Author Topic: Titivating a Pottery Kiln  (Read 2237 times)

Offline awemawson

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Titivating a Pottery Kiln
« on: November 29, 2018, 10:21:09 AM »
Having the drive dog for the Beaver Powered Tooling lost wax cast in bronze started me thinking that really I should be doing this for myself rather than outsourcing it.

In the past I had a full set up, pottery kiln for wax burn out and mould heating, various furnaces, vacuum pump etc etc but have never re-commissioned it since I moved here 11 years ago  :bang:

So today I decided to dig out the pottery kiln and see if it was viable to connect it up. Originally it was a 3 phase 13.5 kW 415 volt beast that I had reconfigured to run off single phase as I didn't have the luxury of 3 phase on tap. Well now I have  :ddb:

First thing was to extricate it from the junk that has accumulated around it  and refresh my memory of how I'd converted it, (probably about 16 years ago). So junk moved and I  firstly emptied it of what had been piled in just prior to the move in 2007. A HUGE 63 amp single phase plug and socket (this draws 54 amps single phase), and amusingly one of the last lost wax burn outs of a recumbent lion, done in sodium silicate sand, that would still be viable to use today

Then putting it on the pallet truck I pulled it into the welding shop for investigation. Pulling off the cover panels to expose all the wiring, my conversion was discovered as 'dead simple' ! All I'd done was parallel up the three incoming phases, as there are three banks of six heating elements, one end of each going to the (neutral) star point, the other end via the control contactor to a phase.

A quick test with a meter showed that I had an earth leakage problem - about 250k to earth from the neutral star point that will easily trip my workshop RCD. Now this is not really surprising - at my last place it was in an unheated workshop at the bottom of the garden (which didn't have RCD protection) and for the last 11 years it's sat in the fireproof annex I built to house the foundry which again has no heating.

So at the moment it is sat with a 4 kW fan heater blowing inside at the elements and we'll see what happens to the leakage.
« Last Edit: November 29, 2018, 04:06:02 PM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #1 on: November 29, 2018, 10:24:22 AM »
. . .cont

Well strangely, although the leakage decreased and resistance initially increased I've just measured it again and it's at 90 - 100 K  Neutral to earth   :scratch:
« Last Edit: November 29, 2018, 11:01:26 AM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #2 on: November 29, 2018, 03:44:32 PM »
Having cooked it for a bit, the earth / neutral resistance is up to 1.5 Meg ohm, but noticeably falls off as the warmth decreases. Separating the ends of the three heating elements from the rest of the electrics shows me that a/ it is the elements giving the leakage and that b/ the right hand side is worse than the others.

No doubt the rather porous firebrick inner insulation that has channels cast in it for the heating elements has got a bit damp, as will have whatever insulation is behind it.

I don't fancy leaving a 4 kW heater running over night, so I've put two 100 watt inspection lamps inside with the door closed as far as the cables will allow. There is a roof vent which I've left open so air should circulate.

I'm pretty sure that if it continues improving it'll be fine to connect to mains in the morning, and then of course the drying out will be somewhat faster.

. . . fingers crossed for the morning  :scratch:
Andrew Mawson
East Sussex

Offline seadog

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Re: Titivating a Pottery Kiln
« Reply #3 on: November 29, 2018, 03:50:00 PM »
Do you have an isolating transformer, Andrew? If it was me I'd leave the earth of and fire it up.

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #4 on: November 29, 2018, 04:01:16 PM »
Yes but not rated at 13.5 kw - I  think mine is 3 kw  and only single phase :clap:

Andrew Mawson
East Sussex

Offline vintageandclassicrepairs

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Re: Titivating a Pottery Kiln
« Reply #5 on: November 29, 2018, 04:51:31 PM »
Hi All,
Andrew,
A dodge we used to use when getting old open frame 3 phase motors that had very low resistance to earth back into service was to connect the winding's in series and then connect a 220v supply across them.
It is usual to see the resistance to decrease again as the plot cools down, especially in Winter time when some of the moisture in the air is re absorbed,  a few cycles of heating will sort it out

John

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #6 on: November 30, 2018, 04:12:25 AM »
This morning the leakage resistance between Earth and Neutral was down to 1.5 M ohm having been warmed by a 100 watt light bulb over night, so I deemed it 'safe to try'.

A quick temporary connection to a 16 amp commando plug, and off she went without drama thank goodness. The Cromartie controller still seems to work, and it looks like the set point is at 200 deg C, which is sensible if I was last melting out wax. Very quickly the temperature got to set point with an overshoot to 215 deg C as might be expected.

I'll leave it on this morning to dry out - each phase is drawing roughly 18 amps when on (yes I KNOW it's on a 16 amp service!) but it's not on much of the time - cycling on / off on the controller.

I was surprised to find that the HN07RN-F 5G1.5 flex for my 16 amp extension cable is actually rated at 19 amps in free air.
« Last Edit: November 30, 2018, 08:43:04 AM by awemawson »
Andrew Mawson
East Sussex

Offline Pete W.

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Re: Titivating a Pottery Kiln
« Reply #7 on: November 30, 2018, 04:56:44 AM »
Your troubleshooting seems to have indicated moisture in the kiln lining.

Still, if it were mine, I'd have a go at those three porcelain terminal blocks with a toothbrush and some washing-up liquid.  (Switch off & disconnect first!! )

Maybe this comment is motivated by envy - the volume of that kiln is only about a couple of orders of magnitude smaller than the volume of my workshop!!

