Gluing Agilent grey plastic - Page 1
Forum section: electronics / general

author: Wartex
author_rank: Frequent Contributor
timestamp: March 08, 2013, 01:29:08 am
content: Hi guys, scores an Agilent PSU from ebay and it has cracks on the front panel and some plastic standoffs are broken. I tried superglue and it holds but extremely weak. They use some sort of PVC-like plastic that doesn't like cyanoacrylate glue. I tried ABS cement and it held better but still broke easily. Does anyone know what type of glue I should use?

author: Psi
author_rank: Super Contributor
timestamp: March 08, 2013, 01:37:49 am
content: Epoxy?If you can drill a small hole in each side and insert a metal support rod it will help.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 08, 2013, 02:12:17 am
content: Take a piece of the exact same material and use a powerful soldering iron to melt pieces together. I have a 200w flat iron for that, i do not know it's original intended purpose. I fixed a lot of motorcycle parts with that and if you fuse them together they act like being one piece.

author: dimlow
author_rank: Frequent Contributor
timestamp: March 08, 2013, 02:29:06 am
content: I second epoxy, but i would use 30 minute epoxy the 5 minute epoxy is ok but 30 minute, once stuck will be a lot tougher. I fix all sorts of with epoxy.Clean the surface with isopropanol and let it dry. Make sure its clamped together for 24 hours. and wipe off the excess before it dries.I use this

author: Adler
author_rank: Regular Contributor
timestamp: March 08, 2013, 02:31:45 am
content: If it is ABS then the best way to repair it is with acetone.Test with a little bit of acetone on an inside area. If it melts, its probable ABS.Now mix some ABS stock with acetone to make a thick goop and use this as a glue on the case. It will weld the part together.pro-tip: lego makes a great ABS stock.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 08, 2013, 02:34:41 am
content: Oh, when superglueing and you want a bit of structural volume just sprinkle sodium bicarbonate on the wet stuff. It will arden like cement.

author: robrenz
author_rank: Super Contributor
timestamp: March 08, 2013, 02:56:34 am
content: MEK methyl ethyl ketone is a slightly better ABS cement than acetone. The problem with gluing cracked plastic pieces is that the glue area is very small and the rest of the plastic has a huge mechanical advantage on the joint. As an example take 2 plastic sheets 2mm thick 50 mm long and 20 mm wide. Glue the 20 mm edges together. Now when you bend that joint there is a 25:1 mechanical advantage (50/2) of the pieces on the joint. So laying another piece of plastic over the joint as a lap joint will help immensly if there is room for it.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 08, 2013, 05:10:00 am
content: I still recommend the plastic welding method. If motorcycle fairings treated like that last through crashes then I assume on the bench gear it will last through its lifetime.Whatever, there are a lot of choices and failed experiments to be made.

author: amyk
author_rank: Super Contributor
timestamp: March 08, 2013, 06:33:27 am
content: To identify the plastic there will usually be casting marks.

author: Psi
author_rank: Super Contributor
timestamp: March 08, 2013, 06:59:46 am
content: Yeah, the 5min epoxy isnt very strong. Use the normal stuff.I found if you put the item in the kitchen oven at 60deg for an hour it will fully cure it.Just be aware that epoxy gets very runny before it cures, so you have to make sure its not going to 'run' out of the area you put it.

author: RCMR
author_rank: Frequent Contributor
timestamp: March 08, 2013, 08:08:11 pm
content: You might want to try a metacrylate adhesive, these are designed fo gluing those waxy plastics and I've found them to be far more suitable than epoxy (which adheres poorly) or superglue (which has the wrong modulus of elasticity and thus fractures too easily).Typical brandnames are Plexus and Hysol.

author: Gall
author_rank: Frequent Contributor
timestamp: March 09, 2013, 10:59:41 am
content: PVC plumbing pipes are glued together. The very good PVC glue is sold for PVC plumbing work. It dissolves the plastic a little bit so that it "welds" together. Sometimes it works on ABS too. I used this kind of glue (generic brand) for repairing broken enclosures.Epoxy is much weaker on PVC than this kind of glue.PE and PP cannot be glued at all but they're rarely used for enclosures.

author: amyk
author_rank: Super Contributor
timestamp: March 09, 2013, 01:03:52 pm
content: Quote from: Gall on March 09, 2013, 10:59:41 amThey're also the easiest to weld together using very low heat.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 09, 2013, 01:06:42 pm
content: There are some glues in the RC hobby shops for PE and PP. They are probably based around acetone or another solvent that dissolves a bit of them like a weld.

author: Gall
author_rank: Frequent Contributor
timestamp: March 09, 2013, 04:09:23 pm
content: PE and PP don't dissolve in acetone or similar solvents. Only tolyene+heat or something like it works for non-cross-linked one. The cross-linked PE cannot be dissolved.Both can be glued but cannot be glued well. They easily go off. Finding a good glue for nonpolar polymers is currently one of open chemistry problems.

author: babysitter
author_rank: Frequent Contributor
timestamp: March 09, 2013, 05:02:47 pm
content: If possible ask plastics-working companies in your neighbourhood. I am working close to a company that manufactures plastic parts for hospitals, using cyanoacrylates and stabilized Tetrahydrofuran.Of the first I got some which was after its expiry date, I think its easy to see how to use.Of the second i have a tiny little bottle, its a solvent for Polystyrol, PVC and PUR at least.Also, a slush of thf-solved MABS is useful too. After evaporation of the THF the MABS stays.BRHendrik

author: Wartex
author_rank: Frequent Contributor
timestamp: March 09, 2013, 06:25:24 pm
content: Hey guys, it's "PC-FR" so i assume it means flame retardant polycarbonate.

author: mzzj
author_rank: Super Contributor
timestamp: March 09, 2013, 08:07:35 pm
content: Polycarbonate should be relatively easy. If possible make the glue joint larger than orginal by adding plenty of extra glue or adding support pieces made of ie. plastic or aluminium.For tricky polypropylene/ethylene and PTFE plastics I would try 3M DP-8005 structural adhesive.

author: free_electron
author_rank: Super Contributor
timestamp: March 10, 2013, 12:38:50 am
content: those cases are ABS plastic. Use MEK. i use an ABS glue from WELD-ON. it's like water. push pieces together , use a syringe and needle to let a droplet of the liquid 'seep in ' using the capilaary effect.done.