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Anonymous Poster #1

Leak Testing Method

01/05/2017 4:00 AM

I am producing aluminium die casted component in which oil is supposed to be filled after assembling other components. But there is a problem of oil leakage after assembly due to casting porosities.

Let us forget the root cause of porosities for some time, I just want to sort out the components having leakage and not having leakage.

Now I have two facilites available with me.

1) Positive pressure: Applying some air pressure and then check for the pressure drop by holding the same.

2) Negative pressure: Evacuating the component and then check for the pressure rise by holding the same.

But the query is how can I compare the result of both test methods?

Is there any method/calculation to compare leak rate of both testing methods?

Which one is better? Why?

Any other guidance/suggestions are most welcomed.

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#1

Re: Leak testing method

01/05/2017 4:07 AM

It depends upon the stored energy in the component, the value of which has been withheld from the forum. Were it to fall into the domain of various local pressure systems regulations then a hydraulic test to a higher pressure would be a requirement before filling with a compressible fluid.

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#25
In reply to #1

Re: Leak testing method

01/31/2017 1:35 PM

It took me a few seconds to understand the picture, that was some boiler explosion!!

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#2

Re: Leak Testing Method

01/05/2017 9:59 AM

Duplicate/repeat thread alert.

Vacuum impregnate with a sealing liquid.

Asking the same question multiple times will not increase the odds of getting the answer you want.

I'd go with #1.

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Anonymous Poster #1
#4
In reply to #2

Re: Leak Testing Method

01/05/2017 12:20 PM

@lyn, Seriously, i haven't asked this before in any forum. Even I can't find any such thread.

Plz provide link, where I can check the answers/discussion.

And do you mean vacuum impregnation? I have already said, let's forget the root cause and accept the casting defect.

I just want to detect the leak components.

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#5
In reply to #4

Re: Leak Testing Method

01/05/2017 12:27 PM

I fail to believe that two individuals could possibly ask the same redundant question.

I believe you are not capable of determining how to solve this problem by yourself and want the forum to do your work for you!

At least admit that you are lost!

Aluminium Die Casting Porosity

"I am producing die casting of an aluminium component in which oil is supposed to be filled after machining the component.


But even though degassification of the molten metal has been done for casting, oil is getting leaked from the component because of porosities remained in the component

I am aware that the die and component's design matters a lot, but needed guidance if any other suggestions are there to improve the quality."

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Anonymous Poster #1
#6
In reply to #5

Re: Leak Testing Method

01/05/2017 12:32 PM

@lyn, even i can't believe. Plz let me check it once.

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Anonymous Poster #1
#10
In reply to #5

Re: Leak Testing Method

01/05/2017 11:34 PM

Seriously, i can't believe it. But its not me. Its a coincidence. By the way, in my case, i have already accepted leakge of component and i just want to compare leak testing mepthods

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#11
In reply to #10

Re: Leak Testing Method

01/06/2017 2:02 AM

I'll leave you with this comment, and note the unbelievable coincidence.

If you remove all the air from inside your "thing" how much pressure will the atmosphere exert on the outside of it? Hint: not much.

If it leaks, do something to stop it.

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#20
In reply to #10

Re: Leak Testing Method

01/06/2017 10:42 AM

Are you Russian? 'cause you're hacking Lyn off.

Either method will give you reasonable quantitative leak rate data based on decay rate of the vacuum drawn or the fixed pressure applied if you use compressible fluid (air) as the test medium. Safety considerations about popping or imploding the part need to be considered when setting the test start pressure and you need a known good part to confirm that leaks aren't in the test apparatus.

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#3

Re: Leak Testing Method

01/05/2017 11:37 AM

Use both, you will detect twice as many defects. LOL

And be sure to add some of that oil before pressurizing any assembly.

Can't you die cast under vacuum, to eliminate the air inclusions? or use g acceleration?

After you get through testing, take half of the leaky parts and attempt annealing them at 20 C less than the melt (if the distortion does not ruin the parts further). Yeah, it probably will not help.

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#7

Re: Leak Testing Method

01/05/2017 12:34 PM

Simple, do some experiments.

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#8

Re: Leak Testing Method

01/05/2017 12:48 PM

On the ALCM , which was made of sand castings, we would flood the inside of the castings with water washable liquid penetrant and dust the outside with the developer powder. Any thru wall leaks were apparent. It was either that or an inside bladder. The leak thru was weld repaired and re-tested after x-ray.

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#9

Re: Leak Testing Method

01/05/2017 4:14 PM

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#29
In reply to #9

Re: Leak Testing Method

02/14/2017 8:44 AM

That might work on wives for leak removal. I don't think it works if the wife is concrete.

I could not get Flex-Seal white to adhere to concrete vessel, hence that idea sunk.

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#12

Re: Leak Testing Method

01/06/2017 8:20 AM

The use of a "negative" or vacuum pressure test would seem highly impractical. A more simple test method, since you indicate a positive pressure test is practical, is to submerge the casting in water after pressure is applied and check for bubbles. Applying a soap solution on the outside instead of submerging is another method to check for leaks as one often does when checking for piping leaks. As Lyn stated, vacuum impregnation is a fix providing your voids aren't humongous. Some die casting machine designs are less vulnerable to porosity but you haven't mentioned what type of machine you are using.

