Page 320 - Injection Molding Advanced Troubleshooting Guide

314 32 Glass Fibers on Surface

32.3.3„ Glass Fibers on Surface Troubleshooting Machine Issues

The key machine-related impacts on glass fibers on the surface include:
ƒ Machine capability
ƒ Machine performance

32.3.3.1„ Machine: Machine Capability
The first thing that must be adequate on a molding machine is the injection
velocity. To achieve an attractive part a molding machine must be able to inject fast
enough to provide a resin-rich surface. If the machine cannot reach a fast-enough
fill velocity the part will have a glassy surface. See Figure 32.2 for an example of
poor velocity linearity between set velocity and actual velocity.

Figure 32.2 Velocity linearity form: notice poor linearity

The second key to a machine being adequate for processing glass-filled material
is the pressure capability. It does not matter how high the velocity can be set if
the machine does not have enough pressure available to achieve the set point.
High-pressure molding machines allow faster fill rates for longer flow lengths.