bonded safety glass - Videokarma.org TV - Video

DaveWM · #1 01-31-2011, 12:48 PM

I don't want to debate the merit of rebonding glass, just want to know if anyone has any experience in CRT construction and how it was done.

I assume the glass was prepped with a degreasing agent, then it looks like the lens was somehow held in place, I assume a jig, then the plastic tape was applied to seal the edges and a resin was poured in thru the little plastic port I see on them. if so it would have to have been pretty low viscosity to not form bubbles or have trapped air pockets?

any ideas on the resin used and a modern equivalent? I was considering trying to do this on an old dud to see how it would work out.

jr_tech · #2 01-31-2011, 01:41 PM

What I have seen a small re-builder do :

1. Clean glass surfaces.
2. Support the tube face up.
3. Lay spacer rods ( nylon? 3/16"?) on the face of the tube on a diagonal, with the ends sticking out about 2" apart at the top of the tube.
4. Place safety glass in position, center and tape around the tube, leaving a gap between the rods.
5. Stand the tube up (support the neck) with the gap at the top.
6. Pour/inject the (heated) resin mix through the gap, slowly to avoid bubbles.
7. When almost full, pull the spacer rods out, top off and tape the top gap.
8. Rest tube on its face (on rubber Donut?) until resin cures... tape leaks if necessary. Any bubbles should rise to the edges of the tube, or may be "fished" with a small piano wire if necessary.
I think the resin was PPG 5252.
jr

DaveWM · #3 01-31-2011, 03:14 PM

ah a heated resin, was it two part like an epoxy or just the heat alone?

I was thinking of useing double sided foam tape to space out the lens, all around the perimeter (would aid in the sealing as well) just like done when just the lens is removed and replace with no bonding agent, but this time do it all around, then do the tape and while holding the tube on its side careful not to deflect the lens, pour in a thin epoxy, close up the opening with some more tape, set down on edge support doughnut.

DaveWM · #4 01-31-2011, 03:20 PM

I guess the real issue is how well the epoxy would adhere to the glass in my previous post, with out knowing that, it would be a waste of time as far as replicating the old bonded technique.

old_tv_nut · #5 01-31-2011, 03:35 PM

Don't know, but I would worry about epoxy being too ungiving - either putting stress on as it cures, or separating. Isn't the original bonding agent rather jello/rubbery (no personal experience, just asking)?

jr_tech · #6 01-31-2011, 03:35 PM

2 part... I think the catalyst was Methyl Ethyl Ketone Peroxide, like one would use with polyester resin. I don't know if the double sticky tape would inhibit curing or cause bubble problems... could take a while to develop a viable process.

jr

update: Yes, the bonding material was fairly "rubbery".

jeyurkon · #7 01-31-2011, 04:08 PM

Sylguard 184 would work quite well without heat. It is a two part silicone RTV.

But, it's expensive.

eberts · #8 01-31-2011, 09:07 PM

In the big tube factories, the resin was a 2 part mix. 2 hoses going to an injector nozzle. The nozzle was inserted into a little plastic round hole which you will see on any Bonded color tube. The operator pressed the button on the nozzle gun, the resin was forced into the cavity very fast under pressure. took about 20 seconds. Next.
In big factories, 90 color tubes were manufactured per hour, 24 hours a day. Minimum batch of one type of tube was 7000 units.

ctc17 · #9 01-31-2011, 10:31 PM

Quote:

Originally Posted by DaveWM

I was thinking of useing double sided foam tape to space out the lens, all around the perimeter (would aid in the sealing as well) just like done when just the lens is removed and replace with no bonding agent, but this time do it all around, then do the tape and while holding the tube on its side careful not to deflect the lens, pour in a thin epoxy, close up the opening with some more tape, set down on edge support doughnut.

Thats how Scotty at hawkeye did it. 1/4" wide foam tape double sided. I bought a roll off him before he closed. It was expensive

andy · #10 02-02-2011, 10:27 AM

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bgadow · #11 02-03-2011, 10:44 PM

I'm just guessing, but I think it comes from absorbing moisture from the air. It would be good to know the real reasonl.

jeyurkon · #12 02-04-2011, 11:00 AM

Quote:

Originally Posted by bgadow

I'm just guessing, but I think it comes from absorbing moisture from the air. It would be good to know the real reasonl.

The real reason might be difficult to determine, especially if more than one type of material was used to bond safety glasses.

With PVA I would expect the problem occurs from drying out. If they didn't add any anti-microbial agents it could also be fungi or bacteria since PVA can biodegrade.

I'm only guessing, but by the time cataracts started to be an issue, bonded safety glass probably wasn't being used anymore and studying the problem wouldn't have been financially justified for the CRT manufacturers.

ctc17 · #13 02-04-2011, 12:20 PM

I have an RCA soaking in an unused bathtub right now. Its been in there for 3 weeks. Another week and ill pull it out and see whats happened.

I cant imagine water touching the stuff but we will all know shortly if the RCA style PVA separates with water.

bgadow · #14 02-04-2011, 10:11 PM

It will, eventually, but it can take a long time. My experience was that the Zenith/Sylvania "green" stuff responds a lot quicker to water than what RCA et al used.