The development of high-precision cold-drawn tubes has been around for a long time, so there have been many changes in its production methods, and the overall progress has been made, so that the quality of its products has also increased. Initially applied is the production method that combines the annealing process and the cold drawn steel pipe process.
The in-line annealing mainly comprises an oxidation furnace and a reduction furnace. The steel strip is directly heated to about 450 degrees in the oxidation furnace until the rolling oil remaining on the surface of the strip is burned to achieve the purpose of purifying the surface. . Then the strip is heated to 700-800 degrees to complete the recrystallization annealing, and after cooling, the desired product is obtained.
After the improvement, an alkaline electrolytic degreasing tank can replace the degreasing effect of the oxidation furnace to complete the production of the pipe. After the original board enters the working line, it is electrolytically degreased, then washed, dried, and then recrystallized and annealed by a reducing furnace with a protective gas, and then enters the zinc pot under sealing.
There is also a direct flame heating method. When the strip is eluted with alkali by alkali, the scale of the surface is removed with hydrochloric acid, washed with water, dried, and then passed into a vertical in-line annealing furnace directly heated by a gas flame. By strictly controlling the ratio of the flame of the gas and air in the furnace, the partial flame is burned, 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 being blown, it is necessary to use the furnace to traverse the steel strip, so that there are many operational problems, so the cold drawn steel pipe industry adopts this method is not much.
Since the cold-drawn tube unit has been produced, its production has been simplified by simply injecting hydrogen chloride gas into the strip in the annealing furnace and bringing the strip to a recrystallization temperature. However, due to the serious corrosion of the equipment, resulting in high equipment maintenance and renewal costs, it has not been widely promoted.