Making of AAC Blocks

AAC Blocks Making

The beginning of the manufacturing process in AAC Blocks begins at first with preparation of raw material. To have a detailed look a list of several raw materials that are required for AAC Bricks are given in detailed form.

Fly-ash or sand

In the manufacturing of AAC Blocks certain key ingredients are required. The first one is fly ash, which is rich in silica, including sand or pond ash. In India, almost all the AAC Bricks

companies use fly ash. The AAC Blocks are made with Fly ash  It is mixed with water to form fly ash to form slurry type of material. Thereafter, several ingredients, such as lime.now the questions is what is fly ash ? here this link  i explain you clearly.

powder, gypsum, ACC cement and aluminum powder are mixed in the fly ash slurry. Another alternative material that can be used in the manufacture of AAC Blocks is sand. All you need is to grind sand with water in a wet ball bill to make sand slurry. Similar to fly ash slurry, the sand slurry is mixed in lime powder, gypsum, cement and aluminum powder.

The AAC Blocks manufacturing process begins with the feeding of fly ash into slurry tank. A man feeds the ash inside the slurry tank to which powder, gypsum, cement and aluminum powder are added.

Limestone Powder

In the production of AAC or Aearcon Blocks lime powder required is taken from limestone, which is crushed into fine powder. If not, it is purchased directly purchasing in the form of powder form from several factories that sell them for such purpose. However, the purchase of lime powder is an expensive affair. Therefore, several AAC Brick manufacturers have their own limestone crushing machines. They are ball mill, jaw crusher, including bucket elevators. The lime powder is stored in tall towers made of brick and mortar.In the manufacture of AAC blocks a crusher is used for grinding lime stone. There is a bag next to it to filter the dust.

Cement

The manufacture of AAC Blocks requires Ordinary Portland Cement (OPC) 53 grade. It should be from a reputed OPC manufacturer. The cement sold by small cement factories is not preferred. This is because there huge variation in the cement quality, which in turn will weaken the Strength in AAC Bricks. This not safe for building construction. Therefore, the big factories that make AAC Blocks have their own cement  making unit as well. This is stored in huge towers.

Gypsum

In the manufacturing of AAC Blocks Gypsum is readily sold in the market. It is available in the form of fine powder, which is stored in huge towers.for more details you can visit this links about gypsum

Aluminum in powder or paste form

There are several manufacturers that sell Aluminum in the form of powder or paste. It is readily available in the factories around AAC Brick manufacturing process. This ingredient is used in small measure to be mixed in the Fly ash slurry. Therefore, its weight or quantity used is manually done. Thereafter, it is put into the AAC Block mixing unit. The next process in AAC Blocks production is Dosing and Mixing.

Dosing and Mixing

The second step in AAC Block production is dosing and mixing. This starts after the preparation of raw material. The process of dosing and mixing forms a very important part in AAC Brick manufacturing. Moreover, it in this process the final quality of the finished product is all that matters for strong material. Therefore, the manufacturer of AAC Bricks or Aearcon Blocks must maintain a perfect ratio in the mixing of all the ingredients. This is done as per the suggested technical specifications in the manufacture of AAC Blocks. It is controlled by several control systems to ensure continuous quality production. This is done by accurate measurement of the ingredients, including lime powder, gypsum, AAC cement, water and aluminum powder. It is released in required quantity as per the given specifications.

In order to manufacture AAC Blocks a dosing and mixing plant unit. At first a correct amount of Fly ash or sand slurry is pumped into the mixing tank. As soon the required weight is poured inside the pumping is stopped. In a similar manner, cement, gypsum and lime powder are poured into individual containers respectively. This is done by using screw conveyors. When each of them is mixed in the prescribed amounts into the mixing drum. It is done by stirring them to make sure they are mixed properly. A temperature between 40 to 42 degrees centigrade is maintained inside the mixing chamber by pumping steam into it. In addition to it, Aluminum powder is fed into it by a small bowl attached to the unit. Thereafter, the mixture is on being mixed properly as according to time mentioned in the technical manual; it is poured into molds by the dosing unit for foaming. This process of dosing and mixing is carried out in a continuous manner. It is because a long gap between pumping or mixing of ingredients will harden the mixed form of mixture. This could lead to choking up the entire system in the manufacturing unit of AAC Blocks.

The manufacturing of AAC Blocks is done completely automatic. From dosing and mixing to getting the final product there is no need for manual work at all. It is totally monitored by control systems. It also involves computers and CCTV cameras. However, in industrial operations there is an option for manual control in case of emergencies that may happen due to system error. Therefore, the control panel and CCTVs help in monitoring the manufacturing of AAC Bricks. They are so useful and maintain safety in the plants.
Casting, Rising and Pre-curing

As soon as the raw material is ready, it is poured into moulds. This process has different names. It is called casting, pouring or moulding. Let us take a look at casting process. When the fly ash or sand slurry is mixed thoroughly with ACC cement, lime powder, gypsum and Aluminum, it is poured into the moulds. They can of several different sizes. However, the average sizes are 4.2m x 1.2m x 0.65m for
160-500 m3/day in size. But, there are some AAC Brick plants that might have moulds of 3m, 4.8m or 6m.

