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Showing posts with label Bulk Density. Show all posts
Showing posts with label Bulk Density. Show all posts

Bulk Density of Refractory Samples

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19-July-2020

Bulk Density of Refractories

This property is important for both insulating and dense refractories (shaped and unshaped). Bulk density (B.D.) is the ratio of the mass of the refractory specimen to the bulk volume of the same or in other words it is the weight per unit volume the refractory (including the volume of the pore space present in that refractory sample).

There are two methods for determination of Bulk Density in case of refractories:


1. Direct measurement method

B.D.= (Weight of the specimen in gm.) ÷ (Volume of the specimen in cc)

2. Direct volume determination method

B.D (gm/cc) = (Dry weight) ÷ (Soaked weight - Suspended weight)

https://www.industry.guru - representative image
Fig: Refractory Shapes (PCPF)
Out of these two methods the ‘direct volume determination method’, which is generally used for irregular refractories, gives more accurate results. The nearer the Bulk density approaches the Specific Gravity the lower is the Porosity. Lower B.D indicates higher porosity, lower strength of the refractory material. The BD will also affect other properties of the refractory such as the load bearing capacity and thermal conductivity etc. Unless there is any specific reason, the aim of a refractory manufacturer is to produce products of higher Bulk Density. The ultimate Bulk Density of the product will depend on a number of factors like - type of raw materials used and their processing, process control at every step during green manufacturing and firing etc.



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

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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.



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