Titanium alloy tubes, a special type of tubing meticulously crafted from titanium alloys, have won widespread acclaim and application in numerous industrial fields due to their superior properties such as lightweight, high strength, high temperature resistance, and corrosion resistance. Their excellent mechanical and stamping properties, coupled with the ability to be processed through welding and other techniques, with welded joints exhibiting strength almost equivalent to the base metal, and excellent machinability, make titanium alloy tubes play an irreplaceable role in various fields, including chemical equipment, petroleum, power, seawater desalination, construction, and everyday consumer goods.
In the manufacturing process of titanium alloy tubes, the precision of the processing technology directly affects the final performance and quality of the tube. From the initial smelting to the final forging, every step undergoes strict control and optimization.
In the smelting stage, advanced plasma gun or electron beam gun technology is used to directly melt the mixture of sponge titanium and intermediate alloys to obtain high-purity tubular hollow ingots. During this process, parameters such as raw material ratios, melting temperature, and melting time are precisely controlled to ensure the ingot's chemical composition and microstructure reach optimal levels. For traditional columnar titanium alloy ingots, a drilling process is used to create tube blanks, and titanium scrap is recycled and remelted to improve material utilization and reduce costs.
Next is the forging stage, a crucial step in the titanium alloy tube forming process. After heating the cast tube blank to a specific temperature, it undergoes three radial forgings. Each forging requires changing the mandrel, and the deformation and movement speed of the tube blank are strictly controlled. Through this series of forging processes, the cross-sectional shape of the tube blank gradually transforms from an initial outer square with an inner circle to an outer octagon with an inner circle, and finally returns to a circular shape. Temperature and speed control are extremely critical during this process, directly affecting the tube's mechanical properties, microstructure, and surface quality. Furthermore, advanced testing technologies and quality control methods are employed during forging to ensure that every detail of the tube meets standards, thereby satisfying various customer needs and application scenarios.
The skew rolling piercing of seamless titanium alloy tube blanks is divided into two processes: two-roll skew rolling piercing and three-roll skew rolling piercing. The application of the three-roll skew rolling piercing process in titanium alloys is partly due to improvements in the titanium alloy material itself, which enhances its machinability, and partly due to improvements and refinements in the three-roll skew rolling piercing process itself.
Titanium tube blanks produced by the two-roll skew rolling piercing method are prone to defects such as peeling, folding, and head cracking on both the inner and outer surfaces, resulting in poor dimensional accuracy. Therefore, the two-roll skew rolling piercing method cannot produce high-quality tube blanks. The three-roll skew rolling piercing method, developed from the two-roll skew rolling piercing method, can not only produce tube blanks with high dimensional accuracy and relatively good inner and outer surface quality, but also thin-walled tube blanks with a diameter-to-wall-thickness ratio greater than 10, significantly improving production efficiency. It is evident that three-roll skew rolling piercing has significant advantages over two-roll skew rolling piercing. In some companies' technological upgrades, two-roll skew rolling piercing utilizes mature design processes from three-roll skew rolling piercing. Furthermore, the inherent technical characteristics of the three-roll skew rolling mill determine its widespread application in titanium alloy piercing.
When titanium tubes undergo secondary piercing, the required reduction in the first piercing is relatively small, resulting in minimal deformation. Therefore, while ensuring mandrel strength, it is easier to pierce compared to single-shot piercing. The smaller reduction in diameter naturally leads to fewer internal folds, reducing inner surface defects. During the second piercing, axial resistance is lower, and with appropriate reduction distribution, inner surface defects are significantly reduced.
Single-shot piercing requires only one heating cycle. Due to the lower thermal conductivity of titanium alloy compared to stainless steel, secondary piercing is also considered to require only one heating cycle. However, considering the specifications of the titanium tube being pierced, the specific number of heating cycles can only be determined in subsequent research.
When using single-pass piercing, the reduction required for single-pass piercing is large. Therefore, when piercing titanium tubes of the same specifications, the rotation speed required for single-pass piercing is relatively high. When piercing twice, the rotation speed of the first piercing machine will not be very high, and the surface quality of the tube blank is relatively better.
