1, the false and inferior rectangular tube is easy to fold up. Folding is the broken line formed on the surface of a rectangular tube, which often runs through the longitudinal direction of the whole product. The reason for the folding is due to the high efficiency of the fake and inferior manufacturers, the big pressure, the ear, the folding when the next rolling is rolled, the folded product will crack after the bending, and the strength of the steel drops greatly.
2, inferior rectangular tube appearance often pitted phenomenon. Ma is due to a defect of groove wear caused by irregular rugged steel surface. Because the manufacturers of inferior and rectangular tubes should pursue profits, they often appear the most exceeding standard of groove rolling.
3. The surface of the fake and inferior rectangular tube is easily scars. There are two reasons: (1) the quality of the shoddy rectangular tube is uneven, and there are many impurities. (2). Fake and inferior factories are simple and easy to stick. 4, the surface of the fake and inferior material is easy to crack. The reason is that the blank is the billet and the air hole is more. The crack is caused by the thermal stress in the process of cooling, and after rolling, there are cracks.
5, the shoddy rectangular tube is easy to scratch. The reason is the shoddy rectangular pipe manufacturers are poor in equipment, easy to burr and scratch the surface of steel products. Deep scraping reduces the strength of the steel.
6, the shoddy rectangular tube has no metallic luster and is light red or has two point two reasons. Its billet is adobe. The temperature of the shoddy and shoddy material is not standard. The temperature of the steel is measured by the eye, so it can not be rolled according to the specified austenite area, and the properties of the steel can not reach the standard naturally.
7, the slender and low horizontal bar of the shoddy rectangular pipe often appears to be full of dissatisfaction. The reason is that the manufacturer has a large negative tolerance, and the pressure of the finished products is several times before. 8, the cross section of the fake and inferior rectangular tube is oval, because the manufacturer in order to save the material, the two of the finished roll before the pressure is large, the strength of this kind of screw steel is greatly reduced, and does not conform to the standard of the shape of the screw steel.
9, the composition of high quality steel is uniform, the tonnage of the cold shearing machine is high, the end face of the cutting head is smooth and neat, and the shoddy and inferior material often has the phenomenon of falling meat because of the poor material, that is, it is uneven and has no metallic luster. And because the manufacturers cut less head, head and tail will appear big ears.
10, the material of the shoddy rectangular tube contains many impurities, the density of the steel is small, and the size is very poor. It can be weighed and checked without the vernier caliper. For example, for screw steel 20, the national standard stipulates that the maximum negative tolerance is 5%, and its single root theory weight is 120 kg when the ruler is 9M. Its minimum weight should be 120 X (L - 5%) =114 kg, and the actual weight of the single root is smaller than 114 kg, and it is the inferior steel%. Generally speaking, the whole phase weighing effect will be better, mainly considering the cumulative error and probability theory.
11, the size of the inner diameter of the shoddy rectangular tube fluctuates greatly. The reason is that l and steel temperature are unstable. 2, the composition of steel is not uniform. 3, because of poor equipment, the strength of foundation is low, and the rolling force of rolling mill is large. Will appear in the weeks changed greatly, this reinforced the uneven stress prone to fracture.
12, the trademark and printing of high quality pipe are more standard.
13, the distance between the rectangular pipe and the diameter over 16 is above IM.
14, the longitudinal reinforcement of shoddy steel is often wavy.