msxc wrote:Hello again!
Hello.
I don't have lots of space in my lab/darkroom, so that was a real limiting factor in planning things (room much smaller than what Graham Saxby recommends for a holo-lab, maybe enough for SBRs
).
From looking online I couldn't get a good idea for the details of good laminar flow bench (I asked about it here- thanks for all inputs!
http://holoforum.org/forum/viewtopic.php?f=6&t=442).
I build my improvised laminar flow hood in rush, and already spend too much time finding available materials. I made everything wrong!
Space in lab is one issue. I will consider make portable laminar flow hood, because this is mostly used during emulsion preparation, not needed later during exposure and processing holograms.
Aside that hood, will try to make at least two filtering units for cleaning air in my lab; 'Cottrell precipitator', and HEPA (or crude version) filter 'air cleaner'. First one is capable to remove dry/wet particles/droplets, by using of high voltage PSU, corona wire/needle and flat plates where particles/droplets collects. It working slowly compared to forced air and HEPA filter, but resulted air is very clean and free of nasty chemicals that may be present in air (oils, other vapors and odors, and everything else that may condense/precipitate on it's surfaces - even water and alcohol vapor if surfaces are sufficiently cold)
HEPA filter, or just crude filter may remove most of the rest of the particles. Actually, this filter should be used first.
During the trip to IKEA I stumped upon the box foe dirty laundry in which I could fit my hands, coating rod and some space for drying plates at the same time(so much easier than building things from wood, and also that is material easy to clean from gelo, dust and any other spillage that will happen inside). Used box is nice since it has a doors, and safe-light can be provided by shining laser through it from outside- light is nicely dispersed and even inside
Kitchen fans are also in the same shop;-). I got one with 360l/h flow and lots of pressure to push air through any filters.
Good idea to use such box. Not sure I can find one, or afford it. Next few days will spend calling my friends, asking whether someone has some idea or box they do not need any more.
Now, from online search and pictures I got the impression that commercial hoods do use almost "bare" HEPA as the stream supply(or it looks like that). HEPA filters are shaped quite honeycom-ish, but why not to use extra stream straightening though.
Yes, they use bare HEPA filter, but different construction than mine. Mine is even NOT HEPA filter as I hoped - surgical masks are just good enough for it's purpose - to remove droplets, and crude dust particles. Googled around, and found this video about difference between surgical and respirator masks ("Surgical masks are NOT respirators").:
http://www.youtube.com/watch?v=ovSLAuY8ib8
And, here is wikipedia about HEPA filters, and possible explanation why they not use anything else but this filter (corrugated aluminum filter separator!):
http://en.wikipedia.org/wiki/HEPA
Other page has some words more:
http://www.macsa.asia/index.php?tpid=0034
"HEPA type or HEPA like filters may be made in similar ways to true HEPA filters and may even resemble them. They do not have to meet the same standards as true or absolute HEPA filters. They often capture only 85 to 90 percent of particles and that percent can fall even lower for particles of 1 micron and below. HEPA type filters are less expensive than true or absolute HEPA filters.
Telling the Difference
Look for the serial number and test results printed on true or absolute HEPA filters. Make sure that the test results at .3 microns are 99.97 percent or above. The size of .3 microns is the testing standard, because most filters will perform better with both smaller and larger particles. Double-check the test results at .3 microns to make sure your filter is a true or absolute HEPA. "
Today found one company in my country (Croatia) which are supplier of various kind of filters:
http://translate.google.hr/translate?sl ... %26id%3D67
Called this company, and guy who talking with me laughing a lot when I mentioned my attempt to make filter with surgical masks. But, after nice conversation, he said that maybe they have some filters that does not pass strict quality tests, and maybe they will give me one for free.
The most interesting concept of laminar flow filter is shown here (only small picture):
Not sure small metallic part serve as for air flow shaping, or not. The name of this product is "AstroCel TM Hood".
Another picture showing different approach:
Name: "AstroCel TM RSC"
All in all, this made it clear to me that I had wrong approach to my construction.
My construction on the flickr picture should be recorded in history of 'hall of shame'
http://www.flickr.com/photos/milan_kara ... otostream/
Corrugated plastic that I found (online shop) is quite same looking as in the linked video. It is soft (no dust when handling) and easy to cut with sharp knife (box cutter). I've used too soft knife that bends when cutting so the edges are not to straight, but it is not a beauty contest;). I couldn't fit to long honeycomb without sacrificing too much of a working space so I used only 2.5cm strips.
Now to the operation. Flame test is not perfect, maybe because of not long channels, but with some tweaking (like putting small layer of pre-filter on the center of honeycomb grid to equalize flow) I can eliminate most of dust. By running the fan for some time before any works, and attacking the working area with powerful vacuum cleaner just before inserting anything it seams that dust is pretty much eliminated.
I don't have yet well established coating routine of working with the box, and I thing that this is as important as box itself. But I think that design is a good base for improvements;). Time will tel:)
Here I have two options; if firm mentioned above provide me something, then I need to built only box and attach fan. If not, then I will consider using different filter (cutting surgical mask, gluing it on wooden frame, and bad result afterward is not fun). Not sure what will appear. As msxc said: Time will tell.
Greatings,
msxc
Greetings,
m--