Blog- Coombe Barton - Building the Churchward 45xx Part Two

RSS Fetcher · January 11, 2015

Soldering the footplate laminates.

Flux

Now there’s a lot written about fluxes. A lot of people swear by this, that or the other flux, all with secret recipes. Some of the most respected people in the field say phosphoric acid, 9% or 12% for more challenging metals, going to as low as 7% or lower for whitemetal. Iain Rice has information on this in Rice, I. (1990). Etched Loco Construction. Didcot: Wild Swan Publications. p. 31.

Now fluxes are hard to post and running out on a Sunday morning is not good for the temper. And they’re relatively expensive, and according to the same book some of the commercial ones are to darned strong, as all you need is that metal will clean enough for solder to flow to join the bits together. So I’ve made my own flux using food grade phosphoric acid (75%) from Brupaks. It’s used for washing yeast in brewing and winemaking.

Making up the flux is as simple as measuring out and mixing. However the accuracy required, whilst not being the same as clinical accuracy, is important, so I’ve been collecting a set of stuff to help me, all of which were internet sourced except as mentioned.

Measuring and ingredients

· Set of cheap plastic measuring cylinders. (10, 25, 50 and 100ml)

· Set of 100ml plastic bottles.

· Set of funnels (Halfords)

· Aromatherapy pipettes (3ml). These are the same as those sold at exhibitions for a lot for a small quantity but a lot less expensive bought in 100s.

· 10ml syringes with blunt needles, intended for refilling printer ink cartridges. Brushes disintegrate.

· Deionised water (Sainsbury’s). Other supermarkets and motor factors are available.

· Brupaks Phosphoric Acid (250ml – 75%). This was posted to me – maybe it’s a food not an industrial product.

Mixing the flux - the bits I have.

Mix quantities.

If you want to follow this path, to make 100ml of the following strength phosphoric acid (nearest ml) you need to mix:

· 5% Strength 7ml 75% Phosphoric Acid plus 93ml De-ionised water

· 6% Strength 8ml 75% Phosphoric Acid plus 92ml De-ionised water

· 7% Strength 9.5ml 75% Phosphoric Acid plus 90.5ml De-ionised water

· 9% Strength 12ml 75% Phosphoric Acid plus 88ml De-ionised water

· 12% Strength 16ml 75% Phosphoric Acid plus 84ml De-ionised water

· 15% Strength 20ml 75% Phosphoric Acid plus 80ml De-ionised water

Soldering

Being in a university where we have a School of Jewellery got me thinking about Jewellery equipment suppliers, and so I’ve bought some soldering blocks. They should prevent me from setting the place on fire too frequently.

Blowtorch

I have several irons – 18W, 25W, 40W and 80W. But when a large area of metal’s to be laminated it’s not so much the heat you want as the spread. Dremel (other brands are available) supplied mine. The advantage (I am told) of blowtorches is that heat can get to a larger area – and we’re laminating two bits of brass. The theory is that if you get an area that’s above the melting point of the solder that the solder will flash through under capillary action and make the joint. This also presupposes that you’ve clamped the bits together well enough. So an arrangement of bolts (the instructions suggest 10BA), clips and potentially wooden clothespegs will do. The arsenal was assembled and the footplate assembly aligned with the help of the bolts. Then clips (clothespegs were too big) held the layers together.

The soldering blocks preventing the place catching fire.

The process of aiming and timing the blowlamp needs to be managed (I've learned) so that it’s hot enough for the solder to flash into the joint but not hot enough to anneal the brass. Bit of softly, softly catchee monkey to start off with, and I was too cautions at first, but a reclean and restart soon got the right temperature for the process to work. Flux was applied using the syringe – sometimes it was a case of requiring more hands.

So the soldering proceeded apace. Nearly forgot that metals, having been in a blowlamp flame, remain hot, but no burning flesh resulted. Reactions, although not quite as fast as they were, were fast enough that time. But it got together, and is now resting in a tub of water to dilute any remaining acid. The water will soon be joined by some mildly alkaline cream cleaner to neutralise any remaining stray hydrogen ions.

So now it needs cleaning and scraping.

These are the ‘before’ photos. The ‘after’ will appear in the next blog post.

Before cleaning - topside of footplate

Before cleaning - underside of footplate.

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