Pattern Coating

The different pattern sections are assembled and glued together with the pouring sprue to form the pattern cluster The pattern cluster is coated with a water-based ceramic slurry which is oven-dried to form a rigid coating over the foam.

The coating acts as a barrier to metal penetration into the sand, provides an escape path for foam decomposition products, stiffens the foam cluster, provides a smooth surface finish to the casting , and affects the heat transfer into the sand during casting.
The coating process must be carefully controlled for thickness, uniformity, and permeability. This is done by monitoring the solids content and viscosity of the slurry and checking the weight and thickness of the dried coating on the pattern.

Two procedures are often used for coating the foam pattern -- dipping and spraying.

Option A - Dipping -- Dip the pattern in a tank with the stirred, viscosity- controlled ceramic slurry.
Option B - Spraying -- Spray the pattern with the viscosity-controlled slurry. Used for thin, buoyant, or fragile patterns with few internal features.

Option A -- Dip coating

Option B -- Spray Coating

Choose the process (Option A-Dipping or Option B-Spraying) which provides the best coating coverage for the cylinder block.