Air bubble in the repair

[Brent Deines]

Moved from "Pit Polish" thread. Originally posted by Screenman.

Although this may need another thread in response to Brent. When we get guys that have been doing repair for quite a while with unhappy results in for training, one of the problems we quite often find is that they are putting too small amount of resin into the injector to allow it to build up sufficient pressure. This varies from injector to injector but when the price of resin is a very small a part of your costs always make sure you have enough in the injector to do the job. I have just carried out a practise repair and before I used the pit filler I shook it up quite a bit. I then put the resin in the pit and picked out the many bubbles, curing tabbed and cured, guess what bubble in pit. Would someone else like to try it and see what results they get.
__________________
33,000 + screen repairs over 18 years and still learning.
Over

[Brent Deines]

[quote="screenman;26427"]Moved from "Pit Polish" thread. Originally posted by Screenman.

When we get guys that have been doing repair for quite a while with unhappy results in for training, one of the problems we quite often find is that they are putting too small amount of resin into the injector to allow it to build up sufficient pressure.
__________________
33,000 + screen repairs over 18 years and still learning.
Over

[Glassdoc]

I still say, his injector is too tight against the windshield. When he releases it and pit fills, thats when the bubble appears.. From air trapped in a leg of the break.. Why is it trapped? Too much injector head pressure flexing the crack so tight air cannot escape, until the injector is removed. It is not a resin problem, nor an equipment problem.. Its a operator problem. Try on the next repair to seat the injector with just enough pressure against the glass to seat but not leak.. Injector seal against glass and maybe 1/4-1/2 turn.. If it does not leak, your good..

[Gedis]

Ok, Im gonna have to try using more resin in the injector. When it comes to tightness I dont think it is to tight. I use half turn on the injector seal and and 4 half turns on the back ones.

What I have noticed is that the bubbles only come up to the drilled pit. I did 4 repairs where I had to drill and 4 without drilling. Quess what!!! The ones w/out drilling came out perfect and the ones that had drilling came up with tiny bubble.... So it has to be something to deal with that!!!

[Glassdoc]

The "back ones" are leveling bolts.. They may not require 4 full turns to level out the injector seal and they may require more than 4 turns on a curved windshield.. It differs.. But, to many turns on them and yes your injector will be applying alot of flex directly to the break area.. The fact that it did not happen to non-drilled repairs proves it is not a resin related issue.. Its operator error, somehow. The injector worked fine on non-drilled repairs also.. So...

Ok, Im gonna have to try using more resin in the injector. When it comes to tightness I dont think it is to tight. I use half turn on the injector seal and and 4 half turns on the back ones.

What I have noticed is that the bubbles only come up to the drilled pit. I did 4 repairs where I had to drill and 4 without drilling. Quess what!!! The ones w/out drilling came out perfect and the ones that had drilling came up with tiny bubble.... So it has to be something to deal with that!!!

[splitpit]

Maybe it's not actually an air bubble but simply the drill hole not getting resin all the way down into it in the first place.

[splitpit]

If you are wiping away excess repair resin before filling the pit it's possible that when you fill the pit, the pit resin is over lapping the drill hole prior to placing your curing tab in place, leaving a void in the drill hole that is not filled.

[Glass Doctors UK]

Watching everone trying to work this out is getting painful. so here is the answer.
As was said it only mostly happens when there is a drill hole which is a clue.

what do we know about the properties of resin?

1) We know that resin cures from the top down
2) we know that resin shrinks when it cures slightly.

Therefore when you cure it a hard skin forms on the surface and the resin then reduces in volume as it contracts after it cures, this has the effect of putting the resin below the hard cured top skin under a progressively increasing vacuum which is why any tiny bits of air like microscopic air bubbles in the pit finish or compressed air in the legs just next to the pit grow as the vacuum takes place during the curing process.

Now you know this you can work out a simple way to eliminate it by part filling the pit to eliminate the vacuum effect.

[Sunrise]

Hello (echo), Hello (echo), Hello (echo), Is there anybody out there?

[mrchip]

were here (echo) were here (echo)..bmw is no different than any other glass..was milky white before repair? if so sun did the damage...if not contaminated with moisture ...rain sensor I believe is at the bottom of window near middle..wouldn't fool with it