High-performance Assel process

Transcription

1 04-631, Innovation in seamless tube rolling technology.0 * X X Р hi 6g High-performance Assel process SMS

2 Assel mill plant production process Classic Assel mill plant Schematic production process Figure 1 The further development of the Meer Assel process The further development of the Assel technology proven over decades is a result of the market demands for tube rolling mills for a wide size range and high product quality, with relatively low investment costs and capacities, depending on the product mix, from approx. 50,000 to 100,000 tonnes per year. Changes in the plant layout and their technological influences on the rolling process The production processes in a classic Assel mill plant and in a modern Assel mill plant are compared in Figures 1 and 2. The piercing process in the barrel-type piercer In the classic Assel mill, the billet is pierced in a cross-roll piercer with barrel-shaped rolls. As a rule, piercing is carried out without greater expansion - billet diameter and hollow diameter are practically identical. A corresponding billet dimension is therefore required for every pass size in the Assel mill. Consequently if a plant has a broad product mix, a large number of billet sizes is required. The piercing process in the cone-type piercer In the new plant configuration, a cone type piercer is used to pierce the billet. Piercing of the billet with cone-shaped rolls enables large expansion and elongation ratios to be achieved. This possibility of large expansion ratios allows different hollow dimensions to be rolled from one billet diameter, thus permitting an optimum adaptation of the hollow dimension to the demanded shell dimensions in the Assel process. The rolling of different hollow diameters enables the number of different billet diameters required to be minimised. Exploitation of the large elongation ratios allows thin-walled hollows to be pierced, thus enhancing the process engineering capabilities of the Assel mill for producing thinwalled shells. Elongation in the Assel mill The production possibilities in the Assel mill have been significantly expanded as a result of design modifications in the construction of the Assel mill stand and the mandrel bar circulation system in the process chain, and as a result of technological measures, i.a. in the roll sizing. Through the use of the NEL (No End Losses) system and the application of the quick lifting and quick closing methods, thin-walled tubes up to d/t* 1 = approx. 30 can now be produced. *' d/t = diameter/wall thickness

3 Design features of the cone-type piercer Cone-type piercer in an Assel mill line PM/DB )L=6 Forming zone - cone-type piercer with Diescher discs Forming range DH/t Design features of the cone-type piercer The cone-type piercer is characterised by the following design features: Vertical roll arrangement; Inclination of the roll shafts by 15 to 20 to reduce the material load; Separate, variable-speed drives for the rolls to permit optimum adaptation of the roll speeds to the rolling conditions; Low-expansion rigid stand construction for precision piercing even with extreme rolling forces; Billet guiding up to the rolls in a tubular guide; Guiding of the rolling stock in the forming zone by means of Diescher discs or guide shoes; Guiding of the mandrel bar and the hollow in 3-roll guides; Stable start-of-rolling conditions owing to the location of the first 3-roll guide in the mill stand proper; Computer-controlled setting of the rolls and guides in the roll gap; Process control by recording of the rolling results for correction of setting parameters and quality assurance

4 Design features of the Assel mill plant Layout of Assel mill plant The high-performance Assel mill plant is characterised by the following features Assel stand design Stand construction of sturdy slab design with minimum frame spring-back under rolling pressure; Individual setting of the rolls using electromechanical drives; Rotation of the roll assemblies using electromechanical drives with position monitoring; Fully automatic setting to optimum rolling parameters determined in practice; Recording and checking of the settings by automatic measurement of the rolling results downline of the Assel mill; Good reproducibility of the settings; Stabilisation of the rolling process using the "quick closing", "quick lifting" and "NEL" systems; Hinged stand upper section for simple roll changing using a roll lifting device. Assel stand in working position Roll changing on the Assel stand

5 Plant designations Rotary hearth furnace Cone-type piercer Assel mill Induction reheating furnace Stretch-reducing mill SRM measuring point 1 SRM measuring point 2 Rotary saw Cooling bed Inlet side of the Assel mill The process is designed for rolling with only one mandrel bar. Mandrel bar retaining device: The mandrel bar is placed into a retaining device with which all the movements of the mandrel bar from the threading process, through the forward or backward movement during the rolling process, up to the retraction of the mandrel bar after the rolling process can be precisely controlled. Entry guides: In order to stabilise the rolling process, the mandrel bar and the hollow are held in 3-roll guides. Mandrel bar cooling: The mandrel bar is designed for internal water cooling. Mandrel bar lubrication: The lubricant is applied to the mandrel bar during the threading process. Outlet side of the Assel mill Specially designed 3-roll guides are used to avoid twisting of thin-walled tubes. The guide rolls rotate synchronously with the speed of shell rotation. Mandrel bar starting poshion Mill centerline _ "-! с ь t F h 1 1 r"tt t F 5 > ' " -... S =K E3" \ \\ 3t» Mandrel bar travel x Jr^ ^V i-a 3 Mandrel bar and hollow move to mill centerline 5. Mandrel bar retraction and loading of next hollow Schematic diagram of the mandrel bar manipulation

