AAC Blocks Manufacturing Process
Step 4 – Demoulding and Cutting
In earlier posts we have seen how slurry is cast in moulds and allowed to rise and gain strength during pre-curing. Once green cake has achieved cutting strength, it is ready to be demoulded and cut as per requirements.
Demoulding and cutting are very critical processes in AAC blocks manufacturing. These two processes play a major role in defining amount of rejection as well as dimensional accuracy of the final product.
Once a mould is out of pre-curing room, it is lifted by a crane or rolled on tracks for demoulding operation. Lifting or rolling green cake is determined by technology deployed. Manufacturing process can be broadly classified as flat-cake and tilt-cake based on how green cake is demoulded and sent to cutting line.
While all previous processes like raw material preparation, dosing & mixing and casting are pretty much same across all technologies, demoulding and cutting process vary vastly depending on technology provider. Differences in demoulding and cutting process are also evident from different types of moulds required by different technology provider.
Primarily cutting process may be classified as flat-cake and tilt-cake based on how green cake is demoulded and sent to cutting line.
E.g. In flat-cake technology, green cake travels horizontally through all processes. Moulds used in such technology have 1 bottom plate and single set of mould wall that covers 4 sides. Mould lies in horizontal position as mould wall is lifted vertically. Green cake is then sent for cutting and from there on to steam curing lying horizontally. Since flat-cake technology is not widely used, we’ll do a comparison of flat-cake vs tilt-cake system at a later stage.
Most commonly used technology among most European and Chinese vendors is tilt-cake technology. In this technology, mould has a side plate (aka bottom plate) and mould walls. During demoulding, mould is tilted by 90o and unlocked leaving green cake sitting vertically on side plate. Crane slowly separates mould from green cake. Green cake remains vertical as it passes through the cutting machines.
Usually tilt-cake technology uses two cutting machines. Horizontal cutting machine is used in the first stage, while vertical cutting machine is used in second stage.
Horizontal cutting machine does not have any moving parts. Cutting operation is achieved by moving green cake through horizontal cutting machine. It has a profile plate that scrapes sides of green cake to give it an even finish. Once profiling is done, horizontal cuts are made through green cake using stationary steel wires. These wires can be adjusted offline to get desired height of AAC blocks or panels. Depending on client preference, some horizontal cutting machines may sport a top crust removal device shaped like an arrow.
Next in line is vertical cutting machine. As the name suggests, it cuts green cake in vertical blocks. Unlike horizontal cutting machine that has no moving parts, vertical cutting machine has cutting assembly mounted on columns and it moves up and down at set speed. Steel wires mounted on oscillating heads are used for cutting through green cake. These cutting wires can be adjusted offline to get desired thickness of AAC blocks. Depending on client preference, some vertical cutting machines may have a suction system for crust removal.
While in most cases green cake is sent to autoclave queue after cutting operation, in certain cases it is sent to a tilting table. Tilting table is used to remove top and bottom layer of crust in green stage. This crust may be recycled by sending it to recycling tank. In absence of a tilting table, crust may have to be separated in white stage and may cause damage to final product due to use of tools like chisels.
AAC blocks manufacturing process (…contd…)