Heating of ingots
Heating of aluminum and aluminum alloy ingots is usually carried out in radiant resistance heating furnaces, resistance heating furnaces with forced air circulation or natural gas heating furnaces. The natural gas heating furnace has fast heating speed and uniform temperature, which is conducive to modern continuous large-scale production.
Determination of Ingot Heating Parameters
System The ingot heating system includes heating temperature, heating and holding time, and furnace atmosphere.
A heating temperature
The heating temperature must meet the requirements of the hot rolling temperature to ensure high plasticity and low deformation resistance of the alloy. The selection of the hot rolling temperature is determined according to the equilibrium phase diagram, plasticity diagram, deformation resistance diagram and the second type of recrystallization diagram of the alloy, and the calculation method is calculated according to the formula.
In the actual production process, in order to compensate for the loss of temperature drop from the furnace to the hot rolling, and to ensure the hot rolling temperature, the temperature of the metal in the furnace should be appropriately higher than the hot rolling temperature.
B Heating and holding time
For the determination of heating and holding time, factors such as the thermal conductivity of the alloy, the ingot specification, the heat transfer method of the heating equipment and the charging method should be fully considered. In order to reduce the oxidation of the surface of the ingot, reduce the energy consumption, prevent the ingot from overheating and burning, and improve the production efficiency. The larger the thickness of the ingot, the longer the heating time required, and the heating time of the ingot can be calculated according to the empirical formula.
Ingot heating process control points:
(1) Before installing the furnace, carefully check the transmission part of the furnace body and the heating elements and other parts, and confirm that the furnace is normal before installing the furnace.
(2) The operation of power transmission, power failure, and temperature change of the heating furnace shall be carried out by the heat treatment worker to notify the instrument worker, and the date, shift, furnace number, fixed temperature, power transmission time, change of fixed temperature and time shall be indicated in the record book. and sign. Except in emergencies, heat treatment workers are not allowed to send electricity, cut off power or change the temperature without authorization.
(3) Before production, prepare ingots, aluminum-clad plates, etc. according to the production task list. When loading the furnace, the inspector will carefully check the alloy, state, specification, quantity, aluminum-clad plate, etc. of the furnace ingots according to the production card, and record them in the production process. on the card.
(4) All types of aluminum plates must be batched and loaded into the furnace according to the same melting order.
(5) The surface of ingots and aluminum-clad plates should be clean, free of oil stains, dust, watermarks, alkali marks, corrosion, peeling, slag inclusion, delamination, pores, air bubbles, metal tumors, and segregation tumors with a height greater than 5.0mm, Defects such as pulling cracks, aluminum beards, etc. The depth of mechanical damage and scraping shall not exceed 3mm, and the ingot used for clad aluminum plate shall not exceed 5% of the actual thickness.
(6) Sawed ingots with cracks are not allowed to be installed in the furnace.
(7) When the short square ingot is installed in the furnace when the actual specification is different from the ingot specification on the production card, the specification on the production card must be modified before it can be installed.
(8) The primary and secondary heating ingots, the milled and non-milled ingots, and the etched and wiped ingots should be protected separately. In case of mixed installation, the heat treatment workers must be notified to take measures: the order should be reasonably arranged when the furnace is installed, and the heating temperature of the ingots should meet the requirements by adopting the middle empty area, partitioned temperature setting, partitioned power failure, and power transmission.
(9) When loading the furnace, before the ingot or aluminum-clad plate is placed on the chain of the heating furnace, an aluminum pad that meets the requirements should be placed on it to prevent the ingot from contacting the chain. The contact surface between the aluminum pad and the ingot must be clean and used according to the If necessary, replace it in time.
(10) The clad aluminum plate should be placed on the ingot and aligned with the bite end.
(11) When the longest residence time of the ingot in the furnace exceeds the specified time, the hot rolling can be carried out when the degree of oxidation will not affect the hot rolling and product quality.
(12) During the heating process, open the furnace door at least twice each time to check whether the heating element is out of phase. If the phase is found to be out of phase, measures should be taken to ensure that the temperature of the ingots out of the furnace meets the requirements.
(13) When the furnace is released, the constant temperature of the furnace, the holding time, and the temperature of the furnace should be checked, and the ingot should be checked for signs of overburning and the degree of surface oxidation.
(14) The heat treatment workers can adjust the heating time by themselves within the range of 1h of heat preservation time, and under the premise of not exceeding the fixed temperature, power transmission, power failure and change the fixed temperature in zones.
(15) After the furnace is released, the heat treatment worker should check whether all the aluminum pads on the lower surface of the ingot have fallen off, and blow off the dust on the surface of the ingot with the wind.
(16) When the surface of the ingot is blackened or has precipitated, it shall not be used for production by hot rolling mills, and a high-level inspection shall be made to see if it is over-burned.
(17) When the temperature is measured in an empty furnace, the maximum temperature difference in the same area during the heat preservation stage shall not exceed 20 °C; when the temperature is measured with load, the maximum temperature difference of the metal in the same area during the heat preservation stage shall not exceed 15 °C. The matching error between the temperature measurement and the temperature digging system does not exceed t5℃.
(18) The furnace body is well insulated, and the outer temperature of the furnace body should not exceed 65°C (except for the furnace door).