Step 1: Obtain Raw Materials
To make a titanium tube blank, the first step is to have qualified raw materials. Titanium in the earth's crust mainly exists in the form of titanium dioxide in minerals such as rutile and ilmenite. Through a series of complex chemical reactions, mainly treating the ore with chlorine and carbon, and then reacting with metallic magnesium, a porous and loose pure titanium like a sponge is finally obtained, which is called "sponge titanium". Its name is very descriptive because its appearance and texture are indeed like a gray metal sponge. This is the foundation for all subsequent processing, and its purity directly determines the quality of the final tube blank. After obtaining the sponge titanium, workers will break it into small pieces of a certain specification to prepare for the next step of smelting.
Step 2: Melting & Casting Into Ingots
Loose sponge titanium cannot be directly processed into tubes. It must be melted into a single, dense metal ingot. Due to titanium's extreme reactivity at high temperatures, it reacts vigorously with oxygen, nitrogen, and other gases in the air. Therefore, the melting process must be carried out in a vacuum or under the protection of inert gases. The most commonly used industrial method is "vacuum consumable arc melting". Simply put, sponge titanium and necessary alloying elements (such as aluminum and vanadium, used to produce the commonly used TC4 titanium alloy) are pressed into electrodes. In a large, vacuumed, water-cooled copper crucible, the electrodes act as "candles", generating high-temperature arcs by self-electrification to melt themselves. The molten titanium is then dropped into a crucible below to cool and solidify, forming the first titanium ingot. To ensure uniform composition and meet purity standards, this process is usually repeated two to three times. The final cylindrical or square titanium ingot obtained is the "parent material" for making tube billets.
Step 3: Forging & Piercing
With a solid titanium ingot in hand, the next step is to transform it into a hollow tube blank. The titanium ingot, after melting, has large grains and an uneven internal structure. It first needs to be forged. The ingot is heated to an appropriate temperature (usually between 800 and 1000°C), and then repeatedly upset and drawn out using a ten-thousand-ton hydraulic press or forging hammer. This process is like kneading dough, which can break down the large grains, refine the microstructure, and compact any possible internal defects, significantly enhancing the mechanical properties of the titanium material. After forging, a smaller-sized, denser bar is obtained. Then comes the crucial step - piercing. The most classic method is "cross rolling piercing", where the heated titanium bar is sent between two counter-rotating rolls. The centerlines of the rolls and the bar have an angle. Under the action of friction, the bar rotates and advances simultaneously, and at the center, it is subjected to a strong shear stress, thus being "forced" to have a hole pierced through it, forming an initial hollow tube.
Step 4: Precision Rolling & Treatment
The rough tubes obtained from piercing are still quite coarse, with uneven wall thickness and imprecise dimensions. Further processing is required. This is typically accomplished through the "tube rolling" process, such as using a cold rolling mill. During this process, the rough tube is placed over a hard mandrel and passed through a specially shaped hole-type roller. As the rolling mill moves back and forth, the tube is gradually rolled, reducing the wall thickness, decreasing the diameter, and smoothing the surface. The dimensional accuracy is significantly improved. Through multiple passes of cold rolling and intermediate heat treatment (known as "annealing", which aims to eliminate the hardening and stress caused by processing and restore the material's plasticity), a titanium tube blank with precise dimensions and excellent performance is finally obtained. Finally, the tube blank is straightened, the ends are cut off, the surface is cleaned (such as acid washing to remove oxide scale), and non-destructive testing is conducted to ensure there are no internal or surface defects. In this way, a qualified titanium tube blank is produced, which is used to manufacture various precision titanium tubes required in the aerospace, chemical, medical, and other fields.
