Best glue for Tufnol?

It's not easy stuff to glue, we use a few grades of Tufnol in our chargers, and the surface doesn't take adhesives very well, it is very porous and has loose fibres around after machining.

Any reason for not using SRBP? What bobbin type and stack are you building? We keep quite a few odd sizes up to 825 X 4" at the factory (UK)

Peter

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Hi Peter,

Thanks for the advice. There's no particular reason for using Tufnol, except that the original (poor and broken) bobbin around the core was made from Tufnol. I was about to order some Tufnol tonight, but after hearing your comments I might not. I had also considered using PVC or acrylic sheet because you can buy cement which dissolves the plastic and makes a strong bond, but both are more expensive than Tufnol. Is SRBP easier to glue than SRBF?

The bobbin will need to fit a core with a 4" x 2.5" cross section, have at least a 4" length available for the winding and be no more than

4.75" in overall length. If you have anything suitable or know where I might buy one, please let me know. I'm also in the UK (Shropshire).

I'm winding a 240 V -> 415 V autotransformer for a phase convertor. The core is a shell type.

Best wishes,

Chris

Hey Chris,

I'm not sure what Tufnol or the SRBF materials are, but PVC and/or acrylic are both combustible, and I would suggest not suitable to be used in a setting like a transformer or even as a coil bobbin.

Take care.

Brian Lawson, Bothwell, Ontario.

Thanks for that thought. I hadn't thought about combustibility so far. Tufnol/SRBF is a type of board made from resin-soaked fabric. It looks a bit like bakelite.

Best wishes,

Chris

Tufnol or SRBF = Synthetic resin Bonded Paper Paxolin or SRBP = Synthetic Resin Bonded paper

Most bobbins are fabricated SBRP or moulded nylon. Quite combustible as stated but that's what is used in probably 95%+ of transformer manufacturing. Even the big stuff uses glass filled poly of some kind or other, paper for insulation and so on.

Very few people run higher than 100 deg C, so all of these are pretty safe, and if the thing catches fire then it is really irrelevent at that point!

Peter

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OK, we are in Luton :-))

Have you looked at the laminations you are going to use, and have you decided on a type?

The Linton & Hirst catalogue is a good start, we can help you out with a bobbin and some lams if it / they fall in what we use regularly, which is almost all smaller stuff up to 638 / 750 / 825 and down to 18 / 35 / 147 sizes.

We also keep winding wire up to 3mm diameter on the shelf (or floor for the bigger sizes!)

Peter

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Tufnol,

after

Chris,

When I was doing the same thing (ie autotransformer for phase converter) I found it cheaper to buy one ready made from Power Capacitors (the people who make Transwave converters) than buy the bits myself. Chap even brought it to an ME exhibition and put it in the boot of my car for me as it was the time my back was playing up!. Neighbour is now using it for his 2 post car lift

Another way I did it when I needed a HUGE one was to get a large

240 -> 240 isolating transformer that had primary and secondary 10v and 110v tappppings - wire the primary and secondary in series and select suitable tappings for input and output. This worked really well as 110 worth of original primary and 110v worth of original secondary became the input 230v so that the 415v o/p floated either side as you want it in this application. I believe that one is still in use in a certain canal repair yard at Dutton Dock by a certain Mr T Leech !

AWEM

Hi Peter,

Thanks very much for the offer of help. I've got the core already. It's a shell type which was a 230 V -> 110 V step down transformer. I got the transformer free and it has a core which is easily disassembled (it's held together with clamps) and a nice ventilated metal enclosure. I calculated the size of wire I needed and have now got a small reel, so the only thing I'm lacking is a bobbin. If I could find an injection moulded nylon bobbin that would be superb. Do Linton & Hirst keep bobbins, or do you get them from elsewhere? The bobbin will need to fit the central leg which has a 4" x 2.5" cross section, have at least a 4" length available for the winding and be no more than 4.75" in overall length. I'm not sure how to interpret the transformer sizes you mentioned...

Many thanks,

Chris

Hi Andrew,

I looked into buying the transformer and called a couple of suppliers (didn't try Power Capacitors - it didn't occur to me that they would deal in transformers), but the cheapest I was quoted was about =A3250. I then got the transformer parts free, so all I've had to buy is the wire so far. I've got the time so I'll probably quite enjoy building the transformer.

Best wishes,

Chris

Not a problem, but the L&H catalogue is at the factory, so I'll have to wait until tomorrow afternoon as I am off to Tyseley in the morning for a spot of commissioning and then up to Leic's and back to Luton.

Peter

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Thanks. No hurry. Post a message here or e-mail ( snipped-for-privacy@cantabgold.net) if you think you might have something suitable.

Many thanks,

Chris

The main other source is special bobbins made for cut lams, which are usually grain-orientated and cut strip type rather than E-I laminations with most people are familiar with.

If it is a 'funny' size then that may require a bit of bodgery... :-))

Peter

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Tufnol is a British trade name for phenolic, mainly paper and cloth impregnated with phenolic resin.

Steve R.

Interestingly this transformer doesn't have "E" and "I" laminations. They are all simple strips. But I doubt there is anything special about them - I think it's just old.

Chris

Having looked at the prices of engineering plastics, I'm very tempted to make the bobbin out of nice plywood. Glue it together, sand the edges, stick it in the oven for a few hours and paint it with insulating varnish. Good idea? Bad idea? What do people think?

Best wishes,

Chris

tempted

Chris,

There is no reason why you could not make the coil on a wooden former, then slide it off and tape it. Don't forget to leave a tolerance for the tape thickness If you lay tape parallell to the axis of the coil on the former before winding it can be then used to stop it all falling apart as you take the cheeks off. You could even losely bind it, then dip it all in varnish.

After all this is how coils are wound for motors.

AWEM

Thanks for the advice. The original coil looked like it had been taped in the way you describe. I was actually thinking of leaving the coil on the wooden bobbin, then fitting the laminations inside the bobbin. I thought it would be easier if I made a bobbin with end plates to stop the turns falling off the end (the transformer will have 8 layers of

2.36 mm wire). I was thinking of using 3/16" or 1/4" birch ply, baked and painted with insulating varnish.

Chris