Jump to content

Built a Kiln on Joe Finch's model. The temperature is stuck at 600 degree celsius.


Rupsa Nath
 Share

Recommended Posts

Hi,

This is the first kiln my husband and I built. The model we followed to the letter is of Joe Finch, as he explained in his book, "Kiln Construction: A Brick by brick Approach".

We have fired this kiln 3 times so far, and every single time it has gotten stuck at 550-600 degree celsius.

About the Kiln:

The Gas Kiln has an inner dimension of 1 cubic meter. The wall is made of regular insulated firebrick + 4" ceramic blanket +outside layer of firebrick again for more insulation. It is a downdraft kiln with two burner ports on either side. Our chimney is about 7 feet tall and the exit flue is equal to the area of the burner ports.

Burners:

We initially did two firings with small burners (model S20) with a Btu of 30,000-83,000 per hour.  And the next model (S80) we took for our third and last firing with a Btu of 120,000-336,000 per hour. I have attached a picture which has the list of burner models so you can see all their specs. 

Gas cylinders:

In India for commerical firings, we get 19kg LPG cylinders, and we are using two of those simultaneously for our gas firing. To keep the pressure from falling too low, I douse the cylinders in room temperature water when they start to ice up in the bottom.

For all the three firings we have done, the temperature always slowed down at  560 degrees celsius, and then stuck around 580 degrees celsius. The first time we kept firing for about 3-4 hours, but there was no progress, and the last time we stayed at the temperature for 1 hour before calling quits. I have added the firing schedule below for the first and third firing so you can see how the temperature had risen. All the numbers mentioned are in celsius.

First firing (Sunny day,                 Third firing (Sunny day,

not much wind)                                  less wind)

1.30 pm    82.1                                   11.47am       215

1.51 pm    191                                     12.05pm      364

3.32 pm     279                                    12.09pm      400

4.42 pm     400.5                                 12.28pm      533

5.36pm      504                                      12.51pm      588.6

6.47pm       551                                     1.46pm         562

7.24pm       570

7.55pm       563

As you can see, we took less time to reach 550 degrees in the third firing with our bigger burners. But all three times, the temperature got stuck at around 580.

I have added pictures of our burners position as well, and we made sure they were outside of the kiln to pull in the air and burn the oxygen.

Based on these figures, do you think:

- Our chimney is too small in height?

- Burners are not enough?

-Some other factor that is stopping the temperature from rising?

Grateful for any advice and suggestions.

Thank you!

 

 

burner models.jpg

82118042_1040051933001618_7613406689865236480_n.jpg

81880409_1077940145884066_2850079682752151552_n.jpg

81819351_722550074940217_705549486193115136_n.jpg

Link to comment
Share on other sites

Your chimney might set your house on fire.

Here's a link to a free handout on kiln design, it has some helpful sections on calculating chimney length and combustion area for natural draft kilns.

https://ceramicartsnetwork.org/wp-content/uploads/2010/05/gaskilnsfreemium.pdf

Edited by liambesaw
Link to comment
Share on other sites

I realize the third pic is kind of an optical illusion but still isn't this kiln venting right into a wood side of your house? Is that safe? I mean I know heat dissipates pretty rapidly but that sure seems close especially since you are talking abut increasing it. I don't know much about kiln construction so just ignore me if my ignorance is showing through.   

Link to comment
Share on other sites

At 1 cubic meter you've got about 32 cubic feet of interior space, so you need a minimum of 500,000 btu/hr, probably more, to get to cone 10. I'm betting your little propane tanks are freezing up more than you think, especially if you're running more than one burner off a tank.

You need a damper to control the secondary air draft and internal kiln pressure. Your burner ports look to be pretty big for a burner of that size.

The lack of safety equipment on the burners is troublesome. They're not even mounted to something that will keep them in place. And it looks like the heat from the chimney is going straight onto the building above?

Link to comment
Share on other sites

It seems obvious now that we need to move the kiln away from the house. Dangerous oversight on our part, which we will rectify immediately.

We have been reading Olsen as well, and he too suggests a smaller burner port. We have it in mind to have a manufactured stand for our burners too. But since were just testing them out now, we thought of propping them up on bricks.

@neilestrick: Do we need a damper only at the exit flue, or somewhere else as well? based on the size of the kiln and according to the calculation provided by Olsen, we got to a chimney height of about 15 to 16 feet high. Does that seem right?

 

 

Link to comment
Share on other sites

21 hours ago, Rupsa Nath said:

It seems obvious now that we need to move the kiln away from the house. Dangerous oversight on our part, which we will rectify immediately.

We have been reading Olsen as well, and he too suggests a smaller burner port. We have it in mind to have a manufactured stand for our burners too. But since were just testing them out now, we thought of propping them up on bricks.

@neilestrick: Do we need a damper only at the exit flue, or somewhere else as well? based on the size of the kiln and according to the calculation provided by Olsen, we got to a chimney height of about 15 to 16 feet high. Does that seem right?

 

 

What has been said here is correct. You will need a damper to tune this as you fire and as your temperature rises. The hotter your kiln gets the greater the draft through it. You need to be able to adjust this during firing to regulate how much secondary air you suck in. In general, the taller you make your flue, the greater the suction can be. You should be able to get a better sense of this by temporarily dampening  at the top to note if there is a significant improvement,  do this for test purposes only. If you confirm the requirement, then install a typical  appropriate damper in your design  which then will  allow the total height to be fine tuned once you are able to fire to temperature.

Edited by Bill Kielb
Link to comment
Share on other sites

1 hour ago, Rae Reich said:

Also, your chimney stack can be lengthened by going horizontal on the ground a couple of feet before rising. That would get it further from the house. I think Olson or Rhodes has an example. It's what we did on my large catenary so the stack didn't need to be so tall. 

This can be offset but make sure you follow a  decent design and you likely (at mimimum) will need a spark arrestor to top it off. It looks quite close to the structure. There are other concerns as well, rules that may state the need for it to be a minimum of 10 feet or more from a window that can be opened for ventilation. Try and research all aspects, this might not be the best placement for the kiln

Link to comment
Share on other sites

  • 1 month later...
  • 1 year later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.