How is pure copper, brass, and bronze smelted? Several problems should be paid attention to in smelting

Casting pure copper and copper alloy is an important class of non-ferrous metals, which is widely used 

in practical production. Commonly used copper alloys can be divided into two main categories according 

to the composition, namely cast brass and cast bronze. Whether it is sand casting or investment casting, 

smelting is a crucial part of the casting production, the smelting of various copper alloys have the same 

place, and there are differences, in many years of production practice, we summarized the pure copper 

and copper alloys (mainly bronze and brass) melting process experience, for the reference of relevant 

personnel.

The smelting equipment used: medium frequency induction furnace, thermocouple, ladle, graphite 

crucible, etc.

How is pure copper, brass, and bronze smelted? Several problems should be paid attention to in smelting

How is pure copper, brass, and bronze smelted? Several problems should be paid attention to in smelting

1. Smelting of pure copper

(1) First preheat the crucible to dark red, and add a layer of dry charcoal or covering agent (borax 63%+ 

broken glass 37%) with a thickness of about 30-50cm at the bottom of the crucible. Then add the corner 

residual material, waste block and bar material in turn, and finally add electrolytic copper.

(2) The added alloying element can be preheated on the stove, and the cold material is strictly prohibited 

from being added to the liquid metal. The charge should be moved frequently throughout the melting 

process to prevent bridging.

(3) The temperature will melt the alloy completely. After the alloy is fully melted, when the temperature 

reaches 1200-1220℃, 0.3%-0.4% of phosphorus copper is added to deoxidize the alloy liquid weight, and 

the following reactions occur between phosphorus and cuprous oxide: 5Cu2O+2P=P2O5+10Cu and 

Cu2O+P2O5=2CuPO3, the resulting phosphorus pentoxide gas escapes from the alloy, and the copper 

phosphate can float on the liquid surface and remove the slag, so as to achieve the purpose of deoxidation. 

The process of deoxidation requires constant stirring.

(4) The final slag out of the oven, alloy pouring temperature is generally 1100-1200℃.

2. Smelting of brass

Copper based alloy with zinc as the main alloying element is brass, divided into ordinary brass and special 

brass two categories. Common brass is a two-element alloy of copper and zinc, mainly used for pressure 

processing. On the basis of ordinary brass, other alloying elements (such as silicon, aluminum, manganese, 

lead, iron, nickel, etc.) are added to become special brass. Casting brass is mostly special brass.

(1) Alloying and metal charge requirements

In the chemical composition of copper alloy, due to the large variation range of main components, the 

appropriate ingredients should be selected according to its performance requirements in the process of 

batching calculation. The chemical composition of the alloy should conform to GB1176-87, and several 

commonly used brass melting ingredients are carried out according to Table 1.

It is required that the charge should be dry and clean, and the dirt rust should be cleaned by blowing sand.

(2) charge ratio

According to the general casting practice, the new material composition accounted for the total weight of 

the charge should be ≥30%, and the return charge should be ≤70%. However, in actual production, we take 

into account that there are more return charges of copper alloy, and when the mass percentage of return 

charges is ≥90% in the ratio of charge, the melting quality is still very good, and chemical spectral analysis 

proves that the composition of the casting is qualified. It is necessary to consider whether the impurities in 

the alloy exceed the standard when the charge is returned.

(3) Preparation before smelting

① Preparation of metal charge: The return charge is the same grade of waste casting, pouring and remelting 

ingot, which needs to have a clear chemical composition. Before entering the furnace, sand is blown to remove 

surface dirt, and after preheating, the furnace is loaded (the first batch of cold furnaces can be preheated with 

the furnace); Electrolytic copper is sand blown to remove dirt, and water is removed after preheating at 500-550℃ 

before it can be loaded into the furnace (the first batch of cold furnaces can be preheated with the furnace; Pure 

metal elements can be preheated on the furnace side before being put into the furnace. The maximum bulk of the 

metal charge should not exceed 1/3 of the crucible diameter, and the length should not exceed 4/5 of the crucible 

depth.

(2) Preparation of crucible and melting equipment and tools: there should be no cracks and other damage affecting 

safety before the use of the crucible, and the new crucible must be slowly heated at low temperature to prevent 

cracks; The old crucible will clean the inner surface of the slag; When the new graphite crucible is used and the 

smelting alloy type is changed, the crucible should melt the same grade series alloy before smelting for washing; 

Stir bars made of refractory materials and graphite must be thoroughly cleaned of residual paint and rust, and 

coated with a layer of refractory materials or brush paint after drying for use; The ingot mold must be thoroughly 

cleaned before use, and preheated to 100-150℃ after coating.

