Titanium alloy melting method is generally divided into: 1. vacuum self-consumption arc furnace melting method; 2. non-self-consumption vacuum arc furnace melting method; 3. cold hearth melting method; 4. cold crucible melting method; 5. electroslag melting method five methods.

1 vacuum self-consumption arc furnace melting method (referred to as VAR method)

With the development of vacuum technology and computer applications, VAR method soon became a mature industrial production technology of titanium, titanium and its alloys today, the vast majority of ingots is the use of this method of production. VAR method is characterized by low power consumption, high melting speed and good quality reproducibility, VAR method of melting ingots with good crystalline organization and uniform chemical composition. Normally, the finished ingot should be produced by VAR melting. At least two remelts are required. VAR method of production of titanium ingots, manufacturers around the world to use the process is basically similar, the difference lies in the use of different electrode preparation and equipment. Electrode preparation can be divided into three main categories, one is the use of continuous pressing according to the portion of material, the whole electrode, excluding the electrode welding process: the second is a single piece of electrode pressing, welding into self-consumption electrode. And by plasma argon arc welding or vacuum welding welded into one; Third, the use of other melting method to prepare casting electrodes.

The technical characteristics and advantages of modern advanced VAR furnace:

(1) full coaxial power input, that is to say, the entire furnace height on the complete coaxiality, called coaxial power supply ', to reduce the phenomenon of segregation;

(2) Electrical calibration in the crucible can be fine-tuned in X-axis direction/Y-axis direction;

(3) With precise electrode weighing system, the melting rate is automatically controlled, realizing constant speed melting' and ensuring the melting quality;

(4) Ensuring the repeatability and consistency of each melting;

(5) Flexibility, i.e., one furnace is capable of producing a variety of ingot types as well as large-scale ingot casting, which can substantially increase productivity;

(6) Good economy. The “coaxial power supply” method can avoid the magnetic leakage caused by the unbalanced crucible supply current. It can weaken or eliminate the unfavorable influence of induced magnetic field on the melting products. It also improves the electric efficiency, thus obtaining ingots with stable quality. The purpose of “constant speed melting” is to improve the quality of ingot casting, through the advanced electric control system and weight sensor to ensure that the length of the arc and the melting rate of the melting process is constant, so as to control the process of coagulation. The segregation phenomenon can be effectively prevented and the intrinsic quality of the ingots can be guaranteed.

Modern titanium melting with VAR furnace in addition to the above two major features, but also to achieve the large-scale VAR furnace, modern VAR furnace can melt diameter 1.5m, weighing 32t of large ingots.

The vAR method is the modern titanium and titanium alloy standard industrial melting method. But there are still the following technologies need to be solved:

First, the electrode preparation method. Preparation of electrode process is very cumbersome. Need to use expensive presses will be titanium sponge, intermediate alloys and return to the residue pressed into a whole electrode or a single small wrench. The single piece electrodes also need to be welded into self-consuming electrodes. At the same time, in order to ensure the uniformity of the composition of the self-consumption electrodes, it is also necessary to configure the fabric, weighing, mixing and other appropriate facilities.

Second, the occasional presence of segregation and other metallurgical defects. Such as component segregation and solidification segregation.

The former is due to the uneven distribution of impurity elements or alloying elements in the electrode, melting to balance the distribution of solidification produced; the latter is due to the raw materials or processes occasionally brought into the high-density inclusions (HDI) and low-density inclusions (LDI), these inclusions can not be completely dissolved during the melting process, resulting in the production of extremely hazardous metallurgical defects such as inclusions.

2. Non-self-consuming vacuum arc furnace melting method (simple NC method)

At present, the water-cooled copper electrode has replaced the titanium industry in the initial stage of tungsten a thorium gold electrodes or graphite electrodes to solve the problem of industrial pollution, thus making the NC method has become an important method of melting titanium and titanium gold, several tons of NC furnace has been operating in Europe and the United States.

Water-cooled copper electrodes are divided into two types: one is self-rotating; the other is a rotating magnetic field, which is designed to prevent arc burns on the electrode.

NC furnace can also be divided into two types: one is in the water-cooled copper crucible melting raw materials, in the water-cooled copper mold casting into ingots; the other is in the water-cooled copper crucible continuous casting raw materials, melting and solidification.

The advantages of NC melting are: (1) the process of pressing electrode and welding electrode can be eliminated; (2) the arc can stay on the material for a longer period of time, so as to improve the degree of homogenization of ingot composition; (3) different shapes and sizes of raw materials can be used, and 100% residual material can be added to the melting process, so as to realize the recycling of titanium.

The NC method, as a primary melting process, is advantageous from the point of view of increasing the recovery rate of the residue and reducing the cost. Normally, NC furnaces and VAR furnaces are used in combination to fully utilize the advantages of each.

3. Cold hearth melting method (CHM method for short)

By the raw material contamination and melting process abnormalities caused by the titanium and titanium ingot metallurgical inclusions defects, has been affecting the titanium and titanium table gold in the aerospace applications. In order to eliminate the titanium alloy aircraft engine rotating parts in the metallurgical mixture, cold furnace bed melting technology came into being.

