Jump to content


  • Content count

  • Joined

  • Last visited

Community Reputation

0 Neutral

About gianda

  • Rank
  1. 48Cuf Gas Kiln Help

    I have highlighted a small piece of text that is worth noting because I think it exactly pinpoints the problem. After the 2 small burners were shut off the kiln took off. If you made no other adjustments besides shutting off the 2 small burners I think that they are not mixing in enough air. I'd try a firing using only the two newer burners and see how even you can get the temperature. If that doesn't work replace the 2 older ones with burners like the other two new ones and give another try. You don't want the temp to rise that quickly. You are trying to do a specific amount of heat work on the pots/glazes in the kiln and time is a component of heat work. If the temp rises too fast, the glazes may not melt completely and the clay may not become totaly mature The pots are great BTW. The brushwork is fantastic. Hi Ben, thanks for the compliments, well, the 4 small old burners wouldn't reach temperature, while the two large ones seam to be doing the work just fine... What I'll try next firing is to use the small burners alone for the first 4 hrs because at low pressures they seem to be doing just fine and the temp rises nicely and steadily... for the last 4 hrs ( 600deg onwards,) I'll shut those 2 off and replace them firstly with 1 single large new burner and then add an extra one when the temperature raise seems to have slowed down a little. Hopefully it'll work! P.s. When the 2 small burners went off, I plugged the holes and left only the two single burners to do the work.
  2. 48Cuf Gas Kiln Help

    Thanks guys, for all the support and help... As said in my last post, problem has been solved... Overall, I think that i was a combination of problems... Undersized burners to start with, burner ports to continue, exit flues maybe, and during the last firing, after finishing the gas on the two small burners, the temp started rising like crazy on the two new larger burners alone from 1184 to 1215 in 8 minutes... ( 1 deg, C every 15 seconds. which at high temps is pretty good as far as my experience goes.) The final temp reached, after the gas on the larger burners run out too was 1235. which was reached in 12 minutes or so... Looking at this, I feel pretty confident that I should be able to get to cone 10 at the next firing... Here a sum up of the changes done for ref. 2 Large burners using 35mm iD SS pipe with 60mm dia burner head and 1.8mm orifice. Burner ports of 75x75mm square. 2 small burners using 25mm iD ss pipe with 45mm dia burner head and 1.2mm orifice. Burner ports of 60mm dia. Exit flue is 7"x4.5" Kiln size is 3'x3'x4'depth chamber. Chimney height is 5' I can post pics of the kiln for further reference, but as of now, after building my first kiln, if I had time I would rip down everything but the chimney and floor and rebuild it from scratch... ( well... lots learned from building this first one) and waiting for the next one... Also here i India materials are really cheap and saved a lot of $ by building my own kiln instead of asking someone to do it for me... ( here there are not many real professional companies that build them anyways...) All in all, my time not counting in the equation I have spent to build the kiln 80,000INR which in $ is about 1330$... Carborundum shelves 1'x2'x1" come at roughly 40$ One 7 meter roll of high temp. 1470 deg C fiber costs about 35$ High alumina bricks 0.56$ a piece Iron comes at little less then 1$/KG so the frame including welding and all set me back 250$ ANYWAYS, one never stops learning! here the pic of the large venturi built from SS off the shelf parts for 15$ each... And here some pics of the pots that came out of the firing @ 1235Deg C. some glazes melted really well... some others not... Some others might have needed a thicker application.... P.s. the pottery went through 2 firings !!! hence the cracks on some of them... first firing @ 1125 and second firing at 1235.
  3. 48Cuf Gas Kiln Help

