Film-Tech Forum ARCHIVE: What is a gate cooling system??

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Posted by Andy Davis (Member # 262) on 12-13-1999, 11:26 PM:

A friend recently told me about a "gate cooling system" and I was wondering what this does and why it would be beneficial. My best guess is that it has something to do with preventing the metal from expanding and warping, thus reducing distortion. But wouldn't projector manufacturers compensate for this? Please enlighten me.

Posted by Ken Layton (Member # 133) on 12-13-1999, 11:46 PM:

You probably mean "water cooled gate" option.
The back of the gate casting has a small loop of copper tubing attached. Water flowing thru the tubing cools the casting thus reducing the temperature of the film to prevent blistering and scorching. Also keeps the machine cooler and improves focus. This option is usually used with 4000 watt lamps (particularly popular in driveins and 70mm equipped theaters).

Posted by John Pytlak (Member # 331) on 12-14-1999, 08:12 AM:

As Ken mentioned, "water cooled" gates are a good option for projectors using lamps greater than 4000-watts. The gates remain cool to the touch, increasing operator comfort during threading. The cooler gate rails are less likely to abrade the emulsion and "bake on" hardened deposits of gelatin emulsion from the film. However, water-cooled gates will NOT prevent film damage from excessive radiant energy ("hot spot" damage including blistering, scorching and dye-migration), since this damage is usually caused by excess radiant energy being absorbed by the film, and not by the film contacting the hot metal parts of the gate. Damage from excess radiant energy is best prevented by using efficient heat filters ("cold mirrors" or dichroic heat filters) and proper alignment and focus of the lamphouse optics to avoid "hot spots".

------------------
John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

Posted by Gordon McLeod (Member # 33) on 12-14-1999, 09:42 AM:

There are several methods of cooling a gate of a projector. The simplist is a stream of air which many shutters provide (the small l shaped blades attached to the shutter)
A blower as used by Simplex and Cinemecanica
and finally a water cell physically attached to the gate to cool that casting with a recirculated water (or coolant)
I always water cool above 2500 watts and usually there is very little perf abrassion even on green prints that high moisture level can cause sticking to the rails when hot

Posted by John Walsh (Member # 168) on 12-14-1999, 10:55 AM:

Would you consiter the Century "Cinefocus" a gate cooling option _and_ improved focus, or just a improved focus alone?

BTW, we sent two JJ's back to Century awhile ago to rebulid, and I got annoyed at them because they didn't drill out the hole for the Cinefocus while they were there. I wanted to add it later, and could'nt do it easily.

Posted by John Pytlak (Member # 331) on 12-14-1999, 01:30 PM:

The Century Cine-Focus system was primarily for improving focus stability by reducing heat-related film "flutter" in the gate. A blower provided positive air pressure on the lens side of the gate. The air flow was probably not enough to actually cool the film. Cine-Focus was often used in conjunction with a very efficient dichroic "Century UVIR" filter, which filtered out much of the harmful ultraviolet and infrared radiation from the lamphouse.

Air cooling and stabilization of the film is not a new idea. Kodak published a paper in the December 1949 SMPTE Journal: "Air Cooling of Motion Picture Film for Higher Screen Illumination" by Frederick J. Kolb. Willy Borberg published a paper "Modulated Air Blast for Reducing Film Buckle" in the August 1952 SMPTE Journal.

Posted by Stefan Scholz (Member # 147) on 12-14-1999, 03:14 PM:

The Bauer projectors always used a compressed air cooling system, which cooled the film and gate. Special compressors were installed in seperate rooms, and send an air stream of 800 hpa through the gate construction and ended in special nozzles to cool the film on both sides. The system prooved to be extremely efficientz, as most heat and absorbed radient energy was taken off the film.
Unfortunately the small compressors and the nozzles were quite noisy, and when the compressor was installed within the projector's foot, like at Bauer U2, it was impossible to sit next to it. This is mainly why the system disappeared. Water cooling has never been efficient in keeping absorbed energy off the film.
I remember, as beeing high school student, we placed nitrate film in the gate, ran our HI arclamps at 65 Amps, and disengaged the safety shutters. The film stayed in focus for nearly 40 minutes, and never caught fire.
Without the blower running, it caught fire immediately, the moment we opened the shutter. This proved quite well on effectiveness.

Posted by Ben Wales (Member # 92) on 12-14-1999, 04:23 PM:

It would be most essential on Xenon's on high current, where I work presently we just installed two new Cinemeccancia Victoria 8's with both water (chilled) gates and air cooled, in addition a heat filter, these have
been fitted with a 7kw Xenon consoles and run only 70mm film at present.

Posted by Gordon McLeod (Member # 33) on 12-15-1999, 12:06 PM:

The original ToddAo install at the Rivoli with the Gertner Ventarcs used refrigerated air jets to cool the film includeing nitrate 35mm

Posted by Charles Lubner (Member # 157) on 12-15-1999, 01:04 PM:

Which Rivoli Theatre? I know of several. I assume you're talking about the one in New York that is no longer a theatre?

I'm curious because I work at the Rivoli Theatre in Cedarburg, Wisconsin (suburb of Milwaukee). Wisconsin also has the Rivoli of LaCrosse, complete with original neon marquee!

Posted by Gordon McLeod (Member # 33) on 12-16-1999, 09:52 AM:

When mentioning Todd-Ao and the Rivoili THeatre (with suitably hussed voices) is referring to there first theatre in New York There are pictures of the booth in one of Cameron's books on projection