Showing posts with label Apparant Porosity. Show all posts
Showing posts with label Apparant Porosity. Show all posts

May 7, 2009

Manipulating the Test Results of Apparent Porosity (AP) During Testing of Refractory Bricks

Apparent porosity (AP) is the percentage ratio of the void space in the refractory specimen to the total bulk volume of the same. AP is one of the most important physical properties for any type of refractory brick that will be certainly mentioned in its specifications. Hence determination of Apparent Porosity is almost a compulsory part of Inspection / Testing of a Refractory Lot. This property becomes more stringent when the refractory brick is of any complicated shape like, checker bricks or nozzle bricks having tongue - groove etc. In such cases often, it remains a cause of worries for the laboratory person conducting inspection.


The results of AP can be manipulated to show less AP% than what the brick has actually and thus, an inspector may be deceived by a laboratory person. But such actions or manipulation of results are undeniably wrong and liable to be penalized or even the whole Refractory Lot may get rejected, if caught red-handed.


Nevertheless, this article is not to discuss the merits-demerits or right-wrong of the action. That is for you to decide. Here I assume that you have made a conscious decision to learn the trick as how to manipulate the results of Apparent Porosity in order to show a better result of a porous brick. Having so decided, below is a guide (trick) on how you can do it:


=>> Apparent Porosity (%) = {(Soaked Wt - Dry Wt) ÷ (Soaked Wt - Suspended Wt)} x 100


=>> To show less AP% we need to increase Dry wt as much as possible.


=>> Make 30% conc. salt solution (i.e. 30gm salt in 100gm water).


=>> Example: To bring down 75 mm std. Brick having actually AP-25% to AP-18%, soak the brick in approximately 30ml quantity of above salt solution so that its Dry Wt. is increased by approx 9 gm. After applying solution from different sides and its complete soaking put the brick in the drier & properly clean itssurfaces after drying.


Better try to know the actual AP before applying/manipulating.


Types of Testing of Refractories [Read]




May 6, 2009

Apparent Porosity and True Porosity of Refractory Samples

Porosity is the percentage relationship between the volume of the pore space and the total volume of the refractory sample. Apparent Porosity does not include the volume of the sealed pores. The True Porosity includes the volume of the sealed pores also. The usual difference between the apparent porosity and the true porosity is of the order of 1 to 2 percent unless the proportion of the sealed pores is high. The true porosity figure is the higher than the apparent porosity figure as the true porosity includes the volume of the sealed or closed pores also. The difference between the two values represents the percent volume of closed pores. Porosity can be controlled by the following:

=> By controlling the texture of the brick i.e. by controlling the size distribution of the particles.

=> By the methods of green manufacturing and composition.

=> By controlling the firing temperature, soaking time etc.

=> Quality of raw materials i.e. the inherent grain porosity of the raw materials used.

Higher the porosity, lower will be the strength of the brick. Bricks with lower porosity will have greater resistance to slag attack and more sensitiveness to fluctuations in temperature. Their thermal conductivity will be more.

Hence, apparent porosity is the percentage ratio of the void space in the refractory specimen to the total bulk volume of the same. There are two methods used for the determination of apparent porosity of refractory materials which are:

=> Boiling point method, and

=> Evacuation method.

Samples (Refractory Specimen) measuring 6.5 cm x 6.5 cm x 4 cm is cut from burnt refractory bricks by a cut off wheel from within its core and cleaned any dust or loose particles adhering to its surface and are dried in an oven at 110OC to a constant weight. For graded materials take 3 to 5 mm size grains and dry at 110OC. It can be determined by following the steps given in any of the Standard Methods for Refractory Testing like - ASTM, Indian Standards (IS), Ghost, DIN etc.

True Porosity (%) = {1 - (Apparent Sp. Gr. ÷ True Sp. Gr.)} x 100

Apparent Porosity (%) = {(Soaked Wt - Dry Wt) ÷ (Soaked Wt - Suspended Wt)} x 100

>> Types of Testing of Refractories [Read]

>> Manipulating the Test Results of Apparent Porosity (AP) During Testing of Refractory Bricks [Read]