EEVblog Electronics Community Forum
Products => Other Equipment & Products => Topic started by: EEVaditya on June 28, 2018, 06:12:41 am
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Hello,
I have a electronic control unit which has got aluminium casing.
Kindly suggest a product which will joint the aluminium casing and its aluminium lid (metal to metal) thereby making it water, oil and dust proof.
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A gasket?
I've had terrible experience long-term with adhesives on Aluminium unless they are applied with the proper prep (ie break down the oxide layer in an inert atmosphere and ensure a good adhesive coverage to ensure bonding to the metal and not the oxide). Of course if it's not thermally sensitive then either an aluminium solder/braze or preferably a TIG to weld it shut.
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What's wrong with bonding the sealant to the aluminium oxide layer?
Thanks
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I want sealant or adhesive which will cure at room temperature.
which will bond, seal the two aluminium parts together.
and can withstand with the moderate temperatures (not too low not too high)
I just want to make the unit waterproof.
I have seen some sealants which are grey in color, and somewhat elastic rubber type when gets cured so those type of.
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Do take note that when you seal the enclosure to keep water out, you are also sealing water vapor inside the enclosure. As atmospheric pressure and temperature change, you may end up with condensation on your electronics.
You may wish to purge and seal with or in an inert gas or include a desiccant (drying agent) within the enclosure.
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What's wrong with bonding the sealant to the aluminium oxide layer?
Long term it has a tendency to come off. Unless the oxide layer is formed by hard anodizing, it tends to be extremely fine and brittle. Not a problem in day to day use as any that comes away immediately re-forms, but if it has glue stuck to it when it comes away then the glue stays stuck to the oxide which is no longer attached to the underlying metal.
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Interesting. We never had issues with that yet we did not use the sealant as a glue but just as a sealant and screwed the lid to the housing.
Another thing to consider is temerature related pressure differences. You might want to use a pressure compensation membrane.
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I have heard of JB Weld epoxy being used for this sort of thing but it would not be my first choice. Some epoxies will bond very well with aluminum:
https://www.amazon.com/Loctite-Hysol-gram-Epoxy-Adhesive/dp/B000WXDLAQ (https://www.amazon.com/Loctite-Hysol-gram-Epoxy-Adhesive/dp/B000WXDLAQ)
https://www.miller-stephenson.com/product/ms-907-two-part-epoxy-adhesive/ (https://www.miller-stephenson.com/product/ms-907-two-part-epoxy-adhesive/)
3M has a bunch of similar industrial epoxies which would be easier to use in a production environment but only one for aluminum:
https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Scotch-Weld-Epoxy-Adhesive-DP420NS/?N=5002385+8710979+8713609+3293241657&rt=rud (https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Scotch-Weld-Epoxy-Adhesive-DP420NS/?N=5002385+8710979+8713609+3293241657&rt=rud)
Could you cut a channel in the walls or lid for a neoprene o-ring?
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rtv silicone,
or a car product called blue hylamar (probably spelt wrong)
it is a liquid gasket for aluminium heads and water pumps.
you put it on and fit the part loosely.
after it sets to a rubber you tighten the part against it - used by rolls royce.
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If you don't need water immersion protection, it would probably do well enough to heavily grease the joint. Use a thick, high temperature grease. Not, like, vaseline, which would run off at elevated temperature.
A gasket would be preferable for maintenance purposes.
If "permanent" sealing is acceptable, then an RTV silicone rubber will do. DO NOT use corrosive (acetic or amine based) formulas!
Tim
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If you want a really good seal then just solder it with whatever the aluminum version of staybrite is. You can take it apart with a torch. It smells like complete shit though.
Steel solders really well, aluminum is a bit harder. The steel flux might be fairly corrosive though.
Might want to coat both sides, clean very well, abrade then join without additional flux. Might be tricky.
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Maybe a good first question would be: what do you want to store in the aluminium casing?