6 Finish-rolling in the stretch-reducing mill V Stretch-reducing mill Finish-rolling of the produced shells into the various hot-finished tube sizes is performed by stretch-reducing or by sizing. In order to ensure the product quality with close tolerances on the produced tubes and to minimise the material losses in the reduction process, SMS Meer offers its CARTA Aechnology System comprising the following main components: CEC Crop End Control WTCA Wall Thickness Control Average WTCL Wall Thickness Control Local The graphs below show practical examples of the use of a crop end control system to reduce end losses and the wall thickness control system to reduce wall thickness deviations. Today SMS Meer offers the use of fully automated, simulation-aided systems in the production process which represent the latest in computer applications for production control and production monitoring. CARTA /Technology System Production planning & control system Technology Toolshop СЯЛТА* CARTA Stand management & CARTA* groove planning groove dressing Process man; SRM Pulpit CEC off CEC on M 6 i 50%. о Reduction of crop end losses Number of tubes Wall thickness deviation [%] Reduction of wall thickness deviation

7 High-performance Assel mill plant Schematic production process Stretch-reducing mill Induction heater Figure 2 The most important technical features of modern SMS Meer Assel mills are: Controlled mandrel bar movement, forwards or backwards - depending on the tube size; Only one mandrel bar is employed in the rolling process; Stabilisation of the rolling process for thin-walled shells during the inlet and outlet phase through the use of the roll quick adjustment systems (quick closing, quick lifting) and the NEL (No End Losses) system; Sturdy stand design with minimum stand springback; Roll setting with high precision and reproducibility; Automatic process control. Benefits to be achieved from the use of the modern Assel mill plant: Expansion of the production capabilities in the thin-wall size range; Reduction in the number of billet diameters required; High charge weights; Low material losses; Better surface quality of the rolling stock; Lower tool costs; Savings in personnel costs; Computer-aided process control and process automation; Better starting material handling thanks to reduction in the starting material sizes. Finish-rolling stage In the classic mill plants, the finish-rolling stage generally consists of a sizing mill with 7-12 two-high stands with limited roll adjustment possibilities. As a result of the forming conditions in the two-high stands, subsequent rounding in a rounding mill is coon practice. The maximum total reduction in the sizing mill is approx %. In new plants, finish-rolling is performed by reducing in up to 28 three-roll stands. Here a total reduction of up to 80% can be achieved in the finish-rolling stage and the number of shell sizes required can be significantly reduced. The roundness of the tubes after reduction satisfies the requirements of all the relevant standards. An additional rounding mill is therefore no longer necessary. Overall, the advantages in the forming stages produce a considerable increase in the charge weights and permit the production of hot-finished tube lengths up to approx. 80 m. In order to make optimum use of the cooling bed width in such cases, the tube strand leaving the stretch-reducing mill is cut with a rotary saw into cooling bed or finished lengths. A rotary saw can be used for cutting tubes with a wall thickness up to approx. 14.

8 Forming stages in an Assel mill plant Billet Pierced billet (hollow) Shell Production range The Assel process is suited to the production of tubes in the diameter range from 25 to with medium and heavy wall thicknesses according to tube grades and standards such as: General seamless tubes e.g. to DIN 2448, DIN 1629; Oilfield tubulars to API standards; Tubes for special applications such as roller bearing tubes, mechanical tubing, etc.; Shells for cold further processing Tube о ф Characteristic data of possible plant types Typical production range for Assel mill plants Plant type Billet Diameter Length Weight Pierced billet (hollow) Diameter Wall thickness Elongation Length Shell Diameter Wall thickness Elongation Length m kg - m - m 4" / 8 " , i П High-performance Assel О Classic Assel Finished tube Diameter Wall thickness Length max. m approx approx Tube wall thickness [] SMS Meer GmbH Ohlerkirchweg Monchengladbach P.O. Box Monchengladbach Germany Phone ( ) Fax ( ) info@sms-meer.com о О)