Production Process and Mill Roll Selection of Seamless Steel Pipe

1. Seamless steel pipe production process
Seamless steel pipe production mainly through the following processes; tube - cutting - heating - perforation - rolling pipe - set (minus) diameter - straightening - cut the first tail - testing - packaging - storage. According to different ways of rolling, seamless steel tube rolling mills can be divided into automatic tube rolling unit, continuous tube rolling unit (MPM two-roll continuous tube rolling unit, PQF three-roll continuous rolling tube unit), assel roll unit, the periodic tube rolling unit, the new rolling mill to MPM pipe rolling unit, PQF three roller pipe mill units are mostly.

Punch machine
Tube perforation is the most important deformation process in the production of seamless hot rolled steel tube. Its task is to pierce the solid tube into a hollow capillary tube. According to the structure of the piercer and the deformation characteristics of the piercing process, while the piercing is the most widely used. The shape of the piercing piercer roll roller, bacteria (cone) and disc three, roller piercing mill roll used in small mills, and large unit perforated machine with bacteria roll. Disc punch machine less application. Regardless of roll shape, in order to ensure the billet billet and perforation process to achieve perforation cone (roll entrance cone), mill cone (roll exit cone) and the roll rolling strip (inlet cone and outlet cone between the excessive part )composition.

Punch roller roll roller is mostly used in the combination of the structure, the two use direct interference combination or keyed interference combination. In this way, when the roller scrapped, the roller shaft can continue to reuse, in order to reduce the cost of the tool. Small piercing machine roller material selection of 45 or 40Cr, quenched and tempered. Large piercing machine roller 42CrMo, quenching and tempering. Roll material At present, the manufacturers choose more miscellaneous, and some manufacturers choose forged 45,55 quality carbon structural steel. Some manufacturers choose 50Mn, 65Mn, 70Mn, 70Mn2Mo, 60CrMnMo other alloy steel or forged steel; hardness range requirements are inconsistent, and some require HB180-220, and some require HB220-260. In order to increase the biting nature, large perforated roll generally processed in the inlet cone depth of 0.8 ~ 1.2mm mesh pattern.

Comprehensive domestic and foreign manufacturers of material selection and use of the situation, the author believes that: the choice of piercing machine roll casting 50Mn, 60CrMnMo medium carbon steel is more appropriate, first, has good strength and wear resistance, the second is suitable for rolling material steel pipe. Hardness control in the HB200-240 more reasonable.

3. Pipe mill
Capillary rolling is the main deformation process of hot rolled seamless steel pipe production, the role is to make the capillary wall thickness close to or reach the finished product pipe wall thickness, and to eliminate the capillary longitudinal wall thickness in the perforation process, in addition to improve barren internal and external surface quality, control barren diameter and roundness. Hollow capillary rolled into the finished product near the shortage of waste management.

a,Automatic pipe rolling machine: Automatic pipe rolling mill is a two-roller irreversible longitudinal rolling mill, which is characterized in that a pair of high-speed reverse rolling mill return rollers are provided behind the work roller to send the once-rolled capillary to the foreground The second rolling, so its production efficiency is lower, most of the domestic units have been transformed or eliminated. Most of the material for the roller chilled cast iron, ductile iron or chilled ductile iron, hardness above HSD50.
b,Two-roller continuous rolling mill: Continuous rolling mill is a more advanced steel pipe rolling mill, which is perforated capillary tube on the long mandrel, after multiple racks arranged in sequence and adjacent rack roll gap 90 ° of the continuous tube rolling mill. Even the material of the roller are mostly chrome-molybdenum infinity chilled ductile iron (also known as pearlite ductile iron), nickel-molybdenum infinity chilled ductile iron (also known as acicular ductile iron), the hardness of the hole HSD50-65. Some of the first foreign-designed continuous rolling rollers are made of forged or graphite steel to further improve the strength of the roll.
c,Three-roller tandem rolling mill: Three-roll adjustable limited mandrel rolling mill (PQF) INNSE Italian company to overcome the inherent limitations of two-roll continuous rolling mill developed and developed, because it will 360 ° hole type is divided into three parts, reducing the speed difference between the bottom of each roll pass and the edge of the line, so the precision of the rolling steel pipe. Small PQF rolling mill roller is a one-piece, using nickel-chromium molybdenum infinity chilled ductile iron, hardness control HSD55-65 is more appropriate; Large-scale PQF rolling mill rolls made assembly type, that the roll wear resistance better nickel chromium molybdenum unlimited chilled ductile iron, shaft with high-strength forging steel, and after quenching and tempering, can be reused, significant cost savings, this structure has been successfully used in Tianjin Pipe Company.
d, Assel tube rolling unit: Assel tube rolling for the three-roll oblique rolling, which consists of three active roll and a mandrel form a ring closed pass. Roller roller body entrance cone, roller shoulder, flat area and exit cone four sections, the material used 4Cr5MoSiV1 forging steel, cast semi-steel or alloy ductile iron, heat treatment hardness: forged steel roll control HSD65-75, semi-steel roll control HSD50 -60, the alloy ductile iron roll control in the HSD55-65 (the material roller for the import unit design, less successful examples in the country).

4. Pipe diameter and diameter reduction
Hot rolled seamless steel pipe production is the last of a waste heat pipe deformation process, its main role is to eliminate the previous process of rolling caused by different outer diameter, in order to improve the hot-rolled finished pipe OD accuracy and roundness. Steel sizing, reducing diameter and reducing the diameter of the hollow body without mandrel bar rolling process. At present, the advanced (minus) diameter machine adopts the three-roll 120 °bisecting roll, the surface quality of the pipe is good after the setting (reducing) machine of the type is adopted, and the specifications of the finished pipe are more. Set (minus) diameter machine roller and shaft with interference fit or key connection, the current use of interference fit. Nickel-chromium-molybdenum infinity chilled nodular cast iron is used for the roll. The blank is produced by centrifugal casting to ensure a dense outer layer with a hardness of HSD55-68. Rolling less than Φ219 the following specifications of the steel pipe, the hardness of the roll can choose between HSD60-68, to ensure the hardness of the hole-type, and better wear resistance; rolling Φ219 more specifications of the pipe, the hole size larger, larger gap, in order to ensure the hole bottom and the edge of the wear and tear do not differ too much, the hardness of the roll can choose between HSD55-61.