Plastics failure mechanism

[N_Cook]

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?

 

[Sylvia Else]

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?

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.

 

[Bob Larter]

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.

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.

 

[Alan Douglas]

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?

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

 

[N_Cook]

http://www.boedeker.com/burntest.htm

Thanks for that, bookmarked and saved to disc

 

[N_Cook]

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

Arrived safely, I wonder what HCl smells like

 

[Sylvia Else]

Arrived safely, I wonder what HCl smells like

Bit like Chlorine, and just as nasty.

Sylvia.

 

[Keeshond99]

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. "

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.