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Phenomena in injection molding process

Release time:2022-03-07

The key link of injection molding is to make various forms of plastic into products or blanks with required shapes. There are more than 30 injection molding methods. Its choice mainly depends on the type of plastic, the initial shape, and the shape and size of the product. Today, the injection molding factory introduces 25 phenomena in the injection molding process:

1. Insufficient injection molding: in plastic processing, the appearance of plastic parts is incomplete due to insufficient cavity filling.

2. Overflow: excess material that overflows into the gap between the clamping surfaces of the mold and remains on the plastic parts in the process of plastic processing and molding.

3. Weld marks: linear marks on the surface of plastic parts, which are formed by the shunting and confluence of several streams in the desert during the injection or extrusion process. The melt does not melt completely at the interface and cannot fuse together, resulting in fusion marks, which will affect the appearance quality and mechanical properties of plastic parts.

4. Wave flow mark: improper melt flow in the mold cavity leads to uneven ring, spiral or cloud shaped waveforms and other defects on the surface of plastic parts.

5. Surface turbidity: refers to cracks and damage caused by cracks on the surface of plastic parts. The phenomenon of cracks on the outside or inside of plastic parts due to long-term or repeated application of stresses lower than the mechanical properties of plastic is called stress cracking. The phenomenon that plastic parts suddenly and completely break due to dead load at a certain temperature is called stress fracture. Cracks and fractures caused by overexposure of some thermoplastic parts at high temperature are called thermal stress cracks.

6. Fracturing: it refers to that through the resin layer covering the surface, one or more layers of reinforcing materials outside the laminated plastic can be seen to have obvious cracks.

7. Wrinkling: surface cracks and obvious separation defects of laminated plastics.

8. Wrinkle: in the process of plastic processing, one or more layers of plastic parts have wrinkles or wrinkled appearance defects.

9. Cracking and whitening: obvious micro cracks on the surface of plastic parts are called cracks, and frost like micro cracks similar to cracks are called whitening. Cracks and albinism are microcracks without cracks. When plastic parts are exposed to certain chemical environment or stress conditions, environmental stress cracking will occur.

10. Silver thread: needle like silver white frost like fine lines on the surface of plastic parts along the direction of material flow.

11. Stripe: linear stripe defect on the surface or inside of plastic parts.

12. Spots: due to poor dispersion or mixing of pigments, there are mica flake like black spots on the surface of plastic parts.

13. Orange peel: surface appearance defects of plastic parts similar to orange peel.

14. Bubble stripe: refers to the bubble layer in foam that is completely different from its inherent bubble structure.

15. Black spots: in the process of plastic processing and molding, the melt is overheated and decomposed under high temperature and pressure, resulting in black carbonization spots on the surface of plastic parts.

16. White spots or bright spots: transparent or translucent plastic films, sheets or plastic parts contain particles with insufficient plasticization, and white spots can be seen when light is transmitted, which is called "fish eyes". If the material is opaque or colored, these spots are called white spots or bright spots.

17. Pitting: regular or irregular pits on the surface of plastic parts, usually with the same depth and width.

18. Filling point: obvious spots on plastic parts when there are wood powder or asbestos and other filling materials.

19. Dark spots: dark spots that appear in the fabric base pressing structure.

20. Scorch and spots: during plastic processing, under the conditions of high temperature and high pressure molding, the melt is carbonized due to overheating decomposition, and the carbonized coke is mixed into the melt, resulting in spotted defects on the surface and inside of plastic parts.

21. Bubbles: in the process of plastic processing and filling, if a large amount of gas remains in the melt or the air in the mold cavity is not all discharged, the defects of small volume or a series of pores will be formed in the molded plastic parts.

22. Vacuum bubble or dark bubble: when plastic parts are cooled and solidified during plastic processing, sometimes the outer surface has been cooled and solidified, but the interior is still in a hot-melt state. Once the central part cools and shrinks, vacuum holes will be generated inside the plastic parts, commonly known as vacuum bubbles or dark bubbles, also known as shrinkage holes.

23. Pinhole: there is a pinhole size through hole defect on the plastic sheet or film.

24. Bubble collapse: in the manufacturing process of foamed plastics, the defect of local density increase due to the destruction of bubble structure.

25. Depression and shrinkage: during the cooling process of plastic processing, the surface layer is cooled and solidified first, and the internal or wall thickness part is cooled and solidified later, so that the internal and external shrinkage speed is inconsistent during volume shrinkage, and the surface layer of plastic parts is stretched inward to form depression, resulting in shallow pits or pits.

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