PTFE/Rubber Hybrid Bearings For Dry-Start Vertical Pumps - Texas A&M .

PTFE/Rubber Hybrid Bearings for Dry-Start Vertical Pumps Yoshimasa Kachu*, Chief Engineer, Bearing Dept. at MIKASA Fumitaka Kikkawa, Ph.D., Director, Industrial Div. at MIKASA Hiroshi Satoh, Ph.D., P.E., Consultant, Professional Pump Engineer MIKASA CORPORATION

Outline ・Introduction of Pumps and Bearings ・Bearing Failure Analysis ・Statement of Problems & Countermeasures ・PTFE/Rubber Hybrid Bearings ・Verification & Results ・Results of Field Application ・Recommended Design ・Conclusions

Plants with Vertical Pumps ・Desalination Plant ・Sewage & Waterworks Plant ・ Thermal / Nuclear Power Plant

Typical Vertical Pumps When Using Rubber Bearings Wet Pump-Feed Line Self-Feed Line Advantages: ・ Stable and durable under normal use ・ Free from most forms of shaft vibration M P Rubber Bearing Disadvantages: ・ Requires feed-water Shaft line Shaft Protection Tube ・ Maintenance for feed-water line is indispensible Impeller

Typical Vertical Pumps When Using Bronze Bearings Advantages: ・ No need for a feedwater line ・ Simple structure and low cost Disadvantages: Shaft Bronze Bearing Impeller ・ Risk of shaft vibration ・ Risk of short life

Bearing Failure Analysis Fishbone Diagram Bearing Structure Lubric. Water Underestimated Quantity Seawater Corrosion No-Replacement Structural Reliability Amount of Rubber Swell Operation Period in Air Lubric. Water Auxiliary System Failure Bearing Failure Aggression on Shaft Sleeves Risk of Self-Excited Vibration Friction Coefficients Allowable PV-Values Wear Resistance Tribology Risk of Half-Speed Whirl Undamping Vibration Characteristics

Examples of Feed Water Defects When Using Rubber Bearings Upper Coupling Shaft Coupling Gland Packing Strainer Discharge Elbow Valve Pump Base Bearing Spider Pump Shaft Seashells collect on the shelf-part. From Outside Facility Shaft Protection Tube Column Pipe Guide Vane Submersible Bearing Discharge Bowl Impeller Suction Ball Seashells collect in the shaft protection tube.

Statement of Problems & Countermeasures Problems Countermeasures ・ Corrosion of Shaft Protection Tubes and Feed Water Piping Eliminate Protection Tubes and Feed Water Piping by adopting Dry-Start Bearings ・ Maintenance trouble for feed-water line Eliminate feed water by adopting Dry-Start Bearings ・ High Wear and Seizure Apply Low Friction Material as the Slide Member ・ High Shaft Vibration Use the Viscoelasticity of Rubber

PTFE/Rubber Hybrid Bearings PTFE Shell Rubber PTFE/Rubber Hybrid Bearings have a three-layer structure: strips of self-lubricating PTFE as a sliding material, elastic rubber, and a metal/resin shell. These bearings never burn out, even when used for short periods under dry conditions at pump start-up. They also minimize shaft vibration.

Brief History of Development 1980 Start of the development Experimental Study of manufacturing method and material mixture ratio of PTFE/Rubber Experimental study of wear using test bearings 1985 Application test to real pumps with full-scale bearing Contributed ‘Turbomachinery of Society Japan’ 1990 Presentation at the 6th International Pump Users Symposium（1989） Improving of swelling rate Experiments on grooves effect Experiments on vibration absorption effect 1995 Contributed two papers to JSME Friction coefficients were measured whenever any adjustment was necessary 2000 ：Means a comparatively long-term work to some extent. ：Means a short term marked work such as a contribution. etc 2005 FEM analysis to see grooves effect Friction coefficient comparison test with other bearings. 2010 Contributed to ‘World Pumps’（No.530 & 531, 2010） Contributed to Journal of The Japan Institute of Marine Engineering Presented at METSⅡ in Doha, Qatar

Measurement of Friction Coefficients Load Direction Air Cylinder Shaft Bracket Thermometer Temperature Controller Solenoid Valve Bearing Shaft Motor Torque Transducer Direction of Shaft Rotation Water Cooler Water Temp. kept (20 22 ） Water Tank Shaft Sleeve

Comparison of Friction Coefficients Friction Coefficients Bearing Pressure 0.25MPa 0.35 0.30 PTFE/Rubber PTFE monolithic Rubber 0.25 0.20 Bearing Size:φ60 60L 0.15 0.10 0.05 0.00 0 0.5 1 1.5 2 2.5 3 3.5 4 Shaft Peripheral Speed （m/s） The PTFE/Rubber Hybrid bearing is more ‘self-alignable’ than the monolithic PTFE bearing.

