Coal tar pitch

PabloPicasso

PabloPicasso

Well-Known Member
Joined
12 Feb 2010
Messages
2,929
Visit site
I've reposted this from the pbo forum. Perhaps it's better answered on here?

Has Anyone got experience of using coal tar pitch?

I have a few questions, although It's not a boaty use that I want it for.

My aim is to use pitch as a pipe bending aid to bend a trumpet bell from straight (the usual way trumpets are) to bent upwards (a la Dizzy Gillespie).

Fill the pipe/bell with pitch and then bend the pipe around a form, and hope the pitch prevents deforming of the roundness, and prevents creasing etc. I'm hoping to get a couple of cheap old trumpets on ebay to practise on.

Any advice on how to use the pitch is what I want. Particularly to stop it sticking to the bell, and what temperature to heat it to to empty the bell after bending.

Thanks
 
I have a lot of experience of pitch; I worked for the Coal Tar Research Association when I was a teenager!

Pitch is brittle when cold; it won't bend. I seriously doubt that it would work for pipe-bending. I suspect you'd stand a good chance of breaking the tube you were bending. At higher temperatures it becomes a viscous fluid, and wouldn't support the tube.

Technically, pitch is always a liquid, and flows even at low temperatures. At room temperatures, pitch will flow very slowly; I've seen sacks of it that had been left for years, and the pitch had flowed out of the sack. However, if subject to rapid bending (and anything happening faster than months is "rapid"!), it behaves as a brittle solid. In fact, glass is just the same - leave it long enough and it flows, but if you try and bend it or hit it, it breaks.

You might get away with asphalt, the residue from oil refining, which contains a high percentage of sand. However, I think that sand on its own would be a better bet.

Cleaning the work piece afterwards would be fun. We used toluene, carbon tetrachoride and acetone to clean lab. equipment, but the first two are not nice stuff, and the second now comes under the bans imposed by the Montreal protocol! Acetone on it's own will not remove all the components of pitch, which is why we used multiple solvents.

Finally, pitch is itself not good to handle; it contains all sorts of carcinogens, and the fumes from it are definitely harmful.
 
if its the right size you could use a spring that's used for bending copper pipe
you would need to anneal the material before and during
have you considered cutting the bend out and soldering a straight section in, this would mean you'd have to try it out before soldering to check the tuning
 
You must log in or register to reply here.

Share this page

Top