Thickness of a rubber gasket?

[Ramadan Ahmed]

Good Evening Everyone,

I want to ask, is there a way of a calculation for selecting the thickness of a rubber gasket (NBR rubber)?
i want to use a custom rubber gasket but im not sure what is the thickness i would need to seal the product from liquid.

Can anyone help me with this matter please?
Thank You.

 

[LittleInch]

Thickness of 3 to 4mm is usual.

Thicker and you risk the gasket itself failing, thinner and it can't absorb any small variances.

Why are you using a rubber gasket?

Type of flange, pressure, temperature?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mfgenggear]

What is the internal pressure
What is the housing made from
What will be the Precision of the interfaces
What type liquid or gas

Look at standard gasket material sold over the
Counter for low pressure automotive application for old style carburetor.

 

[Ramadan Ahmed]

I'm trying to seal a video camera from liquid, it will operate in normal pressure but at high temperature such as 50°C.
this is the rubber seal I designed, I decided to select NBR Rubber for sealing but the part I'm sealing is small as seen in the dimensions that's why I'm confused about the thickness


- will operate at normal sea level pressure
- The housing is made of aluminum
- I'm trying to seal water, like in a rainy weather.

 

[Ramadan Ahmed]

 

[geesaman.d]

The biggest issue with an all-rubber gasket is controlled compression. If you have some kind of standoff surrounding the holes or flange to keep the compression at a reasonable level (say 80% of rubber thickness), it should seal reliably and the fastener torques will not be compromised. The thickness of the gasket will probably be limited by available material thickness and whatever tolerance on surrounding components that will reliably produce 15-25% squeeze.

Judging by the distance between fasteners vs. the width of the gasket section, I hope this is trapped around the perimeter somehow to ensure the gasket does not distort or work its way out of the intended location.

Not using standoffs will result in the gasket material creeping and deforming without limits unless the fastener torques are perfectly suited to the compression of the rubber gasket (which in my experience, is not)

 

[LittleInch]

Suggest a O ring design would be a lot better.

Rigidity of the casing is crucial. Point fixings are not easy to spread the load.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

The material of choice is closed-cell silicone foamed rubber sheet. It has very good compliance. Solid rubber sheet is far too stiff unless the housing and cover have deep sections.

As Littleinch suggests, with thin sections the bolts/screws will pinch down on the rubber, causing the cover to bow up and leave a gap in between.

I also recommend using a desiccant to prevent moisture from condensing inside the housing and causing problems. There are various contained desiccant packages, from the little bags to bigger packages. The better ones include moisture indicating color change components to let the user know it is time to replace them.

 

[mfgenggear]

McMaster Carr catalog
Recommendation 1/16 thick
Neoprene rubber pick a grade that is 220 degree f max,

https://www.mcmaster.com/products/neoprene-rubber/multipurpose-neoprene-rubber-sheets-and-strips/

 

[mfgenggear]

Real easy application is high temperature silicon applied from a tube. General a red color, or blue.
Is used in automotive high temperture application to seal for water

 

[3DDave]

Not all silicone sealants are electronics safe; most use an acetic acid evolution cure. Look for the neutral cure (they produce ethanol or other non-corrosive, I recall) sealants. I know it isn't much acetic acid, but if the camera is left in there and there is any residual moisture, eventually that moisture will get condensed on the electronics and the acetic acid will find a new place to etch.

Both kinds appear to absorb moisture from the air as they cure, but I would not depend on either of them to desiccate the container.

 

[TugboatEng]

Also, the red and blue silicones are highly porous. Black and grey silicones (consumer grade is called "The Right Stuff")perform much better. Grey for machined surfaces and black for sheet metal.

Don't forget about anaerobic sealants. I tend to favor those over silicone if conditions permits.

 

[MintJulep]

A Google search for "gasket design handbook" will find hundreds of free and paid resources.

They will tell you about all of the factors that you need to think about.

Thickness is only one of many.

It seems that you've already designed the seal geometry without thinking about a sealing system. Too bad, that constrains your choices.

 

[mfgenggear]

Yes I forgot about the acidic issue
Here is the proper recommendation

https://www.eevblog.com/forum/beginners/silicone-sealant-(electronics-grade)/

 

[glass99]

The key calculation is the relative stiffness of the cap vs the gasket. If your cap deflects by 0.02" when you screw it down, you are going to need a gasket that is able to take up that movement plus any substrate tolerance without generating too much stress. The dog bone youngs modulus of a 60A solid rubber is approx 500psi, and when poissons ratio effects are taken into account its approx 3x stiffer, lets say 1500psi.

 

[drawoh]

Ramadan Ahmed,

I work out the compression I can apply to my gasket. Knowing how strong your gasket material is, you can easily work out the thickness. If your stuff is inaccurate, you need a thick, soft gasket.

--
JHG

 

[Ramadan Ahmed]

Thank you all for your respond to this post I really appreciate your help on this matter it helped me a lot.