Laser Gas Kiln Help

[Bill Kielb]

1 hour ago, crb said:

The regulator -- the manual specifies up to 300mb so 30mb was going to be tricky to get to top temp I think... 

interesting as 300 mbar (120 inches of WC) is ten times more than what you theoretically should operate the kiln. Your orifices seem to be designed for 37 mbar maximum to produce 24 KW of heat. What pressure did you operate the kiln at towards the end of your firing?

[crb]

On 3/15/2022 at 4:07 PM, neilestrick said:

Were you dampering the flue at all? You'll need to. Kind of an odd setup to have the flue 90 degrees to the burners. For a single burner inlet it would be better to have the flue on the opposite side. It'll be interesting to see if you get cold spots in the front left corner.

Hi Neil, I did get a cold spot in the front left, is there anything I can do to counteract this?

[neilestrick]

3 hours ago, crb said:

Hi Neil, I did get a cold spot in the front left, is there anything I can do to counteract this?

It might be difficult due to the location of the burners and flue, but try to keep more pressure in the kiln. You should have pressure out both spy holes when you put it in reduction. One will have more than the other, but the lighter one should still have a little puff. 

[jevpots]

On 3/25/2022 at 3:07 PM, crb said:

Hi Neil, I did get a cold spot in the front left, is there anything I can do to counteract this?

I find how you arrange the kiln shelves affects the heat circulation. Slightly overlapping bottom to top on the burner side and keeping the backs close to the back wall send to help me. I also have the model with the turbo fan which adds an extra dimension to circulation. I put thermocouples in the top and bottom bung holes to give me extra feedback too.

[Bill Kielb]

23 hours ago, jevpots said:

I also have the model with the turbo fan which adds an extra dimension to circulation.

Hmm, Just curious what is a turbofan? Perhaps a powered burner?

[jevpots]

On 3/28/2022 at 11:34 AM, Bill Kielb said:

Hmm, Just curious what is a turbofan? Perhaps a powered burner?

It's an electric fan under the burner port to boost the air flow to the burner.  Speed is adjustable. Adds an extra dimension to the kiln controls. Turbofan is the name given to it by the manufacturer.

[Mark C.]

I would stack larger taller forms and not as tight in that cold spot to allow more circulation  in that spot-also maybe a flame diversion that forces the flame that direction.

[Bill Kielb]

6 hours ago, jevpots said:

It's an electric fan under the burner port to boost the air flow to the burner.  Speed is adjustable. Adds an extra dimension to the kiln controls. Turbofan is the name given to it by the manufacturer.

So you are referring to a power burner? It’s not atmospheric, it’s powered.

[Nick C-S]

Hallo Chloe

I have a J9 kiln like you and the same problem getting to temperature (it's rated to go to 1300C, max 300mbar of pressure).  My regulator is max 37mbar, just as yours was initially.  (An earlier G7 kiln worked perfectly up to 1300C with this set-up.)

Can you please tell me what regulator type and pressure solved your problem?  Is there advice in your manual about this (I don't have a copy).

Did you change your burners, nozzles or kiln gauge or anything else at all?

Nick Caiger-Smith (Berkshire, UK)

 

[Bill Kielb]

1 hour ago, Nick C-S said:

I have a J9 kiln like you and the same problem getting to temperature (it's rated to go to 1300C, max 300mbar of pressure).  My regulator is max 37mbar, just as yours was initially.  (An earlier G7 kiln worked perfectly up to 1300C with this set-up.)

@Nick C-S
I believe that thread was from 2022, you might want to direct message Cloe (The little envelope at the top right of the page). As far as the pressures you mention, 31 mbar (Her kiln label I think was actually 31 mbar in the label) would be low pressure and require a first AND second stage regulator. 300 mbar is ten times more pressure and requires a first stage only regulator. If your kiln is rated at 300 mbar, it will not run correctly at 31 mbar. To confirm post a picture of the label on the kiln, the pressure and orifice size should match an orifice table at medium pressure for the gas being used. Confirm 300 mbar is correct before operating it at that pressure, it’s not typical.

Most gas kilns need proper damper and gas management so all the heat does not simply go up the flue.

Edited June 12, 2023 by Bill Kielb

[Nick C-S]

Bill, here is a photo of the ‘duty plate’ on my Laser J9.  (Sorry it’s sideways, no means to rotate it that I can see.)  Thanks for your comments.

I don’t know how to direct my query to Chloe (2022 dialogue with you) as you suggest. Have to hope she reads my post.

