Materials Touch Temperature

[var10]

Good morning everyone,

I was researching on some materials that can be easily touched at 400deg C. Presently I have some aluminium jigs that go through the oven for 4 minutes but due to the very obvious reason of high thermal mass of aluminium they are too hot to be touched by bare hands of our production staff. They have to leave it to cool down for 20 minutes and then do the next function. I was looking at some machinable ceramics and titanium to address this issue. But both are very expensive or I am not talking to the right supplier. Since it is just a prototype I just need to make 2 units. I spoke to two companies in China that does prototyping and both can't do ceramics and titanium was $600 USD per piece for o/all dimensions - 140mm x 330mm x 5mm and no complex machining required in the middle.

Open to any material suggestions or supplier suggestions.

Regards,

V.

 

[btrueblood]

Foamed silica blocks can be safely handled at very high temperatures, having very low density and conductivity.

one source:

http://www.cotronics.com/vo/cotr/pdf/58 310M 311.pdf

 

[Dougt115]

A little more definition is needed.

I am assuming you need production to be able to remove the unit from the fixture soon after exiting the oven? And then reuse the fixture for the next unit to go in the oven?

What are the features of the jig? Is it a cookie sheet or a holding fixture? Does the material need to be solid and strong like your aluminum or could a non-conductive insulation like the space shuttle tiles work? Could they just use insulated gloves? Could you just have more jigs?

 

[tomwalz]

We use fire bricks for this sort of temporary fixture. Easy to machine (but very abrasive), cheap, readily available and there is a huge selection.
We buy the soft, insulation fire bricks from a local kiln supply house.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[var10]

@Dought115 - The Jig has two machined sides. The flex that sits on the jig has connectors both sides but not symmetrical. So they need to flip the jig - remove the tape, remove the flex and place it on the other side with solder paste and connector. Put it through the oven again. We don't manufacture a lot of these parts so no point in having more than 2. But they still want this to be done pretty quick as the oven can be used for other parts too and finish the job on this one asap.

Thanks for the material suggestions. I will see if I could find any suppliers that machine fire bricks here in Australia. I presume there are different grades of fire bricks. For my application I would think I need something not too brittle nor soft but still easily machinable.

@tomwalz - when it comes to machining what material would you think is similar to fire bricks. what do you mean by temporary fixture? you don't mean to throw them away after once right?

@btrue blood - I have tried some suppliers in China to machine ceramics but no one wants to do it. I only need two made that is the problem. If it costs me more than $400-$600USD I may as well get them made in Titanium (chinese supplier quoted this price).

Any suggestions where I can get it made in ceramics or fire bricks and get it shipped to Australia?

Thanks guys!

 

[Compositepro]

Is there some reason that a fiberglass felt insulation won't work?

 

[Dougt115]

VAR10 Thanks for the added information.

How about making the touch points removeable so that they don't go in the oven? Make the handles of the clamps so that they can come off quickly.

Put the part on the fixture, tighten down, remove the parts the technician touches, place in oven. When it comes out you put the handles back on flip the unit around remove the handles and put it back in the oven. (Not well stated but I think you can get the idea.)

The attach method would depend on the weight but I think it could be kept simple and quick to use.

The fire bricks that I have seen used in a kiln is like sand stone, very porous, brittle, and creates a lot of grit.

 

[btrueblood]

Felt insulation might work pretty well, if it's just a handling issue. So would a good set of foundry gloves, or oven mitts...

 

[var10]

Thanks again guys!

@composite pro & btrue blood - Do you mean I should stick a layer of felt on aluminium faces? so that it can be touchable? Even if I did cover it with a layer of felt how can I stick the polyamide tape to the flex and jig. Unless I misinterpreted. Please can you clarify?

@dougt115 - The problem is not the placing and removing the flex but removing the polyamide tape. We tape it down to prevent movements during the soldering process as the flex is stiff and tends to not sit flush. So having a separate mechanism is bit pointless or very expensive if I try to include removable assemblies. (But I will look into it)

Thanks,

 

[tomwalz]

http://www.morganthermalceramics.com/products/insulating-fire-bricks-ifb

Cheap, easy to work, very good thermal properties. They are about the size of building bricks.
You can fasten them together with mortar.

These are very soft and porous.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[var10]

Thanks again guys. I finally found some one in China but they have quoted $5000 USD for one piece. I have also tried insulating fire bricks but suppliers don't want to work with them as they are very abrasive.

I only want the part to be touchable, meaning I am not expecting the part to have a huge thermal mass and show no effects of the increased temperature. So potentially some grade of steel would also do the job, but definitely not aluminium which is what we have now.

If not does any one know any place that machines the materials specified by people in this post?

Thanks,

V.

 

[3DDave]

Tough problem. How hot does the aluminum get? I presume you don't need conduction through the jig, so just insulating the bulk of the jig with crumpled aluminum foil should slow heat transfer into the jig, with the item on the jig acting as a barrier from that side. A little FR-4 (I'm guessing on the name, but any circuit board material that can take re-flow should be OK here too) between the foil and the block should prevent heat from flowing back at too high a rate and burning the workers.

I spent a minute looking, but I'm curious about the thermal mass part - I think aluminum is one of the lower ones, but looks high because it's measured on a mass basis, whereas you have a fixed volume. Dividing by density, aluminum is probably lower in heat capacity for the size. The more noticeable problem is that aluminum is more conductive than many metals so it heats and cools more easily.

There are companies that produce foamed aluminum.

http://www.ergaerospace.com/Aluminum-properties.htm

and

http://www.alusion.com/product.html

. I've not bought or dealt with them or any other foamed aluminum producer, but it looks promising for a low stress fast temp cycle. If a smooth surface is required, then screw a thinner sheet to the top so that the operators only contact the foam.