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 >