The quality of refractory castables is the basis for improving the service life of the refractory materials at the rotary kiln head. One of the most important indicators of its quality is the refractory degree (also known as the maximum operating temperature). Under the same conditions, castables of good quality (high refractoriness) are more durable than castables of poor quality (low refractoriness). Through quality and performance comparison, brown corundum-mullite wear-resistant castable was selected. Its quality indicators are shown in Table 1. When using mullite castable with a maximum temperature of 1550°C, its service life is only 3 to 5 months; when switching to brown corundum-mullite castable with a maximum use temperature of 1780°C, its service life reaches 12 months is more than three times the service life of the original refractory castable.
Construction quality of refractory castables at kiln head
The construction quality of refractory castables at the kiln head is a very important link to ensure its service life, including the reasonable ratio of materials and water, the reasonable selection of anchor hook materials and the improvement of the anchor hook structure.
01 Reasonable ratio of ingredients and water
The proportion of water in on-site construction is very critical. When pouring on site, a forced mixer should be used to stir it for 1 to 3 minutes. After the mixture is evenly mixed, add water for mixing. The amount of water added is based on the mass ratio (Material: Water = 100: (5.0 ~6.0)), and the vibration pouring construction can be carried out after mixing for 1~3 minutes.
Clean water should be used for stirring refractory materials, and its pH value is 7~8. The mixed material should be poured within 30 minutes to achieve the best performance of the material.
02 Reasonable selection of anchor hook materials
In order to solve the problem of the refractory castables at the kiln head being damaged too quickly, steel fiber refractory castables once appeared. When pouring the castables, the broken steel wires were mixed and stirred together according to the manufacturer’s requirements, and then poured. After molding and demoulding, the aggregate of crushed steel wires is evenly distributed in the castable to enhance its mechanical strength. This type of refractory castable is called steel fiber refractory castable. However, since this effect on mitigating the damage to the protective layer is not obvious and it brings a lot of trouble to the construction, it has been used less recently. Nowadays, the refractory castables at the kiln head mostly use heat-resistant stainless steel anchor hooks as welding aggregates. This material takes into account the corrosion resistance and heat resistance of the base material.
In order to enhance its own mechanical strength, the rotary kiln anchor hook is made of stainless steel lCr18Ni9Ti with a solid solution temperature of 920~1150℃ and a heat treatment temperature of 850~930℃. Because the material of the kiln head ring iron is Q235, and the stainless steel lCr18Ni9Ti anchor hook is welded with Q235, it is in line with the requirements that the alloy content of the butt weld of austenite and dissimilar steel should not be lower than the content of the austenite side base material, and the welding rod The model is changed to A307, so that the welding quality of the anchor hook is further optimized.
03 Effective improvement of anchor hook structure
The kiln head anchor hook was originally made of polished heat-resistant stainless steel and was directly welded to the kiln head ring iron. After the refractory material was poured and put into use, the anchor hook was subject to thermal expansion. Since there was no expansion space, the service life of the refractory material was affected. For this reason, after the anchor hook is made, a snakeskin tube with a diameter of 10 mm is put on, which eliminates the disadvantage that the anchor hook has no room to expand when heated. Practice has proved that the improvement of the anchor hook structure solves the problem of rapid damage to the refractory castables at the kiln head, and also plays a very good role in extending its service life.