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descaling steel

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John Stevenson27/05/2013 11:42:17
5068 forum posts
3 photos

As many may know I make a lot of special dividing plates, these are made from laser cut blanks usually out of a material called A36 which is a hot rolled steel plate that has a thick oxide layer on it.

There is an alternative material called HRPO which stands for Hot rolled picked oiled, basically A36 but cleaned up, costs more and not every company uses it of has it in the stock you want. They like A36 because the oxide layer stops reflection and also stops any dross sticking the the top surface.

Problem with A36 is the thick oxide coat destroys the tips on drills in a heartbeat, OK for the odd hole and if you heavily centre punch that also helps but many thousands of holes on a CNC is asking for a broken drill, especially in under 3mm sizes.

So what's special about HRPO ? Basically it's been through a commercial picking process, so if we can replicate this it helps with laser cut frames, angle iron and anything that needs to be finished, paint sticks the HRPO better than A36.

Picture of a plate straight from the laser cutters.

Also in the picture is a piece of bronze and a piece of copper to see how these perform. I'll say at this point the process didn't do much for them.

A tub was prepared out of an old plastic 5 gallon suds container by cutting the side out and a 'plate rack' cut on the laser to hold 20 plates which really only applies to me.

The solution used is Cementone Brick and Patio cleaner which is basically a weak hydrochloric acid. Don't buy any cleaner that says GREEN on it, that's just basically soapy water.

I mix this 1:1 with water and in my case it takes 10 litres of solution.
I put these in the tub last night at about 7:00pm and just been out 10:30 am following day and they are all clean and de-scaled, just need a rinse and a wipe with oil.

Even cleans the 'burnt' laser cut edge up.

Thor 🇳🇴27/05/2013 11:58:06
1602 forum posts
45 photos

Thanks for a handy tip John, where I live hot rolled steel (similar to your A36?) is readily available and I use it fairly often. I suppose you use rubber gloves and eye protection when handling HCl.


MadMike27/05/2013 12:28:06
232 forum posts
4 photos

Remember that simply pouring the diluted acid down the drain, after use, will almost certainly p**s off your local water company. Dispose of the residue carefully.

John Stevenson27/05/2013 12:41:41
5068 forum posts
3 photos
Posted by MadMike on 27/05/2013 12:28:06:

Remember that simply pouring the diluted acid down the drain, after use, will almost certainly p**s off your local water company. Dispose of the residue carefully.

It's sold for brushing on the patio ??

Tony Pratt 127/05/2013 13:19:41
1930 forum posts
12 photos
Posted by MadMike on 27/05/2013 12:28:06:

Remember that simply pouring the diluted acid down the drain, after use, will almost certainly p**s off your local water company. Dispose of the residue carefully.

I live in an area with the hardest water going so I would imagine putting 10 litres or so down the drain would not even be noticed by the water company, obviously 1000 litres is a bit different?

As an aside how exactly would one 'Dispose of the residue carefully'?


Thor 🇳🇴27/05/2013 13:32:38
1602 forum posts
45 photos

Tony, if you add sodium carbonate gradually to the residue until it stops fizzing it should be a neutral or slightly alkaline salt solution that you can dispose of in the drain. And as you say, 10L is a small amount and when diluted poses no problem.


Stub Mandrel27/05/2013 17:09:11
4315 forum posts
291 photos
1 articles

They sell even stronger HCl as drain cleaner. It dilutes pretty rapidly, but best to put it down the foul sewer. The things that cause real problems are:

  • Mis-connected dishwashers and washing machines (i/e/ connected to the surface drains that end up in local watercourses)
  • Sump oil (or any waste engineering oil, agine expecially when ending up in surface water)
  • cooking fats and oils (down the sink or loo ends up blocking drains or gumming up sewage works).

I have seen the effects of an estate with plenty of misconnections - a completely dead stream with nothing but a white layer of sewage fungus all over the streambed.


John Stevenson27/05/2013 17:36:20
5068 forum posts
3 photos

If you use it until it stops working it's no longer acid but dirty water.

Come one guys you are taking H&S too far.

Chris Heapy27/05/2013 22:20:28
209 forum posts
144 photos

What you don't wnat is it sitting in your drainage system for while, it will eat the pipes or the cement grouting holding it all together.

