Hot-rolled H-beams evolve from traditional I-beams after optimized structural design. They belong to economical green section steel with outstanding mechanical performance. To begin with, H-beams own rational cross-section dimensions and uniform metal elongation during rolling, so internal residual stress stays low. Compared with standard I-beams, H-beams feature larger section modulus, lighter self-weight, stronger bearing capacity and less raw steel consumption.
في السنوات الأخيرة, H-beams gain wide application across heavy steel construction sectors. Typical scenarios cover large lifting machinery, heavy equipment foundations, long-span support frames, offshore oil platforms and energy engineering projects. Their easy installation and reliable mechanical properties make them a preferred structural material.
Laigang’s large H-beam production line launched in September 2005. The whole core rolling equipment and manufacturing technology were imported from SMS Meer of Germany, with a designed annual output of 1 مليون طن. For raw blanks, the line adopts ultra-thin near-net-shape continuous casting slabs, which rank among the world’s most advanced blank specifications. في أثناء, it applies mature advanced technologies: wide-flame digital heating and compact X-H tandem rolling. These processes support high-efficiency, energy-saving and low-cost section steel manufacturing.
This production line can manufacture H-beams ranging from H250 mm to H1000 mm, nearly reaching the global maximum H-beam production specification. Even so, long-term equipment aging and gradual loss of rolling tooling precision create frequent product defects during rolling. Common defects include workpiece eccentricity, bending and unstable dimensional tolerance. Worse still, simple process adjustment cannot eliminate many of these flaws completely. These problems severely restrict finished H-beam quality and continuous stable production.
1 Tooling System Composition of Universal Rolling Mills
The H-beam rolling flow at Laigang follows two main rolling stages. أولاً, a two-high roughing mill (BD mill) rolls raw slabs into intermediate blanks. التالي, the tandem mill group (TM) conducts reversible continuous rolling to form finished H-beams. The TM set contains two universal mills and one edger mill.
Workpieces pass through UR – E – UF for the first rolling pass. بعد ذلك, the line reverses material direction, and blanks go through UF – ED – UR sequentially. After repeated tandem rolling, finished H-beams exit from the UF mill.
UR and UF universal mills each consist of one set of motor-driven horizontal rolls and one set of passive vertical rolls. Their core function is thickness reduction on the beam web and flange. The ED two-high edger mill only processes flange ends to control final flange height. باختصار, the dimensional accuracy, forming state and metal deformation of H-beams mainly depend on the performance of UR and UF universal mills.
A complete universal rolling mill includes three core assemblies: horizontal roll system, vertical roll system and guide guard system. Horizontal and vertical rolls together form the H-shaped pass system, which directly contacts blanks and completes plastic deformation. لذلك, their assembly positioning precision decides the final dimensional tolerance of H-beams.
على الجانب الآخر, guide guards feed blanks into rolls smoothly and guide finished steel out of the mill. They prevent strip torsion, horizontal shifting and roll winding during production. For this reason, dimensional precision of guide guards directly affects workpiece forming status such as bending and twisting.
1.1 Horizontal Roll System of Universal Mills
The horizontal roll system combines roll chocks and horizontal work rolls. Each chock assembly contains pressure plates, axial sliding plates, main sliding plates and matched housings. One side of the roll system connects to the main drive motor, while sliding plates fit tightly with the mill housing to form an integrated unit.
Any deviation in component size, excessive wear or poor assembly accuracy will deform the whole chock assembly. The error transfers to installed horizontal rolls and finally causes dimensional defects on rolled H-beams.
1.1.1 Roll Chock Pressure Plates
Uneven wear or inconsistent thickness between left and right pressure plates creates height deviation on both sides of the chock. نتيجة ل, horizontal rolls tilt slightly during operation. The H-shaped pass loses its symmetrical shape, and roll gap becomes uneven: one side holds a wider gap while the other side narrows down.
أثناء المتداول, the narrow gap side brings larger metal elongation, and the wide gap side produces smaller elongation. The workpiece bends toward the low-elongation side and forms head offset defects.
فضلاً عن ذلك, worn pressure plates leave gaps between plates and chocks. Apart from roll inclination, the overall rigidity curve of the roll set distorts badly. The rolling pass loses standard geometry, leading to unstable dimensional tolerance of finished steel.
1.1.2 Roll Chock Axial Sliding Plates
Continuous wear reduces the overall width of axial sliding plates. Excessive clearance forms between chocks and mill housings. The whole chock shifts axially inside the housing, which shortens the effective stroke of online axial adjustment. Operators face difficulties in fine-tuning workpiece shape and dimensions.
علاوة على ذلك, offset sliding plates trigger axial movement of the chock. The center lines of upper and lower horizontal rolls fail to align. Calibration work distributes the total deviation to one side of the hydraulic piston and cuts the opposite piston’s adjustable stroke. Adjustment difficulty rises sharply, and stable dimension control becomes impossible.
