[johnnyd]

Anyone no much about this unit? IS Mercury and metal halide the same thing?

NuArc 40-1k Mercury Exposure Unit
1k Mercury Lamp - 110V....Comes with new lamp
Vacuum Blanket size 39.5 x 29.75

 

[ole Jobe]

Mercury vapor light will have lower UV than metal halide, requiring longer exposure time. Most mercury vapor has a warm-up time requiring a shutter to be able to accurately guage exposure. God Bless.

 

[RichardGreaves]

Metal halide lamps for screen making are basically mercury vapor lamps that are specially "doped" - customized with metal additives - that "twist" visible light output into the UV-A range. This is what makes them a graphics exposure lamp. As Jobe wrote, mercury vapor is good, but metal halide is better.

The mercury vapor molecules don't work well until they get to an operating temperature of 2,000°F. That's why they need shutters and an integrator that doesn't measure time, but light volume. As the lamp heats up, the UV output starts as a trickle - then turns into a fire hose as the lamp gets up to operating temperature.

 

[BroJames]

How long does mercury needs to warm up?

 

[RichardGreaves]

I haven't made myself clear. Nobody measures how long - how long is a moving target. They measure UV volume or the temperature. The electricity in your area, the ballast and lamp age all effect warm up time.

As a DIY person, you must calculate the cost of a new lamp, vs. time lost in warm up. Only you know your cost of time and how much money you are losing replacing lamps.

I'm sure you will find you are losing valuable printing time 'saving' money in the screen room.

 

[BroJames]

Saving not too significant amounts of money is not the concern otherwise I wouldn't have sticked to halogens for that long (for 4 or so tubes). I had posted on quite a number of occasion that halogens is a very inefficient exposure unit and a poor source of UV.

My main interest is in knowing when it is safe to start exposing. I've tried 1 minute, then 2, jumping to 4 min. Am thinking to try either 3 o 5 minutes of warm-up next. I do not have as much time to test exposures as I used to last year. My only printing time is early morning at home but have been waking up late for a month or so now. The vision on my right eye deteriorated quite rapidly about that time (where I felt weak for 4-5 days, and don;t know if there is a relationship.Barely have enough time at home for actual printing and have to sub-out some jobs. The free time I have at my shop is spent on the net as I do not have sdpace or water to do printing related activities here.

Sorry for the OT but thought some info might help. Otherwise, will decide on either 3 or 5 minutes warm-up when the time comes.

 

[RichardGreaves]

OK, I'll try another tactic: How are you measuring your exposure?

or

I suggest 10 minutes.

 

[BroJames]

x x x

I'm sure you will find you are losing valuable printing time 'saving' money in the screen room.

This last sentence is actually my main problem - I am losing valuable printing time but not in trying to save a few bucks - just short of time to do simple tests.

OK, I'll try another tactic: How are you measuring your exposure?

or

I suggest 10 minutes.

I am not sure how to answer your first question. I warm up the lights for 4 minutes, then remove the cover to expose the screen? I will be exposing more than 1 screen with my mercury unit soon so the time for the second screen is my concern. A simple step test should go a long way in finding the "best" time for the second screen (if it won't be the same as the first screen) but really short of time now and hope to find more time a few weeks soon.

Your "I suggest 10 minutes" is the kind of "insight" I need at this point. At my current 4 minutes warm up + 2 minutes exposure for the first screen, it gears me up to expect variable amount of exposures for my 2nd to 3rd or 4th screens (unless I warm it up 10 minutes or so?).

I'll continue my test then with 5 minutes or more rather than 3 minutes. Thanks.

 

[BroJames]

Just an update

I haven't got time to test expose my 250w mercury lamp with a 10 minute warmup time or wait for it to reach 2000F but from a "cold start" 2min to 2min 20sec seems to give acceptable results. After that 1min to 1min-20sec also gives acceptable results for the 2nd and 3rd exposures. They are mostly spot images but I've also exposed a few 20-25lpi halftones for my 120mesh. Sorry, been quite busy lately and have not exposed more than 3 screens consecutively.

 

[LivingThread]

not to high jack, but when it comes to this "type" of bulb (meaning a bulb looking bulb and not a tube), what are the ratings we should be looking for?

You say something using the UV-A spectrum, but is there a rating? I mean when talking aquarium metal halides, you can spend a small fortune. What is the range of light we are looking for?

Im sure its a variable, but what makes for a good screen printing photopolymer exposure unit bulb?

 

[RichardGreaves]

... when it comes to this "type" of bulb (meaning a bulb looking bulb and not a tube), what are the ratings we should be looking for?

You say something using the UV-A spectrum, but is there a rating? I mean when talking aquarium metal halides, you can spend a small fortune. What is the range of light we are looking for?

Im sure its a variable, but what makes for a good screen printing photopolymer exposure unit bulb?

As was posted in post #2 - the target spectrum for UV energy is UV-A.

Metal Halide lamps 'doped' for screen exposure are the best for screen making.

 

[Blackwater]

As was posted in post #2 - the target spectrum for UV energy is UV-A.

Metal Halide lamps 'doped' for screen exposure are the best for screen making.

what manufacturer makes these doped halides? I can not find a MH made specifically for screen printing.