Potential Problems Caused by Excessive Back Pressure in Injection Molding
Back pressure is a critical process parameter in injection molding, directly affecting product quality. While high back pressure can increase the density of the melt, it can also lead to a series of problems.
1. Decreased Plasticization Efficiency
Reason: Excessive back pressure increases the resistance of the screw's backward movement, prolonging the plasticization time and reducing plasticization efficiency.
2. Increased Melt Temperature
Reason: Excessive back pressure causes the melt to stay in the barrel for an extended period, resulting in increased temperature due to the shearing action of the screw.
3. Product Quality Issues
Weld Lines: High back pressure can reduce the fluidity of the melt, increasing the occurrence of weld lines and affecting the product's appearance.
Bubbles: Under high pressure, bubbles are more likely to form in the melt, affecting the product's internal structure.
Burn Marks: For heat-sensitive materials, high temperatures can cause burn marks on the product surface.
Dimensional Instability: Excessive back pressure can lead to dimensional instability and warping of the product.
4. Increased Equipment Wear
Reason: Under high pressure, the seals, screws, and other components of the equipment experience greater wear.
5. Material Waste
Reason: Excessive back pressure can cause the melt to stay in the front of the screw, resulting in material waste.
6. Increased Production Costs
Reason: High back pressure leads to longer cycle times, increased product defects, and higher equipment maintenance costs, resulting in increased production costs.
How to Determine if Back Pressure is Too High?
Product Quality Issues: Such as weld lines, bubbles, burn marks, and dimensional instability.
Equipment Operating Status: Increased noise, vibration, and motor overload.
Production Data Analysis: Longer cycle times, higher defect rates, and increased material consumption.
