Common Nylon Injection Molding Defects And Solutions | Mold Plastic Injection


Injection molding process, also known as injection molding, is widely used in the field of Nylon plastic products. It has the characteristics of fast production speed, high efficiency, automatic operation, many varieties of designs and colors, easy to control the size, and the Nylon plastic products have accurate size, which is suitable for large-scale production and complex shape products and other molding and processing fields. Nylon injection molding process is simple and easy to operate, but there are many problems caused by manual operation, or injection equipment, raw materials and other factors. This article covers some some common defects of Nylon injection molding and cause analysis , solutions. 

Defects, Causes And Solutions For Nylon Injection Molding – Nylon Moulding Defects & Remedies 

Nylon products overflow or flash


1.Too much injection pressure

2. The clamping mechanism is worn and the clamping force is too small

3. Material temperature is too high

4. The contact surface of the mold is uneven, and the mold is worn and deformed

5. The mold contact plane falls into foreign matters



1. Reduce injection pressure

2. Repair the equipment and lift the clamping force

3. Reduce the temperature of feed drum

4. Repair the mold

5. Clean the foreign matters in the Nylon injection mold in time


Dents (craters due to high shrinkage)


1. Gate and material channel are too small

2. Material temperature is too high

3. Mold temperature is too high

4. Insufficient quantity

5. Insufficient injection and pressure holding time

6. Injection molded Nylon products are too thick or too thin



1. Gate expansion

2. Reduce the temperature of feed drum

3. Effective cooling mold

4. Adjust the feeding quantity

5. Increase the pressure holding time

6. Design the mold reasonably, and the wall thickness should be as uniform as possible


Weld and meld line


1. Material temperature is too low

2. Injection pressure is too low, injection speed is too slow

3. Mold temperature is too low

4. Many gates

5. Uneven wall thickness of injection molded Nylon products

6. Large amount of release agent

7. Poor cavity exhaust



1. Raise the temperature of feed drum

2. Increase injection pressure and speed

3. Raise mold temperature

4. Properly reduce the number of gates

5. Improve the precision of mold making

6. Reduce the amount of mold release agent

7. Enhanced exhaust

The surface of Nylon plastic molded part is corrugated


1. Material temperature is too low, resin viscosity is large, and fluidity is poor

2. The injection pressure is small and the speed is too slow

3. Low mold temperature

4. The mold gate is too small



1. Raise the temperature of the feed cylinder

2. Increase injection pressure

3. Raise mold temperature

4. Increase the gate

There are bubbles and vacuum bubbles


1. The raw materials contain moisture, solvents or other low volatiles

2. The material temperature is too high, and the heating time is long

3. The injection pressure is too small

4. Nylon plastic products in injection molding are too thick, with different cooling rates on the surface and vacuum bubbles inside.

5. The mold temperature is too low.

6. The injection time is too short.



1. Dry the raw materials before molding

2. Reduce the temperature of the feed cylinder

3 Increase injection pressure

4. Increase the size of runner and gate

5. Properly increase the mold temperature

6. Extend injection time


There are black spots and stripes


1. Black spots appear in plastic decomposition

2. The mold has no exhaust holes or the exhaust position is improper

3. The gap between the plunger and the feed barrel is too large, and the pellets will be decomposed and black when heated in the gap for too long, or the black spots appear due to the wear of the screw due to the hard particles.



1. Reasonably control the process temperature to avoid overheating decomposition of plastic

2. Reasonably open vent

3 Maintain the machine in time and increase the feed cylinder cooling


Plastic injection molded Nylon products are discolored


1. The material temperature is too high, the color will decompose and cause discoloration

2. The plastic stays in the feed cylinder for too long and decomposes when heated

3. Too much lubricant is applied



1. Choose high temperature resistant color powder

2. Reduce the residence time of materials in the feed cylinder

3. Reduce the amount of lubricant


Nylon injection mold products are deformed and warped


1. Short cooling time, Nylon plastic injection mold products are not completely shaped

2. Uneven thickness of Nylon plastic products, uneven shrinkage on cooling

3. Inject twice, the injection pressure is too high

4. Nylon injection mold products are improperly positioned and unevenly stressed

5. Low material temperature or uneven plasticizing temperature



1. Extend the cooling time or lower the model temperature

2. The design of Nylon plastic products strives to be reasonable

3. Reduce the second injection pressure and shorten the holding time

4. Reasonably arrange the position of the jack

5. Raise the temperature of the feed cylinder


Cracks in plastic injection Nylon mold products


1. The mold is too cold

2. The cooling time of Nylon plastic products in the mold is too long, caused by the shrinkage of plastic and metal inserts.

3. The ejection device of Nylon plastic injection mold is inclined or unbalanced

4. The cross-sectional area of the ejector rod is too small or too few, and the distribution is improper

5. The slope of Nylon plastic in injection molding is not enough, it is difficult to demold



1. Raise mold temperature

2. Properly reduce the cooling time, or preheat the metal insert

3. Adjust the ejection position

4. Correctly design and determine the location

5. The design of Nylon injection molding products is reasonable, with a certain slope


Difficult to demold Nylon injection mold


1. The surface of the mold cavity is not smooth enough

2. The mold slope is not enough (especially the deep shape Nylon plastic products)

3. The injection pressure is large, the material enters the gap between the mold inserts

4. The temperature of the mold and the cooling time are inappropriate

5. Mold wear and scratches cause Nylon plastic products flash, difficult to demold

6. Improper exhaust of the mold



1. To improve the mold cavity finish, the best surface is chrome plated

2. Increase the mold inclination

3. Repair the mold

4. When the core surface is difficult to demold, it can increase the mold temperature and shorten the cooling time. When the mold center is difficult to demold, it can reduce the mold temperature and increase the cooling time.

5. Repair the mold

6. Increase the mold exhaust structure 

7. By adding internal and external lubricants


The brittleness of Nylon injection mold products decreases


1. The material temperature is too high, the material is heated for too long, and the plastic decomposes

2. Metal inserts and plastic shrink inconsistently, causing internal stress

3. Plastics are reused more often

4. Excessive moisture in plastic



1. Reduce the temperature of the feed cylinder or reduce the heating time

2. Preheat the insert to ensure that there is enough plastic around the insert

3. Reduce the number of reuse

4. Strengthen the drying of raw materials before injection