How good are empty food-cans as shielded enclosures? - Page 1
Forum section: electronics / rf-microwave

author: RoGeorge
author_rank: Super Contributor
timestamp: April 17, 2022, 03:37:55 pm
content: I was thinking of soldering (in air) a few parts inside an empty tuna-fish can and use it as GND, too. The can feels very sturdy as a box, though I've searched for examples of empty food cans used as a shield box for RF, and couldn't find any (except for Altoids boxes used as enclosure for various DIY electronics, and a metal biscuits box seen in an application note).How come that almost nobody uses food-cans as shielded enclosures for electronics? Is this because the metal sheet used for canning food is not a good shield, or maybe is some other less obvious disadvantage?

author: mawyatt
author_rank: Super Contributor
timestamp: April 17, 2022, 04:02:25 pm
content: Recall the old Heathkit "Cantenna", basically a metal gallon paint can filled with oil and a large 50 ohm resistor, used as a high power HAM transmitter load. Another was the circular metal holiday cookie cans used for shielding sensitive electronics, recall Jim Williams used one for a high sensitivity preamp.Just checked and the BumbleBee Tuna and Campbell's Soup cans are magnetic, so likely one could solder to the case. These should serve fine as a RF enclosure for DIY projects in a pinch.Anyway, thanks for postingBest,

author: RoGeorge
author_rank: Super Contributor
timestamp: April 17, 2022, 04:40:24 pm
content: As a side note, I've noticed most of the SMDs are magnetic, too.Based on that discovery, I've built once a quantum spin based viceto keep the SMDs from jumping into another dimension while probing:https://hackaday.io/project/6289-smd-stickvise

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 17, 2022, 04:48:59 pm
content: The cans are fundamentally fine as shields. Some issues are the need for carefully cleaning, the plastic coating many have on the inside, and the difficulty of fitting an appropriate lid.

author: Ian.M
author_rank: Super Contributor
timestamp: April 17, 2022, 05:40:10 pm
content: The plastic or lacquer coating is typically applied to the steel before the can is assembled, so the end seams may not offer continuous electrical contact. Either select seamless bottom cans or ones with a plain tin interior finish if its important to avoid the seam possibly acting as a Gigaherz range slot antenna.Lids are easy - tin the rim inside and out, then solder it all the way round it to a fractionally oversize piece of tin plate, then file off the sharp edge. Note that if its going to be hermetically sealed, you should tin a spot and drill a 1/16" hole somewhere away from the seam, as a vent, then quickly solder up the hole when the seam has cooled to ambient.Easily removable lids are much harder, unless you teach yourselfTinsmithing.With the correct technique, a heavy duty iron and a good flux, even aluminum cans are solderable with ordinary soft solder, provided you pre-tin and wipe off all areas you need to finally solder. You may find anchovy fillet cans a convenient size for board level screening cans or small handheld projects.

author: BrokenYugo
author_rank: Super Contributor
timestamp: April 17, 2022, 05:48:26 pm
content: Altoids and cookie/biscuit tins are unlined and take solder easily.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 17, 2022, 11:29:41 pm
content: All food cans I could find so far have some film of laque/plastic cover on the inside, indeed. This might be enough reason for why they are not used as electronic enclosures. Also some have very, very sharp edges.But the worst is that they are very, very soldering resilient, either on the inside or on the outside. The soldering gun has 100+ W, and it can easily solder on thick copper clad, it's not the lack of power, it's the type of metal out of which the cans are made. No matter how well scratched are before soldering, or how much flux is used, the solder does not alloy with the can, like the copper clad does. The solder joint seems well spread and in good contact, but the solder peals away when the wire is pulled hard.Another strange fact is the can was barely warm while soldering. If it were to be a copper or an aluminum can instead, it would have become too hot to touch after heating the solder point so long, so it's not a great heat conductor, which makes me think it would be not a great conductor for electricity either, but I didn't try to measure.Oh, and the fumes from the lacquer layer smells like burnt feathers, absolutely horrible smell!Later edit:--------------(the ones I've tried to solder were from tuna fish)Found a paper with a table for the alloy composition used for various types of canned food:Source:https://www.researchgate.net/figure/Percentage-range-composition-of-metals-in-cans_tbl3_271123568And some of the coating materials:https://www.foodpackagingforum.org/food-packaging-health/can-coatingsDOI: 10.5281/zenodo.200633

author: RoGeorge
author_rank: Super Contributor
timestamp: April 18, 2022, 12:05:03 am
content: Wow, found another can from liver paste, and this one solders as easy as copper clad!The ones made out of matte metal doesn't solder, the shiny metal kind alloys perfectly.Though, no matter the metal type, the interior lining fumes smell horrible anyway.

