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John_Reed
User Rank
Iron
Re: reliable Oven
John_Reed   7/9/2015 2:46:23 PM
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My guess is that the designers figured that no damage would occur to the glass at the relatively low temperatures when starting the process. You could switch to an open loop mode and simply set the output variable to 10% or some other reasonable value. The thermal inertia of the system would then limit the rate of temperature rise. Likewise when the operation was over you could just cut power and allow the oven to cool as fast as heat could escape.

In some cases precise closed loop control is not needed, or maybe the oven was designed with "fuzzy logic", which I don't hear of much today.

 

jmiller
User Rank
Platinum
Re: reliable Oven
jmiller   10/27/2013 8:36:41 AM
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I find it funny how engineers sometimes lose face by pushing a sales type question to a sales guy, while a sales guy is perfectly okay to push an engineering question off to an engineer.  Talk about a double standrard.  Oh well, I guess that''s what we get for being so smart.

William K.
User Rank
Platinum
Re: process clarification
William K.   10/1/2013 8:25:54 PM
NO RATINGS
Your description of the process is quite similar to some kinds of heat treatment for metals, which I understand. So my assumption about what matters and what does not matter were fairly correct. Thanks for the additional information.

GlennA
User Rank
Gold
process clarification
GlennA   10/1/2013 8:06:03 PM
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What I did not include was some detail on the process.  The glass was loaded to a carrier completely outside of the oven.  The carrier was moved into the oven.  The heating process ran until the set temperature was reached.  The carrier then exited the oven completely and moved into the air-cooling and tempering station.  The oven was not actively cooled between cycles.

William K.
User Rank
Platinum
Re: reliable Oven
William K.   10/1/2013 3:01:36 PM
NO RATINGS
Rob, yes indeed. But not everybody is willing to tell others that "they have to wait for the boss to tell them" what to say. One time I was in that situation, with every member of our customers group asking me for the same "freeby."  That was a commitment that I was glad to defer, although I am certain that they felt that I was "losing face" by having to pass a sale-type of question to our sales person.

 

Rob Spiegel
User Rank
Blogger
Re: reliable Oven
Rob Spiegel   10/1/2013 2:40:46 PM
NO RATINGS
William K, that's actually a very good possible explanation for the Finland guy's response. A little communication, though, would have helped.

William K.
User Rank
Platinum
Re: reliable Oven
William K.   10/1/2013 2:32:28 PM
NO RATINGS
It is probably the case that the temperatures not covered were not critical at all, and that on temperature rise full heat was totaally satisfactory, and that on cooldown, once the temperature got down to 200C there was no reason to leave the heat on, just let it coast down to ambient. Sometimes it happens that those who know a process very well don't realize that the uninformed don't have a clue as to what matter and what does not matter. And 9it is quite possible that the gentleman was waiting for a response from the home office and did not dare say anything for fear of committing to make expensive changes.

It may also be that the specified range was where the accuracy was guranteed, but that the range was a bit more, but perhaps not in the 1% accuracy area. That happens also. So sometimes what the unknowing may consider a major flaw is instead a detail not worth considering.

Rob Spiegel
User Rank
Blogger
Re: Mind the gap!
Rob Spiegel   10/1/2013 11:07:03 AM
NO RATINGS
TexasTJ, I recenlty had a lengthy conversation with a Finland resident at a trade show. But the effusive conversation may have hinged on the fact that he was originally from Russa.

TexasTJ
User Rank
Iron
Re: Mind the gap!
TexasTJ   10/1/2013 9:58:40 AM
NO RATINGS
I work for a Finnish company.  In addition to what you said, I'll add that Finns aren't a talkative bunch to begin with.

szyhxc
User Rank
Iron
Re: Mind the gap!
szyhxc   10/1/2013 9:55:43 AM
NO RATINGS
My wife slumps glass in a kiln and, in that process, the warm-up rate is not at all critical for the first couple of hundered degree.  Perhaps that may have been the explanation but the resident engineer should have had no problem explaining if that were the case.

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