Danger of Seizure Load Direction Air Cylinder Shaft Bracket Thermometer Temperature Controller Solenoid Valve Teasted Bearing （φ66 246mm） Seal Shaft Motor Torque Transducer A B C D Direction of Shaft Rotation Cooling Water Water Temp. kept 32 Cooler Water Tank Shaft Sleeve Seals were installed after the test bearing was merged into the tank to interrupt the inflow/outflow of water.

Results 90 80 Temperature ( ) Temp. points A, B, and C were measured near the slide surface. The real temp. of the rubber surface was higher. Seizure occurred. Test Condition (1) Bearing Pressure 0.25MPa (2) Shaft Peripheral Speed 8m/s Rubber Bearing seizure Point B 70 Point C 60 Point A 50 40 30 Point D Water Temp. 32 Test stopped. 20 1 Test Time (min.) Temperature ( ) The PTFE/Rubber Hybrid Bearing temperature rose by only about 10 deg. C and stayed almost constant throughout the test. 3 2 PTFE/Rubber Hybrid Bearing 50 Point B Point A stable Point C 40 30 Water Temp. 32 Point D 20 Test Time (min.) 10 20 60

Ball Brg. Motor Strain Gauge Amplitude (μm) 2245 Cylindrical SiC/Rubber 1450 Vibration Characteristics of Bearings Coupling 2000 6000 200 Bearing Shaft Rubber 2000 PTFE/Rubber Fly Whool Test Apparatus Revolution/min The bearings apparently vibrate as long as a cylindrical bearing material like bronze is used. Distributed rubber doesn’t stop the vibration.

Allowable Operation Time in Air Pressure (MPa) BearingPRESSURE (MPa) BEARING 0.6 0.5 5.0 m/s 0.4 6.0 m/s 0.3 7.5 m/s 0.2 Shaft Peripheral Speed 0.1 0 0 20 40 60 80 100 120 140 AllowableRUNNING Operation TIMETime (sec) in Air (sec) Under a normal bearing load, this PTFE/rubber hybrid bearing can be applied to all vertical pumps.

Result of Slide Materials Examination Ratio of Bearing Wear PTFE/Rubber 1.0 PEEK/Rubber 1.1 Polyurethane /Rubber 3.5 Aggression on Shaft Sleeves

Results of Field Application ・Bearing exchange interval Bearing Type Bearing I.D. Rubber PTFE/Rubber φ110 φ240 4 6 years 10 years φ250 and over 4 6 years 9 years ・The lifetime of PTFE/Rubber Hybrid Bearings was confirmed to be 1.5 to 2 times higher than the lifetime of conventional Rubber Bearings.

Recommended Design Self-Feed Line M P Pump-Feed Line Rubber Shaft Bearing PTFE/Rubber Hybrid Bearing Shaft Protection Tube Rubber Bearing Shaft

Conclusions Merits of using the PTFE/Rubber Hybrid Bearing, a component usable with almost all vertical pumps when aiming at ‘dry-start’: No need for a lubrication water system or shaft protection tubes No need for corrosion-prone piping Simple maintenance: no bearing lubrication control required Hardly any vibration Lower cost and lower risk at operation This bearing became the De Facto Standard in Japan. (1200 pieces/year are produced).

Hybrid Bearing temperature rose by only about 10 deg. C and stayed almost constant throughout the test. stable Point A Point B Point C Point D Point B Point A Point C Rubber Bearing 1 2 3 Test stopped. Point D Water Temp. 32 90 80 70) 60 50 40 30 20 ( PTFE/Rubber Hybrid Bearing 10Test Time (min.) 20 60 Test Time (min.) ( ) 20 30 40 50