author: Ian.M
author_rank: Super Contributor
timestamp: April 18, 2022, 12:13:06 am
content: Note the high Chromium content listed for your original cans, which makes it not that far from low-grade stainless steel, hence the poor solderability. The trick to soldering difficult steel alloys easily is to flash plate them with copper to promote wetting. Once the solder has wet the surface the copper rapidly dissolves in the solder leaving a solder to steel bond. See #20 athttps://www.eevblog.com/forum/beginners/soldering-to-strange-metal-contacts/msg3315024/#msg3315024for details.

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2022, 09:33:59 pm
content: Watch out for the coating used inside such cans, recognizable for its greasy feel. Said coating often contains lots of a powerful endocrine disruptor, and can effect health substantially. Thats one of the main reasons why diet sodas often make people gain weight.Find out more by searching on "BPA" or bisphenol S or bisphenol A (a closely related substance)Plastics generally contain an entire plethora of various of what are called "EDCs" They cause a bunch of different maladies and we all have significant amounts of them inside our bodies, They build up in mammals "adipocytes" (Fat cells) and make us store more fat, disrupting our bodies energy balance. - They are now virtually everywhere on Earth.. even in the far Arctic.This (EDCs) is a huge health issue and exposure to these plastics is now theorized to be effecting all humanity and making us chubby. (and making it hard for us to shed that extra weight) They also cause cancer.. like prostate cancer, ovarian cancer, testicular cancer, breast cancers. To the tune of trillions of dollars.. The drugs to treat prostate cancer are among the most expensive drugs sold..Although they were developed with money from the US taxpayer, that doesn't mean they are supposed to be affordable.. to any of us..

author: Ian.M
author_rank: Super Contributor
timestamp: April 20, 2022, 10:18:23 pm
content: Build a USB cantenna! They are ideal for use at caravan sites, marinas and other locations where the paid-for or public WiFi coverage is inadequate.Use a USB WiFi stick that supports or can be modded to support an external antenna, attached to the outside of the can with its antenna port where you need the probe base to be.

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2022, 11:14:38 pm
content: Quote from: RoGeorge on April 17, 2022, 03:37:55 pmDid you see the post about the TetraBrik antennas?Note that a little bit of copper tape under the N-connector will make this a much better antenna by improving the connectivity to the TetraBrik lining.http://www.drivebywifiguide.com/TetraBrikHowTo.htmThe "wokFi" USB dongle idea works really well, and a USb extension does not have coax cable loss, so solves the problem of lossy coax really well.. Stan Swan's web site in New Zealand was a hotbed of creative wifi activity in the early days of the web..And it really does work, it works quite well..References..By (2019-08-01). "Boost Your WiFi Range With Cookware". Hackaday. Retrieved 2022-02-07.Nedevschi, Sergiu (2008). Maximizing Performance in Long Distance Wireless Networks for Developing Regions. University of California, Berkeley. p. 28. ISBN 978-1109096101. Retrieved 25 June 2013.""WokFi" Down South". peteredge.orcon.net.nz. Archived from the original on October 7, 2008. Retrieved 2008-03-18."$10 wok keeps TV station on air". The New Zealand Herald. 2007-02-22. Archived from the original on 2012-09-05. Retrieved 2008-03-18.http://web.archive.org/web/20080229094007/http://www.peteredge.orcon.net.nz/wokfidownsouthedit.htmland especiallyhttp://web.archive.org/web/20080229093431/http://www.usbwifi.orcon.net.nz/Wikipedia summaryhttps://en.wikipedia.org/wiki/WokFiWatch out for that coating the fumes are toxic..Here is some info on Bisphenol S, the latest substitute for bisphenol A. It may be worse than bisphenol A - its a shame the laws work the way they do, they shouldnt be able to replace one EDC with another and claim its an improvement, IMHO.https://pubmed.ncbi.nlm.nih.gov/?term=Bisphenol%20S%20can%20coatings