Heat Resistant Gloves

[Norm Stuart]

Has anyone used this type of flexible PBI / Kevlar blend glove?

http://www.superiorglove.com/extreme-dragon-pbi-kevlar-high-heat-gl...

http://www.amazon.com/gp/product/B00BHMATOW

We've used a typical pair of yellow Kevlar gloves with wool lining to unload hot kiln shelves, shown below.  They are quite stiff and though the Kevlar is rated for hotter temperatures, for short periods, than we deal with, the finger tips of the Kevlar have abraded-off through with repeated moderate temperature use.

http://www.amazon.com/High-Heat-Kevlar-Gloves-14inch/dp/B00HHCXNH6

http://www.baileypottery.com/safetyequip/miscprotection.htm

As we've experienced, Kevlar rapidly loses strength around 160 C / 320 F and sustains cumulative fiber damage even at 200 F.

PBI, (Polybenzimidazole fiber) used to make firefighter jackets, can withstand 400 C / 750 F indefinitely and up to 2,200 F for short periods.  It's quite costly.

Relatively affordable gloves are made with a blend of PBI and Kevlar to maintain the glove structure after the Kevlar fibers have broken.

This is a PBI / Kevlar blend in the typical style of a Kevlar weave glove.  Roughly the same price as the flexible blend.

http://www.amazon.com/gp/product/B007IBNK74/

This is a low-end Kevlar product with, I assume, fiberglass cuffs, sold by Axner.  $25 rather than $125, but far less capable and less durable.

http://www.axner.com/kevlarcono-guardglovessetof2.aspx

[Nadine Mercader]

Thank you Norm for the very thoughtful response!

[Norm Stuart]

Have  we ever experienced any damage from thermal shock?  The short answer is no, otherwise we wouldn't be doing it - but it depends on whose stuff we're dealing with.  You can take a risk with your own stuff.

It's the same choice we face when deciding what speed we use to fire Cone 6.  Well-made ware is glaze fired at the Bartlett Medium-Fast and unloaded below 350 F.  Questionable ware is fired to Cone 6 at Medium and allowed to cool to room temperature on its own.  Yet there are almost always cracks in some of the questionable ware in spite of the slower firing speed and slower cooling.

This is because the cracks are a result of internal stress being relieved during the firing.  Ware made by newer people, with clay of differing degrees of dryness, different degrees of thickness, dodgy design, and slab-ware which is not scored and slipped are at higher risk.

We have an artist who made indestructible slab containers. After he suffered a stroke his containers are fired with the questionable ware and often crack.  The containers look exactly the same to me, but he's clearly making them less well in some manner. Perhaps he can't work as quickly now so the slabs are drying differentially.

If we fast-cool a kiln load we take the plug out of the second peephole and unload the top shelf when the ware is around 250 F according to the mid-center thermocouple.  Some people have been known to prop open the lid an inch to get it cool even faster.  The hot mitts are primarily used to take out the shelf which retains quite a lot of heat, as the bottom portions of the kiln are still hotter. 

While we hear the tink-tink of cooling glaze on ceramic unloading around 250 F, this hasn't produced any visible flaws and our work isn't functional.  It's the same tink-tink sound you sometimes hear weeks after a piece has been fired, just more frequent.  Not recommending this, just saying we often do it.

If you ever need to open a very hot kiln which contains ware which has been fired to cone 5 or hotter, you want to be sure to close it before it gets below 450 F, so it will cool slowly at 420 F for cristobalite shrink.  This is not a problem for bisque firings and low-fire glaze firings as no clay maker would add cristobalite.

Page 57 of this tutorial covers crash-cooling kilns, which is a lot of the same problems you face with raku. 

Electric raku kiln are built so the lid is the kiln floor.  This way the heating elements take their heat with them as the kiln is opened - otherwise the fast cooling is tough on the elements.  Maulik Oza followed this design in making his gas fired raku kiln, mostly for convenience of access.

Kiln Firing Tutorial

Comment by Nadine Mercader 1 hour ago

Are you having any thermal shock issues when you don't wait for it to be completely cooled?

[Nadine Mercader]

When I did raku before I used welder's leather gloves which are fairly long (yes I am small but not tiny and they went 3/4 of the way to my elbows.  I then handled my tongs easily and felt very safe.

Today I was given an old electric kiln 25" diameter and the elements look great.  All I have to do is replace the plug (she had it hard wired).  That means that I will be able to take my small kiln and turn it into a raku kiln.  All I really want is to have someone build me a metal frame and pulley system in order to operate it alone if I wanted to.  I have the venturi burner,  tongs etc...

Are you having any thermal shock issues when you don't wait for it to be completely cooled?

[Norm Stuart]

Just opened our new Extreme Dragon Mittens made of PBI/Kevlar, good to 750 F, with wool inner-lining for insulation. 

They're incredibly more flexible than the traditional bright yellow kevlar mitt with the extra strength of very expensive PBI which has a much higher temperature range than does kevlar alone.

Polybenzimidazole fiber (Wikipedia)

Extreme Dragon Mittens (Amazon)

The men's size has fingers are which are long enough, and the sleeves are long enough for kiln work - but the fingers would be a tight fit initially if you thicker than average fingers.

Why don't we always wait until the kiln is room temperature? . . . Perhaps we should but we don't.  These 14 inch long mittens would definitely be good mitts for Raku. 

Even better, they come in 18 inch and 27 inch lengths as well.  Extreme Dragon Glove Maker's Website