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Home > Tips and Facts > 10 Rules for Good Casting > Rule 5

Rule 5. Avoid Core Blows

Gases from cores or even occasionally from parts of the mold should not be allowed to penetrate the liquid metal. Core or mold blows cause a rather different type of defect than the entrained air bubbles.

  • Cores should be demonstrated to be of sufficiently low gas content and/or adequately vented to prevent bubbles from core blows. (This demonstration might be carried out by a video recording of the filling of the mold without a cope, for instance.)

  • No clay-based core or mold repair paste should be used unless demonstrated to be resistant to the creation of blow defects.

Below is a "core blow" - a trapped bubble containing core gases. Shown at the bottom of the illustration is a bubble trail, ending in an exfoliated dross defect as the result of a passage of copious volumes of core gas. [After Frawley et al. (1974)].

Illustration of a core blow, a trapped bubble containing core gases

Illustrated below is the detachment of a bubble from the top of a core, bequeathing a bubble trail as a permanent legacy of its journey. This bubble may be early enough to escape at the free surface of the rising metal.

Illustration of detachment of a bubble from the top of a core

Next: Rule 6. Avoid Shrinkage Damage >>
Previous: << Rule 4. Avoid Bubble Damage


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Atlas Foundry Company, Inc.
601 N. Henderson Avenue
Marion, IN 46952-3348
Telephone: (765) 662-2525 • Fax: (765) 662-2902
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Call Atlas Foundry today at 765-662-2525 for Gray Iron Casting Services
10 Rules for Good Casting
  1. Provide a Good Quality Melt
  2. Avoid Liquid Front Damage
  3. Avoid Arrest of the Liquid Front
  4. Avoid Bubble Damage
  5. Avoid Core Blows
  6. Avoid Shrinkage Damage
  7. Avoid Convection Damage
  8. Plan Segregation Distribution
  9. Control Residual Stress
  10. Provide Location Points

Article by John Campbell
University of Birmingham
Birmingham, United Kingdom
Reprinted with permission