Advice on diluting phosphoric acid

[Raised On Steam]

I have some 81% PH down phosphoric acid and want to make flux with it but can not seem get the proportions right.

Please someone what's the formula? 

I badly need to get on with my soldering.

[MickD]

Hi,

It depends what you are soldering, White metal or brass?.

For white metal It Is usually  6% dilution and for brass 12% dilution, both with distilled water.

I have used this formulae since starting kit building and had no problems.

Hope this helps,

MickD.

[Catweasel]

12% is a good base ,with a dash of washing up liquid to help it flow better. Make sure you give things a thorough wash afterwards.

[Raised On Steam]

Hi, thanks for the responses!

I'm trying to solder brass and copper wire and some whitemetal parts.

How do you measure out your proportions? If I'm adding 1ml of 81% phosphoric, how much water do I add it to to get the right mix. I'm hopeless at maths and my brain shuts down when I try and work it out. Is it 7:1?

[rcmacchipilot]

Its simple.

 

If 1 ml will give you 81 percent

1 ml (of 81% phosphoric acid ) plus 1 ml of water gives you 40.5 percent

 

so the formula is: final strength (%) =  81% / n+1,      where n is the number of millilitres added to the solution.

 

re arranged: n+ 1  = 81% / final concentration

 

move the 1

 

n ( number of ml's required ) = ( 81% / final concentration)  - 1

 

So using the above formulae, 1 ml of 81% phosphoric acid added to 12.5 mls of water will give you 6%.

 

1 ml of 81% phosphoric acid added to 5.75 ml of water will give you 12%

 

 

Hope that helps

 

Owen

[DonB]

One thing not mentioned:- 

 

ALWAYS add acid to water, 

[JeffP]

"Don't be a fool,

do as you ought ta,

add the acid to the water!"

 

Taught to us by a chemistry teacher.

[Raised On Steam]

Simple!? That formula just fried my brain ha ha!

 

Thanks for the answers, I'll try that this afternoon. I'd been doing it all wrong by the looks of things...

[Raised On Steam]

Well, that didn't work. I mixed it as suggested and added a drop of washing up liquid but - dry joints. I cleaned the brass and copper with a fibreglass pen til they were shining and the iron (with which I'm a bit underwhelmed after reading so many good things) was plenty hot. Still, dry joints.

 

What do you reckon? Superglue?

[Raised On Steam]

I tried mixing up two new batches, no joy. The solder struggles to melt and when it does it just sits there and won't run. The iron seems hot enough as I said and the surfaces are cleaned.

I'm at a complete loss. 

 

It's very frustrating and the model's come to a complete standstill until I can crack the flux problem.

[MickD]

Hi,

It rather sounds as though your iron is not hot enough, or your solder is too high temperature to flow.

How are you using the iron? I cut a small piece from the roll and place it on the joint after applying flux, then apply the iron.

What solder are you using, its not the lead free solder is it??.

MickD.

[Raised On Steam]

Hi, I'm using 60/40 leaded solder with melting temp of 185. I also tried Carr's 145 and didn't do any better. My iron (Antex 50W TC) was so hot I could feel it through the handle. I've tried it at the top of the scale and the bottom.

I've tried to get all the recommended tools so hope it isn't one of those.

So far I've tried bringing the solder to the job, and putting a piece on the joint and neither worked which is why I suspected the flux. Trouble is nobody round my way seems to sell the proper Carr's type flux (I've tried every shop in the area) or I would have just bought some. The other option is having to pay for a courier to deliver a piddling little 100 ml bottle which I thought was just plain daft when I'd read it was possible to make it. Then of course finding a supply of phosphoric acid was another tale of woe which is why I went for the 81% out of desperation as much as anything.

 

I admit I'm not hugely experienced at soldering this way, my background's more in welding and brazing, but I know what should be happening which is why I'm so baffled it isn't working!

 

I'll have another go with the iron on full pelt and see if that changes anything.

 

Other than that - help!

[PhilH]

Are you sure your phosphoric is phosphoric? Thats the first thing....secondly lets go for around 10% as it's easier to work out.

 

So..start with a measure of 81% phosphoric and add the same quantity of water, this will give you 40.5% concentration.

 

Next whatever this quantity (phosphoric + water) is, add the same quantity of water..this will give you 20% ish concentration.

 

Finally,whatever quantity you have now again add the same amount of water, this will give you about a 10% concentration which should be around what you need (i thought most of the commercial fluxes were around 9%) so it's near enough in my book.

 

Anyway, that's how I do it and it seems to work for me using 75% phosphoric acid as used in the mild disinfectant commonly known as tap water....

[micknich2003]

Providing you actualy have Phospric acid, I can't see where you are going wrong. I bought a big bottle off "E Bay" a few weeks ago and mixed it somewhere between ten to one and twenty to one with tap water. Admitedly very hit and miss, for measureing I used a "Shringe" as supplied with computer Ink Filling packs. My "Mix" works well with conventional "Leaded" solder on both brass and nickel silver, and with either my 15w or 75w iron

[Raised On Steam]

I can't see where you are going wrong. 

Nor can I which is why I'm so annoyed about it. I'm doing everything right.

The label on the bottle says 81% Phosphoric acid 9% water. Hydroponic PH down stuff. It was the only kind I could find locally.

