Antifreeze Measures for Winter Construction of Refractory Castables for Heating Furnace

Heating furnace is an important thermal equipment for heating billets in rolling mills. At present, in the construction process of heating furnace, refractory castable has the advantages of short construction period, good heat preservation effect and high overall strength, so it is widely used in various parts of heating furnace lining. During construction in winter, it is generally required that the stirring water temperature should be controlled at 15-35 °C, and the curing temperature should be strictly controlled above 5 °C. Especially in the northern region, the temperature in winter is basically below zero, and the ambient temperature of some construction sites is too low, resulting in poor fluidity of refractory castables and prolonged solidification time. Seriously affect the construction quality and construction progress. Therefore, during the construction of refractory castables in winter, effective thermal insulation measures must be taken, and the temperature of the construction environment should be raised to above 5 °C to ensure that the refractory castables are not frozen and the construction process can proceed smoothly.

1. Influence of construction at low temperature in winter on the performance of refractory castables for heating furnaces

The production and maintenance test of refractory castable samples were carried out under the ambient temperature of 5 ℃, and it was found that the low temperature casting construction had a relatively great influence on the refractory castable. Combined with the technical guidance practice on the construction site, the following impacts are summarized:
(1) Construction at low temperature, it is difficult to stir the refractory castable evenly, thus affecting the forming of the material after construction.
(2) Construction at low temperature, during the stirring and discharging process of refractory castables, the fluidity becomes smaller, and it is easy to form voids during pouring.
(3) The strength of the refractory castable will become lower when it is constructed at low temperature, and it is easier to form a loose state after being frozen, and it is easy to fall off and fall off when the mold is removed.
(4) During construction at low temperature, the free water in the refractory castable will peel off due to the expansion of the icing volume.

2. Antifreeze measures for winter construction of refractory castables for heating furnaces

(1) Antifreeze measures before pouring construction
Antifreeze measures for refractory castables before construction, including antifreeze for refractory castable transportation and storage. During transportation, pay attention to preventing rain and snow, use special winter transportation covering cloth to cover, minimize the intermediate links of multiple transfers, and properly select suitable transportation vehicles. During the storage process, after the refractory castable arrives at the site, it must be placed in a rain-tight warehouse or construction workshop, and stored in a dry and high terrain. Refractory castable moisture back.

(2) Antifreeze measures during pouring
In the process of pouring refractory castables, the following methods can effectively reduce the risk of freezing of refractory castables:
1) Stir and warm with water
Put an electric heater or pass steam into the water storage bucket for stirring water, or burn firewood under the bucket to directly heat the water storage bucket and raise the water temperature to 15~35℃.
2) Add a certain amount of coagulant during stirring
The coagulant can shorten the coagulation time and cause the castable to freeze due to the slow solidification.
3) It should be used as soon as possible after mixing to prevent freezing during transportation.
Try to shorten the distance of transporting materials. After the refractory castable is stirred, it should be transported to the pouring site immediately, and it is advisable to use it up within 15 minutes. During construction in winter, the transportation time should be shortened as much as possible to prevent the refractory castable from freezing in the refractory castable transportation, and the refractory castable should be vibrated in time after pouring into the pouring part.

(3) Antifreeze measures for maintenance after pouring
In winter, after a part of the pouring construction of the refractory castable is completed, thermal insulation and antifreeze measures should be taken in time to ensure that the refractory castable will not be frozen during the maintenance process. The practical maintenance and insulation methods on site are as follows:
1) Maintenance and insulation method 1
Cover the top of the heating furnace, the door of the feeding and discharging furnace and the air leakage of the heat storage box with canvas or plastic film, so as to prevent the cold air from outside the furnace from blowing into the furnace, so as to achieve the effect of heat preservation. When adopting this method, attention should be paid to fire prevention and the safety of high-altitude operations during construction. Because there will be cross operations on the construction site, it is necessary to prevent the electric welding spark from igniting the canvas or plastic film, resulting in a fire incident.
2) Maintenance and insulation method 2
Place a part of iodine tungsten lamps or warm fans in the furnace, and use the principle of thermal radiation to increase the ambient temperature in a certain area of ​​the furnace, so as to achieve the effect of material curing and heat preservation after pouring. When adopting this method, attention must be paid to the personnel's protection against electric shock, the wiring layout, the placement of iodine tungsten lamps or heating fans (so as not to hinder the operation).
3) Maintenance and insulation method three
Put several stoves made of oil barrels in the furnace, ignite the coke or firewood in the stove, so as to increase the temperature in the heating furnace, or ignite the firewood pile on the refractory bricks at the bottom of the furnace, and let the special person take care of adding firewood, which can also increase the number of firewood in the furnace. ambient temperature. Due to environmental inspections, this method is generally not allowed on site. Moreover, the smoke from burning firewood is relatively large, which affects the operation of construction workers and has poor safety. This is a last resort to ensure the construction period when the on-site thermal insulation conditions are limited.
4) Maintenance and insulation method four
Conditional construction sites can arrange pipes to pass steam at the bottom of the furnace to increase the ambient temperature in the furnace. This method is both safe and can achieve thermal insulation effects. The temperature in the furnace is relatively uniform and durable, and is currently a more advocated method.