nexts = nests. My bad on spelling. The nest fit the show side of headliner and used vacuum to hold the part to it, the cut lines had SS blast deflectors to protect the rest of the nest.
The portions of the profile that I had to dwell on to get a sharp corner tended to have their blast deflectors wear though soonest. At first we made new ones, later we just welded them up, quicker and easier.
Wes
Waterjet seems to have a lot of tricky, unanticipated issues. The early ones were hellishly loud, and you had to wear hearing protection when you were in the same room. Is that still true?
-- Ed Huntress
On what we cut, low density fiberglass headliner shells it wasn't too bad. Positioning the nozzle as close to the cut helped keep noise down.
Now on a prototype corvette seat back we were developing for Lear out of many layers of woven glass impregnated via the SRIM process, we upped the orifice to about
0.010" and that was damn loud. Non abrasive WJ wasn't the tool for this, too slow. Anyway, Lear took that back in house and we ended up wasting too much time and resources on that one.Wes
I find the pure water - attacks ? I don't think so.
Chlorine and such will. H2O is stable. If they have electric current flowing in the pipes - possible - it can break down H2O into hydrogen gas and oxygen gas. The hydrogen will attack steel. The oxygen will attack almost anything.
I bet they had a mixed iron and copper system and did themselves in without using current breaks - plastic joints.
Mart> "Tim" wrote:
I watched a demonstration of an abrasive waterjet system cutting 1/8" aluminum and the pump made some noise, but the cutting was under water and did not make noise that I remember. The whole workpiece was under a few inches of water that got pumped in before the cutting started and pumped out to below the workpiece when done.
BobH
That's interesting. I don't remember many details about the waterjets I saw a few decades ago; they were still a curiosity and I didn't spend a lot of time with them. I do remember the noise, however. It was fierce when they were cutting metal. Maybe the underwater cutting came later?
-- Ed Huntress
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the unit's demonstrated at Westech are cutting about 1 inch AL, not too noisy, the jet is about 1/4 inch above the AL - I don't think I'd want my ear next to the jet, but it's certainly quieter than a lot of other cutting tools
We had to guard against using de-ionized water in recirculating cooling systems for extruders (primarily D2 steel). The operations manual from the manufacturer warned against it due to excessive corrosion. Specs were given for water quality.
Of course, this was in boiling service. Cooling was accomplished by small shots of water into the cooling channels in the extruder barrels, which since they were at 2-300 deg C caused the water to immediately flash to steam.
Pete Keillor
DI water attacks copper and copper based alloys quite aggressively. Austenitic stainless steels and nickel base alloys are generally OK, though I have experience with Inconel immersion heaters corroding surprisingly fast, even at relatively low temps (140F) in DI water.
The absence of ions would rule out galvanic corrosion, no?
Steam power plants - all of them run by steam generated. They must use what they call is "holy water". It is as pure as possible as they run very hot pressurized steam. The pipes would clog up if anything was there. Power plants don't blow up in the steam lines due to hydrogen issues weakening the steel. I suspect there was a process or two metal issue. Any two metals leak current. Some are really bad.
Mart> >
I'm not sure that deionized water is in fact free of ions, because the beads used to fill the water treatment gadget are called ion *exchange* beads or media. The implication is that they have traded one kind of ion for another, not that all ions are removed.
Does distilled water attack copper et al? I would think not, because copper stands up to rainwater pretty well.
Joe Gwinn
They use an anion exchange resin to substitute OH- ions for whatever anions were originally present, like Cl- or whatever, then a cation exchange resin to take out positive ions like Na+ and replace them with H+, then (at neutral pH, anyway) the H+ and OH- form water except for the residual 10-7 M of each from the dissociation equilibrium. If one of the two beds is saturated you get either acid or base coming out - one time in freshman chem lab all our titrations came out wacky and it turned out the "neutral" DI water we were using to dissolve our standards was really pH 2 :-). Oh, it doesn't matter which bed comes first, and in disposable cartridges the resins are frequently mixed. Since DI water has no pH buffering capacity any little contaminant can shift the pH substantially. Any that has been exposed to air for a while will usually be down around pH 5 or so from dissolved carbon dioxide
----- Regards, Carl Ijames
I always wondered just how this was supposed to work. Thanks.
I sounds like in a home system it may be difficult to achieve and maintain neutral pH, as one or the other bed will always be a bit ahead.
Joe Gwinn
The exchanged ions are hydrogen ions and hydroxyl ions. H + OH -> H2O
Rainwater is a long way from distilled water, at least here in the Northeast. I can't speak to whether distilled water and DI water affect copper differently. I wouldn't think so, but my experience is limited to choosing materials compatible with DI water for industrial processes.
If you wanted exactly neutral very pure water, yes it would be slightly tricky. In practice you don't care about exactly neutral pH so it is easy - each resin takes out whatever is there of each charge and all that is left is water. Yes, a tiny amount of acid or base can shift the pH, but you don't care precisely because the buffer capacity is so low - any tiny amount of anion or cation you add on purpose will be enough to completely swamp out any slight initial acidity or alkalinity. It's only when you run it through one resin and not the other (or one resin is saturated and the other one isn't) that you have a problem. Say you start with salt water and all the Na+ is exchanged for H+ but the Cl- isn't exchanged for OH-: you just made HCl, hydrochloric acid :-).
----- Regards, Carl Ijames
Ahh. I was worrying about corrosion of for instance copper, and if I understand the implications of the above, for instance a bit of salt in the feedwater will cause the deionizer to produce hydrochloric acid, which will dissolve the copper in no time. People are far more tolerant of dilute HCl than copper and stainless steel, so what's good enough for drinking may not be good enough for a boiler et al. I'm sure that there are better deionizers, but still...
Joe Gwinn
Menhirs?
Joe
Let me try again. There are two parts to the deionizer, one that removes cations and one that removes anions. So long as both are working, the water that comes out is at neutral pH. No acid or base is produced. If there is table salt in the water, NaCl, the cation portion will remove the Na+ and release H+, and the anion portion will absorb the Cl- and release OH-. Since there were equal amounts of Na+ and Cl- to begin with, equal amounts of H+ and OH- will be released and they will combine to produce water, H2O, at neutral pH. It is only when one half malfunctions that there is a problem, and it is easily detected by monitoring the output pH. Deionizers are a standard way to clean up water for all kinds of applications.
----- Regards, Carl Ijames
I know that total ions must balance to yield zero net charge, but what caught my eye is the following:
"It's only when you run it through one resin and not the other (or one resin is saturated and the other one isn't) that you have a problem. Say you start with salt water and all the Na+ is exchanged for H+ but the Cl- isn't exchanged for OH-: you just made HCl, hydrochloric acid :-)."
Ahh. I read the first sentence too fast. OK.
Joe Gwinn
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