Short-Stress-Line Mill Bearing Assembly and Accident Response

The short-stress-line mill features high rigidity, easy disassembly and simple operation. Short-stress-line mill bearing assembly quality directly decides the stability of bar rolling production. This paper covers standard short-stress-line mill bearing assembly steps, typical bearing failure modes and on-site troubleshooting plans for steel plants.

The short-stress-line mill boasts light weight, high overall rigidity, low elastic deformation and convenient maintenance, so steel mills widely adopt this equipment. Harsh high-speed heavy-load working conditions easily trigger bearing damage. With standardized short-stress-line mill bearing assembly and online monitoring, workers can quickly replace faulty bearings to reduce production losses. This article helps rolling plants stabilize production and raise finished product output.

The mill base includes a fixed stationary part and a movable lifting part. Sliding plates connect these two sections, supporting accurate hydraulic locking and groove shifting.

Hydraulic screw-down enables precise product shape control and cuts manual labor intensity.

An elastic balancing unit stabilizes rolling dimensions and effectively controls mill springback.

Bearings for short-stress-line mills consist of inner rings, outer rings, rolling elements and cages. Rolling elements sit between inner and outer rings, while the cage keeps components spaced properly.

The inner ring mounts on the roll neck and rotates synchronously with the roller. Contact surfaces between rings and rolling elements are defined as raceways.

Rolling elements include balls and various rollers such as tapered and spherical rollers. The cage evenly distributes rolling elements and prevents scattering during fitting. Normally, the cage bears no external operating load.

Table 1 and Table 2 list fit data for roll necks, chock cavities and bearings, formulated according to hot rolling operating characteristics.

Bearing radial internal clearance depends on structure, lubrication type, rotating speed, surface roughness, load and assembly interference. Engineers need to select suitable clearance by analyzing actual rolling working conditions.

First, measure key dimensions of the bearing chamber before assembly. Remove burrs from chock inner bore chamfers and check contact surface roughness if necessary.

Second, slowly press the bearing outer ring into the chock with a press. If no press is available, tap the circumference gently with a copper hammer. Never strike the bearing with an iron hammer.

Next, heat the bearing inner ring via electromagnetic induction or oil heating (90~100℃, max 120℃). Fit the heated inner ring onto the shaft rapidly. Install a demagnetizer for induction heating to avoid magnetic impurity adsorption.

Finally, complete bearing combination assembly after the inner sleeve cools to room temperature. This practice prevents insufficient clearance and component damage caused by forced fitting.

Four-row cylindrical roller bearings deliver excellent limiting speed and radial load capacity, yet cannot withstand axial force. Common models include FC, FCD and FCDP.

When selecting bearing structures, analyze rolling force distribution based on mill layout and rolled piece stress. Also evaluate disassembly and inspection convenience during maintenance.

Double-row angular contact ball bearings undertake mill axial thrust. They bear limited small radial loads and restrict roller axial shifting to stop abnormal rolled piece deformation.

These bearings carry the main axial thrust for rolling mills and support a small amount of radial force. They lock roller axial displacement during mill adjustment to prevent shifting.

Installation of this bearing type is simple, and workers do not need to adjust axial clearance manually. Two styles are available: double half inner ring and double half outer ring.

Alternating loads act on bearing contact surfaces during operation. Variable deformation resistance of different rolled pieces creates uneven bearing stress and triggers failure. Major faults and solutions are listed below.

① Inner ring longitudinal cracking: Caused by improper interference fit, poor lubrication or internal material stress. Control fit tolerance precisely, optimize lubrication and strengthen material heat treatment inspection.

② Outer ring fragmentation: Resulting from mismatched chock size, excessive rolling force, impact load or damaged seals. Inspect chock wear, adjust rolling parameters and check seal integrity.

③ Rolling element fragmentation: Related to surface spalling, unqualified raw materials or overload impact. Implement regular bearing replacement and verify load limits before bearing selection.

The cage equally separates rolling elements and guides their movement on raceways. It operates passively and does not bear rolling radial or axial loads.

Many bearing burnout accidents originate from broken cages. Extended service life widens gaps between rolling elements and cage pockets, creating abnormal vibration and friction. Foreign hard particle contamination, rivet detachment and roller jamming also cause cage damage.

Workers should inspect pocket clearance and replace aging bearings timely. Optimize component fit, reinforce sealing, improve rivet quality and complete daily online inspection to reduce failure risk.

Over-tight thread connection between outer thread sleeves eliminates thrust bearing axial clearance. Excess preload removes lubricant and creates dry friction, leading to rapid temperature rise and bearing burnout. Lubrication system blockage can also cause the same fault.

Dismantle and reassemble operation-side components. Use a torque wrench to control screw tightening torque and reserve proper axial clearance. Apply grease evenly after assembly. If overheating recurs, check oil supply of the distributor and pipeline.

For lubricating hole processing defects, tap threads on through holes and seal openings with set screws to avoid grease leakage.

Check lubricant quality and fill each lubrication point regularly. Replace deteriorated grease on schedule or upgrade the lubrication system.

Follow standard assembly dimensions to guarantee proper radial and axial bearing clearance during fitting.

Dismantle bearing assemblies periodically to clear iron scraps and impurities. Change sealing rings regularly to stop cooling water from emulsifying grease.

Optimize chock structure from the design perspective to balance bearing load and extend service life.

Bearing faults also include seizure from wrong assembly, fatigue pitting and inner ring bursting. Except fatigue pitting, most failures can be avoided with standardized short-stress-line mill bearing assembly. Bearing fitting requires high precision, and refined operation effectively cuts accident frequency.

Steel rolling technology keeps advancing. Domestic wire and bar production lines feature low investment and fast returns, so more manufacturers put new units into operation. Modern short-stress-line mills develop toward higher rigidity and operating speed, requiring continuous bearing structure optimization.

Optimized short-stress-line mill bearing assembly and high-quality bearing parts reduce bearing failure rates, stabilize mill operation and raise overall production value for steel rolling enterprises.