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Flame polishing...

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Post Wed Jul 02, 2003 11:50 pm

Flame polishing...

Hi guys & gals,

Can anyone give 'us a quickie on how to do a bit of flame polishing? I'm really keen to give it a go. I saw an example of it yesterday and was very impressed.

cheers

Lee
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Post Thu Jul 03, 2003 5:57 am

It depends on what you want to flame polish , essentially acrylic starts deforming at about 150c (becomes like rubber) and melts burns at about 300 or so- however different types of acrylic (cast or extruded) melt or burn at diff temps in a different way.
The easiest way to tell what acrylic you are polishing is to take a small piece and burn it.
Cast acrylic will burn with a crackling flame and will NEVER drip flaming molten bits , extruded (the cheaper stuff) will burn with a silent flame and will drip molten burning bits. Cast responds less well to flame polishing than to extruded , however flame polishing extruded which is a very stressed acrylic due to mnfgring process is sometimes fraught with danger , it introduces a LOT more stress intot the material and can easily result in crazing or stress cracks which actually might only appear some time on - worse than this is the fact that if you use the wrong solvent to clean the acrylic , it crazes instantly or introduces further stress.

Flame polishing is really a way of making the acrylic melt and then resolidify
No one tool does flame polishing , and the type of flame you use is sort of critical (the shape , temperature , force and gas)
Best is to use a butane flame , some other stuff like kerosene etc can introduce soots etc into the acrylic.
Temperature is critical , too cold and you damage the acrylic trying to get heat into it , too hot and you sizzle the stuff.
The shape and force of flame is also critical , flame polishing an edge with a broad flame front is going to round the edges , trying it with a needle point is just as useless.
The flame front should be a little broader than what you are trying to polish , the blue part of the flame should be used and the speed of polishing needs to be controlled.
What you do is to get a bit of heat into the edge you are trying to polish by going back and forth over the are quickly with a wide flame , you then use the narrower flame and run slower over the edge you are polishing . It is WAY better to do a few passes rather than try with a single pass and its a lot better to polish with a soft flame than a hard flame (the torch should not be hissing or spitting)
It is better to flame polish an edge "bi directionally" IE NOT dead onto the edge , but point the flame at about 45 degrees down and polish the bottom half of the edge , this avoids putting a lot of heat into the sharp part and means that the flame front is not hitting the flat surface , flip the sheet and do the other edge. This will avoid rounding and "flame condensation" marks on the surface
We use thos Cadac Gas cylinders and have a nozzle that can be interchanged and can control the force of the flame , these are cheap and can be bought from any hardware store .
We also use pencil soldering type torches for fine detailed areas.
If you see distortion after flame polishing , you are too hot or are moving too slowly , if you see frosting or a less than clear edge/surface , you are too cold or moving too fast.
Really , all you have to do to perfect flame polishing is practice , there is no "formula" or perfect guide line.
The thing is , flame polishing will NOT be a quick fix for bad cuts , deep scratches and the like. Saw marks MUST be sanded out and the edge finish should be really good to achieve a good result. The biggest problem with flame polishing is thermal stress , rounding off of square or sharp features and distortion.(Espcially if its a glued or fabricated item)

Flame polishing large surface areas is the most difficult , here temp and speed are really critical as is the cleanliness of the acrylic , this will remove fine hairline scratches , but deep stuff has to be buffed , it also affects the optical properties of clear and can distort the mirror flat finish of solids.
We avoid flame polishing where possible , however most of our acrylic is laser cut , thus it already has a beautiful polished edge cos of the laser.
If you can buff an edge , like square cut panels , its a lot better and you get a slightly better finish (however rounding is a big problem and you need various grades of polishes and buffs and its real dirty and really risky with small parts and powerful buffs), obviously if its a complex shape buffing is not always possible. When we do flame polish stuff , we anneal it after , IE heat it up to under deformation point and let it cool slowly , this removes stresses.
Its really pretty easy to do and doesnt require any major investment in machinery, just practice.
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Post Thu Jul 03, 2003 7:47 am

Thanks for your detailed reply Rodney,
I've got quite a few offcuts from my suppliers bin of various thicknesses and clear/ coloured pieces. It's something I'd like to learn so I will practice on these off cuts and let you know how I go. The signs I'm looking at doing are small, only 300mm x 180mm of 4.5mm cast clear acrylic.

Cheers

Lee
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Post Thu Jul 03, 2003 8:50 am

Leeroy,

With all due respect to Rodneys post I think he's made flame polishing sound a lot more daunting than it actually is. I saw Rodneys award / trophy that he made and can understand that he probably requires near perfect results but for standard acrylic signs flame polishing is quite straight forward.

Although we now use one of awltechs flame polishing units we managed for a few years on the most basic kit which comprised of butane gas canister, air canister and a simple pencil torch.

Using 5 or 6mm cast acrylic with a 20 gauge nozzle in the torch, we achieved very good results. It does depend on the quality of the cut of the material because you will never get rid of deep saw marks or chips. We've found that getting a good neat cut on the marerial is also important because if the protective film is intact with no raggy edges you can flame polish with the film on - which obviously protects the acrylic against the flare marks you can get if your not carefull. This is a technique which allows us to polish frosted acrylic aswell, which is very unforgiving as far as the flare marks are concerned.


