Foam Parts with a High-Gloss Surface
When producing thermoplastic parts, sink marks resulting from shrinkage in thick-walled sections can be reduced considerably through the use of chemical or physical blowing agents. However, surface quality suffers greatly when injection molding foam parts in this manner. The surface often appears porous and exhibits streaks.
The surface blemishes caused by the blowing agent can be avoided by increasing the temperature of the cavity wall. This presents problems from an economic standpoint, however, because the cycle time is increased significantly.
The newly developed Indumold process resolves this dilemma by rapidly raising the temperature of the cavity’s surface to the required level during the injection molding cycle and then cooling it just as quickly to the base level. Other “variothem” processes are frequently characterized by heating and cooling rates that are too slow, so that cycle times are extended to unacceptably long values. The Indumold process can eliminate these drawbacks to a great extent, since the necessary temperature gradients are achieved within a few seconds: the cycle time remains the same under ideal circumstances or is only slightly longer than with conventional injection molding.
The process avoids formation of weld lines, improves accuracy of replication and reduces molded-in stress near the surface. This makes it suitable for producing thin-walled parts, chrome-plated parts or microinjection molded parts.