Vacuum by the side of road

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Rich Feldman
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Vacuum by the side of road

Post by Rich Feldman »

Near my work is a road where people sometimes leave unwieldy trash, to avoid a costly visit to the dump. This week a most unusual object appeared: a single-use bottle of high vacuum.
20230105_113214.jpg
I bet it would float in water, neck-up. Might it serve as a sensitive hydrometer for some range of liquid density?

It was there on Tuesday and Thursday. The way I've de-vacuumed a few of these is to file a scratch on evacuation tip, then break it off by tapping far end of a long straight stick. A rain-swollen creek is not far away, but inappropriate and unsafe to approach for the float experiment.
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Bob Reite
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Re: Vacuum by the side of road

Post by Bob Reite »

Back in my days of TV set repair, I would just cut off the evacuation tip with side cutters of dud CRTs that were not going to get rebuilt.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Rich Feldman
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Re: Vacuum by the side of road

Post by Rich Feldman »

Thanks for words of experience, Bob.
In the meantime I remembered a different way to gently let the vacuum out:
Punch through thin sheet metal at the EHT anode connection with a sharp awl.

I came that way this morning after packing safety glasses etc. Someone had moved CRT onto the grass and broken off its neck. Now is it worth getting help to retrieve the 100 pound (?) object for float experiment,then having to pay $25 to drop it off at e-waste facility?
20230106_111306.jpg

Who thinks it would sink? Float with screen horizontal? Float at an angle?
Opportunity for some fun with an obsolete artifact, one specimen of more than 1 billion manufactured.
All models are wrong; some models are useful. -- George Box
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Rich Feldman
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Re: Vacuum by the side of road

Post by Rich Feldman »

Experiment will be done next week. I'm not so sure the CRT will float level. Where's center of buoyancy, and how does it move when the float heels at small angles?
bigtube3.jpg
bigtube1.jpg
After more consideration, center of gravity is probably even lower than CB, unlike typical boats and ships.
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Richard Hester
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Re: Vacuum by the side of road

Post by Richard Hester »

Yeah, I saw that thing, too, as it was right up the road from where I work. That particular road is a magnet for donut artists and clandestine dumpers of various garbage and non-functional appliances.
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Rich Feldman
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Re: Vacuum by the side of road

Post by Rich Feldman »

Richard, sounds like we are work neighbors. Maybe meet for lunch some day.
Meanwhile I don't want to wear out my welcome in Shipping area at work.
Scrounged a wooden crate that's almost perfect size for float experiment, except much deeper than necessary.
I need to get the CRT weighed, and now guess it's close to 200 pounds. (?? Was lifted into my car by hand with 1 helper.)
Be fun (in a nerdy way) if it can be floated in 1 cubic foot of water.
crt_lift.jpg
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Bob Reite
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Re: Vacuum by the side of road

Post by Bob Reite »

200 pounds? And to think that I lifted those things by myself back in the day.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
Richard Hester
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Re: Vacuum by the side of road

Post by Richard Hester »

Most of that weight is likely the faceplate of the CRT. The last jug-style TV I bought was a 27" Panasonic - the size was dictated by what I could lift. The load was very unbalanced (heaviest at the front), and there were no handles molded into the TV case to assist with lifting.
Tyler Meagher
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Re: Vacuum by the side of road

Post by Tyler Meagher »

I think it will float assuming the TV screen does not have a hole in it. At 200lbs it will float in fresh water if its volume is at least 3.2 ft^3. The orientation will be where the CG and the CB are aligned pointing to the center of the earth. It will have a specific orientation because the CG and CB are different. Looking at the picture I would guess the neck will be pointing up since the the front looks to have more mass and the center of buoyancy looks closer to the neck. Our robosub team did some simple measurements on our autonomous sub to find the center of gravity and the center of buoyancy. The location of these are important for thruster placement. By hanging the object by a single point creates a line pointing through the CG, or CB if submerged in water. The intersection of a couple measurements will provide the location of the CG or CB. The volume is easily measured by weighting the object in water compared to in air. I'm interested in seeing the results of your measurements.
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Rich Feldman
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Re: Vacuum by the side of road

Post by Rich Feldman »

We did the float experiment for the first time yesterday. Star Wars day and the last day before my CRT-picking partner begins a months-long road trip.
20230504_190212.jpg
The 250-pound CRT floated, screen horizontal, in 1/4 of its weight of water. Draft between 7 and 7.25 inches.
We can be much more scientific next time.
Here's a picture in which water hasn't been partly drained.
crt_float_1.jpg
Along they way, CRT short edges were fitted with some steel channels for easy lifting and tilting using an engine hoist.
In this picture the trunnion pins are offset, making CRT hang at an angle, from which we located the center of gravity. Look how flat that screen is, in final generation of consumer color CRT's.
crt_float_2.jpg
It's nice to be easily amused. :)
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Jim Kovalchick
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Re: Vacuum by the side of road

Post by Jim Kovalchick »

I thought it would continuously flip horizontally until smacked on the side 🤣...a joke only old timers might get.
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Rich Gorski
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Re: Vacuum by the side of road

Post by Rich Gorski »

A good smack on the side was my last resort if the horz sync knob didn't work. Hey, think of all the leaded glass viewports that could be made from that faceplate for a fusor. Very little if any X-ray will get through at least up to 31.5kV. Btw, that steel band around the perimeter is under tension. It puts the faceplate under compression as a cheap form of implosion protection. During my days at Zenith Electronics Corp there was a department dedicated to perfecting this implosion protection system. They had a pendulum swing a heavy weight into the faceplate to test that glass didn't spray out at the viewers if a kid decided to throw his toy at it. The system worked.

Trinitron used Sony's advanced electron gun system. It's really amazing how complex the electron optics was in the last days of the CRT. They were not simple rotationally symmetric Einzel lenses but complex 3D electrode shapes that encompassed all three beams. These shapes required 3D electron optics software to design.
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