(4) Preparation of covering agent and flux

① Charcoal should be packed into a sealed baking box, baked at not less than 800℃ for 4h, when used to prevent 

moisture absorption.

② The covering agent is composed of borax 63% and broken glass 37%, and dry charcoal can also be used as the 

covering agent. The covering agent should be dried and the debris removed.

(5) alloy melting process

First preheat the crucible to dark red, and add 20-40cm thick charcoal at the bottom.

② Add electrolytic copper, quickly heat up and melt the intermediate alloy in the order of high melting point and 

low melting point (if any), and finally add back the charge, while adding charcoal to ensure that the alloy liquid 

level is not exposed to the air.

(3) Smelting brass generally also needs to be deoxidized, after the copper is all melted, the temperature reaches 

1150-1200℃, adding phosphorus copper (calculated with P accounting for 0.04%-0.06% of the weight of copper liquid) 

for deoxidization. After the practice of deoxidization and non-deoxidization, the surface quality of deoxidized castings 

is better than that of non-deoxidized castings.

④ Add alloying elements according to the composition requirements of each alloy grade: add aluminum copper 

intermediate alloy at 1100-1120℃, add pure zinc and pure aluminum in batches at 1100℃-1150℃ and stir. When melting 

silicon brass, silicon should be added first, then zinc; Zinc should be added before lead when melting lead brass. The 

addition temperature of zinc element should be controlled, and if the temperature decreases after adding zinc, the 

intermediate power supply can be provided. When the temperature of alloy liquid is higher than 1200℃, zinc is not allowed 

to be added.

⑤ Baking slag, adjust the alloy liquid to the casting process card required temperature, quickly baked pouring. The casting 

temperature of the alloy is one of the factors affecting the casting properties. The general oven temperature is ZCuZn38:

1100-1130℃; ZCuZn40Pb2:1080-1100℃; ZCuZn31Al2:1120-1140℃; ZCuZn16Si4:1100-1140℃.

6 Smelting two different grades of alloy, its chemical composition has an effect, the middle should be washed. For example,

the crucibles and tools used to melt tin bronze after smelting aluminum bronze must contain aluminum, which is the most 

harmful element in tin bronze, although aluminum is an acceptable component in aluminum bronze.

After the general copper alloy is deoxidized, qualified castings can be obtained. However, for aluminum bronze, aluminum 

brass, silicon bronze, etc., it is easy to oxidize to produce high melting point oxides Al2O3, SiO2, so that castings form slag, 

which needs to be removed after refining, commonly used refining agents are: mass ratio of 60% sodium chloride +40% 

cryolite or 20% cryolite +20% fluorite +60% sodium fluoride.

3. The smelting of bronze

Cast bronze can be divided into tin bronze and tin-free bronze according to its composition. Tin bronze is a copper-based 

alloy with tin as the main alloying element. It has good wear resistance, corrosion resistance, good strength and plasticity. 

Tin-free bronze has aluminum bronze, lead bronze, silicon bronze, etc., containing different main elements, such as aluminum 

bronze is a copper-based alloy with aluminum as the main alloying element.

(1) Alloying ingredients and metal charges require several commonly used bronze alloy melting ingredients according to Table 2.

Requirements: 0.7% ~ 0.9%Ni and 0.3% ~ 0.4%Mn are allowed in ZCuAl10Fe3 alloy to improve the mechanical properties of 

the alloy.

(2) The new material composition of the total weight of the charge should be ≥30%, and the return charge should be ≤70%.

(3) Preparation before smelting The preparation before bronze smelting is the same as that for brass smelting. Charcoal should 

be packed into a sealed baking box, baked at not less than 800 ° C for 4 hours, to prevent moisture absorption when waiting. 

Straw ash should be ground into powder, remove moisture, dry thoroughly, and pay attention to moisture when used. The 

covering agent should be dried and the debris removed.

(4) There are many types of cast bronze in the alloy smelting process, and only several typical alloys are discussed here, and 

other copper alloys of the same kind can be used for reference.

Melting of ZCuSn10Pb1 and ZCuPb10Sn10:

First preheat the crucible to dark red, and add 20cm-40cm thick charcoal at the bottom.

② Add electrolytic copper, quickly heat up and melt, and then add the return charge, while adding charcoal to ensure that the 

alloy liquid level is not exposed to the air.

③ After the return charge is melted, the phosphorus copper is added (generally accounting for 0.5% of the weight of the charge, 

and the phosphorus copper used in melting the phosphorus tin bronze can be all added).

