Skip to main content

Why the vacuum should be done for AAC Blocks?

 Purpose of Evacuation:

Before steam is often entered into the autoclave, the autoclave must be evacuated by reducing the pressure within the autoclave with the utilization of vacuum from the air pump or steam ejector. 

Hereby the existent atmosphere within the autoclave is removed.

By keeping the evacuation pressure below the saturation pressure of water, which is out there within the green cakes, steam is released from the green cakes as a desired side effect.

Air and hydrogen which are still present within the green cakes are scavenged from the autoclave by this self-formed saturated steam.

Why the vacuum should be done for AAC Blocks?

The vacuum is mandatory.

This will remove the entrapped air from autoclaves.

Otherwise, liquid steam marks are going to be visible after autoclaving.

Those blocks are sensitive and have a tendency to break easily. If it's not broken, please keep the separate stacking/drying for a couple of days.

If there's no vacuum, do the purging of steam.

Purging is nothing but the entry of steam from one side and the exit from other side.

By evacuation, the air is removed from the autoclave and the cakes.

Evacuation (vacuum) should be done up to -400 mbar (for 45 minutes). 

Normally it (from 0 to -400 mbar) takes 10 to 15 minutes to achieve the same. 

It should be maintained between -300 to -400 mbar for the next 30 minutes.

This is done to achieve the uniform temperature distribution of the cake.

Common Mistake operators do between Evacuation and Rising of Autoclaves

Generally, operators switch off the Vacuum pump immediately after Evacuation.

Afterwards, they proceed for closing the Valve.

This is the common mistake noticed in most of the factories.

Make sure that the Valve (Vacuum) should be in closed condition before switching off the pump.

Otherwise it will suck the atmosphere air and our purpose of evacuation will not be met.

(BookNuts and Bolts of AAC Blocks Manufacturing - Srinivas Goud Chikati)


Popular posts from this blog

Recipe Calculation for AAC Blocks

Recipe is nothing but knowing the dry weight (batch weight) of one batch or one cake. To find out dry weight, we should know the desired dry density of final block. Let us work on the density of 600 kg/m³. Batch Weight = Density x Mould volume Density = 600 kg/m3 Dimensions of the mould : Length = 4840 mm = 4.84 M Width = 1250 mm = 1.25 M Height = 670 mm = 0.67 M Volume of the mould: 4.84 M x 1.25 M x 0.67 M = 4.0535 M³ Batch Weight = 600 x 4.0535 = 2432 kg (We have taken mould height 670 mm, which is actually depth of the mould. Generally we maintain the cake height equal to mould level. But in some AAC factories, cake height may be 650 mm or 680 mm depending on the parameters like quantity of returns required, sinking of cake, uneven surface of the cake, etc., In this case cake height should be taken to calculate the volume.) Batch weight or Dry weight consists of binders (Cement and Quicklime), Fly ash or Sand, returns and anhydrite. Usually th

What is Aluminium Powder? Why it is used in AAC Plants?

  Aluminium Metal powder or paste Aluminium powder, which is commonly used as a reaction agent in AAC Plants, is a fine granular powder made up of Aluminium Metal. Process of Manufacture: The aluminium powder is usually manufactured in many forms such as flaky particles, granulated powder (atomised aluminium) etc. There are different processes one can use for the production of aluminium powder. The metal is melted in furnaces, and the temperature is maintained around 720 to 760 C. Atomised Aluminium is produced by blasting the stream of molten Aluminium into small articles by air jet. For this purpose, an atomiser is employed which consists of a straight tube with lower end dipped in molten metal and upper end terminating as a little orifice. A jet of hot air under pressure is passed through armular opening near the top which impinges on a stream of molten Aluminium drawn by suction through the orifice. This results in the formation of small particles of Aluminium. Th

AAC vs Non AAC Blocks

  Why Autoclaving is required when Non Autoclaved Aerated Concrete Blocks are available in the Market? The matrix and the firmness of the AAC products are made due to autoclaving.  AAC vs Non AAC Blocks Technically, such product will start cracking by itself  when it approaches equilibrium moisture content  after a couple of years. In the case of ordinary concrete products, there are  no shrinkage troubles during the drying operation. But in foamed or aerated concrete the mixture is air  and if manufactured without autoclaving, drying  shrinkage will cause cracking. The calcium silicate hydrates formed during  autoclaving is more stable than the one formed of  cement at room temperature. Autoclaved products have low shrinkage. Cement will need four weeks to achieve its final  strength at room temperature whereas, autoclaving  takes only 12 hours. to get desired strength. The mechanical strength will not be very high and  through the drying, the shrinkage is going to be  excessive. It i