Green BD (Bulk Density), Burned BD and Moisture Content of Green Mixture (Powder) of Alumina Refractory Bricks

Before going into large scale production of any product, based on their R&D work and the results obtained from pilot scale production laboratory has to fix certain parameters (recipe of production for that product) and provide it to the production department which the latter will follow in order to meet the required specifications and quality of that product. Two such important parameters required for manufacturing any type of refractory bricks are the ‘Moisture content’ of the green mixture (powder) and ‘Green BD’. Here our focus will be on the practical aspects of these two parameters of refractory bricks particularly those containing various percentages of alumina (Al₂O₃%). 

The amount of moisture or water present in the green mixture (powder) of alumina containing refractory bricks help in green binding and also add plasticity. But beyond a certain percentage, water or moisture present in the green mixture of refractory bricks would be harmful leading to an increase the rejection percentage mainly due to -

(i) Increase in porosity and

(ii) Development of radial cracks in refractory bricks.

Suggested Article: Effects of Compacting Pressure on Sintering and other Properties of Refractory Bricks

What should be the maximum percent of moisture, green BDs corresponding to the different values of burned BDs of refractory bricks having different Alumina content (Al₂O₃%) etc. are given in the following table:

Refractory Bricks (Al2O3%)	Moisture%	Burnt BD	Green BD	Factor (Gr.BD/Br.BD)
40.00	7.00	2.20	2.36	1.073
45.00	6.50	2.25	2.41	1.071
50.00	6.50	2.45	2.62	1.069
60.00	5.50	2.50	2.65	1.060
70.00	5.50	2.60	2.75	1.058
75.00	5.00	2.65	2.78	1.049
80.00	4.50	2.70	2.82	1.044

Related Article: Bulk Density of Refractory Samples

Refractory composition, production of Magnesia Carbon Refractory Bricks and their properties

In one of our previous posts on Magnesia Carbon refractory bricks (MgO-C), we have already discussed on the selection of various raw material ingredients required for the production of MgO-C refractory bricks with an emphasis to their grading etc. In this article we bring you one MgO-C (Mag Carbon) refractory brick composition and further guidance (tips) on its production along with the tested results of some of the refractory properties of the brick made from this composition.

Refractory Composition (Formulation) for MgO-C Refractory Bricks

Item No	Raw Materials	Grading (mm)	Quantity
1	China 97FM (Fused Magnesite)	2.0 - 4.0	18 %
2	do	0.6 - 2.0	42 %
3	do	0 - 0.6	20 %
4	China 98FM or Seawater DBM 98 HD	Flour (Ball Mill Fine)	7.5 %
5	Coarse Flaky Graphite (94% LOI)	– 0.10 (> 40 %)	12.5 %
6	Al-metal Powder		3 parts
7	Si-metal Powder		1 part
8	Liq. Resin (Durez-40)		3 parts
9	Solid Resin (Powder)		0.6 parts
10	Hexamine		0.25 parts
11	MEG (Meth. ethyl glycol)		0.6 parts

Mag Carbon Refractory Bricks - Production (Tips)

=> Mixing Sequence:

(A) First co-mix item nos. 4, 5, 6 and 7 together in a Ball Mill for at least 6-8 hrs, unload and keep separate.

(B) Mix MEG with (0-0.6) DBM fraction (item 3). Then add the co-mix powder made in step (A) to it and remix.

(C) Take (2-4) & (0.6-2) DBM grading (item no 1 and 2), add hot Resin (item 8). Mix thoroughly to get perfect coating. Add mixture made in step (B) and remix the batch intensively. Now add powder Resin (item 9) then, Hexamine (item 10) and mix it finally. Keep the mixture (powder) in closed polythene bags 35-40 kg in each bag, for ageing 8-12 hrs.

=> Heat the liquid Resin to 60-65^OC before mixing. Heating reduces the viscosity and thus help for better coating.

=> Don't use any mixture after it has dried up. Try to make mixture in perfectly pre-calculated quantities as reuse of such mixture (powder) even by adding more MEG is not advisable and should be avoided as far as possible.

=> While making any shaped brick by pneumatic Ramming it must be done continuously until the shape is complete.

=> Don't keep mixture (powder) uncovered.

=> Also read: Ideal Grain Size Distribution of Refractory Raw Materials Mixture for making Mag Carbon Bricks

Properties and Test Results

Magnesia Carbon Bricks - Properties

Properties	Results
MgO %	94 (min)
Fixed Carbon %	8 (min)
Green BD (gm/cc)	3.1 (min)
Coked BD (gm/cc)	2.95 (min)
AP % (after coked after coked in reducing atmosphere at 1000OC )	14 (max)
AP % (original condition)	7 (max)
CCS (kg/cm2)	450 (min)
MOR at room temp (kg/cm2)	140 (min)

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