1.1.3 Roll Chock Main Sliding Plates
Heavy wear on main sliding plates fails to lock chocks firmly inside the housing. Horizontal rolls lose reliable positioning and increase adjustment difficulty. Rolling stability declines significantly. في نفس الوقت, periodic rolling impact transfers extra vibration to the whole drive system and damages its running stability.
1.2 Vertical Roll System of Universal Rolling Mills
The vertical roll system includes vertical work rolls and vertical roll boxes. Vertical rolls install inside dedicated boxes, and the whole box fits into the mill housing. Together with horizontal rolls, they build the full H-beam deformation pass. Vertical roll surfaces process the two flanges of H-beams. Two key factors determine vertical roll tooling precision: positioning accuracy of vertical rolls and fitting tolerance between vertical roll boxes and mill housings.
1.2.1 Position Dimension Precision of Vertical Rolls
This index refers to assembly clearance between vertical rolls and their boxes, covering two core control points: fitting gap between box window and vertical rolls, and base dimension of vertical roll boxes.
1.2.1.1 Fitting Gap Between Vertical Roll Box Window and Vertical Rolls
Excessive clearance (A1 and A2) inside the roll box window creates extra movable space for vertical rolls. Vertical rolls sink down and form a horn-shaped gap. The gap between vertical rolls and the top horizontal roll shrinks, while the gap between vertical rolls and the bottom horizontal roll widens. في الإنتاج, finished H-beams show thin top flanges and thick bottom flanges. Severe deviation leads to scrapped products.
1.2.1.2 Base Dimension of Vertical Roll Boxes
Deviated base dimensions bring two typical failures. أولاً, vertical roll surfaces cannot fully attach to horizontal rolls during calibration, and pass calibration fails completely. ثانية, mismatched fitting tolerance distorts the joint between box pipelines and cylinder head connectors. Cooling water leaks heavily and weakens vertical roll cooling performance.
بجانب, tilted vertical rolls inside boxes form horn-shaped gaps. Workpieces produce upward or downward bent heads, and the uneven flange thickness defect (thin top, thick bottom) appears repeatedly, which may trigger mass scrap.
1.2.2 Fitting Size Between Vertical Roll Boxes and Mill Housings
If the outer dimension of vertical roll boxes is too small, operators cannot push boxes into mill housings smoothly. If the dimension is oversize or the horizontal height differs on two sides, vertical rolls tilt after equipment startup. Top and bottom flange thickness becomes inconsistent, and serious bending head defects cause steel stacking between mill stands.
1.3 Guide Guard System
This universal mill adopts beam-mounted guide guards. Fixed brackets on cross beams lock all guide units. Two factors dominate the precision of the whole guide system: عرض & length of guide guards, and matching tolerance between beam seat grooves and cross beams.
1.3.1 Width and Length of Guide Guards
Overwide guide guards make side walls squeeze the passing blank. Surface scratches form and lower finished steel surface quality. Over-narrow guide guards lose stable positioning for workpieces. Blanks bite the roll unevenly, and steel stacking accidents occur easily.
If guide guards are too short, the clearance between front and rear guides enlarges. Workpieces shift sideways during rolling and cause jamming. If guide guards are too long, the gap between two guard units becomes too tight. Operators cannot adjust guard positions freely, and roll change work takes extra time.
1.3.2 Matching Between Beam Seat Grooves and Cross Beams
Excessive clearance between beam sliding plates and beam seat groove sliding plates cannot lock cross beams horizontally. أثناء المتداول, beam assemblies swing left and right following workpiece movement. Connected guide guards swing synchronously. Large gaps form between roll surfaces and guard cutting edges, which greatly raises the risk of steel stacking faults.
2 تحسين العملية & Precision Control Standards
Based on all above factors that damage tooling assembly precision, we formulate unified tolerance limits for each key dimension. A complete standard table of precision control points and daily maintenance rules is released for on-site management. The table clearly records qualified precision indexes, allowable tolerance ranges and standardized restoration measures. This document guides regular precision recovery work and lifts overall equipment precision management level on the production line.
3 خاتمة
- The main factors damaging horizontal roll system precision are worn chock pressure plates, axial sliding plates and main sliding plates. These defects trigger head offset, unstable dimensional tolerance, poor rolling stability and intense rolling impact.
- Unreasonable fitting gaps between vertical rolls and roll box windows, deviated roll box base dimensions and mismatched sizes between roll boxes and mill housings reduce vertical roll assembly precision. The direct product defect is uneven thickness between top and bottom flanges of H-beams.
- Improper width/length of guide guards and excessive clearance between beam seats and cross beams damage guide system precision. Typical resulting faults include surface scratches on H-beams and frequent steel stacking accidents during rolling.
