The development of high-precision cold-drawn tubes has a long history so far, so many changes have taken place in its production methods, and the overall progress is progressing, so that the quality of its products has also increased. At the beginning, the production method combining the annealing process and the cold drawn steel pipe process was applied.
This in-line annealing mainly consists of an oxidation furnace and a reduction furnace. The strip flame is directly heated to about 450 degrees in the oxidation furnace until the remaining rolling oil on the surface of the strip is burned to achieve the purpose of surface purification . The strip is then heated to 700-800 degrees to complete the recrystallization annealing. After cooling, the desired product is obtained.
After improving it, an alkaline electrolytic degreasing tank can be used instead of the degreasing effect of the oxidation furnace to complete the production of the pipe. After the original plate enters the operation line, it is subjected to electrolytic degreasing, then washed with water, dried, and then recrystallized and annealed in a reduction furnace with a protective gas, and then enters a zinc pot under a sealed condition.
There is also a direct flame heating method. When the strip is eluted with alkali, the surface oxide scale is removed with hydrochloric acid, and it is washed and dried before entering the vertical in-line annealing furnace heated by a gas flame. By strictly controlling the flame burning ratio of gas and air in the furnace, incomplete flame burning is performed, thereby causing a reducing atmosphere in the furnace.
This kind of production process is complicated, mainly when the unit is stopped, in order to prevent the strip from burning out, the furnace needs to be moved laterally away from the steel strip, so there are many operational problems, so this method is not used by the cold drawn steel pipe industry.
Since the cold-drawn tube unit is available, its production has become simpler, as long as the hydrogen chloride gas is sprayed into the strip in the annealing furnace, and the strip reaches the recrystallization temperature. However, due to the severe corrosion of the equipment, which caused high equipment maintenance and replacement costs, it has not been widely promoted.