Page 316 - Injection Molding Advanced Troubleshooting Guide

310 32 Glass Fibers on Surface

„ „32.2„ Glass Fibers on Surface
Troubleshooting Chart

Table 32.1 shows the glass fibers on surface troubleshooting chart.

Table 32.1 Glass Fibers on Surface Troubleshooting Chart
Molding Process Mold Machine Material
slow fill velocity lack of venting machine capability moisture content
low melt temperature hot runner temperatures machine performance viscosity
low mold temperature flow length glass content
gating

„ „32.3„ Glass Fibers on Surface
Troubleshooting

32.3.1„ Glass Fibers on Surface Troubleshooting Molding Process
Issues

The molding process can have a large impact on glass showing on the surface of a
part. Some of the process factors that influence cosmetics of a part include:
ƒ Slow fill velocity
ƒ Low melt temperature
ƒ Low mold temperature

32.3.1.1„ Molding Process: Slow Fill Velocity
A slow fill velocity will tend to allow the glass fibers to come to the surface of the
part. Normally the faster the mold is filled the better the surface will appear. A fast
fill creates a resin-rich surface that will help keep the surface looking uniform and
not glassy.
If glass on the part surface is a problem verify that the fill time and fill only weight
of the part match the documented process setup sheet. Transferring early can lead
to end of fill locations being more glassy-looking then the rest of the part.
If the fill velocity is not optimized try filling faster to determine the impact on the
glassy appearance. Make sure that the machine is not running at a point where it
has become pressure limited (fill pressure greater than 90% of maximum available