30 common problems in the injection molding process and countermeasures

1. When the machine is first started, the product runs phi (flying edge), and after a period of production, the product lacks glue causes and solutions.

The melted glue in the injection molding machine tube at the beginning of the machine is heated for a long time, the viscosity of the melt glue is low, the fluidity is good, the product is easy to run the phi, and after a period of production, the melt glue constantly takes away the heat, resulting in insufficient melt glue, high viscosity, poor fluidity, so that the product lacks glue. After a period of production, gradually increase the material tube temperature to solve.
 

2. In the production process, the product is short of glue, sometimes increasing the injection pressure and speed are not effective, why?

After a period of production, the molten glue keeps taking away the heat, resulting in insufficient molten glue, high viscosity, and poor fluidity, which makes the product lack glue. Increase the material tube temperature to solve the problem.
 

3. The reason and solution of oval product.

The product ellipse is due to the uneven glue entry, resulting in uneven pressure around the product, which makes the product ellipse, use three points of glue entry to make the product into the glue evenly.
 

4. The requirements of precision products for moulds.

Require good steel of mold material, small elastic deformation and small heat rise coefficient.
 

5. The purpose of acid resistance test.

Product acid test is to detect the internal stress of the product, and the location of the internal stress point, to eliminate the internal stress of the product.
 

6. The causes and solutions of metal inserts in products that are susceptible to cracking under stress.

Putting inserts in the product, in the injection molding due to hot tears melt glue encounter cold inserts, will form internal stress, so that the product strength decreases, easy to crack. In production, the inserts are preheated.
 

7. The reasonableness of the mold exhaust point and the selection method.

Mold exhaust point is unreasonable, not only can not play the exhaust effect, but also will cause product deformation or size change, so the mold exhaust point should be reasonable. Choose the mold exhaust point, which should be in the product last walk full of glue and product trapped in the place of gas-burning open exhaust.
 

8. The product is easy to brittle crack causes and solutions.

Products easy to brittle crack is the product use of water mouth material and secondary material too much to cause the product easy to brittle crack, or material in the material tube stay too long, causing the aging of the rubber so that the product easy to brittle crack. Increase the proportion of new materials, reduce the number of times the water mouth material is recycled, generally not more than three times, to avoid the long stay of rubber in the material tube.
 

9. Add glass fiber products easy to appear the causes and solutions of the pan-fiber.

It is due to low melt temperature or low mold temperature, insufficient injection pressure, resulting in the glass fiber in the rubber can not be well combined with plastic, so that the pan-fiber appears. Increase the melt temperature and mold temperature, and increase the injection pressure.
 

10. Influence of feed port temperature on the product.

The too high or too low temperature of the feed port will cause the machine to return unstable material and make the feeding amount unstable, which will affect the size and appearance of the product.
 

11. The causes and solutions of white spots on transparent products.

Transparent products with white spots are caused by cold glue inside the product or dust inside the material. Increase the temperature of the injection nozzle, add cold material well, and pay attention to the preservation of raw materials to prevent dust from entering.
 

12. What is the injection capacity of injection molding machine.

Injection capacity PW = injection pressure (kg/cm2) × injection volume (cm3) / 1000
 

13. What is the injection horsepower of the injection molding machine?

Injection horsepower PW (KW) = Injection pressure (kg/cm2) × Injection rate (cm3/sec) × 9.8 × 100%
 

14. What is the injection rate of the injection molding machine?

Injection rate V (cc/sec) = л/4×d2×rd2: material tube diameter r: material density
 

15. What is the injection thrust of the injection molding machine?

Injection thrust F (kgf) = л/4 (D12 - D22) × P × 2D1: cylinder inner diameter D2: piston rod outer diameter P: system pressure
 

16. What is the injection pressure of injection molding machine?

Injection pressure P (kg/cm2) = [л/4×(D12-D22)×P×2]/(л/4×d2)
 

17. What is the plasticizing capacity of injection molding machine?

Plasticizing capacity W (g / sec) = 2.5 × (d/2.54)2 × (h/2.54) × N × S × 1000/3600/2h = screw front tooth depth (cm) S = raw material density
 

18. What is the system pressure? What is the difference with injection pressure?

System pressure (kg/cm2) = the highest working pressure set in the oil pressure circuit, injection pressure refers to the actual pressure of the injection molding machine, the two are not equal.
 

