heating Element Construction

[Asellith]

I am looking at building a machine to help me do some iron on hemming over long distances (5' - 9') I can do it with an iron but that's labor intensive. I would like to have a 1" wide by 2 foot or longer aluminum element that can be heated to about the temperature of an iron. I still need to get specs from the manufacturer to find the optimal temp and time so I can automate it. I'm going to build a clamp into it so that I can fold the fabric and then clamp this element to it and release it after the time has lapsed. First iteration will be manual but if I need to scale up the operation I can try to automate the  entire system later.

Anyway I need a place to start with heating and controlling the temperature of aluminum flat stock. Is it as simple as a current controlled supply feeding power through the bar with a temp sensor feedback? Also how do I make sure the entire element maintains an even temperature? I'm assuming power needed is calculated by the current and the resistance properties of the aluminum but how do you determine thermal conductivity and efficiency?

[Soeren]

Hi,

Anyway I need a place to start with heating and controlling the temperature of aluminum flat stock. Is it as simple as a current controlled supply feeding power through the bar with a temp sensor feedback? Also how do I make sure the entire element maintains an even temperature? I'm assuming power needed is calculated by the current and the resistance properties of the aluminum but how do you determine thermal conductivity and efficiency?

Nah, if it was that easy it wouldn't be any fun 

Trying anyway, you'd quickly get into trouble where they were terminated - aluminum oxide manifests faster than you can remove it (literally, scrape with a knife on a piece of alu and right at the back of the edge, oxide will have formed).
Add to that, the fact that aluminum expands and contracts a lot in such app. (Just listen to an "iron" when it's heating up or cooling down).

Haven't you ever opened an iron? On the aluminum plate is a conventional heating element, similar to what's in a cooker and that's what you need to replicate - along the entire length of the bar.

Using a single heating element and a bar of a certain thickness, it will have the same temperature along its length. Just make sure you don't loose heat where it's fastened, or you may get lower temps there.
Use some kind of spring loading to hold the heating element, as it will have a different expansion than the alu and will have to be able to keep different rates, dor the bar will bend.

I think a much better way to do this would be a couple of heated (motorized) rollers where the hem is run through. This would take some arrangement like a couple of light gates to ensure the fabric is going straight and stays far enough in between the rollers and perhaps some means to brake either "side" of the hem to steer it straight.
At least, it would be cheaper and would work with any length of fabric.

[Asellith]

I have some ideas in my head but for the near future it looks like it will be a ton of podcasts and my trusty iron till I can generate the capital to increase my capacity. I had thought of the wheel idea as well but if I do that it will feed the fabric in then fold it correctly and press it on the wheel. That will all feed an actual sewing machine. If I end up building it, I'll probably use an axon to control it and then enter it in a future contest

[Admin]

I'm assuming power needed is calculated by the current and the resistance properties of the aluminum but how do you determine thermal conductivity and efficiency?

Thermal conductivity of most materials can be determined in lookup charts, or googling.

Also, read this entire page, where the last section has equations to calculate what you want:
http://en.wikipedia.org/wiki/Thermal_conductivity

[nickc]

mcmaster-carr sells heat tape with various temp ranges and controllers with or without feedback control. Sandwich the tape between two pieces of flat stock. Aluminum has very good conductivity so it will heat up quickly.  Because of it's high conductivity, passing current through it to try and heat it will not work.

 

[Asellith]

Well it turns out Martelli www.martellinotions.com/ Makes a sewing machine add on that binds edge of a quilt. They happen to be Pensacola natives and after talking with them they are going to sew it for me at half the cost of normal hemming. However I do need to put a smaller fabric product together with a backing called wonder under. Its an iron on backing. Process involves an iron and a wet press cloth. I plan to experiment with sandwiching multiple pieces together between some aluminum plates and bolt them together with a layer of fabric,wonder under, wet cloth, and parchment paper to protect it. Then stick it in the oven for a minute or so to fuse the glue. Not sure if it will work but if it does I can then add more layers and do several pieces at one time.

[Admin]

Just an FYI, copper is much more thermally conductive than aluminum. But it is however also much more expensive . . . no big deal though as you just want a thin sheet anyway, no?