Help with Flash Venting and Kiln Program

[Karramandi]

Hi,

I'm in the middle of doing my first glass fuse in my Paragon SC2 kiln.  I entered a program for fusing the glass as shown here.  Everything was working fine, got really excited that my first fuse was doing great.  I flash vented the kiln by opening the door just an inch (no more) down to 516*C and then closed the door.  About 5 - 10 minutes later the alarm was going off telling my that the temperature had risen too much.  Can anyone tell me why this happened?  I'm still trying to get the temperature to stick at 516*C for 30 mins but it's just not happening

My program was

Segment 1  Ra1 250  *C 593  Hold 0
Segment 2 Ra2 278 *C 816 Hold 10
Segment 3 Ra3 999 *C 516 Hold 30  (this was when I opened the door)
Segment 4 Ra4 117 *C 399 Hold 0
Segment 5 Ra5 144 *C 25 Hold 0


What did I do wrong?

Thanks in advance for any help

Yvonne

[Flyingcheesetoastie]

Do you need to flash vent/crash cool a kiln this small?  I would have guessed that's your problem right there!

[Karramandi]

Thank you for such a quick response, I'm sitting on the edge of my seat.  It took me over 2 weeks to actually pluck up the courage to fire my first piece - lol

I've no idea, I just followed the instructions in the back of the Contemporary warm glass and also the instruction leaflet that came with it.  Th instruction leaflet that came with the kiln says that if you prop the door open then program a fast cooling rate. I thought I did that by programming a rate of 999 to bring the temp down to 516*C.

Thanks again
Yvonne

[julieHB]

What you do when you flash vent is to let out the warm air. If your kiln is brick walled the heat still stored in the walls will cause the temperature to rise again. I have a fibre lined SC2, and that one will cool much quicker. The kiln shelf holds heat, though, and will cause the temperature to rise as well, but not as much as a brick lined kiln. To be honest I never bother with flash venting, but I've only fused small pieces like pendants etc. The reason for venting (I think) is to prevent devitrification, but with the bullseye glass that has never been a problem for me.  There might be other reasons for flash venting as well, and I am sure someone will come along soon and let us know.  

I advise to decrease Ra4 to 78deg/Min, and after that you can stop the program (segment 5 unnecessary), and just let it cool naturally in the kiln.

[Karramandi]

Thank you Julie.

It's pendants and earrings that I'm doing.  I've no idea what the glass is as I picked it up in a bargain bucket at Pearsons when I did a course there.  I didn't combine the glass, I just layered another piece cut from the same sheet of glass so that I didn't have problems with compatibility for my first fuse.  I will be ordering a load of Bullseye next week though, I just couldn't wait til then

The kiln is fibre walled and I'm using the shelf that came with the kiln on it's stilts.

Thanks for the info on the program.  I did wonder if the sample firings in the back of the book were for larger pieces or not.  Huge learning curve here but SO excited

Thanks again
Yvonne

[Flyingcheesetoastie]

I wouldn't bother to flash vent a kiln this small, unless you are wanting to see what the work is doing at top temp to gauge if it's gone hot enough etc.  The kiln will naturally cool down fast enough at 999 to avoid any devit which is caused by going too slowly from top temp down, but more commonly caused by mucky glass or tin side up with float glass reacting to things.

I think I have the book you are referring to and it's a great reference point but I believe was written before many of these small kilns started being made for glass.

If you have any other questions then please feel free to post or PM me too, I have a slight kiln fixation!

[Karramandi]

Rachel,

Thank you so much for your help.  I've managed to reprogram it with the new cool down rate so I'll just leave it now to do it's stuff. 

I'm so excited to try again though and can't wait til tomorrow

Thanks

Yvonne

[julieHB]

I was hoping you would come onboard and explain things, Rachel!  

And yes, as Rachel says, I do open the kiln when it's at the end of fusing time, not to vent, but to see if it needs to fry a little longer!!

When I fuse small pieces, like jewellery stuff etc. I don't ramp up slowly in the SC2: This is the approximate program I use for full fuse of thin jewellery pieces:

Ra1: full, temp1: 810-830 degC, Hold1: 1 10-30min
Ra2: full, temp2: 500 degC, Hold2: 30-60min
Ra3: 78 deg/Hr, Temp3: 371 degC, Hold3: 0min
0000

However, If you grind the piece so that it needs fire polishing it is imperative to ramp up slowly to about 630 deg C to avoid the white milky looking grinding marks!!

[Zeldazog]

Segment 1  Ra1 250  *C 593  Hold 0
Segment 2 Ra2 278 *C 816 Hold 10
Segment 3 Ra3 999 *C 516 Hold 30  (this was when I opened the door)
Segment 4 Ra4 117 *C 399 Hold 0
Segment 5 Ra5 144 *C 25 Hold 0

I don't flash vent (did a couple of times, usually when in a tearing hurry, then I found out it could cause problems with my kiln, so no more), like everybody says, no real reason for it.  When I have vented my kiln, I have seen it rise back almost up to the temperature it was at when I opened it, even when I have allowed it to drop a lot.  But its a firebrick kiln, they're very well insulated, so simply hold the heat in, as Julie HB explained.

You shouldn't open the door at 516 - this is the top of the annealing zone - between top temperature and this, the glass can cool quickly, but (depending on glass) 520 down to 370 is the annealing cool down, it needs go slowly, not quickly. 

My usual program, using Bullseye from

Segment 3 - As fast as possible to 517 *C.  Hold for 30 minutes (or an hour depending on size of piece, thickness, how many times in kiln)
Segment 4 - 83 dph to 371 *C - hold 0
As fast as possible down to 50 *C.

Everybody does things slightly differently, depends on the glass, the kiln, the fuser.  Even two kilns the same model can behave differently, so you may find you have to play to find out your ideal fusing temperatures. 

I'd also question whether flash venting could cause uneven heat distribution in a front loader?  Mine is a top loader, so heat goes straight up and out, but a front loader, might leave more heat at the back, I don't know?

[julieHB]

Dawn, a front loader always has uneven heat distribution  Even if the door is insulated, the pieces at the front are never "as cooked" as the items at the back. Sometimes this can be used to an advantage (as in wanting to fill the kiln, but don't want all the pieces to be fused equally much), but for slumping etc, it can be a disadvantage. Using the kiln shelf helps somewhat.

Having said that - you can fit a bead door to a front loader  Not that I have done it, they cost a fortune!! My little kiln has yet to give me a blister, though, even if I am garaging 

[Flyingcheesetoastie]

Have to agree here, even my little bead cube that is currently running flat glass tests varies greatly from the back of the cracker/batt/shelf to the front, despite bunging up it's mandrel holes!

[Zeldazog]

Dawn, a front loader always has uneven heat distribution 

Good point, Julie!

[Margram]

I used this schedule posted by Helen P: http://www.frit-happens.co.uk/forum/index.php?topic=36.0 (second post down)(Haven't got time/energy to compare it with what's already been suggested - feeling sleepy  )

[Karramandi]

Thank you everyone for all your help.  I really appreciate it. 

I won't find out until tomorrow morning how it went but I'm going to have another go tomorrow with the new information. Can't wait.  I think is a new addiction!

Thanks once again
Yvonne
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