The fluidity of plastic has a direct impact on the injection speed of plastic injection machines. Plastics with different flow properties need to be matched with different injection speeds during the injection molding process to ensure smooth mold filling and excellent product quality. The following points illustrate its impact:

1. The impact of highly liquid plastics on injection speed:
Faster injection speeds can be used: plastics with good flowability such as polypropylene (PP) and polystyrene (PS) flow smoothly in the mold and are suitable for medium to high speed injection, which can effectively shorten the molding cycle.
Easy to fill complex mold structures: High fluidity materials can quickly fill thin-walled or fine parts in the mold cavity at high speeds, reducing defects such as short shots.
Excessive speed can easily cause flow marks: Although the fluidity is high, if the injection speed is too fast, the melt may leave obvious flow marks and seam lines in the mold, affecting the surface quality.

2. The impact of low liquidity plastics on injection speed:
Slow or segmented injection speed is required: materials such as polycarbonate (PC), polyamide (PA), and polyoxymethylene (POM) have poor flowability and require higher melting temperatures and injection pressures. The speed should not be too fast to avoid melt flow interruption or pressure accumulation.
Rapid speed can easily lead to short shots or flash edges: Low flow materials may not flow smoothly to the end of the mold cavity during high-speed injection, resulting in incomplete filling of the mold, and are also prone to flash edges due to local high pressure.
Need to cooperate with high temperature and high holding pressure: For materials with poor fluidity, it is often necessary to increase the melt temperature appropriately and extend the holding time appropriately to ensure that the injection speed is effective.

3. Liquidity affects the filling path and speed setting:
When the mold filling path is long or the structure is complex:
High fluidity materials can be quickly filled;
Low liquidity materials need to reduce their speed to avoid rapid cooling or interrupted filling.
Thin walled products or products with rich details:
Usually relies more on high liquidity materials;
At the same time, precise control of injection speed is required to ensure surface and structural integrity.

4. The linkage between temperature and fluidity affects injection speed:
High temperature enhances fluidity, allowing for higher injection speeds;
When the temperature is low, the fluidity decreases, and the injection speed needs to be reduced to prevent incomplete mold filling or material degradation.

5. Different plastics have different tolerance for injection speed windows:
|Material | Liquidity | Recommended Injection Speed Characteristics|
| ------------ | --- | -------------- |
|PP (polypropylene) | High | Can be injected at medium to high speeds, with strong fluidity|
|ABS | Medium | Requires medium speed injection to prevent air streaks and weld marks|
|PC (polycarbonate) | Low | Slow injection, combined with high temperature and high pressure|
|PA (Nylon) | Low | Requires high temperature, stable medium speed injection|
|HDPE (High Density Polyethylene) | High | Can be injected at high speed, but be careful of warping|

6. The relationship between injection speed and material thermal sensitivity:
Plastics with high heat sensitivity (such as PVC): have moderate fluidity, but if the speed is too fast, it will decompose due to local overheating, and the speed needs to be controlled.
Non thermal sensitive materials (such as PE, PP): allow for a wider range of injection speeds and more flexible adaptation.