rolling defects of H-shaped steel

Five Common Rolling Defects in H-beam Production

In recent decades, with the advancement of continuous casting technology and the improvement of online computer-controlled rolling automation, the H-beam production process has become increasingly mature. The rolling process from special-shaped billet to finished product is limited by conditions such as relatively low temperature of the rolled piece and deterioration of metal plasticity. The first thing is to prevent transverse metal flow during the rolling process. The method is to ensure that the diameter ratio of the driven horizontal roller and the driven vertical roller of the universal frame is controlled at 3:1. At the same time, when designing the pass pattern and adjusting the rolling mill, it is necessary to ensure that the extension of the legs and the waist of the rolled piece are consistent, otherwise it will affect the accuracy of the size and integrity of the finished product.

According to the process flow, steel defects can be divided into three categories: steel defects, rolling defects and finishing defects. This article mainly explains the five common rolling defects of H-shaped steel.

1.Roll marks

Roll marks are generally divided into two types, namely periodic roll marks and non-periodic roll marks.

Periodic rolling marks are regularly distributed on H-beam steel. The two rolling marks appear in the same part of the rolled piece and at the same depth. The distance between them is exactly equal to the circumference of the roll where they are located. Periodic rolling marks are ridges or pits on the surface of the rolled piece caused by the loss of meat from the roll or the presence of iron oxide scale in the pass.

Non-periodic rolling marks are caused by serious wear of the guide device or collision of mechanical equipment such as rollers, which causes the steel to be scratched and then rolled to form ridges or missing flesh on the surface of the steel. Most of them are distributed along the rolling direction.

2. Fold

Folding is a common defect similar to cracks. After pickling, you can clearly see that there is a crack on the cross section of the fold that is connected to the outside world. Folding is caused by improper pass design or improper adjustment of the rolling mill. Ears are formed at the opening of the pass due to interference and filling. After rolling, the ears are pressed into the body of the rolled piece, but cannot be welded to the body, the depth of which depends on the height of the ear. In addition, improper design or severe wear of the arc between the waist and legs will cause grooves and edges on the surface of the rolled piece, which will also form folds after rolling.

3. Waves

H-shaped steel waves can be divided into two kinds: one is the waist wave with a washboard shape; The other is leg waves that crest and trough at the leg ends. Both kinds of waves caused damage to the shape of H-shaped steel. The wave is caused by the inconsistency of the elongation of each part in the hot rolling process. When the waist pressure is too large, the waist extension is too large, and the leg extension is small, so that the waist wave is formed, and the waist can be pulled apart when it is serious. Leg waves occur when the legs are extended too much and the waist is extended too little. There is another reason for waves to form. This is when the steel section, especially the waist thickness and leg thickness design ratio is unreasonable, in the process of steel cooling, the thinner part is cold first, the thicker part is cold later, and under the action of temperature difference, a large thermal stress is formed inside the steel, which will also cause waves. The solution to this problem is: first of all, we should design the pass reasonably and try to make the uneven deformation complete in the first few passes; In the finishing track, the waist and leg extension of each part of the H-shaped section should be consistent; To reduce the temperature difference between the waist and leg, spray the leg of the rolled piece behind the finished hole to accelerate the waist cooling, or use the vertical cooling operation.

4. Round the legs

The rounded corner of the H-shaped steel leg end means that the part between the leg end and the two sides of the leg is not straight, and the outline is short of meat than the standard section, and the whole leg end is not full. There are several reasons for the round corner of the leg end: first, the deep cutting pass of the billet machine is worn, and the rolled out leg becomes thicker. When entering the next hole, the leg end can not be processed well because of the wedge. Second, when the universal unit is rolling, due to the speed mismatch between the universal frame and the edge rolling machine, the phenomenon of pulling steel caused by excessive tension occurs, so that the leg of the rolled piece can not reach the required height, so that the leg end can not be vertically processed in the rolling hole, and the leg end will be rounded; The third is that the population side web is offset during the whole rolling process, so that the rolled part deviates from the pass symmetry axis when biting A, and the above defects will also occur.

5. Asymmetrical leg length

There are two kinds of leg asymmetry of H-shaped steel: one is that the upper leg is longer than the lower leg; The other is that one leg is long on the upper leg and the other leg is long on the lower leg. General leg length asymmetry is often accompanied by uneven leg thickness, and slightly longer legs are slightly thinner. Shorter legs are thicker. There are several reasons for the asymmetry of leg length: one is that in the process of opening, because the billet does not cause the deflection of the positive pass during the cutting depth, the special-shaped billet appears one leg thick and one leg thin, although the pressure distribution is reasonable in the later rolling process, it is difficult to correct, and finally the leg length asymmetry is formed; The other is the universal rolling mill horizontal beam alignment. The axial dislocation causes the side pressure of the vertical roll to the leg to be seriously uneven, forming a diagonal distribution of the leg length asymmetry.

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