The most important feature of the CHM method is the melting, refining and solidification process separation, that is, the molten charge into the Ling furnace bed after the first melting, and then into the cold bed of the refining zone for refining, and finally in the crystallization zone solidified into ingots. The significant advantage of CHM technology is the formation of a congealed shell on the cold bed bed wall, which has a “stagnant zone” that captures high-density inclusions (HDI) such as WC, Mo, Ta, etc. At the same time, in the refining zone, the retention of low-density inclusions (LDI) particles in the high-temperature liquid is extended to ensure the complete dissolution of the LDI, thus removing the inclusion defects efficiently. In other words. The purification mechanism of cold hearth melting can be divided into two kinds of specific gravity separation and melting separation.

3.1 Electron beam cold hearth melting method (EBCHM method for short) Electron beam melting (EB for short), is the use of high-speed electron energy, so that the material itself generates heat to melt and refine the process. An EB furnace with a cold hearth is called an EBCHM, and the EBCHM method has excellent features not found in conventional melting methods:

(1) Effective removal of high density inclusions (HDI) such as tantalum, molybdenum, tungsten, tungsten carbide, etc. and titanium nitride. Low-density inclusions (LDI) such as titanium oxide;

(2) Can accept a variety of charging methods, titanium residue recycling is easier, that is, you can use other melting method can not be used in the waste, can still produce pure titanium ingots, significantly reduce the cost of the product;

(3) Samples can be taken directly from the metal liquid to analyze and test;

(4) Can produce shaped ingot billet, reduce the production process, reduce the consumption of raw materials, improve the yield;

EBCHM method also has the following disadvantages:

(1) Melting needs to be carried out under high vacuum conditions, so it is not possible to use titanium sponge with high chloride content for direct melting;

(2) The alloying elements are volatile and it is difficult to control the chemical composition.

3.2 Plasma Cold Jealousy Bed Melting Method (cylinder called PCHM method)

PCHM method using inert gas ionization generated by the plasma arc as a heat source, can be from low vacuum to near atmospheric pressure in a wide range of pressure to complete the melting. The significant feature of this method is that it can ensure that alloy components with different vapor pressures can be melted without any significant The method has the ability to provide improved metallicity of the traditional table, and it can realize the melting of diversified alloys, and it is a melting method that is more economical than the traditional melting method. With this method of melting, for titanium and titanium alloys, the ideal ingot can be obtained in a single melting. The advantages of modern PCHM method are:

① Low investment in equipment, easy to operate, safe and reliable;

② Different kinds and forms of raw materials can be used, and the recovery rate of residue is high;

③ Ensuring the chemical composition of diversified alloys;

(iii) The chemical composition of diversified alloys is guaranteed; (iv) The expensive inert gas can be recycled and reused, thus reducing the production cost.

The disadvantage of the PCHM method is the lower electrical efficiency, and the similarity between EBCHM and PCHM is that both can eliminate HDI and LDI. generally, the former is more suitable for melting pure titanium, while the latter is more suitable for alloys. Like the VAR method, the above two methods have achieved a wide range of automated process control, including process parameters (melting speed, temperature distribution during melting and solidification, compositional changes during melting, degree of removal of insoluble inclusions, etc.) and quality.

4. Cold Crucible Melting Method (CCM method)

8O s American ferrosilicon company, the development of a slag-free induction melting process, the CCM method to industrial production applications for the production of titanium ingots and titanium precision castings. In recent years, in some economically developed countries, the CCM method has started to industrialize the production of titanium ingots with a maximum diameter of l m and a length of 2 m. The CCM melting process is carried out in a metal crucible consisting of water-cooled curved blocks or copper tubes that are not electrically conductive to each other, and the most important advantage of such a combination lies in the fact that the gap between each of the two blocks is a reinforcing magnetic field, which produces strong stirring and uniformity of chemical composition and temperature. The biggest advantage of this combination is that the gap between the two blocks is an enhanced magnetic field, the strong stirring produced by the magnetic field makes the chemical composition and temperature consistent, thus improving the quality of the product.CCM method has the characteristics of both VAR method and refractory material crucible induction melting, no need for refractory materials, do not need to make electrodes can be obtained at a time of melting the composition of the uniformity of the high quality of ingots without the crucible contamination.CCM method has the advantage of low cost of equipment and easy operation compared with the VAR method, but at present, this technology is still in the stage of development.

5. Electroslag melting method (ESR method for short)

ESR method is the use of electric current through the conductive slag when the charged particles collide with each other, and the conversion of electrical energy into heat. That is, with the slag resistance generated by the thermal energy to melt and refine the charge. ESR method using self-consumption electrode in the inactive slag (CaF2) for electroslag melting, it can be directly melted and cast into the same shape of the ingot billet, and has a good surface quality, suitable for the next process of direct processing. The advantages of this method are:

(1) The ESR furnace is fully coaxial to ensure the reproducibility of the best quality ingots;

(2) Axial crystallization of the ingot, dense and homogeneous organization;

(3) Very high precision electrode weighing system and melting rate control system;

(4) Simple equipment, easy to operate. The disadvantage is that it can not drain the slag on the ingot pollution.