Heated bed: Wall Tile instead glass

Hi, i'm dont know where to post this topic due dont find "heated bed" related subform.
I have a custom made heated bed with some 6.8 ceramic resistors and 6A 12V PSU.
My thermistor was broken. the heated bed was go really hot !.
Tile doesnt broken but some pieces was "sodered" onto ABS.
Glass sure was broken by high temp.

I think wall tile is better than glass for heated bed.
As u see, i dont use PTFE tab.

wall tiles is easy to find, multiple colors an sizes, cheap, easy to cut, flat surface, less flexible than glass for big printers..

Hi,

I was going to try out a wall tile as a bed, but realised it would have to be heated for it to work. How did you attach your resistors to the tile? Do you have a photo perhaps?

One thing I noticed with the tiles I have (which I found in the basement) is that there is a slight lip on one edge. Other than that it seems pretty flat.

I was a bit worried from hearing about tiles "exploding" but maybe I should give it a go. In a controlled environment of course.

Cheers,
Gary

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

Of course, i have attached some captures:
* Material (over a custom beared dispenser with test parts recycled):

* Glue used for resistors (this cement is used for mufflers or similars and can handle up to 1000ºC):

* Final print with that ABS over tile (custom piece, need learn more skeinforge):

* Final print take of heated bed (you can see particles of tile in the final plastic printed):

* PSU used for heated bed (12v 80w, 6.6A):

* Resistors:


Tile is 200x200mm
Resistors all are 6R8 (6.8 Ohm) 5W ceramic. Price 0.418€ each.
Remember my thermisor was broken so i'm running too hot my heated bed.
There are connected 2x4 so resistance is (6.8*2)/4 = 3.9 ohm.
As you can see, need to be less close.
Tomorrow i'll go to buy more resistors and re-plug then for bigger area covered.

About Tile explosion, i think that is for roof cement due have a abestos layer. but i'm not expert. sure my tile is very hot and not explode yet... but 3 glases breaks for now...

Edited 2 time(s). Last edit at 10/05/2011 01:41PM by danx3.

The glass or tile or any material breaks due to stresses caused by thermal expansion. The hot areas want to be bigger and the cold areas want to be smaller. In a brittle material, when hot and cold areas are close together, these areas pull and push against each other. This causes tension or compression in the part. Tension or compression caused by heat is called thermal stress.
Now some important questions. .. I used a lot of subjective terms in that description - hot, cold, close, etc. How can one tell if a material is going to explode due to thermal stress? The coefficient of thermal expansion allows materials to be compared to each other (as well as directly predicting stress levels and potential part failure if a few other details are known). Www.matweb.com is a great source for thermal expansion coefficients.

Compare thermal expansion of soda lime glass (windows and other common applications), borosilicate glass (Pyrex, schott brands, cookware, heat sensitive applications), quartz, and floor tile ceramics (tiles are made of a variety of ceramics some better some worse for this). Quartz is extremely thermal stress resistant, borosilicate is good, and most soda lime glasses have large coefficients and break easily due to relatively small temperature gradients.

Tyro

I do not have much knowledge about tile, but there are few kind of tile in the market for this moment . and one of them declared 'pure porcelain', I am not a expert on the field either .

Now that matweb is back. ..
plonly one porcelain is listed - no clue if it is representative.
[www.matweb.com]
9.50e-6/K

Bleh matweb sucks for glasses appearently.
Here is a comparison [hyperphysics.phy-astr.gsu.edu] note the factor of 2 from from soda-lime (ordinary) to borosilicate and factor of 8 from there to quartz. The borosilicate should be good enough and is a bunch cheaper than the quartz.

Tyro

Perhaps a more suitable figure of merit is the thermal expansion coefficient divided by thermal conductivity, because a high thermal conductivity will reduce temperature gradients.

Another point is that thermal stress can be avoided even when the thermal expansion coefficient is high, as long as the temperature is kept very uniform over the entire plate.

You can also use ceramic tiles, limestone tiles and porcelain tiles etc. All these tiles are nice and available in different colors,shapes,designs. You also find all these tiles in reasonable price.

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limestone tiles

I work for a highend ceramic manufacturer. If you look in my blog under the improvements area you will see the print bed I use a dense alumina ceramic plate ground flat and parallel to within .0002" it works beautifully so far. The only problem is it costs over $1000. Dont worry I didnt pay for it it was scrapped due to a chip.

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Ryan
Quality Engineer & Hobbyist
thingsandtrains.blogspot.com