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Cement Refractories

Nedmag is one of the few producers in the world capable of producing DBM with a purity close to 99%. Most DBM suppliers do not get beyond a purity of 97%. High purity leads to better refractory properties

Using , you can produce magnesia spinel bricks for the rotary kiln which can withstand the highest levels of mechanical, chemical and thermal stress.

purity

  • high magnesia oxide content
  • low lime content
  • zero free lime content
  • low level of impurities

Thermal stress can be caused by local overheating, especially in the first lining zones, when using alternative fuels. This has a weakening effect on the microstructure of the brick. The effect is reduced by using a high-purity raw material. nedMag 99 has a high magnesium oxide content (98.5% MgO), combined with a low silica content (0.12% SiO2) and a high lime/silica ratio (>4:1). Since no low melting phases are formed, this results in very good resistance to high temperatures.

Chemical stress created by corrosion can lead to a weak microstructure and to spalling of the magnesia spinel brick. Using high purity Dead Burned Magnesia with a high magnesium oxide (98.5% MgO) content and low lime content (0.74% CaO) limits the risk of corrosion. Using in magnesia spinel bricks leads to reduction of spalling phenomena in the rotary kiln.

A magnesia spinel based brick is not sensitive to the formation of low melting calcium aluminate phases in the lining of the rotary kiln during clinker production.

The absence of free lime results in a highly hydration-resistant product. Both the magnesia sinter and the magnesia spinel brick made from have a long storage life.

But it is not only a high MgO content which is important for good refractory properties. These can also be affected by the chemical composition of the remaining impurities. The composition of is beneficial thanks to a high lime/ silica ratio and a low and properly controlled boron level.

Mechanical stress like erosion may lead to abrasion of the magnesia spinel brick. A high lime/silica ratio promotes the formation of high melting tri-calcium silicates (>1,900.C). High melting phases increase the abrasion resistance of the brick. Using with a high magnesium oxide content and high lime/silica ratio (>4:1) results in less abrasion of the magnesia spinel brick in the rotary kiln.

Too much boron in the magnesia sinter causes the formation of low melting phases with calcium oxide in the magnesia spinel brick. This makes the brick more sensitive to high temperatures. Using with a low and properly controlled boron level (0.01% B2O3) prevents the formation of low melting phases in the magnesia spinel brick.

An unfavourable microstructure in the raw material can easily lead to weak spots in rotary kiln bricks. For this reason, Nedmag Industries’ synthetic production process generates a fine, homogeneous structure of the DBM.

microstructure

  • optimum crystal size: 70 µm
  • very homogeneous microstructure due to the synthetic process
  • low porosity and homogeneous distribution of small pores (1-2.m)
  • high density: minimum 3.40g/cm3

In a rotary kiln, different kinds of mechanical stress occur. This can cause mechanical tensions within the magnesia spinel bricks, leading to spalling of the bricks. The optimum crystal size of (70 µm) increases the elasticity of the brick and reduces spalling.

has a high density of minimum 3.40 g/cm3 and a homogeneous distribution of very small pores. This results in magnesia spinel bricks with a very low permeability which limits gas and alkali infiltration. This gives a longer life in severe conditions where alternative fuels are used.

Due to the synthetic production process, Nedmag is able to produce a product with a very consistent composition. This makes easy to handle in the production process of the magnesia spinel bricks.

Due to its composition and characteristics, based refractories are better able to withstand extreme stress, of whatever kind. This makes them ideally suited to kilns fed with alternative fuels. Using in the upper and lower transition zones optimises the operating conditions of the rotary kiln and increases its practical value.

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