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#21
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Aluminum composite reportedly stronger, lighter than carbon
On Wed, 10 Oct 2007 15:49:48 -0700, Fred the Red Shirt
wrote: On Oct 9, 11:53 pm, Steve Hix wrote: In article .com, Fred the Red Shirt wrote: ... Obviously you have not seen how a telescope mirror ages over the years. Guess again. Well then you should have observed that the transparency increases between cleanings. It's easy to recoat the mirror, so it's not so much of a problem, certainly less of one than dealing with silver corrosion. While it is not a technologically daunting task, it is not cheap for IF you have the equipment (vacuum chamber, heater for vaporizing Aluminum) it's relatively simple. One of our Astronomy club members does up to 10 or 12" for the locals. IIRC his favorite source of Aluminum is peeling the foil off gum wrappers although regular Aluminum foil works. It just takes more power. It doesn't take a super high vacuum either. Just one high enough to develop a plasma although that's not part of the process. On local used the chemical process for coating which worked pretty well, but the coating isn't nearly as even as vacuum deposition. larger mirrors especially when you consider shipping. I have a 17.5" mirror that will need realuminizing when I finally get around to putting it into a scope. It has been cleaned exactly once, but the coating is nearly gone entirely after 30 years in storage. Offhand, do you know anyone who recoats mirrors that size? Not that size, but there are a number of labs that do the work and I think I saw a couple of links listed. Roger (K8RI). |
#22
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Aluminum composite reportedly stronger, lighter than carbon
On Thu, 04 Oct 2007 02:36:51 -0500, cavelamb himself
wrote: Orval Fairbairn wrote: In article , "Wayne Paul" wrote: I just saw the following on rec.aviation.soaring and thought it might be of interest to this group. From the Delft University: http://www.compositesworld.com/news/...October/112036 Wayne HP-14 "6F" http://www.soaridaho.com/Schreder They have to get the Young's Modulus to match, otherwise either the aluminum or the matrix material will be carrying most of the load. Anything coming from anything labeled "Green" is automatically suspect, in my book, until I see a second (or third) opinion. Copy that. Orv. I was a little bewildered how replacing he construction material was going to save mega bux. Seems more like it would COST mega bux to redesign for it... Oh well, it's Green, therefore wonderful? I don't think I'd call Aluminum a "green" material. Roger (K8RI) Right... Richard |
#23
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Aluminum composite reportedly stronger, lighter than carbon
On Oct 15, 4:44 am, "Roger (K8RI)" wrote:
On Wed, 10 Oct 2007 15:49:48 -0700, Fred the Red Shirt wrote: On Oct 9, 11:53 pm, Steve Hix wrote: In article .com, Fred the Red Shirt wrote: ... Obviously you have not seen how a telescope mirror ages over the years. Guess again. Well then you should have observed that the transparency increases between cleanings. It's easy to recoat the mirror, so it's not so much of a problem, certainly less of one than dealing with silver corrosion. While it is not a technologically daunting task, it is not cheap for IF you have the equipment (vacuum chamber, heater for vaporizing Aluminum) it's relatively simple. One of our Astronomy club members does up to 10 or 12" for the locals. IIRC his favorite source of Aluminum is peeling the foil off gum wrappers although regular Aluminum foil works. It just takes more power. Surface Preparation (cleaning) is extremely important as traces or organics (from handling( will prevent adhesion of the aluminum. Texereau recommends final cleaning by electron bombardment in the vacuum chamber. It doesn't take a super high vacuum either. Just one high enough to develop a plasma although that's not part of the process. On local used the chemical process for coating which worked pretty well, but the coating isn't nearly as even as vacuum deposition. Described by Texereau also, assuming you mean the chemical silvering process. larger mirrors especially when you consider shipping. I have a 17.5" mirror that will need realuminizing when I finally get around to putting it into a scope. It has been cleaned exactly once, but the coating is nearly gone entirely after 30 years in storage. Offhand, do you know anyone who recoats mirrors that size? Not that size, but there are a number of labs that do the work and I think I saw a couple of links listed. The place to ask would be sci.astro.amateur. I asked OP as it looked like maybe he might know one. -- FF |
