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Process of smelting

  • Author:Sun He
  • Source:www.xy-global.com
  • Release on:2021-11-04

(1) Charge treatment

The charge should be cleaned before use to remove rust, grease and other dirt on the surface. Leaving time is not long. Cleaner surface of aluminium alloy ingots and metal-Shaped returning charge can not be sandblasted, but the iron filter screen and inserts mixed with the charge should be eliminated. All charge should be preheated before being put into the furnace to remove moisture attached to the surface and shorten the melting time by more than 3 hours.

(2) Preparation of crucible and melting tools

New crucible shall be cleaned and carefully checked for penetration defects before use. Sand blowing shall be carried out before use and preheated to dark red (500-600 degrees) for more than 2 hours to remove water and combustible substances adhering to the inner wall of the crucible. When it is cooled to below 300 degrees, carefully clean the inner wall of the crucible and spray paint at a temperature not less than 200 degrees. The crucible must be dried and dried thoroughly before it can be used. Smelting tools such as pressure ladle, stirring spoon, pouring ladle, etc. must be cleaned of residual metal, scale and other contaminants before use, preheated at 200 ~300 C and coated with protective coating. To avoid direct contact with aluminium alloy and contamination of aluminium alloy. Coatings are usually blended with zinc oxide and water or water glass. Dies and melting tools after coating are preheated to dry at 200 ~300 ~C before use.

(3) Control of melting temperature

The low melting temperature is not conducive to the dissolution of alloy elements and the exhaust of gas and inclusions, and increases the tendency of segregation, cold insulation and under-casting. Moreover, due to insufficient heat of riser, the casting can not be compensated reasonably. It is pointed out that the melting temperature of all aluminium alloys should be at least 705.
Degree and should be stirred. Excessive melting temperature not only wastes energy, but also results from higher temperature, more hydrogen absorption, larger grain size, more serious oxidation of aluminium and more serious burning of some alloy elements, which leads to the decrease of mechanical properties, deterioration of casting and mechanical processing properties, weakening of effect of modification and reduction of air tightness of castings. Production practice has proved that rapid heating up of the alloy liquid to a higher temperature and reasonable stirring can promote the dissolution of all alloy elements (especially refractory metal elements), remove the scum and then drop to pouring temperature. In this way, the degree of segregation is small and the amount of molten hydrogen is small, which is conducive to obtaining uniform and dense alloys with high mechanical properties. Since the temperature of an aluminium melt is difficult to judge with the naked eye, a thermometer should be used to control the temperature regardless of the type of furnace used. Temperature meters should be checked and maintained regularly. Thermocouple bushings shall be cleaned periodically with metal brushes and coated with protective coatings to ensure the accuracy of temperature measurement results and prolong service life.

(4) Control of melting time

In order to reduce the oxidation, gas absorption and iron dissolution of aluminium melts, the retention of aluminium melts in the furnace should be minimized.