    In bernoulli's principle the talk about "potential energy" is in terms of pressure not BTU's.... If the PSI on the pressure regulator at the cylinder is the same both for a, lets say, 1.6mm diameter hole or a 1.8 dia hole, the gas quantity coming out of the orifices might be the same, only the speed at which the gas travels will be different. if the gas travels faster it should create more venturi effect ... As far as secondary air, the inlets are quite big,,, If you do a test with the burners out of the kiln it is quite easy to determine the flame quality and to see if enough primary air is there or not... This is mostly due to burner design.... i.e. I can have a perfect burner design, but if the orifice is way over or under sized, it will work at a % of its real efficiency. I will have to do an empirical test... and go down from 1.8mm dia at 3.5psi to a 1.6 and maybe 1.4 at a slightly increased pressure and see if there is too much turbolence or if the flame burns better...
  4. 48Cuf Gas Kiln Help

    For gas kilns in The Olsen book it states that the exit flue port should be equal to the area of the inlet ports sizes. On rule of thumb NB 2 it would come out to 90Sq".... 3 times more then what i have now... By rule 3 it should come to 63 sq " ( double) An by rule 1 which is on the book ( 2 large square ports at 3"x3" + 2 round ports at 2"1/2 dia = 34sq")
  5. 48Cuf Gas Kiln Help

    If I go by this and consider the kiln to require 12K BTU per CUF it will come to 36x12/8=54 SQ INCH my flue size now is 7"x4.5"= 31.5 SQ INCH I don't think an increase in flue size by 40% more or less is the solution... especially if the burners are homemade ... I consider it to be more of a orifice size/ air inlet problem. But this said, I am planning to remove 2 bricks and add 2 1/2 bricks to the flue gate, thus increasing the flue size by 13.5sq" ... to 45SQ" and block off part of it to make it roughly 37-38 sq". If area of flue opening (inside) is usually close to or equal to area of burner port opening ....
  6. 48Cuf Gas Kiln Help

    Hi Mart, Having a look at the orifices the other day, I discovered the old ones in the small burners were 1.2mm dia. The other issue is the pressure... the more pressure you put in the line, the more gas will come out, and with a LPG cylinder you can get up to 25 PSI. But the burner size and design as well as pressure and orifice are all influential to a good flame with enough btu's. Anyways... the big burners with a 1.8mm hole seamed to do well up to 3.5psi after which the flame quality deteriorated... I'm now curious to print out a chart I've found on the net for different drill size and output of BTU's at different pressures and check with smaller size orifice at higher pressure. It could well be that my burner is not able to generate enough venturi effect and is therefore not sucking in enough primary air to mix in the fuel. Apart from that otherwise the kiln is quite responsive and I don't think there is a circulation problem... i.e. if the kiln is not reducing and I blast the gas though causing reduction, it takes less then 3 seconds for the unburned green gas flame to come out of the chiminey... FOR your info, attached the PDF with orifice sizes which helped me to find out the burner tip size and orifice size... How did you arrive at 3 mm? I searched around a bit and I found out that 3 mm (0.11811") is going to give you close to 105K BTU , so you are about 21 BTU's short per burner, or 84 BTU in total. EDIT: and if you are "reducing", you need to give it more air from intake. Can you make the burner holes bigger, so more secondary air gets in? PS! Do not take my word for it, I am not a pro nor even a noob Gas Orifice Capacity Chart.pdf cat0454.pdf Gas Orifice Capacity Chart.pdf cat0454.pdf
  7. 48Cuf Gas Kiln Help

    Hi marcia, the efficiency of the two single large burners stops at 3.5 psi (I could fit a .2mm smaller orifice though and the increased velocity of the gas at the same pressure should be able to drag in more air. The larger burners primary air is regulated by a dial/disc and the secondary is pretty big at a square 3" in side size.
  8. 48Cuf Gas Kiln Help