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@EEVaditya I think you want a solution for Electronic Control Unit (ECU) casing and cover fixture (shown in attached image) so that water or any other liquid solution won't enter inside the casing, like Engine Control unit.
I think liquid gasket can be used.
Not sure whether it last for a long period.
@stj have you ever try rtv silicone for electronic casing?
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yes, i have tried rtv in the past to seal masthead antenna amplifiers after repair.
just make sure the surfaces are clean and buy neutral cure stuff.
it comes in 3 types, acid cure, alkaline cure, and neutral cure.
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yes, i have tried rtv in the past to seal masthead antenna amplifiers after repair.
just make sure the surfaces are clean and buy neutral cure stuff.
it comes in 3 types, acid cure, alkaline cure, and neutral cure.
Does it come of easily if you want to repair it ?
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depends on how porous the surfaces are, but you can clean it off with a scraper or flat screwdriver.
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If it doesn't need to be submerged: don't make it water or airtight. You can't. You'll always get water vapour inside which then condenses. A better approach is to conformal coat the circuit boards and make sure water can escape from the enclosure. Besides the water vapour condensing a small leak won't get the electronics wet and the water can still get out.
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@jtronix, yes I exactly need the same.
any suggestions for neutral cure rtv silicone sealant or gasket makers.
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rtv is used in the building trade to seal baths and sinks to the tilling - go look in diy centers.
it comes in big 300-400ml cartridges for beer money.
example:
https://www.everbuild.co.uk/product/450-builders-silicone/ (https://www.everbuild.co.uk/product/450-builders-silicone/)
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My application is in the automotive sector.
The surface will be metal. any rtv silicone sealant or gasketing product? or liquid gasket maker?
different people use different terminologies.
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read the datasheet at that link - metal or glass etc. no problem.
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Do take note that when you seal the enclosure to keep water out, you are also sealing water vapor inside the enclosure. As atmospheric pressure and temperature change, you may end up with condensation on your electronics.
You may wish to purge and seal with or in an inert gas or include a desiccant (drying agent) within the enclosure.
This can't be stressed enough. Many underestimate this. Maybe it's better for the user to encapsulate it (and put it on a vibrating plate to get the air bubbles out.)
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working on some rtv silicone gasket maker (neutral cure). but any more suggestions and recommendations are always welcomed.
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what happen to aluminum body if sealant is used other than natural cure?
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"Regular" RTV produces acetic acid during curing:
https://code541.gsfc.nasa.gov/Uploads_materials_tips_PDFs/TIP%20044R.pdf (https://code541.gsfc.nasa.gov/Uploads_materials_tips_PDFs/TIP%20044R.pdf)
Here are some details about Aluminium and acetic acid:
http://www.electrochemsci.org/papers/vol9/91005496.pdf (http://www.electrochemsci.org/papers/vol9/91005496.pdf)
When I thought of these issues, I was more concerned about the effect of acetic acid on the electronics and soldering (not sure if it is valid...).
I have an un-opened tube of American Sealants #388 neutral cure silicone standing by for some future application. The rest of my silicone sealant stock is "marine grade" and probably emit acetic acid during curing.
http://www.americansealantsinc.com/388-electronic-grade-silicone/ (http://www.americansealantsinc.com/388-electronic-grade-silicone/)
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Acetyl and amine based silicones are murder. The resulting acetic acid corrodes most metals, including aluminum and copper (but not stainless). Or the resulting ammonia corrodes aluminum, copper and a few others (but not steel, and maybe not tin).
Neutral cures I think are alcohol based, which is too mild to affect any metal that's not already affected by water.
Water is the curing agent, by the way. Water breaks the alcohol or acetate or ammonia off from the silicone backbone, causing the silicone molecules to stick together. A perfectly air tight joint will not cure, and perfectly dry air will not cure (although I'm not sure that that's enough of a problem even in very dry desert areas, as long as there is still some moisture in the air).
At least, this is true for some types, but I don't know what all kinds are out there. The only kinds that don't need air exposure of some sort are two-component, of course.
Tim