The liner is the key component of perforation bombs and armor-piercing, whose performance directly affects the penetration depth and piercing armor-piercing shells and after the explosion. In the early days, it uses turning process to fabricate copper rods and iron rods to form the liner shape or press-molding process to copper plate and iron plate. But these process has lower productivity, low dimensional accuracy and less prone to clogging of the perforation. With the development of powder metallurgy, powder sintering gradually replaced the cover plate liner, the production process is simplified, and overall efficiency has been improved.

However, due to the cover wall is thinner, easily deformed during sintering, poor surface fineness, it needs some optimization. Warm flow compaction can form the large component with a complex shape or structure and uniform density distribution, which is beneficial for the further expansion of tungsten copper material applications. It combines the advantages of injection molding and warm compacting process, which improves the flowability of the mixed powder by the viscosity changing of the binder. There are some experiments shows that the density distribution of W-70Cu liner by warm flow compaction is more uniform and the penetration is more stable.

Overall, compared with the injection molding suitable for the smaller components, warm flow compaction is more suitable for the larger components with complex structure and shape. It has higher requirements on the granularity of raw material and is sensitive to the temperature changes and the amounts of binder. Low temperature may cause mixing powder flow properties deteriorated, so that the tungsten copper shaped charge density distribution can not be molded or uneven. High temperature may obviously separate the two phase (the mixed powder and the binder). The excessive amount of adhesive may cause infiltrated tungsten skeleton pore through the large, so that the density decreases and easily deformed. In addition, warm flow compaction combines the advantages of injection molding and warm compacting process, and it can effectively improve the density, the penetration depth and armor capability of tungsten copper liner, which is the ideal choice for tungsten copper liner manufacturing in the future.

Tungsten copper liner is a kind of psudoalloy that composed of W and Cu, which is immiscible and forming compound with each other. So it is difficult to fabricate by common pressing-sintering process, the most widely used in tungsten copper products is powder metallurgy (PM), which includes infiltration and activated liquid-phase sintering. Infiltration presses tungsten powder into a compact, at a certain temperature pre-sinter the porous tungsten skeleton with density and strength. And then the low melting point of the molten liquid copper is infiltrated tungsten skeleton in order to obtain tungsten copper alloy with fully densified. The main mechanism is the liquid metal wetting porous matrix metal, under the effect of capillary forces along the inter-particle pore liquid copper flows and fills pores of the porous tungsten skeleton.

According to the sintering temperature, infiltration process can be specifically divided into sinter tungsten skeleton at high temperature + Cu infiltrated and sinter composite powder at low temperature + Cu infiltrated. Sinter tungsten skeleton at high temperature + Cu infiltrated presses tungsten powder into a compact before sinter and infiltrated Cu at 1800-2200℃. Since the tungsten powder at a high temperature to fully restore the remaining low-melting impurities and sub-oxides can be restored by evaporation gasification and thermal decomposition was removed, thus prepared tungsten copper shaped relative density of 99.2% comprehensive and excellent performance.

However, it also has some disadvantages, such as long production cycle, the control parameters are many and complex and high production cost. While sinter composite powder at low temperature + Cu infiltrated is mixed with a small amount of induced copper before sintering and infiltration. Generally, induced copper content of about 2.5% -3.5% and the granularity is similar to tungsten powder, which can effectively improve the compacting performance and the flowability of liquid Cu. But too much of the added amount of copper will result in enrichment-induced infiltration of copper, so that the overall the density of tungsten copper liner decreases.

Grinding
Grinding electrode will produce radioactive dust into atmosphere. So it is recommended during grinding should make up a dedicated grindstone and local dust extraction. Besides, a simple filter mask is necessary unless you contact with small number of electrodes (less than about 20 per year). On the other hand, if the grinding wheel is not fitted with a protective viewing screen, eye protection should be worn. What’s more, the air extract from the grindstone should be collection so that the particles are deposited into a substantial disposable bag and will not release to the atmosphere just in case of ingestion or inhalation by welders.

After finish welding process, the area round the grinding wheels should be cleaned daily with a vacuum cleaner to remove dust particles. Besides, welders should be encouraged to wash their hands or whole body.

Welding
Some hazardous substance of thoriated tungsten electrode does occur during welding but it is a very small amount and the corresponding level of radioactivity is extremely low. However, wearing mouth, nose and eye protection during welding would further reduce any risk of contamination, and make welders more safety.

Alternatives to thoriated tungsten electrode
Lanthanum, cerium, yttrium and zirconium oxides can all be used with tungsten to produce lanthanated, ceriated, zirconiated and yttriated tungsten electrodes. Compared with thoriated tungsten electrode, they are all marginally radioactive, so the risk is even lower than with thorium oxide, so no specific precautions are needed. At the present, especially in developed counties they prefer to use these electrodes to place thoriated tungsten electrode. Among these rare earth tungsten electrodes, ceriated or lanthanated tungstens electrode are acceptable alternatives to thoriated tungsten electrode, particularly with a DC current, while zirconiated tungsten is preferred for AC current welding. There are very minor differences in the arc voltages required for equal currents between the various alternatives. Consideration should be given to justifying the use of thoriated tungsten electrodes in preference to other suitable alternatives.

Introduction
Thoriated tungsten electrode has low work function, stable welding performance and long service life, so in the early time it was widely used in welding industry.

Tungsten electrodes are used in tungsten inert gas (TIG) or plasma welding. During the welding process the electrode, arc and weld pool are protected from atmospheric contamination by an inert protective gas. A tungsten electrode is used in welding industry because it can withstand very high temperatures without melting or erosion. It is usually made by powder metallurgy and is formed to various sizes after sintering. Besides, according to different doped rare earth oxides, it can be divided into different types. Oxides used are primarily those of zirconium, thorium, lanthanum, yttrium or cerium, and doped quantity is usually 1%-4%. All these oxides greatly improve arc initiation, especially when direct current (DC) welding is employed.

Hazards
As we know thorium (Th) is slightly radioactive with a long half life and emits mainly alpha (α) particles, but occasionally some beta (β) and gamma (γ) radiation is emitted. Thoriated tungsten electrode was made by 2%thorium oxide, therefore, a low level radioactive material which contains in electrode, and it will cause small external radiation hazard and an internal hazard from ingestion or inhalation to welders. The external hazard estimated for a welder holding an electrode for a long time is a very small fraction of the maximum permissible radiation dose and it is concluded that the external radiation hazard is likely to be negligible. However, to achieve maximum arc stability the electrode tip should grind to a conical point before use and the shape is maintained during use by regular regrinding. During the grinding process, particles of electrodes may be produced with thoria on the surface. These dust particles that create the major hazard, as they may be inhaled. On the other hand, during welding, electrode will release hazardous substance, if welder ingestion or inhalation by accident it will harm to their health.

Storage
It is recommended that thoriated electrodes are stored in steel boxes with clearly labelled. When stored in closed boxes, there should no significant hazard in handling and storage. 10 pieces electrodes for one plastic box can be handled by welders safely without any special precautions.