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ARSCLIST  February 2012

ARSCLIST February 2012

Subject:

Re: ovens for baking tapes

From:

Jim Lindner <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Sun, 19 Feb 2012 07:45:48 -0500

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More then most people will ever want to know about ovens.... most people can stop reading here - - - - 

You want an oven that will hold the temperature very, very stable and ideally will allow you to insert a temperature sensor so that you really know what is going on inside. So there are two things going on - one is the stability of the ovens own thermocouple and control system and the other is the ability to insert an external probe. Why would you need that? Because you will find that you may want to put an external sensor somewhere specific in the oven and most importantly because you do not want to trust the thermocouple that controls the oven at this low a temperature - it is the very lowest part of the range for any oven - so you want an alarm that will go off if the min or max are wrong.

Temperature stability is your number one concern but there are ovens with lots of features which can be helpful, particularly if you want to do some research or try some different ideas. So in terms of ovens that will be optimal, consider only Laboratory grade ovens. These are designed to be very temperature stable. Some Lab ovens are designed for process or production work, and expected to be opened and closed frequently and so recover quickly, others are designed to maintain an environment for weeks or months and so are not designed to recover quickly, you get the idea - there are many different ovens that are designed to be used for different types of applications.

Any oven that you want to consider has to have a chamber large enough to hold what ever you might want to put in it. Better too big then too small. That sounds obvious, but there is a tradeoff with insulation because the larger the chamber the more insulation and heat generating capacity is necessary for ovens that are designed to maintain the temperature and come up to temperature from ambient quickly. So if you are buying one online - which is likely what almost everyone will do, you need to make sure the chamber size is big enough. 

You never ever want to consider ovens used in food preparation. Their expected temperature range is not optimal - even if it is a "warming oven", and far too inaccurate in terms of heat stability. For an oven of this type - being 20 or more degrees off is no big deal, but it is for baking tapes.

You will likely be thinking - but I am only going to 150F and you are correct - and most ovens are designed to go much higher then that, and in fact this temperature is well below the accurate range for many ovens.

Here are some ideas.

Environment Chambers as a category often have lots of features that are ideal for this kind of work. Many allow you to vary and maintain the RH of the chamber as well as the barometric pressure. Many have stainless steel (the real stuff - not the stuff they use for a cheap sink at Home Depot. Environmental chambers can have very sophisticated controls that allow you to ramp the cycles - you can control how long the warm up cycle is, and the baking, and the cool down and you can even have the temperature change during your cycle. Most environmental chambers are expected to work at temperatures higher then the range for this work - but they certainly are out there. Environment chambers usually expect other outside "services" like water and a drain and maybe even compressed air depending on the design, so be certain that you have the requirements to support the oven. Some REQUIRE these - so if you buy a used one thinking that you will just not "turn on that part" think again, most have safety systems that will not allow them to run without those services on.

Incubators
The temperature needed for this work can be usually accommodated by a class of "ovens" called incubators. Incubators are typically used for biology, so they are used by a wide variety of organizations that work with samples that need incubation from testing services or departments in hospitals to research departments. The advantage of incubators is that the temperature range for baking is more of the expected range of these products - so they "expect" to work at 150 degrees F and just a big higher, so it is more of the range they are designed to run in. They also tend to have some handy features, like an electrical outlet in the oven for example - which you may not need now or ever, but they are part of what this class of device has.

Lab Ovens and Dehydrators
It turns out that some Dehydrators can do both heating and dehydration, while most ovens do not control RH at all. Whether you need RH control will depend on your ambient location. If you are in a naturally dry area all year long you may be able to get away with an oven with no RH control - but if you are in a location where the RH is high or can change during the year, you likely will need some kind of RH control in the area where the oven is - or inside the oven, or both. You want to bake - not steam the tapes. Now you are likely thinking that this is not an issue because the heat will reduce the RH, and that is likely the case - but now consider the RH once the tapes will go in, and how fast you may or may not want the RH to change once the mass of tape gets in there. Depending on the air flow- whether gravity or convection - horizontal or vertical, it may take a while to get where you want it to be - so being able to control RH is very nice - consider a project where you have had to clean tapes with distilled water to remove contaminants for example - depending on the kind of work you do, some of these features may be useful.

Things to watch out for
Ovens and incubators can get expensive, environmental chambers extremely expensive.There are many used ovens out there, and you could do worse then look in Ebay. But you need to be very careful - some ovens can get contaminated as part of the process in which they were employed, so you don't want an oven that was involved in an industrial process that outgassed, some of which is now baked into the oven chamber forever. Also ovens can be abused and their thermocouple can be wasted and ovens can develop control system problems (another reason for the external thermometer). Ideally you want to test the oven before you buy it to make sure it holds the temperature set. Again I remind you that the temperature range is VERY low for tape baking and many ovens are not designed to maintain this extreme low end of their range, and if they were used at 400 for 10 years, may not even turn on at all at 140. Many older ovens have mechanical systems for control - they may have an electronic read out but the control is mechanical so you need to figure that out. There are certainly ovens with mechanical control that will do a good job for you, but you need one that has not been abused and will hold the chamber stable at this very low temperature. So how many times have I used the word "abused" in this paragraph? I did it for a reason - you need to be very careful.

Finally, if you want to buy a new one, where do you look? You could do worse then looking at any number of companies that supply Laboratory equipment to universities, hospitals, and high schools. Fisher Scientific for example offers several lines of ovens. I owned a "Blue M" oven and was extremely pleased with it. They make hundreds of different kinds and if this is your first time doing this, it is a good idea to call a couple of the companies up and talk to a sales person. My experiences have been that they can point you in a number of directions and will ask you a whole bunch of questions that you likely did not even think of - like do you have 220v or how wide is your doorway.... and they can explain some of the features. They talk to scientists all day long so they know a great deal about what features will be available, some will be unnecessary and others will be things that had never occurred to you and will be helpful on that 1 project 4 years from now.....



Jim Lindner

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On Feb 18, 2012, at 11:07 PM, [log in to unmask] wrote:

> Archivists and Techies,
> 
> What are recommended ovens for baking tapes with SSS?
> 
> I am of course looking at price, and I don't need one that will go to 1800 degrees. If it topped out at 150 F that would certainly be enough for what I need.
> 
> Also something that does not shut itself off or can be programmed for a specific length of time.
> -- 
> Joe Salerno
> 

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