Vertical roll bearing on universal mill is a key vulnerable part on H-beam hot rolling lines. Its shaft lock fault easily triggers unplanned production shutdown. This research takes vertical roll bearings from SMS Meer TM large H-beam reversible universal mills as research objects. It identifies typical shaft lock failure modes and analyzes impact-induced root causes. It also puts forward targeted structural and process improvements. Field data proves these measures greatly lift the service performance of vertical roll bearing on universal mill.
1. Vertical Roll and Vertical Roll Bearing on Universal Mill
Vertical rolling machines are essential equipment in steel production.
They shape steel blanks to required dimensions.
Vertical roll housings share three features:
rational roll design,
solid frame structure and efficient transmission.
These features lead to similar early failure patterns of supporting bearings.
Vertical roll bearing on universal mill fails most frequently among all bearings on H-beam hot rolling lines. Such faults heavily disrupt continuous production. Donc, this paper studies vertical roll bearings fitted on imported SMS Meer universal mills.
A complete large H-beam rolling line contains one two-high reversible breakdown mill (
BD)
and one tandem universal mill unit.
The unit follows UR–E–UF layout:
universal roughing mill,
edger mill and universal finishing mill.
Four vertical rollers install on UR and UF stands. Every roller matches one set of vertical roll bearing on universal mill.
A single vertical roll weighs 10–17 tons.
Rolled billets drive its rotation during operation.
Its theoretical maximum speed reaches 10 MS,
and peak load stands near 6000 kN.
Operators use water for cooling.
Rolling ambient temperature stays below 40℃.
The bearing adopts oil-air lubrication with 460#
gear oil.
Roll diameter ranges from 880 mm à 980 mm. Workers carry out turning after rolling roughly 3000 tons of steel. Turning volume depends on roll wear. The whole vertical roll gets scrapped once its roll ring fails.
Each H-beam grade needs 5–9 reversible rolling passes. One rolling cycle finishes within 3–5 minutes.
The roll ring inner bore forms an interference fit with bearing outer surface. Interference value ranges from 0.075 mm à 0.122 mm. The bearing inner ring makes transition fit with the vertical roll spindle. Maximum clearance reaches 0.06 mm, and maximum interference hits 0.025 mm.
2. Failure Forms & Root Causes of Vertical Roll Bearing on Universal Mill
Shaft lock acts as the main early failure form for vertical roll bearing on universal mill.
It shows two typical symptoms.
D'abord, severe cage wear occurs. Wear debris fills spaces between rollers and raceways.
Deuxième, cage beams fracture. Rollers squeeze together and slide along raceways instead of normal rolling movement.
Field analysis proves impact loads during rolling trigger shaft lock faults. Two working conditions generate such impact force.
2.1 Impact Force Generated at Steel Biting
A full rolling cycle includes steel biting,
stable rolling and steel discharging.
Rollers and raceways maintain normal contact during rolling.
The vertical roll sinks under self-weight without steel inside the mill.
Rollers and raceways then stay in abnormal contact status.
Contact status switches instantly when steel enters the mill. Existing working clearance creates impact force between rollers, cages and inner ring ribs. Such clearance includes axial gaps and radial displacement after cage assembly. Larger clearance brings stronger impact.
2.2 Inertial Impact Force During Rotation Direction Switch
Vertical rolls run at 190 r/min during reversible rolling. The roll changes rotation direction rapidly between steel biting and steel discharging. Fast direction shift creates huge inertial impact force between rollers and cage pockets.
Rollers have much higher hardness than cage materials. Repeated impact creates continuous plastic deformation on cage beams and finally causes fracture. High contact stress also wears cage pocket surfaces. Accumulated debris worsens operating conditions and leads to shaft lock of vertical roll bearing on universal mill.
3. Improvement Measures for Vertical Roll Bearing on Universal Mill
This study proposes two categories of solutions. One strengthens cage material. The other cuts impact force during bearing operation.
3.1 Raise Cage Strength
Operators apply carbonitriding treatment to bearing cages.
This process lifts hardness on both surface and core zones.
After carbonitriding, ordinary low-carbon steel cages reach mechanical performance close to surface-quenched 40# acier. Higher strength improves resistance against repeated impact deformation.
3.2 Reduce Impact Force in Operation
(1)
Machine bottom and side surfaces of cages.
Lower total cage weight and cut inertial impact during rotation switch.
(2) Apply micro-stretching technology on cages. Shorten pocket length by 0.3 mm for model 380690 palier. Narrow inner ring raceway width by 0.5 mm. The change reduces axial gaps among rollers, pockets and inner raceways.
(3) Shrink bearing axial clearance. Adjust axial clearance of 380690 bearing from 0.7–0.8 mm to 0.45–0.55 mm.
(4) Optimize cage pocket slope pressing process. Reduce radial coordinate from 1/2 plate thickness to 1/3 plate thickness. It limits radial movement of cages.
(5) Control assembly precision. Cut radial displacement after cage assembly from over 0.8 mm to below 0.5 mm.
4. Application Effect of Improved Vertical Roll Bearing on Universal Mill
All improvement measures go through on-site verification.
On the large H-beam production line,
annual shaft lock failure rate drops from 8%
to less than 1%.
Average bearing service life exceeds 195 heures.
The value stands 11.43%
higher than imported bearings.
On the medium H-beam rolling line, vertical roll bearing on universal mill has zero shaft lock faults within two years. Its minimum service life reaches 5×10⁴ tons of passed steel. It fully meets the performance standard of imported bearings and realizes domestic substitution.
Manufacturers extend this optimization scheme to other rolling equipment. Typical equipment covers roughing mill vertical bearings on hot strip lines, plate mill vertical bearings and four-row tapered roller bearings on reversible cold mills. All applications gain satisfactory results.
5. Conclusion
D'abord,
repeated impact loads cause shaft lock faults of vertical roll bearing on universal mill.
Impact force comes from steel biting and frequent rotation direction switch.
It leads to cage wear and beam fracture.
Deuxième, cage hardening treatment and precise clearance optimization effectively suppress abnormal impact and wear.
Troisième, optimized bearings exceed imported products in service life and stability. The technology supports low-failure and high-efficiency operation of hot rolling production lines.
