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Old 16-01-2014, 15:07   #1
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Looking for someone to Spin weld a fitting

Need a little help.. Does anyone know a craftsman in Broward or Palm Beach county who can spin weld (see below) a fitting onto my older tank. Oddly two marina foreman were not aware of the process either.

I tried two tank shops who sell new tanks- neither will do it. But both offered to sell me a new tank. Anyone have any contacts?

Thanks

Bill

What's a spin weld? Spin welding is a method of welding fittings onto plastic tanks by rotating the fitting at 20,000 rpm and then mating it to the tank. Friction heat melts the plastic and forms a clean and uniform weld. It is much neater than a conventional heat weld using a heat gun.

See video spin welding video - Bing Videos or formal definition here How to Spin Weld on a Water Tank | eHow
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Old 16-01-2014, 15:35   #2
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Re: Looking for someone to Spin weld a fitting

I don't know who could spin weld for you, but what about using a bulkhead fitting with gaskets or "o"rings ?

These fittings are used on many commercial tanks. All you need is an access port big enough to put the fitting into the tank.

Also Vetus sells them, if you need to have "marine".

The welded connections seem to be a point of failure on many tanks.

Cheers,
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Old 16-01-2014, 16:06   #3
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Re: Looking for someone to Spin weld a fitting

I looked at mechanical fittings, and even bought one from Grainger. Th issue is that the fill is located in the corner of the tank,there is just not enough room for the nut the mechanical needs on the inside of the tank.

Thanks for the reply..
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Old 16-01-2014, 16:14   #4
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Re: Looking for someone to Spin weld a fitting

I watched the first video in your link - interesting. I may be mistaken but the tool they are using looks like an ordinary woodworkers router. the chuck to hold the fitting looks to be the hard part.
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Old 16-01-2014, 16:44   #5
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Re: Looking for someone to Spin weld a fitting

If you have the tank out, just have it welded. Weld on a pre-threaded boss or weld in a pipe. All spin welding i know of is NOT done in situe but in the welder's shop with special equipment. It is generally used where you plan to do a few thousand identical welds. If its a metal tank, any competent TIG welder can do it.
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Old 16-01-2014, 17:00   #6
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Re: Looking for someone to Spin weld a fitting

Quote:
Originally Posted by Snore View Post
I looked at mechanical fittings, and even bought one from Grainger. Th issue is that the fill is located in the corner of the tank,there is just not enough room for the nut the mechanical needs on the inside of the tank.

Thanks for the reply..
OK corner is tricky.

Maybe you thought of this, but what about nut on the outside and cut away as much of the "mushroom" head as you need to make it fit inside. These generally have seals on both sides, so if you have to cut away so much on the inside fitting that the inside gasket will not work there will still be the outside gasket.

If this is the top of the tank, you can also get a good seal with butyl; but I would not use it where constantly immersed.
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Old 16-01-2014, 17:17   #7
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Re: Looking for someone to Spin weld a fitting

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Originally Posted by NahanniV View Post
OK corner is tricky.

Maybe you thought of this, but what about nut on the outside and cut away as much of the "mushroom" head as you need to make it fit inside. These generally have seals on both sides, so if you have to cut away so much on the inside fitting that the inside gasket will not work there will still be the outside gasket.

If this is the top of the tank, you can also get a good seal with butyl; but I would not use it where constantly immersed.
Played with that also. Attached is a photo, they stuck this fill all the way in the corner.
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Old 16-01-2014, 18:19   #8
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Re: Looking for someone to Spin weld a fitting

Aren't these tanks around $200-300? Seems like getting a good weld done is going to cost that much. More if they have to travel.

Mark
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Old 16-01-2014, 18:24   #9
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Re: Looking for someone to Spin weld a fitting

Peggie Hall has recommended a type of fitting for use in plastic tanks that I think would work in your situation. As I recall it is a large rubber grommet that you put into the hole and then shove a piece of pipe through it. I've never tried it but Peggie has recommended it several times.
I wish I could remember the name! Maybe Peggie will come along and tell us.
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Old 16-01-2014, 18:30   #10
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Re: Looking for someone to Spin weld a fitting

Your spin welding sounds a lot like a process that I am familiar with called friction welding, that is often used with thermoplastics. The modern equipment that I have seen in the past several years has all been short-stroke high-frequency vibration type. Sorry, but I don't have a one-off job-shop to point you to.

