Reasons for the Damage of Refractory Castable

July 05, 2018

1. The castable refractory in the cement kiln

Refractory castables are widely used in cement industry due to their low production cost and convenient construction. At present,it’s mainly used in the preheater,feeding pipes, front and rear kiln,tertiary air ducts and cooling machine,which are complex and difficult to brickwork.The normal service life is usually more than one year.

2.Abnormal damage in use

The castable at the top of the grate cooler is abnormally dropped,such as falling off after several hours of production, then the steel plate is roasted,the rotary kilneye castable service life would be short. If a cement plant is less than three months,obvious damage occurred,first,the end face appeared detached,the main body showed slight cracks and a little shedding.As a results, there will be larger cracks and obvious lumpy shedding occurred in the short term. All these results caused maintenance of the kiln and shut down,which will affect production.

3.Analysis of abnormal damage

3.1 The drop of anchor caused the castable refractory shedding

The anchorage plays a role of tightly sticking to the container wall during the use of castable,maintaining in the integrity of the castable body and increasing the bending resistance of castables. In the parts of the castable fell off, it’s found through inspection that the anchors were removed from the roots in many places,and only a few welding spot marks are retained,which was obviously caused by the open welding of the dowels at the solder joints.Pieces fall off.

3.2 Repeated and severe changes in temperature cause rapid deterioration of castables

The thermal shock stability of the castable refractory is poor,and severe temperature changes can easily cause damage.For example, the cooling zone of a rotary kiln(especially the kilneye),it is not only subjected to constant erosion of the clinker,but also continuously subjectd to secondary wind and high temperature clinker in the kiln,the kiln lining material is sometimes buried under high temperature materials and sometimes exposed to flame,causing the surface temperature of the lining material to change contemporaneously with the rotation of the kiln,with a temperature difference of more than 200℃,affecting the depth 15 to 20mm,according to the kiln speed 3.5r/min, the changes temperature rise and fall repeatedly caused thermal fatigue of the surface layer of the castable. If the cold kiln,this temperature change is more severe. They are all cause of the castable refractory damage. It can be found out during the inspection and surface of the remaining part of castable has the phenomenon of exfoliation and dropping in the 20 to 50mm depth range, which is mainly caused by thermal fatigue. Jundao provides you high quality refractory materials.

3.3Construction reason

Castable refractory have a strict construction requirements and must be operate in accordance with this requirement to ensure good physical properties of the castables. For example,a company decided to replace the castable refractory at the top of high temperature zone of grate cooler. In order to ensure the projects is put into operation according to the scheduled plan, the construction team adopts the overall pouring method. Expansion joints are not set aside as required. At the same time, in order to facilitate the construction, the amount of water used is obviously larger than the required amount. What is more serious is that once the construction is completed, it will be ignited and heated up,and it will be fed on schedule. Jundao Believes that due to rapid temperature rise,resulting in a sharp increase in the temperature of castables, a large number of rapid internal evaporation of water, resulting in a larger expansion stress, which makes the pouring material burst and exfoliate,causing large area fall accidents.

The above operation obviously violates the construction requirements of refractory castable. First, water amount not controlled well, and the effect of water addition on the strength of castables refractory is very large. Second,no expansion joints are reserved (should be kept at about 1.5m each at intervals),which will inevitably produce a large expansion force in the temperature increase.   

3.4 Kiln abnormal operation

The abrupt change of temperature is often found in other production conditions such as ignition or kiln and kiln coating shedding,which caused the pouring material to produce huge internal stress and damage due to thermal fatigue.In areas where aire cannos are installed, the life of castable refractory at this location is reduced due to the frequent opening and stopping of air cannons. In addition, the huge mechanical stress generated during the operation process of the rotary kiln due to the deformation of the cylinder body caused the kiln liner to be subjected to periodic pressure and loose pressure, resulting in the deep damage of the whole castable refractory.

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