Different classifications of copper alloy smelting

1. Smelting of pure copper

(1) Preheat the crucible to dark red, and add a layer of dry charcoal or covering agent with a thickness of about 30-50cm on the bottom of the crucible. Then add the leftovers, waste blocks and bars in turn, and finally add electrolytic copper.

(2) The additional alloying elements can be preheated on the stove, and cold materials are strictly prohibited from being added to the liquid metal. During the entire melting process, the charge should be frequently moved to prevent bridging.

(3) Raise the temperature to melt the alloy completely. After the alloy is fully melted, when the temperature reaches 1200-1220°C, add phosphorus copper deoxidizing 0.3%-0.4% of the weight of the alloy solution, and the phosphorus and cuprous oxide will react as follows: 5Cu2O+2P=P2O5+10Cu and Cu2O+P2O5= 2CuPO3, the generated phosphorus pentoxide gas escapes from the alloy, the copper phosphate can float on the liquid surface, and the slag is removed, thus achieving the purpose of deoxidation.

(4) Finally, the slag is removed from the furnace, and the pouring temperature of the alloy liquid is generally 1100-1200°C.

The copper-based alloy with zinc as the main alloying element is brass, which is divided into two types: ordinary brass and special brass. Ordinary brass is a binary alloy composed of copper and zinc, mainly used for press processing. Adding other alloying elements (such as silicon, aluminum, manganese, lead, iron, nickel, etc.) on the basis of ordinary brass becomes special brass. Cast brass is mostly special brass.

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

(2) Ratio of furnace charges According to general casting practice, the composition of new materials should account for ≥30% of the total weight of furnace materials, and the recycled materials should be ≤70%. However, in actual production, we consider that copper alloys have a lot of recycled materials. When the mass percentage of recycled materials is ≥90% in the proportion of furnace materials, the melting quality is still very good, and the chemical spectrum analysis proves that the composition of the casting is qualified. When there are many returned materials, it is necessary to consider whether the impurities in the alloy exceed the standard.

(3) Preparation before smelting ①Preparation of metal charge: The return charge is the waste castings, risers and remelted ingots of the same brand, and needs to have a clear chemical composition. Before entering the furnace, remove the dirt on the surface by sand blowing, and install the furnace after preheating (the first batch of cold furnaces can be preheated along with the furnace); the electrolytic copper is removed by sand blasting to remove dirt, and after preheating at 500-550°C to remove moisture, (The first batch of cold furnace melting can be preheated with the furnace; pure metal elements can be preheated on the side of the furnace before entering the furnace. The maximum size of the metal charge should not exceed 1/3 of the diameter of the crucible, and the length should not exceed the depth of the crucible 4/5. ②Preparation of crucible, melting equipment and tools: Before using the crucible, there should be no cracks and other damages that affect safety. The new crucible must be heated slowly at low temperature to prevent cracks; Clean; when using a new graphite crucible and changing the type of smelting alloy, the crucible should be melted with the same brand series of alloys to wash the furnace before smelting; the stirring rod made of refractory materials and graphite must be thoroughly cleaned of residual paint and rust, and coated with a layer Dry the refractory material or paint it before use; the ingot mold must be thoroughly cleaned before use, and preheat to 100-150°C after painting the paint for use.

(4) Preparation of covering agent and flux ①Charcoal should be put into a sealed oven and baked at no lower than 800°C for 4 hours, and prevent moisture absorption when it is ready for use. ② Covering agent, dry charcoal can also be used as covering agent. Covering agents are required to dry and remove debris.

(5) Alloy smelting process

①Preheat the crucible to dark red, and add 20-40cm thick charcoal to the bottom.

② Add electrolytic copper, rapidly heat up and melt, then add intermediate alloys (if any) in the order of high melting point first and then low melting point, and finally add back the charge, and add charcoal at the same time to ensure that the alloy liquid level is not exposed to the air.

③Smelting brass generally also needs to be deoxidized. After the copper is completely melted, when the temperature reaches 1150-1200°C, phosphor copper (calculated as P accounting for 0.04%-0.06% of the weight of the copper liquid) is added for deoxidation. The actual comparison between deoxidation and non-deoxidation shows that the surface quality of castings after deoxidation is better than that without deoxidation.

④ Add alloying elements according to the composition requirements of each alloy brand: add aluminum-copper master alloy at 1100-1120°C, add pure zinc and pure aluminum in batches at 1100-1150°C and stir. When melting silicon brass, silicon should be added first, followed by zinc; when lead brass is melted, zinc should be added first and then lead. The adding temperature of zinc element should be controlled. If the temperature drops after adding zinc, power can be transmitted in the middle. When the alloy liquid temperature is higher than 1200℃, zinc is not allowed to be added.

⑤ Remove the slag from the furnace, adjust the alloy liquid to the temperature required by the casting process card, and then quickly take it out of the furnace and pour. The pouring temperature of the alloy is one of the factors that affect the performance of the casting. The general furnace temperature is ZCuZn38: 1100-1130°C; ZCuZn40Pb2: 1080-1100°C; ZCuZn31Al2: 1120-1140°C; ZCuZn16Si4: 1100-1140°C.

