Previously, in part 1, we described the situation and discussed the heat-treatment operation. In this blog we will finish with a discussion of our observations and the remedy. Did you figure out what might be wrong based on our initial discussion of the problem?

Observations

The observations made were as follows:

  • The uncontrolled austenitizing temperature was (personal estimation) approximately 1700°F.
  • The radial quench ring on the induction coil was not delivering the quench medium in a uniform manner at the austenitizing sequence.
  • There was also a slight hesitation on rotation of the individual component rotational tables, which were located on the main drive table.
  • Because of the differing cross-section dimensions on the product, cracks were being initiated on the thin sections of the component.
  • The quench-medium solution (water) was not being cleaned on a frequent basis, and machining debris (swarf/shavings) was being allowed to build up in the cooling system. This was causing some of the quench-ring holes on the coil to become blocked.
  • There was also a considerable time delay before the treated components were tempered.

Remedy

The following remedies were initiated:

  • Clean the quench-medium filtration system on a daily basis to remove any debris caught in the filter.
  • Use a 5% polyalkaline-glycol solution and measure the quench-medium solution strength on a daily basis.
  • Reduce the induction heating power to reduce the risk of overheating the component and produce a lower austenitizing temperature of approximately 1530°F.
  • Introduce a small continuous tempering furnace to operate at a tempering temperature of 300°F to temper immediately after austenitizing.
  • Random sampling of three components (one every 3 hours) to ensure the appropriate results are being obtained.
  • Clean out of the quench-medium sump weekly to ensure an uncontaminated solution of PAG to the quench ring on a repeatable basis. 

Results

The problem was resolved within five days. The corporate philosophy was that because the induction unit was newly purchased, there should not have been problems. Any machine or furnace needs regular pre-planned maintenance in conjunction with good housekeeping in order to maintain functionality and repeatability. Preventive maintenance is always better than catastrophic maintenance.