Measures to solve the fracture problem in the production of prestressed steel wire and steel strand

External quality control measures:
One of the measures to solve the fracture problem in the production of prestressed steel wire and steel strand is the external quality control. Generally speaking, the drawing stage of the rod is highly susceptible to the influence of the oxide scale, which leads to diversified quality problems. In this regard, lubricant should be evenly applied on the surface of the 82B rod to reduce the probability of drawing breakage. The most critical thing is to follow the treatment process, and its important processes (pickling, phosphating) are analyzed as follows.

Pickling process: The use of hydrochloric acid for wire rod cleaning, its advantages are to save heating procedures, shorten cleaning time, etc., compared with sulfuric acid cleaning liquid, its safety and cleanliness is higher. In this process, strictly control the pickling time and pickling concentration, the appropriate pickling time is 12min~18min, and the concentration of hydrochloric acid is 5%~19%. If the pickling time is too long, it is easy to break the rod. If the pickling time is too short, it will increase the resistance of the drawing operation. Phosphating process: At the end of this process, the rod is placed in a mixed solution to provide conditions for an electrochemical reaction to form a coating of zinc phosphate.

Improve the drawing process:

The second measure to solve the problem of fracture in the production of prestressed steel wire and steel strand is to improve the drawing process. The direction of improvement of wire drawing process tends to draw compression rate, mold design, lubrication, cooling, straightening, etc. Based on the quality of the strand, the drawing compression rate should be reduced appropriately. If the compression object is high carbon steel, the compression rate should be reduced continuously. Among them, the 760/9 straight-through wire drawing machine has the advantage in stable drawing. It should be noted that steel production units should dynamically understand customer needs and refer to national standards to ensure steel dimensional accuracy and performance. During the mold design, the working cone Angle is adjusted to 10°~15°, and the diameter of the sizing belt is 0.2cm~0.5cm. This is the basic requirement for ensuring the stability of the steel strand and reducing the wear probability. In the production and drawing stage of steel strand, lubricating powder is added according to the situation to reduce energy loss and extend the service time of the mold. According to the test, 2~4 times with coarse lubrication powder, 6~10 times with fine lubrication powder. For the steel wire cooling link, the mold cooling, drum cooling and other contents are implemented in details, in order to achieve the ideal cooling effect, the temperature should be dynamically measured, so that the mold temperature, drum temperature within the specified range, once the temperature is found to suddenly rise or fall, the team personnel should be notified in time, and start repair measures, so as not to affect the quality of the steel wire. After the end of the processing task, the rod straightening treatment to avoid the formation of internal stress, and to ensure the strength of the steel wire.

Necking fracture:

The third measure to solve the fracture problem in the production of prestressed steel wire and steel strand is the shrinkage fracture. This kind of fracture occurs in the production drawing process, the tension operation error in the production of prestressed steel wire and steel strand, or the estimated high coefficient of prestressed friction of steel wire will cause the shrinkage neck fracture. For example, when the steel strand is produced, the actual estimated friction system is high, and when the prestressed tension is provided according to the friction system, the steel strand as a whole will be subjected to the force beyond the load, resulting in the internal steel wire to be broken at random points. Under normal circumstances, the distribution of necking break points in prestressed steel wire and steel strand is irregular, and after the first steel wire breaks, more break points will be generated, which will affect the strength of prestressed steel wire and steel strand products.

The fracture impact spectrum of strand cable is calculated effectively:

The fourth measure to solve the fracture problem in the production of prestressed steel wire and steel strand is to calculate the fracture impact spectrum of steel strand cable effectively. The first is the cable load unloading path of the strand cable. The failure of the strand cable usually occurs instantaneously and is random. At present, there are few studies on the change of the cable force value at the moment of failure. At the moment of failure, the cable force decline curve of each strand is different, which will have a certain impact on the calculation of impact response spectrum. In order to simplify the calculation, based on the experiment, the cable force time history, failure time (about 2ms) and the cable force decline curve at the moment of failure are obtained by taking the first failure of 5 strand cables as the research object. Secondly, the shock response spectrum of the strand cable is calculated by fitting the curve of the cable force change at the moment of failure of each strand cable according to the function, and then entering the Matlab program to get the shock spectrum of the broken cable. However, this is time-consuming and labor-intensive, and function fitting needs to know the cable force value at the key point, while obtaining the cable force value requires external instruments and equipment, and it is difficult to obtain the cable force value in real time in the actual engineering structure.