1. Blending and Insufficient Glue in Products During Initial Start-up and After a Period of Production: Causes and Solutions
When the machine is first started, the molten plastic in the injection molding machine's barrel has a low viscosity and good flowability due to prolonged heating, making the product prone to blistering. After a period of production, the molten plastic continuously carries away heat, resulting in insufficient molten plastic, higher viscosity, and poor flowability, leading to insufficient glue in the product. This can be resolved by gradually increasing the barrel temperature after a period of production.
2. Insufficient Glue in Products During Production: Sometimes increasing injection pressure and speed is ineffective. Why?
After a period of production, the molten plastic continuously carries away heat, resulting in insufficient molten plastic, higher viscosity, and poor flowability, leading to insufficient glue in the product. This can be resolved by increasing the barrel temperature.
3. Oval Product Causes and Solutions
Oval product shape is caused by uneven glue injection, resulting in uneven pressure around the product. Using a three-point injection method ensures even glue injection.
4. Requirements for Molds in Precision Products
The mold material should have good rigidity, low elastic deformation, and a low coefficient of thermal expansion. 5. Purpose of Acid Resistance Testing
The purpose of acid resistance testing is to detect the internal stress of the product and the location of stress points, in order to eliminate internal stress.
6. Causes and Solutions for Cracking of Metal Inserts in Products under Stress
When inserts are placed in a product, the hot molten plastic encountering the cold insert during injection molding creates internal stress, reducing product strength and making it prone to cracking. Preheating the inserts during production is recommended.
7. Rationality and Selection Method of Mold Venting Points
Improper mold venting points not only fail to provide venting but can also cause product deformation or dimensional changes. Therefore, mold venting points must be rationally selected. Venting points should be placed at the last point where the product is fully filled with plastic and at areas where air is trapped.
8. Causes and Solutions for Product Brittleness
Product brittleness is caused by using too much sprue or recycled material, or by prolonged residence time of the material in the barrel, causing material aging and making the product brittle. Increase the proportion of virgin material and reduce the number of times sprue material is recycled (generally no more than three times) to avoid prolonged residence of the material in the feed tube.
9. Causes and solutions for fiber blooming in glass fiber reinforced products
This is due to low melt temperature or mold temperature, and insufficient injection pressure, causing the glass fiber to not bond well with the plastic, resulting in fiber blooming. Increase melt temperature, mold temperature, and injection pressure.
10. The impact of inlet temperature on products. Excessively high or low inlet temperature will cause unstable material return, resulting in inconsistent material feeding and affecting the product's size and appearance.
11. Causes and solutions for white spots on transparent products
White spots on transparent products are caused by cold glue entering the product or dust in the material. Increase nozzle temperature, add a cold slurry well, and carefully store the raw material to prevent dust from entering.
12. What is the injection capacity of an injection molding machine?
Injection capacity PW = Injection pressure (kg/cm²) × Injection volume (cm³) / 1000
13. What is the injection horsepower of an 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 an 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 an injection molding machine?
Injection thrust F (kgf) = л/4 (D₁² - D₂²) × P × 2 D₁: Cylinder inner diameter; D₂: Piston rod outer diameter; P: System pressure
16. What is the injection pressure of an injection molding machine?
Injection pressure P (kg/cm²) = [π/4 × (D1² - D2²) × P × 2] / (π/4 × d²)
17. What is the plasticizing capacity of an injection molding machine?
Plasticizing capacity W (g/sec) = 2.5 × (d/2.5⁴)² × (h/2.5⁴) × N × S × 1000 / 3600 / 2h = Screw tip depth (cm) S = Raw material density
18. What is system pressure? How does it differ from injection pressure?
System pressure (kg/cm²) = The highest working pressure set in the hydraulic circuit. Injection pressure refers to the actual pressure of the injection molding machine; the two are not equal.
19. Requirements for hydraulic oil in injection molding machines:
(1) Appropriate viscosity and good viscosity performance
(2) Good lubricity and rust prevention
(3) Good chemical stability, not easily vaporized into a gel
(4) Good anti-foaming properties
(5) Low corrosiveness to machine parts and sealing devices
(6) Low flash point and solidification point.
20. The Influence of Hydraulic Oil Viscosity on Injection Molding Machines
When the system's operating environment temperature is high, a higher viscosity oil should be used; conversely, a lower viscosity oil should be used. When the system's operating pressure is high, a higher viscosity oil should be used because sealing is more difficult under high pressure, and leakage is the main problem. Conversely, when the system's operating pressure is low, a lower viscosity oil is preferable. When the operating speed of the hydraulic system's working parts is high, the oil flow rate is also high, which increases pressure loss but relatively reduces leakage; a lower viscosity oil is preferable. Conversely, when the operating speed of the working parts is low, a higher viscosity oil is preferable.
21. Retraction Position Setting
Correct retraction position = Gland travel position + Screw overtravel distance.
22. Importance of Retraction Position Setting
An overly large retraction position setting will cause oxygen absorption during material return, leading to material oxidation and bubble formation. An overly small setting will result in high pressure inside the barrel, excessive shear force causing material decomposition and nozzle drooling. The position error should not exceed 0.4mm.
23. Melt Position Setting
Melt position = Product weight / (Maximum stroke / Maximum melt volume)
24. Main Advantages of Gas-Assisted Injection Molding (GAM)
It can evacuate the core of thick materials to create hollow tubes, saving material and shortening cycle time; using gas in injection molding allows for uniform pressure distribution, and the gas can compensate for the volume shrinkage of the plastic during cooling and solidification through expansion; it reduces internal stress in molded products, thereby improving shape stability and eliminating deformation and warping.
25. Piston rod outer diameter smaller in the middle and larger at both ends:
This is caused by uneven product shrinkage due to overheating of the center pin, resulting in a piston rod outer diameter that is smaller in the middle and larger at both ends. The center pin can be made of phosphor bronze, a material with fast heat dissipation. Venting should be done in the middle of the product in the mold.
26. Cracking after screen printing on spherical surfaces:
Cracking occurs after screen printing due to surface stress on the product. Increasing the mold temperature reduces stress; stress can be eliminated by annealing.
27. Easily broken gate edge on eyeglass frames:
High injection and holding pressures lead to residual internal stress at the gate edge, causing the product to easily break. Minimize injection and holding pressures and appropriately increase the mold temperature to solve this problem.
28. Easily cracked when screwing in the four pillars of the electrical appliance casing:
The presence of water lines in the pillars causes them to easily crack during assembly. Increase venting in the mold, appropriately increase the mold temperature, and increase the injection speed to reduce water lines.
29. Product Deformation Issues
Product deformation is mainly caused by uneven heat shrinkage or by internal stress within the product itself.
30. Bubble Issues in Transparent PC Shells
Insufficient raw material drying, uneven glue thickness in the product, poor mold venting, and easy decomposition of raw materials can all cause bubbles in the product. Ensure thorough drying, increase mold venting, and minimize uneven glue thickness.
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