DEMAG TABLET (L)

Product Description:

Demag Tablet is the compressed powder of Potassium Aluminium Fluoride, which is a commercial grade, fused solid, inorganic salt, containing a non - stoichiometric mixture of potassium hexa fluorominate (K3AIF6) and potassium tetra fluorominate (KAIF4). This tablet is used to remove Magnesium from aluminum melt.

SPECIFICATION:

Potassium Aluminium Fluoride fused solid, inorganic salt, containing a non - stoichiometric mixture of potassium hexa fluorominate and potassium tetra fluorominate K3AIF6 and KAIF4 with typical composition and properties as follows:

Chemical composition of Tablet:

Ingredient Potassium (K) Aluminium (Al) Flourine (F)
Compostion (%) 25 - 30 18 - 20 35 - 45

Shape and Size:

Forms Std. Size (mm) Std. Weight (gm)
Cylindrical
Tablet
Dia: 70,
Height - 30

250 ± 25

Alloy Grade Density (gm/cc) Complete break time and dissolution time
(in minutes) inside melt at 720 - 750°C
Cylindrical
Tablet
Dia: 70,
Height - 30

250 ± 25

Appearance: Gray white crystalline
Absorbed moisture: 1% max.
Density : 2.7 gm/cc
Solubility in H2O at 25°C: 0.25 gm/ 100ml
Melting point: 560 - 580 °C
Decomposition: Decomposition starts slowly at approx. 615 - 700°C to KF and AIF3 (gaseous)
Flammability: Non - flammable
Reactivity: Does not react with air and moisture at normal Temperature. Contact with acid or acid fumes may liberate hydrogen.

 

No ImageOn the addition to the aluminium melt around 700 - 750°C, reacts and decomposes to KF and AIF3 (gaseous). This gaseous product helps in degassing the molten metals and it reacts with Mg (Ca & Li) and forms its fluorides as MgF2 in molten aluminium alloy.

3Mg(in liquid) + 2AlF3 2Al + 3 MgF2

Mg (in liquid) + 2KF 2 K + MgF2

The stability of compound increases with increasing negative value of Gibbs energy of formation, with a few exceptions the stability decreases from the fluoride down to the sulphides in the following order. Fluorides >chlorides>oxides>sulphides

Gibbs free energy for the formation of MgF2 has more negative value than the Gibbs free energy of MgCl2, thus MgF2 is more stable than MgCl2 into the melt and does not dissociate as MgCl2. Thus the fluorides fluxes are suitable and it's also environmental friendly than chloride fluxes.

Several useful magnesium alloy contain magnesium in quantities 0.2 to 10%. Wrought alloy such as AA3004 (can body- 1%Mg) or A15182 (can end- 4.5% Mg) containing high levels of magnesium. And casting alloy 518 and 520 contain 8 and 10% magnesium respectively. These alloys constitute a significant portion of scrap market and are therefore available for recycling/remelting. Recycler often need to produce new alloy products with lower magnesium content, and secondary smelter producing die cast and foundry ingots also need to produce low magnesium content alloy.

There are three types of damaging process 1) chlorination 2) use of tablets of fluorine/ chlorine flux 3)the injection of AIF3 or NaAIF4/Na2AIF6 , SF6,

The criteria of the selection of the flux for demagging should be on the basis of –

1) reactivity (determined by equilibrium constant of reaction)

2) stability of the reaction product(determined by thermodynamic data gibbs free enery)

3) echo friendly

As mentioned above in characteristics of Potassium Aluminium Floride tablet as it fulfils all the requirements it is used effectively as demagging flux to remove the Mg from aluminium alloy melt (in place of chlorine gas). The active fluorides in the melt react with Mg and forms Magnesium fluoride. It can also help to remove other alkali and alkaline metal as Ca and Li.

The addition of Demag tablet is done in 1:8 ratios i.e. Add 8kg of Demag tablet in order to remove 1 kg of magnesium form Al melt. This ratio holds only for higher composition of Mg (i.e Mg > 0.3 %) into Al melt and Mg target removal up to 0.3 - 0.2%. To remove Mg below 0.2% is little bit difficult and for this the addition rate can go higher. The addition rate can followed as:

Mg content in the Al melt (%) Target Mg content into the Al melt (%) Addition rate ratio i.e. (addition of Demag Tablet to remove 1 kg of Mg)
Mg> 0.3 0.3 1: 8
Mg>= 0.3 0.2 - 0.1

1:12 to 1:13

The following guide to the efficient use of Demag Tablet for alloy additions in Aluminum cast houses.

Wait until the Aluminum bath has reached a holding temp of approx. 700°C to 750°C dissolution will be slower at tower temp. For better performance addition of Demag Tablets can be made as follows:

1. Move any dross which has build up on the surface of the melt to the sides of the furnace. This will allow the tablets to sink quickly under Aluminum melt and react efficiently.

2. Add the tablets at different points around the furnace to ensure an even distribution.Hold the bath for    at least half an hour to ensure complete dissolution and complete reaction.

3. Once the Demag tab dissolved, stir the furnace thoroughly, preferably from bottom of the bath to the Top. This will ensure maximum efficiency and uniformity of reactions with Mg through out the area.

4. Both temp and composition can be checked before casting begins.

Tablet wrapped with AI foil or plastic shrink and pocked in corrugated box. Each box contains   10 Kg or 15 of Material. Pocking can also be changed as per customer requirement.

Use dry place to store material.

Material Safety Data Sheet can be supplied on demand.