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Yingkou Yanshi Mining Co., Ltd

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Address: Daling Village, Guantun Town, Dashiqiao City, Yingkou City

The reason for the crack of casting light powder in boiler furnace

2023-02-06 14:53:10

It is a dangerous phenomenon that cracks appear after castable building of light pulverization boiler. This situation must be dealt with in time to avoid the occurrence of accidents. The reasons for cracks are as follows:

One: the construction technology is unreasonable

(1) The "gray-water ratio" of castable is not well controlled during mixing. After adding too much water, the inner porosity of the material after casting molding is high, the strength of the material is reduced, the natural solidification time is too long, and the health time is lengthened. Add too little water, material fluidity is not good, vibration is not dense, easy to leave pores, caves, and so on, the strength will be greatly reduced.

(2) Mixing time and vibration time are not well controlled. Mixing time is too short, the material mixing is not uniform, not dense, strength is reduced; The pouring of castable shall be rammed by ramming machine in layers. The vibration time is too long, the material is easy to produce stratification, fine powder floating on the surface, aggregate sinking at the bottom, resulting in the material strength is reduced and easy to flake. The castable is used up within 30 minutes after mixing, and should be poured to the specified thickness and height in one time. Castable construction should be carried out in the environment above 5℃, because the temperature is too low, the material is not easy to solidify, even if solidified, is also a false solidification phenomenon, castable generally should be continuous casting, in the previous layer of castable initial solidification, should be the next layer of castable finished. If the construction gap exceeds its initial setting, it should be treated according to the requirements of the construction joint.

(3) The demoulding time is not well controlled. Strip the castable before it has hardened. It can be removed only when the strength of the castable can ensure that its edges and corners are not damaged by demoulding. The bearing formwork shall not be removed until the castable reaches 70% of the strength. In order to facilitate demoulding, the pouring surface of all molds should be coated with oil before pouring.

(4) The health time of castable is not well controlled. There should be enough natural drying period after boiler masonry, so that most of the water in the refractory layer can be precipitated, to prevent a large amount of water in the oven can not be discharged in time, so that the refractory layer burst and fall off.

(5) The quality control of oven is not good. Oven is to remove the free water and crystallizing water that can not be excluded from the natural drying of lining materials, and at the same time to high temperature curing of castable to achieve a certain strength.

Before oven, furnace lining material must have a certain natural strength (sufficient health period) to proceed. Oven principle "should be long not short, should be slow not fast". According to the preset oven curve, the heating speed should be uniform and stable, control the constant temperature time and temperature, and keep the temperature fluctuation no more than ±20℃. Prevent too fast temperature rise, moisture can not be discharged in time, break through the wear resistant layer; Secondly, to prevent the temperature gradient in the refractory and wear-resistant layer is too large, resulting in huge thermal stress, so that the wear-resistant refractory layer cracking, convex, off.

Wear-resistant refractory layer outer steel shell (such as return leg, cyclone cone) opening and discharging steam hole is too little, also can not be ignored.

Two: the structure design is unreasonable and the quality of castable is poor

2.1 Unreasonable design of light burning powder refractory and anti-wear structure

(1) The expansion joint design of refractory wear-resistant material is unreasonable. The number of annular and longitudinal expansion joints is not enough. After boiler operation, wear-resistant refractory materials are heated, volume expansion, extrusion, crack. The expansion joint at the connection between wear-resistant refractory castable and firebrick at the inlet flue of cyclone separator is changed from 5mm to 10mm, and sufficient clearance is reserved to meet the expansion requirements. The expansion joint is changed to Z-shape to prevent boiler ash from penetrating and scouring the insulation layer. Expansion joint filling material requires bull cortex refractory fiber felt on both sides to prevent refractory mud immersion in the filling material. The design interval of the annular expansion joint is changed from 1500mm to 1000mm. For large areas such as the outlet flue of the separator and the cone of the separator, the casting surface is changed from (2.5 × 2.5m) to a small square (1.5 × 1.5m) one-time forming masonry, and the expansion joint is set at the same time. The width of the expansion joint is no more than 3mm. The filling material requires strong rigid plywood to prevent deformation when shaking. After the boiler runs, the plywood burns at high temperature and the space becomes an expansion joint.

(2) The cyclone separator cylinder is equipped with brick lining supporting plates along the height to achieve the purpose of layered unloading of brick walls. According to the calculation of the actual firebrick weight of the cylinder, the design of one layer of supporting plates cannot reach the purpose of unloading, so the supporting plates are changed to two-layer layout according to the actual situation on site. The wear-resistant refractory castable supporting plate of the riser of the refeeder is arranged in 4 layers instead of 3 layers, and the spacing is reduced to 2.5m to achieve layered castable unloading.

(3) The shape of the Y-type nail in the boiler needs to be improved, and the heat resistance of the material is stronger. It is best to make the Angle of 60 ~ 80°, ensure the top shape of the nail, in order to enhance the grip of the nail on the castable.

Grab nail, air cloth plate, slag pipe, air pipe are metal materials, after heating expansion coefficient is much greater than the expansion coefficient of refractory materials, if not pretreatment, metal and refractory contact surface will form mesh cracks, resulting in cracking, falling off. Refractory contact metal surface to remove oil and ash stains and evenly coated with more than 1mm asphalt. To ensure the concentration of asphalt and smear thickness, resolutely eliminate the use of asphalt paint instead of asphalt oil.

2.2 The quality of refractory wear-resistant materials is not up to standard

(1) The matching and bonding between the aggregate and the matrix of wear-resistant materials has an important impact on the wear resistance of the materials. The mismatch of aggregate and matrix will lead to cracks in the material body after forming, and the poor combination of aggregate and matrix will lead to erosion of the matrix, and then the aggregate is isolated, and then fall off. In this way, even if the aggregate has excellent wear resistance, it is useless. The best wear resistant material is the matrix and aggregate are worn at the same rate.

(2) wear-resistant refractory materials after the storage period, material failure, part of the material improper storage, moisture deterioration, can also cause boiler masonry quality unqualified.



Address: Daling Village, Guantun Town, Dashiqiao City, Yingkou City

Phone number: 13904172088