④ Add zinc, tin and lead in turn (according to the ingredients), the former charge is completely melted, and then add the next 

one, and constantly stir the alloy liquid.

⑤ Adjust the alloy liquid temperature between 1100-1150℃.

(6) baking slag, and then add phosphorus copper (generally 0.1% of the weight of the furnace), deoxidize, evenly stir, and sprinkle 

a layer of straw ash on the surface of the alloy liquid, adjust the alloy liquid to the casting process card required temperature 

(generally 1130-1180℃), quickly poured.

ZCuAl10Fe3, ZCuAl10Fe3Mn2 melting:

These two alloys cannot be melted in a crucible that has melted other grades of alloys.

② Preheat the crucible to dark red and add the prepared flux. (Flux composition: cryolite 20% (mass percentage), sodium fluoride 

60%, calcium fluoride 20%).

③ Add the low-carbon thin steel sheet preheated to about 200 ° C and the return charge at the same time, stir the alloy after 

melting, and heat up to 1150-1180 ° C.

④ Add 0.3% of the weight of the alloy phosphorus copper deoxidation, and add flux.

⑤ The pure aluminum and pure manganese preheated to 200 ° C (according to the ingredients) are added in batches, each batch 

is added, and the mixing rod is pressed into it to melt rapidly, and the composition is constantly stirred to uniform, and the 

temperature of the alloy liquid is finally adjusted between 1120-1220 ° C.

(6) Cover the slag with straw ash, adjust the alloy temperature according to the casting process card (generally 1160-1200℃), and 

then quickly adjust the casting.

4. Safety matters

Safe production is the basic requirement of the casting industry, and the smelting of pure copper and copper alloys must be done:

(1) The operator should wear protective equipment, keep the workplace clean, and do not allow water and debris.

(2) Before opening the furnace, check whether the equipment used is intact, and if there are unsafe factors, it should be eliminated 

in time.

(3) It should be carefully checked and confirmed that there is no explosive and dangerous materials in the charge before preheating.

(4) smelting casting tools, such as stirring rods, iron spoons, slag removal tools, etc., shall not be in contact with alloy liquid without 

preheating.

(5) The remaining alloy liquid should be poured into the preheated ingot mold, and it is not allowed to be poured directly on the 

ground or back into the furnace.

5. Several problems should be paid attention to in smelting

(1) The smelting time should be controlled

The time used from the beginning of melting to the end of melting (alloy out) is called melting time. The length of the melting time 

will not only affect the productivity, but also significantly affect the quality of the cast. Because the melting time increases, the element 

burning rate of the alloy will increase, and the opportunity to inhale will increase. Therefore, the melting should be completed in the 

shortest possible time. If permitted, the preheating temperature of the charge should be increased as far as possible, and the operation 

should be compact and the action should be rapid.

(2) The mixing rod used for smelting should be a carbon rod

Some elements in copper alloys, such as iron and lead, exist in the form of mechanical mixtures when melted. Some elements, due to 

different densities, have a tendency to produce specific gravity segregation stratification. Practice has proved that these elements in 

the process of melting and pouring, easy to cause chemical composition unqualified, resulting in mechanical properties unqualified. 

To overcome this phenomenon, it is necessary to use the role of stirring, which is an indispensable link in melting and pouring. However, 

in the period of temperature measurement and cooling, generally do not need to stir. The material composition of the stirring used is 

generally suitable for graphite. This is because if other agitators, such as iron rods, are used, the iron rods melt during the agitation 

process, and the chemical composition of the alloy is affected. At the same time, if the preheating temperature of the iron rod in the 

furnace is relatively high or the stirring time is long, the oxide on the iron rod will enter the alloy liquid as impurities; If the preheating 

temperature of the iron rod is low, the alloy will adhere to the iron rod when stirred, which can be observed in production.

(3) The use of covering agent in melting

For smelting copper alloys, the amount of covering agent is generally: 0.8%-1.2% of the weight of the charge when glass and borax are 

used, because the thickness of the covering layer should be maintained at 10-15cm; When using charcoal, the amount is about 0.5%-0.7% 

of the weight of the charge, and the thickness of the covering layer should be maintained at 25-35 cm. The removal time of the covering 

agent is generally carried out before pouring, and too early will increase the oxidation and suction of the copper alloy. If charcoal is used 

as a covering agent, and the slag blocking effect is good, the covering agent can also be removed, so that it also plays a slag blocking role

in the process of pouring, and the effect is more ideal.

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