Hot and cold rolling techniques are utilized in the manufacturing process of titanium sheets and strips.
Two distinct approaches, namely belt type and block type, are employed for the production of láminas de titanio.
- The band method entails the slab being rolled into a roll through hot rolling, followed by subsequent processes of cold rolling, heat treatment, and others, until it reaches the desired thickness and state. Finally, the roll is cut into titanium plates or sheets using a cross shear machine.
- The block method involves cutting hot-rolled titanium into pieces, followed by cold rolling, heat treatment, and other processes to produce blocks. The strip method, on the other hand, has higher productivity and yield but requires large equipment, high investment, and complex production technology. It is used when there are conditions and a cooperative production setup with a strip hot mill. In the absence of such conditions, thin hot strip production is achieved by single hot mill rolling. The resulting strip is then welded into tape coils and further processed through cold rolling and subsequent processes to produce placa de titanio and titanium sheet.
The slab undergoes heating and hot rolling on a hot rolling mill to produce medium and thick plate products or cold rolling billets.
Due to titanium’s high affinity for hydrogen absorption and oxidation at elevated temperatures, the heating temperature for titanium and its alloy slab is typically maintained between 850°C and 1150°C. The heating time depends on the heating method and the size of the blank. When using a flame furnace for heating, it is imperative to strictly control the atmosphere inside the furnace to ensure a micro-oxidation environment.
To ensure minimal cold processing, it is recommended to maximize the hot rolling rate when producing titanium plates and sheets.
For strip production, the process involves initially rolling a thick slab multiple times on a rolling machine, followed by further hot rolling in a continuous rolling machine or a rolling mill with an in-furnace coiler until reaching a thickness of 2-3mm.
Alternatively, the slab can be rolled on a hot rolling machine to a thickness of 6-8mm before being formed into a coil or welded. In the case of block production, a single hot mill is typically used, with the possibility of requiring two or three heating cycles. The hot rolling process, surface treatment, subsequent heating, and repeated hot rolling cycles are employed to achieve the desired thickness of the titanium plate or sheet.
The surface treatment of titanium plate or sheet involves the removal of the oxidized layer that forms during the heating, hot rolling, and annealing processes. This treatment can be achieved through two main methods: alkaline pickling and sandblasting (shot) pickling.
Alkaline pickling entails immersing the product in a heated alkali solution (NaOH) containing an oxidant (NaNO3), followed by rapid quenching with water. Next, the product undergoes pickling in a nitric acid solution containing fluoride ions, and is subsequently washed and dried. On the other hand, sandblasting (shot) pickling involves using compressed air to propel sand (or iron shot) onto the surface at high velocity, effectively removing the oxide layer. Afterward, the product is pickled and dried. It is worth noting that treating the waste alkaline solution and alkaline waste gas in the alkaline pickling process can be complex and costly.
Cold-rolled pure titanium is typically rolled at or slightly above room temperature, while certain titanium alloys undergo heating to approximately 100 to 200℃ before rolling. The work hardening rate of titanium and titanium alloys is rapid. For pure titanium, the overall processing rate between two annealing stages should not exceed 50%, whereas for titanium alloys, it should not exceed 30% to 40%. Multiple intermediate annealing and cold rolling steps are required to produce thin products such as titanium plates or titanium sheets.
Annealing consists of two stages: intermediate annealing and final annealing. Intermediate annealing is typically done in a non-vacuum furnace, followed by pickling to eliminate surface oxidation. Final product annealing is commonly performed in a vacuum furnace for a bright and clean finish. To enhance strip surface quality post-annealing, degreasing should be done prior to the process.
The completion and evaluation of various products adhere to their respective delivery conditions. The finishing stage entails rolling, straightening, and cutting the final product. Inspection tasks encompass sample examination, assessment of appearance quality, and verification of dimensional tolerances.