Steel square pipes - the subtleties of technology

This profile is considered to be exclusively structural, in other words, it was originally designed for use in various technological designs. Frames of this profile are more stable and strong, compared with structures made of round or even rectangular pipes. This profile is most widely used in construction technologies.

This article will provide a brief overview of the most common technologies for the production of core products from different types of steel. It will also indicate what specifically the GOST standards for square steel pipes regulate their release.

Common Technologies

The entire volume of manufactured products can be divided into two large groups:

• Seamless;
• Welded.

As for the first group, seamless designs are born thanks to rolling technologies, which, in turn, are divided into hot and cold rolling. The group of longitudinal structures is made by joining a metal profile using welding technology.

Hot rolling technology

• Hot rolling mills use a solid cast or stamped, compressed steel billet, preheated to a temperature of at least 1200? С. By multiple molding, the rough sleeve is brought to a certain size. After that, it goes to the intermediate rollers, where the square is shaped into the workpiece.
• Next comes the so-called mandrel.. With the help of this technological process, from a solid and pre-crimped workpiece, something similar to the desired section is obtained. In the monolithic blank, a through hole is being pushed through and rolled out.
• After that, the preheated rough billet with a through hole is transferred to the finishing line of the hot rolling mill. Here, depending on the mill calibration, the product is already brought to the desired section. After the walls are rolled to the planned thickness and the shape is almost ready, it is sent to the line called the refrigerator.

• The fact is that in order for the metal to retain its elasticity, it must gradually cool down under natural conditions.. Otherwise, with a sharp cooling, the metal can be hardened, the result will be a strong, but fragile design.
• But that's not all, before the customer is released, the pipes are processed on special calibration machines and without fail pass the technical control department, where the compliance with the GOST standards for square steel pipes is checked. Moreover, each product is personally, with its own hands, the quality control inspector checks and signs for its quality.

Cold rolled technology

Both the cold-rolled technology itself and the mills where this product is manufactured are significantly different from hot forming.

In some sources, such products may be referred to as seamless.

• Initially, the rough billet sleeve is not made with a mandrel, but by upsetting or drawing a blank from a whole steel sheet.
• After that, on the roughing rollers, the pipe billet rolls out to an intermediate state, at which the planned wall thickness is achieved. At this moment it is still round, since in this form it is much easier to process, plus the accuracy of processing increases many times.
• Next, the product enters a special press, equipped with a corresponding mandrel. On it, the design is given the desired shape and sent to the calibration line.

• Minor defects are eliminated on the finishing calibration line and the wall thickness is brought to perfect condition.
• The product is almost ready, but due to repeated squeezing and molding of the metal, its properties change greatly, it loses its elasticity, it becomes more durable and brittle as a result of the deformation of the crystal lattice.
• To return to the metal the required specifications use the technology of "vacation". To do this, the metal is heated to a temperature of about 700 ° C and allowed to cool slowly.
• Pipes of some types of steel, treated in this way, after cooling down, may slightly lose their geometry, and lead them simply. To correct this unfortunate misunderstanding, the goods are sent for editing, which is done with the help of special correct machines and then to the Quality Department.

Important: in spite of external similarity, cold and hot-rolled structures differ not only in technical characteristics. In particular, the wall thickness and, accordingly, the weight of the steel square pipe produced by the cold rolling mill will be significantly less. Hot-rolled tubular products have thicker walls and more weight.

Welded longitudinal constructions

Technological instructions for the manufacture of longitudinal structures are not so complicated and less energy-intensive.

Accordingly, the cost price and the final price will be much lower.

• Initially, a dimensional billet is cut from the steel sheet to produce the product. Professionals call it strip. The strip dimensions must exactly match the sweep area of ​​the future pipe.
• When the strip is ready, it is sent to a special machine on which the shape of the future product is given to the metal. It is a hydraulic system of rollers and rolls, at the output of which an intermediate blank of square shape is obtained, but with a seam still open.

• Next, the rough formed billet enters the welding line. The most common is electric arc welding. She welded dimensional structures with a wall thickness of more than 2 mm. For example, a square pipe 100x100x4 of steel, so demanded in construction, is welded by electric arc method and regulated according to GOST 8639 82.
• Thin-walled structures are welded using special technology in induction furnaces, which allows to obtain a high-quality hermetic seam.
• At the end of the production line, the product is traditionally tested by OTK controllers, where, in addition to traditional parameters, the quality of the weld is monitored on special equipment.

Range and technological standards of structures

It is impossible to tell about all the calibrations of square pipes existing at the moment in a small article; for this, there are corresponding GOST standards for square steel pipes. To make it easier for you to understand the wilds of state standard markings, we combined them into a table, where we indicated which standards for which products were developed.

Important: GOST 12336 66 for a steel square pipe gauge was canceled in 1981, after which TU 14-2-361-79 was used. Which, in turn, were replaced in 1989 by TU 14-2-849-89, still in force today.

I would also like to note that a square tube made of stainless steel, as well as all profiled products from alloyed and non-ferrous metals are regulated according to GOST 8645 82.

The video in this article shows steel profiled structures.

Conclusion

Steel profiled pipes are used everywhere, they can be found on children's playgrounds, most of the lightweight bimetallic fences are made of them, and finally, not a single modern construction can do without steel shaped structures of various sections.