But how long will those take to dry my pears?
On Mon, Nov 19, 2018 at 5:47 AM Stadem, Richard D <[log in to unmask]>
wrote:
> If you really need to use an oven, I cannot say enough good things about
> Shel Labs ovens. I have been purchasing and using them for 15 years, and
> the first one still works perfectly. The ones I have purchased all are run
> 24/7/365. There have been very little, if any, repairs or replacement parts
> needed. For the companies I work for, I'm required to characterize the oven
> chambers at different temperature settings as part of the qualification
> process, where I place a mass with a thermocouple attached at different
> parts of the oven to ensure there are no hot spots or cold spots (no
> significant delta Ts). In the chambers of these ovens, no matter where the
> mass is placed, the oven temperature varies by less than 2 degrees C over
> time. Typically the temperature delta is more like +-1 degree C. Excellent
> ovens, extremely competitive pricing.
> https://sheldonmanufacturing.com/shel-lab I have also done this for
> many other oven brands that were quite good, but some not so reliable and
> others not as accurate.
> Note; when qualifying any convection oven, please note that if you simply
> dangle a floating thermocouple inside an oven but it is not attached to any
> significant mass, you will never get an accurate temperature reading for
> two reasons, the first is that air movement inside ANY oven during normal
> operation and with doors opening/closing will cause some variation. The
> second reason is that ALL convention ovens that use heated elements also
> have a certain percentage of infrared energy, albeit a very small
> percentage. With a mass consisting of a cubic inch of steel, for example,
> your thermocouple will constantly read anywhere from 3 to 6 degrees higher
> in an "average" size (perhaps 8 ft.2 oven set at 105 deg. C, than the same
> exact thermocouple dangling inside the same oven but not connected to
> anything. The mass is required to measure the additional IR energy; a
> dangling welded bead TC will not pick it up.
> So when characterizing an oven, you want your TC to be connected to some
> type of mass. It will not only provide a more accurate reading, but the
> mass sees the same temperature as a circuit board or other object, and it
> will be a much steadier or constant reading. That is why ovens are
> manufactured with the controller TC fastened to the inner wall or some
> other mass inside the oven. If it were dangling in air, the controller
> would be working overtime to keep the temperature the same, constantly
> overshooting either too cold or too hot. Whatever you put in an oven has a
> certain mass and is unaffected by an occasional door opening/closing for
> less than 30 seconds or so, and is also not affected by minor temperature
> variations from swirling air currents. You want a mass that is somewhat
> representative of the objects you are baking, that way your TC will see the
> same temperatures as the product being baked. The TC mass does not have to
> be exactly the same as the product.
>
> But I also wanted you to know that you can achieve a saturated moisture
> content of less than 10% (removal of 90% of total moisture under worst
> conditions) for reeled parts in a DR Storage drybox, any of the models that
> run at 5% RH or less. It takes about two weeks to achieve that level of
> dryness with no heat applied. DR Storage also makes heated dryboxes which I
> think would reduce the time, but I have never used or qualified one of
> those. http://www.dr-storage.com/en/ I have been using these after
> using other brands for years and years, they are much better. Their
> desiccant containers and controllers are modular, so after about 15 years
> or so you may have to replace them, but you don't have to ship the whole
> drybox back to the manufacturer to do so, any maintenance person can
> service them right in your factory. Cheap and efficient. Better recovery
> times when doors are opened.
>
> I purchase these through a distributor called www.salesjw.com. They have
> excellent service.
> I have no monetary interest in any of these. It is simply that after
> working in this industry for 45 years I know a little bit about what works
> and, ahem, what else is out there.
> Dean
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Vargas, Stephen M
> Sent: Thursday, November 15, 2018 1:23 PM
> To: [log in to unmask]
> Subject: [TN] Drying Oven
>
> Good afternoon:
>
> I am looking for an economical oven that will allow us to bake
> moisture sensitive parts at a low temperature (40 degrees C, </= 5% RH).
> This is for SMT parts that are not conducive to placing in a high
> temperature oven due to package considerations (T&R, etc.). Offline
> responses welcome. Thanks in advance.
>
> Regards,
> Steve Vargas
>
> If you don't have time to do it right, when will you have time to do it
> over?
> John Wooden
>
> Lockheed Martin RMS-Rotary and Mission Systems
> Polaris Contract Mfg.
> 15 Barnabas Rd
> Marion, MA 02738
> 774-553-6192
> [log in to unmask]<mailto:[log in to unmask]>
>
> P Please consider the environment before printing this e-mail
>
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