Cast Iron Cracking Inspection 6

[NEWTKUO]

I am working on a pump housing project. The cast iron housing some cast iron housing comes in with invisiable crack. We manufacture pumps by volume, there is no time to do one by one check. Is there any way I can check? Chemical or Mechanical? Thank you for the help!

 

[CESSNA1]

NEWTKUO: By invisible cracks I assume you mean "hairline" cracks in/on the casting that are accessible. The fastest, but not necessarily the best, is by inspection under magnification. Better, but slower and somewhat more costly are:

Dye penetrant such as Zyglo, dye-chek, and others
Magnetic particle

You may also wnat to look at the casting process/item design, to minimize/eliminate the possibility or cracking.

regards
Dave

 

[ctopher]

Major aircraft mfg use dye penetrant with a type of black light. The crack shows very well. I don't know the details of what they use.

Chris
Sr. Mechanical Designer, CAD
SolidWorks 2005 SP0.1

 

[MintJulep]

Dye penetrant will only show cracks that come to the surface.

Magnetic particle will show sub-surface cracks.

However, both of these methods are visual inspections.

Quality cannot be inspected into a product. You need to address the underlying quality issues at your foundary.

 

[BillPSU]

MintJulep is right on. The reason for the crack must be discovered and eliminated. It probably isn't even a crack. Its porosity or shrink or inclusions. Whatever it is, talk to the foundry.

 

[MikeHalloran]

If you work with castings, you have to make some choices to balance the costs of:

- Inspecting all incoming raw castings 100 pct or by sampling or not at all.

- Inspection by dye penetrant, magnetic particle, or air leak test.

- Accepting that some castings, and some entire lots of castings, will be flawed, saving the cost of upfront inspection but spending the cost of replacing castings that fail or otherwise become unsatisfactory at various stages of production or in customers' hands.

- Inducing the founder to inspect the castings before shipping them, e.g. by paying him to do so.

- Immersing the raw castings in Loctite (290?) penetrating sealant to close up the smaller cracks and areas of porosity.

Except for estimating or measuring the various costs and throughput of the options, it's not really an engineering problem, it's a business problem.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[CoryPad]

Radiographic testing for defects appears to be a good option - it can be automated to avoid high labor costs associated with manual/visual inspection.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Rich2001]

The problem with RT inspection is that if the cracks are not perpedicular to the RT source & film the hairline cracks will not be noticable.

MT and PT are both good method for finding cracks, though PT can only find surface cracks. You need to determine if a subsurface crack is a problem.

A few other techniques that you might want to investigate are; ACFM & Eddy Current.

A technique that is fast and can be used to inspect cast iron for cracks is ACFM (Alternating Current Field measurement). This technique can be automated and provides a record of the results.

You might want to investigate eddy current testing, along with the determination of cracks, you can obtain data on the part's hardness differences, chemistry changes, and surface roughness.

 

[yates]

Rich2001
Don't you mean parallel to x-ray beam, rather than perpendicular.

Problem should be sorted out so that every casting does not have a crack. If you're worried about inspection costs (although this does depend upon casting shape) hit the damn castings with a hammer. You should be able to detect a more clunky and less ringing sound if the casting is cracked. You then apply MT or PT only to those castings that clunked, or were doubtful.

 

[btrueblood]

Cast grey iron always clunks. The high graphite damps vibrations extremely well.