Causes of Weld Lines in Molten Plastics During Injection Molding

Author: MULAN - Plastic Molding Manufacturer

During injection molding, linear welds form when molten plastic encounters insertion holes, areas of inconsistent flow rates, and areas where fill flow is interrupted and multiple strands converge in the cavity because it cannot fully fuse. In addition, sprue injection molding will also produce welded joints, and the strength and other properties of the welded joints are very poor. The following injection mold processing manufacturers will share with you the reasons for the weld marks caused by molten plastic during the injection molding process.

1. Processing: 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 weld seams. 2. When the injection pressure and speed are too high, there will be jetting and weld seams. 3. The speed should be increased and the back pressure should be increased to reduce the viscosity of the plastic and increase the density.

4. The plastic should be dry well, and less recycled materials should be used. If the amount of release agent is too much or the quality is not good, weld seams will appear. 5. Reduce the clamping force to facilitate exhaust.

2. Mold: 1. When there are too many gates in the same cavity, the gates should be reduced or set symmetrically, or set as close to the weld as possible. 2. When the weld exhaust is poor, an exhaust system should be installed. 3. The sprue is too large, and the size of the gating system is improper. Set the gate to prevent the melt from moving around the hole of the insert, or use less inserts as much as possible.

4. If the wall thickness changes too much, or the wall thickness is too thin, the wall thickness of the parts should be made uniform. 5. If necessary, the mold injection manufacturer should open a fusion well at the weld to separate the weld from the workpiece. 3. Plastics: 1. For plastics with poor fluidity or poor heat sensitivity, lubricants and stabilizers should be added appropriately.

2. Plastic contains a lot of impurities. If necessary, the injection mold processing factory recommends that you replace it with high-quality plastic.