The common quality defects of welded pipe in the sizing section of used welded pipe machine can be divided into three categories: dimensional tolerance defects, surface defects and straightness defects. According to these three types of common sizing section welded pipe quality defects are described in detail.

Dimensional tolerance defects

The adjustment of the size of the welded pipe simply exceeds the upper or lower difference is far less difficult than the size fluctuation. The large fluctuation of the outer dimension of the welded pipe refers to the large change of the outer dimension in the longitudinal measurement direction of the welded pipe, which is close to or beyond the tolerance range of the welded pipe, commonly known as "section difference". There are two kinds of phenomena: periodicity and randomness. Take the round tube as an example. See the table below for their causes and adjustment measures.

Surface defects

The surface defects of sizing welded pipes mainly include pits, bumps, indentations, scratches, oxide layer intrusion, etc. The causes and solutions are similar to those of molding. These defects are allowed to be removed for general-purpose pipes, but the removal depth must not be lower than the negative deviation of the nominal wall thickness, otherwise they should be discarded. As for the surface quality requirements of used welded pipe machine manufacturing medium and high-grade furniture pipes, automobile pipes, API pipes, etc., the requirements stipulated in the agreement between the two parties should be met.

Here, we will talk about the common rolling angle defects in (square-moment) special-shaped pipes. The rolling angle defects are divided into single-sided rolling angles and double-sided rolling angles. The method of judging is to use your finger to cross the pipe surface horizontally to the corner arc. If there is a slap in the hand, it indicates that there is a rolled corner defect. In most cases, only one or two corners are rolled.

There are roughly five main reasons for the formation of the rolling angle: (1) The rolls are dislocated and the tube surface is crushed; (2) The roll gap is too large, and the pass line is not long enough; (3) The shaping allowance is too large, and the tube corner is blocked by the roll gap. Corner crushing; (4) The single pass rolling pressure is too large, and the edge of the pass will crush the tube surface; (5) The roll deviates from the rolling center line, resulting in excessive rolling force on a corner, and the corner is crushed. For rolling angle defects, firstly check in reverse according to the mapping principle, and then take corresponding corrective measures.

Straightness defect

The straightness defect here refers to the straightness of the line, including bending, twisting and twisting. During the production of welded pipes, the straightness often changes. The essence of straightness is various stress balance problems in the pipe body, and the sudden change factors affecting the stress balance are mainly material changes, including width, thickness, hardness, etc. It is only explained by the hardness change. After the stress of the straightening system is balanced, it indicates that the system recognizes the existing hardness, and the welded pipe produced by the system is "naturally" straight; however, once the hardness changes, the system does not recognize the new hardness, the stress When the balance is broken, the welded pipe bends; without manual intervention, the pipe bends forever until it is readjusted and a new stress balance system is established. This reminds the operator from one side that in the normal production process, if the straightness of the welded pipe suddenly changes, it is necessary to think that something must have happened in the production process.

Similarly, when the equipment accuracy, cooling system, ambient temperature, operation adjustment and other. change, the existing balance between the invisible welded pipe unit and the welded pipe will be hidden, resulting in the bending of the welded pipe. As far as changes in ambient temperature are concerned, I believe that most of the adjustment workers have this experience: the unit that produced well the day before, the original crew came back to start up after a night of shutdown, and found that all the welded pipes produced were bent. This is actually the invisible factor of temperature, which involves a thermal balance problem. The thermal balance of the welded pipe unit means that after the unit runs for a certain period of time, the temperature of the equipment parts, bearings, hole type, coolant, etc. all rise to a certain height, so various stresses reach a tacit agreement with the welded pipe at that time and are in a balanced state; After the overnight shutdown, the temperature of the unit parts, bearings, rolls and coolants are all in a cold state, which is difficult to achieve stress balance with the hot welded pipe at once, so the welded pipe is bent.

For used welded pipe machine, some of the defects of welded pipes and the reasons for the formation of defects are obvious, and some are more concealed; Therefore, for the disposal of some welded pipe defects, it is not possible to simply discuss the matter, but to have a global concept, and use a systematic concept to guide the adjustment of welded pipes and the search for the cause of defects.