Refractory castables and measures to improve their service life

Refractory castables and measures to improve their service life

01. Frontier Overview

With the development of new dry cement production technology, the corresponding refractory materials have also made great progress. In addition to the breakthroughs in conventional refractory bricks, the performance of refractory castables has become more and more perfect, and is widely used in amorphous parts of kilns. As we all know, refractory castables are a kind of amorphous refractory materials that have not been calcined. They are made of refractory aggregates, refractory powders and binders in a certain proportion; during construction, they have good fluidity after adding water and stirring, and then they are formed and cured (baked at a certain temperature system) to make them solidify and harden. The use characteristics of refractory castables are as follows: First, the masonry structure has few joints, strong integrity, good sealing, and can avoid the infiltration of clinker powder during application and operation; second, it is easy to anchor and convenient to construct, which is conducive to improving masonry efficiency and masonry quality; third, the raw materials are widely available, which is convenient for comprehensive utilization of resources, and the delivery time is short, which can reduce inventory and related costs accordingly. Based on these advantages, the application ratio of refractory castables in cement burning systems has increased year by year. Taking the 5000t/d new dry kiln as an example, the ratio of refractory castables to refractory bricks has reached 1:1.

02. Measures to speed up the service life

Refractory castables are generally a kind of high-temperature resistant concrete, so it also conforms to the theory of concrete. For example, the amount of water added is the fundamental reason for controlling whether the refractory castable can achieve the designed strength. However, driven by interests, some construction parties will add a lot of water to the casting material to speed up the construction progress during the construction of refractory castables, which leads to the service life of the kiln refractory lining after construction being much lower than the design requirements, and even serious problems have occurred after half a year of use, and it must be overhauled (while the well-constructed refractory castables do not need overhaul for 3 to 5 years). We know that the investment in refractory materials accounts for a small proportion of the entire plant construction investment (about 2% to 4%), but its impact on the future operation of the entire system is very large. The loss of one day's shutdown due to a refractory lining accident can be as low as hundreds of thousands or even millions of yuan, so ensuring the high operating rate of the firing system can achieve high-quality, high-yield and low-consumption operation of the system.

03. Strictly implement the following regulations

(1) The amount of water added to the castable must be strictly controlled in accordance with the instruction manual and must not exceed the limit. Under the premise of ensuring the construction performance, it is better to add less water rather than more.

(2) The mixing time of the castable should not be less than 5 minutes. A forced mixer should be used during operation. When mixing, it is better to dry mix first, then add 80% of the amount of water, and then slowly add the remaining water depending on the dryness and wetness until a suitable working consistency is obtained.

(3) The castable material poured into the mold frame should be immediately vibrated in layers with a vibrator. The height of each layer should not exceed 300mm, and the vibration interval should be 250mm. When vibrating, try to avoid touching the anchors, do not damage the insulation layer, do not vibrate or re-vibrate the same part for a long time, and slowly withdraw the vibrator after seeing the slurry on the surface of the castable to avoid segregation and voids in the castable layer.

(4) When pouring a large area, it should be constructed in blocks. The pouring area of each block should be about 1.5m². The expansion joint should be set according to the design and should not be omitted. The expansion joint should be set in the middle of the anchor interval.