Refractory castable is a kind of amorphous refractory material. Because of its simple production process and convenient construction, it is widely used in cement industry. At present, it is mainly used in the deformed front and rear kiln, cooling machine, preheater cyclone cone and feeding pipe, as well as some complicated shapes in the three air pipes that are difficult to lay refractory bricks. In recent years, some enterprises are gradually replacing those parts of the brick that are easy to collapse (such as the mixing chamber) with castable, so that people pay almost as much attention to the construction of refractory castable as to the masonry of refractory bricks in the kiln. However, due to various reasons, some accidents such as spalling and bursting occur during the use of refractory castables. QUNHUI believes that the main factors affecting the use of refractory castables are as follows:

(1) Design and construction quality of anchoring parts

For castable linings, the anchors (pegs) are the basis on which they are attached to the housing. Its design and construction quality directly affect the service life of refractory castable, often encountered in the production of the anchor material selection or design equivalent diameter is too thin problems, which may make the anchor can not withstand the force of refractory castable at the use temperature and soften deformation, resulting in the collapse of the whole block accident. Similarly, if the arrangement of the anchor is too dense or the bang expansion joint is too small, there will also be internal stress caused by the mismatch of thermal expansion between the refractory castable and the anchor during heating, which will lead to loose spalling of the refractory castable in serious cases. Some enterprises ignore the welding quality when welding the anchor parts (such as severe oxidation of the shell and unqualified welding quality), and also make the castable accident after a period of use. Therefore, when designing and constructing anchorage parts, the material, form and arrangement should be selected according to the specific conditions such as the use temperature, thickness and use position of refractory castable, and the expansion joint reservation and welding quality of anchorage parts should be handled well.

(2) Moisture content in refractory castable construction

Refractory castable is composed of refractory aggregate, fine powder and binder, but many of its properties depend to a considerable extent on the variety and quantity of the binder. However, many refractory castables have been equipped with high aluminum cement at the factory, and the only parameter that can be adjusted during construction is the amount of added water, so controlling the amount of added water is the key to ensure the strength of refractory castables. The factors affecting the amount of water added in actual construction are mixing time and vibration technology level.

When mixing, a forced mixer is generally used, which should be dry and evenly mixed before adding about 80% water for 2-3min, and add the remaining 20% water according to the dry and wet conditions, until the fluidity meets the vibration requirements, the total time should be no less than 5min.

The addition of water does not begin to play a role until 3 minutes after stirring. This period of time is generally about 3min for the plain material, and about 3.5min for the steel fiber reinforced type. For some units, the whole process from adding water to discharging vibrating is only 3min, or even shorter. In this way, although the construction progress can be accelerated, the water added is much more than the reference water. In addition, in the process of vibration, excess water is discharged with fine powder, which changes the reasonable grading of particles and increases the porosity of castable, thus affecting the strength of castable. On the other hand, the level of vibration also affects the amount of water added. Unskilled vibrator, in order to vibrate the homogenate layer, requires high slurry fluidity, increase the amount of water under the same conditions, therefore, the construction of refractory castable to strictly control the amount of water, and arrange skilled vibrator construction, for the castable to play its excellent performance to lay a good foundation.

(3) Maintenance of castable

Maintenance is one of the important factors affecting the performance of castable, and it is also the most easily ignored factor. Curing is to give the binder in the castable a time to set and harden so as to obtain sufficient initial strength. The curing system is related to the binder type of castable. The hydration speed of high aluminum cement is fast, the hydration heat after forming is mostly concentrated in the release within l0 hours, the heat is concentrated, the internal heat is not easy to dissipate, and it is easy to evaporate the water necessary for hydration of the cement near the surface, preventing its continued hydration, and it is also easy to destroy the castable body due to internal stress. Therefore, after the construction of castable should be timely maintenance, depending on the specific situation to decide whether to remove the mold or not, maintenance, can be wet sack or wet mat covered on the castable surface and timely sprinkling water to keep wet state, for the inconvenient part (such as the wall, the top wall) can be sprayer on the castable surface water maintenance. The maintenance time is not less than 2 days, and the first 24 hours should be frequently sprayed. In production, it is often found that some enterprises shorten the maintenance time in order to one-sided pursuit of output, or do not maintain at all, which often causes problems in the back of baking, which is inadequate.

(4) Baking of refractory castable

Baking is the most direct and critical factor affecting the performance of refractory castables. Baking is to remove more free water and chemically bound water. Proper baking can improve the service life of refractory castable; However, if the baking is not proper and the temperature rises too fast, the refractory castable will crack, flake or even burst due to the poor moisture removal. In order to blindly shorten the baking time as soon as possible, many enterprises have a refractory castable explosion accident, but delay the feeding time.

For the castable in the preheater, it can be baked together with the refractory brick in the kiln on the basis of ensuring the slow temperature below 600 ° C, otherwise it must be carried out separately. For the new construction castable in the cooling machine, it is best to bake with a drying lamp or wood, and take measures to reduce the two or three air temperatures after feeding, so as not to heat up too fast, and the temperature difference between the inside and outside the castable is too large, resulting in internal stress resulting in accidents.