Introduction of the performance and production process of
refractory magnesia carbon brick
Magnesia carbon brick is a refractory material made of
high-melting-point alkaline magnesium oxide (melting point 2800 °
C) and high melting point carbon material which is difficult to be
infiltrated by slag, adding various non-oxide additives and
combining carbonaceous binder. Magnesia carbon bricks are mainly
used in converters, AC arc furnaces, linings of DC arc furnaces,
slag lines of ladle, and the like.
Magnesia carbon brick Usually, the melting loss of magnesia carbon brick is carried out
by reacting magnesia with slag on the working surface. The melting
loss rate depends on the nature of the magnesia itself and on the
size of the magnesia particles. Larger particles have higher
corrosion resistance, but they are more likely to escape from the
working face of the magnesia carbon brick to the slag. Once this
happens, the rate of damage of the magnesia carbon brick will be
Magnesia carbon brick The absolute expansion of large particles of magnesia is larger
than that of small particles. In addition, the expansion
coefficient of magnesia is much larger than that of graphite.
Therefore, in the MgO-C brick, the large particle/graphite
interface of magnesia is produced at the interface of small
particles/graphite of magnesia. The stress is large, and the crack
generated is also large, which indicates that the critical grain
size of the magnesia in the MgO-C brick is small, which has the
effect of relieving thermal stress.
Magnesia carbon brick From the aspect of product performance, the critical particle size
becomes smaller, the open pores of the product decrease, and the
pore diameter becomes smaller, which is beneficial to the
improvement of the oxidation resistance of the product; at the same
time, the internal friction between the materials is increased, the
molding is difficult, and the density is lowered. Therefore, in the
production of MgO-C bricks, it is very difficult to generalize the
critical particle size of magnesia-silica. It is often necessary to
determine the critical particle size of the magnesia based on the
specific conditions of use of the MgO-C brick. In general, MgO-C
bricks used in places with large temperature gradients and intense
thermal shocks need to choose a smaller critical particle size;
while those requiring high corrosion resistance, the critical grain
size required is required.
1. Magnesia fine powder Magnesia carbon brick
Magnesia carbon brick In order to maintain the overall uniformity of the thermal
expansion of the particles and the matrix portion of the MgO-C
brick, the matrix portion needs to be mixed with a certain amount
of fine powder of magnesia, and also the structure maintains a
certain integrity after partial oxidation of the matrix.
However, if the fine powder of magnesia is too fine, the reduction
rate of MgO will be accelerated, thereby accelerating the damage of
the MgO-C brick. Magnesia sand less than 0.01mm is easy to react
with graphite, so it is best not to mix such too fine magnesia when
producing MgO-C bricks. In order to obtain MgO-C bricks with
excellent performance, the ratio of magnesia to graphite of less
than 0.074 mm in MgO-C bricks should be less than 0.5, and if it
exceeds 1, the porosity of the matrix portion is sharply increased.
2, the amount of graphite added Magnesia carbon brick
Magnesia carbon brick The amount of graphite added should be considered in combination
with different bricks and different parts of the brick. In general,
if the amount of graphite added is less than 10%, it is difficult
to form a continuous carbon network in the product, and the carbon
may not be effectively exhibited; the amount of graphite added is
more than 20%, the molding is difficult during production, cracks
are easily generated, and the product is easily oxidized.
Therefore, the amount of graphite added is generally between 10%
and 20%. According to different parts, different amounts of
graphite are selected. The melting loss of MgO-C bricks is governed
by the oxidation of graphite ink and the dissolution of MgO into
the slag. Increasing the graphite can reduce the erosion rate of
slag, but it increases the oxidation of gas phase and liquid phase.
3, mixing Magnesia carbon brick
Magnesia carbon brick The graphite is light in density and tends to float on top of the
mix during mixing, making it incompletely in contact with other
components in the furnish. High speed mixers or planetary mixers
are generally used. When producing MgO-C bricks, if the feeding
order is not paid attention to during the mixing, the plasticity
and formability of the slurry will be affected, thereby affecting
the yield and performance of the product.
Magnesia carbon brick The correct order of addition is: magnesia (coarse, medium) → binder → graphite → magnesia powder and additives mixed powder.
The mixing time varies slightly depending on the mixing equipment.
If the mixing time is too long, the graphite and the fine powder
around the magnesia are easily peeled off, and the mud is dried due
to the large amount of solvent in the binder; if it is too short,
the mixture is uneven and the plasticity is poor, which is not
favorable for molding. .
4, molding Magnesia carbon brick
Magnesia carbon brick Molding is an important way to increase the packing density and
densify the structure of the product. Therefore, high-pressure
molding is required, and the pressing is strictly carried out
according to the operating procedure of light weight, heavy weight
and multiple pressurization. When producing MgO-C bricks, the
density of bricks is commonly used. Controlling the forming
process, the higher the tonnage of the general press, the higher
the density of the brick, and the less binder required for the
mixture (otherwise, due to the shortening of the distance between
the particles and the thinning of the liquid film, the bonding
agent is partially localized, resulting in several The structure of
the product is not uniform, which affects the performance of the
product and also causes the elastic aftereffect to cause the brick
5, hardening treatment Magnesia carbon brick
Magnesia carbon brick The phenolic resin-bonded MgO-C brick can be heat treated at a
temperature of 200 to 250 ° C. The resin can be directly
(thermosetting resin) or indirectly (thermoplastic resin) hardened
to give the product a high strength, and the general processing
time is 24 ~32h, of which 50~60°C needs to be kept warm due to
resin softening; 100~110°C needs to be kept warm due to large
amount of solvent evaporation; 200~250°C needs heat preservation
due to condensation hardening of the bonding agent.