1. What is a bubble?
Air bubbles are formed when air cannot escape from the mold and remains in the finished product. The gas is encased by the forward cold material and cannot be discharged from the mold gap, inlet hole, exhaust hole, etc. The bubble position is usually in the last filled area. The reason for the formation of bubbles is usually that there is no vent hole in the final filling area or the vent hole is not large enough. Another common reason is that the product has rapid changes in the thickness of the product (the thicker areas are filled first).
Second, the cause of the air bubbles in the plastic knife and fork
The gas that has not escaped will form a vacuum or bubbles in the product. If it is short shot (underfilled), the gas that is not discharged will form bubbles in the product or cause stains on the surface of the product due to combustion. In order to remove bubbles, we can improve the filling mode by reducing the injection speed, increasing the exhaust, or setting the exhaust hole in the proper position. The bubbles are due to the excessive ratio of flow length to wall thickness. In this case, it is possible to increase the exhaust gas by changing the thickness ratio or setting an exhaust hole in the bubble formation area (for example, adding a thimble).
Three, plastic knife and fork bubble solution
1. In terms of product design
Change the product design to reduce the thickness ratio. This can minimize the impact of stream length.
2. In terms of mold design
Pay attention to the setting of exhaust holes. Add vent holes in the last full area. Specially set vent holes between parts, such as parting surface, sub-hole, thimble hole, slider.
3. Redesign the runner system
Changing the sprue system can change the filling mode. The method is to make the final post-filling area at the proper exhaust position.
4. The vent hole is large enough to ensure that the gas can escape in time during injection
However, it should be noted that if the vent is too large, burrs will be produced. The recommended vent size is 0.025 mm (0.001 inches) for crystalline plastics and 0.038 mm (0.0015 inches) for non-crystalline plastics.
5. Adjust molding conditions
Reduce the injection speed. High injection speed will cause the formation of bubbles. Reduce the injection speed to allow enough time for the air to escape from the vent.