I have a question for any pipe smokers in the group. It is often
claimed that too much carbon build up inside the pipe bowl--the
cake--can cause the bowl to crack. It seems to me the only way this
could happen is if the thermal expansion of carbon is significantly
greater than that of briar wood. Can anyone confirm or deny this?
I've not smoke a pipe for over 30 years now; but I never heard of that
being a problem. I never let the cake build up all that much either I
guess. Anything is possible, but in reality, wouldn't the cake also expand
to the center of the bowl and relives some of the stress if it did expand
more than the bowl?
The "cake," so far as I recall, was unburned tobacco residue. The briar
merely charred on breaking in, thereafter the burning tobacco was contained
within the "cake," which was periodically thinned to maintain capacity and
avoid the taste of partially burned tars.
Also, in spite of assertions otherwise, expansion takes place in the
direction of least resistance. If the coefficient of expansion were
radically different, the "cake" would flake off on its own.
Well if the cracking is true, and it probably
isn't, it would be due to thermal expansion for
two reasons. First, the thickness of the carbon
is relatively thin so it won't expand much,
regardless of the expansion coefficient. Second,
the thermal expansion of carbon is significantly
less than that of the wood.
Consider that the inner portion of the bowl, whether lined with carbon
or not, operates at a much higher temperature than the outer portion
does. A thick carbon cake offers the advantage of insulation, allowing
a somewhat higher temperature differential. The carbon cake is more
dense than wood, and most likely doesn't have much resilience (it's
brittle), thus has nowhere to go but outward when heated. Since the
wood bowl constrains the carbon cake, a thick cake could crack a weak
wooden (or meerschaum) bowl when hot. But lots of other things crack
pipe bowls, too. Briarwood makes good pipe bowls in part because it is
resistant to cracking.
So even if briar and carbon had identical coefficients of expansion, the
carbon's higher temperature and lack of resilience could result in a
cracked bowl. But mine usually crack for other reasons.
If heat is the primary culprit, then an uncaked bowl would be much more
likely to crack than a bowl lined with a carbon cake since the cake
provides insulation. But in a bowl without cake, burnout will occur
The specific claim I am questioning is that a thick cake is a cause of
cracking a bowl. I'm not sure I understand your claim that given equal
coffecients of expansion the higher temperature of carbon along with
lack of resilience could cause a crack in the bowl. Are you saying that
the heat is what causes the crack and not the thickness of the carbon?
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