Plastic repair: when all else fails ...

[Analog Kid]

Another successful repair on something that seemed hopeless.

Subject here is an acrylic microphone holder for the mike for my Sony Walkman Professional recorder. Bought in 1995, it's about 30 years old, so no wonder it cracked. Right at the weak point where you'd expect it to break.

I tried epoxying the pieces together, but unfortunately I mixed it wrong and it stayed a bit gummy, never set hard. I was about to chuck the whole thing when I thought of other successful saves I'd done where I put patches or reinforcements on things.

The two pieces still sorta stuck together, so I got some of my styrene strips (left over from my model railroading days: love that stuff!), cut some small pieces and made a small dam around the area over the break, using super glue. Then I mixed some of my liquid epoxy (not the "glue" I'd used before), measured and mixed it carefully, then poured it into the "dam" so it would cover the entire break.

After it set, it held together very nicely. Now I'm just waiting for the other side to break ...

Moral of the story is this: If you can't make a good repair where two thin pieces join, consider making a bridge or patch over the join which may be just as strong or stronger.

Epoxy is great stuff. The liquid I use actually came from the trash somewhere, years ago; it's made by Douglas and Sturges of San Francisco, who provide art-making materials to sculptors and such. Stuff sets super-hard, even after all the years I've had it. Plus it's perfect for repairs like this since it's pourable.

[David Hess]

I think epoxy and cyanoacrylate are the wrong things to use for plastic repairs where a suitable plastic solvent for welding is available.

I have repaired several Tektronix oscilloscope covers using strips of polystyrene and plastic welding cement, as shown below.

[Fraser]

Plastic welding using a solvent designed for the task is my “go-to” repair method as well. I found the issue with epoxy and some other adhesives was that the surface preparation had to be just right as the adhesive forms a bond to it, rather than actually becoming part of the substrate being repaired. I repair laptop cases with modellers ABS plastic welding solvent and that works well. The two faces to be joined melt in the presence of the solvent and the plastics combine before returning to solid ABS after solvent evaporation. I do sometimes add reinforcement in the form of ABS plastic modelling sheet or square section ABS bar. I have also used JB Weld “metal” epoxy to reinforce repaired areas where it is not visible and even rebuilt plastic screw towers by filling them with JB Weld ‘metal’ epoxy followed by drilling and tapping for machine screws in place of self tapping types that can split the screw towers.

I have also seen people repair ABS plastics using common plumbers pipe weld. This is different to modelling plastic welding solvent as it normally contains a percentage of ABS ‘fillers’ and so is thicker to fill voids in its original role. ABS scrap plastic may be added to modelling plastic solvent in the same way to form a coloured plastic filler for holes and voids.

Fraser

[Analog Kid]

A solvent-welded joint can be good, especially in easily melt-able materials like acrylic. (When I was modeling with styrene, solvent welding was the best way to glue that stuff together.)

In this case, first of all the joint was probably too thin for such a repair to hold securely: there just wasn't enough material for a strong-enough bond. And after the first botched epoxy job I couldn't have solvent-welded the joint anyway. You really need two surfaces that fit together pretty much perfectly for this to work. Plus I don't really have the right solvent on hand: I've tried acetone, which sorta-kinda works, but something like MEK would be a lot better. (Or perhaps even PVC or ABS pipe gluing stuff.)

I think in this case, and in others that I've done, there's plenty good adhesion between the substrate (plastic) and epoxy to give a good serviceable repair. Not appropriate in all situations, of course, but it does work well in many of them.

[daisizhou]

Initially I also thought epoxy resin was a good repair adhesive,But then I discovered that epoxy isn't perfect.

Sometimes epoxy resin does not bond well to the base material and is very brittle after curing.It is only suitable for some static display items, such as models, .......

Many parts need to withstand the test of physical mechanics. Epoxy resin cannot withstand long-term durable use, but temporary fixation is acceptable.

Now I usually use a soldering iron to weld plastic materials and add metal wire in the middle. This way of repairing works very well.


If I were to repair it, I would use metal wire (red and green wire) to make a rough shape, use a soldering iron to solder the metal wire into the transparent plastic, and then use the same material to reinforce it.
Although it looks ugly, it is guaranteed to never be damaged and is reliable and strong.

I call this method "reinforced concrete repair," where rebar refers to the metal wire and concrete refers to the plastic material.

[themadhippy]

I've tried acetone,

chuck some abs scraps in with it ,sticks like to a shit blanket

[wraper]

I repair ABS with K-flex 110 solvent (for diluting specialized foam rubber pipe isolation glue) with great results. This stuff is really potent, great for removing most of paints and adhesives too

[CatalinaWOW]

Thing like this are my 3D printer go to.  I have always had difficulty with solvent welding.  It can be difficult to determine the appropriate solvent.  They are always volatile, toxic and often hard to source.  In my case the interval between applications often exceeds the storage life of the solvent.   And properly fixturing to hold the pieces in place while the solvent sets can be difficult.

