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Casting Cu-Base Alloys

Source:Non-ferrous Casting Author:Shenyang Yongyingda (YYD) Industrial And Mining Mechanical Co.,Ltd 2014-12-22 23:12:19    Click on the:
Metal bath covering and purifying to provide oxidation protection, and gases absorption is accomplished by using charcoal, broken glass, graphite, salt ammoniac (NH4Cl), natrium carbonate (soda) (Na2CO3), borax (NH4)3P(BO4)2, potash (NaNO3). The process of purifying relates to solid particles conversion (inclusions, oxides) into liquid state whereto they being specifically lighter float out and turn into slag.
Degassing is conducted in order to remove gases from melt, first of all from hydrogen. Extreme hydrogen stability is considered as the main reason for porous casting appearance with copper and its alloys. Particularly harmful effect has simultaneous presence of hydrogen and oxygen.
Oxygen is present in Cu2O form. Water vapor creation appears with reduction when, in the course of melting procedure, oxygen comes into contact with hydrogen.
(Cu2O)+ {H2} ↔ [2Cu] + {H2O}
In this case, gaseous inclusions (bubbles) appear inside the melt, since vapor within copper and its alloys remain insoluble. The reaction is of reversible nature, enabling hydrogen recreation and its melt dissolution - "hydrogen copper illness". Practically, we can get simultaneously both hydrogen and oxygen in the melt.
One way to remove hydrogen is to melt it in vacuum. This is a very expensive procedure. Blowing hydrogen out with inert gases (N, Ar) represents other possibility and it is based upon Dalton's Law of partial pressures. Apart from degasification, blowing out enables an intensive melt mixing that promotes floating out of inclusions and oxides. This method does not ensure complete hydrogen elements based salts application and some other gases.
Deoxidization is carried out in the end of the melting procedure for the reason of oxygen removal. For this reason it is applied copper and phosphorous alloy Cu3P with 15% P. It is customary practice to add 0.5% of melted metal. Beryllium can also be used for deoxidization since it exerts much stronger effect.
Pure copper casting temperature ranges between 1150-1180°C i.e. approximately 100°C over melting temperature.
Copper alloys are classified into the following groups:
1. Bronzes. They include copper alloys with Sn, AI, Ni, Mn, Si, Be, Cr etc.
Tin bronzes
Lead-tin based bronzes
Red cast
Lead bronze
Aluminium bronze
Beryllium bronze
2. Brasses. Cu-Zn alloys with up to 50% Zn. Impurities: Pb, Mn, AI, Fe, Sn, Sb, As, P.
"Tombak" → Zn ≤ 33%
Color: ranging from red → yellow brass color → Zn gray-white
α Ms: Zn ≤ 39%
β Ms: 39 < Zn < 45.5
γ Ms: 45.5 < Zn < 50
Special brass types
The best mechanical characteristics have Zn 30-40% alloys. Hardness increases with Zn% raise and it is accompanied with simultaneous plasticity reduction. With the temperature raise, it an abrupt strength decrease appears with these materials. Apart from Zn, they contain other intentionally added elements: Mn, AI, Fe, Sn, Ni, Co, Si, etc.