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Fastener weather proofing torque
2

Fastener weather proofing torque

Fastener weather proofing torque

(OP)
I have a question about gasket seating/torque but for a single washer type gasket vs a flange gasket

I have an electronics enclosure that is bolted into place with external fasteners

but we need to meet some weather proofing spec from the customer, so we are trying to put small rubber washers/gaskets on the fasteners because the customer did not want RTV

so I have done flange gasket torquing per ASME pcc/sec viii and o-ring clamping, but this one is stumping me

any advice?

RE: Fastener weather proofing torque

Get some Seelscrews(R) - standard machine screws with o-rings mounted under the heads. Torque per normal (non sealing) requirement.

Like these: https://www.mcmaster.com/sealing-screws

If you just type sealing screw into their search box, you get other types as well (hex and socket heads, etc.). Or visit the mfg. website. Or use Amazon. Or google.

Edit: forgot to mention, but just putting an oring under a screw head almost never works, because the ring tends to pooch out when the fastener is tightened; at best you get sealing but not a tight screw and it loosens, at worst you get no sealing and the screw still loosens. The exception is when you cut a perfect counter-bore and -sink combination to have the oring squeeze into (SAE hydraulic glands, e.g.); most standard orings are too big to make this work with most standard screw heads.

RE: Fastener weather proofing torque

Use a bonded elastomer washer under the screw and tighten the screw to normal torque specs.

Ted

RE: Fastener weather proofing torque

Just to add to the comments above, while a simple nylon/rubber washer under a bolt can work in a pinch - mostly in non-critical applications - good luck achieving anything approaching reliable torque/preload application in the joint or retention of that torque/preload.

As mentioned Seelscrews (or similar) are definitely a good option, but just to flesh out additional options:

https://www.mcmaster.com/93783A029 - bonded rubber/steel washer for under a bolt/screw head (allows for controlled crush of rubber seal and then preload applied against the steel portion)

https://www.mcmaster.com/93781A029 - bonded rubber/steel washer for under a nut or washer (similar to the above bonded washer but it also seals on the threads)

https://www.mcmaster.com/91339A130 - thread sealing nut (bonded rubber seal which seals on the nut face and threads of mating bolt/stud)

APM Hexseal also has a good catalog and I've had good luck with some of their products (some of the products in McMaster I think are directly from them - like the seelnuts).

RE: Fastener weather proofing torque

(OP)
thanks for the ideas, Ive never had to do something like this, my first instinct was the RTV at the interface inside and out, but that was shot down quickly

Quote (chez311)

https://www.mcmaster.com/93783A029 - bonded rubber/steel washer for under a bolt/screw head (allows for controlled crush of rubber seal and then preload applied against the steel portion)

https://www.mcmaster.com/93781A029 - bonded rubber/steel washer for under a nut or washer (similar to the above bonded washer but it also seals on the threads)

I think those are the ticket

RE: Fastener weather proofing torque

Korichnevijgigant,

How much control do you have over the whole arrangement? If your screws and bolts are outside the sealed volume, then sealing of fasteners is not an issue. Your next choice is some fairly elaborate engineering. Can you measure the thickness of a gasket and compress it some known distance?

Is this going to be taken apart by maintenance people?

--
JHG

RE: Fastener weather proofing torque

1) What is the enclosure material?
2) Are you (re)designing the enclosure?
3) Is the fastener screwed into a hole that is tapped into the inside of the enclosure? Can the bottom of the hole be sealed before assembly if that is where the problem comes from?

Engineering is not the science behind building. It is the science behind not building.

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