Visible Defects – Pinholes

How do you ask for process help?

As experienced centrifugal casters know, having the proper machinery is only part of the equation for achieving quality castings. Process and metallurgy also play a critical role. Defects can be machine related but can also be related to process.

A number of defects occur in centrifugal casting that may or may not occur in static casting. Defects can be related to Pouring, Spinning, Temperature, Material, or Coating.

In order for CCMCO to help solve process problems for our customers we need as much data to troubleshoot as possible.

Send a photograph if you have it and include detailed data.  Some examples of data to include are:

  1. Size of casting.
  2. Location of defect. For example is it located all over the casting or specifically in one place.
  3. Alloy being poured.
  4. Degassing process being used.
  5. Coating type and application method.
  6. Pouring temperature.
  7. Initial spin speed and changes to spin speed once pouring is complete.

One common defect most of us who work with different alloys are familiar with is pinholes.

Pinholes and blow holes are frequently material related.  They are often produced because of gas entrapped in the metal during solidification.  Gas can come from the metal or can arise from excessive moisture in the coating, core material or binder, or sand material or binder.

Location of pinholes can also tell a story about the cause.  On a horizontal tube, if the pinholes are concentrated on one end of the tube the cause might be different than if the pinholes are spread over the entire tube length.

When customers come to us saying they are getting pinhole defects in their castings, the first potential solution we suggest is to improve their metal degassing process.  If this does not solve the problem then we start looking at other potential causes.

Don’t forget, when troubleshooting process defects, details matter!