    Hello everybody! sorry for the long wai in my reply, but spent some time welding the new stainless burners and did a firing this sunday! So, started the firing ( Glaze) with the 2 old burners with a smaller orifice ( 1mm dia) and all went fine. After 700C added the 2 new burners which have a pipe dia of 1"1/4 and an orifice of 1.8mm (enlarged the air ports) In between power went off 2 times so couldn't monitor the temp. increase properly and it got stuck a couple of times. Gas finished on the 2 small burners and all of a sudden temp. increased steadly and at a much faster rate, from 1160C to 1235C after which even the gas of the 2 larger burnrs finishes... From 1000C all the firing was just slightly reducing ( and some rockwool in between fell on one of the burners also stalling the kiln for some time till I discovered the problem.) From what I can say till now I do think that given the extra gas the kiln would have reached temperature, as the increase was steady and fast ( 1deg C every35-40 sec.) from 1160 to 1235. But as the kiln was always reducing with all 4 burners I guess another way to go about it is to use just two... as the 2 new burners can handle the requirement as it has shown... As far as the exit flue goes, to decrease the reduction, I could enlarge slightly the outlet flue... ( from 900C upwards I had to keep the top peep hole open ( 2"x3" ) otherwhise either the gas pressure was too low even with the closed hole, or with more gas going in it would reduce.... With the open peephole, a 4" to 5" slow flame was coming out but temp. rising. Total damage for this firing. 3 full commercial cylinders 19KG gas each 1-1/2 domestic Cylinder 14kg each total gas used 78Kg of LPG (100US$ here in India). ANy idea if this sounds right for a 1280 firing in my kiln size (4'x3'x3')? I'm kind of convinced I should be using about 1/3 less gas then this... Thanks guys! Ps. here the pic of the old small burners with a tip dia just shy of 2" inner tube dia of 1" . the new ones are nearly 2"1/2 inner tube dia 1'1/4
  9. 48Cuf Gas Kiln Help

    Hi Guys, am in Italy at the moment and will be back in India on the 31st July. Then I'll get some pics and post them but here a couple more info on the burners. They are made from off the shelf water/gas connection tubes and elbows I think, ( as I don't have them here with me) they are 1-1/4" dia. the design is much like the B/W Diagrean just below the colou picture. the only machined parts are the venturi funnel in ALU which has a dial/disc on a thread. The orifice can be removed and changed over and the burner head has the ring with the small holes on it, and the center is hollow. As Ben says, I do feel that it is an air intake problem. and I feel it has to do with primary air, as the secondary has a 3-1/2" diameter ( straight hole). (The burner head is 2-1/4" and rests 1-1/2" away from the port) As far as primary I have tried to open the air to its max, but without success. And at this point I think that ( having tried both smaller and larger orifices) the problem may rest in the size of the burners tubes. i.e. I think that the smaller orifice "sprays" a cone which is the right size for this tube, but that increasing the orifice size, the "spray" cone gets wider thus reducing the sucking action of the venturi. As each burner ( and expecially venturi's) are specifically designed for a cerain operation condition ( BTU, pressure, orifice size) I feel that it may well be that the burner size is too small for the orifice I'm trying to use and that with a smaller orifice, which is right for the burner won't give the required BTU's. ( new burners are not a huge issue as being in India I can get them made for a very very reasonable price. ) If I only knew before that the guy who supplied them to me didn't have a clue I would have probably tried to make them on my won or purchased them online... Till the pictures come bear with me! P.S here some pics of pots and the open kiln with the 130 deg underfired pots... If you want to see out web is www.italyindiadesign.com and FB is www.facebook.com/italyindiadesign hear from you soon guys, Gianda
  10. 48Cuf Gas Kiln Help