 

Just had another go and left the iron on for ages to warm up and the handle was red hot but the solder refused to even melt. It boils the flux away fine but leaves the solder. The bit won't even tin! I'm wondering if my Antex is a dud. Also the temperature control screw is a bit hit and miss - nowhere does it say what is hotter and what cooler, just a few vague lines. Yet I've read that Antex are the best for the job.

 

I'm not enjoying my experiences of soldering so far and will have to resort to superglue (which I don't want to do - all this soldering kit has cost me money) if I can't sort it out soon. I need to get going.

[MickD]

Hi,

Have you tinned the bit properly? If you haven't you will never solder properly,

I use a tip tinner which I have had for years, but you can rub the tip with a very fine abrasive to remove all the crud then dip the tip in to the flux and apply to the solder.

This should leave a nice shiny silver tip. But don't rub the tip too hard as this will remove the coating on the tip.

MickD.

[Raised On Steam]

I tinned the bit the first time I switched it on. Thereafter it refused to tin and the solder just blobs off it.

I have read about tip tinner and I'll have a look and see if anybody in my area sells such a thing.

Watch this space.

[MickD]

Hi,

Think that's your problem, If It Isn't tinned properly you will never succeed.

Rub the tip very gently with wet & dry to get rid of the gunge then coat the tip with solder.

If the solder blobs & rolls of the tip it isn't tinned properly. Keep trying, Its the only way, probably no-body succeeds at the first attempt, It's a case of trial & error.

You will probably wonder what the head banging was all about when you do get the hag of It, best of luck.

MickD.

[Raised On Steam]

Well I ventured out to (it seems) the one place I could find a pot of tinner and while I was there I bought some spare bits for the Antex. Finally when I got home I had a go with medium heat (I've figured out the scale I think) and some of the 145 and managed to tin one of the  new bits! I even managed to join two pieces of copper wire together. Success!

 

It's all still a bit reluctant to comply but I'm hoping this has more to do with my learning curve and it's a question of practising now. Hopefully the main sticking point has been overcome.

 

Now I need to crack soldering white metal to brass and I might start making some progress.

[MickD]

Hi,

Remember to tin the brass with 145 before trying to join the white metal to it. Also it is best practice to use different bits for W/M & brass

MickD.

[96701]

Could the iron have been to hot and destroyed the coating?

[Nicktoix]

I have been using phosphoric acid as flux for over 40 years. I dilute it by eye to around 15% with tap water. It works well for all the commonly used solders and metals used in modelling. No use for stainless steel. No need for different fluxes for different solders or odd dilutions. Wash off thoroughly with water after use.

BUT DO NOT USE ON ELECTRICS.

[Jol Wilkinson]

Well I ventured out to (it seems) the one place I could find a pot of tinner and while I was there I bought some spare bits for the Antex. Finally when I got home I had a go with medium heat (I've figured out the scale I think) and some of the 145 and managed to tin one of the  new bits! I even managed to join two pieces of copper wire together. Success!

 

It's all still a bit reluctant to comply but I'm hoping this has more to do with my learning curve and it's a question of practising now. Hopefully the main sticking point has been overcome.

 

Now I need to crack soldering white metal to brass and I might start making some progress.

Is it an Antex temp. controlled soldering unit, the type with a base station? If so you need to run the iron at about 75 - 100 deg. C above the solder temperature.

 

I have found that the flux is strong enough if the brass changes colour slightly (goes paler) when you apply it.

[ozzyo]

Can you put a photo of the iron and bit up on here please. When I have to tin a new bit I tend to do it like this, heat the iron to about 400 deg. then dip the tip in liquid flux then apply a lot of 188 deg. solder dip the bit in the flux again and have a look at how the bit looks (I like to get about 1/4" of tinning all around the bit) then flick off all the excess solder, you should then have a nice shiny bit.

 

The size of the bit that you are using can / will have an effect on how the joint will be made. I tend to use a 6mm dia. bit for most of my work only going down to the small bits for when I'm doing small bits of pipework etc. In this photo I'm using a 6mm bit to solder a pick-up wire to a 4mm Alan Gibson plunger pick-up, for this job I think that I was using 145 deg solder and running the iron at 315 deg.

 

One thing that I don't like about 60/40 solder is the rossin flux that is in the solder as it can and will burn on the bit, to help stop this I wipe the tip on my jeans (pure cotton don't do this if your wearing man made fabric pants),

 

OzzyO.

 

[Raised On Steam]

I've been run off my feet working today and I haven't had a chance to deal with the older bit yet, it looked black and sooty. I put a fresh tip on yesterday and tinned it with 145.

 

My WM solder is Carr's 100 so according to the packet it doesn't need pretinning, do you generally do this anyway? I'll change bits before attempting WM soldering again.

 

The iron's a brand new Antex TCS 230 50W with the little screw head on the handle for adjusting the temperature. Despite my angry/scared rantings earlier it is a nice bit of kit (in the right hands….) and I'm sure once I start making progress I'll be more comfortable with it.

 

I left the brass strip and copper wire I've been practising with without washing just to see what would happen and apart from a slight milkiness there doesn't seem to be much corrosion happening (24 hours have passed) so I still wonder if my acid dilution is right.