Case Studies

Acid Rollers Improvements to increase the reliability of acid rollers in a wool processing plant

Our client in the Wool Processing Sector has been suffering serious failures of their squeeze rollers in the acidification stage of their Carbonizing Plant.  The squeeze roller’s function is to squeeze free moisture out from the wool during the cleaning process.  The environment around this particular roller leads to a high rate of stress corrosion cracking.  The design of the roller incorporates replaceable stub ends.

The client has suffered damage to seal faces and bearing lands, as well as cracking of shafts:

Over time, the extra number of replacements and repairs has resulted in the fits and tolerances moving away from acceptable standards which has then further increased the failure rate. 

     In collaboration with the client, Ingenia assisted with a phased approach to improve the roller reliability:

  • In the first phase:
    • The aim was to improve the Stub End bolted flange connection design details:
      • We reviewed the tolerances, fits and bolted connection geometry against those required to meet the duty and many details were corrected.
      • We assessed the root cause of the unacceptably high failure rate of the bolts.  They were suffering fatigue failures due to the combination of poor fit and marginal load capacity.  The number of bolts was increased and fits corrected to reduce the actual load on each bolt.
    • We also assisted with reviewing the capability of the incumbent repairer which ultimately led to a change of repairer.
  • In the second phase:
    • We produced full repair procedure including Inspection and Test Plan (ITP) for the Stub Ends, including future weld repairs, which covered when welding is acceptable, how it should be carried out and the quality finish requirements to ensure an “as new” standard for repaired rollers.
    • We redesigned the Stub End which was snapping at radius diameter transitions.  FEA analysis was used to reduce stress concentrations and consequent fatigue risk.
  • During the third phase:
    • We added a slinger ring to resist acid ingress into the seals and bearing.
    • We improved the seal design by adding a labyrinth seal in front of the existing lip seal which when purged with grease are expected to have minimal wear and retain the sealing function.  The lip seal alone wears prematurely in the harsh environment and becomes in-effective very quickly.

      Finite Element Analysis to check stress patterns and levels:

  The results of this assessment were used to refine the design:

 

The final machined Stub Ends look beautiful:

The client and Ingenia are expecting an increase in life from weeks to around 3 years which has very large operations and maintenance savings.

The expected financial benefit of this work is in excess of $150,000 pa derived from less outages and reduced maintenance costs.