14 undesirable phenomena in nylon injection molding process and corresponding solutions

Time：2024-12-11 08:25:13 / Popularity： / Source：

Nylon plastic products are precise in size, suitable for mass production and molding processing fields such as complex-shaped products.
Injection molding process is simple and easy to operate, but there are also many problems caused by manual operation, injection molding equipment, raw materials and other factors.
How should we solve some undesirable phenomena that are easy to occur in nylon injection molding process?
Following are 14 undesirable phenomena that are easy to occur and their corresponding solutions.

1. Nylon plastic products are not fully injected

Cause analysis:

Solution:

1. Low mold temperature
2. Injection feed barrel temperature is too low
3. Insufficient feed volume
4. Mass of nylon plastic products exceeds maximum injection volume of injection molding machine
5. Injection pressure is too small and injection speed is relatively slow
6. Nozzle temperature is low and material condenses at outlet (dry tip)
7. Plunger or screw returns too early and injection time is insufficient
8. Gate is too small, too thin or too long
9. Mold has no vent or is improperly positioned, etc.

1. Increase feed barrel temperature
2. Reduce mold cooling water and increase mold temperature
3. Increase feed volume
4. Choose equipment suitable for injection volume of nylon plastic products
5. Appropriately increase injection pressure
6. Increase nozzle temperature
7. Ensure appropriate injection time and pressure holding time
8. Increase mold gate
9. Mold needs to be reasonably designed with an exhaust device

2. Overflow or flash

Cause analysis:	Solution:
1. Too high injection pressure 2. Wear of clamping mechanism, too low clamping force 3. Too high material temperature 4. Uneven contact surface of mold, wear and deformation of mold 5. Foreign matter falls into mold contact surface	1. Reduce injection pressure 2. Repair equipment, increase clamping force 3. Reduce feed barrel temperature 4. Repair mold 5. Clean foreign matter in mold in time

3. Dents (collapse caused by large shrinkage rate)

Cause analysis:	Solution:
1. Gate and channel are too small 2. Material temperature is too high 3. Mold temperature is too high 4. Insufficient feed amount 5. Insufficient injection and holding time 6. Injection molded nylon products are too thick or have a large thickness difference	1. Enlarge gate 2. Reduce feed barrel temperature 3. Effectively cool mold 4. Adjust feed amount 5. Extend holding time 6. Reasonably design mold, wall thickness should be as uniform as possible

4. There are welding marks (combination lines)

Cause analysis:	Solution:
1. Material temperature is too low 2. Injection pressure is too low, injection speed is too slow 3. Mold temperature is too low 4. There are too many gates 5. Nylon plastic products have uneven wall thickness 6. More release agent is used 7. Poor cavity venting	1. Increase temperature of feed barrel 2. Increase injection pressure and speed 3. Increase mold temperature 4. Appropriately reduce number of gates 5. Improve mold manufacturing accuracy 6. Reduce amount of release agent 7. Enhance venting

5. Nylon plastic products have ripples on the surface

Cause analysis:	Solution:
1. Material temperature is too low, resin viscosity is high, and fluidity is poor 2. Injection pressure is low and speed is too slow 3. Mold temperature is low 4. Mold gate is too small	1. Increase temperature of feed barrel 2. Increase injection pressure 3. Increase mold temperature 4. Increase gate

6. There are bubbles and vacuum bubbles

Cause analysis:	Solution:
1. Raw material contains water, solvents or other volatiles 2. Material temperature is too high and heating time is long 3. Injection pressure is too small 4. Nylon plastic product is too thick, cooling speed inside and outside is different, and vacuum bubbles are generated inside. 5. Mold temperature is too low. 6. Injection time is too short.	1. Dry raw material before molding 2. Reduce temperature of feed barrel 3. Increase injection pressure 4. Increase size of runner and gate 5. Appropriately increase mold temperature 6. Extend injection time

