HT Oven - placing the elements

T

tristan44

Joined
Feb 19, 2013
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3
Hi,

I am looking to get a HT oven with the inside dimensions: 19" deep 16" wide 7" high and have contacted a company that custom builds these kind of things. However, they say that they will only place the heating elements in the ceiling and so I am wondering what you guys think of that?

Will it work any good?

/Joel
 
Maybe. Maybe not.

There are lots of variables and very few people have a handle on how they all interact.

If you need something specialized, it makes sense to go to a specialist. If you are going to a specialist, the basic setup tends to be that you either take their advice or you find another specialist.

I'd certainly want to know what projects they have done that are similar to your proposal and try to speak to the customer(s) about the performance of the equipment. If you have not had a sit-down discussion with their technical guy, it's a very good idea to do so as early as possible.

Much of the time, I get to see specs for equipment that would be really expensive to make exactly to the spec and would perform quite poorly. With a bit of discussion and teasing out what the equipment really NEEDS to do, it's more often than not the case that one or two things can be changed to both reduce cost and improve real-life performance.

Note that often the guy you want to speak to will not be the sales guy and the sales guy will almost certainly not want to let you near the technical guy.

Most HT ovens have the elements on the sides and this seems to work pretty well. However the 16" width is much wider than I'd normally expect to see for a knife oven and I suspect the normal rules of thumb are likely to fall down at such extreme proportions. The proportions are much more in line with some of the glass kilns and many of these are top-element only. I gather glass kilns are not good for HT of steels, but I don't know how much of that is due to the layout and how much is due to the fact that glassworking and HT of steels are vastly different processes and that optimizing for one will give poor performance on the other.
 
There's nothing special about an electric kiln for heat treating steel or ceramics or glass! They are the same thing! It simply comes down to internal temperature. The oven must be able to reach and accurately hold the required temp for the chosen steel. This is regardless of size, shape, color and whatever other design you want to throw in! Accurately holding temperature is the only thing that matters! An oven of that size, having elements in the top only, does not seem adequate for the heat treatment of steel, IMHO.

It may be though. Find out how many Watts output given the size, and you will know.
 
your furnace dimensions are just different and a little strange for heat treating blades. 19x16x7, you are heating 1.25 cu ft. 7x7x19 you are heating 0.55 cu ft, less that half the volume, it would require half the wattage to do the same job. why not walls and ceiling or just walls? Take a read thru this http://www.joppaglass.com/elements/dudleys_element_paper_2015.pdf a good design how-to. my small furnace is a Paragon and has elements on side and back wall. My big furnace is a Lindberg and has elements top, bottom and sides.
 
Thank you all for writing! A lot of interesting points.

The inside dimensions, and specifically the width is for making batch heat treatment possible. I don't want to do one blade at a time.

I have a 16A fuse so the maximum effect I can use for the oven will be 9KW.

I see a lot of ovens having elements in both floor, walls and sometimes ceiling. That's why I am concerned about the ceiling only construction. If you put in several knives so that the floor cools down, will it be able to gain back the temperature in any good way or just cause uneven temperature. That's my thinking.
 
My oven has elaments in the roof and I love it. The coils run over ceremic rods and coils are evenly spaced out front to back. But you said you have a "16 amp fuse", what voltage. 16 amps is not much unless your talking about 220v. At 110v and 16amps you only have 1,760 watts and 220 would be 3,520 watts. I can't remember exzactly but my oven is 20-25amps and the chamber is 5.5"x5"x31.5". You need to calculate surface area of your oven and watts per square inch. I did the math to compare my ovens surface area to yours and this is the results.
My oven has 716.5 in^2 and 4400watts that's 6.14w/in^2
Your oven has 1,098 in^2 and 1,760watts (16amp 110v) that's 1.6 w/in^2
Or 3,520watts (16amp 220v) is 3.2 w/in^2

Hate to tell you this but 16amps at 110 is a joke and I don't think it would ever reach a usable temp. Even at 220 I think it would take awhile time to come up to temp.
 
Pretty much my thinking, thinking it may have trouble reaching temps needed. I'm building an oven right now, with internal size 6"x6"x18". Elements on each side. And going to be 220v. Plenty of room to do several blades at once, but small enough to heat up quickly & keep entire package more manageable.
 
Nice thing about having the elaments in the roof is you can have a small heat treat oven and still put multable blades in at once becaus you don't have to wory about having blades to close to the elaments in the walls becaus there is none.
 
tristan44 said:
Thank you all for writing! A lot of interesting points.
The inside dimensions, and specifically the width is for making batch heat treatment possible. I don't want to do one blade at a time.
I have a 16A fuse so the maximum effect I can use for the oven will be 9KW.
I see a lot of ovens having elements in both floor, walls and sometimes ceiling. That's why I am concerned about the ceiling only construction. If you put in several knives so that the floor cools down, will it be able to gain back the temperature in any good way or just cause uneven temperature. That's my thinking.
Click to expand...

your math does not work. 9kw and 16amps is 560volts. 16amps and 240v is only 3500watts for 1.25 cu. ft.
my furnace is 14 x 7.5 x 5.25 in(0.3 cu ft) and is heated by 4800 watts. you might be better off buying a used lab furnace.
 
kinda curious where the watts per square inch or centimeter recommendations come from. my big furnace is a Lindberg 51442 1200C box furnace. power consumption is 4800w. interior is 14 x 7.5 x 5.25 in. (35.6 x 19.5 x 13.3cm) or 2800 sq cm/435 sq in wall area, volume of 9000 cu cm/0.32 cu ft. so we have 1.7 watts/sq cm, 11 watts/sq in, 0.535 watts/cu cm, 15kw/cu ft. the four elements are encapsulated and are located in walls, top and floor
 
Been away a few days, but anyway: the voltage is 400v 3- phase (Im in Europe).

A fuse of 16A can handle 9kw on 400v, that's why I want to go with the maximum for my fuses. It's costly to up the fuses.
 
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