开云体育

Exciting Moments :)

James Lerch #12 开云体育 Greetings All, ? To stimulate a little conversation, I thought I'd recount a few of my more "Exciting" moments during a few recent coating runs :) ? Good Times #1 ? Things were going well, but perhaps it was a little cold for Florida (~40f).? So I'm in the process of evaporating some Al, actually I was almost done.? Anyway I've got my eyeball right next to my 1/4" thick viewing window, watching the 'Magic' as the coating forms, when I hear a LOUD "TINK" followed by a hissing noise!!!!!!!!!!!!!! ? After quickly turning my head away from the chamber and stepping back a few paces, I waited for the chamber to implode :)? Thankfully it didn't, but ya never know..? ? After a few seconds I regained my courage and started looking around to see what was going on.? ? In one smooth motion,?I scanned the chamber and mirror inside, both of which appeared to be in one piece still.???Next on the list were the pressure gauges, which were rising rapidly!? I quickly killed the evaporative power source, Cold trap power and Diff-Pump power, and started closing the Diff-Pump valve as fast as possible, still not sure what was going on! ? After venting the chamber, I started investigating.? First the mirror coat looked pretty funny, with odd waves going across it.? After a little more investigation, I found the culprit.? The 2" diameter 1/4" thick plate glass electric pass thru for my heater power had fractured!!!? The odd waves on the mirror coating were caused as the air streamed into the chamber, past the evaporating Al, and onto the mirror. ? The glass appears to have fractured from thermal imbalance caused by the "Cold" chamber and the rather hot bolt conducting the high current into the tungsten heaters.? OOpps :) ? I've since replaced the 1/4" thick piece of glass with a nice big square piece of 3/4" thick scrap I had lounging around (BTW, a diamond wet saw cuts glass like butter!!)? No problems since then. ? One good thing I learned from this?is just how tenaciously my two part Silicone weather strip adhesive holds the glass the steel!? I thought I could just 'peel' the glass off the chamber with a razor blade, WRONG.? In the end I used a hammer to pulverize the glass into dust, which STILL stuck to the?chamber like no tomorrow!? In the end I had to use a 4" grinder to grind the silicone and remaining bits of glass of the steel chamber. ? Good Times #2 ? I'm with a friend, demoing the 'Junkyard Coating rig',? things are going really smoothly.? We just finished the fascinating glow discharge light show and had starting evaporating Al, onto the mirror.?Next thing I know the lights are out and everything is QUITE!? Ahh HELL the breaker TRIPED! ? Fortunately I was smart enough to use a electro-pneumatic valve on the Diff pump fore line, So I know when the power went off the valve would have snapped shut protecting the hot oil in the diff pump.? UNFORTUNATLY I wasn't smart enough to turn the switch controlling the valve off PRIOR to resetting the breaker! (WHOOPS!) ? Since it took a few minutes to blindly find my way to the breaker box, AND my rough pump won't hold a vacuum when its turned off.? The moment I flipped the breaker the diff pump fore line valve snapped open, exposing the diff pump to the much higher than normal fore line pressure.? As you can guess this made a NASTY mess inside the chamber, as the high pressure wave went backwards thru the diff pump and blew hot oil all inside the chamber! ? NOTE TO SELF, its time to install that relay and a pair of push buttons to control the fore line valve!!!? Worse part is I had considered doing this during the build, but never got around to it :(? ? The ideal mechanism would be a push button that would trigger a relay, the relay would in turn power itself AND power the fore line valve.? To close the valve a second push button would interrupt the power to the relay, allowing it to turn off, thus powering down the relay AND closing the fore line valve.? In the event of a power outage, when the power came back on the valve wouldn't instantly snap open making such a horrendous MESS! :) ? I guess we'll chalk this one up to a little "On the Job Training" :)? Oh, and BTW, the mirror in the chamber was OH MY GOD ugly :O? ? Amazing what a little hot oil on fresh Al will do! ? ? I guess that's it for interesting experiences lately, anyone else have some to share? ? ? Take Care, James Lerch (My telescope construction,testing, and coating site)

Previous Topic Next Topic