Among titanium-processed materials, products made by rolling hot-rolled coils are mainly used in power station condensers, plate heat exchangers, chemicals, construction, etc., and the output accounts for about 80% of the processed materials.
Titanium materials mainly include hot-rolled, and cold-rolled strips, welded pipes, and bars and wires. The production characteristics of titanium materials are that they are carried out using steel processing equipment. According to the inherent characteristics of titanium materials, equipment, and processes are continuously improved to improve production efficiency, dimensional accuracy, and surface quality of processed materials to meet the use requirements of different purposes.
1. Hot-rolled strip coils
Titanium hot-rolled strip coils use the same slabs as thick plates as raw materials. During hot rolling, a two-roller rolling mill or a four-roller furnace coil rolling mill is usually used. To eliminate the surface oxidation diffusion layer generated by hot rolling, the heating temperature of the hot-rolled strip coil should be set as low as possible while ensuring stable rolling and being able to be rolled into strips. Generally, the rolling temperature of titanium in the furnace coil mill is 750~840℃, the pass reduction is 25%-50%, the final rolling temperature is controlled at 660~730℃, and the coiling temperature is 640~690℃.
Due to the uneven residual stress and thermal hysteresis, the hot-rolled coil has a poor plate shape, so annealing is required to eliminate stress. The surface of the annealed coil not only has hot rolling and annealing oxide scales but also has surface defects during hot rolling and surface hardening layers caused by oxygen diffusion when the billet is heated. These are the root causes of surface defects of cold-rolled plates, so they must be thoroughly removed in the descaling process.
When the surface defects or surface hardening layers during hot rolling cannot be completely removed by pickling, they can be removed by mechanical grinding. The grinding amount is about 10μm per time, and 2~3 grindings are performed according to the surface defects. In addition, when there is a requirement for the flatness of the coil, sometimes cold rolling with a small reduction is performed before grinding. Due to the high activity of titanium, grinding chips adhere to the sanding belt during grinding, clogging the holes, reducing the grinding efficiency, or easily causing burning. Therefore, appropriate grinding conditions and sanding belts should be selected. In addition, the powder formed by grinding is ignitable, and cooling measures such as water or water-soluble oil can be used.
2. Cold-rolled plate
Cold-rolled titanium plate uses hot-rolled coils (thickness of 3~6mm, width of 600~1600mm, single coil weight below 10t) as raw materials. The general production process is annealing, descaling, cold rolling, cleaning, vacuum annealing, flat rolling, straightening, and finishing (slitting, plate shearing, etc.).
To remove the oxygen diffusion layer during hot rolling, mechanical methods such as shot peening and pickling are generally used in combination, and the removal amount is about tens of microns. If the removal amount is reduced, the oxygen diffusion layer will sometimes not be removed cleanly, and the remaining surface will reduce the yield of subsequent processes. Therefore, correctly measuring the thickness of the oxygen diffusion layer and accurately checking the hot-rolled surface oxide layer is the key to controlling the descaling amount.
Titanium has significant anisotropy, and it is difficult to cold-roll titanium alloy thin plates, thin strips, and foils using ordinary two-roller and four-roller mills. Because the unit pressure is high, it causes great elastic deformation and flattening of the rolls. Therefore, a mill with a smaller diameter working roll (Sendzimir type) or a multi-roller mill with multiple rolls in the vertical direction (such as a UC mill) is used for rolling. The Sendzimir mill uses an integral arch and rigid structure with short columns. The mill has a high modulus, a small working roll diameter, and a tower-shaped support roll system. The first intermediate roll end has a taper and can move axially. The roll shape adjustment is achieved through an eccentric mechanism and a support bearing. The strip has a large tension during rolling. At the same time, a large amount of process lubricating oil is given, which can greatly reduce the pressure of the metal on the roll, reduce the elastic deformation and bending of the roll, and obtain a good surface.
When titanium is cold rolled, since titanium is an active metal, in the roller bite area if the amount of reduction per pass is large or the rolling speed is fast, the surface finish will be reduced, and it is difficult to meet the surface requirements of electronic materials. This is the thermal adhesion phenomenon between the roller and the material. At this time, the tiny wear powder generated is attached to the surface of the roller or the plate, making the surface rough. Therefore, compared with stainless steel of the same size, the amount of reduction and rolling speed should be lower, the number of passes should be more, and the viscosity of the rolling oil should be higher. In addition, to prevent the rolling surface from sticking, ceramic rollers are also used.
The work hardening caused by cold rolling must be annealed to obtain the required mechanical properties. The recrystallization temperature of pure titanium varies slightly due to the impurity composition and cold working rate, which is about 450~550℃. Generally, annealing is performed in the range of 600~800℃. If the annealing temperature is high or the annealing time is long, it will soften due to grain growth, which improves the formability, but it also leads to disadvantages such as surface roughness.
Non-Ferrous Crucible Inc. provides a variety of commercial Pure Titanium (CP Ti) and Titanium alloys in wire, sheet, bar, tube, and other forms. We also provide Titanium expanded/stamped mesh, Titanium wire mesh, Titanium fittings, Titanium flange, and Titanium machining components. Please send your request to inquiry.crucible@winnewtech.com.