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Old 24th Feb 2024, 7:33 pm   #1
G6Tanuki
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Default Brittle Brass Syndrome?

In recent months I've come across several examples of fractures in brass.

[1] - a press-fit bush on the spindle of a trimmer in a WWII-era BC348 receiver where the bush had split along its length.

[2] - The dial-pointer on an early-50s Hallicrafters receiver, the 'hub' that was pressed on to the tuning-capacitor spindle had split radially so it no longer gripped the spindle.

[3] - One of the radials on my 144/432MHz collinear antenna, a brass threaded ferrule has a stainless-steel rod force-fitted into a longitudinal hole bored into the ferrule. A fracture along the length of the part where the rod was fitted into the ferrule, so the rod would drop out easily.

I can accept the first two as being problems that have only come to light after seven or eight decades [which is 7 or 8 times the design-life of the equipment!] byt my collinear is only about five years old.

Anyone else seen this issue? And what have you done about it? In [1] I replaced the offending trimmer with something near-enough; in [2] I bludgeoned the brass bush out of a 'pie dish' type tuning-cord-pulley and soldered it to the pointer then used the screws in the bush to attach it to the tuning-gang spindle.

In [3] I cut a thread on a 1/4-wave length of 8mm brass rod and used that to replace the failed ferrule-and-stainless-rod radial.

So in all cases a fix was found, but even so, it's annoying.
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Old 24th Feb 2024, 8:46 pm   #2
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Default Re: Brittle Brass Syndrome?

Quote:
Originally Posted by G6Tanuki View Post
Anyone else seen this issue?
Yes, loads of times.

The antenna is likely to be due to acid rain.

I've had the rotted brass trimmer issue.

As for the acid rain effect, when I lived on the Lincolnshire fens, the soil was very acidic and I had brass joints on buried copper water pipes completely disintegrate causing ponds to appear in the back garden and me having to dig the pipes up and replace fossilised and crumbling joints. The funniest thing that happened when I was there was when the water board replaced the main in the road and happened to connect up a long redundant water pipe that ran across the bottom of my garden to a long demolished row of cottages. I woke up in the morning and opened the bedroom curtains to look out on a lake at the bottom of my garden. I guessed what had happened and went and turned off the brand new stop cock that had suddenly appeared where one hadn't been before - I think they must have found a long forgotten and buried old turned off stop tap and just connected it back up again and turned on the supply. Once the water had all drained away, I turned the stop tap back on again and watched where the water started to appear from. Just out of interest I then dug down in that spot and found an old copper water pipe with just the cut ends butted together. At first I thought someone must have been having some sort of joke laying cut pipe ends together with no joint until I cleaned the ends of the copper pipes with sandpaper which showed they were covered in a film of solder. What had happened is that over the decades, the brass fitting had completely dissolved away, leaving just the copper pipe ends with the original solder. I ended up digging up most of the rest of the pipe and found that all the joints had gone the same way except right near the end where the terminations would have gone to the four cottages there was just the fossilised remains of a couple of brass 'T' junctions. I wouldn't have believed it if I hadn't seen it for myself. I think it was after this that my own supply pipe failed and it was the same old brass joint problem. I dug it up after noticing a lush grass soggy patch in the middle of the lawn in the middle of a hot dry summer and as soon as I touched the exposed brass fitting it just crumbled and disintegrated into fossilised bits.

So yes, acid rain, acidic soil and an acidic atmosphere will annihilate brass by dissolving away all the zinc content.
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Old 24th Feb 2024, 9:51 pm   #3
emeritus
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Default Re: Brittle Brass Syndrome?

Gunmetal fittings used to be recommended for use with agressive waters. Not the sort of thing your local plumbers' merchant is likely to stock, especially with the increasing use of plastic water pipes and fittings.
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Old 24th Feb 2024, 10:58 pm   #4
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Default Re: Brittle Brass Syndrome?

I remember we had another thread on metal components becoming brittle with age, die-cast models can be affected by "zinc pest" caused by impurities in the metal.
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Old 24th Feb 2024, 11:02 pm   #5
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Default Re: Brittle Brass Syndrome?

We get that on brass musical instruments at work - I’ve always regarded it as an issue related to the high calcium in the atmosphere and water supply in the Bristol area.
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Old 24th Feb 2024, 11:23 pm   #6
David G4EBT
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Default Re: Brittle Brass Syndrome?

Dezincification.

Lots about it on internet, and about how the effects depends on the proportion of zinc:copper, and environmental aspects such as slightly acidic/alkali exposure. EG:

https://wieland-chase.com/dezincification/
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Old 25th Feb 2024, 1:05 am   #7
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Default Re: Brittle Brass Syndrome?

I found the CRT brass retaining strap on my TV22 had gone brittle and had broken in two places. The strip had lost all strength and it just broke as soon as it was flexed. I replaced it with rubber cut from a bike tyre innertube.
It is the only time I have seen Brass deteriorate.
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Old 25th Feb 2024, 1:33 am   #8
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Default Re: Brittle Brass Syndrome?

The brass collars on some octal valves like the 6Q7GT are frequently cracked.
I also see this in the grooved tubes used for bulb holders.

Could it be due to the effects of 'work hardening' when they were pressed into shape?
Is it possible to prevent it by a final annealing process?
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Old 25th Feb 2024, 9:36 am   #9
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Default Re: Brittle Brass Syndrome?

I've seen a lot of brass valve screening cans split down the sides.
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Old 25th Feb 2024, 2:08 pm   #10
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Default Re: Brittle Brass Syndrome?

