Large Section Ceramic Injection Moulding
Abstract
Ceramic injection moulding is already established as a production technique for complex
shaped ceramic components. However the process is limited to thin section mouldings
generally not exceeding a wall thickness of 10 mm. The global objective of this work is
to describe and understand the aetiology of defects which preferentially appear in thick
injection moulded ceramics, and to find ways to overcome these problems.
The following stages are examined mould-filling, solidification, binder removal and
sintering. Different moulding techniques; conventional moulding, modulated pressure
moulding, insulated sprue moulding and low hold pressure moulding were applied.
Moulding thicknessw as systematicallyv aried (15,20,25, and 35 mm).. Hold pressures
and times were closely controlled and found to be decisive processing parameters for
defect creation. The use of insulated sprue moulding prevented void formation in 25 nun
thick mouldings and the application of low and constant hold pressures (>5 MPa) led to
a reduction of residuals tressesin the mouldings.
An intensive study was carried out on the binder removal stage in which the catalytic
removal of the polyacetal binder enabled removal of the binder from sections of 35 nun
thickness. The reaction and transport kinetics during binder removal were studied and
close observations were made out on various defects which could appear during
interrupted binder removal.
Differential shrinkage of the ceramic components during sintering was studied and could
be tracked back to flow-induced particle alignment during mould filling. The sintering
behaviour of the alumina feedstock used in this study was compared with an equiaxed
zirconia powder injection moulding suspension.
The phenomenon of jetting in large section mouldings and the creation of spherulites
during solidification of the polymer were found to influence moulding structure.
Authors
Krug, SteffenCollections
- Theses [4121]