overmolding glass 2

[cambria]

I have a sensor which is a small delrin cylinder, to the end of which a small lens is adhered. I am contemplating an insert mold where we incorporate the lens into the body. The reason is to guarantee that the lens stays there over the lifetime of the product. We are currently using a custom epoxy and special processing techniques.

I will need a resin like delrin that is resistant to fluids - water, solvents etc.

Any suggestions?

 

[MikeHalloran]

Overmolding will not lock in enough strain to keep the joint from leaking.

You could mold a Delrin part with fingers or some other detail to locate and retain the lens while the epoxy cures.



Mike Halloran
Pembroke Pines, FL, USA

 

[cambria]

Thanks - we are doing things like that now and it is well established. The lens is accurately placed and held during cure. Its the amount of time and labor involved in the process that is a problem.

 

[MikeHalloran]

If the time is lost waiting for the adhesive to cure or just to kick, you might talk to your adhesive supplier about a photocured variant.

If the time is lost in assembling/ aligning/ centering the lens, that's a different problem.


Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

I second the motion by MikeHalloranfor a UV cured Epoxy if as he says this is your problem. Epoxy will be fastest and cheapest.

The only elastomer that is capable of making s good seal when used with glass in a situation AS posted are some of the Silicones.
I would contact someone like Nusil or Dow with your problem.

 

[cambria]

Thanks. None of that works. UV epoxy is not an epoxy. Solvents and vapors have adverse effects on UV adhesives. We use a custom optical epoxy that works well. The total time involved is what I need to reduce - lens attachment and assembly of the unit.

Returning to the question: overmolding of glass. Silicones dissolve in some solvents. Delrin, with a similar molecular outer shell to Teflon, does not like to share electron sites with other materials - ie its slippery and has other properties. Delrin is a bit higher temp during injection, was hoping to find an alernative or better material as well as methodology.

 

[unclesyd]

I will have to take exception to the statement that UV cured adhesives are not epoxies, granted there are other adhesives, mainly Acrylic that can be UV cured. I am setting here looking a two cut sheets and the MSDs of two materials that are definately label Epoxy. I have been using them as such for a number of years.
I think if you look around you can find an Epoxy that is UV curable. It may not be exactly the same base as the one you are mow using but it will be close. If you have the usage, people like MasteBond or any manufacturer of adhesives can put you on top on the correct formula.

May I ask what precludes the use of other based adhesives?

 

[cambria]

Thanks - I have tins of the UV stuff labeled epoxy as well.

But this is not the question the question was overmolding glass. I give up - I'll just go do it and see what happens.

 

[unclesyd]

Don't go away mad like everyone else I was try to help with a very limited knowledge about the problem posted in the OP. People on this Forum could care less about what the actual end use will or sales potential it is just one has to know the environment that your are getting into.

Would it be possible to treat the edges of the glass. I know this is an extra step but could speed up things overall.

Could you possibly use a ceramic cement?

http://www.sauereisen.com/adhesives/lamps.aspx

 

[cambria]

Thanks - not mad. The lens is a custom formed shape, in the form (if you will) of a bowler hat. Edage can be treated. At issue is the assembly time required for this portion of the process. The lens sits into a special base, and at this time we epoxy it down. This works but it is a precision process on a one by one basis. But this is not the entire assembly. We have other components that go into the assembly in a certain sequence, and the epoxy part causes a 24 hour dent in the operation. By overmolding I was hoping to have an assembly that would go immediately to the next step. We have been doing this for years now, and I have a "wall of shame" of all the cans of epoxies and adhesives we have tried. Environment: high density vapor fumes in a variable temperature but not exceeding 60 C. If I have to stay with epoxy, I have the one now. On ceramic, we in fact have another project - same technology - where we use ceramic cement with success. I am trying to find an alternative to the epoxy process.

 

[Compositepro]

Cure times for epoxies can be greatly shortened by using a higher temperature. Are you doing a room temp. cure? A 24 hour cure at room temperature may give less cure than 1 hour at 150F.

Higher temp cures (and over molding) introduce issues with differing CTE between glass and plastic.

 

[cambria]

Pot time is 25 minutes (custom epoxy) then overnight room temp. Proof will be in the pudding. We shall try it out. The first response in this string needs to be checked out - that the seal wont be tight enough.

 

[unclesyd]

Have you considered the use a solder alone are with an adhesive for two part system?

Tow sites that have information on glass soldering.

http://www.indium.com/search/search.php?zoom_query=glass+soldering

http://www.aimspecialty.com/index.html

 

[cambria]

I had great hopes for Indium solders, comes out they dont like fluids much. We were looking at glass frit - same idea in a way - "low temp" glass. We looked at going with an inductive heater - use an aluminum base for the lens - and melt the glass or the indium solder. The Indium suppliers felt they could not guarantee the material in fluids or polarized fluids. Glass frit might be the answer but it seemed like we were exchanging one long process with another.

 

[lumenharold]

When you say a bowler hat profile I am picturing a pronounced lip at the lens edge. Would it be an acceptable alternative to over-molding to ultrasonically or chemically weld a retaining ring over edge of the lens? I think you would be facing the same issues as over-molding (loose fit) but you won't have the tooling and handling issues. Perhaps at that point you could use a fast cure epoxy as a sealer and let the plastic do the retaining.

Harold
SW2010 SP1.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[cambria]

Thats exactly where we are now. Delrin body, aluminum base, epoxy drops, lens goes on, delrin retention ring with ultrasonic weld. What I had been hoping for is a magic one shot deal where I could overmold the lens onto the body.

I guess, in the end, we have evolved the answer anyway. There are probably other ways, but reading this string of responses I think leads you to where are now, (+ or -).

thanks everyone for your time and good thoughts.

 

[unclesyd]

If you haven't talked to these people in you quest I would definately give Reltek a call as they cover a lot of ground. If nothing else something store in the wind farm.

http://www.reltekllc.com/adhesives-for-glass-and-ceramics.html

 

[lumenharold]

Last night when I was typing my suggestion for the retaining ring I was trying to recall the company we worked with on a quote a couple years ago. Apparently they over-mold glass frequently.

http://www.apollooptical.com/

Harold
SW2010 SP1.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[MikeHalloran]

All I can think of for a one-shot deal is to eliminate the retaining ring and ultrasonic bonding,
and extend the main body so that the lens seats in a counterbore,
then apply the adhesive at the bottom of the c'bore, and press the lens in.

The disadvantage is that it mechanically centers the lens on the o.d., the axis of which is not always coincident with the optical axis of the lens. If you've been centering the lens optically by manipulation, or mechanically by using the sagitta of the lens and the bore of the retaining ring, it would be a step or two backward.




Mike Halloran
Pembroke Pines, FL, USA

 

[cambria]

Thank you for the links. Promising. Time will tell. Thank you all for your inputs, each were valuable contributions.

doug