3D printing does require you to generate a model for the part, but on a piece like this it is quick and easy.  And provides the opportunity to add features.

[David Hess]

One of the reasons that epoxy may not work well for plastic repair is if plasticizers are present in the plastic, they can outgas into the epoxy turning it "soft".

[NE666]

Where aesthetics aren't important I've had good success using desoldering braid as the 'bridging'/'rebar' material. It's braided structure offers good permeability for the adhesive in use, allowing it to be well incorporated into the weld, and it helps to trap and hold in place lower viscosity glues during the cure.

[5U4GB]

I've tried acetone, which sorta-kinda works, but something like MEK would be a lot better.

Both acetone and MEK should be OK. If you want to do it properly you'd use dichloromethane but that's somewhat nasty stuff and unlikely to be stocked at your local hardware store.  A cheap source for small quantities is the Drinking Bird toy, provided you can find one where the liquid hasn't been dyed some garish colour.

[David Hess]

Both acetone and MEK should be OK. If you want to do it properly you'd use dichloromethane but that's somewhat nasty stuff and unlikely to be stocked at your local hardware store.  A cheap source for small quantities is the Drinking Bird toy, provided you can find one where the liquid hasn't been dyed some garish colour.

I am in New Hampshire where so far all of the better solvents are banned, leaving me with only acetone which I can buy locally.

[BILLPOD]

Good Morning Analog Kid,  my go-to for such repairs is JB Weld, which is an epoxy 'filler'.   The 2 parts, have to be mixed accurately in a 1 to 1 proportion and mixed thoroughly.   It takes a while to harden, and surface preparation is important, but The only failure I've had is with polyethylene, but NOTHING sticks to that.

[antenna]

Polycaprolactone (instamorph and the like).  Just heat up a cup of water and shape a new part.

[MarkL]

For plastic repairs I have two go-to's:

1) Plast-Aid:

    https://www.plast-aid.com

This is a 2 part solvent-based plastic glue/filler that hardens like a rock.  It will bond chemically if the plastic is susceptible to the solvent, or mechanically which can be imrpoved by roughing up the surface.  The consistency can be anything from a pourable liquid (good for casting), to hand moldable putty, depending on the ratio of powder to solvent.  Working time is a few minutes.

The hardened color is translucent white,  An accessory kit adds acrylic mixers for color matching, and fiberglass cloth for embedding to add extra strength.


2) "Same Stuff" Professional Plastic Welder (aka ProWeld and Tenax-7R):

    https://micromark.com/products/micro-mark-r-same-stuff-professional-plastic-welder-refill-2-fl-oz

This is your basic methylene chloride solvent.  Not as strong as the above, but good for cracked parts where the fix needs to be visibly unobtrusive.  Application can be a bit tricky because it spreads by capillary action, so you need to keep your fingers and clamps off the joint.  Needle applicators that can carefully control minute amounts work well, like this one called "Touch-N-Flow":

  https://www.amazon.com/Flex-I-File-Touch-N-Flow-Applicator/dp/B07JPY3VHH

[jfiresto]

For plastic repairs I have two go-to's:

1) Plast-Aid:

    https://www.plast-aid.com

This is a 2 part solvent-based plastic glue/filler that hardens like a rock....

The SDS suggests Plast-Aid is a 2-component MMA-based adhesive, which is what I would have tried.

[Analog Kid]

Good Morning Analog Kid,  my go-to for such repairs is JB Weld, which is an epoxy 'filler'.   The 2 parts, have to be mixed accurately in a 1 to 1 proportion and mixed thoroughly.   It takes a while to harden, and surface preparation is important, but The only failure I've had is with polyethylene, but NOTHING sticks to that.

Sorry, not a fan of JB Weld here. It's basically epoxy plus other stuff--filler as you pointed out. Which doesn't necessarily make it stronger than just epoxy, only able to fill gaps. It's not "as strong as steel", as the marketing for it wants you to believe.

My liquid epoxy is as strong as any adhesive I've ever used.

Another thing about epoxies: if you want strong, don't use the 5-minute stuff; definitely not as strong as the slower-setting ones. Basically the slower the set, the stronger the bond (assuming, of course, that you mixed it properly). Plus it helps to heat it up as it cures.

[5U4GB]

Polycaprolactone (instamorph and the like).  Just heat up a cup of water and shape a new part.

I'd thought of Polymorph and Sugro and similar as well but it's not going to work for something like this, to get the necessary strength you'd have to make it quite thick which means you'll end up with a lump of coloured snot holding your mike in place.

[5U4GB]

1) Plast-Aid:

    Warning, read below before clicking

Anyone using NoScript and subject to epileptic seizures may want to avoid clicking on that link.  Good grief, did the web designers actually test what their site looked like when viewed with common browser add-ons?  And how do you get a strobe effect like that without using JS?

For people outside the US where it'll be harder to get, it's methyl methacrylate with PMMA as filler so you should be able to find it locally under different names.  Just not at Bunnings.

[Bud]

Plus it helps to heat it up as it cures.

