I'm thinking of buying a small hobby kiln for firing clay cups, models etc. Something with a space about 250mm x 250mm x 250mm . ideally it would plug into a 13A socket (yes some do).
Does anyone have any good or bad experiences such things.
many thanks
Robert
Kilns usually do what they say on the box.
The question is what controller does it come with?
Also what temperature are you firing at? And how often?
I've got a couple of kilns that I use for fused-glass work (lower temperature than pottery - prob. 850c max).
In glass work we use firing schedules that involve ramping to a specific temperature at a given rate and holding at that temp. before moving on to the next segment - so 'programming' the kiln can be a bit laborious (most controllers use a small number of keys - so it's a bit like programming central heating). As I understand it - pottery kilns tend to heat to a top temperature and then cool down 'naturally' - some use a clay 'cone' which breaks at the top temperature.
So - things to look out for
- ease of 'programming' (if you need anything more complicated than 'heat to top temperature then stop')
- ease of loading - top-loader or front-loader
- suitable for 13A supply (naturally!)
- do you need to see inside the kiln when it's firing? - peep-hole or window, or just lift the lid?
- where you're going to install it (the outside of most kilns gets warm
- how warm depends on the amount & type of insulation) and they can be heavy
I built my 'big' kiln - 4ft x 2ft - and one of my kiln gurus in the USA put it simply "It's a box that gets hot...."
In glass-work - the golden rule is 'The kiln you bought is always one size smaller than you need' - but it all depends on what you want to be doing with it. Adrian
There are several suppliers of hobby pottery kilns and materials, all of which are reliable IMO.
I have three kilns, two electric and one gas. The smaller of the two electric ones, an Aurora kiln from Potterycrafts, runs off a 13 amp socket.
But what you need will depend on what you want to do, and in particular what sort of clay you want to use and what temperature you want to fire to. Broadly speaking, there are two categories: earthenware and stoneware. The former is fired to temperatures in the order of 1050-1100°C, the latter 1250-1300°C. Earthenware clays are often red-firing, fired pieces are slightly porous and chip and break more easily than stoneware pieces, but a wide range of colourful glazes and decorating techniques are available. Stoneware tends to be less porous after firing and is stronger so less prone to chipping and breaking, but the range of colours tends to be narrower and more subdued.
Potterycrafts do a range of circular top-loaders that have an upwards-opening lid, three of which will run off a 13A socket, Mercury, Aurora and Comet
Then they have a range of front-loaders, a bit like a domestic oven,
I also have a larger electric kiln from Kilns and Furnaces, 7kW, that is wired in to a cooker outlet, although I don't think they do my model any more, one of their Sure-Fire Mk II range, TLB112; requires a
30 amp supply.Then there is Podmores, who also do a range of kilns in the size and wattage you're looking for. I don't know details, but I'm sure they're OK. Also Cromartie Hobbycrafts do kilns. I don't have experience of either, but I'm sure their products are OK. Google for them and read their catalogues.
You will probably need a programmable controller, to control the rate of temperature rise and switch the kiln off when it gets to top temperature. AIUI the Potterycraft kilns come equipped with a controller and kiln furniture (the latter are temperature-resistant shelves and props for standing pots on, in layers, like oven shelves, and most commonly used with deep kilns; there's not usually enough head-room in a shallow kiln to warrant more than one layer). But whether other suppliers include a controller and kiln furniture, I don't know. You don't actually _need_ either, although something to control the rate of temperature rise is very useful, as is some form of temperature indicating device so you know when to turn the kiln off. This can be a thermocouple and electronic indicator, or pyrometric cones, that bend as the temperature you are aiming for is approached
Ask, if you want more advice.
Kiln sitters!! Given kiln controllers are more affordable I would avoid using "cones"
Maybe, but the OP needs to think of the largest item he's going to fire.
There's a s/h Potterycrafts 'Mercury' kiln on Ebay ATM, a lot cheaper than new. Buyer collects Colchester
Yes and if you are using clay, I trust its in an outbuilding not in the home. I had a friend who tried this at home and the whole place was full of clay dust in three weeks.
Brian
It doesn't have to be like that. All my stuff, potters wheel, electric kilns, glazes etc., with the exception of the gas kiln, is in a spare bedroom. There's a mat on the floor on both sides of the door, but otherwise no special precautions other than keeping things reasonably clean and brushing the floor every few weeks.
Can I go off at a tangent: Are there kilns that run off two 13 amp plugs, perhaps running two elements independently? To save running a separate supply for a larger kiln. Would that be allowed?
Ideally, these would be plugged into two separate ring mains, but I guess it would not be too much of a problem if it is one ring main and there is nothing else power-hungry plugged in.
Isn't that what 3-phase is for ?
Not commercially available that I'm aware of, but that doesn't mean someone hasn't made their own. As electric kilns go up in power and if still single phase, they are wired into cooker switches and such-like, with cabling of appropriate size similar to that used for high-power showers directly back to the CU. My 7kW kiln has either 6 or 10mm cabling (can't remember which, off hand, but it's big) going back to its own little CU with a 63A RCD. But much above 7KW and you start talking 3-phase.
No comment, other than it sounds like a really bad idea, but I expect the electricians here will be more forthright!
That's my thought, too. It's probably a bad idea. But really no worse than having a couple of 3KW fan heaters plugged in, so I'm not quite sure why it's a bad idea? :)
s etc. Something with a space about 250mm x 250mm x 250mm . ideally it wo uld plug into a 13A socket (yes some do).
2 fan heaters are short term loads, at least at the 3kW setting. A kiln wou ld run for hours. If you live on your own and make sure you always disconne ct other large loads a ring could certainly do the job within ratings. But if someone else puts on kettle, dishwasher & washing machine it's likely to trip or run hot. It would still function, but running cable so hot it gets soft isn't good practice, and might melt somewhere if not installed ideall y. And the trips wouldn't do your glassware any good.NT
You'd have to have separate poles on all switches/controllers for each "side" of the kiln, and probably double insulation between the two sides, so that if somehow one half was on and the other half was unplugged, there'd be be no way for the loose plug to accidentally become live, or for some "gunge" to get across the filaments of the different sides and trip either or both RCDs, if they exist.
If they're both plugged into one double 13A socket you might exceed the
20A limit (which is what they're tested to for overheating).The average user won't know if a given socket is near the end (bad), or middle (better) of the ring, so you could get 26A point loads [or higher given that fuses don't pop at 13.01A] supplied mostly by one cable of the ring, which is close to the maximum allowed current of a 2.5mm^2 T&E cable even in its best case.
thank you all for your replies. there are indeed a number of things to think about, many of which do not have an answer at this stage :-(
Regards,
Robert
I installed a kiln for my tenant and I treated it as a cooker. Gave it it's own 30A radial circuit with double-pole isolation.
I doubt a kiln heater runs for hours. I imagine it gets up to heat, then does what any ordinary oven does - turns on and off to keep about the same temperature.
Andy
Perhaps an expert will come along, but bear in mind they are about 4 times as hot as a domestic oven at its highest setting. So, either they have simply fantastic insulation or there'll need to be a lot of heat input just to keep it hot. Both, maybe.
Is heat loss some power of the temperature difference?
Kilns take a good few hours to heat up. My small 3kW kiln takes about
8 hours to reach 1250°C, running more-or-less flat out all the time. At that temperature, the heat losses require almost continuous power to hold the temperature steady.
The room must get boiling hot in the summer?
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