Plastic processing is the general name for various processes that convert synthetic resins or plastics into plastic products. It is a large production department in the plastic industry. Next, let's introduce the precautions for plastic processing and other knowledge.

Precautions for plastic processing

The shrinkage problem in plastic processing is one of the common problems in plastic processing. For plastic products with high surface quality requirements, shrinkage is a thorny problem. With the continuous improvement of plastic processing technology, it is imperative to minimize plastic processing shrinkage and improve product quality.

In the thicker position of injection molded plastic parts, such as ribs and protrusions, the shrinkage is more serious than that in the adjacent position, because the cooling speed of the thicker area is much slower than that of the surrounding area. Different cooling rates will lead to the formation of depressions at the connecting surface, that is, shrinkage marks. This defect will seriously limit the design and molding of plastic products, especially large thick wall products, such as the inclined shell of the TV and the shell of the display. Shrinkage marks must be eliminated for products with strict requirements such as household appliances, while plastic processing shrinkage marks can be allowed for products with low surface quality requirements such as toys.

The reasons for forming shrinkage marks in plastic processing include processing methods, component geometry, material selection, mold design, etc. The geometry and material selection are usually determined by raw materials and are not easy to change. However, there are still many factors about mold design that will affect the shrinkage link of plastic processing. Cooling channel design, gate type, and gate size may have a variety of effects. For example, a small gate such as a tubular gate cools much faster than a tapered gate. Premature cooling at the gate will reduce the filling time in the cavity, thereby increasing the probability of shrinkage marks. For the molding process, adjusting the processing conditions is a direct method to solve the problem of plastic processing shrinkage. Filling pressure and time significantly affect the shrinkage effect. After the part is filled, the excess material continues to fill the cavity to compensate for the shrinkage of the material. The too short filling stage will lead to increased shrinkage and eventually produce more or larger shrinkage marks. This shrinkage solution can not reduce the shrinkage mark to a satisfactory level, but the molding workers can adjust the filling conditions on site to improve the shrinkage mark.

Plastic processing troubleshooting

1. Under note: in plastic processing, the shape of plastic parts is incomplete due to insufficient cavity filling.

2. Overflow and flash: in the process of plastic processing and molding, the surplus material overflows into the gap of the mold closing surface and remains on the plastic part.

3. Fusion mark: a linear mark on the surface of plastic parts, which is the shunt and convergence of several streams of molten materials in the mold during injection or extrusion. The molten materials are not fully fused at the interface, and they cannot be fused, resulting in fusion marks, affecting the appearance quality and mechanical properties of plastic parts.

4. Wave flow mark: due to the improper flow of molten material in the mold cavity, resulting in the uneven defects of the annual ring, spiral, or cloud-shaped waveforms on the surface of plastic parts.

5. Surface turbidity: refers to cracks with voids on the surface of plastic parts and the resulting damage. The phenomenon that cracks occur outside or inside 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 complete a complete rupture due to the constant load for a certain time at a specific temperature is called stress rupture; Thermal stress cracking refers to cracks and cracks that occur when some thermoplastic parts are overexposed to higher temperatures.

6. Fracturing: refers to the obvious cracks in one or more layers of reinforcement material outside the laminated plastic that can be seen through the resin layer covered on the surface.

7. Wrinkle: a defect that causes cracks and obvious separation on the surface of laminated plastic.

8. Wrinkle: the appearance defect of creases or wrinkles on one or more layers of the surface of plastic parts during plastic processing.

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

10. Silver grain: needle-like silvery white frost-like fine lines produced on the surface of plastic parts along the direction of material flow.

11. Stripes: linear stripe defects on the surface or inside of plastic parts.

12. Speckles: dark spots of mica flakes on the surface of plastic parts due to dispersion or poor mixing of pigments and other reasons.

13. Orange peel: the uneven appearance defect like orange peel on the surface of plastic parts.

14. Bubble stripe: refers to the bubble layer in foamed plastics that is very different from its inherent bubble structure.

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

16. White spots or bright spots: there are no fully plasticized particles in transparent or translucent plastic films, sheets, or plastic parts. When light is transmitted, white particles can be seen. This kind of particle is called "fish eyes". If the material is opaque or colored, such particles are called white dots or bright spots.

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

18. Filler spots: obvious spots caused by the presence of fillers such as wood powder or asbestos in plastic parts.

19. Dark spot: dark stain appearing in the laminate structure based on fabric.

20. Scorch and paste spots: in the process of plastic processing, under the conditions of high temperature and high-pressure molding, the molten material is carbonized due to overheating decomposition, and the carbonized coke is mixed in the molten material, forming a defect of spots on the surface and inside of the plastic part.

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 completely discharged, the defects of a small volume or series of pores will be formed inside the plastic part after molding.

22. Vacuum bubble or dark bubble: when plastic parts are cooled and solidified during plastic processing, due to the different cooling rates inside and outside, sometimes the outer surface has been cooled and solidified, but the interior is still in a hot-melt state. Once the central part is cooled and contracted, vacuum holes will be generated inside the plastic parts. These holes are generally called vacuum bubbles or dark bubbles, also known as shrinkage holes.

23. Pinhole: pinhole size through-hole defect in plastic sheet or film.

24. Deflated foam: the defect of local density increase caused by the destruction of cellular structure in the manufacturing process of foamed plastics.

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