Page 204 - Injection Molding Advanced Troubleshooting Guide

194 21 Cloudiness

21.3.2„ Cloudiness Troubleshooting Mold Issues

Potential mold-related causes for cloudiness include:
ƒ Water leak
ƒ Surface of mold
ƒ Hang up areas

21.3.2.1„ Mold: Water Leak
If the mold has a crack that is allowing water to enter the cavity the result can be
cloudiness. If cloudiness is the problem and other root causes have been elimi-
nated inspect the mold for potential water leaks. A water leak in a mold can be
difficult to detect. Sometimes water drops will be obvious on a mold surface but
other times the drops will be very small and may not even appear until the mold
has been pressurized with clamp tonnage. When checking for a cracked mold leak-
ing water it is always a good practice to clamp up on the mold at tonnage to see if
the clamp tonnage causes any water to seep through a crack.

21.3.2.2„ Mold: Surface of Mold
To optimize the transparency of a molded part the mold surface should be pol-
ished. If the polish is inadequate light will be scattered resulting in a reduction in
transparency. Areas of the mold that are not polished but rather are textured will
also impact the scattering of light.
Another issue that can occur on the mold surface is buildup of material byprod-
ucts. The buildup can reduce the polish level on the mold resulting in a milky re-
duction in transparency.
Review the mold surface to make sure that there are no areas lacking in polish or
have a surface buildup. If the mold surface is dull it may need to be cleaned with
something like Zapox to remove buildup, or polished with diamond paste to correct
an area lacking in polish.

21.3.2.3„ Mold: Hang Up Areas
If the mold has a hot runner system there can be locations that trap material lead-
ing to drag out over time. Areas of particular concern include the sprue opening,
any 90° corners, mismatch between components, valve pins, spreader tips, and
internal heaters. Any area that results in a hang up of material can cause defects
long after a material or color change has occurred. Even if only transparent mate-
rial is ever run through the mold, a poor material change in the barrel can put
contaminated material into the manifold.
If the mold will run different colors or materials ensure the hot runner supplier is
informed prior to building the manifold. The supplier can focus on eliminating
dead spots that can cause material to hang up.