Yes, both acidic and alkali. The acidity from the outside and the alkali water from within with the pipes and I've had exposed brass pipe elbows fail where I am now due to the alkali water within. Water pipe brass fittings are a bit off topic, but demonstrate the effect quite well.

Yes, I've also had the brass collars on valves split and also screening cans as mentioned. If I stop to think about it I'm sure I'll think of loads more instances. Then there's the brass pin sockets in valve bases that get eaten away. The worst case I ever had was the bases in an old Truvox tape recorder that were so bad that they'd cracked most of the valves and caused them to go to air.

I've never seen it with any of the brass within old clocks though.
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Old 25th Feb 2024, 3:13 pm   #11
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Default Re: Brittle Brass Syndrome?

Yes I have had the old style press on brass screen cans used with Octal valves split along the side where they are pushed over the chassis mount flange.
Of course we have all had the brass tuning-fork contacts in Mcmurdo type 7/8/9 pin valve sockets fracture at the Base of the fork...

It seems that brass does not like being under tensional stress.

Add in some stress raisers caused by quick and dirty manufacturing techniques, or by corrosion, and work hardening (ever noticed how springy brass battery contacts always seem to fracture along the line of any folding) and it will only fail faster.

Rivets used to attach the contacts to the Paxolin in Yaxley type wafer switches being another one, I remember one well used attenuator I had, which was intermittent and which rattled when shaken. Taking the screening can off, a load of broken brass contact fingers fell out. No point trying to repair...
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Old 25th Feb 2024, 6:26 pm   #12
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Default Re: Brittle Brass Syndrome?

I don't see any connection between Tanuki's brittle brass and Techman's (well known) dezincification. Not do I blame acid rain for dezincification. Some soils are naturally acidic, some alkaline and some may well be neutral.
Here in the Isle of Man, tap water is "oift" and gunmetal fittings mandatory (I think) for copper pipework joints, as is leadless solder for the same reason. When I lived in N.Staffs, the tap water was very hard (lime) and ordinary brass fittings the norm for pipework, though gunmetal still required for underground work.
With regard to the Brittle brass, I have seen it, but have no knowledge of the reason. Maybe is it long term work hardening?
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Old 25th Feb 2024, 8:28 pm   #13
G6Tanuki
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Default Re: Brittle Brass Syndrome?

Yes I don't see my brass failures to be at all attributable to environmental issues like 'acid rain' or dezincification because of exposure to acid/alkali water. I am sure the cause is mechanical - stress and tension and possible work hardening.
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Old 25th Feb 2024, 8:47 pm   #14
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Default Re: Brittle Brass Syndrome?

The brass cases around Hallicrafters (SX24 and SX28) S Meters are prone to multiple splitting. I have two which have suffered in this way. As you say nothing to do with corrosion.

Fortunately I had some plastic pipe of exactly the right internal diameter to sleeve them with.
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Old 26th Feb 2024, 6:01 pm   #15
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Default Re: Brittle Brass Syndrome?

Work hardening definitely occurs with brass, if you try to cold roll brass each pass takes more and more effort and results in a much more brittle material. I don't recall annealing, but my guess is that it would work just as well as it does with pure copper.

However, the example of brittle brass mentioned don't sound likely they could have experienced anything like enough deformation to become brittle by a work hardening process, post manufacture. More likely there is something going on at at the 'crystal boundary level' that evolves over time.

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Old 26th Feb 2024, 8:24 pm   #16
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Default Re: Brittle Brass Syndrome?

Have seen brittle brass cracks on very thin rolled parts, not on anything else. Considered the parts to be beyond repair.

{I'm reasonably certain that the quality of the alloy (what impurities are present in what proportion) is a major factor in dezincification. I've dug up parts from the 20th century which have started to flake, yet a victorian brass toasting fork, having developed a uniform dark copper colour, seems to have no loss of integrity or spalling. I suppose the method of manufacture may also be an influence.}

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Old 27th Feb 2024, 2:37 am   #17
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Default Re: Brittle Brass Syndrome?

The problem is particularly prevalent on parts manufactured in, or shortly after the last war.
Non ferrous metals were in short supply, and cheaper alloys often used. Including recycled material of unknown composition.
Lighter weight components were also used to save scarce materials.
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Old 27th Feb 2024, 11:38 am   #18
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Default Re: Brittle Brass Syndrome?

As David says in post 6 - - heaps of info on de-zincification of brass on the internet.
My two pennoth - - left electronics behind when I left the RAF in 1975 - - to become a commercial diver. One main underwater job over the following years was examining &/or replacing sacrificial zinc anodes on the hulls of fishing boats. Also occasionally was asked to examine &/or replace flange to flange bonding on inboard brass pipework - seacocks in the bog & engine room etc.

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Old 27th Feb 2024, 12:35 pm   #19
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Default Re: Brittle Brass Syndrome?

I'd guess that several books (encyclopaedias?) have been written on failures in brass, and that all of the effects and problems in the above replies come in to the overall picture.

Once the failure has happened, hiding it probably needs a "cunning plan". But whether or not anything can be done in advance to help alleviate or delay the problem is interesting. Annealing has been mentioned, but I don't know anything about annealing brass.

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Old 27th Feb 2024, 11:52 pm   #20
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Default Re: Brittle Brass Syndrome?

Yes, brass does require annealing to remove work hardening caused by manufacturing processes such as drawing and bending. A place I worked in for a while (Boosey & Hawkes, they made brass musical instruments) had an oven based around a long conveyor belt that ran through the main factory area.

So some failures of brass parts might be due to inadequate annealing, to add to the other causes previously mentioned. above.
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