Problems existing in integral cold ramming furnace lining

Problems existing in integral cold ramming furnace lining

The material cold ramming paste used at high temperature for a long time is in a state of thermodynamic non-equilibrium. With the rise of temperature, some physical and chemical reactions will occur in the coking of the binder in the cold ramming paste, which will bring a certain volume change, which may harm the stability and life of the lining of the mine furnace.  If there is a large shrinkage in the process of use, it may crack the furnace lining and lead to the occurrence of furnace accident.  On the contrary, if larger expansion occurs, it may cause greater stress in the furnace lining and lead to the destruction of refractory materials in the furnace lining.  Therefore, the expansion and contraction of cold ramming paste is a process of thermodynamic change, which is not suitable for the whole ramming furnace lining of mineral heating furnace.

FIG. 1 is a typical expansion/shrinkage curve of the cold ramming sintering process, in a free-standing pattern. The heating rate is 3 ℃ /min, the maximum temperature is 950 ℃, and the holding time is 3 h.  The expansion/shrinkage curves of cold ramming paste will be different due to different Raw materials, but all cold ramming paste will go through a process of expansion, contraction, secondary expansion, secondary contraction, and third expansion, which is the inevitable result of the pyrolysis and polycondensation process of cold ramming paste binder in the roasting process.

In figure 1 delta LA coking period is to point to paste the biggest expansion rate, in front of the delta LA paste has experienced a major expansion - contraction - again, the paste from the plastic to plastic, before this, paste is soft plastic, therefore -arc furnace lining paste before the coking can buffer the expansion of the carbon block by deformation force, itself will not be damaged,  The expansion force transmitted is too small to destroy the lining layer and furnace shell of the carbon paste.

After the point of △LA, the paste will shrink and lose plasticity due to the coking of the binder.  At this time, it is equivalent to the low load stage of the furnace.

△LB point refers to the expansion rate at 950 ℃, which is equivalent to the end of the furnace.

△LC point refers to the expansion rate at 950 ℃ for three hours, which is equivalent to the gradual stabilization stage of the furnace within one year of production.  The actual operating temperature of electric furnace carbon brick in mine heat furnace is about 1200 ~ 1 500 ℃, and it has not reached this temperature after 950℃△LC point, and the cold ramming paste has been sintered. At this time, the cold ramming paste sinter block and the electric furnace carbon block are synchronous expansion, which is equivalent to the normal production stage of the mine heat furnace.

Expansion/shrinkage rate of cold ramming paste = △LA-△LC, △LA is the starting point of expansion/contraction stress, and △LC is the stable point of expansion/contraction stress, so △LA-△LC can not be large, generally not more than 0.8%, too large difference of contraction stress will make cold ramming paste crack.

The expansion of cold ramming paste can reach more than 3% before coking (about 200 ℃). Although the paste is soft and plastic, the deformation of 10 m is also amazing. If the expansion force reaches a certain extent, the lining of cold ramming paste will be bulged and the effect of ramming will be destroyed.  The shrinkage of the cold ramming paste after coking is also amazing within the range of 10 m, but the integral cold ramming paste lining is gradually completed from the center to the periphery and from the upper layer to the lower layer in the sintering process. The plastic paste that has not reached the coking temperature has eliminated part of the thermal stress, so the overall thermal stress of the integral cold ramming paste lining is not large.  However, the accumulation of local thermal stress can also cause cracks in furnace lining.

-arc furnace structure characteristics and are not afraid of cold dao paste up expansion/contraction, the upper furnace charge pressure is not enough to cause cold dao paste expansion/contraction caused by the stress accumulation, lining is a circular -arc furnace, the structure around the same, so the cold dao paste coefficient of linear expansion/contraction is enough to know that have much impact on furnace lining