Analysis Of The Causes Of Welded Joints In Plastic Products

The molten plastic in the cavity meets in the form of multiple strands due to the intrusion of the insert holes, the discontinuous flow rate, and the region where the filling flow is interrupted, and a linear weld seam is produced because it cannot be completely fused. In addition, in the case of gate injection molding, a welded joint is formed, and the strength at the welded joint is poor. The main reasons are as follows:

1.Processing aspect

(1) The injection pressure and speed are too low, and the temperature of the barrel and the mold temperature are too low, so that the melt entering the mold is cooled prematurely and a weld seam occurs.

(2) When the injection pressure and speed are too high, a spray will occur and a weld seam will appear.

(3) The rotation speed should be increased, and the back pressure should be increased to decrease the viscosity of the plastic and increase the density.

(4) The plastic should be dried well, and the recycled material should be used less. If the amount of the release agent is too much or the quality is not good, the welded joint will appear.

(5) Reduce the clamping force and facilitate the exhaust.

2. Mold aspect

(1) If there are too many gates in the same cavity, the gate or symmetrical setting should be reduced, or as close as possible to the fusion joint.

(2) Exhaust system should be opened if the exhaust at the weld joint is poor.

(3) If the sprue is too large and the pouring system is not properly sized, the gate is opened to avoid the flow of the melt around the insert hole, or the insert is used as little as possible.

(4) If the wall thickness changes too much, or the wall thickness is too thin, the wall thickness of the part should be uniform.

(5) If necessary, a fusion well shall be opened at the weld seam to disengage the weld joint from the workpiece.

3. Plastics

(1) Lubricants and stabilizers should be added to plastics with poor fluidity or heat sensitivity.

(2) Plastics contain a lot of impurities, and if necessary, change the quality of the plastic.

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