1. Dissolution of gas
The gases that can be dissolved in copper are mainly hydrogen and oxygen. Diatomic molecular gases cannot be directly dissolved in metal melts. The dissolution process of gas is: atoms adsorbed on the metal surface - atoms dissociated into elemental gas - diffuse into the metal lattice to form solid solutions and compounds. Hydrogen and oxygen are harmful elements in copper. They can not only reduce the performance of copper, but also may lead to the occurrence of "hydrogen disease". Copper ingots contain a certain amount of oxygen, but if excessive oxygen or hydrogen is dissolved, it will be the main cause of ingot quality accidents. Therefore, when smelting copper, measures must be taken to block the source of gas and avoid or minimize the contact of air, moisture, oil and various pollutants with the melt. The dissolution process of gas is to eliminate the "adsorption" condition, making the dissolution process unable to be established.
(1) The binding force between gas and metal.
The hydrogen atom of elemental gas has the smallest radius and is an extremely reactive element. It can be dissolved in almost all metallic liquids and solids. In many metals, hydrogen accounts for 60% to 90% of the total gas content, so metal absorption is often called "hydrogen absorption". Oxygen also has a strong affinity with copper in liquid, and there is oxygen absorption or oxidation, so Cu2O is formed and dissolved in the copper liquid.
(2)Temperature and time
(3) Diffusion speed of gas in liquid copper
(4) The relationship between hydrogen and oxygen in molten copper
The relationship between the content of hydrogen and oxygen in liquid copper is inversely proportional to less oxygen and more hydrogen, more oxygen and less hydrogen. This can explain why TP2, which is completely deoxygenated, is more sensitive to hydrogen damage than T2.
2. Copper smelting
Charcoal is often used as a covering and deoxidizer when smelting copper. Its deoxidation is only performed on the surface in contact with the liquid metal, so it is called a surface deoxidizer. For deoxidized copper (such as TP1, TP2), while using charcoal to deoxidize, phosphorus copper is also used for final deoxidation before coming out of the furnace. Phosphorus copper can sink into the molten pool and dissolve in the entire molten pool, and interacts with the oxidation in the molten metal. Material interaction, deoxidation effect is significant.
In the above two deoxidation reduction reactions, gases are produced, namely CO, CO2 and P2O5. These gas products can bring hydrogen with them to escape from the liquid surface on the way up from the melt. But compared with deoxygenation, this dehydrogenation is secondary or limited.
3. Effect of gas on ingot casting
In routine production, bubbles on copper materials can be caused by extrusion or ingot casting, and are accidental defects in technical waste. The quality responsibility for the long-term and abnormally large number of bubbles lies in the previous process - casting, which is caused by the pores in the copper ingot.
The pores in the copper ingot are filled with gas. Smaller pores can be pressed together after processing, but may be exposed as surface defects - peeling during subsequent processing steps. When there are many pores in the copper ingot, there will be larger pores at the same time. At this time, blistering will occur in the middle and rear sections of the extruded tube blank. The blistering is mostly distributed continuously along the extrusion direction and becomes more serious toward the rear end (the remaining end of the extrusion). , and the bubbling distribution in the circumferential direction is irregular. Those with severe blistering cannot be repaired and can only be scrapped, while those with milder blisters will be repaired and then entered into the stretching process. However, peeling and inclusions are exposed during stretching, which has a greater impact on the yield. When extruding smaller tube blanks with water seal, due to the high cooling intensity and small bubbling (the gas has no time to gather and expand), many defects such as peeling and inclusions are exposed during the subsequent cold rolling-drawing production process, and the tube ends. Partial splitting occurred. After annealing, the drawn pipe will show a large amount of rash-like blistering. The difference from the blistering of the extruded billet is that the bubbles are mostly discontinuous and smaller. The big bubbles are like rice grains and the small ones are like needle tips. They are not easy to detect with the naked eye and need to be You can detect it by feeling it.
Another reason for the blistering of copper tubes is that the ingot is a supersaturated copper solid solution, which distorts the crystal lattice, causing third-type stress and reducing plasticity. During extrusion or annealing, due to temperature changes, hydrogen precipitates from interfaces such as grain boundaries or inclusions extending along the extrusion direction to form bubbles.
(1) Electrolytic copper must comply with standards; recycled materials from bubbling tubes are not used to produce red copper.
(2) Loading materials (materials should be "oil-free, water-free, and non-mixed") must be loaded multiple times and fully filled to fully eliminate the water vapor adsorbed by the charge. Concentrate on filling a furnace in 2 to 3 times, and do not put in too many times.
(3) The charcoal must be dry (calcined charcoal is preferred). ***Charcoal must be added immediately after loading, with a covering thickness of 100mm~150mm to meet the requirements of preventing air inhalation, deoxidation and heat preservation.
(4) The furnace door must be closed in time after the charge is melted.
(5) Calcium chloride (dehydrating agent) is installed in the dryer of the gas generation system and replaced in time to absorb moisture in the gas. The gas hood should be properly covered, and the gas should be turned on 5 to 10 minutes before discharge to fully remove the original air in the hood.
(6) The spindle base should be dried and preheated with gas, and
