Friction increase after coffee and coke spilling?

[catibon]

Hi everybody.

I experienced a weird behaviour of a steel inertial latch whose reliability is currently doubtful.
We performed a spill test in which the latch:
1) was immersed in black coffee and then allowed to dry for three hours;
2) then immersed in coke and again allowed to dry for three hours;
3) finally immersed in diet pepsi and allowed to dry for three hours.

Well, after this spill test the latch experienced a DECREASE of the friction coefficient. We were expecting an increase due to obstruction of the fluids residues.

How can we explain that??

Catibon

 

[zdas04]

The reason you do tests is to find out stuff you don't already know. Maybe the inherent lubricity of the solids in one or more of the liquids exceedes the stickiness in the others?

Am I understanding correctly, was this a sequential fouling of a single latch without evaluating the performance between tests? Maybe the coffee has good lubricating qualities that overcame the stickiness of the soda's?

David

 

[TheTick]

All these fluids are acidic. Perhaps the acid improved the surface finish (i.e. by removing corrosion?)?

Honesty may be the best policy, but insanity is a better defense.

http://www.EsoxRepublic.com

-SolidWorks API VB programming help

 

[catibon]

Hi David.
Thanks for your reply.
We actually tested the latch after spilling in sequence the three liquids and without evaluating intermediate behaviour. This latch will be part of a seat in such a way that it will be difficult to visually inspect it, unless we take the seat in pieces (which occurs not always).
We want to be sure that dust and dirt or liquids spilled by mistake by the seated person, don't worsenthe latch performance.

I hope now it's clearer
Claudia

 

[debodine]

Because I work in aviation under the placard-mandating FAA, perhaps you could simply placard the latch with approved liquids that can be spilled to improve the latch activation and prohibit spilling of liquids that degrade the latch activation?

<tongue-in-cheek>

debodine

 

[fcsuper]

What residual did you expect to remain in from those drinks? Perhaps and analyst of the ingrediants of those drinks the the state in which they appear in those drinks is necessary. Also note that only one of those drinks had sugar in it. The other two would not have produced a stickiness. Is that what was expected? I'm more curious than anything here.

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group

 

[MikeHalloran]

Coke is rumored to eat metal in days, and presumably could improve surface finish in a few hours.

Perhaps the expected results would be obtained with sugared drinks, like Gatorade and V8 Splash, or drinks containing fat and solids, like milk.



Mike Halloran
Pembroke Pines, FL, USA

 

[MiketheEngineer]

Coke WILL eat metal in a few dasy!! Try it.

Makes a very good car battery post cleaner... Make sure to wash well afterwards..

 

[MintJulep]

It has always been my experience that coffee with cream and sugar always gums things up.

It is possible that three hours was not suffient to really dry the thing out, so that there was a lubricating film of liquid.

 

[IRstuff]

Additionally, since it was first in the sequence, with Diet Coke last, there's every possibility that the subsequent spills dissolved and washed away the coffee and the Coke. May be the sequencing was intentional?

TTFN

FAQ731-376

 

[catibon]

Hi guys, thanks to all.

The latch is subjected to big and time-short forces. I thought that maybe in this case, passed the stickness condition at the beginning, since the speeds involved are very high, the viscosity of the residues on the surface would make the latch more "slippy".

What do you think? Bad science fiction?

Claudia

 

[CoryPad]

How long was the immersion in Diet Pepsi? If it was longer than 2 minutes, you likely removed all of the Coke residue.

Residues may have an effect, but you need to replicate the surface conditions they impart. Perhaps an eye dropper to apply the product may be better.

Regards,

Cory

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

 

[scastillo]

You need more data. Take a 500ml bottle of Tucher Bajuvator Double Bock. Pour a small amount on the latch. Consume the rest. Wait two minutes. Test the latch's coefficient of friction. Test your own coefficient of friction. Repeat until the latter falls below zero.

 

[MikeHalloran]

Isn't there an ASTM standard for that?



Mike Halloran
Pembroke Pines, FL, USA

 

[TheBlacksmith]

My Great Grandfather and my Grandfather, both plumbers, used coca-cola to free up rusty fittings. Pour a little on, take a break and drink the rest of the bottle, take apart the fittings. They said it was a combination of the effervescence and the acid that made it so effective.

 

[vpl]

Claudia

It sounds like what you need is a test that better replicates your concerns -- perhaps starting off with a test plan. Remember back to grade school and science fair projects (assuming you did those) where you had to come up with a hypothesis before you did your experiment? That's what's needed here. You need to write down what substance you're going to try and why you think it will cause the latch's performance to deteriorate, thinking through the properties of the contaminating substance.

I agree with those that noted that the substances used were all acidic and only one contained sugar. Something you might want to think about (besides using products with milk and sugar) is throwing some dust and crumbs in there (you know, the powdered doughnut to go with the coffee, the Big Mac with the Coke ...) Alcohol (as humerously suggested byscastillo) would also be good as it contains a lot of sugar. Or if the latch is encased by foam, then minute particles of foam that get dried out and brittle because of the liquids. Generally, the liquid is usually only the transport medium. It's the small particles carried by the liquid that will get caught in the latch and stick to it.





Patricia Lougheed

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[GregLocock]

I hate to say it but this could be a good place to apply a Taguchi designed experiment.



Cheers

Greg Locock

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

 

[berkshire]

Hoo boy , I want to see the Taguchi grid for this one.

B.E.

 

[catibon]

Thanks to all.
Actually I'm only the checker for this experiment and I will definetely suggest to lab guys to repeat it again. For example writing a good test plan before.
Hopefully we'll come out with reasonable results.

Claudia

 

[Compositepro]

How do you know the latch was actually dry?. Liquids in a gap or hole can take days or weeks to dry without elevated temperature and air circulation.