Raw material selection
The raw material taste should improve with the taste of brass varieties. When smelting non-essential brass, if the quality of the charge is reliable, sometimes the use of old material can reach 100%. However, in order to ensure the quality of the melt and reduce the burning loss, the usage of relatively finely divided charge such as various sawdust or zinc chips should generally not exceed 30%. Experimental surface: When using 50% cathode copper and 50% brass old material, the required smelting time is the longest and the energy consumption is the highest. If the zinc ingot is preheated to 100~150℃ and fed in batches, it is very beneficial for it to sink and melt in the molten pool quickly, which can reduce the burning loss of the metal. Adding a small amount of phosphorus can form a more elastic oxide film composed of 2ZnO.p2o2 on the surface of the molten pool. Adding a small amount of aluminum, such as 0.1%~0.2%, can form an Al2O3 protective film on the surface of the molten pool, and help to avoid and reduce the volatilization of zinc and improve the casting conditions. When a large number of old materials are used to smelt brass, appropriate pre-compensation should be made for some elements with relatively large smelting losses. For example, the pre-compensation amount of zinc is 0.2% when smelting low-zinc brass, the pre-compensation amount of zinc is 0.4%-0.7% when medium-zinc brass is smelted, and the pre-compensation amount of zinc is 1.2%-2.0% when high-zinc brass is smelted.
Melting process control
The general order of additions when smelting brass is: copper, old material and zinc. When smelting brass from pure metal ingredients, the copper should be melted first. Generally, when the copper is melted and overheated to a certain temperature, it should be properly deoxidized (eg with phosphorus) and then the zinc should be melted. When the charge contains the old brass charge, the charging sequence can be adjusted appropriately according to the actual conditions such as the characteristics of the alloy components and the type of the smelting furnace. Because the old material itself contains zinc, in order to reduce the melting loss of the zinc element, the old brass material should usually be added and melted at the end. However, large pieces of charge are not suitable for final charging and melting. If the charge is wet, it should not be added directly to the melt. If the wet charge is added on top of other unmelted charge, it will create a drying and preheating time before it is melted, which is not only beneficial to avoid melt inhalation, but also to avoid other accidents. Zinc addition at low temperature is a basic principle that must be followed in almost all brass smelting processes. Adding zinc at low temperature can not only reduce the burning loss of zinc, but also help the safety of smelting operation. When smelting brass in a power-frequency iron-core induction furnace, it is generally unnecessary to add a deoxidizer because the melt itself, that is, the transitional molten pool, contains a large amount of zinc. However, when the melt quality is poor, 0.001%~0.01% phosphorus can also be added according to the total weight of the charge for auxiliary deoxidation. Adding a small amount of copper-phosphorus master alloy to the melt can increase the fluidity of the melt before it is released from the furnace. Taking H65 brass as an example, its melting point is 936°C. In order to make the gas and magazine in the melt float and discharge in time, without causing a lot of volatilization of zinc and inhalation of the melt, the melting temperature is generally controlled at 1060~1100°C. The temperature can be appropriately increased to 1080~1120℃. After “spitting fire” 2 to 3 times, it is cast in the converter. Cover with baked charcoal during the smelting process, and the thickness of the covering layer should be greater than 80mm.
Post time: Jul-07-2022