Ti 6242 titanium is a very active metal, in the liquid state, and oxygen, nitrogen, hydrogen and carbon reaction is quite fast, so titanium alloy melting must be in a high vacuum or inert gas (ar or ne) protection. Melting crucible with water-cooled copper crucible, the specific melting process has three main ways: (1) non-self-consuming electrode arc furnace melting alloy melting in a vacuum or inert gas protection. The process mainly prepares electrodes for self-consumption electrode melting. (2) Vacuum self-consuming electrode arc furnace melting A self-consuming electrode made of titanium or titanium alloy is used as the cathode and a water-cooled copper crucible as the anode. The melted electrode enters the crucible in the form of liquid droplets, forming a molten pool. The surface of the molten pool is heated by an electric arc and is always in a liquid state. The bottom and the surrounding area in contact with the crucible are subjected to forced cooling, resulting in bottom-up crystallization. The liquid metal in the molten pool solidifies and becomes titanium ingot. (3) Vacuum self-consumption electrode condensation shell protection melting Melting device schematic. This furnace is developed on the basis of vacuum self-consumption electrode arc furnace, it is a kind of melting and centrifugal pouring into the casting of shaped parts of the furnace type. Its biggest feature is that there exists a layer of titanium alloy solid thin shell between the water-cooled copper crucible and the molten metal, the so-called congealed shell, and this layer of congealed shell of the same material serves as the lining of the crucible, which is used to form the melting pool to store the titanium liquid, and avoids the contamination of the crucible to the titanium alloy liquid. After casting, a layer of congealed shell left in the increase loss can be used as the crucible lining.
In recent years, with the development of science and technology and production needs, successive research and development of melting titanium alloy and other active metal new methods and equipment, mainly electron beam furnace, plasma furnace, vacuum induction furnace, etc., and get a certain degree of application. However, from the comparison of power consumption, melting speed, cost and other technical and economic indicators, self-consumption electrode arc furnace (including condensing shell furnace) melting is still the most economical and applicable melting method. Due to the physical - chemical properties of titanium, making the casting process of titanium alloy, whether the rate of modeling materials is the process has its own unique requirements and characteristics. First, the requirement of very high refractoriness modeling materials; Second, the pouring must be carried out in a high degree of vacuum or inert gas protection, and sometimes also attached to centrifugal force. Connecting shell material is different, melt molding shell is divided into three different systems.
(1) Pure graphite shell system. Graphite powder of different grain sizes is used as refractory filler and sand spreading material, and resin is used as bonding agent. High strength, light weight, low cost and wide source of raw materials. Suitable for centrifugal or gravity casting.
(2) Refractory metal surface layer shell system. For the composite system, in addition to the surface layer due to different modeling materials (tungsten powder and other refractory metals) need to take a special process, the back layer from the modeling materials to the shell-making process are the same as the cast steel investment casting.
(3) Oxide ceramic shell system. The face and back layer of the shell are made of oxide as modeling material, thus the shell has high strength and the thermal conductivity is the smallest among the three types of shells, which is suitable for pouring thin-walled castings with complex shapes.
Titanium castings cast with the above three types of shell system, in the chemical composition and mechanical properties of the difference is very small; but there is a significant difference in surface quality, the latter two types of shell shrinkage is significantly smaller than the graphite shell, and thus the casting dimensional accuracy.
