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How Much Difference Does A De-Airing Pug Mill Make?


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#1 docweathers

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Posted 01 February 2014 - 07:41 PM

I'm thinking about upgrading my old bluebird  non de-airing  pug mill to de-airing. Since this may be a lot of work, I want to make sure that, in practical terms, it really makes a meaningful difference to have the de-airing feature.


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#2 Babs

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Posted 01 February 2014 - 08:41 PM

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Posted Yesterday, 10:48 PM

The main difference, between de-airing or no, is not having to wedge the clay. You turn on the de-airing vaccum while still mixing the clay. Then, leaving the vacuum working, you switch from mixing (let the auger completely stop) to pugging. After you have emptied the pugmill, turn off both the vacuum and the pugger. For heaven's sake, remember to open the vacuum line and release the pressure. By the way, the vacuum pressure should be between 20 & 25 PSI before switching from mixing to pugging.

 

I use reclaimed clay for throwing, else why have a pugmill? Mark, I don't work in porcelain, but porcelain is why they finally came out with a stainless steel Peter Pugger--because it's not supposed to compromise the clay.

 

I've had my Peter Pugger for almost eleven years, and my back and wrists thank me. It may keep me playing in the mud into my nineties, which is better than hanging out at the senior center's bar.

 

Shirley

This may help.



#3 clay lover

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Posted 01 February 2014 - 11:05 PM

I only have a de-airing so don't know any other kind, but man, the clay is perfect.  NO wedging.  A slap or 2 to get it into sort of round and away we go. cone up, cone down, repeat, open, throw.



#4 Mark C.

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Posted 02 February 2014 - 12:07 AM

I have only used a non-deairing pug and I believe it will big  big difference -I'll post my results when mine shows up and i use it.

Mark


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#5 docweathers

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Posted 02 February 2014 - 01:22 PM

Mark

 

I look forward to seeing the results of your tests


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#6 neilestrick

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Posted 02 February 2014 - 01:23 PM

Pugmills are not great mixers. That's why they make mixers. For me, the only reason to pug would be to de-air.


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#7 Wyndham

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Posted 02 February 2014 - 04:43 PM

The other reason I think is that feeding bagged clay through pugger allows for the clay to re orientate from the 8x8 block down to a smaller workable pug. Clay in 25 lb bags start to setup some and you also need to change the spiral that the larger pug mill introduced.

Because some clays like Bmix or Loafer Glory can be quite firm, the pugger can change the clay to soft plastic throwable clay by going through the pugger, same as wedging does

Wyndham 



#8 Norm Stuart

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Posted 02 February 2014 - 05:00 PM

John Baymore and others have convinced me that air pockets in ware do not cause ware to explode in the kiln firing.  What apparently matters for the exit of water and burn-out gases is the total clay thickness, minus the thickness of any void in the clay.

 

As a consequence someone has asked me why anyone bothers to de-airing clay?

 

I don't have an answer. 

 

Is it just a tradition to de-air clay or does it make the clay better in some way? 

 

It's seems like an aerated clay could be just as useful as an airless clay, although the cohesive plasticity would be lower.



#9 Wyndham

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Posted 02 February 2014 - 08:53 PM

I have noticed that if I don't de air clay from my bluebird, I get air pockets in my ware that I have to use a needle tool to get them out.

That's just my experience.

Wyndham



#10 JBaymore

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Posted 02 February 2014 - 09:20 PM

If you are getting airbubbles in the clay......... more arm (as in wedging more).  ;)   (.....more cowbell!.......)

 

Air bubbles in clay are not the explosion generators... but they are REALLY annoying when you are throwing on the wheel.  Also in a highly pyroplastic clay, a small airpocket in the body wall CAN tend to expand a tiny bit making a small "blister" on the surface.

 

best,

 

.......................john


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#11 Benzine

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Posted 02 February 2014 - 11:38 PM

John, isn't the biggest issue with air bubbles/ pockets in wares, that they are a structural weakness?
"Anything worth believing, is worth questioning"

#12 Norm Stuart

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Posted 03 February 2014 - 04:44 AM

I use drop wedging for the initial forming of slabs, while the potters rams horn wedge.  We all agree these actions temporarily make the clay less hard (penetration plasticity) and more cohesive (cohesive plasticity).

 

a.)  Big Ceramic store tech pages suggest wedging or pug milling mixes more dry areas of the pug with wetter areas;

b.)  according to the Alfred Particle Orientation Lecture, wedging mixes weak shear planes create by the manufacturers pug milling; 

c.)  my guess is it's more important that any type of wedging temporarily breaks up the static bonds between clay particles which have developed over time, allowing the clay particles to again easily slide past each other for a while. (An analogous situation is boiling water, which breaks the accumulated hydrogen-hydrogen bonds between each water molecule, permitting the boiling water to freeze into ice structure faster than room temperature water where the hydrogen-hydrogen bonds need to be first broken, giving off  heat, before they can freeze into an ice matrix.)

 

These processes all create greater cohesive plasticity, and greater softness (mechanical plasticity).  I suspect these changes are far important in imparting desirable clay properties than any particular particle orientation different types of wedging produce.  Given all this it seems like a clay mixer, as Neil mentions, should impart these same traits better than a pug mill as it doesn't impart the frictional clay shear problems pug mills can create.

