Preventing Glaze From Running On Pipes

[JamesP 1]

So I am curious if I need to place something over the inlet flues to redirect the flow of the flame so it doesn't just shoot straight up. Anyone know? Here is a picture to base my question off of: http://community.ceramicartsdaily.org/gallery/image/8861-firing/

 

JBaymore I know you are following the topic still, maybe you could help me figure this out. I just need to cut the shelves to allow for more air flow. I want to make sure that all that work will show to be successful and not wasted time because I didn't block the flame from going straight up which would be avoiding going in between the shelves. Thanks for your time.

[Guest JBaymore]

One trick that could possibly help with gas flow in the bottom is to put a SMALL chunk of HARD refractory hardbrick laying across those short bricks in the firebox area.  Like a piece maybe 1" wide and 1" thick by the length needed to span over the two bricks.  Repeat that over each burner.  These brick pieces will need to be very good quality, for longevity.  They will take a beating.  NOT insulating firebrick.  It will also act as a "radiant".... like an electric kiln element, moving heat energy via radiant transfer (line of sight)  into the bottom layer.

 

I'd also change those short bricks on the sides of the burners in the firebox to hard firebrick.  Again.... needs to be good quality ones.  Harsh atmospheric, flame abrasion, and high temp environment. 

 

Also ... you need some space between the shelves and the walls and the shelves themselves.

 

And looking at the picture, I am confused by the posting arrangement.  You said the shelves were the same size, I though.  You only need three per shelf (blue boxes). 

 

 

Hope this helps.

 

best,

 

.....................john

[Guest JBaymore]

I am going to move this entire thread into the "Equipment" forum section.  It has turned into more of a "kilns" thread than a glaze thread.

 

best,

 

..............john

[Marcia Selsor 1,877]

Nice diagram, John.

In the big Olsen updraft I fired, there were 4 burner coming in under the shelves that were sitting on 1/2 bricks and there were channels directing the flames towards the outer edges. James, do you have anything coming in under your bottom shelf? Just wondering. I think John's diagram with the rearranging of posts and the diversion brick will help tremendously with the circulation. Just give it (the flames) more space to roam around the load.

 

Keep us posted on how its going and make sure to note every change you make.

 

Marcia

[neilestrick 4,455]

It all just looks too cramped to me, too. Kilns need space to breathe and move air around. My last gas kiln was 24 cubic feet of actual stacking space plus about 20 cubic feet of open space for the fireboxes, bag walls, and breathing room around the shelves.

[Guest JBaymore]

It all just looks too cramped to me, too. Kilns need space to breathe and move air around. My last gas kiln was 24 cubic feet of actual stacking space plus about 20 cubic feet of open space for the fireboxes, bag walls, and breathing room around the shelves.

 

 

One of the most interesting things about wood kilns I discovered the first time I was in Japan years ago... was the amount of space in the kilns that is not filled with shelves or work.  We tend to try to cram stuff in to the max.  Pieces in every cubic inch. They tend to let the fire 'work on the pieces' more.  I started stacking my wood kiln looser... and got WAY better results.

 

best,

 

..............john

[glazenerd 1,598]

Will go back to the original question-

 

The quick fix to any glaze run is alumina hydrate in 0.50 to 1% additions. The second fix is to reformulate using calcium as the primary flux, with higher percentages of alumina molarity. The alternate fix is to use a stoneware body with much higher percentages of alumina in the body.(leeching). Assuming direct flame, high alumina molarity would be advisable.

 

and here I thought Timothy Leary was dead.

 

Nerd

[neilestrick 4,455]

I think he can't really fix the glaze issues until the kiln issues are fixed. And the glaze issues may not really be an issue once the kiln is firing evenly.

[Guest JBaymore]

I think he can't really fix the glaze issues until the kiln issues are fixed. And the glaze issues may not really be an issue once the kiln is firing evenly.

 

That's why I moved the thread here...... Kiln first.  Terribly uneven firings....... unusable unless you want to use about 4-7 different glazes... one per different section of the kiln.

 

Fix the kiln.... might "fix" the glazes.

 

best,

 

.............john

[JamesP 1]

I have not yet cut the shelves to incorporate the space that is needed, but I will do that this week and also add these 1x1 hard bricks you speak of. I was also thinking of lifting those bottom shelves up 4inches so that the flame could be under them a bit more. Would that be to much space or should I try it out? That was very helpful thank you

[Mark C. 4,729]

Raising them may help the bottom get hotter-I would do 3 inchs 1st

[neilestrick 4,455]

Yes, raising the bottom should help.

[Babs 1,186]

not getting into the kiln side of things as I know nothing about that, but if you were to stopper/plug the basins of the pipes prior to dipping into glaze stem first as suggested, then the bowls of the pipes would be free of glaze prior to firing.. a toothpick in te other orifices would not allow glaze to penetrate there either.

