Tube Mill Fault Analysis——Weld Cracking Phenomenon

The appearance of gaps refers to the phenomenon that the welds are not bonded together. The length of the gaps is generally more than a few centimeters or even longer. The main reasons are as follows:

(1) Pass wear

As the extrusion roll hole pattern wears, the hole pattern (R) size gradually becomes larger. When using hot-rolled steel strip as the raw material of welded pipe, when there is a negative deviation in the width of the steel strip or when the steel is slightly pulled, the quality of the weld will have quality problems.

The most serious is the generation of slotted pipes. Therefore, it is necessary to constantly check the inner wool of the welded pipe, increase the extrusion amount of the extrusion roller, or replace the new pass in time.

(2) Bearing damage

When the bearing of the squeeze roller is only slightly damaged, there will be weld quality problems such as trachoma tubes and welded tubes. Once the bearing is seriously damaged, the extrusion roller has no extrusion force on the weld seam of the tube billet, so the weld seam becomes fully open, accompanied by other quality accidents. At this time, we can also observe the squeeze roller with damaged bearing, and the swing amplitude will increase with the degree of bearing damage.

(3) Magnet bar

The magnetic bar will form a magnetic field during the welding process of the tube blank, and the high-frequency current can be highly concentrated in the "V"-shaped area of the weld, so that the weld reaches a high temperature point in a very short time. If there is no magnetic rod in the tube, it will have a great influence on the proximity effect and skin effect of high frequency current. The most obvious feature is that the weld seam is black and red, without splashing sparks, and the weld seam is fully open. Sometimes even if it is welded, it is a false weld, and there will be a popping sound when the pipe is sized. If the magnetic rod fails or the installation position is not appropriate, the welded pipe will also burst, even if it does not crack, its strength is also very low. At this time, due to insufficient hot spot temperature, the weld is generally yellow or light blue and cracking is urgent.

(4) Material

Due to the chemical composition of the raw materials, although the welding process is relatively normal, the welds will crack and appear urgently. Sometimes the pipes will crack when they are sized, accompanied by the sound of weld brittleness. At this time, the color of the weld is relatively blue, indicating that the temperature is still normal. Sometimes we can see that the crack of the weld deviates from the center of the weld, which is the adhesion of the edge of the base metal to form an irregular crack. This phenomenon is simply a brittle crack caused by the chemical composition of the raw material.