Plastics bonding

[Franklinstein]

I'm typing this on a recently-restored and upgraded 2400c. It came with an original AC adapter (which I had to repair), and its floppy drive. There's a long story involved with this one, but I'll spare you.

The next problem: The 2400c's floppy drive has a little flip door on the front. The door doubles as a stuff keeper-outer when it's closed, and a stand when it's open.

Anyway, the door is held on there by two little hinges. These two little hinges are two curved pieces of plastic bonded to two other curved pieces of plastic. Mine are in the process of coming apart (ten years of use and abuse will do that).

Does anybody have any suggestions as to an adhesive that would provide a strong, permanent bond between plastics? I'd like to attack this before it the little plastic hinge dealies actually break off.

 

[equill]

I've been interested in ABS (acrylonitrile butadiene styrene) to ABS bonding for a while, but your question prompted me to look for some clues. A quick Google on 'ABS bonding' netted the information that ABS is soluble in acetone (I'm not completely convinced, despite that styrene is a component. So should the acrylic portion dissolve in chloroform, but ...), methyl ethyl ketone (a solvent in PVC cements), tetrahydrofuran (not for the unprepared) and methylene chloride. I shall give it a go and report back.

If your parts are but cracked, and not separated, running pure solvent into the cracks, and then leaving the parts pressed firmly together for several days, should be very effective. For large gaps, however, some of the same plastic dissolved in the solvent is a better bet as a gap-filler. The only rub at the moment is, 'Which solvent?'

There appears to be a commercial cement for the purpose, which you may care to look at. The makers play very cute about the solvent, however, which turns out to be methyl ethyl ketone 99%, with 0.8% ABS dissolved in it. At least MEK is readily obtainable for electrical conduit joining.

de

 

[alk]

MEK will do it. MEK is also highly carcinogenic. Be careful when using the stuff.

I've had reasonable luck with super glue (of all things). I don't know which particular supplier I was using or if a solvent was an ingredient. I had a problem with some cracks on a camera recently, and the stuff melted and rebonded the plastic "rivets" that held the case together. Worked like a charm.

Peace,

Drew

 

[Bunsen]

I used superglue recently to fix some broken Bakelite. Searched the web, and that was the recommended glue. /shrugs/ Worked a treat.

 

[equill]

Bakelites are brittle phenol formaldehyde resins. Common forms of 'superglue' are cyanoacrylates, best used for non-porous materials to make a tenacious bond, which has, however, low shear resistance. Franklinstein may do best to stay with cements that are more closely related to his materials and their particular stresses during use.

It should also be added that MEK is not considered to be a high risk to animal (including that of H. sapiens sapiens) health. What risk there is, which is flammability rather than toxicity, can be ameliorated with effective ambient ventilation.

de

 

[Charlieman]

Thanks for the info about MEK, Equill. For twenty years, it has been difficult to buy as an industrial chemical in the UK -- it was commonly used in the printing industry prior to that time to rejuvenate offset blankets and rollers, and the offset roller application has a clear connection to vintage calculators and printers.

From the Health and Safety notes, I understand that MEK is still available in the UK (and presumably EU) as a *scientific* chemical (and *professional* industrial chemical).

Returning to the original post, what sort of size cracks are you talking about? How big are the "little hinges"? A photo might help. Gluing tiny things to anything rarely works, but there are alternatives.

 

[Charlieman]

Common forms of 'superglue' are cyanoacrylates, best used for non-porous materials to make a tenacious bond, which has, however, low shear resistance.

Cyanoacrylates were commonly used in the 1990s to attach "security devices" to computers etc. As Equill notes, the bond has poor shear resistance. If somebody has glued a security eye to your Mac or printer case, insert a screwdriver through the eye and twist clockwise until you feel resistance. Twist a bit harder and then relax. Repeat anti-clockwise. And iterate. Eventually, the glued-on fixing will fall off without damage to the case.

 

[equill]

Thanks for the info about MEK, Equill. For twenty years, it has been difficult to buy as an industrial chemical in the UK ... From the Health and Safety notes, I understand that MEK is still available in the UK (and presumably EU) as a *scientific* chemical (and *professional* industrial chemical). ...

After carefully paring off the moulded-on security icon with a sharp chisel, I carved a vertical rectangular hole in the case of my 512Ke, thereby obliterating the 'security lug' hole and as few signatures inside the bucket as possible. Into the hole I put the centre portion of the alternative battery cover, provided by Dove with the upgrade, and having ready-made provision to mount the SCSI DB-25F port. It was a force-fit, prevented from going right through the case by my also having left a rectangular flange of plastic around the shaped opening for the female DB-25 and locking pillars. The end result is a recessed well in which the female connector and pillars are flush with the outer case surface.

Then hied I me to Bunnings (a hardware supermarket chain) for some pure MEK, which is freely available in Australia as a PVC-U pipe cement primer for both electrical and plumbing use. It is used to clean/wet the ends of pipes before the more viscous cement is brushed on and the pipes are force-fitted into their unions. Into about 50mL of MEK in a glass jar with a screwcap and gasket I put the surviving fragments of the Dove battery door, and left the lot overnight. The solution was still quite freely-flowing, but completely opaque from the dissolved ABS. With a piece of 2-mm brass tube, crimped almost shut at one end to make a 'pipette', I ran ABS solution into the inside and through-case joints. Worked a treat. After four applications at intervals to allow the free MEK to evaporate, I could no longer see the joints. I'll give it a week to let the MEK dry thoroughly, and then see how the joint survives the insertion force of attaching a SCSI cable to the female SCSI port mounted on my improvised recess.

So, MEK is a good solvent for ABS plastic.

de