Molybdenum Crucible: Repair or Replace, Three Criteria for the Decision

After a molybdenum crucible has been in service for a while, it may deform, scratch or thin locally, and whether to keep running, repair or replace is often settled by experience alone. Breaking the decision into separate criteria reduces both defect-laden operation and premature scrapping.

Check Wall Thickness and Where It Thins

Measure the remaining wall thickness at the bottom and side walls and compare it with the original drawing. Where thinning is concentrated near the melt line or at the bottom centre, the pressure and thermal conditions are more severe, so continued use should be given lower priority. Keep the measuring points fixed so successive readings can be compared, and write the data into the crucible history.

Check Cracks and the Extent of Deformation

If a surface crack has penetrated the wall or sits at a stress concentration such as a weld or a fillet, repair has limited value. Slight deformation can be assessed for straightening, but straightening itself introduces new stress, so the subsequent service conditions must be confirmed. Changes in diameter and roundness affect the clearance to the induction coil.

Check the Service Stage and Associated Cost

For a crucible near the end of its expected service stage, the time gained by repair may not cover the cost of the next removal and reinstallation, in which case replacement is the safer choice. If there is only surface contamination or light scratching, cleaning and polishing will restore it.

Inspection Before Repair

Before repair, carry out dimensional measurement, wall thickness testing and surface inspection, adding non-destructive testing where necessary to establish the extent of the defect. The inspection data is both the basis for repair and the baseline for judging whether the crucible can continue in service afterwards. A crucible repaired without inspection data is hard to evaluate afterwards.

After a new crucible enters service, record the batch, installation date, operating temperature and any abnormalities. Photograph the failure mode of an old crucible and analyse it together with the inspection data. Once records accumulate, purchasing and operations can judge the replacement rhythm more clearly.

For repaired parts, state the repaired area and inspection results at delivery so the user can adjust process parameters accordingly.

If the crucible is used only for small-batch trial production, repair may offer better value; in continuous production, the risk of downtime weighs more. Including the application scenario in the decision is more complete than looking at the defect alone.

Write the conclusion into the crucible history so it can be compared later.

Whether repairing or replacing, keep the service records and inspection data to build the basis for the next decision.

For crucible inspection and service record practice, together with the supply of matched electrodes and crucibles, see the manufacturer information entry point.