19. Requirements of hydraulic oil for injection molding machine.

(1) appropriate viscosity and good viscosity performance
(2) good lubricity and rust resistance
(3) good chemical stability, not easy to gasification into gum
(4) good foamability
(5) the corrosiveness of the machine parts and sealing devices to be small
(6) ignition point (flashpoint) requirements, the freezing point should be low.
 

20. Hydraulic oil viscosity on the impact of injection molding machine?

When the system working environment temperature is higher, the oil with higher viscosity should be used, and vice versa, the oil with lower viscosity should be used. When the system working pressure is higher, the higher viscosity should be used, because in high pressure, sealing is more difficult and leakage is the main problem.

Conversely, the system working pressure is low, it is appropriate to use less viscous oil, when the working parts of the hydraulic system operating speed is high, the flow rate of the oil is also high, then the pressure loss will also increase, while the leakage is relatively reduced, it is appropriate to use lower viscosity oil, conversely, when the working parts moving speed is low, it is appropriate to use higher viscosity oil.
 

21. The setting of loosening and retreating.

Loose back the correct position = over the rubber ring moving position + screw offside distance.
 

22. The importance of the loose-back position setting

If the loosening and releasing position is set too large, it will cause the return material to absorb oxygen, make the rubber oxidized and produce bubbles. If the position is set too small, the pressure in the barrel will be too high and the shearing force will be too high to make the rubber decompose and the injection nozzle salivate. The position error should not exceed 0.4mm.
 

23. Melting position setting

Melting position = weight of the product / (maximum stroke / maximum melt volume)
 

24. The main advantages of gas-assisted injection molding (GAM)

It can evacuate the core of thick material to make hollow tubing, which can save material and shorten the cycle time.

The use of gas in injection molding allows for uniform pressure distribution, and when the plastic cools and cures, the gas can compensate for the volume shrinkage of the plastic through expansion.

Reduce the internal stress of molded products, thus improving shape stability and eliminating deformation and warpage.
 

25. The piston rod outer diameter is small in the middle and large at both ends?

Due to the unbalanced shrinkage of overheated products in the middle hole pin, resulting in a small outer diameter of the piston rod in the middle and large at both ends, the middle hole pin cocoa is made of phosphor bronze material with fast heat dissipation, and the mold is exhausted in the middle part of the product.
 

26. Spherical screen printing after the cracking problem

Due to the existence of stress on the surface of the product, causing cracking after screen printing. Increase the temperature of the mold to reduce the stress, the method of annealing can be used to eliminate stress.
 

27. The problem of easy to break the edge of the water mouth of the glasses frame

The residual internal stress on the edge of the water outlet is caused by the high injection and holding pressure, which makes the product easy to break.
 

28. The four pillars of the electrical shell are easy to crack when playing screws

Due to the existence of water trap line in the pillar, the product assembly pillar is easy to crack, the mold to increase the exhaust, appropriate to increase the mold temperature, accelerate the injection speed to reduce the water trap line.
 

29. Product deformation problem

Product deformation is mainly caused by unbalanced product deformation during heat shrinkage, or due to the product itself being under the action of internal stress to make the product deformation.
 

30. Transparent PC shell bubble problem

Insufficient drying of raw materials, uneven thickness of the product, poor exhaust of the mold, easy decomposition of raw materials may cause product bubbles. Fully dry, increase the mold exhaust, and minimize the uneven thickness of rubber.