 

http://www.bigcerami...lay_mixers.html

"It seems that only wheel throwers want clay that has been de-aired.  And many of the non de-airing pug mills on the market today mix the clay with very little air even without a vacuum.  Vacuums do tend to dry the clay out a little. And some potters don't like them because the vacuum is one more thing to break. But if you have a de-airing pug mill, the vacuum can be turned on and off as desired."

 

Creating slabs or sculpture, I slit any occasional air bubble I find to release and press them out.  It doesn't seem to be a common incidence.

 

We made a decision early on not to stop recycling clay primarily because our discounted price from nearby Laguna Clay provided savings of less than $1 per hour put into clay recycling as a large percentage of clay scraps or slop become slip - plus the fact that we typically stock 12 different clays, so the recycled clay had unknown COE and performed poorly both for throwing and sculpture.

 

Does my new understanding of wedging or mixing clay accurately reflect the benefits of why this is done before using clay?   Are there aspects I'm still missing or have wrongly understood?

 

If you are getting airbubbles in the clay......... more arm (as in wedging more).  ;)   (.....more cowbell!.......)

 

Air bubbles in clay are not the explosion generators... but they are REALLY annoying when you are throwing on the wheel.  Also in a highly pyroplastic clay, a small airpocket in the body wall CAN tend to expand a tiny bit making a small "blister" on the surface.

 

best,

 

.......................john

 

John, isn't the biggest issue with air bubbles/ pockets in wares, that they are a structural weakness?



#13 JBaymore

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Posted 03 February 2014 - 09:10 AM

John, isn't the biggest issue with air bubbles/ pockets in wares, that they are a structural weakness?

 

Yup, that too.  But usually there are only one or two... so not a HUGE issue. But it COULD be.

 

best,

\

............................john


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#14 JBaymore

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Posted 03 February 2014 - 09:13 AM

I'd say that you pretty much "got it" Norm. 

 

best,

 

...................john


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#15 neilestrick

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Posted 03 February 2014 - 11:00 AM

Mixers mix on a large scale, getting dry areas and wet areas combined into a consistent mix, but full of air, too. But for clay particles to bond well, they cannot have tiny air pockets between them. Each particle must be throughly wetted, with just a thin layer of water between each particle, as we discussed in our recent plasticity discussion. This is why non de-aired clay is often referred to as being 'short'. The clay particles don't bond as well, and the clay tears easier and doesn't hold form as well during the throwing process.


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#16 neilestrick

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Posted 03 February 2014 - 11:03 AM

The other reason I think is that feeding bagged clay through pugger allows for the clay to re orientate from the 8x8 block down to a smaller workable pug. Clay in 25 lb bags start to setup some and you also need to change the spiral that the larger pug mill introduced.

Because some clays like Bmix or Loafer Glory can be quite firm, the pugger can change the clay to soft plastic throwable clay by going through the pugger, same as wedging does

Wyndham 

 

I often hear people talk about the spiral of the pugger, and have never found it to be an issue. By the time you cut up your clay and make it into balls, you're not dealing with a total spiral, but a small section of one. And if you wedge, you're creating a new spiral. And if you cone the clay during the centering process, any spiral that existed is gone, and replaced by a new spiral from the wheel.


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#17 Norm Stuart

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Posted 03 February 2014 - 01:50 PM

Now that makes sense.  An industrial scale mixer essentially demands a de-airing pugmill -- or the invention of one if they didn't already exist.

 

Mixers mix on a large scale, getting dry areas and wet areas combined into a consistent mix, but full of air, too. But for clay particles to bond well, they cannot have tiny air pockets between them. Each particle must be throughly wetted, with just a thin layer of water between each particle, as we discussed in our recent plasticity discussion. This is why non de-aired clay is often referred to as being 'short'. The clay particles don't bond as well, and the clay tears easier and doesn't hold form as well during the throwing process.



#18 neilestrick

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Posted 03 February 2014 - 04:06 PM

Industrial scale doesn't matter. Even a small mixer or non de-airing pugmill does nothing to eliminate tiny air pockets.


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#19 WillowTreePottery

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Posted 11 February 2014 - 05:02 AM

Last year I began to have some pretty severe arthritic problems in my hands an wrists after 30 yrs of making pottery,  I had only used an old relic of a peter Pugger  borrowed from a school. I have upgraded to the new Shimpo mixer/pugmill

 http://www.tuckerspo...uemart&Itemid=1

 

I am a walking ad for this machine.  I can mix and pug out about 100 pounds a couple of times a day and it is always the perfect consistency.  Easy to use, reconstitutes dry scrap in no time at all and it means far less waste in my studio.    Best money I have ever spent,   It deairs clay perfectly and if I want a bit more aeration or plasiticity i just don't run the vacuum as long or add some vinegar to the mixer.

 

Kathy



#20 docweathers

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Posted 11 February 2014 - 10:58 PM

That's one expensive machine. You must do a huge amount of pottery to justify it. I think you have convinced me to upgrade my little hundred dollar pug mill to de-airing.

 

thanks for the perspective


Larry

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