#24
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Aluminum composite reportedly stronger, lighter than carbon
On Fri, 26 Oct 2007 09:53:04 -0700, Fred the Red Shirt
wrote: On Oct 15, 4:44 am, "Roger (K8RI)" wrote: On Wed, 10 Oct 2007 15:49:48 -0700, Fred the Red Shirt wrote: On Oct 9, 11:53 pm, Steve Hix wrote: In article .com, Fred the Red Shirt wrote: ... Obviously you have not seen how a telescope mirror ages over the years. Guess again. Well then you should have observed that the transparency increases between cleanings. It's easy to recoat the mirror, so it's not so much of a problem, certainly less of one than dealing with silver corrosion. While it is not a technologically daunting task, it is not cheap for IF you have the equipment (vacuum chamber, heater for vaporizing Aluminum) it's relatively simple. One of our Astronomy club members does up to 10 or 12" for the locals. IIRC his favorite source of Aluminum is peeling the foil off gum wrappers although regular Aluminum foil works. It just takes more power. Surface Preparation (cleaning) is extremely important as traces or organics (from handling( will prevent adhesion of the aluminum. Texereau recommends final cleaning by electron bombardment in the vacuum chamber. Which reminded me, my friend uses that plasma for the final cleaning. Thats a lot of electronic bombardment. :-)) It doesn't take a super high vacuum either. Just one high enough to develop a plasma although that's not part of the process. On local used the chemical process for coating which worked pretty well, but the coating isn't nearly as even as vacuum deposition. Described by Texereau also, assuming you mean the chemical silvering process. I do and it was. larger mirrors especially when you consider shipping. I have a 17.5" mirror that will need realuminizing when I finally get around to putting it into a scope. It has been cleaned exactly once, but the coating is nearly gone entirely after 30 years in storage. Offhand, do you know anyone who recoats mirrors that size? Not that size, but there are a number of labs that do the work and I think I saw a couple of links listed. The place to ask would be sci.astro.amateur. I asked OP as it looked like maybe he might know one. I had forgotten about that group and I used to follow it. Roger (K8RI) |
#25
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Aluminum composite reportedly stronger, lighter than carbon
On Oct 26, 2:04 pm, "Roger (K8RI)" wrote:
On Fri, 26 Oct 2007 09:53:04 -0700, Fred the Red Shirt ... Surface Preparation (cleaning) is extremely important as traces or organics (from handling( will prevent adhesion of the aluminum. Texereau recommends final cleaning by electron bombardment in the vacuum chamber. Which reminded me, my friend uses that plasma for the final cleaning. Thats a lot of electronic bombardment. :-)) How big is his vacuum chamber? What sort of vacuum pump(s) does he use? One large enough for a 17.5" mirror is rather non-trivial. Assuming a 20" diameter cylindrical chamber, the top and bottom would need to support over 3000 pounds each, if the work is done at sea level. -- FF |
#26
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Aluminum composite reportedly stronger, lighter than carbon
Fred the Red Shirt wrote:
How big is his vacuum chamber? What sort of vacuum pump(s) does he use? One large enough for a 17.5" mirror is rather non-trivial. Assuming a 20" diameter cylindrical chamber, the top and bottom would need to support over 3000 pounds each, if the work is done at sea level. Is it really that hard to build a vacuum chamber? Seems to me that the most pressure it'll ever experience is about 15psi (1 bar), while it's trivial to build/buy pressure containers that can handle 10-100x that much (positive) pressure. Certainly if building a 1 bar vessel 20" in diameter is daunting, building a submarine (or worse, a deep-sea bathyscaphe, which have reached depths of almost 36,000 feet below sea level, resisting a pressure of about 1,100 bar) would be unthinkable. Or am I missing something? Mark "under pressure" Hickey |
