by The quality of refractory castable preforms is closely related to the preparation process.
The preparation process will significantly affect the microstructure and uniformity of the material.
For example, insufficient vibration time in the vibration forming process of ceramics or refractory materials will prevent the smooth discharge of bubbles in the material, increase the porosity, and make the slurry not vibrate evenly, resulting in a large number of defects on the surface, These are the source of crack generation and propagation.
At the same time, a batch of materials are manufactured, and the immaturity of the preparation process will lead to the difference between the advantages and disadvantages of the materials.
For the erosion wear experiment, when studying the erosion wear mechanism of a material, because multiple samples produced do not show different properties, it will affect the results of the erosion wear experiment and even draw misleading conclusions.
Since this situation will occur in the early stage of erosion test, we first talk about the influence of some important operations in the preparation process on the wear resistance of castable preforms for reference.
(1) The curing system is the same as that of on-site construction.
Even in the laboratory, the formed castable preforms need to be cured.
Because the cement bonded castable is used in this experiment, how to improve the bonding strength between cement and aggregate and fine powder is very important.
The curing time and curing method are discussed in turn.
The hardening of castable preforms is closely related to the surrounding humidity.
The preparation and curing process of this experiment are carried out under laboratory conditions, which does not necessarily meet the on-site construction conditions.
All demoulded samples will be dried at 110 ℃ for 24 hours.
Fig.
1 shows the relationship between curing time (1D, 2D, 3D), curing mode (demoulding and non demoulding) and volume wear rate.
Several conclusions can be drawn from Figure 1: (1) with the increase of curing time, the volume wear rate decreases, indicating that a long time of curing has a good effect on the wear resistance of castable preforms, but it basically meets the requirements in two days without demoulding curing.
Although the wear rate will decrease with the increase of time, the impact is limited; (2) Non demoulding curing is obviously better than demoulding curing, and the wear resistance of castable obtained by non demoulding curing is basically good.
Fig.
1 Relationship between curing system and volume wear rate of castable preforms (abrasive amount: 20kg; erosion angle: 45 °; abrasive speed: 10.8m/s) curing refers to the dehydration process of castable preforms, and the amount of added water is also related to the curing time.
During demoulding curing, the preforms have a wide range of contact with the surrounding air, and the moisture is released rapidly during the curing process, It is not conducive to higher strength of cement.
During the test, it is found that the quality of precast parts of different castables will change to varying degrees during the curing process.
For example, the curing quality in air is generally small.
The content of cement in the preform is high, which will make the material more dense and better wear resistance in the hydration process.
During the curing process, try to keep the moisture in the precast parts of castable, and water the surface properly.
(2) The amount of water added will vary in different environments.
Taking the construction process of on-site castable as an example, too little amount of water will lead to poor fluidity and difficult pouring.
Too much will also affect the strength of castable after molding, so it is necessary to add an appropriate amount.
Carry out the best water addition experiment in the laboratory environment.
When the water addition is less than 5%, its fluidity is very poor, the exposed degree of large aggregate is very high, and the apparent porosity of the surface is high.
Therefore, set the minimum water addition for the test to 5%, as shown in Table 1, which shows the relationship between the water addition and the volume wear rate.
It can be found that the best condition is that the amount of water is about 7.5%.
Table 1 water addition and wear test of castable preforms are carried out under the conditions of erosion time of 20min, erosion angle of 45 ° and abrasive speed of 10.8m/s.
During the test, it is also found that the difference of raw materials has a great impact on the precast parts of castable.
For example, the firing process of high alumina bauxite clinker used will be different from different places of origin, and the influence of artificial factors is greater.
The castables made of different bauxite clinker may have good local wear resistance and poor wear resistance of other parts, The uniformity of castable preforms is poor, so the sample blocks used in the test should try to use the same batch of products from the same manufacturer, or use high aluminum homogeneous materials with better and more uniform quality.
Figure 2 shows the volume erosion rate test results of the original forming surface and internal section of the high aluminum castable preform under the erosion angles of 30 °, 45 ° and 60 ° respectively.
At the erosion angles of 30 °, 45 ° and 60 °, the volume wear rates of the original forming surface and inner section of the high aluminum castable preform are 0.056mm respectively ³/ G and 0.017mm ³/ g、0.082mm ³/ G and 0.030mm ³/ g、0.112mm ³/ And 0.06g ³/ g。 Their volumetric wear rate increases with the increase of erosion speed, and the volumetric wear rate of internal section is less than that of original forming surface.
Fig.
2 Relationship between angle change and volume wear rate of high aluminum castable preforms (erosion time: 4min, erosion speed: 6m / s, feeding speed: 1kg / min) high aluminum castable preforms are brittle materials with mechanical characteristics of brittle materials, high hardness, high brittleness and relatively high compressive strength.
In the erosion process, they also meet the erosion wear behavior of typical brittle materials.
When the erosion angle is a small angle of 30 °, the main ways of material erosion wear are cutting and ploughing, while at the same high angle of 90 °, the erosion wear mechanism is mainly the formation and propagation of cracks caused by brittle fracture.
For this “aggregate matrix” refractory, the eroded surface is often enriched by the matrix with low hardness and relatively low strength..
