Ed Anderson wrote:

 >

I beg to differ on the topic of heat and UV being the only thing

that

will

cause plastic to decay. What about chemical attack? Molded in

stress,

stress

corrosion, moisture contamination, dielectric breakdown. I design

plastic

parts for a living. I don't know who the hell Arhenius is, but to me

that

just looks like a standard reaction rate equation applicable to just

about

all reactions. It is exponential, but where is the intercept? At

zero

Kelvin? What is that little constant k? This is far too general a

form

of

this equation to be making application specific conclusions.

 SNIP

Beware the Giant equation with many terms of questionable accuracy

raised to

many powers. Also beware the oversimplified equation. You can

probably

make

this equation work by measuring E, k, and T for a SPECIFIC case. Do

you

have

good data on what these are for various plastics with various

solvents?

Is

it good within 5%, 10%, 30% for all the solvents or combinations

seen in

an

underhood application,  who knows? What happens when you have a 30%

error

for the value of a constant and place it in an exponential equation?

Pure

science meets engineering.

Monty

Thanks Monty,

    Always great to hear from someone with both knowledge and experience

in

a particular area.  From what you related, my polyurethane casting
supporting my throttle body and fuel injectors is undoubtedly doomed to

a

short life.  I have had a chunk soaking in 100 LL gasoline for over a

month

now and no deteoriation is evident to visual observation  - i.e. no

crazing

or film build up on the surface.  Probably should stay away from auto
gasoline with all of its additives.  Again, thanks for the education.

Ed Anderson

I agree Monty did a great job.
You need to heat that gasoline to about 200 F Ed.
Also there is the issue of: Does the plastic material support combustion?

Paul Lamar

Paul,

The specs on the plastic indicates it does not readily support combustion.
I could get it to char and smoke with a propane torch, but it did not
produce a flame or appear to support combustion.  While undoubtedly a
sterner test of the plastic, I think I'll pass on the 200F gasoline in my
shop{:>). Actually,  with my fuel injectors now setting at the top of the
tubes, I've noticed that the outside of the tubes now condense moisture out
of the air apparently due to the cooling effect of evaporating gasoline in
the tubes. The first time I saw it I though I had a fuel leak from the
"plenum".  Tubes are cool to the touch.

Ed Anderson

That is a HP plus. Good news on the non burning. BTW did you notice any
difference in the fuel burn on your last trip?

Paul Lamar
 
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