[JamesP 1]

So I tried to cut my silicon carbide shelves with a diamond coated brick saw blade, haha wasted $65 dollars. I wish I would have known to use tungsten carbide blade. Any way I had to improvise so I used some shelves from an old electric kiln I bought and tried to convert to gas.  You can see the pics of what I have done to solve the problems I have been having ( http://community.ceramicartsdaily.org/gallery/image/8897-bottom-shelf/) Ill post pics of the results when the kiln is finished to see if all went well with these few fixes in the kiln. Thanks again

[JamesP 1]

I accidentally let the kiln fire to cone 10 instead of 8 when I was posting pics for this thread. Hopefully I didn't over fire.

But this firing was much better and easier. 

 

(221F)12am warm kiln with door open, close door at 12:45am 

(414F)1:05 seal door damper on 2/3 and gas is at 1/8 open

(615F)3:05 Turn gas up to 3/8

(1440F)6:15 Turn up 5/8

(1884F)8:15 Turn up 6/8

(2155F)11:30 Turn up 7/8

(2222F or near)12:30 What cone 10 hit already >) | cone 8 is not visible in bottom peep hole so I guess that hit too.

 

Seems like a darn near even firing if cone 8 on the bottom fell. Just hope I didn't leave it on to long, but I wouldn't think I did if at 11:30 cone 8 still wasn't bending. I also fixed my pyrometer with a new part.

 

[Guest JBaymore]

I'm a bit worried that those electric kiln shelves are not going to have liked cone 10 in reduction.  They look like corderite shelves.  We'll see when you open it.

 

The spacing the way that is stacked looks MUCH better for gas flow thru the unit.  Not perfect... but way improved.

 

best,

 

.................john

[Mark C. 4,729]

The stack does look way better but as John said those electric shelve will take a beating at cone 10-any mullite shelve will warp sooner or later at cone 10.

The best saw to use is Wet Diamond saw-harbor freight sells a junker that will work.Diamonds work best on brinks and shelves for cutting even a dry diamond is better than any carbide saw.

[Mark C. 4,729]

On another note is best to have the last cones go down slow as the glaze melt is better. So next fire a bit less gas or more reduction so cones move slow and end of fire.

[bciskepottery 963]

I accidentally let the kiln fire to cone 10 instead of 8 when I was posting pics for this thread. Hopefully I didn't over fire.

Given the rate of temperature rise, you may not have hit cone 10 -- maybe more like 6 plus, if my calculations are not in error:

 

(221F)12am warm kiln with door open, close door at 12:45am

(414F)1:05 seal door damper on 2/3 and gas is at 1/8 open

(615F)3:05 Turn gas up to 3/8

(1440F)6:15 Turn up 5/8 -- 825F rise in about 3 hours, or 275F per hour

(1884F)8:15 Turn up 6/8 -- 444F rise in about 2 hours, or 222F per hour

(2155F)11:30 Turn up 7/8 -- 271F rise in about 3 hours, or 90F per hour

(2222F or near)12:30 -- 67F rise in one hour

 

Heat work is most important the last 180 degrees of the firing (see Mark's comment above re slowing down). Per Orton's charts, hitting 2222F at somewhere between 67F and 90F per hour would get you to cone 6 (2232 at 107F rate of climb).

[Guest JBaymore]

 Per Orton's charts, hitting 2222F at somewhere between 67F and 90F per hour would get you to cone 6 (2232 at 107F rate of climb).

 

I can just about guarantee that that pyrometer reading he is using is off.  I'd guess he is using Type K thermocouples.....like most people.  Type K thermocouples are crap above about cone 6.  They go non-linear and anything but a GOOD meter unit will not have the programming to compensate for that non-linearity in the signal.  And even then... they do not read accurately enough to compare to cones at the high end.  ASTM does not rate Type K for cone 9-10 use.  Potters use them for high fire because they are cheap.  After about cone 6... they tell you if you are climbing, stalling, or dropping.

 

Here are the upper temperature LIMITS (not the non linear points the "top end")  for Type Ks at various gauges:

 

Gauge of wires

 

        8                     14                   20                    24                 28                   30

1260 [2300]     1090 [2000]      980 [1800]      870 [1600]     870 [1600]     760 [1400]

 

Even 8 gauge is not good for cone 9-10.... and if you fire fast cycle... it is WAY not good.

 

best,

 

........................john

[Mark C. 4,729]

My platinum one's for my oxygen probes reads pretty good at cone 10-I also have hooked up the type ks  in both kilns but I can see the difference and its big.

That should only be used as a general guide to heat rise not exacting schedules. I tend to think of how fast does the cone move  in terms off heat work.The more of this you do the better you get at it.If its weekly or more often its second nature I think.

[Guest JBaymore]

The good thing about the platinum ones is when they eventually die.... you can make a ring out of them. 

 

best,

 

.................john