Causes of Increased Temperature in Steam Turbine Thrust Bearings
Release time
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Jan 25,2026
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The turbine thrust bearing serves as the core component for axial force balancing and rotor axial positioning within the unit.
Causes of Elevated Temperature in Turbine Thrust Bearing Blocks
The turbine thrust bearing serves as the core component for axial force balancing and rotor axial positioning within the unit. It also functions as a critical safety device to prevent axial movement of the rotor and protect the steam flow path. Its primary functions encompass load-bearing, positioning, lubrication, and protection. Designed to withstand tens of tons of axial thrust generated by steam during turbine operation, it directly determines the unit's steam flow efficiency and operational safety.
1. Fully bearing the rotor's axial thrust to balance axial forces;
When steam in the turbine flow path performs work on blades, dividers, and steam seals, it generates immense axial unbalanced thrust (reaching 30–80 tons in supercritical/ultra-supercritical units) due to pressure differentials and impact angles. This is the fundamental cause of rotor axial movement. The thrust bearing, through the interaction between the thrust plate and thrust bearing pads, absorbs the entire axial thrust of the rotor. This force is then transmitted via the bearing housing to the turbine frame and foundation, making it the sole axial force balancing component of the unit. The pads, constructed from Babbitt alloy, form a flexible load-bearing surface in conjunction with the lubricating oil film. This design evenly distributes thrust loads, preventing localized stress concentrations that could cause pad damage.
2. Precisely limiting rotor axial movement to ensure axial center position;
Thrust bearings comprise working thrust pads (primary thrust pads bearing normal forward thrust during operation) and non-working thrust pads (secondary thrust pads bearing reverse thrust during load shedding or sudden steam parameter changes). The clearance between these pads (thrust clearance) defines the rotor's axial movement limit. Through bidirectional constraint of the bearing shells, the rotor's axial position is fixed at the design reference point. This strictly maintains the axial flow clearance between the rotor and stator (cylinder, stator blades, partition, steam seal) and the axial clearance of the steam seal, preventing contact and abrasion in the flow path.
3. Forming a liquid hydrodynamic oil film cavity to ensure frictionless axial lubrication of the thrust disc;
During rotor rotation, lubricating oil is drawn into the wedge-shaped gap between the thrust disc and bearing block, forming a liquid hydrodynamic oil film. This completely separates the thrust disc from the Babbitt alloy bearing surface, transforming metal dry friction into liquid friction via the oil film, significantly reducing the friction coefficient. Simultaneously, circulating lubricant dissipates friction-generated heat, maintaining the Babbitt bearing surface temperature ≤85°C (optimal operating range: 60–80°C) to prevent softening or melting due to high temperatures.
4. Overload Safety Protection;
When excessive axial thrust causes bearing overheating or rotor axial movement exceeds limits, the protection system triggers emergency shutdown interlocks. This prevents bearing meltdown, which could lead to blade fractures in the flow path or cylinder deformation.
Causes of excessive bearing block temperature include:
● Excessive parallelism deviation between thrust bearing blocks and thrust plate; inconsistent bearing and journal cam angles cause localized overheating in specific block areas. When the journal cam angle significantly exceeds the bearing cam angle, upper blocks on the thrust surface overheat relative to lower blocks. Conversely, when lower blocks bear greater thrust, they overheat relative to upper blocks.
● Excessive runout of the thrust disc due to rotor manufacturing quality. This causes significant thrust differential across thrust bearing blocks during operation. Under high-speed, continuous running conditions, the constant large variations in thrust per block disrupt the stable establishment of the oil film, leading to elevated temperatures across the entire working surface.
● Excessive thickness variation within thrust bearing blocks or between adjacent blocks. Significant thickness differences within a block or between blocks cause thicker blocks to bear greater thrust than thinner ones during operation, resulting in elevated temperatures in certain thicker blocks.
● Block lapping issues: Inadequate lapping of individual blocks or poor overall block-to-block lapping results in poor contact between blocks and thrust plates. During overall lapping, blocks must be properly seated and subjected to axial thrust to achieve true contact surfaces.
● Inadequate thrust clearance: Due to measurement errors or bearing misalignment, insufficient thrust clearance reduces lubricant flow, impairs oil film formation, and elevates bearing block temperatures.
● Uneven thrust distribution across upper and lower thrust surfaces: In combined thrust-supporting bearing housings, insufficient locating pin interference causes misalignment during assembly. This results in uneven thrust distribution across the upper and lower thrust surfaces, leading to temperature inconsistencies in the thrust-bearing shells. Partial or individual shells may overheat.
● Inappropriate spherical tightness of the thrust combined bearing on the support side. The spherical tightness designed for the unit is based on ideal conditions, but in actual production, the surface finish of the spherical surface and its seat often fails to meet design requirements due to manufacturing or installation factors. During operation, the bearing's self-alignment capability under thrust load is poor. This results in uneven thrust distribution across the thrust bearing blocks, causing elevated temperatures in certain blocks. This phenomenon typically manifests as noticeable shifting of the high-temperature zones within the blocks as the unit load varies.
● Abnormal oil film formation: Insufficient clearance in the thrust bearing blocks themselves, combined with issues in the manufacturing or positioning of the oil seal rings, causes the oil seal ring's shoulder to become jammed against the block during rotor rotation. This prevents free movement, disrupting normal oil film formation. Consequently, a thin oil film or near-friction operating state develops between the bearing block and thrust disc, leading to elevated block temperatures (where the high-temperature zones and peak values remain relatively stable).
● Improper adjustment of oil seal clearance in combined thrust-support bearings: Incorrect clearance adjustment causes the oil seal to press against the shaft during operation, preventing the spherical bearing from self-aligning under thrust loads. This results in excessive axial thrust and elevated temperatures on certain thrust bearing blocks.
● Increased axial thrust on the unit: Scale buildup in flow passages, steam seal plate detachment, excessive steam seal clearance, blade erosion deformation, or increased radial steam seal clearance in flow passages will amplify the steam pressure differential before and after each stage's partition plate, thereby increasing axial thrust.
● Insufficient thrust bearing oil supply;
This will cause bearing block temperature to rise. Prolonged operation under oil-deficient conditions will accelerate bearing block wear.
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