On Friday 20 November 2009, John Harris wrote: >Hm. I don't think carbide bits were around in 58, so it looks like the >foreman was not too far off. > >The fast oxidization of aluminum during cutting is an interesting effect. > >In the early 60s, we were making small electronic modules by soldering tiny >Fairchild ICs to printed circuit cards, using locally made hot nitrogen >soldering. There was a wall powered gadget that extracted nitrogen from the >air, and a bell jar that held the nitrogen at 1/2 PSI. A plastic tube fed >the nitrogen to something that looked like a normal soldering iron, except >that the tip was a hypodermic needle with a blunt tip. The nitrogen came > out of the needle tip hot enough to melt (reflow) the solder at the joint, > but while doing so flooded the area around the joint with nitrogen to > prevent oxidation. > >You do not need the heat but maybe a low flow of nitrogen to the cutting >point may stop the oxidation long enough for the next cutting edge to get >there. Anyone have any ideas on how the gadget running from wall power that >made the nitrogen worked? > >John > No more chemistry than I've learned would tend to make me think there was a chemical in there that absorbed the oxygen as the air passed by, probably was either replenished by the night crew, or heated to reverse the process at some point in the unmanned day. Something along the lines of the dehydrators we use for pressurizing transmission lines at broadcast facilities. They run the air thru silica gel to dry it, then reverse the valves & dump the air being pulled in back to atmosphere and heat the tank of gel to drive the water back out of it about once a day, or in the better ones, every x hours of accumulated running time. As for the chemical used to pull oxygen, I wouldn't have a clue, but common sense says that is going to generate heat just as a fire would. All I know is that one isn't going to have an air reduction (compress to liquid and controlled evaporization of the liquid compressed air) system in a wall wart supply. Possibly in a refrigerator sized compressor I suppose as we presently have a portable oxygen generator on site for the wife's use as she has COPD. Given the pressures involved, I wouldn't expect to ever see that reduced to a wall wart sized device so it almost has to be chemical based.
>----- Original Message ----- >From: "Leslie Newell" <les.new...@fastmail.co.uk> >To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >Sent: Friday, November 20, 2009 8:43 AM >Subject: Re: [Emc-users] How Exactly does a Mister Work > >> In general flood with a water based coolant will shift more heat than a >> mist system. Flood also usually shifts the chips better. On the down >> side it is very messy and can actually reduce the life of carbide >> tooling. >> >> Carbide tooling can take a lot of heat but it hates thermal shock. The >> cutting edges of a milling cutter operating in flood coolant will get >> heated rapidly while they are actually cutting then suddenly cooled as >> they hit the coolant. This can cause cracking and chipping. Oil has a >> much lower thermal capacity and conductivity than water so it doesn't >> cause as much thermal shock. To a large extent you can get around the >> problem by using high pressure flood coolant to make sure the cutter >> does not get a chance to heat up. >> >> So why are mist systems still fairly rare in industry? Two main reasons >> spring to mind. 1) flood keeps the work and machine at an even >> temperature so you don't need to allow for thermal expansion. 2) Flood >> has always been used. If it works, why change it? >> >> In my experience carbide works well with oil misters, HSS needs flood or >> a heavy mist of water based coolant. >> >> Les >> >> John Harris wrote: >>> Hi All, >>> Back in the late 50s when, as a young apprentice, I was >>> turning knobs on a milling machine as part of my education, the shop >>> foreman replaced the flood system on the mill with a new-fangled mister. >>> The mister feed tank was filled with the same stuff that was used for >>> the flood system. That is water with 15(?) percent soluble oil. >>> >>> The foreman told me that the mist cooled the part and the tool by >>> evaporating the water, and the oil gave some lubrication to the cutting >>> action. Also misting greatly aided the water evaporation compared to the >>> flood system. >>> >>> As the foreman is by now no longer with us, I feel safe in raising the >>> question, was what he told me true? If it was, why are you now using >>> only oil that is much less efficient in absorbing heat by evaporation >>> than water? >>> >>> Regards all. I love reading the chat. >> >> ------------------------------------------------------------------------- >>----- Let Crystal Reports handle the reporting - Free Crystal Reports 2008 >> 30-Day >> trial. Simplify your report design, integration and deployment - and >> focus on >> what you do best, core application coding. Discover what's new with >> Crystal Reports now. http://p.sf.net/sfu/bobj-july >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > >--------------------------------------------------------------------------- >--- Let Crystal Reports handle the reporting - Free Crystal Reports 2008 > 30-Day trial. Simplify your report design, integration and deployment - > and focus on what you do best, core application coding. Discover what's > new with Crystal Reports now. http://p.sf.net/sfu/bobj-july >_______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users > -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> Emacs, n.: A slow-moving parody of a text editor. ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
