Why are the dimensions of the PU part smaller than those of my mould?
Every PU system will shrink during crosslinking. PU systems cure with an increasing core temperature. This means that heat is released during crosslinking. Crosslinking sections cooling down lead to a volume shrinkage. The extent of volume loss is influenced by several factors:
1. The shrinkage depends on the contour and wall thickness of the parts. The data sheet tells you shrinkage values which were measured at a specified geometry in the lab and are only to be taken as an orientation value. The shrinkage can vary depending on the part geometry.
2. Fillers: Unfilled systems have higher shrinkage values than filled systems. By adding filler the shrinkage can be reduced. Please note that filler also affects the mechanical values.