Turning Perspex rod

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

More :

These large engineering components in Acrylic are usually made by more complex and more controlled processes than gel plus hardener .

Acrylic in ready made bar and sheet form can be heat moulded into shapes . In principle it can also be injection moulded but there are many more problems than are found in more amenable plastics and injection moulded components are a bit rare .

Neil asks about Airfix glue . I don't know the answer to that one and Airfix were always a bit cagey . The question reminded me however about Slaters MEK glue (MeKPak ?) – this was absolutely lethal and several people had hospital visits after being rendered unconscious including George Slater himself . It could be bought in model shops by anybody .

[macmarchParticipant @macmarch]

Well, you learn something new every day. Didn't know about flame polishing Perspex.

When I was an apprentice we made marine equipment that had perspex components. Some of these were glued together. The chemi lab made up the 'glue' , this was a colourless liquid Araldite that had a usable life of about 10 minutes. It was a question of paint the sufaces, bond, clamp together then leave for 24 hours. Parts were often stuck the wrong way round etc. Up to the canteen to get 1 pint boiling water into which about 20 catering tea bags was stewed for an hour or so. Overnight this softened the araldite .

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

MEK is apparently Methyl-Ethyl-Ketone according to the one and only reference I could find . Toxic at just 200 ppm – open the bottle in a small room and you've had it .

Guess only : Airfix glue is the same solvent but with pre-dissolved Styrene in it to make it more viscous and sticky and to significantly reduce vapour emission and hence toxicity .

Perspex glue is Chloroform with pre dissolved Perspex in it for the same reasons .

[Michael Cox 1Participant @michaelcox1]

MEK ( methyl ethyl ketone, butanone) is a very common industrial solvent widely utilised in cellulose paint thinners. It is much less volatile than acetone. I would not advocate sloshing it around in a small room but opening a bottle is very unlikely to cause any problems. Because it is less volatile than acetone (which is widely sold and used to remove nail varnish) it is safer both from a fire hazard and a toxicity point of view.

MEK is a good solvent for Perspex (plexiglas, polymethyl methacrylate) and can be use for solvent welding it.

Mike

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Michael C ,

The various people apparently came to grief when using MEK in small unventilated rooms – the average model railway room in fact . Also one case arose from leaving open jar in sunlight .

I like it when this forum works well – lead in question – initial answers – detail points clarified – job done !

Regards ,

Michael Williams .

[Billy MillsParticipant @billymills]

Perhaps there are a couple of important points left.

Cast and Extruded are very important distinctions, the mechanical properties of these two types are quite different. Cast tends to have more internal stresses as supplied which tends to increase as you machine it. It is normal to anneal -around 90C- to remove these stresses. ( this stress from machining is also common to many other plastics). Cast Perspex is in some ways like glass to work.

It might be that the stress cracking that Gray experienced in old Perspex could have been fixed by annealing.

The whole story can be seen here **LINK**. This is the most detailed account of using Perspex that I have seen and also has a section on how the material reacts to many common chemicals.

Billy.

[Sub MandrelParticipant @submandrel]

This is all interesting stuff. Was MEK in the old glue or the new?

Neil

[JAParticipant @ja]

Chloroform in air and sunlight oxidizes to Phosgene. Phosgene will kill you and was used as a poisonous gas in The First World War. This is why Chloroform is always kept in a dark coloured glass bottle and is never inhaled directly.

JA

[Michael Cox 1Participant @michaelcox1]

There is a good summary of the toxicology of MEK at this link:

http://www.ccohs.cas/oshanswers/chemicals/chem_profiles/mek/health_mek.html

All chemicals should be treated with respect not alarm.

Mike

[Chris TriceParticipant @christrice43267]

Most of the MEK solvent based glues for polystyrene plastic kits aren't tenacious enough for acrylic. It's also worth mentioning there are two types of Tensol cement. One is air drying and the other has a catalyst to cure it. The latter is what you want for laminating sheets because obviously the airdrying version would stay wet inside once the edges had set. Both are quite syrupy and VERY odourous. I'm tolerant of most thinner/paint/resin/glue aromas but this stuff is pungent. Both can be thinned with Dichloromethane/Trichloromethane but obviously you need to watch evaporation in big sheets. The air drying Tensol, not unsurprisingly tends to shrink down a lot as it dries and although the catalyst type does too, it's does so far less. The airdrying one also tends to stay a little soft even when dry where the catalyst type becomes as hard as the acrylic and may be sanded and polished in the same way.

Superglue takes to acrylic exceptionally well but most of the superglue accelerators you can spray on to speed up the setting tend to embrittle the surface of the acrylic and you get the cobwebbing mentioned previously on the surface.

Edited By Chris Trice on 30/12/2012 02:05:56

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Billy Mills on 29/12/2012 17:55:28:

The whole story can be seen here **LINK**. This is the most detailed account of using Perspex that I have seen and also has a section on how the material reacts to many common chemicals.

Billy.

Thanks for posting that link, Billy

An excellent reference !

MichaelG.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

(1) Can't find any further definate information on original Airfix glue – it was formulated nearly 60 years ago and nothing much was ever published .

Couple of clues though :

It had a certain solidity – it would form lumps – so it is likely to have had the filler material mentioned earlier .