    Hi Ben, Thanks for the long and clear reply, I think that we need as you said to put in more heat. and considering the increased pressure which we try to push in towards the end and the resulting stalling in temp, I could deduce that there is not enough air going in or that the combination of the size of the venturi and the orifice is not right. As pointed out by Wyndham here is the venturi burners website, but they don't state what size orifice comes with the burners. ""Here's a link to the MR750's I'm using http://www.wardburne...uriburners.html"" On the other hand it is not really an option to get two more burners which are not reaaly effective... I'd rather gather some good info and ( as I'm in India, ) get 4 new ones made from scratch for cheap rather then having to break through the floor of the kiln. At the moment we're running 4 pieces of 2" burner head but I fear that the venturi burner size is small for the orifice size we need using only 4 burners. diam. in inches Btu/NG Btu/LP Model A B C 7"wc 11"wc 1 psi 2 psi 5 psi 10 psi 20 psi Price B-1 8 1.38 1.85 5,500 5,900 9,700 13,900 21,600 30,700 43,000 $145.00 B-2 11 2.25 2.75 13,900 9,000 14,800 20,900 33,200 46,700 66,400 $199.00 B-3 12 3.25 2.75 41,600 34,200 55,300 77,500 123,000 175,900 246,000 $215.00 B-4 17 3.75 3.5 67,800 55,300 89,800 126,700 200,500 286,600 403,400 $229.00 B-5 21 5 4.12 81,600 89,800 145,200 205,400 324,700 462,400 649,400 $375.00 LOOKING at the above table I see that the 2.25" B-2 burner they offer only goes to 66,400BTU at 20PSI, whilst the B-3 3.25" goes at 5PSI at 123BTU... Shame they don't specify orifice size, as 4 of these burners would do the job. By the orifice table size, It comes out that I should use a 3mm dia hole... I just need to double check with someone who has venturi burners and similar size kiln... Our kiln is IS-8 high alumina briks sides lined with 1" of rockwool, top is full Rockwool, chiminey is IS-8 bricks and door is IS-8 bricks on the inside, 1 layer of 1" rockwool and insulation firebricks on the outside. Thanks for any help! Gianda
  11. 48Cuf Gas Kiln Help

    Wyndham, Thanks for the link, just one more question, whith a simple ruler/scale could you measure the orifice size for me.... Some rough measure, no need to go down to .1 mm and again how many burners you have for how many cuf. and pressure u use. thanks! gianda
  12. 48Cuf Gas Kiln Help

    Thanks Wyndham, this helps quite a bit. What are the sizes/diameter of your 6 orifices? All the same or different sizes so to be able to compare with my calculations before increasing sizes of burners and orifice. Before rebuilding the chiminey I think I'll try with the burners... much cheaper and less time consuming if it works. thanks.Gianda
  13. 48Cuf Gas Kiln Help

    Hi Wyndham in PSI we go from 3PSI at the start of the firing to 11-12PSI towards the end. we do have two lines, each with 1 pressure regulator for 2 burners. (Total 4 burners) Anything above 12-13 PSI gives reduction problems. and as said before we get stuck at 1120-1150 deg Centigrade. Thanks, Gianda
  14. 48Cuf Gas Kiln Help

    Line is fine being a LPG cylinder pressure is not an issue... the Orifice size also I can drill myself... or buy ready ones here in New Delhi... The info I needed though is more in relation to the calculations I made about the BUT's needed and orifice size and if the burners we have are able to support such an increase in orifice size... Otherwhise, I'll have to make new burners... thanks again!
  15. 48Cuf Gas Kiln Help

    For reduction we normally, during and at the end of the firing after soaking block partially the chiminey with bricks at the top and lower the primary air intake. As for the Fuel we use LPG. We are based out of india, and the gas provider is probably the last person who is able to help us. Also the guy who made the burners for us is postponing his visit to check them out and not showing any interest in it at all. As far as it goes, the burners are identical to the ones fitted to our old 27cuf kiln. same nipples/orifices and all. Afther telling him that our new kiln was 36cuf he said the nipples/orifices are fine being the same as for the old kiln. I made a couple of calculations and estimated as per the Kiln book ref. the BTU imput required to be: 14K BTU per cuf. or kiln X 36cuf= 504KBTu Now if we divide this number by 4 burners we will get a result of 126KBtu per burner. This should give an orifice size of 3mm diameter. The ones we have now are nearly half this size. lets call it 2mm. I'm not sure if the tube burners we currently have are big enough to support this size orifice and take in enough primary air. ( the burners have an aluminum cone shaped primary air controller and fixing for the orifice, the body of the burner is made of normal 1" pipe and the burner head is 1-3/4" dia.) The top burner in the pic looks more or less like ours... only our one has a conical primary air fitting and one single orifice and is much more rustic, being built with off the shelf pipes. Morelike this one, just with a L shape: Ps.thanks for the nputs