How to identify high-quality rectangular tubes?

How to identify high-quality rectangular tubes?

Rectangular tube is a hollow long strip of steel, also known as flat tube, flat square tube or square flat tube (as the name suggests). When the bending and torsional strength are the same, the weight is lighter, so it is widely used in the manufacture of mechanical parts and engineering structures.

Identification method of rectangular tube

1. Shoddy rectangular tubes are prone to folding. Folds are various creases formed on the surface of a rectangular tube, and this defect often runs through the entire longitudinal direction of the product. The reason for the folding is that the counterfeit and inferior manufacturers pursue high efficiency, and the reduction is too large, resulting in ears. Folding will occur in the next rolling process. The folded product will crack after bending, and the strength of the steel will drop greatly.
2. The surface of fake and inferior rectangular tubes often has pockmarks. Pockmarked surface is a defect of irregular unevenness on the surface of the steel due to severe wear of the rolling groove. Because manufacturers of fake and inferior rectangular pipes want to pursue profits, the groove rolling often exceeds the standard.
3. The surface of fake and inferior rectangular tubes is prone to scarring. There are two reasons:
(1) The material of fake and inferior rectangular tubes is uneven and there are many impurities.
(2) The guides and guards of fake and inferior manufacturers are poorly equipped and easy to stick to steel.

4. The surface of false and inferior materials is prone to cracks. The reason is that its billet is adobe, and the adobe has many pores. During the cooling process, the adobe is subjected to thermal stress, causing cracks, and there are cracks after rolling.
5. Fake and inferior rectangular pipes are easy to scratch. The reason is that the manufacturers of fake and inferior rectangular pipes have poor equipment, which is easy to produce burrs and scratch the steel surface. Deep scratches reduce the strength of the steel.
6. The fake and inferior rectangular tube has no metallic luster, it is light red or there are two reasons. 2. Its blank is adobe. The rolling temperature of counterfeit and inferior materials is not standard. Their steel temperature is measured visually, so they cannot be rolled according to the specified austenite region, and the performance of the steel cannot meet the standard.

7. The horizontal ribs of fake and inferior rectangular tubes are thin and low, and often appear to be full and dissatisfied. The reason is that the manufacturer has a large negative tolerance, and the pressure of the first few passes of the finished product
8. The cross-section of the fake and inferior rectangular pipe is oval. The reason is that in order to save materials, the reduction amount of the first two passes of the finished roll is too large. standard.
9. The composition of high-quality steel is uniform, the tonnage of the cold shear is high, and the end face of the cutting head is smooth and neat. However, due to poor material quality, the end face of the cutting head often has meat loss, that is, unevenness and no metallic luster. And because the manufacturer's products have less cut heads, big ears will appear at the head and tail.

10. The material of fake and inferior rectangular pipes contains many impurities, the density of steel is relatively small, and the size is out of tolerance. In the absence of vernier calipers, it can be weighed and checked. For example, for rebar 20, the national standard stipulates that the maximum negative tolerance is 5%, and its single theoretical weight is 120 kg when the length is 9M, and its minimum weight should be: 120 X (l-5%) = 114 kg , The actual weight of a single piece weighed out is less than 114 kg, which is fake and inferior steel. Generally speaking, the effect of whole phase weighing will be better, mainly considering the problem of cumulative error and probability theory.

11. The inner diameter of fake and inferior rectangular tubes fluctuates greatly because of:
(1) The steel temperature is unstable and has yin and yang sides.
(2) The composition of the steel is uneven.
(3) Due to poor equipment and low foundation strength, the rolling mill has a large bounce. There will be large changes in the same week, and such steel bars are prone to fracture due to uneven stress.

12. The trademark and printing of high-quality tubes are relatively standardized.
13. The distance between rectangular tubes with a diameter of 16 or more is above IM.

14. The longitudinal bars of false and inferior steel rebar are often wavy.