Has anyone ever tried this?

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Has anyone ever tried this?

This topic has 26 replies, 16 voices, and was last updated 5 December 2015 at 09:39 by Anthony Kendall.

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3 December 2015 at 16:20 #214997
Philip Rowe
Participant
@philiprowe13116
Sorting out some old files earlier today, I came across some notes that I had made as an apprentice more years ago than I care to admit to. Amongst lots of notes was one that I had completely forgotten about and which I don't even know is correct.

Apparently a test for stainless steel is to coat it with copper sulphate solution, which some of us may remember was used as a marking out fluid. If the solution dries and sticks to the steel it is not stainless. If it simply wipes off after drying, then it is a stainless steel.

I have never tried this and no longer have access to any copper sulphate to prove or disprove the idea, I wondered with all the vast wealth of knowledge and experience on this site if anybody could confirm or deny this.

I vaguely recall sitting in a classroom during my apprenticeship at a division of G.E.C. during the early 60s and being fed all sorts of facts and figures, most of which I have forgotten, so I presume this is where my notes originated from.

TIA

Phil
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3 December 2015 at 16:20 #15816
Philip Rowe
Participant
@philiprowe13116
3 December 2015 at 16:52 #215000
Chris Evans 6
Participant
@chrisevans6
Phillip, I can not answer your question but I also served my time at the GEC. Moulded Plastics Division toolroom from 1963 until 1970. Where where you ? I know they had sites all over the country.
3 December 2015 at 16:57 #215001
Tractor man
Participant
@tractorman
Hi Phil,

I was taught that trick by a Sheffield cutler to sort stainless out from carbon steel knife blanks. The actual indicator is if the metal becomes copper plated it is plain steel, if it stays bright then its stainless. The cutler just had a largish lump of copper sulphate crystal on his bench and if he needed to check if it was stainless he would just wet the steel and rub the crystal on it like a touchstone. Works really well.

Stainless steel will actually rust if its not polished I was told, so lumps of raw steel could be indistinguishable from each other in the workshop.

I still have a small bottle of copper sulphate solution made up to test steels if necessary.

Regards Mick
3 December 2015 at 16:58 #215002
Tim Stevens
Participant
@timstevens64731
The surface of Stainless is certainly less reactive, in fact in most environments it is described as passive – which is why it does not rust etc. So, you may well be right, but I suggest it may depend rather on the grade of SS, and indeed on the nature of the CuSO4. if it is acidulated (with sulphuric acid usually) it might work differently from the blue vitriol on its own.

Regards, Tim
3 December 2015 at 17:01 #215003
Rik Shaw
Participant
@rikshaw
Phil – call me old fashioned but I still prefer copper sulphate as a marking out fluid but not for stainless as it just runs of without leaving a film of copper. I suppose its one of the reasons its called stainless! Just use a magnet – its less messy.

Rik
3 December 2015 at 17:05 #215006
Chris Evans 6
Participant
@chrisevans6
"Just use a magnet it's less messy" but not for the 400 series stainless which is magnetic.
3 December 2015 at 17:16 #215011
Rik Shaw
Participant
@rikshaw
………and here's me thinking a four hundred series was a Rover.
3 December 2015 at 17:37 #215013
I.M. OUTAHERE
Participant
@i-m-outahere
We used copper sulphate solution to check the hardchrome plating on rollers , if you wipe the roller down with a rag that had been dipped in copper sulphate solution it would react where the chrome had been ground off .

There is a catch to using it for stainless and that is you could have a carbon steel bar or rod that has been plated so a magnet test would be useful as well .

The next thing is to test if it is stainless or monel , from memory another acid test .

I vaguely remember something about austenitic manganese steel not being magnetic either

Edited By XD 351 on 03/12/2015 17:38:46
3 December 2015 at 19:52 #215023
Philip Rowe
Participant
@philiprowe13116
Interesting to see all the responses, seems that my notes were correct after all. Thanks to all for the information, it never ceases to amaze me the wealth of knowledge that can be found here.

Chris, I did my time at MOV (Marconi Osram Valve) in Hammersmith, I see from Google earth that it is now a Tesco supermarket but nice to see that the original staircase and lift shaft tower with an ornate copper dome roof has been incorporated into the modern architecture. I suppose in the world of micro electronics, big glass cased valves and cathode ray tubes generating unwanted heat don't have much of a place, although presumably somebody must be making big transmitting valves. Maybe someone here can put me right?

Phil
3 December 2015 at 21:05 #215030
Neil Wyatt
Moderator
@neilwyatt
http://www.ampvalves.co.uk/product-category/valves/

My Vox Vt20 combines a digital sound processor with an EL81 that it uses to generate overdriven valve sounds – it is amazing the range of sounds it produces and you can even 'dial in' an artists rig and be reasonably confident of getting a fairly close sound that can be tweaked to a good representation. If only I could play as well as it sounds…

Neil
3 December 2015 at 21:56 #215036
Chris Evans 6
Participant
@chrisevans6
Philip, you where a long way from me in Brum. Happy days and a very good training at the GEC. I did six years as an apprentice toolmaker and still can't see how modern apprenticeships can be done in three years.
4 December 2015 at 08:37 #215059
Muzzer
Participant
@muzzer
One of my student sponsorship / vacation jobs was with GEC EEV in Lincoln where they made microwave duplexer valves etc. On the same site they also made the last of the massive copper and glass thyrotrons. You could almost have climbed inside some of them, they were that big. Like the duplexers, they were manufactured using mechanical processes (bright brazing, mechanical fitting etc).

