Analysis of the causes of swelling, blistering, and shock lines in injection molded products

Some plastic parts quickly appear swelling or blistering on the back of the metal insert or in particularly thick parts after molding and demolding. This is because the plastic that has not been completely cooled and hardened releases gas and expands under the action of the internal pressure penalty.

solution:

1. Effective cooling. Reduce the mold temperature, extend the mold opening time, and reduce the drying and processing temperature of the material.

2. Reduce the filling speed, reduce the forming cycle, and reduce the flow resistance.

3. Increase the holding pressure and time.

4. Improve the situation that the wall surface of the part is too thick or the thickness changes greatly.

Analysis of Causes of Shock Patterns in Injection Molded Products

On the surface near the gate of rigid plastic parts such as PS, dense corrugations are formed with the gate as the center, sometimes called shock lines.

The reason is that when the melt viscosity is too large and the mold is filled in the form of stagnation, the material at the front end will quickly condense and shrink as soon as it touches the surface of the cavity, and the later melt expands and the shrinking cold material continues the process The continuous alternation causes the material flow to form surface vibrations as it advances.

Solution:

(1) Increase the temperature of the barrel, especially the temperature of the nozzle, and also increase the temperature of the mold.

(2) Increase the injection pressure and speed to quickly fill the mold cavity.

(3) Improve the size of runners and gates to prevent excessive resistance.

(4) The mold exhaust should be good, and a sufficiently large cold slug well should be set up.

(5) Do not design the parts to be too thin.