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In recent years, with the increasing use of refractory castables in the market, various use problems have begun to appear, among which the problems involving castable cracking account for a large proportion. Compared with the previous refractory materials, the construction process of the castable is relatively simple, and the baking time is not long. So what are the reasons that many users report that the castable will crack after baking? The following is a brief analysis of Zhengzhou Anrui Refractory.

Reason 1. Unreasonable structural design

The expansion joint design of refractory castable is unreasonable. The number of circumferential and longitudinal expansion joints is not enough. After the boiler runs, the materials are heated, the volume expands, squeezes each other, and cracks occur. The expansion joints of the wear-resistant refractory castable at the entrance of the cyclone separator and the refractory brick were changed to 1cm, and sufficient clearance was reserved to meet the expansion requirements. The expansion joint is changed to a Z shape to prevent boiler ash from penetrating and washing away the insulation layer. Expansion joint filler material requires refractory fiber blankets on both sides to prevent refractory mud from immersing in the filler material. The filling material requires rigid plywood to prevent deformation during shock. After the boiler runs, the plywood burns at high temperature, and the space becomes an expansion joint.

The nail, air distribution plate, slag discharge pipe and air pipe are metal materials, and the expansion coefficient after heating is much greater than that of the refractory material. If pretreatment is not performed, a network crack will form on the contact surface between the metal and the refractory material. Cause cracking and falling off. When the refractory material contacts the metal surface, it is necessary to remove oil stains and ash stains, and evenly apply asphalt of 1 mm or more. To ensure the concentration of asphalt and the thickness of the application, it is absolutely forbidden to replace asphalt oil with asphalt paint.

Reason 2. Unreasonable construction process

The "grey water ratio" of the castables is not well controlled during mixing. Too much water is added, the porosity inside the material is high after the casting material is formed, the strength of the material is reduced, the natural setting time is too long, and the curing time is extended. Too little water is added, the material has poor fluidity, the vibration is not dense, it is easy to leave pores, caves, etc., and the strength will be greatly reduced.

The mixing time and vibration time are not well controlled. The mixing time is too short, the material is mixed unevenly, not dense, and the strength is reduced; the pouring of the casting material should be shaken in layers by a vibrating machine. If the vibration time is too long, the material is prone to delamination, the fine powder floats on the surface, and the aggregate sinks to the bottom, resulting in a reduction in the strength of the material and easy peeling. The castable is used up within 30 minutes after mixing, and it should be poured to the specified thickness and height at one time. Castable construction should be carried out in an environment above 5 ℃, because the temperature is too low, the material is not easy to solidify, even if it is solidified, it is also a phenomenon of false solidification. The castable should generally be continuously cast. Before the initial layer of castable is set, The next layer of castable should be poured. If the construction gap exceeds its initial setting, the construction joint shall be treated.

The demoulding time is not well controlled. The castable is demolded before it has hardened. It should be removed only when the strength of the castable can be ensured and its edges and corners are not damaged by demoulding. The load-bearing formwork should be demolished only when the castable reaches 70% of its strength. To facilitate demoulding, all casting surfaces of the molds should be coated with a layer of engine oil before pouring.

Reason 3. Poor quality of castable

The matching and bonding of aggregate and matrix in refractory castables have a very important effect on the wear resistance of the material. If the bond between aggregate and matrix is poor, it will cause the matrix to be eroded first during erosion, and then only left Aggregate condition, and then shedding. If this is the case, no matter how good the abrasion resistance of the aggregate is, it will eventually crack. In addition, if the castable has passed the storage period, the material will fail, some materials will be improperly stored, and will deteriorate due to moisture, which can also cause later cracking.