Therefore, before casting, a thin layer of oil is used for coating the inside of the moulds. It is only to make sure the mixture does not stick to the inner layer of the moulds. Chemically, Aluminum reacts with Calcium Hydroxide and water to form Hydrogen, when the slurry is mixed and poured into greased moulds. Several million tiny bubbles of Hydrogen are released during this chemical reaction. Therefore the mixture of slurry expands due to the formation of tiny unconnected cells. It may be two times the volume of the slurry. It is just like the Idli or Dosa mix that expands on mixing it. You must also note that the bubbles that generate during AAC Bricks production are not connected. Moreover, they are closed bubbles, whereas in CLC blocks, they are open bubbles. The size of the bubbles is 2 mm to 5 mm. The cells in them make the AAC Blocks light in weight. They support the insulating properties in AAC Bricks. Thereafter, as the whole process is completed the time for curing begins, which is for a certain period of time. This in turn makes them strong for cutting that is done with wires.

The time taken for expansion and the process before curing is one to four hours. The expansion depends on mixing of raw material and climatic conditions. It must be added that the weather plays an important role in the expansion process of AAC Blocks. Therefore, constant temperature must be maintained, which highly recommended in the pre-curing area. Because of this it is popularly known as ‘heating room’ for pre-curing. This is done by deployment of radiation pipes for heating indirectly. Another area that must be taken care of is that the green cake should not be exposed to vibrations. This will allow for cracks in the AAC Bricks. They will be rejected in quality control and plenty of material will go for waste.

Casting process in the production of AAC blocks

When the green cake turns solid and hard at the end of pre-curing process, it is cut by wire per standard or customer requirement. The process of pre-curing in AAC Bricks manufacturing is not a complicated process. However, it must be closely monitored. Especially, it is the duty of the slurry machine operator to monitor rise in slurry during adding and mixing of raw material and other ingredients, such as lime powder, gypsum, cement, water and aluminum powder. A constant feedback must be provided to dosing, mixing and casting operators. Often, cracking, sinking occur during AAC Blocks manufacturing.

Demoulding and Cutting of AAC Blocks

In the previous process of manufacturing the AAC Blocks, it has been explained in how the slurry is cast into the moulds, where it is kept to expand and grow hard and strong. Thereafter, as it becomes hard for cutting it is ready to be removed from the moulds. Then, it is cut according to required size and shape.

In AAC Blocks manufacturing, the process of demoulding as well as cutting is a critical process. They both are an important part in that defines the accuracy in dimensions of AAC Bricks. They also ensure that the finished product does not face any manufacturing defects and are rejected for building construction purpose.

A crane is used to lift the mould from the pre-curing room and rolled onto the rail tracks on which it is transported for demoulding operation. The deployment is done by an automated process. It is all done by precision and timing. The process of production of AAC Blocks can be defined in flat-cake and tilt-cake. This is how green cake is demoulded. Lastly, it is sent for cutting into standard size.

The demoulding and cutting depends completely on the provider of technology for production of AAC Blocks. In all the earlier process of raw material preparation, dosing & mixing and casting; it pretty much the same across in all technologies. demoulding and cutting process vary vastly depending on technology provider. This can be seen from the size of the moulds.

The cutting process is classified as flat-cake and tilt-cake. It is based on how green cake is demoulded and sent for cutting.

For example: green cake travels horizontally throughout the process in flat-cake technology. Moulds used in such technology have There is a one bottom plate and single set of mould wall that covers all the four sides of the mould. The mould wall is lifted vertically, but the mould lies in horizontal position as the green cake is then sent for cutting. Thereafter, it goes under steam for curing in horizontal manner. Now, flat-cake technology is not widely used. Therefore, let us make a comparison of it against tilt-cake technology.

European and Chinese vendors is tilt-cake technology, which is common thing among them. It is nothing but the mould has a side plate or bottom plate, including mould walls. The mould is tilted by 90 degrees in the demoulding process. It is unlocked, leaving green cake sitting vertically on the side plate. Thereafter, the crane separates the green cake from the mould. The green cake is in vertical position while passing through the machine for cutting. Moreover, technology in tilt-cake makes use of two cutting machines. At first, horizontal cutting is done and later vertical cutting.

There are no moving parts in horizontal cutting machine. The cutting is done by moving the green cake through it. A profile plate scrapes the sides of green cake to make the finished product look smooth and even in shape. Thereafter, horizontal cuts are made through green cake using stationary steel wires. Several adjustments can be made to the wires offline to get the height required for AAC Blocks or Aearcon blocks. This finally depends on the preferred dimensions of the client. In some horizontal cutting machines a top crust removal device shaped like an arrow is visible.
Demoulding and cutting process in Horizontal cutting machine Horizontal cutting machine using stationary wires

The vertical cutting machine is the next in the production line of AAC Blocks manufacturing. It cuts the green cake into vertical blocks. It has no moving. It only has cutting assembly mounted on columns, which move up and down at a programmed speed. There are steel wires that are mounted on oscillating heads that are used for cutting through green cake. They can be adjusted offline to get the desired thickness for AAC Bricks. This is again dependent on preference of the client preference. There is suction for removal in certain vertical cutting machines.
In most of the cases, green cake is sent to autoclave queue after cutting operation. However, in certain operations it is sent to a tilting table. This technology is to remove top and bottom layer of crust in green stage. This crust is recycled by sending it to a recycling tank. The absence of a tilting table could cause damage to final product due to use of tools like chisels. Therefore, they will may have to be separated in white stage.

1)ADVANTAGES AND DISADVANTAGES OF AAC BLOCKS 

 2)FREQUENTLY ASKED QUESTIONS ON AAC BLOCK

 3)ADVANTAGES OF CLC BLOCKS           

4)FREQUENTLY ASKED QUESTIONS ON CLC BLOCKS