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Introduction

A steel manufacturer was experiencing continued failures of bearings on their Cold Rolling Mill. NSK engineers conducted an application review and found the highly contaminated operating conditions were causing the unexpected failures. This resulted in costly unplanned shutdowns and a reduction in production ratios. NSK STF bearings, made of a long-life Super-Tough Steel, were recommended. STF is made specially to combat debris contamination that enters the lubricant. After a four month running trial, the bearings were sent back to factory for inspection. The laboratory found a residual life between 29-50 months. To date the customer has replaced the bearings once per year during the annual scheduled maintenance.

Key Facts

  • Cold Rolling Mill
  • Highly contaminated operating conditions
  • Extremely short bearing life: 3-4 months
  • The analysis of bearings and grease sample revealed contamination was reason for the failure
  • NSK Solution: Long-life Super-Tough Steel, Spherical Roller Bearings
  • Longer life with superior resistance against wear, seizure and heat
  • Significant increase of bearing life from 3-4 months to 29-50 months
  • Cold Rolling Mill
  • Long-Life Super-Tough Spherical Roller Bearings

Value Proposals

  • The NSK Technical Department analyzed grease samples and inspected the bearings to find the root cause of failure
  • NSK Engineers recommended Spherical Roller Bearings in Super-Tough Steel
  • After a four month trial (equivalent to the original bearing lifetime), bearings were disassembled and returned to the plant for analysis
  • The results showed that the bearing still could work in operation (10 times the initial lifetime)
  • Significant cost savings were achieved based on reduced bearing replacement rate, less unexpected line stops, less manpower due to line stops

Product Features

  • Special material
  • Innovative heat treatment technology
  • Outperforming standard bearing steel
  • TF, NTF, HTF STF, WTF – material to cater to all your environments
  • Up to 10 times service life with contaminated lubrication
  • Up to twice the service life under clean lubrication
  • Up to 4 times the service life at 160°C
  • Less than one-third the rate of wear
  • 40% improvement in seizure resistance

Cost Saving Breakdown

Before Cost p.a. NSK Solution Cost p.a.
Costs for standard Spherical Roller Bearing per year $10,290 Costs for Super-Tough Steel Spherical Roller Bearings per year $3,430
Three hours/stop to replace bearings
Three unexpected stops/year
$9,647 No unexpected downtimes
Bearings are replaced in the annual scheduled maintenance
$0
Three hours of downtime to replace bearings
Three unexpected stops per year
$1,286 Mounting Costs
Included in the annual scheduled maintenance
$321
Total Costs $21,223 $3,751

Reference:SS-E-7004

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