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How to Eliminate Sealant Contamination

Posted by Andy Marin on Tue, May 30, 2017 @ 08:51 AM
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Customers often ask us how sealant is removed from machined features, like tapped holes. Customers assume that the holes are masked, but that is far from the truth. In this blog, we will discuss what in the vacuum impregnation process enables a casting to be properly sealed without excess cured sealant in unwanted areas (sealant contamination).

 

Sealant in hole.png

This feature has excess sealant. The excess sealant will cause quality and assembly issues.

What is the problem?
Sealant contamination  causes parts to not be usable. Excess cured sealant  affects part quality and assembly. Castings will be rejected by quality control since fasteners  will not thread into tapped holes on mating parts. The castings with sealant contamination are often scrapped since it is very difficult to rework.

 

How is it caused?
During the impregnation cycle,vacuum and pressure trap the uncured, liquid  sealant in the porosity as well as any other casting openings. Many systems are not designed to fully remove the sealant from undesirable locations.  When the sealant cures to a hard polymer, the sealant left behind in the tapped holes and threads can cause assembly problems in manufacturing downstream. In some systems:

 

  • The wash module does not fully remove the undesirable sealant.
  • There is no centrifuge to remove and recover excess, liquid sealant prior to the wash cycle.
  • The  system places multiple parts in a large basket. By layering the parts, features will be masked by other parts and will not get fully washed.
  • The water in the wash module is not drained or regulated after use, so water ladend  with sealant from previous cycles is used to wash upcoming parts.

 

How is it solved?
Sealant contamination can be eliminated by transitioning from sealing parts through an outdated  system to sealing castings through single-piece flow vacuum impregnation equipment. The benefits of single-piece flow equipment are:

 

  • Incorporating part fixtures custom designed to the casting.
  • The wash water is filtered and regulated during use so that it does not contaminate  parts.
  • The use of a high speed centrifuge to remove and recover excess sealant prior to the wash cycle.
  • The use of modern sealants, engineered for wash ability so that the sealant washes off during the wash/rinse cycle.
  • The comprehensive wash, part rotation, oscillation and overspray completely emulsifies and removes excess sealant prior to cure.

 


No sealant in threads.png

This casting was sealed in an HVLV. The blacklight shown on the tapped hole proves that there is no sealant in undesirable features.
Due to the benefits mentioned above, this casting does not have any sealant contamination.

 

Conclusion
Eliminating sealant contamination is done through a holistic approach to the vacuum impregnation process. All of Godfrey & Wing’s vacuum impregnation equipment is engineered to properly seal casting with no risk of sealant contamination. This is why Godfrey & Wing’s equipment seals porosity with a first time through (FFT) recovery rate of over 99%.  

 


 

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Topics: vacuum impregnation processes, Sealant contamination

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