7. There are black spots and stripes

Cause analysis:	Solution:
1. Black spots appear when plastic decomposes 2. Mold has no vent or vent position is improper 3. Gap between plunger and feed barrel is too large, pellets are heated in the gap for too long, decompose and turn black, or black spots appear due to wear of screw caused by hard particles.	1. Reasonably control process temperature to avoid overheating and decomposition of plastic 2. Reasonably open vents 3. Timely repair machine and increase cooling of cylinder

8. There are silver threads and streaks

Cause analysis:	Solution:
1. Product of material decomposition enters mold cavity, resulting in streaks 2. Moisture content in raw material is too high, and water vapor is mixed in material to produce silver threads 3. Raw material contains volatile substances	1. Lower temperature of feed barrel 2. Preheat and dry raw material before use 3. Dry and preheat raw material before

9. Discoloration

Cause analysis:	Solution:
1. Material temperature is too high, color decomposes and causes discoloration 2. Plastic stays in feed barrel for too long and decomposes due to heat. 3. Too much lubricant is applied	1. Choose high temperature resistant color powder 2. Reduce residence time of material in feed barrel 3. Reduce amount of lubricant

10. Deformation and warping

Cause analysis:	Solution:
1. Cooling time is short and nylon plastic products are not completely fixed 2. Thickness of nylon plastic products is uneven, and shrinkage is uneven during cooling 3. Inject twice, injection pressure is too high 4. Ejector of nylon plastic products is improperly positioned, and force is uneven when ejecting 5. Material temperature is low or plasticizing temperature is uneven	1. Extend cooling time or reduce mold temperature 2. Design of nylon plastic products should be reasonable 3. Reduce second injection pressure and shorten holding time 4. Reasonably arrange ejector position 5. Increase feed barrel temperature

11. Cracks appear in nylon plastic products

Cause analysis:	Solution:
1. Mold is too cold 2. Nylon plastic product cools down in mold for too long, plastic and metal inserts shrink differently 3. Ejector device of nylon plastic products is tilted or unbalanced 4. Cross-sectional area of ejector rod is too small or number is too small, and distribution is improper 5. Slope of nylon plastic products is not enough, and demolding is difficult	1. Increase mold temperature 2. Appropriately reduce cooling time, or preheat metal insert 3. Adjust ejection position 4. Correctly design ejection position 5. Nylon plastic products are designed reasonably and should have a certain slope

12. Sticking to mold (difficult demoulding)

Cause analysis:

Solution:

1. Surface finish of mold cavity is not smooth enough
2. Mold slope is not enough (especially for nylon plastic products with deeper shapes)
3. Injection pressure is high, and material enters gap on the edge of mold insert
4. Mold temperature and cooling time are not appropriate
5. Mold is worn and scratched, causing nylon plastic product to flash and difficult to demould
6. Improper mold venting
7. Raw material itself sticks to mold

1. Improve finish of mold cavity, preferably chrome plating on the surface
2. Increase inclination of mold
3. Repair mold
4. When core surface is difficult to demould, mold temperature can be increased and cooling time can be shortened. When center of cavity is difficult to demould, mold temperature can be lowered and cooling time can be increased.
5. Repair mold
6. Add mold exhaust structure
7. Add internal and external lubricants

13. Peeling and stratification

Cause analysis:	Solution:
1. Raw material contains a mixture of different plastics with poor compatibility 2. Impurities are mixed in material 3. Flow of raw materials is different, and melt index is quite different	1. Improve performance of raw materials by adding compatibilizers 2. Carefully check feed barrel and feed port before injection to keep these parts clean 3. Try to make melt index of the materials close

14. Decreased brittle strength

Cause Analysis:	Solution:
1. Material temperature is too high, material is heated for too long, plastic decomposes 2. Metal inserts and plastic shrink inconsistently, causing internal stress 3. Plastic is reused many times 4. Plastic contains too much water	1. Reduce temperature of feed barrel or reduce heating time 2. Preheat insert to ensure that there is enough plastic around insert 3. Reduce number of reuses 4. Strengthen drying of raw materials before injection

Master above 14 solutions, nylon injection molding process will become simpler, if you encounter common adverse phenomena, just try it!

Gud Mould Industry Co., Ltd