Graphite dust on electronic circuits - Page 1
Forum section: electronics / general

author: biank88
author_rank: Contributor
timestamp: January 22, 2022, 08:43:56 pm
content: Hi everyone!Recently I've been dealing with electronic circuitry that unfortunately has to"breathe" air rich in graphite powder.The graphite powder comes out of the exhaust port of big dry-run vacuum pumps (rotary graphite vane pumps).Most of the electronics boards present only some circuit traces covered by the graphite dust.It appears that the graphite particles are somehow "attracted" only to some traces or components.(See attachments)Do you have any experience on this matter?Thanks a lot.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 22, 2022, 08:57:36 pm
content: Electric flields can act as a electrostatic dust filter. Such a picture was common with old CRT circuits and other high voltage circuits. The usual household dust is at least non conducting. With humidity it may still cause trouble, like arcing and creapage.With graphite I would consider a conformal coating or hermetic seal to the circuit.

author: Bud
author_rank: Super Contributor
timestamp: January 22, 2022, 10:36:29 pm
content: The dust may cause leakage and disrupt the normal operation of the circuit. You seem to have optocouplers and high kiloOhm resistors on the board, those may be vulnerable if covered by dust, let alone carbon dust. You better take care of the issue.

author: Stray Electron
author_rank: Super Contributor
timestamp: January 22, 2022, 11:52:05 pm
content: Air laden with graphite dust sounds like a big safety no-no anyway. Your site is a dust-air explosion waiting to happen.

author: ajb
author_rank: Super Contributor
timestamp: January 22, 2022, 11:53:01 pm
content: What Kleinstein said, but also seems like the best place to solve this problem is at the source, by filtering the exhaust of these vacuum pumps. Aside from the effect on electronics like this there could be health risks depending on the concentration, and also it's just plain messy.

author: Cerebus
author_rank: Super Contributor
timestamp: January 23, 2022, 03:59:53 am
content: Quote from: Bud on January 22, 2022, 10:36:29 pmIn other news: water is wet.

author: Cerebus
author_rank: Super Contributor
timestamp: January 23, 2022, 04:05:42 am
content: Quote from: ajb on January 22, 2022, 11:53:01 pmI'm a little surprised to find that they aren't filtered already. An exhaust filter on a vacuum pump is standard practice. For pumps with oil in them you get oil mist in the exhaust, which can be both a health and explosion hazard and the situation with a dry vane pump is also obvious from what we see here. Of course it is possible that the pumps are fitted with dust traps but someone has failed to maintain them and they are overflowing with crap.

author: floobydust
author_rank: Super Contributor
timestamp: January 23, 2022, 04:30:07 am
content: Had a big carbon dust problem at power plants I worked at. Source was the carbon brushes for excitation slip rings on the 430MW generators. The brushes had a problem wearing out fast and unbelieveable how the fine dust got into everything. It made it through all the plant HVAC somehow.The control system circuit boards, IT server room - despite dedicated HVAC/air conditioning the dust got in. We put in extra-fine filters on the ducts which did collect a bunch but the problems of residue on the boards was too late. The buildup is only a problem on HV traces and components, or high impedance circuits.We would pull boards and do a brief ultrasonic wash to get it off. The carbon sticks to things.I'd also seen the buildup at restaurants cooking with mesquite, the charcoal soot was in computers but I'd use compressed air (assuming generated ESD did not kill things).

author: mzzj
author_rank: Super Contributor
timestamp: January 23, 2022, 06:41:46 am
content: Quote from: Stray Electron on January 22, 2022, 11:52:05 pmI think that for a dust explosion you need more dust than couple of vacuum pump seals produce when they wear down.OP's situation is generally bad news for electronics.

author: biank88
author_rank: Contributor
timestamp: January 23, 2022, 10:54:11 am
content: I know this is a huge problem.The anomaly is that most of the dry-run vacuum pumps I've encountered come with just a silencer on the exhaust port, no additional particulate filter is equipped nor suggested.Reading several pump manuals no one mentions any adverse effect of the graphite particulate, especially for human health or electronics.

author: MarkF
author_rank: Super Contributor
timestamp: January 23, 2022, 10:55:29 am
content: Let me tell you a little story and you can decide:Many years ago, one of my co-workers was getting a comm rack up and running. A lot of the rack consisted of opamps and TTL logic gates on PCB that plugged into a backplane. Each PCB only contained 5 or 6 chips. Anyway, my co-worker was going through the rack testing each logic gate and circling the working gates with a pencil. You guessed it! Nothing was working. Some else took over and found the pencil marks. After having all the boards cleaned and reinstalled, the comm system worked like a champ.So... Don't circle you chips with a pencil.True story.

author: jonpaul
author_rank: Super Contributor
timestamp: January 24, 2022, 09:17:34 am
content: Bonjour, Every vacuum pump I have seen has a silencer and exhaust filter.Yours may have a torn or expended filter or none at all.Graphite dust can be from eroded rotaty pump seals.The vacuum pump needs inspection and service at least for the seals and filter.Suggest to seek professional advise or find a vacuum technology forum.Kind Regards,Jon

author: biank88
author_rank: Contributor
timestamp: January 24, 2022, 07:24:16 pm
content: Quote from: jonpaul on January 24, 2022, 09:17:34 amRotary (Carbon) Vane, akarotary-dry-run, vacuum pump example with no exhaust filter (see the attachment).There is only a spring loaded silencer but no particulate filter on the exhaust port.