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#13

Re: Leak Testing Method

01/06/2017 8:28 AM

Buy a hand held helium leak detector - they aren't grossly priced. Fill with helium under pressure and you'll find leaks. We've been using them here where I work for two decades. Despite the ominous warnings lately about a helium shortage, it still seems to be available.

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#15
In reply to #13

Re: Leak Testing Method

01/06/2017 8:49 AM

I agree! Helium Mass Spectrometry is a common enough method. https://en.wikipedia.org/wiki/Helium_mass_spectrometer

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#16
In reply to #13

Re: Leak Testing Method

01/06/2017 10:02 AM

hydrogen is cheaper, and might leak faster probably even than helium, or nearly as fast if not faster. Hydrogen will not particularly harm aluminum parts.

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#17
In reply to #16

Re: Leak Testing Method

01/06/2017 10:14 AM

Hydrogen is flammable. We don't use it because we have two choices - large production area which has welders or small rooms to test in. A 4% LFL is a bit risky in a small room. We might get by in the vicinity of the welders as 4% LFL is large number in a large production building, but why risk it? I'm sure Safety would not allow it. The OP can decide on this for where the part must be for testing.

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#14

Re: Leak Testing Method

01/06/2017 8:48 AM

You should already have known factors, known failure repeatability... RED RABBIT

(repeatable factors for both or #1 at least.) Kgf/m2

"repeat your failures to avoid them"

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#18

Re: Leak Testing Method

01/06/2017 10:25 AM

Given your description of the application, I would suggest the positive pressure method. Assuming that the part is under positive pressure in application, it makes the most sense to test for leaks under similar conditions. Also, consider pressurizing it with the oil if possible.

If you are simply trying to sort leaking and not leaking parts, it shouldn't be necessary to measure leakage rate.

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#19

Re: Leak Testing Method

01/06/2017 10:41 AM

It depends on a number of factors. Not all leaks are symmetrical (they can have different leak rates in different directions). I would think that since your parts are leaking from inside to outside, that's the direction you want to test from. After you establish a test direction, you must figure out the leak rate you can accept. In your case, it might be volume of oil per unit time at a specified pressure drop. If you require a more sensitive test, you can switch from oil to gas. ASNT (American Society For Nondestructive Testing) handbooks are a good source of information.

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#21

Re: Leak Testing Method

01/06/2017 11:12 AM

There are 2 other methods I used for leak testing which don't even require pressure and give good results. Depending on the size of the casting and its configuration you can either fill it with 1) kerosene or 2) Liquid fluorescent penetrant.

Set on clean white surface and leave for awhile. Either of those 2 liquids will seep through porous aluminum in a short amount of time. Did both a number of times with aluminum sand castings which are typically much less porous than die castings.

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#22

Re: Leak Testing Method

01/07/2017 3:17 PM

What information are you expecting to get from the calculations? Are you searching for the relationship of the 2calculations or is it something else? Fluids will act differently depending on what your doing.

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#23

Re: Leak Testing Method

01/08/2017 5:15 PM

Non-invasive techniques to test porosity (like imaging) are likely to be more expensive than just sealing the aluminium and batch testing (or similar) to make sure the problem has disappeared. Air pressure testing is unlikely to work in my opinion unless you are willing to spend a lot of money on an expensive test setup and sensitive measuring equipment.

Water pressure testing is a better bet and a lot cheaper. For example sealing the component so it is air tight and then placing it overnight in the bottom of a 40 gallon drum full of water and checking the next day if moisture has made it through the aluminium walls into the sealed air cavity.

This is what we used for testing the porosity of our brass box castings.

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#24

Re: Leak Testing Method

01/31/2017 1:34 PM

Haven't you already asked this question a few months ago?

If not, search for it and you will have all the answers you need.

Posting anonymously does not allow me the possibility to check who it was.

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#26

Re: Leak Testing Method

02/14/2017 12:29 AM

It is good to use Positive pressure and dip it in to the water and you can directly see where the air leak from.

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#27
In reply to #26

Re: Leak Testing Method

02/14/2017 3:26 AM

Works well with loud wives too, I hear!!!

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#28
In reply to #27

Re: Leak Testing Method

02/14/2017 8:42 AM

Yes, but you must act as a Baptist, and go for complete immersion. A Methodist (sprinkler), might not ever prove where the loud sonic blasting is issuing from.

wifey started in on me this morning, I just ignored her. That starts the day off right.

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#30
In reply to #28

Re: Leak Testing Method

02/14/2017 8:58 AM

I was raised Baptist(dear God) and the discussing I can hear relates to "face up or face down"testing. How do you know which to start with?

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#31
In reply to #30

Re: Leak Testing Method

02/14/2017 9:55 AM

If face down does not work, the leak is on the other end.

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