Storage, mixing and molding

2- Storage, mixing and molding of raw materials

 

AAC block production line with annual capacity of 150 000 m3

Capacity description:
  • Main raw material: Silica Sand
  • Cutting machine size: 4.2 meter
  • Mould net size (after cutting): 4.2 x 1.2 x 0.6 m
  • Autoclave: Φ 2 x 31.5 m, 6 set
  • Mould Quantity 26 pcs, steam trolley 63 pcs, mould pallet 152 pcs
  • Boiler: 6 Ton/hour, 16 bar pressure.
  • Land requirement: total factory 20 000 m2, workshop about 6000 m2
  • Water consumption: 250 Ton/day
  • Gas consumption: 6250 m3/day
  • Electricity consumption: about 6000 kw/day
In order to obtain 150 000 m3 AAC block per year, so within 300 working days per year, we should produce 500 m3 AAC block per day.
Per mould size 4.2 x 1.2 x 0.6 = 3 m3, in order to obtain 500 m3 per day, we
should pouring and cut per day 500 m3 ÷ 3 m3 = 167 moulds.
Total working time should be within 22 hours per day (except autoclave section).

 

Raw materials
The finial formula will be designed by Supplier’s engineers according client materials
For Example 550kg/m3 AAC block, we need the raw material list as following, just for reference:

Raw material requirements

The specified requirements of the raw materials are ideal value. Even if raw materials deviate from these values, it is still possible to produce good Aerated concrete.
The final data, the plan and any additional machines must be clarified on a case by case basis.

Cement: the strength of AAC product mainly depends on cement which provides calcium materials. The cement suits to the AAC product depending on its type and label. Ordinary Portland Cement 42.5 should be first choice. 

Lime: one of the main raw materials of AAC; the main effect is to provide efficient calcium oxide with cooperation of cement making calcium oxide react with SiO2、Al2O3 in hot water then to produce calcium silicate hydrate. Therefore, lime is also the main resource of strength. Effective calcium oxide of lime should not less than 65%; over 80% is perfect and should accord with JC/T621-1996.

 

Gypsum: Gypsum is the foaming regulator in AAC which dispels quicklime and postpones slurry’s densification.

Aluminum paste and powder:  There must be foaming materials working as foaming agent making air holes to form porous structure.

Physical characteristics of AAC block:

B04 grade:      average density 400 – 425 kg/m3,    pressure 2.0 – 2.5 Mpa
B05 grade:      average density 500 – 525 kg/m3,    pressure 2.5 – 3.5 Mpa
B06 grade:      average density 600 – 625 kg/m3,    pressure 3.5 – 5 Mpa

 

Workers arrangement: (only for reference, depend on local condition)

 

 

AAC block size:

Raw material storage

Sand, cement, lime, gypsum, aluminum paste should be stored separately in the materials
stock yard, transport them to workshop when use them.
Silica sand is transported from the storage silos to be ground into fine sand slurry dispersed in a wet ball mill, and then stored in the sand slurry Silo with agitator and density measurement
It is important to constantly and continuously keep the specified density and adjusted either manually or automatically.

 

 

Dosing and mixing

 

The sludge of sand, the return sludge, lime, cement, gypsum, aluminum agent and water are determined automatically in accordance with the prescription of respective product in the mixer.

 

Molding, Fermentation and Demoulding

 

Pouring:

Pouring mixer, each time pouring will control within 5 minutes, max 5.5 minutes.
Now we use Germany AAC-concept design, the pouring time could control within 5 minutes.
5 minutes x 167 mould = 835 minutes ≈ 14 hours ≤ 22 hours.

Pre-curing, fermentation:

Usually the pre-curing time will be 3 hours in one cycle, per day we can have 7 cycle times pre-curing (within 22 hours), so 167 mould ÷ 7 cycle = 24 mould per cycle.
The minimum we need is 24 mould to working in pre-curing room per cycle, because moulds
need to return, oil painting and maintenance, so we add extra 2 moulds (total 26 moulds) to guarantee the production.
In order to guarantee the pre-curing time and efficiency, the pre-curing room is
designed in ferry cart two side by two lines, in order to send or take out each of mould.

 

A certain amount of mass from the mixer will be paid into an oiled mold consisting of two parts and extremely tight seal. In this mould, the cellular concrete cake ferments approx.
2.5 – 3 hours in a 50 – 55 °C heated fermentation chamber, in order to cure at temperatures well defined.
The mould has been specifically designed for the switching operation is then performed. It consists of a torsion-free structure with tapered sidewalls and being removable from the top. This will remove the cake from the mould smoothly and flawlessly. The bottom of the mould and the walls always join accurately, so as to form a perfect unity.
The mold shrinkage of the bottom of the forms – also called stripping – and subsequent transport is performed by means of a gantry system. The green cake is the subject of very few manipulations – gently – so that damage such as cracks that are later seen elsewhere after autoclaving does not arise.