During the sintering process, a new bed structure is formed due to melting of the material and then crystallization and solidification - changing the original particle diameter, shape factor, and volume shrinkage of the layer. The decisive factor here is the melting temperature of the solid phase material (or the solidification temperature of the melt) and the maximum temperature that can be achieved by sintering. Figure 6 depicts the variation in the structural parameters of the layer along the height of the sinter layer.

In the mixed layer, the dried layer and the sintered ore layer, the bed structure does not change. The mixed layer and the dried layer have a large specific surface area and a small porosity, so that the heat transfer efficiency is high, the temperature rises quickly, but the gas permeability is not good. The sintered ore layer has a small specific surface area and a large porosity, so the gas permeability is good, but the heat transfer efficiency is low, and the cooling rate is not fast. The changes in the bed structure mainly occur in the combustion and fusion consolidation layers. At the beginning of the combustion layer, as the material has not yet reducted, the combustion particles become smaller and the porosity increases slightly. With the occurrence of reflow, the porosity decreases, and the degree of remelting becomes higher. As the shrinkage rate increases, the s decreases. To the consolidated layer, the porosity increases rapidly due to the reduction in the shape factor. The change in specific surface area is mainly in the combustion melting stage, and A _s rapidly becomes smaller as the particles become larger. The consolidated layer A _s remains almost unchanged.
(IV) Resistance loss of the material layer In the early years, Lm Ramsin proposed the following formula for the resistance loss of bulk material:
Δp=AhW ⁿ (5)
Where Δp—the resistance loss of the bulk layer;
A, n - - the coefficient determined by the size of the pellet shape;
h———layer height;
W———The velocity of the airflow through the layer.
Since A and n vary according to the shape of the pellet and the particle size, the surface area of ​​the pellet and the velocity of the air have a great influence on the A, n coefficient. The measured pressure loss is very different from the calculated value. Therefore, the formula is used for sintering. difficult. Later, EW proposed another equation based on the experiment [2]:

Where P—the permeability index of the layer;
Q————The air volume passing through the material layer, m ³ /min;
A———furnace area, meter ² ;
h———layer height, mm;
Δp———layer resistance, millimeter water column;
m, n - - coefficient. [next]
The gas permeability index of the material layer refers to the gas flow rate per unit area under a unit pressure gradient. Therefore it is an indicator of the permeability of the layer. Its unit of measurement, the United Kingdom adopts the British system called BPU, Japan uses the metric system (6 type of comment unit) called JPU.
The m, n in the formula can be determined by experimentation.

1) If Δp and P are unchanged, change the air volume to get the corresponding Δp value. The logarithmic value is plotted in Figure 7(a), and its slope is equal to m:
lgQ=lgK+mlgΔp
As can be seen from the figure, m = 0.6 under the test conditions
2) If Δp and P are unchanged and the height h of the layer is changed, the relationship between h and Q can be obtained. The logarithmic value is plotted in Fig. 7(b); the slope is equal to n:
lgQ=lgK-nlgh
Under the test conditions, n=0.62
From the above two sets of tests can be obtained:

In fact, n is closely related to the particle size of the sinter and the sintering process.
Particle size 10~0mm n=0.55
6~0mm n=0.6
3~0mm n=0.95

Sintering process before ignition n=0.6
Ignition instantaneous n=0.65
When sintering n=0.6
After sintering n=0.55[next]
According to recent research, the particle size composition and operating system of sintered materials have different effects on the m, n coefficients. Figure 8 shows the effect of the particle size composition of the material on m, n. Only when the material particle size composition is uniform, the m and n values ​​differ slightly. Figure 9 is the combined result of the above study.

Only when the porosity of the layer is large, when the height of the layer and the negative suction pressure are low, the values ​​of m and n are close. Therefore, m=n=0.6 in the Voi period formula is conditional. Pay attention when applying this formula for quantitative analysis.
The advantage of the Voyce formula is that it is simple to calculate and basically reflects the relationship between the main process parameters in the sintering process. The main disadvantage is that the content of the gas permeability index is not shown, and the factors affecting the gas permeability are not seen.
DW (MitchelI) considers the relationship between them by controlling the most basic factors of the airflow in the bulk layer, using the empirical formula of the Carman resistance factor and the Reynolds number Re.

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