Before casting, molds are coated with a thin layer of oil. This is done in order to ensure that green-cake does not stick to molds. While slurry is mixed and poured into greased molds, Aluminum reacts with Calcium Hydroxide and water to form Hydrogen. Millions of tiny Hydrogen bubbles are released due to this reaction. This leads to the formation of tiny unconnected cells causing the slurry mix to expand. Such expansion may be twice its original volume. This process is called rising. These cells are the reason behind the lightweight and insulating properties of AAC blocks. Once the rising process is over, green-cake is allowed to settle and cure for some time. This ensures the cutting strength required for wire cutting.
Usually rising and the pre-curing process takes around 1-4 hours. Rising is dependent on raw material mix and weather conditions. As the reaction is affected by weather conditions, it is recommended to maintain a constant temperature in the pre-curing area. Due to this, pre-curing is also referred to as ‘heating room pre-curing’. This can be achieved by deploying radiating pipes for indirect heating. It should be ensured that green-cake is not subjected to vibrations during pre-curing or else it might develop cracks.
At end of the pre-curing process, green-cake is hard enough to be wire cut as per requirements. Pre-curing is not a complicated process, but it should be monitored constantly. Pre-form defects (cracking, sinking, etc..) mainly occur during the process.