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Let's talk plastics

cinci5

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This is good stuff. Thanks Paul. I tried to fix a leaking wedco gas jug the other day and ended up making it worse. I was using a woodburner tool , the kind that heats the tip and then you can draw or write on wood,, and I tried melting some weed trimmer string to fill the gap. Since I’m not a welder of any sort and know nothing about it, what would have been the best way to fix a puncture on a gas jug?
Next time use a zip tie. Usually but not always same material easier to use also. Plus Harbor Freight has a great/cheap plastic welding kit. HDPE needs HDPE to weld with. Anything that holds oil, gas, antifreeze, most garbage cans etc. is HDPE Member of SPE (Society of Plastics Engineers) class of '75
 
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MustangMike

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Repair pics:
 

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legdelimber

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What type of plastic is that dingy-semen looking stuff that you find in the gearboxes of things like Wen brand electrics saws or drills?
You can often see some sort of, lighter colored, filler/flow lines in it.
Seems there's almost always something in the craigslist ads that "just needs a new gear" and it's made from that stuff.
And NLA of course!

A while back, I was looking for a coffer grinder for someone. Thought i might have found one.
The company touted that it stocked/had repair parts to keep their units going for many years.
I scrolled through the parts listings and...
Seemed ok, until, I noticed that the reduction gear was made from that spooge-plastic.
I just went with a direct drive burr unit/brand instead.

VCRs, Cassette decks, drills, etc. After rotted rubber belts, the most common problem that I saw was a gear, (made from that spooge stuff), was broken (always split into two pieces) and always NLA (while many other parts still listed as available).
Those gears usually were split well before the motor brushes were worn out.

I generaly looked for signs of them splitting on a flow line or the "fiber" or an injection point, but the splits always seemed to start at the root of a tooth.
Amost never any striped or distorded teeth it seemed, just the whole part splitting.
 
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Stump Shot

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The only food for thought information I can share is, that we(myself and some other vintage snowmobile buddies) have had some old snowmobile tanks welded by a local fella and he asked us to supply him with another similar non-repairable tank, that he used to cut strips out of to make his own "welding rods". He told us this guaranteed a match and the welds he made would hold up, which they did. Not sure if that gives any inspiration to this conversation or not, but there it is for what it's worth.
 

blades

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never been fond of the plastic intake manifolds, likely because i have had to replace to many from cracks , warpage ,or some ying yangs impact wrench set way too high torque wise.
 

Paul Fithian

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That fella was pretty sharp in using some old tanks for welding "rods"

Think of "plastics" as you would metal, many different ones with big differences in attributes. You have to use similar materials when welding.
 
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Paul Fithian

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never been fond of the plastic intake manifolds, likely because i have had to replace to many from cracks , warpage ,or some ying yangs impact wrench set way too high torque wise.

All the automakers went to nylon for intake manifolds for the same reason they do anything: Lower cost, less weight, and better performance.

Biggest improvement with a molded nylon intake is that the interior runners are smooth, unlike the rough "pebble" surface you get with sand cast aluminum. You don't need to extrude hone a nylon intake manifold. In the early 90's, we documented a 5% improvement in torque/HP when a nylon intake replaced the same design cast aluminum one.

If you observed breakage on one of these, someone along the way violated the rules, either in part design, molding, or abuse after use.

This one's a lost core variant that was on my 2001 Sport Trac, made in Germany by Montaplast for a Kӧln built 4.0 L V6. Perfectly functional after >250,000 miles. Material code for this part is PA66GF35, or 35% glass filled 6/6 nylon. This weighs ~ 1/2 of what an aluminum one weighs, costs less, and performs better. It will outlast the vehicle if treated right.
Ford 2001 4.0 SOHC Intake Bottom 255K Miles.jpg
Ford 2001 4.0 SOHC Intake Top 255K Miles.jpg
 
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Paul Fithian

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What type of plastic is that dingy-semen looking stuff that you find in the gearboxes of things like Wen brand electrics saws or drills?

