What are the processes involved in the melting and casting of titanium ingots?
The melting and casting process of titanium ingots mainly includes multiple stages such as refining raw materials, refining, mold preparation, bundling electrodes, smelting, casting, cooling, and cleaning. The following are the main three processes of the titanium ingot melting and casting process: batching, bundling electrodes, and casting introduction:
1. Refining raw materials:
The melting and casting process of titanium ingots begins with refining raw materials. Generally speaking, the main raw materials are titanium ores, such as rutile, ilmenite, etc. These ores need to go through processes such as ore beneficiation and crushing to extract titanium dioxide (TiO2) with higher purity.
The titanium dioxide obtained is refined into high-purity chlorinated titanate through methods such as atmosphere, solvent or chemical reaction. This process also involves a series of separations, purifications and chemical reactions to ensure that the final product has the required purity. Titanium alloy determines the proportion of alloy elements according to the following principles:
(1) The allowable fluctuation range of alloy elements and impurity content and the optimal composition range required for the alloy to obtain optimal performance;
(2) Smelting method and number of smelting times;
(3) The burning loss rate and evaporation rate of alloy elements during the vacuum waste smelting process;
(4) Addition methods and physical properties of alloy elements.
Generally speaking, for elements with high ignition loss rate and easy volatilization, their component proportions should be close to or exceed the upper limit, while for elements that are less prone to volatilization loss, their component proportions should be in the middle range of the required range.
2. Inhibition of electrode blocks
Mold preparation:
Mold preparation refers to preparing the mold for casting, i.e. the final shape of the titanium ingot. Typically, this involves using special sand molds or other high-temperature-resistant materials to prepare the appropriate mold for the shape of the final product. The main requirements for electrodes in consumable smelting are:
(1) Sufficient strength;
(2) Sufficient conductivity;
(3) Straightness;
(4) The alloy elements in the electrode are reasonably distributed;
(5) Free from moisture and pollution.
There are two methods for preparing integral electrodes: pressing (also divided into vertical pressing and horizontal pressing) and extrusion (also divided into horizontal and vertical). The more commonly used method is the suppression method.
The density of the electrode block is related to the pressed raw material. Generally speaking, the density of the electrode block must be greater than 3.2g/cm3 to meet the melting requirements. Generally, a press with a pressure of 300 to 500MPa is used.
Electrode assembly welding is to assemble and weld pressed single electrode blocks into electrodes of the required cross-section and length for consumable arc melting. Argon shielded plasma welding, vacuum plasma welding and electron beam welding are often used in industry. In order to prevent the mixing of high specific gravity inclusions, tungsten arc welding is generally not used. The purity of argon gas for welding is 99.99%.
3. The period from the start of power supply to the completion of all melting of the charge (except for the solid arch bridge above the molten pool) is called the charge melting stage.
In the early stage of smelting, the specific resistance of the newly added charge is large, the electrodes are in direct contact with the charge, and the charge is heated by the resistance heat of the charge. At this time, the input current is small but relatively stable, and resistor heating dominates during this period. But it didn't last long. When the charge under the electrode melts to form three "crucible molten pools", arc heat is generated between the electrodes and the "crucible molten pool", heating the charge, and the molten pool gradually expands outward until the three electrodes are connected. "Big Melt Pool". During the transition from the "crucible molten pool" to the "large molten pool", due to the reduction of the unmelted furnace material, its specific resistance gradually becomes smaller, so the resistance heat of the furnace material gradually decreases; and the arc heat between the electrode and the "crucible molten pool" The proportion of output gradually increases. About half an hour from the onset of melting, arc heat becomes dominant. The above-mentioned "transition period" is an unstable period of melting of high titanium slag. First, because the resistance of the line through which the current passes (electrode → crucible pool → unmelted furnace material → crucible pool → electrode) changes with time; secondly, the solid material above the "crucible pool" often collapses into the molten pool, causing violent reactions, Causes the slag to boil. Moreover, this "material collapse-slag boiling" phenomenon is irregular.
