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Die Casting News

Leaker Die Casting Defect May Be Reduced by Proper Use of Lubricants

Posted by Hill and Griffith Company on Aug 16, 2017 3:19:44 PM

NADCA EC-515 Die Casting Defects Course Review, Basics for controlling die casting defects - By Dr. Steve Midson

  • The leaker die casting defect is another form of shrinkage problems
  • There may not be any large voids, in fact, there may not be any visible porosity
  • All that is needed is a continuous path and enough space for gas or liquid to get through

Leaker-Die-Casting-Defect-Solution-1.jpg

  • This size of the space between dendrites depends on the temperature differences that existed at the time of freezing and the ability to feed new metal in during freezing
  • The center of the casting, or the last point to solidify will have a loose dendritic structure that is porous
  • The skin, however, is not porous - thus most casting would allow at least a little gas to pass through if it were not for the dense non-porous skin

Leaker-Die-Casting-Defect-Solution-2.jpg

  • It takes a break in the skin (usually on both sides of the casting) to generate a leak through the wall
  • One way that a break occurs is when the last point to solidify is on the surface. When this happens, the surface generally has the rougher or frosty appearance, and the dendritic structure is close to the surface
  • Another way is to expose a break by machining off some of the surface

Leaker-Die-Casting-Defect-Solution-3.jpg

  • The break in the surface often is from a machining action on one side and a shape condition on the other so that a hot spot is generated on the surface
  • The first correction should be to try to minimize the temperature problem on the surface
  • This can be done (sometimes) by running this area cooler in the die; changing spray patterns, changing or adding a water line; changing to one of the high heat transfer die materials
  • The temperature difference between die halves is something to look out for (not over 100 deg f max)
  • Remember that heating up a cold section can also help restore thermal balance
  • Adding radius where possible around the leaker area is a good idea, but can only help so much - adding more than about a .18 to .32 inch (4 to 8 mm) radius does not help much
  • Adding pressure in that area can help - squeeze pins can work well; Moving a feeder gate near the leaker area can help if the pressure is managed correctly
  • Also, check the metal temperature - a lower injection temperature may make a little difference, but it may also cause other problems
  • It is best to give every opportunity for a good skin to develop in the area where the leaker appears, be sure the die surface in this area is very smooth and clean.

(Thanks to All About Metallurgy for posting this PDF. We'll cover other aspects of die casting defect control by the proper use of die casting lubricants from the course in upcoming blog posts)

(If you liked this article you might also like this post on, "Die Casting Defects")


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