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You mean fiberglass? Won’t work. The resin is a thermoset, not a thermoplastic, and cannot be heat-welded. Plastic welders are good for waxy thermoplastics like polyethylene that can’t be chemically bonded.

Rick “on the off-chance it’s not a troll question :)” Denney

no...I mean plastic...like sousaphone bells.

I guess I’ve never seen a sousaphone bell that wasn’t a thermoset. If it hardens chemically with a two-part hardener, it’s not thermoplastic to any great extent and it needs a chemical rather than heat bond.

Polyester resin with a separate hardener is like epoxy—not heat-weldable. That’s the usual plastic binder for fiberglass.

ABS can be welded but it’s easier to use a solvent weld. Same with hard PVC. Waxy thermoplastics like molded polyethylene can be heat-welded but not chemically welded or adhered. Polycarbonate (Lexan), polypropylene, and acrylic can be welded, too.

Rick “So what are these bells made of?” Denney

I've had pretty good luck with PVC glue...

One of the few fiberglass bell flares that I've encountered were very OLD 22K sousaphones...

Mostly, I've encountered have been fiberglass elbows glued to plastic bell flares.

Epoxy is a total fail.

Isn't the last section of the bell flare plastic not fiberglass? I thought it transitioned.

On another note. For the next bell I renovate, I'm thinking of embedding a wire somewhere in the curved edge. Seems like this would strengthen any repaired cracks.

tj

Is it one of the "waxy thermoplastics like polyethylene"? Now that I think of it, I have seen a video of someone using heat for a plastic repair, with some wire across the break for reinforcement, but don't recall what the article was.

Polycarbonate - Lexan etc. - can be cemented with dimethyl chloride, if you have a connection who can get you the stuff. I've done it, and it seems to be holding up OK. Survived in a gate checked soft bag with extra handling.

Polypropylene, there's no way I know of.

donn wrote: ↑Wed Mar 29, 2023 1:36 am ...Polypropylene, there's no way I know of.

Yeah. Fox student bassoon bodies and even one of the professional models are made of that material, it's much less brittle... one gets the feeling that it's almost a bit flexible. I've never seen a crack or break in any of those bassoon joints.

Tim Jackson wrote: ↑Tue Mar 28, 2023 9:31 pm Isn't the last section of the bell flare plastic not fiberglass? I thought it transitioned.

On another note. For the next bell I renovate, I'm thinking of embedding a wire somewhere in the curved edge. Seems like this would strengthen any repaired cracks.

tj

Maybe just put a brass bell with a fiberglass body...
Somme of the 1960's brass bells weren't >quite< as thick as 1950's, plus some brass bells have been buffed down.
(I'm thinking of the "top-heaviness" issue.)

In recent internet travels to learn more about the plastic King sousa that we've had for ~30 years now, I did see mention on one vendor's page that mentioned that the body was Fiberglass, while the bell was ABS.

Polypropylene can be heat-welded. I actually have a heat welder for plastic that uses hot air rather than a wire. Have to regulate the compressor down to nothing—10 psi or something—to keep from blowing holes. I’ve used it for repair of PP waste tanks. Just like arc welding, it takes a bit of skill and the right filler rods.

Epoxy won’t stick to waxy thermoplastics like PE and PP. and it’s less good than solvent welding with PVC and ABS. If I had to guess, a plastic sousa bell would be PVC or ABS, because they are cheap.

Rick “whose last experience with a fiberglass sousaphone was a King made in the 60’s—don’t recall a joint in the bell” Denney