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Plastics failure mechanism

I've never seen reference to this mechanism, so transcribed and placed here.

From (UK) Hacker GP42 record player of 1966, technical bulletin, not dated but probably close to '66

"Investigation over a period of time of reports of knob breakages have shown that the adhesive used to fix the chrome trim has affected the material and caused the knob to fracture after a period of time. A further investigation by the manufacturers disclosed that the material used in one batch of knobs was an incorrect type. DIAKON was the material specified and POLYSTYRENE was used in error. Unfortunately there is no way in which we can easily differentiate between these materials other than by a flame test. "

Where I used to work , there was a flow-chart wall-chart for identifying plastics by flame test, smell/smoke character when burnt and other basic characteristics, anyone know of a WWW version somewhere?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook
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I'm sure modern health and safety departments would have kittens at the thought of an employee deliberately igniting plastics for the purpose of determining the resulting smell.

Sylvia.

Reply to
Sylvia Else

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Too true! To be fair, though, the common method of doing it is to poke the plasitc with a hot wire and see the effect and smell the odour, so one should not be creating clouds of smoke/fumes. How the plastic reacts to the hot wire is also a clue to its 'type'. I saw a description at one of the sites my wife was on about Jewellery as to the smells and effects on the plastics commonly used for orimental purposes such as Bakelite, Catalin, acrylic, ABS and so on, but I don't recall which one it was. Googling 'plastic jewellery' sould turn up something.

Neil S.

Reply to
nesesu

Yeah, same here. The closest I can recall seeing to that was a US army tech guide for identifying metals based on the kind of sparks you got when you hit it with an angle-grinder.

--
    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------
Reply to
Bob Larter

My chart is from "Materials In Design Engineering", February 1959. It doesn't appear to be posted on the net anywhere. I could send you a scan.

Alan

Reply to
Alan Douglas

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Reply to
Rick

dated

Thanks for that, bookmarked and saved to disc

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

Arrived safely, I wonder what HCl smells like

Reply to
N_Cook

Bit like Chlorine, and just as nasty.

Sylvia.

Reply to
Sylvia Else

I forgot to mention this in my earlier post. The causative mechanism is stress corrosion cracking. The solvent in the glue, in the presence of the stress caused by the tightening of the setscrew or by the stress caused by stretching the knob to fit over a push-on shaft, precipitates the shattering of the knob.

While stress corrosion cracking in metals is well known, it also occurs in many plastics. A crack will start at the plastic surface and propagate perpendicular to the applied stress. In addition to solvents, ozone can cause stress corrosion cracking in many plastics. Gasoline will cause stress corrosion cracking of polyethylene terephthalate; this is the reason that you should never store gasoline in PET soft drink bottles.

--
73, Dr. Barry L. Ornitz  WA4VZQ
    BLOrnitz48@charter.net
Reply to
Keeshond99

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