TECHNET Archives

November 2018

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Stadem, Richard D" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D
Date:
Mon, 26 Nov 2018 13:57:39 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (1 lines)
That is easy to determine. Pretend the pears are circuit boards of varying diameters and types, then:



·         Take a sample of 24 pears from 3 groups, 8 small diameter, 8 medium diameter, and 8 larger diameter of equally varied types. You can determine the tolerance range of each group, ie, small is 2” to 2.25” at its widest diameter measured crosswise to the length of the pear, medium is 2.25” to 2.5”, and large is anything over 2.5”. Disregard outliers assuming you have a minimum initial or maximum initial diameter limit for drying pears.



·         Weigh two pears from each group initially and record the weights.



·         Immediately after the initial weighing, place the pears in your oven or dryer



·         Every hour, remove the two samples and weigh them, record the weight, and immediately place back into the dryer



·         Continue doing this with the two samples from each size group, leave the others aside for the time being.



·         When the pears have reached the desired level of “dryness” as per your particular requirements, which can be subjective, record the final “dried” weight of each and the time required to achieve that perfect dryness level for each size group.



·         To validate, dry the rest of the 6 samples from each size group, subjecting them to the drying process for the same length of time determined to be optimum for the initial two samples. Do not make any changes to the drying parameters, one set should work well for all 3 size ranges if the time requirement is met.



·         For unusually wet or dry crops, the amount of time can be varied according to the delta vs. lambda derivitive time where there is little change in dryness after that point, ie, no real detectable measurement in taste or texture from dried pears of other seasons. This would need to be determined over time.



·         8 samples from three groups covering 95% or better of the size range of the entire dry-able crop (all pears within the 3 size limits) will provide you with a 98% probability of satisfaction within those three size ranges, per my calculations. These calculations were based in statistical data pulled out of my ass.



·         Happy Monday. SKOL, VIKINGS!





From: Wayne Thayer [mailto:[log in to unmask]]

Sent: Friday, November 23, 2018 12:18 PM

To: TechNet E-Mail Forum; Stadem, Richard D

Subject: Re: [TN] Drying Oven



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]<mailto:[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<http://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]<mailto:[log in to unmask]>] On Behalf Of Vargas, Stephen M

Sent: Thursday, November 15, 2018 1:23 PM

To: [log in to unmask]<mailto:[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]><mailto:[log in to unmask]<mailto:[log in to unmask]>>



P Please consider the environment before printing this e-mail


ATOM RSS1 RSS2