#27
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Aluminum composite reportedly stronger, lighter than carbon
"Mark Hickey" wrote in message ... Fred the Red Shirt wrote: How big is his vacuum chamber? What sort of vacuum pump(s) does he use? One large enough for a 17.5" mirror is rather non-trivial. Assuming a 20" diameter cylindrical chamber, the top and bottom would need to support over 3000 pounds each, if the work is done at sea level. Is it really that hard to build a vacuum chamber? Seems to me that the most pressure it'll ever experience is about 15psi (1 bar), while it's trivial to build/buy pressure containers that can handle 10-100x that much (positive) pressure. Certainly if building a 1 bar vessel 20" in diameter is daunting, building a submarine (or worse, a deep-sea bathyscaphe, which have reached depths of almost 36,000 feet below sea level, resisting a pressure of about 1,100 bar) would be unthinkable. Or am I missing something? Maybe, maybe not. Round pressure vessels keep their shell walls in tension, hence the more pressure the better they hold their shape. Vacuum vessels are just the opposite, and quite often much easier to collapse than one might naturally assume. I can say I once built a round vacuum chamber out of rolled 1/4" aluminum. It was approximately 18" long and 18" in diameter. The bottom was 3/8" aluminum, and the top was 1" clear plastic. The chamber was successful with up to an near perfect vacuum, and used many times without failure. At maximum vacuum, the bottom would dish approximately 1/8 to 3/16" inch, an the plastic top would dish about 1/2". I have a chamber I use now for another purpose, but it is only 6" in diameter. The top for it is just 3/16" tempered glass. Hope the number might help your estimates. Max |
#28
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Aluminum composite reportedly stronger, lighter than carbon
Maxwell wrote:
"Mark Hickey" wrote in message ... Fred the Red Shirt wrote: How big is his vacuum chamber? What sort of vacuum pump(s) does he use? One large enough for a 17.5" mirror is rather non-trivial. Assuming a 20" diameter cylindrical chamber, the top and bottom would need to support over 3000 pounds each, if the work is done at sea level. Is it really that hard to build a vacuum chamber? Seems to me that the most pressure it'll ever experience is about 15psi (1 bar), while it's trivial to build/buy pressure containers that can handle 10-100x that much (positive) pressure. Certainly if building a 1 bar vessel 20" in diameter is daunting, building a submarine (or worse, a deep-sea bathyscaphe, which have reached depths of almost 36,000 feet below sea level, resisting a pressure of about 1,100 bar) would be unthinkable. Or am I missing something? Maybe, maybe not. Round pressure vessels keep their shell walls in tension, hence the more pressure the better they hold their shape. Vacuum vessels are just the opposite, and quite often much easier to collapse than one might naturally assume. I can say I once built a round vacuum chamber out of rolled 1/4" aluminum. It was approximately 18" long and 18" in diameter. The bottom was 3/8" aluminum, and the top was 1" clear plastic. The chamber was successful with up to an near perfect vacuum, and used many times without failure. At maximum vacuum, the bottom would dish approximately 1/8 to 3/16" inch, an the plastic top would dish about 1/2". I have a chamber I use now for another purpose, but it is only 6" in diameter. The top for it is just 3/16" tempered glass. Hope the number might help your estimates. Max You know, an ABSOLUTE vacuum is only 15 psi... |
#29
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Aluminum composite reportedly stronger, lighter than carbon
"cavelamb himself" wrote in message ... You know, an ABSOLUTE vacuum is only 15 psi... Correct, one atmosphere, what is your point? |
#30
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Aluminum composite reportedly stronger, lighter than carbon
On Nov 1, 6:07 pm, "Maxwell" wrote:
"cavelamb himself" wrote in message ... You know, an ABSOLUTE vacuum is only 15 psi... Correct, one atmosphere, what is your point? Wrong. Absolute vacuum is 0 psia. At sea level that will be about -14.7 psig. Go to Death Valley or underwater and it will be less. -- FF |
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