Solutions for the Damage of Refractory Castable

July 06, 2018

1.Choose anchor material and electrode material correctly,avoid anchor parts falling off.

Because the steel plate,anchors and welding rods are not of the same material,the thermal expansion at each location is inconsistent during the use of heating,resulting in a huge thermal stress,which can easily lead to cracking of the solder joints,which caused the anchors to fall off together with castables. Therefore,when choosing the anchor and welding rods,be sure to use the same material as the steel plate of the kiln equipment to avoid the cracking of the solder joint due to different expansion.In addition, try to use a single anchor with more solder joints or increase the length of the solder joints to improve the soldering firmness.If the ‘Y’ shaped anchor can be replaced by ‘L’ shape, or even the ‘L’ shape can be crossed into an ‘X’ shaped welding, the anchor ability of the anchor material when the castable is very thin can be increased to prevent falling off.

2. Improve the thermal shock properties of castable or use castable with better thermal shock stability

The castables with corundum as aggregate have good high-temperature wear resistance and good resistance to liquid-phase attack,but the corundum based castable does not have microcracks and large internal pores,its thermal shock resistance is relatively poor compare with other aggregate. After the corundum mullite composite refractory castable is applied,the thermal shock resistance of the casting is significantly improved.

3.Improve the quality of castable,increase heat capacity and reduce the amount of temperature fluctuations

The internal thermal stress of castable is caused by the great change in the heat of the castables, and affects Q of the castables, mainly in three aspects: mass m, the heat capacity Cp and the temperature difference ΔT, Their relationship Q=m·Cp·ΔT. Increasing the mass and heat capacity or reducing the temperature difference during use can all make the heat change gradient of the castable material under the same heat transfer conditions slow down, and greatly reduce the thermal stress damage.The use temperature of the castable part is determined by the firing system and will not change much during the entire process.Similarly,the heat capacity is a property of the castable itself.The heat capacity value is the same for the same castable,and the heat capacity values of the castables with similar properties are also not much different.Therefore, the most effective way is to increase the amount of heat enthalpy of the castable by raising the quality of the casting,to achieve the purpose of reduing temperature fluctuations.

Improving the quality and volume of the castable can also increase the overall mechanical strength of the castable refractory, so as to redcue the mechanical stress damage caused by the deformation of some castables in the operation process. For example, in Dec 2017, a company made technical transformation for the castable for a 5000t/d rotary kiln production line,which greatly increased the axial pouring length of the kiln, from the original 600mm lengthened to 1000mm, make the actual quality of the castable refractory was 50% higher than the original.After transformation, the service life of castable of the kiln has increased to 1 years or more compared to the original average less than 3 to 5 months or less. 

 4. Improve construction quality

Before castable construction,the work area and surrounding environment must be kept clean in order to prevent non clean material from polluting the refractory materials. Construction tools and equipment should also be kept clean.If a more common hydraulic refractory castable material is used,the corresponsing fluidity is poor under the water amount that satisfies its strength,which has a certain impact on the construction. Any increase in water based on this will reduce the castable refractory strength.Therefore,some operators arbitrarily increase the amount of water to facilitate the construction,resulting in a decrease in the performance of the castable pouring. Besides the addition of water, there is stirring time to affect the fluidity of castable refractory. 

The fluidity of the castable will start to work after stirring for a certain period of time.(about 3 min), so it must be operated according to construction instructions of the refractory castable.This requires that before and after the construction,the factory must check the working procedures of every specific step in the masonry process. The fluidity of the castable will start to work after stirring for a certain period of time.(about 3 min), so it must be operated according to construction instructions of the refractory castable.This requires that before and after the construction,the factory must check the working procedures of every specific step in the masonry process. 

In addition, curing and baking are also important factors which affecting the performance of castable refractory. The curing is to give the binder in castables a solidification and hardening time,and obtain enough initial strength. The key to control the curing period is the humidity of castables(should be kept moist), curing temperature (at 15~35℃) and time.The roasting process is that after the castable are hardened,the ramaining water is evaporated, and the sintering process is promoted at high temperature to further improve the physical properties of the castable.The main control in the baking process is the heating rate,which is generally 15 to 35℃ per hour. Once the temperature rise begins,the heating process can not be interrupted or stopped until the temperature rise ends. Otherwise, the furnace lining should be cooled very carefully, and when the temperatures is reheated, it must be carried out according to the prescribed procedures.

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