature melts is poor, and it is easy to form weld marks. If the inner and outer surfaces of the plastic part produce welding fine lines at the same location, it is often due to poor welding caused by too low material temperature. In this regard, the temperature of the barrel and nozzle can be appropriately increased or the injection cycle can be extended to promote the increase of the material temperature. At the same time, the flow of cooling water in the mold should be controlled, and the mold temperature should be appropriately increased.

Injection Molding Machine
Under normal circumstances, the strength of the weld line of the plastic part is poor. If the corresponding part of the injection molding machine mold is locally heated to increase the local temperature of the welded part of the molded part, the strength of the welded part of the plastic part can often be improved.

If low-temperature molding process is required due to special needs, the injection speed can be appropriately increased to increase the injection pressure, so as to improve the melting performance. A small amount of lubricant can also be appropriately added to the raw material formulation to improve the flow properties of the melt. The structural parameters of the injection molding machine mold gating system have a great influence on the welding condition of the flow material, because the poor welding is mainly caused by the splitting and confluence of the melt. Therefore, it is necessary to adopt the gate type with less shunt as much as possible and choose the gate position reasonably to avoid inconsistent filling rate and interruption of filling flow. If possible, a one-point gate should be used, because this gate does not produce multiple streams, the melt will not merge in two directions, and it is easy to avoid welding marks.

If there are too many or too small gates in the gating system of the injection molding machine, the positioning of multiple gates is incorrect or the distance between the gate and the flow material fusion is too large, the inlet part of the main runner of the gating system and the runner section of the branch runner Too small, resulting in too much material flow resistance will cause poor welding, resulting in more obvious welding marks on the surface of the plastic part. In this regard, the number of gates should be reduced as much as possible, the gate position should be set reasonably, the gate cross section should be enlarged, the auxiliary runner should be set, and the main runner and branch runner diameter should be enlarged.

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