Stoneware Clay

8 Nov, 2008 in art pottery by admin

Stoneware Clay

Screening A Million Tons Uninterrupted

A Kason in-line Pneumati-Sifter VIBROSCREEN® circular vibratory separator has screened over one million tons of clay over 25 years without an equipment failure and shows no signs of quitting, according to John Taylor, production manager of The Pfaltzgraff Co., a 190-year manufacturer of stoneware products.

The system moves raw materials from any of ten 50-ft high silos containing clay, silica, alumina, lime and other ingredients through a pneumatic conveying system to a central weigh hopper. Ingredients are weighed in sequence and discharged as 3000 lb (1360 kg) batches into a pressurized surge hopper equipped with a rotary airlock valve that meters 600 lbs/minute of material into the 60" (1525mm) diameter in-line sifter.

The sifter, designed for 14.7 psig pressure, removes agglomerates, paper scraps and other foreign particles larger 0.074-inch (1880 micron), preparing the clay that will form the stoneware "body" and determine its finish. Magnets upstream and downstream of the screener remove iron particles.

"Elbows of the pneumatic conveyor lines wear out every 10 to 12 months because the system runs highly abrasive materials three shifts per day, five days per week," explains Taylor, "but aside from screen changes every two years, nothing on the Kason unit has worn out, including the gyratory motor which we lubricate periodically," he says.

How the screener operates

The circular vibratory screener is equipped with an imbalanced-weight gyratory motor that imparts multi-plane inertial vibration to two spring-mounted screening decks, causing oversize particles to vibrate across the screen surface in controlled pathways to the screen periphery where they are discharged. Screening efficiency improves by forcing the particles to pass over a maximum amount of screen surface.

The unit screens a 3000 lb (1360 kg) batch in 5 minutes in-line with the pneumatic conveying system. To prevent sharp, angular particles from blinding screen apertures, the screener is equipped with a "ball tray" anti-blinding device consisting of elastomeric balls that are captive in a narrow space below the top #10 mesh (0.074-in,1880 micron) working screen and above the #4 mesh (0.187-in, 4750 micron) ball screen. Vibratory action of the screener causes the balls to bounce against the underside of the working screen, dislodging particles wedged in screen apertures.

Oversize particles exit through a discharge spout at the periphery of the top frame. Screened clay exits the bottom frame discharge into a holding hopper, then into a pug mill, which mixes the clay with water before it is conveyed through an auger, cut, wrapped in plastic and stored for up to three months. The stoneware production takes place in numerous manufacturing processes.

Oldest pottery maker in USA

The Pfaltzgraff Company was founded in 1811 in York, PA by the Pfaltzgraff family of German immigrants. In addition to being a leader in casual dinnerware, the company markets stainless steel flatware, and glass beverageware.

The company takes pride in its tradition of craftsmanship, service and quality, to which the screener contributes. "The screened particles are crucial for the fine finish of our dinnerware, and help make our fine product at a consistently high level," says Steve Blouse, parts coordinator.

"For any piece of equipment to operate for 150,000 hours without a hiccup is unusual, which is why we notified Kason about it," adds Taylor.

About the Author

Kason Corporation manufactures circular vibratory screeners and centrifugal screeners for scalping and dewatering applications, as well as fluid bed dryers, coolers and moisturizers. For information contact Kason Corporation, 67-71 East Willow St., Millburn, NJ USA 07041, 1-973-467-8140, www.kason.com.

What is the best type of kiln for some one just starting out?

I am about to graduate from high school and have 3 years of experience making pottery through the class that school offers; I want to buy my own supplies and possibly open a studio. I know a lot about stoneware clays, glazes, and under glazes, but not much about the running of the kiln since the teacher handles it. I believe the one we have at school is electric... What type of kiln do you recommend? Any information is greatly appreciated!

Pity they didn't teach that important stuff.
To some extent it depends on what you are making. On a small scale, electric kilns are much more portable and up to a certain size can be run off the kind of power delivered for kitchen ranges and electric driers. But once they get above a certain size, they require massive amounts of electrical service and become very difficult to move.
Most potters who do a lot of work use gas in a fairly large kiln, building up a run where there may be dozens or even hundreds of pieces in the kiln before it is turned on. Gas kilns give a lot more control over the atmosphere in the kiln which allows many more glazing effects. And a large kiln reduces the fuel cost for each piece. However a large gas kiln must be out of building, but usually under a roof so on a sort of patio so the hot gases do not damage the building.
I think it is critical, if you are going to have your own studio, that you somehow get experience firing a kiln under various conditions. Either get a job with a ceramics operation or take short classes that focus on kiln usage. If nothing else, bug your instructors to provide information during these last months of high school. Every potter I know, from my sister on out, keeps a note book of temps and timing and results with the various glazes and your instructors should have instilled this in you, providing firing data and discussing results with you - at least after the first year.

Making low carb.(emissions) cone 10 stoneware clay