Nick

 

[PeterH]

1 hour ago, Nick C-S said:

I don’t know how to direct my query to Chloe (2022 dialogue with you) as you suggest. Have to hope she reads my post.

 

Click in the icon to the left of her post, this will open up her profile.

Click in the icon near the top of the page.

Compose and send a "personal message", which she will receive by email.

With luck she will reply either by email personal message or via this thread.

PS I believe that your email addresses aren't shared in this process..

Edited June 15, 2023 by PeterH

[Bill Kielb]

1 hour ago, Nick C-S said:

Bill, here is a photo of the ‘duty plate’ on my Laser J9.  (Sorry it’s sideways, no means to rotate it that I can see.)  Thanks for your comments.

Yep, 0.3 bar IS 300 mb so your kiln ought to have orifices sized for this higher pressure which means they will be much smaller than Chloe’s kiln marked as 31 Mb (see below) So assuming someone has not changed the orifices you will need a regulator to drop tank pressure down to 0-300 Mb. About ten times more than Chloe. Max pressure does not necessarily mean operating pressure though.

So I would suggest double check the current orifice size, confirm the operating valves are rated to at least 300 mb just to be sure this will operate safely on 0-300 mbar. Raw tank pressure can be more than 10 bar or 10,000 mbar so proper regulation is important.

Chloe’s  tag below for reference

 

Edited June 15, 2023 by Bill Kielb

[crb]

Good morning, almost a year and a half since I started this thread and the kiln has been firing consistently beautifully until this week. 

My kiln roof collapsed (the lining inside) last week (it had been on its last legs for a while) and we replaced it at the weekend, replicating the same fitting and materials as before.
BUT my firing on Monday suddenly needed almost double the pressure to get to the top temp (150mb was enough to reach the top temp before -- this time it took to 250mb), today I started the kiln as normal at 6 this morning but still needed double the pressure to get the same temp rise and then about 2 hours into the firing the kiln started turning itself off and reigniting say about every 10/15mins.

I've turned the whole system off, checked the valves were clear (as much as I could from the under and side I'm waiting for the kiln to cool to check no debris has fallen from inside the kiln) and swapped the bottles over to full tanks (although the other bottles still had half tanks). Restarted the kiln and again every 10/15mins the kiln shuts off and reignites. 

I've got in touch with my gas plumber but just reaching out to see if anyone has had the same problem/has any ideas about what's going on? 

 

[Bill Kielb]

3 hours ago, crb said:

BUT my firing on Monday suddenly needed almost double the pressure to get to the top temp (150mb was enough to reach the top temp before -- this time it took to 250mb), today I started the kiln as normal at 6 this morning but still needed double the pressure to get the same temp rise and then about 2 hours into the firing the kiln started turning itself off and reigniting say about every 10/15mins.

More and more pressure would indicate airflow issues, so did you ever come to terms with the operation of a damper? Also cycling on and off would indicate operating limit or high limit. How is this kiln controlled? Pictures here would help. I see pilot safety and a spark igniter in an earlier picture so this kiln likely has a high limit as well. 

My best guess, the flue passage behind the back wall is restricted and not clear, so maybe collapsed somewhat and the high limit sensor might be located in this passage and not sensing the true temperature of the kiln or it is set low or just out of calibration.

So things to check: everything free, clear, not obstructed or collapsed …..l and how is the kiln safety or high limit intended to work?

Edited September 28, 2023 by Bill Kielb

[neilestrick]

I'd pull the burners and make sure they didn't get a bunch of crud in them during the collapse and rebuild.

[Mark C.]

I would clean out the orfices with a small hand helt drill bit to make sure they are clean

[crb]

On 9/28/2023 at 12:23 PM, Bill Kielb said:

More and more pressure would indicate airflow issues, so did you ever come to terms with the operation of a damper? Also cycling on and off would indicate operating limit or high limit. How is this kiln controlled? Pictures here would help. I see pilot safety and a spark igniter in an earlier picture so this kiln likely has a high limit as well. 

My best guess, the flue passage behind the back wall is restricted and not clear, so maybe collapsed somewhat and the high limit sensor might be located in this passage and not sensing the true temperature of the kiln or it is set low or just out of calibration.

So things to check: everything free, clear, not obstructed or collapsed …..l and how is the kiln safety or high limit intended to work?

Thank you!

Yep all correct, when the kiln had cooled I saw debris had fallen into the burners (I'd covered them but not well enough it seems!) gave it a good clean and now firing smoothly today but requires double the pressure again. 

I have the manual now kindly given by a member here and the pressure increase matches the sample firing given in the manual - just trying to get my head around why it needed less gas before. I think the kiln is now well-sealed and repaired, so is there less airflow? The dampers are adjusted at the top of the kiln across the top vent. I will take pictures.

[Bill Kielb]

5 hours ago, crb said:

gave it a good clean and now firing smoothly today but requires double the pressure again. 

I have the manual now kindly given by a member here and the pressure increase matches the sample firing given in the manual

Hopefully all works for you

On 9/28/2023 at 3:06 AM, crb said:

then about 2 hours into the firing the kiln started turning itself off and reigniting say about every 10/15mins.

Ever figure out what was turning it off and on again?

[crb]

On 9/30/2023 at 1:34 PM, Bill Kielb said:

Hopefully all works for you

Ever figure out what was turning it off and on again?

It was a safety thing -- it (understandably!) didn't like the debris in the valves.

Unpacked the kiln this morning -- beautiful firing and in the shortest firing timeframe reflecting the original manual. So happy a potter all round!

[cspindler]

Hello.  I’m a UK potter looking for help in diagnosing problems with a Laser J12N downdraft kiln, which runs off LPG and has 4 burner ports.  Following a recent repair to replace a collapsing ceiling, the kiln now requires more gas to make it to temperature (cone 9/10) and the reduction has become very patchy.

The interior ceiling was repaired using a piece of 25mm ceramic fibre board with a temperature resistance of 1260C.  Above this, under the metal roof,  we inserted a layer of 25mm ceramic fibre blanket plus a layer of 25mm ceramic fibre board, both with a temperature resistance of 1260C.   

When we removed the old insulation under the metal roof, we discovered the remains of a metal bar at the back of the kiln just in front of the flue opening (see photo showing position) which had corroded away.  It looked like it may have supported a thin layer of ceramic board/blanket.  We didn't replace this metal bar when doing the repair.  

Prior to our “fix” it would take us about 8-9 hours to reach cone 9/10 using one 19kg tank of LPG.  We typically put the kiln into reduction at about 1000C using ceramic bricks in the flue opening.  In terms of reduction achieved within the kiln, pieces on the bottom shelves would be slightly less reduced due to proximity to the burner ports but pieces above would be nicely reduced with those on the top shelves achieving the heaviest  reduction.

Following our “fix” we found that one 19kg tank of LPG was no longer enough to get to cone 9/10 so we purchased a changeover valve to allow for a second tank.  Also the levels of reduction within the kiln are now very unpredictable.  But  generally, pieces on the bottom shelves are not reduced at all and neither are pieces on the top rear shelf.  Pieces on the middle shelves are the only ones showing any amounts of reduction.

After we had done a couple firings, we noticed that the piece of hardboard we'd used to replace the interior ceiling had shrunk from the back wall and was already showing signs of cracking.    Also, our first few attempts of using the change-over valve were a bit bumpy.  In both instances, the pressure/flow of gas from the first tank had already dropped quite low when we initiated the changeover.  We didn’t completely lose flame before engaging the next tank but it did drop quite low for about 5 minutes.

So before embarking on another fix I'm looking for some guidance on how to do it correctly.  Specifically, I have the following questions:

• What could be the cause(s) of the need for more gas and the change in nature of the reduction within the kiln?
• Should we be using ceramic fibre board / blanket that has a temperature resistance higher than 1260C?
• Should we be using ceramic fibre board / blanket that is thicker than 25mm?  Or is there a total thickness of insulation that we need to achieve?
• Does anyone know the purpose or importance of the metal bar at the back of the kiln?
• Could the issues we encountered with the cut over valve have contributed to the lack of reduction on the bottom shelves?  Is there a different/ better way for us to manage the change over?

Any other thoughts/comments/suggestions beyond the above are certainly welcome!  Many thanks in advance for your help!

Clare

[neilestrick]

@cspindler  How was the original ceiling constructed?

[Mark C.]

1260 in my world 2300 degrees  which is just at the temp you are firing to so 1st its going to shrink and crack

You need higher temp materials for cone firing in kilns for repeated firings. I would use 2600 degree fiber (you can convert as I had to to see what this temp is )

Fiber board and fiber rolls shrink and they shrink the most at maximum limits and thats where you are right at cone 10.

Even bricks at their limit will spall over time-say like acone 10 brick kiln with K2300 soft bricks they spall after reapeated firings. I have laerned this about 40 years ago in my kiln building life.

Repalce all the 1260c with higher limit materials-they will cost more.

The metal in that photo (photo needs to show a larger area so one can see what it is (a chimmney stack or kiln lid? )It looks like part of kiln frame and if thats true you need it.

I would need to see the inside of kiln ceiling and outside better to advise on the that metal bar and whats it doing. better and more photos

If you have used up the 1st tank and its low pressure less gas ,well yes it can affect reduction very much

25mm is what we call 1  inch and you need in my mind a minimum  of  6 inchs or 16 centimeters for a kiln ceiling of fiber for cone 10 firings. More would be better

You only need the hot face to be 2600 degree material-say the 1st 2 inchs thgen the cheaper 1260 material can be the rest of the make up to get -9 inchs of ceiling in total you need

My guess is you are losing the heat through kiln ceiling.Lots of heat

Fiber board for me shrinks  and cracks more and I prefer fiber blanket with buttons to hold it up but this will fail over time.. It's not the best for ceilings because of this.. You can fold it in U shapes and compress it with stainless rods and steel ends and it works well for flat ceilings this way.

I have a salt kiln made this way with a 9 inch thick ceiling and the rods are about 6 inchs up from hot face. I folded  the  2 foot wide blanket  in half and cut it to make the 9 inch folded tacos(this takes about 22 iches of 2 inch thick fiber as tghe fold trakes up length  and compressed them in a wood form and rammed a sharpened treaded stainless rod (use nuts on ends ) through them with a flat bar on each end to compress the tacos into a tight flat roof that is a uni solid one piece unit that sides on kiln walls.

[cspindler]

On 1/20/2024 at 1:25 AM, Mark C. said:

1260 in my world 2300 degrees  which is just at the temp you are firing to so 1st its going to shrink and crack

You need higher temp materials for cone firing in kilns for repeated firings. I would use 2600 degree fiber (you can convert as I had to to see what this temp is )

Fiber board and fiber rolls shrink and they shrink the most at maximum limits and thats where you are right at cone 10.

Even bricks at their limit will spall over time-say like acone 10 brick kiln with K2300 soft bricks they spall after reapeated firings. I have laerned this about 40 years ago in my kiln building life.

Repalce all the 1260c with higher limit materials-they will cost more.

The metal in that photo (photo needs to show a larger area so one can see what it is (a chimmney stack or kiln lid? )It looks like part of kiln frame and if thats true you need it.

I would need to see the inside of kiln ceiling and outside better to advise on the that metal bar and whats it doing. better and more photos

If you have used up the 1st tank and its low pressure less gas ,well yes it can affect reduction very much

25mm is what we call 1  inch and you need in my mind a minimum  of  6 inchs or 16 centimeters for a kiln ceiling of fiber for cone 10 firings. More would be better

You only need the hot face to be 2600 degree material-say the 1st 2 inchs thgen the cheaper 1260 material can be the rest of the make up to get -9 inchs of ceiling in total you need

My guess is you are losing the heat through kiln ceiling.Lots of heat

Fiber board for me shrinks  and cracks more and I prefer fiber blanket with buttons to hold it up but this will fail over time.. It's not the best for ceilings because of this.. You can fold it in U shapes and compress it with stainless rods and steel ends and it works well for flat ceilings this way.

I have a salt kiln made this way with a 9 inch thick ceiling and the rods are about 6 inchs up from hot face. I folded  the  2 foot wide blanket  in half and cut it to make the 9 inch folded tacos(this takes about 22 iches of 2 inch thick fiber as tghe fold trakes up length  and compressed them in a wood form and rammed a sharpened treaded stainless rod (use nuts on ends ) through them with a flat bar on each end to compress the tacos into a tight flat roof that is a uni solid one piece unit that sides on kiln walls.

Mark,

Thank you so much for your quick and thorough reply.  I had only found out after doing the repair that the materials I'd been given were 1260C and thought that wasn't enough.   But it's good to have your confirmation here and your suggestions on how much total thickness of insulation we should be aiming for.   

I'm attaching here some general images of the kiln showing 1) front on view of the exterior and hood; 2) interior view (post fix, where you can see the shrinkage and cracking in the ceiling) and 3) close up showing flue opening and hood.   

I will send separate messages with images of the roof, which will hopefully better explain the positioning of the corroded metal bar. 

[cspindler]

On 1/19/2024 at 10:50 PM, neilestrick said:

@cspindler  How was the original ceiling constructed?

Hi Neil,

The original ceiling was fibre board with ceramic pins inserted which then were attached with wires to metal cross bars that spanned across the top underneath the metal roof piece.   The attached pictures show 1) the interior post repair, but which is very similar to what it looked like before and 2) the top of the kiln with metal roof piece removed showing the cross bars where the pin wires were attached.