Gone are those days – and its parent company of course….
4 December 2015 at 08:50 #215062
Geoff Theasby
Participant
@geofftheasby
Large transmitting valves (Well, large to radio amateurs) are still made in Russia, and marketed under the Svetlana name. I think EL34, KT66 vales etc., are still made new, to cater for the valve amplifier hi-fi enthusiasts. There are also oodles of 'new-old stock' left over from the 60s easily available.

Geoff
4 December 2015 at 09:33 #215070
Anthony Kendall
Participant
@anthonykendall53479
Time to look at a real valve methinks – one with vapour cooling….
4 December 2015 at 09:47 #215074
hth
Participant
@hth
Hi

A ham friend of mine works for Eimac ? in California, where they still manufacture vacuum tubes to this day . He told me they do special stuff for the US military , Radar sets use Magnetrons I think thats right . But they also make and recondition tubes for commercial FM transmitters . Valve technology is still alive in various applications .
4 December 2015 at 10:54 #215078
Muzzer
Participant
@muzzer
Yes, magnetrons for microwave / radar. At EEV, I made a tester for evaluating the leakage of duplexers with a quick change fixture. The driving magnetron was something like 50kW pulsed maritime unit and there was no safety interlock. If I turned on the magnetron without a duplexer in the fixture, you could smell the ozone…

The safety hazard from microwave and radar is surface heating of the skin and organs – no cancer hazard, as the energy is safely below that required for ionisation (eg X-rays etc). You might suffer skin burns and possible eye damage if you played your cards right.

Duplexers are used to automatically connect / disconnect the shared waveguide / horn (aerial) between the transmitter and receiver. When transmitting, the energy due to the magnetron causes a spark gap in the receiver waveguide to break down. The resulting short circuit, carefully positioned a quarter of a wavelength from the junction, causes the receiver circuit to be seen as an open circuit and thus the sensitive receiver is protected.

This work at EEV was years ago – around the time of the Fauklands conflict. IIRC, the Exocet missiles used EEV components. It was no place for a young engineer back then – I seemed to be the only one under 50. Retaining staff was challenging and they struggled to find new product concepts. They are now trendily called E2V (wow) but at least it appears they have a viable and sustainable business and the LIncoln site still makes microwave stuff.I expect the thyrotrons are long gone, mind…

Murray
4 December 2015 at 11:05 #215079
KWIL
Participant
@kwil
Happy days!!
4 December 2015 at 13:45 #215088
Anthony Kendall
Participant
@anthonykendall53479
Muzzer, the valve above is an EEV valve, built at Chelmsford. It produces 125kW of audio.
4 December 2015 at 14:31 #215091
Muzzer
Participant
@muzzer
Wow. An eighth of a megawatt of sound – that would make your ears bleed! What's that for – sports stadia etc? Psychops? I expect they will be replaced by Class D amplifiers now (soon?).

When you say vapour cooling, do you mean some kind of phase change is involved or do you mean some form of inert gas circuit? I've used boiling Flourinert (boils at 70C at atmospheric pressure) for cooling power semis, which allows amazing power densities without heatsinks but my only experience of (fan-cooled) power valves was in a 1kW 2m linear amp back in the radio amateur days even before EEV.
4 December 2015 at 15:08 #215093
Martin Kyte
Participant
@martinkyte99762
We used Traveling Wave Tubes for Radar Power Amplifiers and they did generate X-Rays.

Martin
4 December 2015 at 17:11 #215103
Anthony Kendall
Participant
@anthonykendall53479
Muzzer, what you see is half of the class B (push-pull) modulator stage of a 250kW hf transmitter. If memory serves me right, in order to modulate a 250kW a.m. transmitter to 100% modulation you need 125kW of audio.

The 250 kW rf stage has two identical valves but in class C, also with vapor cooling.

By vapor cooling I mean water is boiled in the boiler the valve sits in and there is a small amount of waterflow to top it up which goes over a weir and flows down the pyrex tubes. The steam goes outside to be condensed and back in the tank. Hope I have this right from school but the latent heat of vaporisation of pure water is 539cal per gram, so by letting the water boil at 100 deg C, you can transfer the heat with 1/539 of the waterflow that would be required for water cooling at 99 deg C.

Incidentally, the valve sits on a viton O ring to seal it which is about 8in diameter and 1/4 in cross-section – just like a big version of what we might use on our locos.
4 December 2015 at 17:36 #215106
Bazyle
Participant
@bazyle
When I drilled holes in macaroni at Stanmore we had a vibration test rig that ran 1MW across the audio frequency range. Nothing ever lasted 30 seconds the first round and they had to run an hour to pass. Housing estate now but some more of the products have just gone for a holiday in the Middle East.
4 December 2015 at 18:45 #215111
Geoff Theasby
Participant
@geofftheasby
Anthony, if you wish to modulate an Amplitude Modulation signal to 100%, you need similar audio power to RF power. The BBC only modulates to about 30%, I believe.

On a visit to Moorside Edge transmitting station near Huddersfield, in the days before the IRA was active, the engineer allowed a bit of the cooling water out of the PA anodes. As it was distilled water, ie a 'perfect' insulator, he could run it over his hand without receiving a shock from the HT supply.

Geoff
4 December 2015 at 19:33 #215112
Russell Eberhardt
Participant
@russelleberhardt48058
Posted by Martin Kyte on 04/12/2015 15:08:47:

We used Traveling Wave Tubes for Radar Power Amplifiers and they did generate X-Rays.

Still used, even in space applications.

Russell
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