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Bending and welding acrylic sheet?

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An Other12/08/2017 18:09:35
58 forum posts

As always, there were several articles in old copies of ME - I have one dating from 1949 or 1950 which deals with bending and jointing with different plastics materials. An important point the article makes is that when acrylic plastic is heated, the edges tend to 'flare' or expand. If a tube is rolled using this heated material, the ends appear to bell out. The article in ME advises making tubes longer than required, then cutting to length to get rid of the expanded ends.

The same comments apply to bends - unless controlled by a former, then the bends tend to 'expand' at the edges of the material (hard to explain, but obvious when it happens). This may be a problem with large tubes.

I have successfully made large curved pieces by placing a flat sheet of plastic on a large metal former, then shoved the whole lot in an oven. Let the oven heat up, and watch the plastice carefully - it will flex in various directions, then quite abruptly drop to conform to the former - then take it out immediately and let it cool naturally.

I appreciate your comments about adhesives, but I remember in the RAF back in the 60's ordering cans of 'Perspex adhesive' from stores - it never seemed to work very well, and there were no instructions, and it didn't seem to be sticky - now I know it was cyanoacrylate adhesive - superglue (in 1 pint cans!)

John Reese12/08/2017 18:23:37
380 forum posts

Disclaimer: I have never worked with Plexiglas (Perspex) myself. My father did. He got hid joints perfectly fitted then used a syringe to apply acetone to the joint. The acetone wicked into the joint abd created a solvent weld. Would that work in your application?

Eugene12/08/2017 19:22:56
96 forum posts
2 photos

Mike posted, "I've always understood that perspex can be solvent welded with chloroform."

Indeed it can. I used to make up 5 litre batches of such cement in the lab. for making Perspex plating barrels. These get a tremendous physical battering, but I can't remember a joint failing in normal use. The construction was all lap and housing joints.

The method was to heat the chloroform up in a large glass beaker and dissolve powdered perspex in it.

Can't remember the quantities off hand, but I always made sure the fume cupboard was working before I started the job, and got the cigarette smokers out of the way!

Eug

Eugene12/08/2017 20:27:27
96 forum posts
2 photos

 

Just to add ..... when the maintenance / fabrication guys made a few smaller barrels (hexagonal I think about 9 inches across flats), they used a home made strip heater something similar to the one John described.

However instead of a fixed bed one side was hinged; all they did was just lift that side, hold it steady at the required angle and switch off the heat. There are DIY versions described on YouTube.

From memory the edges were then held together with a big, cemented, exterior lap joint using another bit of angled Perspex strip.

Eug

 

 

Edited By Eugene on 12/08/2017 20:28:27

John McNamara13/08/2017 08:56:07
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Upon reflection from memory the Perspex sheets were bent by hand in mid air over a form than placed between two parallel cleats in a board until they had cooled sufficiently to hold their shape. there could be no blemishes on the bend it had to be perfect.

I am pretty sure the gap in the table was bounded by water filled steel tubes, so the radiant heat of the dull red element was narrow band under the Perspex.

The man that did this work was a fine craftsman he came from Westphalia Germany. I have lost contact... A pity.

Regards
john

Edited By John McNamara on 13/08/2017 09:00:08

Vic13/08/2017 09:58:38
1301 forum posts

I spoke to a guy who worked for a company who specialised in this type of work. One of the things he mentioned is that acrylic absorbs water and needs to be dried in an oven for several hours before any attempt is made to bend it.

Russell Eberhardt13/08/2017 10:10:40
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Am I the only grumpy old git who gets annoyed by the use of an adjective in place of a noun.

Acrylic sheet, yes. Acrylic plastic, yes. Acrylic, what does that mean? Have you ever heard of white metal being called white?

Sorry, end of rant.  Not getting at anyone here.  It seems to be common usage.

Russell

Edited By Russell Eberhardt on 13/08/2017 10:13:02

Mike13/08/2017 10:14:45
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Just out of curiosity, where does polycarbonate come into all this, or is it just another name for Perspex? Years ago I tested polycarbonate shooting glasses after a claim that they would deflect a .22 rifle bullet at 25 yards. In fact they just appeared to be "bulletproof" - the impact generated heat which caused the hole to close up after the bullet had passed through. Sorry to wander off the subject...

mark smith 2013/08/2017 10:25:29
493 forum posts
271 photos
Posted by Eugene on 12/08/2017 19:22:56:

The method was to heat the chloroform up in a large glass beaker and dissolve powdered perspex in it.

Can't remember the quantities off hand, but I always made sure the fume cupboard was working before I started the job, and got the cigarette smokers out of the way!

Eug

Eugene chloroform isnt flammable.

ega13/08/2017 11:12:02
670 forum posts
74 photos
Posted by Russell Eberhardt on 13/08/2017 10:10:40:

Am I the only grumpy old git who gets annoyed by the use of an adjective in place of a noun.

Acrylic sheet, yes. Acrylic plastic, yes. Acrylic, what does that mean? Have you ever heard of white metal being called white?

Sorry, end of rant. Not getting at anyone here. It seems to be common usage.

