Many learned discussions have been held and focused on the reduction of gear distortion. The aspect of distortion is both critical and mandatory to produce quality metallurgically sound gears. This is true whether the gear heat-treatment process is induction, flame hardening or surface treatment.

Oil prices from the Middle East, which have escalated significantly over the past 20 years, have just recently experienced a reduction (not a significant reduction, but nonetheless a reduction). This writer believes that the current reduction in price will be short-lived. There will also be an ever-increasing price for quench oils. This will certainly necessitate the heat-treatment operation to protect its investment made in quench oil to maintain the quenching system to a higher level than has been previously maintained.

It is recommended that the users of quench-oil systems should seriously consider a regular inspection of their oil through testing and analysis. There are many industrially recognized tests that can be performed and integrated into a regular and routine maintenance program. The following is some points of concern that one might consider in order to preserve the quality and effectiveness of their quench oil.

  • Regular inspection for particle matter that can be present in the oil, such as oxide scale, fines and soot.
  • Regular inspection of the oil for water contamination. This can also be a serious fire risk if the water content reaches excessive proportions.
  • Regular inspection of pneumatic systems, particularly in an integral-quench furnace. At the center-door lift-system cylinder, pneumatic cylinders (if not maintained) can leak air into the furnace. The air will generally have moisture contamination from either/both, compressed air or high humidity levels in the shop air.
  • Regular inspection of the oil for contamination by decomposition, particularly if the quench oil is maintained at high operating temperatures for marquenching procedures.
  • Regular cleaning of the quench oil should also be seriously considered in order to maintain a high level of quench effectiveness. A reasonable interval is every six months, depending on the method and frequency of quenching.
  • Regular desludging of the furnace quench tank should be a standard operating procedure and a part of the preventive maintenance plan.
  • Regular inspection of the quench-oil agitation system should be made. A simple thing to observe in the quench system would be to check that the agitation impellers are turning and have not fallen off the impeller driveshaft.
  • Regular inspection and cleaning of the filters that are present on the oil-quench pipework (suggest weekly).
  • Regular inspection and cleaning of the external heat exchanger, especially if the system is a tube internal-cooling system.
  • Regular inspection of the external air cooling system (if the water-cooled heat exchanger has been replaced and substituted with an air cooler).
  • If you are sending out the quench oil for cleaning, ensure that the oil drums that contain the potentially contaminated oil are very clearly marked for identification on return. This is most important because contaminated oil can be put back into the quench tank if the drum is not identified in a manner that everyone knows whether it is contaminated or cleaned oil.

The cost of good quench oil will only increase before it decreases. That operating investment in the quench oil can be protected with good and effective oil maintenance. An alternative method of quench oil would most likely be the use of blended poly-alkaline glycols. This method of quenching can be a useful substitute to that of oil. The base material, being water, is an ecologically friendly quench medium. One singular major advantage of a poly-alkaline glycol system is that it is not a fire risk. It does, however, necessitate its own maintenance. The viscosity maintenance is generally done on a daily basis with a simple refractometer. Remember to account for drag-out during the quenching procedure. A monthly maintenance would be to check the quench medium viscosity.