Phenomenon: Iron oxide scale and water enter the lower bearing housing of the vertical roll, the lower bearing has oil while the upper bearing has no oil and is rusted, and there is black effluent on the outside of the bearing housing. The following detailed analysis can be made regarding the causes of the burning of the vertical roll bearing of the rolling mill:

The core fundamental cause: Foreign object intrusion and lubrication failure lead to severe damage to the bearing

The invasion of iron oxide scale and water (main causes) :

Seal failure: This is the most direct and primary cause. The vertical roller is in a harsh environment, with a large amount of iron oxide scale particles and high-pressure cooling water directly eroding the end face seal of the bearing housing. The original seals (such as lip seals, labyrinth seals, packing seals or their combinations) have aged, worn, been damaged or failed, or the design and selection of the sealing structure are unreasonable (unable to withstand the impact of such a large number of fine and hard particles and high-pressure water), resulting in the continuous invasion of external oxide scale and water into the interior of the bearing housing.

Excessive clearance at the sealing area: Poor sealing, wear or excessive clearance at the installation surface of the bearing housing end cover, or the mating surface between the bearing housing body and the roller neck, etc., becomes a channel for the entry of iron oxide scale and water.

Severe failure of the lubrication system (key factor) :

The damage of contaminants to grease: The invaded iron oxide scale is a hard abrasive that will mix into the grease, sharply increasing the internal friction and wear of the bearing, destroying the oil film and causing abrasive wear. The water that enters simultaneously will: dilute the grease; reduce the viscosity and load-carrying capacity of the grease.

Disrupting the structure of grease: leading to the decomposition of the grease soap base and the precipitation of base oil.

Corrosion: Water coming into contact with iron components, especially when combined with iron oxide scale, can easily induce rust, as you have observed in the upper bearing.

Accelerate the oxidation of grease: Promote the oxidation and deterioration of grease.

Uneven lubrication of the bearing cavity (lack of oil in the upper bearing) : You have observed that "the lower bearing has oil, while the upper bearing has no oil and is rusted", which indicates: insufficient supplementary lubrication or uneven distribution: The lubrication point may be located at the lower part. Under the effect of gravity, the newly replenished grease is difficult to effectively reach and fill the entire bearing cavity, especially the upper bearing area. Or the grease supply volume/cycle of the entire lubrication system is unreasonable.

Contaminants cause oil passage blockage: Incoming iron oxide scale, water, and deteriorated/hardened grease (black effluent) may clog the oil passage leading to the upper bearing or the internal oil passage.

Seal failure leading to grease leakage: While the intrusion of contaminants damages the sealing effect, it may also cause grease to leak from the failed seal under the action of pressure or gravity (one of the sources of external black outflow).

The direct cause of the fault development process and burnout

Initial stage (contamination entry and lubrication deterioration) : The failed seal allows a large amount of iron oxide scale and water to enter the bearing cavity. Contaminants rapidly contaminate and damage the lower bearing and the original grease in the cavity.

Critical stage (lack of lubrication and rusting of the upper bearing) : Due to uneven distribution of grease, the effect of gravity, and possible oil passage blockage/leakage, the invading contaminants (especially water) are more likely to concentrate in the upper area. The upper bearing has been in a state for a long time without effective fresh grease protection (" no oil "), and the continuous presence of water has led to severe rusting (" rusted "). At this point, the upper bearing is basically operating under conditions of no lubrication or extremely poor lubrication (deteriorated grease containing a large amount of abrasives and water).

Accelerated deterioration stage (abnormal friction and high temperature) : Rust on the upper bearing causes pitting and spalling on the raceway and rolling element surfaces, increasing frictional resistance.

The oil-free or low-oil state leads to dry friction or boundary friction between the rolling elements and the raceways.

The mixed iron oxide scale particles act as abrasives, severely wearing down the working surface of the bearing.

Although the lower bearing "has oil", this oil has been severely contaminated (containing water and iron filings), and its lubrication efficiency has sharply declined, and it is also in a state of accelerated wear.

The frictional torque increases sharply, generating a large amount of heat.

Burning stage (overheating, alloy melting) : Under heavy load (rolling force) and high-speed rotation conditions, abnormal friction generates a huge amount of heat.

Lubrication failure leads to the inability of heat to be effectively carried away.

The internal temperature of the bearing rose sharply, far exceeding the design limit.

High temperatures cause a decrease in the hardness of bearing steel materials (tempering softening or even phase transformation), and local plastic deformation occurs on the surfaces of rolling elements and raceways.

Extreme high temperatures cause local alloy melting inside the bearing, resulting in sintering and welding phenomena (ablation, adhesion), and the bearing is completely jammed (seizing). This is the essential process of "burning".

Manifestation (Black outflow) : Abnormal high temperatures can simultaneously cause severe carbonization and decomposition of the residual grease in the bearing housing, forming a black viscous substance in a charred or tarry state, which will be squeezed out from the seal failure or gap (" black outflow on the outside of the bearing housing "). This is also a clear sign that the bearing has seriously overheated and even the internal materials have begun to melt.

Summarize the chain of reasons

Seal failure --> Leads to the continuous intrusion of iron oxide scale and water into the bearing cavity.

The invading iron oxide scale (abrasive wear) and water (corrosion, dilution, and destruction of grease) --> cause the grease to deteriorate rapidly.

Improper structural design/maintenance (such as poor lubrication point position, unreasonable grease supply strategy, and oil passage blockage) --> leads to the lack of effective lubrication in the bearing cavity (especially the upper bearing) and the accumulation of contaminants.

The upper bearing is short of oil and severely rusted -> Under heavy load and high speed, extreme friction, dry friction and high temperature occur.

The lubrication of the contaminated lower bearing deteriorates --> Friction and heat continue to increase.

Abnormal high temperature -> Causes the oil to carbonize (black effluent), the steel to soften and deform, and eventually local melting and burning (seizing).

Suggested solution directions

Thoroughly inspect and renovate the sealing system: Replace high-performance seals: Select multi-protection seals specially designed for the harsh working conditions of steel plant rolls (such as: heavy-duty split labyrinth seal + high-performance wear-resistant V-shaped combination sealing ring + auxiliary air seal or magnetic fluid seal). Ensure that the sealing material (heat-resistant, wear-resistant, water-resistant), structure and size can effectively block high-pressure water and fine iron oxide scale particles.

Strict installation and maintenance: Ensure that the seal is installed properly, and regularly inspect the wear of the seal and replace it.

Inspect/repair the sealing installation surface: Repair worn end covers, roller necks and other mating surfaces.