Phase 1: Natural drying process of smelting furnace lining (basic steps before starting the furnace)

1. The core purpose of natural drying

The furnace wall, bottom, and top of the smelting furnace are all built and formed by a layer of water containing mortar, refractory bricks, and magnesia sand knots. The entire refractory masonry is filled with a large amount of free adsorbed water. If this type of water enters the drying stage and rapidly heats up, the water will rapidly expand and vaporize in a short period of time, causing huge internal stress to tear the refractory masonry, resulting in irreversible damage such as cracking, bulging, and peeling of the furnace lining. Natural drying is an essential pre drying process that relies on natural air convection to slowly remove free moisture from the surface and shallow layers of refractory masonry at room temperature, significantly reducing the dehydration pressure during the subsequent drying stage, and fundamentally avoiding the problem of rapid heating cracking of refractory lining in the early stage of drying.

2. On site operation method for natural drying

During the natural drying stage, ignition and heating are strictly prohibited throughout the process. Dehydration operations are completed by relying on the flow of ambient air. The specific operating points are as follows:

1. Fully open all ventilation channels:

   Fully open all furnace doors (feeding door, slag removal door, maintenance door, discharge chute cover plate) of the melting furnace, and at the same time open all flue gates and flue dampers of the flue system, to open the complete air flow channel from the furnace to the flue and chimney, allowing room temperature air to freely circulate inside the furnace, continuously taking away the water vapor evaporated from the refractory masonry, and accelerating the overall drying rate. If natural drying is carried out on a closed furnace door, water vapor will accumulate inside the furnace for a long time, resulting in extremely low drying efficiency and the occurrence of moisture regain in refractory materials, completely losing the meaning of natural drying.

2. Dry environment control:

   Try to maintain smooth ventilation in the factory where the melting furnace is located, and avoid working in a closed factory during rainy season and high humidity environment; If the humidity in the factory building remains above 70% for a long time, industrial fans can be installed around the furnace to force air circulation and improve the efficiency of water vapor discharge. During the drying process, there is no need for human intervention in temperature, and the entire process relies on a natural environment at room temperature to complete dehydration.

3. It is strictly prohibited to close the furnace door halfway:

   During the whole natural drying cycle, except for the extreme rainstorm weather, which requires temporary covering of the furnace mouth to prevent rainwater from pouring into the furnace, all furnace doors and flue gates must be kept open at other times to ensure continuous air convection drying.

Classification criteria for 3 natural drying cycles (differentiated by furnace repair level and season)

There is no fixed and unified value for the required duration of natural drying, which is mainly determined by four factors: the repair level of the furnace, the overall volume of the furnace body, the thickness of the refractory masonry, and the completion season of construction. The industry has formed mature duration control standards:

1. Newly built melting furnaces and overhauled melting furnaces:

   These types of furnaces have their entire lining removed and rebuilt, with the thickest refractory masonry, highest moisture content, and longest drying cycle. In summer, the environmental temperature is high and the air humidity is low, and the natural drying time should not be less than half a month (15 days); In winter, the temperature is low, the air drying ability is weak, and the evaporation rate of water vapor is slow. The natural drying time should not be less than 30 days (one month); Large tonnage and large capacity melting furnaces (10 tons and above) need to extend the drying cycle by 3-7 days on this basis.

2. Smelting furnace after intermediate repair:

   The intermediate repair only extensively repairs the refractory layer of the local furnace wall, furnace bottom, and flow channel. Most of the overall furnace lining retains the original old refractory layer, with a much lower moisture content than the new furnace and the major repair furnace. Its natural drying time should not be less than one week (7 days); If the repair area is concentrated in thick knotted magnesium sand layers such as furnace bottom and aluminum liquid contact layer, it needs to be extended for more than 10 days.

3. Minor repair of smelting furnace:

   Minor repair only involves repairing the peeling of the refractory layer in a small area, sealing the furnace mouth, and repairing the flow channel locally. The amount of refractory material used is small, the water storage capacity is low, and the natural drying time can be controlled within 3-5 days; Even if the furnace is restarted after a short-term shutdown, if there is any moisture regain in the lining during the shutdown period, it must be naturally dried for 2-3 days.

Only when the natural drying cycle meets the standard and the free water on the surface of the refractory masonry is fully evaporated, can the next stage of baking operation be carried out; If the natural drying time is forcibly shortened and the furnace is directly dried, there is a high probability of large-scale cracking and scrapping of the furnace lining, greatly shortening the overall service life of the melting furnace.