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Repair Burnt Out HF Plastic Welder?

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Asking for a little help on this one, an old HF Plastic Welder. It's the early type with just a wand, a hose and a pressure gauge that you are supposed to connect to a compressor, and a electrical cord to the wall. The wand receives both air and current and contains a ceramic element wound with resistance wire.

I've had it for at least ten years and carefully heeded the warnings to always turn on air first before connecting the cord, and always wait ten minutes after unplugging to turn off the air. But last time I used it, the compressor lost power, I didn't notice and the air ran out before I figured out what had happened. The welder stopped working.

I don't think spare parts are available -- the welder (of this type without a fan) hasn't been offered by HF in years. So I'm hoping for a MadModder style fix, if possible. Any help would be appreciated.

Here are some pics. They are respectively, overview, first side near end, second side near end, far end and cord end:

I've checked with an ohmmeter, and narrowed down the location of a break. There are 7 coils of resistance wire in 7 holes in the ceramic shell. They are all connected in series.

One of the incoming line terminals is presently connected to 2 of the coils, and the other is connected to the remaining 5. The break is somewhere in that second coil, and it isn't at either of the ends. So it's somewhere inside the second hole in the ceramic element.

Can that be repaired?

Steve, nichrome wire is available on the reel, The Scientific Wire Company carry it. Before it has been heated it can easily be formed into your coils round a suitable mandrel. Once heated it becomes very brittle so unwinding your coils is likely to end in tears, similarly rescuing wire from other appliances will be hard.

As a kid I made several attempts to scrounge nichrome wire from used 1 kw fire bars and was only successful when I was given a brand new one !

About the only practical way of terminating it is a mechanical joint such as a nut and bolt as the oxide layer prevents brazing. Soldering is obviously no use due to the running temperature. I did once manage to spot weld some to end tags using a lethal capacitor bank.

Thanks , Andrew. That was kind of what I imagined would be the problem(s), but wasn't sure if there was some way of getting around it. I mean other than winding new coils -- which I imagine is both expensive for a one off repair, and not so easy in itself.

Too bad HF's mfr in this case hadn't got the concept of a thermal switch.

I wonder if we might come up with a MadModder plastic welder of our own?

The requirements are pretty simple -- some focused hot air of not very great velocity, and not very high temperature.

--- soldering iron element?

I don't know how many watts this welder was, but I used to attach a router speed controller to the input to dial down the temperature. The "manual" said to adjust via airflow, but that was much too coarse an adjustment, and also changed the welding characteristics. Heat control was much better.


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