Likely Delrin, Celcon, or similar POM material, often used in gears. If it failed, someone violated the rules.

Plastic part breakage always starts at a sharp internal corner, where stress concentration exceeds material strength
 

MustangMike

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Great information on the manifolds. I know back in the day we always wanted to replace the cast iron manifolds with aluminum due to much less weight and cooler temperatures, which increase HP (the cooler the charge, the more oxygen in the air).

Sounds like plastic makes it even lighter and cooler, real good stuff.

I've run my SC both with and w/o an intercooler, and the difference would blow your mind. Not only does it develop a ton more power with the intercooler, but it is also a far smoother operation and much more linear (and less peaky) power.

I hated it w/o the intercooler and love it with it. It is "factory smooth" operation. FYI, when I purchased the Whipple twin screw Ford Performance was doing the tune, so it is 50 State emissions legal.

Originally, Whipple overstated the power of the non-intercooled kit. I called Whipple and complained about it. At first, he tried telling me I was full of crap, but when I argued with him, he agreed to "verify" the information with Ford. He called me back a few days later and apologized to me and gave me a great deal on upgrading to the intercooled version. They were advertising the intercooled kit numbers for the non-intercooled kit. The difference was 75 Hp.
 

Paul Fithian

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Great information on the manifolds. I know back in the day we always wanted to replace the cast iron manifolds with aluminum due to much less weight and cooler temperatures, which increase HP (the cooler the charge, the more oxygen in the air).

Thanks @MustangMike !

Another factor I didn't mention is that a nylon manifold also enables lower air temperature to the head. Aluminum is a great heat conductor, many heat sinks are made out of it. Nylon is an insulator, and transfers much less heat from the head/engine to the air charge.
 

legdelimber

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Paul Fithian, Much appreciation for you stepping in with info about the plastics!
I used to grab & read any trade journals that landed in the breakroom.
Plastics were an interesting animal. Was amazing how much stuff went into figuring on mosture or odor absorption before and after making the packaging. The dimensional issues from it, etc.
Helped to understand why keeping the trimmer sting in water helps with line weld and tangling.

Learning about the high voltage discharge used to micro-etch plastic sheet so that ink would stay put was interesting. We reworked the contact/discharge bars for that station..
The small shop that I worked in, did a lot of maintenance and up-fit bits or prototype things for some of the local food and small consumer goods companies.
 

FergusonTO35

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Great thread! I've always wanted to learn plastic welding, unfortunately very little info out there on it. Automaker Saturn used plastic body panels and they were way ahead of the curve in every way before GM turned them into another forgettable clone. Far as I'm concerned those first generation SL/SW/SC cars are better than many made today. They were really common when I was wrenching and it was pretty rare to get one in for anything other than maintenance.
 

2stroker

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Paul,
Thanks for starting this thread and providing this interesting information.
I'm trying to help out a chainsaw friend that has a couple Solo Twin fuels tanks that have cracked in several spots and won't hold fuel.
I'm investigating 3D printing them and wondering what type of material we could use. I would like to make them in two pieces and "glue" them together? (nylon and PL?)
On the chance we could repair the existing tanks, how can I determine the type of plastic it's made of? This is a saw manufactured in the mid 60"s.
Does anyone else need a replacement 611 Twin tank?

2stroker
 

Paul Fithian

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Happy to help!

You can 3D print parts out of nylon with the right printer and filament.

WIth a proper flange setup in the part design, PL Premium should work. But I'd immerse a chunk of cured PL Premium in gas for some time before I could be sure of that.
 

MustangMike

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I don't think PL Premium is intended for continuous immersion in gas. Even though it is indoor/outdoor it is not even recommended for water immersion. It seems to work fine for repairing a gas can if the leak is on the top of the can (brief immersion is fine).

I think an epoxy would work better.
 
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