I personally think flame polishing transforms a simple acrylic sign alltough we diamond polish aswell which gives excellent results on straight edges we have to rely on the flame polisher for curves and other odd shapes

I think you'll be surprised how easy it is to get good results.




Best of luck,

Glenn
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Post Thu Jul 03, 2003 9:13 am

Hey Glenn,

After Rodney's reply, I thought "why not..." I went out and got a butane / mapp torch and gave it a crack. I was really impressed with the results straight away. I'm getting a small distortion about 2mm into the acrylic. I'll go in tomorrow and get a sharper flame which hopefully fix it.

I can see what you say about Rodneys post. Man that guy does some excellent finishing to his jobs, the finish I'm looking for is not to his standards.

Rodney, if you put as much thought and time into your jobs as you do into your posts...You must have some very happy customers. Thanks heaps guys...I'm having a ball playing with this gear.

Still melting stuff...Lee
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Post Thu Jul 03, 2003 10:20 am

I agree with both

Rodney has a wealth of experience in his field and i think will be an asset to the UKSG. However, a small critism, i think he has a large company with all the kit for every angle of signmaking. Not everyone has this. I like his posts because we have the kit and his advice we try or know.

What you should do is follow his advice but use the old adage. KEEP IT SIMPLE STUPID (KISS). A perfect finish like rods may not be required for some jobs. A simple gas blow torch will do a great job and will cost a £10 inc gas. Just play with offcuts and see what YOU think.

As signmakers we are normally over critical. We notice things that customers dont. This doesnt mean lower your standards, it means dont over stress yourself.

"My comments only"

P.S Keep it up Rodney

Tex
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Post Thu Jul 03, 2003 12:41 pm

Yes - I know I do tend to sometimes overcomplicate things sort of :)
I did actually say it was real easy and all you need is practice and minimal kit.
I do a lot of industrial and fabricated acrylics , where specs , sizing , structural rigidity and longevity is paramount , we tender a lot and work for folk who specify down to the nut and bolt used - so I do tend to gat a little anal.
There is one thing I want to add , when we attempt a new process etc , I tend to push to the limits , that way I know how far we can go and what problems are likely to develop , I have been burned too many times with doing the simple bits succesfully and then the job specs change and then the doo-doo hits the fan:)
It is a fact of life in my business that I have the worst type of ultra fussy customers , we have learnt to deal with them and give them what they want or better - it costs us a lot to do so which is a pain , however they are prepared to pay for it

How do you diamond polish ? We have never done it or tried it? Vertical belt sanders with diamond belt or discs?
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Post Thu Jul 03, 2003 4:26 pm

Rodney,

Re Diamond polishing - We use a German made machine called the AF110 Diamond Edge Polisher from a company called AF Acryl.

In simple terms the acrylic is fed along a track gripped and held at the right height to pass over the cutting head.

The cutting head is a rotating unit which houses a synthetic diamond responsible for material take- off & a natural diamond which does the polishing.

The machine can take material upto 25mm thick x any length. The 25 mm can be made up of any thickness acrylic eg:- 12 x 2mm thick acrylic sheets.

The benefits of diamond polishing are that it DOES get rid of saw marks and polishes to a much higher standard than flame polishing.

The down side is the cost - £9,000 - £10,000 per unit. A lot considering all it does is polish acrylic edges.

Regards,

Glenn
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Post Thu Jul 03, 2003 4:32 pm

cost - £9,000 - £10,000 per unit


Flaming hell (hot)
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Post Thu Jul 03, 2003 10:31 pm

And dont spray your acrylic if you have flame polished it, it will craze like krazzzy, always polish with a mop as this dont stress the perspex like a flame does.

Yes this is the voice of experience talking :roll:
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Post Thu Jul 03, 2003 10:35 pm

Re: Flame polishing...

Hay leeroy I got a burner from dicksmiths 2 years ago for flaming perspex edges(small black thing you can buy refile butain cans for). very simple I run a steal ruler down the sides get all the scratchs runing in the same direction then flame it. If you dont have a flame run your ruler down the sides then sand with wet&dry with some soapy water then rub with some cuting compound, not hard and dosent take long.
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Post Thu Jul 03, 2003 10:58 pm

Cheers Luke,
I'll go into trickie dickies this weekend to have a squiz at another nozzel. I think I'll just need a finer flame. the one I have is far too wide and it licks on the flat edge ( face). I've gotta tell ya though, I've had a lot of fun doing it. I should have it sorted by the end of the weekend.

How's it going for you in the mother land? I've got cousins living in Essex (Gods own country for East Londoners).

Lee
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Post Fri Jul 04, 2003 9:06 pm

Re: Flame polishing...

realy mate how old is she, I could call round. :D
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Post Fri Jul 04, 2003 9:50 pm

Actually the one I'm thinking of is thirty four, red hair very cute...Hang on...SECOND cousin...Yuck. I'm off this subject...I'm not from Tassie you know.

L

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