I dimly recall an electrolytic method of descaling and removing thick corrosion from iron/steel. I'll have to search for it again though. Essentially it was very effective and the article I read described how rusted items (old wagon implements I think it was) dug up from the earth could be completely descaled.

Ian S C28/05/2013 14:21:00
7468 forum posts
230 photos

The electrolitic method works ok. If you don't like strong acids, citric acid will do the job, just takes longer, Most of the scale falls to the bottom of the container, and when you are finished with the acid, you can tip it down the drain, its proberbly less dangerous than Coka- Cola (you could use that too). Ian S C

Tony Jeffree30/05/2013 12:42:07
499 forum posts
11 photos

Yep, Coke works just fine, and probably Pepsi too - basically dilute phosphoric acid with added flavourings and bubbles. I wonder if this is how they make Irn Bru...? smiley

There are other similar (to the patio cleaner) products sold for cleaning grout and cement residue off tiles/slabs - there's one available on Amazon for £14 (£3/litre) that is 36% hydrochloric acid which would need rather more dilution before use than the Cmentone one (which looks to be 5-10% as far as I can tell):



Edited By Tony Jeffree on 30/05/2013 12:43:10

oldvelo04/06/2013 02:17:54
294 forum posts
56 photos

Hi can I point you to this site on setting up to clean with "Electrolosys"

I use this method for ceaning up steel and cast iron parts ready for painting or Blacking.


Hopper04/06/2013 04:13:53
6197 forum posts
321 photos

Just have the garden hose running down the drain as you tip in the spent acid. Then leave hose running for a while afterwards to make sure acid is not sitting in your drain pipes.

John Stevenson04/06/2013 09:17:37
5068 forum posts
3 photos

Can I try and make a point ?


When the acid has stopped working and won't clean any more plates it's no longer acid but dirty water.


But if I had bought this stuff for the purpose it's made and sold for, I would have sloshed this on the yard and brushed it down the drain.


So it's OK to use it as directed but not OK to clean rusty parts and steel plates with it ???????????


Enquiring minds DON'T want to know. blush


Actually glad this post has surfaced as it's just remined me. On Sunday clearing a shed out I found a set of dividing head change wheels, probably brand new but stored for years and gone rusty.



So popped then in the solution, just remembered them and fished them out, wrinse under tap and this is what i have now.



No messing with batteries, power supplies etc just bung it into a tank and leave for a day.

Edited By John Stevenson on 29/06/2013 13:02:19

Cyril Bonnett11/10/2013 00:23:51
244 forum posts
1 photos

Vinegar works just as well, cheap stuff out of Lidls, remember not to do this in your workshop the fumes will cause other steel objects to rust,


Jerry Wray11/10/2013 08:23:50
84 forum posts
4 photos

Cyril provided a link to as site discussing this subject.

One of the posters there mentioned muratic acid as if this is some arcane product of the alchemist's art.

Muratic acid = hydrochloric acid. It's a synonym. Now hardly used. There's enough attempts to disguise the real properties of chemicals without resorting to ancient history.


jonathan heppel11/10/2013 08:49:41
99 forum posts

There is one caveat I can think of. Hydrochloric acid gives off highly corrosive fumes that will rust any ferrous metal they land on- particularly in damp air.

General advice is to use it out of doors or at least outside the workshop, A safer alternative is phosphoric acid, either from the net or a farm shop.

Stub Mandrel11/10/2013 17:34:04
4315 forum posts
291 photos
1 articles

I've been regrouting the bathroom. I got some 'acid detergent' that contains phosphoric acid. It states that it 'removes rust stains when concentrated' at about £6 for 2 litres I fancy it could be quite effective (it's ruining my skin...) I'll try it on something.


John Coates12/10/2013 07:39:59
558 forum posts
28 photos

Thanks for this John

I'd bought some of this for de-rusting as had read about it before but have not used it yet

Your tips are excellent and I'll follow them to tackle some tooling I have made but needs a de-rust before blacking e.g. a locking bar for my motorcycle tyre bead breaker, wheel spacers

t'other John

_Paul_30/05/2014 23:30:05
543 forum posts
31 photos

Apologies for raising one of John's old threads from the dead but Toolstation have Cementone Brick & Patio Cleaner 5L on offer for £6.73 spend over a tenner and the delivery is free.


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