What is this stuff Kingspan - tell me more ?
The plan is to rough mill oversized blanks of a motor end plate
(roughly 125mm diam x total of 37mm deep) with deep lugs that I have
to make, use it as a pattern for a casting (home foundry), and then
finish (cnc) mill the casting.
Kingspan are the manufacturers of a foam insulation product usually foil
clad that comes in a range of thicknesses according to U value needed.
It is similar to the generic 'blue foam' referred to by others apart from
the foil and being a mid to dark biscuit colour.
I could tell you some answers to that question, for instance mylar or even
polyethylene films, but as you'd have to kill me after I won't :(
It won't work, especially as a foundry blank, the very rough initial result
will expand slowly for days, and then be dimensionally unstable for several
months. After all that, it will still have some too-big holes in it too, and
be very uneven.
Use polystyrene foam instead, it's cheaper, better, much more regular and
much less toxic than PU foam (which gives off cyanides when heated),
especially the home-made sort of polyurethane foam.
"Blue" polystyrene foam building foam is particularly good, fine grained,
strong and rigid, but even ordinary expanded polystyrene foam insulation
should do, and it will be much much much better than polyurethane from a can
or two-pack. Promise.
Sheffield Insulations for example will usually supply blue foam, try
www.sheffins.co.uk for a local branch and give them a ring.
"Sweet dreams are made of
that gets you
in the seam
And I feel like
BTW, blue foam mostly comes in 2 foot by 4 foot sheets (or larger), and
should cost under £20 for a 50 mm thick sheet. A similar-sized sheet of
ordinary expanded polystyrene foam should cost well less than a fiver :)
-- Peter Fairbrother
Always retaliate first.
Pre-emptory retalitation works! Iraq didn't attack the us with chemical
weapons, because we got in there first and STOMPED them!
A comment from someone who works in the polyurethane industry.
PU foam either rigid or flexible does not give off cyanide when heated
unless at very high temp in the absence of air (=pyrolysis). It is
cured polystyrene which evolves cyanide on combustion. However the
2-pack urethane systems do give off some diisocyanate as the foam
cures and inhalation of that must be avoided. The DIY rigid foam cans
("one component foam") can also release a small amount of diisocyanate
so if used, make sure there's plenty of ventilation until the foam has
IMHO Bob Minchin's advice is the best - get some ready made rigid
polyurethane foam such as Kingspan. It will cut with a fine saw and
you can pin the panels together with wooden meat skewers.
Some years ago CDT teachers were encouraging kids to carve blocks of
polystyrene and use them as a formers for simple foundry casting with
aluminium - like lost wax casting. Sugggested items were things like
lamp bases for subsequent finishing on the lathes. There were a few
nasty cases of cyanide inhalation as the polystyrene flashed in
contact with the molten metal.
Sometimes ya gotta pull rank ...
Once upon a time I was a research chemist investigating UV degradation
mechanisms in polyurethanes. I have also studied the condensation of
substituted ethylenes, including styrene, and done work on many other
polymers. That was all a lot of years ago now, but I haven't forgotten the
The idea that polyurethane does not give off cyanide and polystyrene does is
complete nonsense. The truth is the other way round.
It is said to be "spin" (actually lies) put about by the PU industry, but I
don't know where the story actually came from.
Cyanide from burning polyurethane foam in furniture still regularly kills
people, probably at least 50,000 per year worldwide. Yes, that many. There
are zillions of studies, and you've probably heard that anyway. Polyurethane
foam is used in furniture, not polystyrene.
Wrong. Pyrolysis is what happens when foam is used as a foundry blank, or at
least in the lost-foam process ... but polyurethane foam _does_ give off
cyanide both when it is heated, and when it burns.
A quick Google turns up:
" One of the proximal toxicants is HCN liberated from the
nitrogen-containing polymers, like polyurethane,"
Or "Cyanide toxicity from the thermal degradation of rigid polyurethane
which has a nice list of the nasties involved.
That's not only incorrect, it's chemically impossible. Polystyrene does not
contain the element nitrogen, cyanide does. As do polyurethanes.
Polystyrene can give off nasties like toluene and acrolein when heated or
burnt - but not cyanide.
Yeah! I was wondering about that, too.
Like you I am a former polymer chemist. I could not for the life of me
think where the nitrogen (half the cyanide group) was going to come from
in polystyrene, except as an impurity.
LONG way from saying that polystyrene is safe when pyrolised (either
burnt or exposed to foundry hot metals) but NOT cyanide. It still
generates plenty of nasties.
Blue foam or blocks of PU better than poured. Another possible source of
PU foam - shops that make surfboards/waveskis and the like. They will
have offcuts fromt he blanks that are just so much indutrial rubbish to
Peter Fairbrother wrote:
I've read the other posts [even answered one] but seriously if you want
to use expanding polyurethane as a casting material then the mos readily
avilable materials for the mould is polypropylene [PP], polyethylene
[PE] or High Density polyethylene [HDPE]. These can be obtained in
sheets by cutting up plastic bottles, buckets warming with a heat gun
(on low setting) and flattening out.
How do you know you have PP, PE or HDPE? Simple - take a small piece,
ideally about the size of a match, set fire to it [one of those mini
torch type lighters is good for this] and blow out the flame.
TWO SAFETY POINTS-
1. Hold it in such a way to not burn yourself, molten plastic sticks
like a bastard to the skin and burns until you get it off.
2. Do this somewhere well ventilated; if it is NOT one of these three,
the fumes could be very toxic.
LOOK at the flame as it burns -
If it is a bright sooty or smokey flame the plastic is usually
polystyrene, PVC or polyurethane. When you blow it out the smoke will be
black. This smoke will be toxic so stop the test here. PET also gives
this result but is very hard to work and deforms badly at temperatures
over 76 degrees Celsius so it's a dead loss anyway.
If the flame is not sooty or too smokey [about the same as a candle]
then CAUTIOUSLY smell the smoke. If it smells like candle wax then it's
one of our three
A somewhat simplified explanation follows, the gory details involve a lot of
In a hydrocarbon flame - polystyrene, like petrol, is a hydrocarbon, made
only from hydrogen and carbon atoms - the burning fuel can grab one atom
from a molecule of oxygen, leaving behind a lone atom of oxygen (known as a
radical). These radicals are highly reactive, they make oxygen molecules
look inert by comparison, and they can react with an otherwise fairly inert
nitrogen molecule from the air.
Cyanide is a compound of nitrogen and carbon, the cyanide ion has the
formula CN-. There is no similar mechanism for carbon to react with nitrogen
gas in a flame - there is no way for a carbon-nitrogen bond to form - which
is why you don't get cyanide produced when petrol (or polystyrene, or
candlewax, or diesel, or butane, or any other hydrocarbon) burns.
There have to be carbon-nitrogen bonds, as exist in polyurethanes or
nitriles, already in the fuel before cyanide can be produced.
Note that smoke from burning polyurethane can contain concentrations of
cyanide hundreds of times higher than the typical concentration of NOx in
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