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Topic: Enarc reflectors cracking - why?

Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 11-09-2002 03:05 PM

Subject says it. I was talking with a theatre owner today who has had several Enarc reflectors in a row crack in the middle of a reel (which rules out the possibility of an operator opening the lamphouse before it cools down). He currently has two cracked reflectors and is reluctant to buy new ones since his last few have only lasted a few days before cracking.

Any thoughts as to what might be causing this? Does anyone besides Marble sell Enarc reflectors?

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Dick Prather
Master Film Handler

Posts: 259
From: Portland, OR, USA
Registered: Feb 2002

posted 11-09-2002 03:28 PM

Scott, It sounds like the mount may be too tight so when the mirror heats up and expands it cracks. Does the crack start by one of the mounts or retainers? I don't know what kind of quality the reflectors have but there must be enough room to expand. If he has an origional one he could compare diameters. Another problem is soot from the carbons usually going up the reflector. If this is not wiped off the mirror will crack. Again because of the soot preventing even expansion. We use to use a baby diaper, new of course, to clean them and a good Bon Ami cleaning when ever needed.

Unless someone has a stash of them, Marble is probably his best bet.
Dick

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 11-09-2002 03:43 PM

The CPI/Marble reflectors from Japan are metal backed and tend to hinder expansion so they are more prone to cracking
Even if the crack it reely doesn't effect the light output all that much
The other possiblity is downdrafts coming back down the stack blasting it with a blast of cold outside air
There is in the national carbon bullitens info on the different types of cracks

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Jack Ondracek
Film God

Posts: 2348
From: Port Orchard, WA, USA
Registered: Oct 2002

posted 11-09-2002 06:28 PM

Back in my Enarc days, we learned the hard way about the soot build-up that Dick mentioned. Slow striking was one culprit, as keeping the carbons close together (or maybe even touching too long) could result in a slanted (sooty) flame aimed at the reflector.

As I recall, the diaper treatment worked best between carbon trims while the reflector was warm. The diaper would tend to "bind" on the glass until you polished off the surface soot, then it would move much smoother. The Bon-Ami treatment was required much less often, and the reflectors lasted much longer.

After that, our major problem was with the copper drippings pitting the glass... but that's another story, I guess.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 11-09-2002 08:18 PM

"Temper" the new mirrors. You won't have any problem with them breaking.

It is a procedure that can take several hours to do. From a cold start, strike your arc and let it run for 30 seconds, and break the arc. Let it sit for another 30 seconds, and re-strike. Let it run for about a minute, then break the arc. Let it sit for another 30 seconds, and re-strike. let it run for a couple of minutes, and break the arc, let it cool down for a minute and re-light. Continue this procedure until you can get a full 20 minute run.

It has been many years since I tempered a mirror, so my timing procedures could be rusty. I am sure Dick and some others will give you a more accurate minute run and cooling run that I can.

But if you have the damper set properly and your tail flame is correct along with the mechanical positioning of your lamp (such as the projection angle) and the updraft is normal, there should not be any problems with mirror breakage.

As good housekeeping practice dictates, get a proper "strike" so soot is not blown all over the place, and the mirror should be wiped free of the soot and ash after each reel. Be sure to use a lint-free clean rag when you do this.

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 11-10-2002 09:28 PM

Thanks for the suggestions; I'll pass them along when I run the afternoon shows there tomorrow.

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 11-10-2002 11:01 PM

We used to alleviate somewhat, the problem of copper drippings pitting the reflectors by putting steel wool in the "ash-tray" into which the drippings fall. Splattering was much less of a problem.

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