How are plastic P-Traps made?

[reyemka]

I'm wondering if someone can explain how plastic p-traps are made.


Here is a picture of what I'm talking about.

http://www.hardwarestore.com/media/product/243923_front200.jpg

 

[MikeHalloran]

The elbow part is probably made by itself and bonded to the return bend.

As for that, I don't know how they _are_ made, but I can conjecture a few ways they _might_ be made, depending on volume and tooling money.

- Mold it as a tee, and form it to a U while it's still warm, letting it cool in a fixture.

- Mold it to final shape, with two arcuate cores, withdrawn before ejection. Very difficult machining, but no more impossible than a submarine gate.

- Mold it to final shape, with a sectional core, having the sections chained together and yanked out at ejection.

- Mold it over a lowmelt core, and boil the core out.


It's probably done some other way; none of those really appeal to me.

Maybe you can look inside and find witness lines that will give you a clue how it's done.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

The 90deg bend is one moulding, the 180 deg bend is another. They are then assembled after moulding, probably by solvent cement, but possibly by a frictional welding process.

As for the mould, they will have a retracting core mechanism. The moulds will be expensive.

In theory, they could also be done with meltable cores like bismuth tin alloys or even ice but in practice these solutions have cost, accuracy or environmental problems.

Regards
Pat
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[reyemka]

Thanks for the responses. I should have said that I was only asking about the 180 deg bend.


Is it possible to mold a S shape (ie 2 180deg bends)?

 

[MikeHalloran]

Sure it is.

.. How much money have you got?



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

You have to be able to get the cores out. That leaves only the option of meltable cores for the S bend. Meltable cores were used on automotive plastic inlet manifolds at one stage, but they are now mainly multiple pieces welded together because of the cost and ecological problems with bismuth tin cores. The cores need a slightly lower melting point than the softening point of the plastic. Manifolds are normally glas fibre reinforced nylon 6.6 which does not soften until about 250 deg C.

Regards
Pat
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[cpretty]

Gas Assisted Injection Molding (GAIM) could be used.

http://machinedesign.com/article/gas-assist-molding-not-just-for-hollow-parts-0809

Plumbing P-Traps are not made this way as is is generally used for higher value product. Engine manifolds etc have been done like this.

TruDesign