⑥Smelting two alloys of different grades, when the chemical composition is affected, the furnace should be cleaned in the middle. For example, use crucibles and tools that have smelted aluminum bronze to melt tin bronze, and the crucible and tools must contain aluminum. Although aluminum is a qualified component in aluminum bronze, it is the most harmful element in tin 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 form high melting point oxides Al2O3 and SiO2, so that the castings form slag inclusions, which need to be refined to remove.

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, which has good wear resistance, corrosion resistance, good strength and plasticity. Tin-free bronze includes aluminum bronze, lead bronze, silicon bronze, etc., which contain different main elements. For example, aluminum bronze is a copper-based alloy with aluminum as the main alloying element.

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

(2) Ratio of furnace charge The composition of new material should account for ≥30% of the total weight of furnace charge, and the recycled charge should be ≤70%.

(3) Preparations before smelting The preparations for bronze smelting are the same as those for brass smelting. Charcoal should be put into a sealed oven and baked at no lower than 800°C for 4 hours, and prevent moisture absorption when it is not used. Straw ash should be ground into powder, remove moisture, dry thoroughly, and pay attention to moisture protection when ready to use. Covering agents are required to dry and remove debris.

(4) Alloy smelting process There are many types of cast bronze, only a few typical alloys are discussed here, and other similar copper alloys can be used for reference.

Smelting of ZCuSn10Pb1 and ZCuPb10Sn10: ① Preheat the crucible to dark red, and add 20cm-40cm thick charcoal to the bottom. ② Add electrolytic copper, heat up rapidly and melt it, then add back charge, and add charcoal at the same time to ensure that the alloy liquid level is not exposed to the air. ③ After the furnace charge is melted, add phosphor copper (generally add 0.5% of the furnace charge, and all the phosphor copper used when melting phosphorus tin bronze can be added). ④ Add zinc, tin and lead in sequence (according to the ingredients). After the former charge is completely melted, add the next one and keep stirring the alloy liquid. ⑤ Adjust the alloy liquid temperature between 1100-1150 ℃. ⑥ Slag out of the furnace, add phosphorus copper (generally 0.1% of the weight of the furnace charge), deoxidize, stir evenly, and sprinkle a layer of straw ash on the surface of the alloy liquid, adjust the alloy liquid to the temperature required by the casting process card (generally 1130 -1180°C), quickly out of the oven and poured.

Smelting of ZCuAl10Fe3 and ZCuAl10Fe3Mn2: ① These two alloys cannot be melted with a crucible that has melted other alloys. ②Preheat the crucible to dark red, and add the prepared flux. . ③ Add the low-carbon thin steel sheet preheated to about 200°C and the furnace charge at the same time, stir the alloy after melting, and raise the temperature to 1150-1180°C. ④Add 0.3% of the alloy weight of phosphor copper for deoxidation, and add flux. ⑤Add in batches of pure aluminum and pure manganese (according to ingredients) preheated to 200°C, and press them in with a stirring rod for each batch to melt rapidly, and keep stirring to make the ingredients uniform, and finally adjust The temperature of the alloy liquid is between 1120-1220°C. ⑥ Cover the slag with straw ash, adjust the alloy temperature (generally 1160-1200 ℃) according to the casting process card, and then quickly adjust the casting out of the furnace.

4. Several problems should be paid attention to in smelting

(1) The smelting time should be controlled. The time from the start of feeding to the end of melting (alloy out of the furnace) is called melting time. The length of the melting time will not only affect the productivity, but also significantly affect the quality of the castings poured out. Because the melting time increases, the element burning rate of the alloy will increase, and the chance of getting gas will increase. Therefore, the melting work should be done in the shortest possible time. If possible, try to increase the preheating temperature of the charge, and the operation should be compact and the action should be rapid.

(2) Stirring rods for smelting should be carbon rods. Some elements in copper alloys, such as iron and lead, exist in the form of mechanical mixtures when they are melted. There are also some elements that have a tendency to produce specific gravity segregation and stratification due to different densities. Practice has proved that these elements are likely to cause unqualified chemical composition and unqualified mechanical properties during the process of smelting and pouring. To overcome this phenomenon, stirring must be used, which is an indispensable part of melting and pouring. However, stirring is generally not required during temperature measurement and cooling. And the material component of the stirring thing used is generally suitable to use graphite. This is because, if other stirrers such as iron rods are used, the iron rods will melt during the stirring process, which will affect the chemical composition of the alloy. 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 oxides on the iron rod will enter the alloy liquid and become impurities; if the preheating temperature of the iron rod is low, the alloy will It must adhere to the iron rod, which can be observed in production.

(3) The use of covering agent during smelting For smelting copper alloys, the amount of covering agent is generally: 0.8%-1.2% of the charge weight when using glass and borax, because the thickness of the covering layer must be kept at 10- 15cm; when using charcoal, the dosage is about 0.5%-0.7% of the weight of the charge, and the thickness of the covering layer should be kept at 25-35cm. The removal time of the covering agent is generally carried out before pouring, and if it is carried out too early, it will increase the oxidation and gas absorption of the copper alloy. If charcoal is used as the covering agent and the slag blocking effect is good, the covering agent may not be removed, and it can also play the role of slag blocking during the pouring process, and the effect is more ideal.