Visible Defects – Raining

Visible Defects-Raining

Experienced centrifugal casters know that 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 castings 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.

The Raining defect is unique to horizontal centrifugal casting.  Raining is when metal rains or falls from the top of the mold to the bottom while the mold is spinning.  Although it can be difficult to see, you can witness this phenomenon by looking into the opposite side of the rotating mold from which the metal is being poured.*

Why is Raining Considered a Defect?

Raining can cause a few problems on the ID of the casting that are worth solving.

  1. Raining results in oxidization of the metal “raining” from the roof of the mold causing a bad casting.
  2. A common result is that raining will cause an excessive amount of dross on the ID of the casting.
  3. Raining can cause turbulence of the metal in the mold and can upset the temperature gradient of the molten metal, thus preventing directional solidification.

Possible Causes And What To Do To Solve This Problem:

  1. Pouring metal into the mold at too high a pouring rate. Reduce the pour rate, particularly the pour rate of the last half of the metal poured into the mold.
  2. Spin Speed is too Low. Increase the mold spin speed.

Please try these solutions and let us know if they helped you get rid of Raining in your castings! If your defect persists, please get in touch.

*Always keep yourself safe when around spinning equipment or molten metal.   When looking into the rotating mold, do so from a safe distance.