Seamless "sanitary fit" welds are made in plastic tubing using external heat sources. They make certifiable welds that are quite reliable. This is often done by automatic controlled-cycle equipment.

Hand-held hot air guns, that get used with 1/8" plastic filler rod, also exist. In talented hands, they can produce good results.

Spin welding is not your only option.

If you want to play around & experiment a little, you could make up a fixture to hold your part, chuck it in an electric drill & spin it against the tank opening until it feels gooey, then let it cool & see what you end up with. Years ago, before I had much industrial experience with plastic welding, I made a little tool that went in a cordless drill that I used to roll crimp plastic shotgun shells. It worked better than I ever expected it to. Plastics tend to be pretty forgiving as long as you have everything clean & you don't burn them.

Do you know what type of plastic you have? Ploy Prop? LDPE? Etc.
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Old 16-01-2014, 19:43   #11
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Re: Looking for someone to Spin weld a fitting

Can you simply epoxy the fitting in place? There are plenty of two part epoxies designed to bond plastics together, and they'll guarantee a water tight seal.

I've used spin welding in high volume manufacturing but have never seen it done on a one off scenario. Typically the parts need to be held with custom fixtures designed specifically for the application. Thus it become cost prohibitive for low volume applications.

Use caution with a more DIY spin weld approach, you may bond only a portion of the interface, which will seem water tight initially but could soon fracture and start leaking.
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Old 16-01-2014, 19:53   #12
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Re: Looking for someone to Spin weld a fitting

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Originally Posted by colemj View Post
Aren't these tanks around $200-300? Mark
Actually, the proper replacement tank is out of production. For one to buy the correct tank total cost $600. The alternative is an off the shelf size that would have less capacity. Trust me for $200 I would not be messing with this!

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. As I recall it is a large rubber grommet that you put into the hole and then shove a piece of pipe through it. .
As stated previously, this was tried and there is not enough room for the mechanical fitting.

Quote:
Originally Posted by pbiJim View Post
Your spin welding sounds a lot like a process that I am familiar with called friction welding, that is often used with thermoplastics. ......


Hand-held hot air guns, that get used with 1/8" plastic filler rod, also exist. In talented hands, they can produce good results.
....
Spin welding is not your only option.
.
Yes friction welding is the same as spin welding.

While I have heat welded, it can be a challenge to get a good heat weld around the perimeter of a round fitting- not impossible- but a PITA. If I can find a guy who spin/friction welds, I can bring the tank to their shop and 5 min later have a clean weld.

Thanks
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Old 16-01-2014, 20:49   #13
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Re: Looking for someone to Spin weld a fitting

If you find a spin weld shop, by all means, please go with them. If you come up empty, you just might talk me into machining you a custom bolt-on fitting with O-ring seals, just for the fun of overcoming the challenge. I'm in the Palm Beach area & I have a prototype-oriented machine shop. I would ask you to provide the raw materials & bring the tank to my location. I could probably find time next week.
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Old 20-01-2014, 14:15   #14
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Re: Looking for someone to Spin weld a fitting

Snore, Peggie Hall saw this thread and sent me an email with a link to the fittings she likes. They can be mounted pretty close to the edge of the tank.

How to Install a Uniseal

This is what Peggie told me.

"We used 'em all the time to add or relocate tank fittings. 6-8" of PVC pipe is the hose barb....unless you're installing a discharge fitting on the top of the tank and need a pick-up tube...in which case, just use as long a piece of PVC as you need. It should touch the bottom, be cut at about a 25 degree angle...45 leaves too much in the tank, any shallower angle can trap TP or solids that haven't had time to dissolve under it.
Or just use plastic plumbing fittings from the hardware store if you need a 90 or a 45. They don't leak as long as there's no stress side to side, or up/down on the hose. Still, I'm leery of using a Uniseal at the bottom of a tank...best to use for inlet, vent or discharge fitting in the top of the tank."


Peggie also reminded me that Ronco sells over 400 sizes and shapes of very high quality tanks. They may have a suitable replacement.
Ronco Plastics - Marine Water Tanks, RV Water Tank, Auto Detail Tanks, Water Tanks

As a thank you to Peggie, I'd like to plug her book. Every boat owner with a head should read it!


Get Rid of Boat Odors by Peggie Hall
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Old 20-01-2014, 14:45   #15
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Re: Looking for someone to Spin weld a fitting

That is a standard Makita woodworking router although any make will do. You might want a medium to heavy duty router so it won't bog down. You can rent them for $15 to $25. And you can buy that special driving tool here.
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