Russell

Edited By Russell Eberhardt on 13/08/2017 10:13:02

"acrylic" first appeared in the COD in the sixth edition of 1976 where it was both adjective and noun (in that order). My most recent popular dictionary (Chambers Concise) gives it first as a noun! By way of contrast, Collins COBUILD based on computer-analysed word frequency treats acrylic as an adjective.

"Wight" can be a noun.

I am certainly a GOG but I try not to get annoyed by these things.

Russell Eberhardt13/08/2017 11:13:39
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Posted by Mike on 13/08/2017 10:14:45:

Just out of curiosity, where does polycarbonate come into all this, or is it just another name for Perspex? Years ago I tested polycarbonate shooting glasses after a claim that they would deflect a .22 rifle bullet at 25 yards. In fact they just appeared to be "bulletproof" - the impact generated heat which caused the hole to close up after the bullet had passed through. Sorry to wander off the subject...

Polycarbonate is not the same as Perspex. Perspex, Plexiglass, Lucite, etc., is polymethylmethacrilate. Polycarbonates are polymers with carbonate groups, much stronger than Perspex.

Russell

Clive Foster13/08/2017 11:34:12
1085 forum posts
19 photos

Vic

Interesting comment about acrylic absorbing water and being tricky to bend if it isn't dried first. I wonder if thats the root reason for our standard practice back in the day being to always get new material if it was to be bent or glued. Stuff on the rack or in the cupboard being kept for simple flat windows and the like. Which, to be fair, was mostly what it was used for.

Mark

Whether or not a gas is flammable doesn't really affect the wisdom of getting cigarette smokers out of the way if there is a reasonable chance of anything beyond very minor leakage into the local air. Good chance of decomposition or reaction when the gas passes over the hot tip. Ofttimes with byproducts rather nastier than the original.

Clive.

mark smith 2013/08/2017 11:52:52
493 forum posts
271 photos

Clive, i was just making the point as it reads like theres a risk of explosion.

Many people immediately assume its flammable due to the over powering smell,it also has a high boiling point compared to many  other flammable risk solvents.

The main risk with chloroform ,is if you have an old bottle of it lying about , it can decompose into phosgene gas (like used in trench warfare in WWI) Adding ethyl alcohol to the bottle if storing helps stop this. Most chlroform usually has this or something else in it but repeated opening the bottle causes loss of the alcohol .

Edited By mark smith 20 on 13/08/2017 11:55:04

Clive Foster13/08/2017 12:20:23
1085 forum posts
19 photos

Cheers Mark

So it is chloroform which goes to phosgene then. Was fairly sure it went to something horrible but couldn't remember what.

Funny how what you know affects how you interpret what you read. Never occurred to me that what Eugene wrote could be taken as reference to fire or explosion risk. Absolutely right that it could be read that way. But I knew about the decomposition thing so that was all I saw.

Clive.

Neil Wyatt13/08/2017 12:58:32
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The adhesive for acylic/perspex is called tensol. easily available, I suggest reading the MSDS and manufacturers data sheet.

I found it easy to sue, but some I got off ebay had gone thick and I couldn't suck it into a syringe.

Did a great job of gluing PLA to acrylic,

Circlip13/08/2017 13:13:27
831 forum posts

" Was fairly sure it went to something horrible but couldn't remember what."

Same reason for not smoking over a "Trike" (Trichloroethylene) degreasing tank.

Regards Ian.

Steve Pavey17/08/2017 10:02:28
245 forum posts
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Posted by Neil Wyatt on 13/08/2017 12:58:32:

The adhesive for acylic/perspex is called tensol. easily available, I suggest reading the MSDS and manufacturers data sheet.

I found it easy to sue, but some I got off ebay had gone thick and I couldn't suck it into a syringe.

Did a great job of gluing PLA to acrylic,

We used to have two grades of Tensol, one as thin as water and the other quite viscous. Perhaps you were supplied with the latter?

Neil Wyatt17/08/2017 16:58:18
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Posted by Russell Eberhardt on 13/08/2017 10:10:40:

Am I the only grumpy old git who gets annoyed by the use of an adjective in place of a noun.

Acrylic sheet, yes. Acrylic plastic, yes. Acrylic, what does that mean? Have you ever heard of white metal being called white?

Sorry, end of rant. Not getting at anyone here. It seems to be common usage.

The battle was lost on that word years ago, from Chambers:

acrylic noun any of various synthetic products derived from acrylic acid, especially acrylic fibre, acrylic paint or acrylic resin. adj relating to, containing or derived from acrylic acid.
ETYMOLOGY: 19c as acrylic acid; otherwise 20c: from Latin acer sharp + olere to smell.

George Clarihew17/08/2017 19:10:11
45 forum posts

Acrylic, bit like doing the electroluxing.

Hoovering, as in vacuuming the floor, funny language this english

Neil Wyatt17/08/2017 19:11:57
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Posted by mark smith 20 on 13/08/2017 10:25:29:
Posted by Eugene on 12/08/2017 19:22:56:

The method was to heat the chloroform up in a large glass beaker and dissolve powdered perspex in it.

Can't remember the quantities off hand, but I always made sure the fume cupboard was working before I started the job, and got the cigarette smokers out of the way!

Eug

Eugene chloroform isnt flammable.

No, but smoking in the presence of chlorine-containing vapours is not conducive to long life and happiness.

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