[ARC5] restoring rusty metal tubes

[J Mcvey]

 This thread reminds of the time when I bought some metal tubes from a shady company.They had brushed up some rusty tubes and painted then with "Rust-Oleum" ( a spray paint for use on outdoor metal products).I send them back for a refund!

    On Wednesday, September 15, 2021, 10:10:17 AM EDT, Brian Clarke <brianclarke01 at optusnet.com.au> wrote:  
 
 <!--#yiv3857502343 _filtered {} _filtered {} _filtered {}#yiv3857502343 #yiv3857502343 p.yiv3857502343MsoNormal, #yiv3857502343 li.yiv3857502343MsoNormal, #yiv3857502343 div.yiv3857502343MsoNormal {margin:0cm;margin-bottom:.0001pt;font-size:12.0pt;font-family:"Times New Roman", "serif";}#yiv3857502343 a:link, #yiv3857502343 span.yiv3857502343MsoHyperlink {color:blue;text-decoration:underline;}#yiv3857502343 a:visited, #yiv3857502343 span.yiv3857502343MsoHyperlinkFollowed {color:purple;text-decoration:underline;}#yiv3857502343 p.yiv3857502343MsoListParagraph, #yiv3857502343 li.yiv3857502343MsoListParagraph, #yiv3857502343 div.yiv3857502343MsoListParagraph {margin-top:0cm;margin-right:0cm;margin-bottom:0cm;margin-left:36.0pt;margin-bottom:.0001pt;font-size:12.0pt;font-family:"Times New Roman", "serif";}#yiv3857502343 span.yiv3857502343EmailStyle17 {font-family:"Calibri", "sans-serif";color:#1F497D;}#yiv3857502343 .yiv3857502343MsoChpDefault {} _filtered {}#yiv3857502343 div.yiv3857502343Section1 {}#yiv3857502343 _filtered {} _filtered {}#yiv3857502343 ol {margin-bottom:0cm;}#yiv3857502343 ul {margin-bottom:0cm;}-->
Hello Leslie,
 
  
 
The external envelope of the metal tube can reach 270°C.Ordinary gloss enamel will blister and peel off. Any rust removal product thatuses phosphoric acid will form a coating of iron phosphate – good forpreventing further corrosion. But, it does reduce the thickness of the metaltubing. No pot of phosphoric acid I have used has mentioned survival at 270°C.
 
  
 
My suggestion, echoing but also eschewing advice from some ofour erstwhile US cousins is:
 
1.      Test the tubes for heater continuity, emission, gain and gas.Manufacturers usually understate the specifications so that published figuresare often less than you achieve with a NIOB tube; a new tube should be at least25% better than spec. So, any tube that is not close to spec becomes a good candidatefor small-arms target practice.
 
2.      Mark (scratch, engrave) the phenolic base indelibly with thetype nomenclature. Scratching the nomenclature into the metal tube is a sureway to start later corrosion. Probably not a good idea to engrave the end ofthe octal key, because that part often gets broken off.
 
3.      Gently remove the rust by abrading with green Nylon mesh pot cleaner.Leave the old paint in place wherever you can. A wire buff will remove some ofthe metal – where the metal is thinner it will get hotter.
 
4.      Apply a metal primer that will withstand 270°C,eg, a paint designed for baking.
 
5.      Spray on an auto engine exhaust black paint formulation thatwill finish matt – most auto parts shops carry it. A gloss finish will notradiate heat as well as a ‘black body’.
 
6.      If you are a dab hand at calligraphy, rewrite the nomenclatureover the black matt with a high temperature white paint. Artist’s acrylicprobably won’t cut it. I got some high temperature white matt from an autoparts store for redoing a toaster. Spray the paint into a small pot and scribewith a fine artist’s brush or a tooth pick – prefer the brush because it holdsmore paint; the tooth pick may give a blobby result.
 
  
 
Cheers, Brian, VK2GCE
 
  
 
From:arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On BehalfOf Leslie Smith
Sent: Wednesday, 15 September 2021 9:14 PM
To: arc5 at mailman.qth.net
Subject: [ARC5] restoring rusty metal tubes
 
  
 
Hello all!
 
I bought a box full of metaltubes recently.  12A6, 12K8, 12SK7 and so on.  Many have anunattractive amount of rust on the surface, some have a small amount. None belong to a class I would call 'collectable'.
 
Can anyone advise what I can doto preserve these?  My thoughts are along the lines of clean the metalcase with a buffing wheel; after that re-paint with gloss spray.  Allobservations welcome.  I would like to save a box of common, not tooflash, but probably quite functional metal octal tubes.
 
73s from Australia.
 
Leslie
 ______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: https://www.qsl.net/donate.html  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20210915/9a74e85a/attachment-0001.html>