It smelled of almonds in solvent . The competitiive brand FROG glue smelled sickly sweet and chemically – like some cellulose hairsprays . Different viscosity to Airfix as well .

Some modern plastic kit makers apparently supply standard Tensol 12 in small tubes .

(2) MEK glue was just a trade name as far as anyone knew when it was introduced . Only much later did anyone question what was in it . Whilst chemical m-e-k was certainly the main ingredient I have heard that eary versions had an admixture of Xylene . If this is true it may explain why it had such a pungent smell and explain the various mishaps that people had .

(3) Clear Acrylic has some non obvious uses :

Bent rods and cut shapes will transmit light reasonable distances and around corners . Depending on the chosen geometry light can leak out all along or the bulk of the light can come out of the remote end .

It is super material for generating electrostatic charges – strong sparks on a dry winters night .

(4) I've been watching the Royal Institution Christmas Lectures . After a few dull ones in some previous years this years lectures were excellent in many ways . Chemistry with lots of splendid demonstrations .

Regards ,

Michael Williams .

[Chris TriceParticipant @christrice43267]

Airfix originally supplied it in small rubber bulbs in the kits but after a while the practice stopped. It almost certainly had styrene disolved into it to thicken it and to slow evaporation. In those days you put it on the part and then brought the parts together. I’m talking the old tube cement. Humbrol did their version as part of the Britfix range of adhesives. The first liquid solvent cement I remember using was Slaters Mek-Pak although this had a perfume all of its own.

Edited By Chris Trice on 30/12/2012 11:22:30

[Chris TriceParticipant @christrice43267]

Ironically, balsa cement which was acetone based often made a better adhesive for things like ABS which the glues for styrene kits didn’t really touch despite containing a proportion of styrene.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Sometimes an Airfix kit was unglueable . Most kits supplied were made from a semi rigid self coloured plastic which could be glued easily . Occassionally , and seemingly randomly , kits were supplied made from a creamy white and very soapy plastic that defied all attempts to fix together with Airfix type glues . Only recourse was to use unpleasant things like Bostik and UHU and literally 'stick' them together .

[Chris TriceParticipant @christrice43267]

That was mostly the model figures and some of the military vehicles which were intended more as toys. The actual construction kits were always styrene. Some of the VERY early and highly collectable kits were moulded in acetate.

[Sub MandrelParticipant @submandrel]

I remember the little bulbs, ten the white and blue tubes. Yes, when it went 'off' it left behind a brittle, transparent material. If you made a mistake and went back to repair it and were too greedy with the glue, eventually the plastic would go soft beyond the joint. It wcoudl take weeks to go hard again – how many times did you come back to a model finished teh night before to find it had 'done the splits'.

You could make a sort of plastic putty by dissolvinjg sprue in glue (I now it is technically 'runners' not sprue but everyone called it sprue when I was a kid.

The biggest loss is that of the transparent display stands – apparently the moulds have been lost. Remember how the bit at the top always broke off?

Most of my planes used to hang off nails in the wall. I knew when my mum had dusted them as she would repair them at random trying to huide the damage – I don't know how many times I said leave the repairs to me!

Neil

[Chris TriceParticipant @christrice43267]

Posted by Stub Mandrel on 30/12/2012 17:53:11:

The biggest loss is that of the transparent display stands – apparently the moulds have been lost. Remember how the bit at the top always broke off?l

Au contraire:

**LINK**

[Chris TriceParticipant @christrice43267]

Here you go Neil:

 

Edited By Chris Trice on 30/12/2012 23:35:34

[Sub MandrelParticipant @submandrel]

Hi Chris,

You've made a happy man feel very old…

Neil

[Chris TriceParticipant @christrice43267]

I've got about 400 kits in the loft acting as insulation, mostly Airfix and all pre mid seventies. I've got about a dozen of the glass bottles of paint which are approaching 45 years old yet with a two minute shake visually look as good as the day they were filled.

[Sub MandrelParticipant @submandrel]

Hi Chris,

Unassembled? Must be worth a bomb!

I have about twenty part-used tinlets mostly from the 70s. It takes a LOT of stirring and the addition of a drop of proper thinners (not white spirit) and you can get t to perk right up.

Neil

[Chris TriceParticipant @christrice43267]

Yep, unassembled and worth a bob or two.

I worked my way through most of the Airfix range when I was younger so this collection is happy memory stuff. I also collect space related kits too, again because of my sixties inspired interest in the space programme. In addition I restore and build replicas of movie models and alot of those were dressed in kit pieces so finding and scavaging the original kits is all part of it. By osmosis, one gets drawn into finding allied things to do with modelling like the glues and paints and the accesories of the period.

[Cyril BonnettParticipant @cyrilbonnett24790]

I have used MEK for a number of years to fix ABS plastic, in some cases the component has failed again but not along the line glued. MEK like many solvents should be used in well ventilated workshops, it was used as a degreaser in some garages and is readily available.

https://en.wikipedia.org/wiki/Butanone#Health_effects

[Chris TriceParticipant @christrice43267]

The Wiki link says a solvent for Polystyrene. What was the product you were gluing Cyril?

[Author]

Posts