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
accelerated.
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. Damaged.
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 llight
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 to crack.
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.
