Rust inhibitor on steel chassis grounding point? - Page 1
Forum section: electronics / general

author: g00se
author_rank: Contributor
timestamp: August 01, 2024, 05:03:27 pm
content: I have a device with a metal chassis using powder coated steel. I need to ground the chassis through a metal hex standoff that makes an electrical connection with PCB ground near a power jack.We have been using a serrated lock washer on the exterior mounting screw to penetrate the powder coat and make an electrical connection between the chassis and the standoff.This requires that the serrated washer be placed properly and not lost on subsequent reassembly.I was looking at switching to the use of a laser engraved spot on the inside of the chassis to allow bare steel to contact the standoff directly, but I am worried that this will be a source of long term corrosion on the steel.It looks like there are conductive grease corrosion inhibitors that are used on steel, something like NO-OX-ID "A-special".Does anyone have a better recommendation on how to ground the chassis, or a conductive rust inhibitor that is industry standard?thanks!

author: thm_w
author_rank: Super Contributor
timestamp: August 01, 2024, 09:25:17 pm
content: Can you use a swaged standoff onto the steel instead of what you are describing? Sounds like its a standoff attached to the PCB.Normally you'd mask off the area during powder coat. But if you are already laser engraving other areas that might make sense too.You can get captive star washer screws, though they are not super common.

author: g00se
author_rank: Contributor
timestamp: August 01, 2024, 10:39:54 pm
content: My fabricator didn't want to mask the powder coat, but I was planning on the washer anyway. I am engraving the serial number with the laser, so doing this with the laser doesn't cause any problem.Here is a photo of the laser engraved area around the mounting hole:and with the standoff:

author: thm_w
author_rank: Super Contributor
timestamp: August 02, 2024, 12:58:20 am
content: Thats a super tall standoff, I don't know if they normally make swaged that long.https://www.mcmaster.com/products/swage-standoffs/https://www.mcmaster.com/products/pem-style-standoffs/press-fit-threaded-standoffs-with-closed-end/no-ox looks like its good, or just regular dielectric grease, if you think its necessary:https://www.practical-sailor.com/boat-maintenance/conductive-greases-vs-corrosionCaptive star or kep star on the back could be the easiest solution.But if the user is regularly having to remove the board, whats easier, remove it from the outer case side or the board standoff side, and leave the standoff in place?

author: coppercone2
author_rank: Super Contributor
timestamp: August 02, 2024, 03:51:58 am
content: probobly should press in a brass grounding point with a press that you can screw into, or have a stud that sticks out.If they got a laser machine I think they can get a stupid pressThere is so much less room for error for a safety ground if you can install a solid post. Or braze it on, like a proper braze on grounding point, or capacitivly weldedI think anything less for a produced product is just silly. A electrical can gives you a threaded bit to ground into, they don't expect a bolt and nut. It will be much more stable if you have a stud or threaded hole that is fused with the chassis.http://www.npfasteners.com/selfclinch/nsog-tech.htm

author: g00se
author_rank: Contributor
timestamp: August 02, 2024, 12:22:48 pm
content: Yes, we have PEM inserts in other locations, this location cannot use one for assembly reasons.I am assembling a few hundred of these in my garage, so I am going to test the NO-OX-ID approach and see how that goes.Thanks