EMA Plastic Weld

Attempting repair of a small item yesterday … I had my usual difficulty when applying ‘Plastic Weld’

Can one of the expert ‘plastic-modellers’ please suggest a suitable brush [or equivalent] for use on tiny jobs ?

I usually end-up trying to use the tip of a watchmaker’s screwdriver … but the solvent mostly evaporates before it gets to the job.

The directions say ‘use a small brush to apply’

Thanks

MichaelG.

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http://www.plastruct.co.uk/

Edited By Michael Gilligan on 12/03/2023 10:09:36

Hi Michael, usually its a special purpose dispenser which which depressed bring some fluid upto the top level, and small paint brush, but better is the bottle which has a squeezable rubber teat, that has a fine hollow needle . A hypodermic syringe would work , i use a old glass type one to which the needle goes on the end.. however its a steady pressure or you will flood it! No brush hairs ect ...The container type drains back down automatically. Some schools suppliers have listed like hindleys or technology supplies. Eye protection is advisable! Chloroform used to work great on abs! and acrylic....🤪

vic

I use a small length of PTFE microbore tubing. Capaillay action draws it up and better atttraction to the plastic draws it out. For bigger jobs a pvc micropipette works but pressure from evaporatom can blow it out. If you don't release the bulb completely you can control the blow-out by releasing pressure on the bulb slightly.
Random ebay example www.ebay.co.uk/itm/333838705736?

It is always best to use capillary action to draw the solvent into the joint line. Apply the solvent to the back side or inside of a corner when possible.

Robert.

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I’m comfortable with the process, Robert … been doing it for years

… but I’ve been wasting far more solvent than I use, because I have never found the right applicator.

The PTFE microbore tube sounds like a good answer to my question

… Thanks.

MichaelG.

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Edit: __ just purchased 4m of 0.3mm bore, thin-wall for £1.91 with free postage !!

Edited By Michael Gilligan on 12/03/2023 11:06:58

This may or may not be relevant but you never know.

Our mechanical workshop makes its own welding solution for perspex. Not that I’m suggesting you do likewise but it’s easy for them to get the chemicals from stores and we have fume cupboards. The pertinent point is they add small amounts of the plastic to be bonded to the mix which makes it thicker and less prone to evaporation.
You probably knew all that, if so sorry.

regards Martin

No need for ‘sorry’ Martin … but yes I’m aware of many ‘tricks of the trade’

My dad did a lot of clever stuff with Perspex.

In the particular case that prompted my question, I don’t think it would have been feasible to thicken the solvent.

MichaelG.

A quick update:

Robert’s suggestion of small-bore silicone rubber tubing was excellent

… unfortunately my choice of 0.3mm bore brought its own little problem : the surface tension effects are so strong that the solvent withdraws slightly into the tube and doesn’t leave the cut-end ‘wet’ !

[ For future use, I will be ordering some of the next-size-up. ]

With patience and a stereo microscope, I eventually managed to get some solvent into the joint … only to find that the plastic [which appears to be carbon-loaded] is one of the few that does not dissolve in ‘Plastic Weld’

Episode 2 __ Purchased a small tube of Loctite ‘Super Glue Original’ and realised how enormous the small nozzle looks under the microscope. … Managed to flood the joint with it, and then peel-off all the half-dry excess with a scalpel.

The component is now having some time to cure … after which I will know whether the whole exercise was futile.

MichaelG.

Michael, A lot of the superglues that you can purchase from the pound shops have microbore nozzles in with them.

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Thanks for mentioning that, Bernard [could you put a number on ‘microbore’ please?] … but this tube was on clearance-offer at my local Tesco for £1 and ‘brand loyalty’ kicked in [realising that I would almost certainly only get one go at this repair].

MichaelG.

Michael, As far I am able to test they are 0.45 mm at the tip.

Thanks, Bernard

MichaelG.

Did no-one else notice the following, above?

Apply the solvent to the back side

Cheers, Tim

Michael, as a frequent user of plastic solvents I have found the best 'tool' for applying small amounts of solvent is a fine pointed but full bodied artists paint brush. The brush is held so that the solvent stays in the brush but allows capillary action to draw the small amount required from the brush into the join, i.e. not pointed directly down to the part. It doesn't need to be an expensive brush, the best I've found for shape and longevity are the 'Boldmere' brand from 'The Works' - quite inexpensive for what they are.

Super glue of course is another matter, the thin type will run everywhere if not controlled properly - a paint brush is of no use of course but a simple sewing needle reversed in a holder of some kind - mines in a pin chuck - with the eye of the needle outwards is. I have small slices of aluminium drilled with 3mm holes a few mill deep to act as 'inkwells' for the cyano. The glue is picked up in the eye of the needle and transferred to the part. - if you use the pointed end of a needle the glue runs back up the needle a short way and is impossible to apply. There are of course, commercial, photo etched, equivalent applicators available but a needle works well

Needless to say but be aware of where your fingers are - any solvent will quickly leave a fingerprint impression and the cyano of course even more quickly ensuring that the part becomes an extension of your fingers!

Many years back I bought one of the micro bore applicators - a very small hypodermic needle attached to a thin walled plastic tube reservoir. To use it's stood in a bottle of solvent to allow it to fill before using on the parts. The needle quickly becomes contaminated with residue plastic inside and impossible to remove and it stops working - it still sits in the drawer!

Best - Tug

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Many thanks for that, Tug … it’s exactly the advice that I was seeking when I first posted

The immediate problem, of course, morphed into something different when I discovered that the plastic in question was [to all practical purposes] insoluble.

MichaelG.

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Edit: __ for info. I clumsily broke one end off the flat-cable retention insert on a Raspberry Pi

It takes no load [the clip is just there to stop it getting lost], but I thought I should try bonding it back in place.

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Edited By Michael Gilligan on 13/04/2023 09:27:22

I bought a litre of chloroform, the acrylic solvent, from Italy back in the day. Goods in free circulation and all that guff. Bought it on a whim because I had never seen it for sale before. It arrived nil problemo.

It sits in the shed waiting for the day when my need will outweigh breaking the seal

Tubes from a covid test kit could be used to apply small quantities of adhesive?I have been useing them for oil.

Frank

The immediate problem, of course, morphed into something different when I discovered that the plastic in question was [to all practical purposes] insoluble.

Yes Michael, I should have said about varying plastics but as you said 'plastic modellers' I thought you were meaning the part was styrene.

Some plastics simply will not glue with anything whilst others adapt to varying solvents/adhesives. Polyethylene springs to mind - far too waxy for any adhesive I'm familiar with.

Epoxy may be better on your part, especially if you can reinforce it with a small pin of some kind but even that won't always be successful.

Good luck with it.

Tug

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So did I, Tug … I presumed it might be ABS

Exactly what it is, I don’t know … but it clearly demonstrates that short carbon rovings are not the universal panacea

The breakage was caused by my arthritic clumsiness, but the failure mode shows both a brittle failure and a de-lamination … as the attached snapshot of it ‘loosely re-assembled’ will hopefully illustrate:

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This is the repair job that confronted me ^^^ and at that time I presumed that ‘solvent welding’ would be the right approach … it was a surprise and a disappointment to find that the material is unsuitable for that process.

MichaelG.

Here is my Super Glue repair

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I have no idea how long it will last but, as mentioned, the clip is under no stress once it’s in place.

I will probably get some sort of extension cable for the camera, so that this wedge doesn’t need disturbing again.

MichaelG.