JB Weld gets really warm as it cures, doesn't it

[jfiresto]

Plus it helps to heat it up as it cures.

JB Weld gets really warm as it cures, doesn't it

Epoxy does give a stronger bond if you heat it as it cures. For example (UHU PLUS ENDFEST 300) with a 90 minute pot time:

• 20°C  12h  1200 N/cm^2
• 40°C  3h  1800 N/cm^2
• 70°C  45m  2000 N/cm^2
• 100°C  10m  2500 N/cm^2
• 180°C  5m  3000 N/cm^2

[coppercone2]

omfg. They use epoxy for aerospace.


It does not like bonding to some things. Low surface energy plastics need acrylic epoxy, and for some reason things like copper work alot better if you give it an oxide coating. Its strong.
It seems to have trouble with exceedingly thin things (panels), that is why PCB copper is oxidized slightly before bonding.

There is really no stronger glue then epoxy.

Solvent welding is another story, if you have a tight fit... it should actually weld (meaning its as strong as the parent material). It has zero gap filler capabilities. It should wick in and cover the entire bond area from capillary force or whatever happens there.

I strongly recommend using the gel type solvent, for bonding acrylic or lexan, unless your parts are premium quality. If you just hand make some stuff from acrylic, the thin solvent is not satisfactory. It's hard to get all the cuts and holes to be perfect enough to work with thin solvent... it needs to be like master carpenter (you can't do trickery with clamps like a basic carpenter) or machine shop quality cuts and fits. I put some of my acrylic 'rods' on a lathe and its not even close to being able to 'fit together' right for pure solvent welding into drill holes. https://www.tapplastics.com/image/pdf/PB-IPS16.pdf

Otherwise it needs to be SQUARE and DAMNED FLAT.

New carbide saw, with the correct tooth count, minimum, for true solvent welding. And all your shit needs to be dead flat, no warped old panels / recycling. Like you peel (with gloves on) and then immediately glue. And the saw needs to be SQUARE.

I think working with acrylic to solvent weld is extremely hard. The gels are like a great hack



My real recommendation is to get some long tiny bolts (like M2), I fixed many plastic bullshits with that. Like a pair of noise reducer earmuffs. Like any plastic was gonna hold in that spring loaded shit. I nearly had a break down thinking about how to fix that with adhesives, before I realized it can be bolted if the bolts are low clearance enough.  good riddens.  A tiny long screw is gonna be really damn strong, with tiny washers. For dynamic applications use thread locker purple with them. I was gonna do a filler, milling, fitting, gluing, before I realized two god damn bolts fixes it.  . This is where those stupid drill pens pay off (so long its not wobbly and you get swiss drill bits), for making tiny repair holes in irregular plastic surfaces. I paid off my pen drill, swiss bits and box of bolts with 1 repair on expenisve 3m crap that looked like it took 500 hours in cad to design . Get some extra diameter micro washers for those, and I would recommend flat head drive rounded mini bolts, with the reduced head profile, usually the crux is that it can't stick out very much. If the head is dome it usually can skid through obstructions. A countersunk screw is 100% clearance, but often the plastic its fixing is just not thick enough to allow for it, so you need big washers. Unless you countersink the washer slightly and precisely to allow for maximum clerance with a countersink screw. And get the little nut driver, its essential for repairs using tiny bolts on weirdo plastic shit, so it can hold the nut without you going nuts

[erkko]

And how do you get a strobe effect like that without using JS?

Thats how, probably. But yes, sad state of affairs... Do we need NoCSS plugin?

<img ... class="lazyload lazyload--fade-in" ...>

.lazyload--fade-in {
  -webkit-filter: contrast(0%) brightness(190%);
  filter: contrast(0%) brightness(190%);
  transition: filter .4s,-webkit-filter .4s;
  -webkit-animation: shimmer .1s ease infinite;
  -moz-animation: shimmer .1s ease infinite;
  animation: shimmer .1s ease infinite;
}

[BradC]

For people outside the US where it'll be harder to get, it's methyl methacrylate with PMMA as filler so you should be able to find it locally under different names.  Just not at Bunnings.

If you find a good source, let me know. I've found Devcon Plastic-Welder at Blackwoods, and what looks like a decent glue here :  https://acrylictech.com.au/product/acri-bond-210/

Plast-Aid looks good in the way it's packaged, but I've tried sourcing it from multiple places and had no luck. I have some Araldite 2022-1 which I sourced from China, but it looks like it's either counterfeit or past expiry. It goes off and sets up, but takes 3-4 times the data sheet specs to do so.

I have 2L of Dichloromethane in the fridge in my shed. Now that does a great job. Chloroform works well too but I'm out of that.

[David Hess]

Plastruct Plastic Weld is the best welding cement I have used:

https://www.amazon.com/Plastruct-Plastic-Weld-applicator-Bottle/dp/B00FDFWJD8

Which is about 85% methylene chloride (dichloromethane) and 10% methyl ethyl ketone according to the MSDS.  I suspect the balance is dissolved polystyrene.