It looks to be a handy bit of kit. 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest design change-note!

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #8 on: November 30, 2018, 06:18:40 AM »
Pete, the whole inside will be re-wired when I've proved that the lining has dried. I did give them a bit of a wipe but whatever it is it isn't just sitting there!

By the time the walls of the kiln are taken into consideration it's not that big inside actually.

It's been cooking all morning ranging from 195 to about 210 deg C while I get on re-building the 90 degree powered tooling adaptor for the Beaver CNC lathe
« Last Edit: November 30, 2018, 08:45:11 AM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #9 on: November 30, 2018, 07:06:51 AM »
Years ago, the test to see if someone was still breathing when near to death was to hold a mirror close to their mouth, and the moisture will condense as a mist.

. . . well it works for damp kiln linings  :clap:

Holding a 6" square glass mirror tile over the ceiling vent, dead obvious that a fair amount of moisture is being driven off    :thumbup:
Andrew Mawson
East Sussex

Offline tom osselton

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Re: Titivating a Pottery Kiln
« Reply #10 on: November 30, 2018, 05:24:36 PM »
I wouldn’t have thought about testing the kiln like that.

Offline Pete.

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Re: Titivating a Pottery Kiln
« Reply #11 on: December 01, 2018, 06:32:40 AM »
Did you check it's pulse too? Should be 50hz.

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #12 on: December 01, 2018, 06:48:36 AM »
Well funny that you say that Pete. When I first connected it I was concerned what each phase was actually drawing, so I used my Fluke  376 clamp meter, and each phase was drawing EXACTLY 50 amps  :bugeye:

Yikes I thought well over twice what it should draw - then I noticed the 'Hz' symbol on the screen - that was the frequency - up till then I didn't know the meter had that facility and I must have accidentally put it in frequency measuring mode   :ddb:

. . .so yes I did take it's pulse  :lol:


Today I cranked the set point up to 650 degrees C and let it heat up. 650 is the volatilisation  temperature of PLA printing filament I'm told.
Andrew Mawson
East Sussex

Offline DICKEYBIRD

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Re: Titivating a Pottery Kiln
« Reply #13 on: December 01, 2018, 08:03:25 AM »
Milton in Tennesee

"Accuracy is the sum total of your compensating mistakes."

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #14 on: December 01, 2018, 08:16:32 AM »
Yes that stuff burns out at a lower temperature, but at £100 per kg as compared to £10 for PLA it's not all saving !
Andrew Mawson
East Sussex

Offline DICKEYBIRD

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Re: Titivating a Pottery Kiln
« Reply #15 on: December 01, 2018, 09:48:19 AM »
Ouch, I reckon kilowatts are a lot cheaper!  I missed that minor price difference. :bugeye:
Milton in Tennesee

"Accuracy is the sum total of your compensating mistakes."

Offline mattinker

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Re: Titivating a Pottery Kiln
« Reply #16 on: December 02, 2018, 07:01:13 AM »
Yes that stuff burns out at a lower temperature, but at £100 per kg as compared to £10 for PLA it's not all saving !

When using a plaster based investment, you need to get it nearly that hot to drive out the excess water molecules! The kiln will take it there easily, so it's really a win win situation. I've seen a couple of articles on lost PLA casting, I'm looking forward to seeing your results!

Induction furnace coming out of retirement?

Regards, Matthew

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #17 on: December 02, 2018, 01:54:36 PM »
Well Matthew it's certainly a lot more accessible now the kiln it out of the way !


Are we going to see you this Christmas ?
Andrew Mawson
East Sussex

Offline mattinker

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Re: Titivating a Pottery Kiln
« Reply #18 on: December 02, 2018, 04:02:34 PM »
Well, I'm coming over from the 22nd to the first, so we should be able to get over to see you some time then! I'll PM you nearer the time!

Cheers, Matthew

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #19 on: December 03, 2018, 02:57:12 PM »
So I've now fitted the proper Commando input socket - underneath so that if necessary the kiln can go flat against a wall.

Petew will be pleased to see that those ceramic stand off insulators have cleaned up nicely  :ddb:

Not sure quite yet where it is going to live long term  :scratch:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #20 on: December 04, 2018, 09:04:11 AM »
It's obviously the day for putting things back together !

This morning I put the covers back on the kiln having passed it as 'safe for use', but before I did I took the precaution of photographing the label on the Cromartie controller for future reference. I assume from the serial number '94-01348' that it was made in 1994.

..still need to find a permanent home for it  :scratch:
Andrew Mawson
East Sussex

Offline tom osselton

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Re: Titivating a Pottery Kiln
« Reply #21 on: December 04, 2018, 04:18:55 PM »
That’s quite the beast! Is powdercoating next?

Offline awemawson

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Re: Titivating a Pottery Kiln
« Reply #22 on: December 04, 2018, 04:43:58 PM »
I don't mess around with little toys you know Tom  :lol:

. . .now powder coating - there's a thought  :thumbup:
Andrew Mawson
East Sussex

Offline tom osselton

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Re: Titivating a Pottery Kiln
« Reply #23 on: December 05, 2018, 04:08:32 PM »
I don't mess around with little toys you know Tom  :lol:

. . .now powder coating - there's a thought  :thumbup:
Well we all like the surprise of tools surfacing as easy as “ Hold my beer “  :beer:
It’s the space thing I have a 24x28 garage that is slowly getting filled I just have to be careful on what I drool over.  :thumbup: